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Sample records for meso-aryl-substituted subporphyrins dipolar

  1. Group 9 Metal Complexes of meso-Aryl-Substituted Rubyrin.

    PubMed

    Soya, Takanori; Osuka, Atsuhiro

    2015-07-20

    Invited for the cover of this issue are Takanori Soya and Atsuhiro Osuka at Kyoto University. The image depicts Group 9 metal (Co, Rh, and Ir) complexes of meso-aryl-substituted rubyrin and a meteorite approaching to the atmosphere. A large amount of Iridium is often contained in meteorites. Read the full text of the article at 10.1002/chem.201501080. PMID:26042817

  2. Intramolecular electron transfer reactions in meso-(4-nitrophenyl)-substituted subporphyrins.

    PubMed

    Copley, Graeme; Oh, Juwon; Yoshida, Kota; Shimizu, Daiki; Kim, Dongho; Osuka, Atsuhiro

    2016-01-25

    A2B-type meso-(4-nitrophenyl)-substituted subporphyrins have been synthesized and shown to undergo very fast photoinduced intramolecular charge separation (CS) and charge recombination (CR) between the subporphyrin core and the meso-4-nitrophenyl group in CH2Cl2 as probed by femtosecond time-resolved transient absorption spectroscopy. Red-shifted emissions were detected from charge-separated states as a rare case for porphyrinoids. PMID:26645430

  3. Photophysical Properties and Adsorption Behaviors of Novel Tri-Cationic Boron(III) Subporphyrin on Anionic Clay Surface.

    PubMed

    Tsukamoto, Takamasa; Shimada, Tetsuya; Takagi, Shinsuke

    2016-03-23

    Two types of +3-charged subporphyrin derivatives with m- and p-methylpyridinium as the meso-aryl substituents were designed and synthesized. Their photophysical properties with and without anionic saponite clay were investigated. These cationic subporphyrins were suitably designed for adsorption on the saponite nanosheet surface with their photoactivity. Absorption and emission spectra of these subporphyrin-saponite complexes exhibited strong bathochromic shifts due to the flattening of the molecules on the nanosheet. This behavior was observed as drastic visual changes in their luminescence colors. Additionally, aggregation behaviors were not observed in the saponite complexes even at high dye loading levels for both subporphyrins. Moreover, under such condition, their fluorescence properties on the saponite surface were not only maintained but also enhanced without unexpected deactivations despite the dye molecules are densely introduced on the solid surface. These findings are beneficial for applications of the dye-clay complexes to photofunctional materials such as strongly luminescent materials, highly sensitive clay sensors and artificial photosynthesis systems.

  4. β,β-(1,4-Dithiino)subporphyrin Dimers Capturing Fullerenes with Large Association Constants.

    PubMed

    Yoshida, Kota; Osuka, Atsuhiro

    2016-06-27

    β,β-(1,4-Dithiino)subporphyrin dimers 7-syn and 7-anti were synthesized by the nucleophilic aromatic substitution reaction of 2-bromo-3-(4-methoxyphenylsulfonyl)subporphyrin 4 with 2,3-dimercaptosubporphyrin 5 under basic conditions followed by axial arylation. Additions of C60 or C70 to a dilute solution of 7-anti (ca. 10(-6)  m) in toluene did not cause appreciable UV/Vis spectral changes, while similar additions to a concentrated solution (ca. 10(-3)  m) resulted in precipitation of complexes. In contrast, dimer 7-syn captured C60 and C70 in different complexation stoichiometries in toluene; a 1:1 manner and a 2:1 manner, respectively, with large association constants; Ka =(1.9±0.2)×10(6)  m(-1) for C60 @7-syn, and K1 =(1.6±0.5)×10(6) and K2 =(1.8±0.9)×10(5)  m(-1) for C70 @(7-syn)2 . These association constants are the largest for fullerenes-capture by bowl-shaped molecules reported so far. The structures of C60 @7-anti, C70 @7-anti, C60 @7-syn, and C70 @7-syn have been determined by single-crystal X-ray diffraction analysis. PMID:27238619

  5. meso-(4-(N,N-dialkylamino)phenyl)-substituted subporphyrins: remarkably perturbed absorption spectra and enhanced fluorescence by intramolecular charge transfer interactions.

    PubMed

    Inokuma, Yasuhide; Easwaramoorthi, Shanmugam; Yoon, Zin Seok; Kim, Dongho; Osuka, Atsuhiro

    2008-09-17

    A series of meso-(4-(N,N-dibenzylamino)phenyl)-substituted subporphyrins was synthesized by means of Buchwald-Hartwig amination protocol. Substitution of the amino group at the 4-position of the meso-phenyl substituent resulted in a remarkable red shift in the absorption spectra and drastic enhancement of fluorescence intensity probably as a consequence of intramolecular CT interaction. These characteristics have been utilized to construct a cation-sensing system by appending a 1-aza-15-crown-5 unit to subporphyrin that displays large spectral changes upon cation binding.

  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. First hyperpolarizabilities of dipolar, bis-dipolar, and octupolar molecules

    NASA Astrophysics Data System (ADS)

    Yang, Si Kyung; Ahn, Hyun Cheol; Jeon, Seung-Joon; Asselberghs, Inge; Clays, Koen; Persoons, André; Cho, Bong Rae

    2005-02-01

    A series of dipolar ( 1), bis-dipolar ( 2), and octupolar molecules ( 3) containing 1, 2, and 6 dipolar units within a molecule has been synthesized and their hyperpolarizabilities were analyzed. The βHRS increases in the order, 1 < 2 < 3. The 'monomeric' βzzz increases by approximately twofold from 1 to 2, whereas βzzz of 2 and βxxx of 3 are similar. Noteworthy is the parallel increase in the hyperpolarizability tensor with the λmax.

  8. Vertically coupled dipolar exciton molecules

    NASA Astrophysics Data System (ADS)

    Cohen, Kobi; Khodas, Maxim; Laikhtman, Boris; Santos, Paulo V.; Rapaport, Ronen

    2016-06-01

    While the interaction potential between two dipoles residing in a single plane is repulsive, in a system of two vertically adjacent layers of dipoles it changes from repulsive interaction in the long range to attractive interaction in the short range. Here we show that for dipolar excitons in semiconductor heterostructures, such a potential may give rise to bound states if two such excitons are excited in two separate layers, leading to the formation of vertically coupled dipolar exciton molecules. Our calculations prove the existence of such bound states and predict their binding energy as a function of the layers separation as well as their thermal distributions. We show that these molecules should be observed in realistic systems such as semiconductor coupled quantum well structures and the more recent van der Waals bound heterostructures. Formation of such molecules can lead to new effects such as a collective dipolar drag between layers and new forms of multiparticle correlations, as well as to the study of dipolar molecular dynamics in a controlled system.

  9. 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.

  10. Pseudopotentials for an ultracold dipolar gas

    NASA Astrophysics Data System (ADS)

    Whitehead, T. M.; Conduit, G. J.

    2016-02-01

    A gas of ultracold molecules interacting via the long-range dipolar potential offers a highly controlled environment in which to study strongly correlated phases. However, at particle coalescence the divergent 1 /r3 dipolar potential and associated pathological wave function hinder computational analysis. For a dipolar gas constrained to two dimensions we overcome these numerical difficulties by proposing a pseudopotential that is explicitly smooth at particle coalescence, resulting in a 2000-times speedup in diffusion Monte Carlo calculations. The pseudopotential delivers the scattering phase shifts of the dipolar interaction with an accuracy of 10-5 and predicts the energy of a dipolar gas to an accuracy of 10-4EF in a diffusion Monte Carlo calculation.

  11. Quantum fluctuations in dipolar Bose gases

    SciTech Connect

    Lima, Aristeu R. P.; Pelster, Axel

    2011-10-15

    We investigate the influence of quantum fluctuations upon dipolar Bose gases by means of the Bogoliubov-de Gennes theory. Thereby, we make use of the local density approximation to evaluate the dipolar exchange interaction between the condensate and the excited particles. This allows to obtain the Bogoliubov spectrum analytically in the limit of large particle numbers. After discussing the condensate depletion and the ground-state energy correction, we derive quantum-corrected equations of motion for harmonically trapped dipolar Bose gases by using superfluid hydrodynamics. These equations are subsequently applied to analyze the equilibrium configuration, the low-lying oscillation frequencies, and the time-of-flight dynamics. We find that both atomic magnetic and molecular electric dipolar systems offer promising scenarios for detecting beyond mean-field effects.

  12. Dipolar Nanodomains in Protein Hydration Shells.

    PubMed

    Martin, Daniel R; Matyushov, Dmitry V

    2015-02-01

    The network of hydrogen bonds characteristic of bulk water is significantly disturbed at the protein-water interface, where local fields induce mutually frustrated dipolar domains with potentially novel structure and dynamics. Here the dipolar susceptibility of hydration shells of lysozyme is studied by molecular dynamics simulations in a broad range of temperatures, 140-300 K. The real part of the susceptibility passes through a broad maximum as a function of temperature. The maximum shifts to higher temperatures with increasing frequency of the dielectric experiment. This phenomenology is consistent with that reported for bulk relaxor ferroelectrics, where it is related to the formation of dipolar nanodomains. Nanodomains in the hydration shell extend 12-15 Å from the protein surface into the bulk. Their dynamics are significantly slower than the dynamics of bulk water. The domains dynamically freeze into a ferroelectric glass below 160 K, at which point the Arrhenius plot of the dipolar relaxation time becomes significantly steeper.

  13. Two-dimensional dipolar nematic colloidal crystals.

    PubMed

    Skarabot, M; Ravnik, M; Zumer, S; Tkalec, U; Poberaj, I; Babic, D; Osterman, N; Musevic, I

    2007-11-01

    We study the interactions and directed assembly of dipolar nematic colloidal particles in planar nematic cells using laser tweezers. The binding energies for two stable configurations of a colloidal pair with homeotropic surface alignment are determined. It is shown that the orientation of the dipolar colloidal particle can efficiently be controlled and changed by locally quenching the nematic liquid crystal from the laser-induced isotropic phase. The interaction of a single colloidal particle with a single colloidal chain is determined and the interactions between pairs of colloidal chains are studied. We demonstrate that dipolar colloidal chains self-assemble into the two-dimensional (2D) dipolar nematic colloidal crystals. An odd-even effect is observed with increasing number of colloidal chains forming the 2D colloidal crystal. PMID:18233658

  14. 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.

  15. Independent EEG Sources Are Dipolar

    PubMed Central

    Delorme, Arnaud; Palmer, Jason; Onton, Julie; Oostenveld, Robert; Makeig, Scott

    2012-01-01

    Independent component analysis (ICA) and blind source separation (BSS) methods are increasingly used to separate individual brain and non-brain source signals mixed by volume conduction in electroencephalographic (EEG) and other electrophysiological recordings. We compared results of decomposing thirteen 71-channel human scalp EEG datasets by 22 ICA and BSS algorithms, assessing the pairwise mutual information (PMI) in scalp channel pairs, the remaining PMI in component pairs, the overall mutual information reduction (MIR) effected by each decomposition, and decomposition ‘dipolarity’ defined as the number of component scalp maps matching the projection of a single equivalent dipole with less than a given residual variance. The least well-performing algorithm was principal component analysis (PCA); best performing were AMICA and other likelihood/mutual information based ICA methods. Though these and other commonly-used decomposition methods returned many similar components, across 18 ICA/BSS algorithms mean dipolarity varied linearly with both MIR and with PMI remaining between the resulting component time courses, a result compatible with an interpretation of many maximally independent EEG components as being volume-conducted projections of partially-synchronous local cortical field activity within single compact cortical domains. To encourage further method comparisons, the data and software used to prepare the results have been made available (http://sccn.ucsd.edu/wiki/BSSComparison). PMID:22355308

  16. Dipolar ferromagnets and glasses (invited)

    SciTech Connect

    Rosenbaum, T.F.; Wu, W.; Ellman, B.; Yang, J. ); Aeppli, G. ); Reich, D.H. )

    1991-11-15

    What is the ground state and what are the dynamics of 10{sup 23} randomly distributed Ising spins We have attempted to answer these questions through magnetic susceptibility, calorimetric, and neutron scattering studies of the randomly diluted dipolar-coupled Ising magnet LiHo{sub {ital x}}Y{sub 1{minus}{ital x}}F{sub 4}. The material is ferromagnetic for dipole concentrations at least as low as {ital x}=0.46, with a Curie temperature obeying mean-field scaling relative to that of pure LiHoF{sub 4}. In the dilute spin limit, an {ital x}=0.045 crystal shows very unusual glassy properties characterized by {ital decreasing} barriers to relaxation as {ital T}{r arrow}0. Its properties are consistent with a single low degeneracy ground state with a large gap for excitations. A slightly more concentrated {ital x}=0.167 sample, however, supports a complex ground state with no appreciable gap, in accordance with prevailing theories of spin glasses. The underlying causes of such disparate behavior are discussed in terms of random clusters as probed by neutron studies of the {ital x}=0.167 sample. In addition to tracing the evolution of the glassy and ferromagnetic states with dipole concentration, we investigate the effects of a transverse magnetic field on the Ising spin glass, LiHo{sub 0.167}Y{sub 0.833}F{sub 4}. The transverse field mixes the eigenfunctions of the ground-state Ising doublet with the otherwise inaccessible excited-state levels. We observe a rapid decrease in the characteristic relaxation times, large changes in the spectral form of the relaxation, and a depression of the spin-glass transition temperature with the addition of quantum fluctuations.

  17. 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.

  18. Reaching Fermi degeneracy via universal dipolar scattering.

    PubMed

    Aikawa, K; Frisch, A; Mark, M; Baier, S; Grimm, R; Ferlaino, F

    2014-01-10

    We report on the creation of a degenerate dipolar Fermi gas of erbium atoms. We force evaporative cooling in a fully spin-polarized sample down to temperatures as low as 0.2 times the Fermi temperature. The strong magnetic dipole-dipole interaction enables elastic collisions between identical fermions even in the zero-energy limit. The measured elastic scattering cross section agrees well with the predictions from the dipolar scattering theory, which follow a universal scaling law depending only on the dipole moment and on the atomic mass. Our approach to quantum degeneracy proceeds with very high cooling efficiency and provides large atomic densities, and it may be extended to various dipolar systems. PMID:24483874

  19. Spatial density oscillations in trapped dipolar condensates

    SciTech Connect

    Lu, H.-Y.; Zhang, J.-N.; Qiu, R.-Z.; Yi, S.; Lu, H.; Pu, H.

    2010-08-15

    We investigated the ground-state wave function and the free expansion of a trapped dipolar condensate. We find that dipolar interaction may induce both biconcave and dumbbell density profiles in the pancake- and cigar-shaped traps, respectively. In the parameter plane of the interaction strengths, the oscillating density profile in a harmonically trapped dipolar condensate occurs only when the interaction parameters fall into certain isolated areas. The relation between the positions of these areas and the trap geometry is explored. When a box potential is used to confine the condensate, spatial density oscillation becomes a generic feature. By studying the free expansion of the condensate with an oscillating density profile, we show that the spatial density oscillation is detectable from the time-of-flight image.

  20. 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.

  1. On the interaction of dipolar filaments.

    PubMed

    Messina, René; Spiteri, Ludovic

    2016-08-01

    The interactions of dipolar filaments such as magnetic needles and chains in strong homogeneous magnetic/electric field are investigated theoretically. Revisiting the case of uniformly magnetized/polarized parallel needles of finite size L and separated by a distance R , all the relevant regimes of attraction and/or repulsion are properly addressed and discussed. At short inter-needle separation ( R/L ≲ 0.2, the repuive pair potential of two facing needles is governed by R(-1) in strong contrast with R(-3) at long separations (R/L ≳ 2.5). This softening is attributed to an efficient long-range screening owing to the relatively long needle extension in this regime. This whole understanding of dipolar needles effective interaction is then used to grasp that of dipolar chains made up of spherical dipolar beads. When excluded-volume correlations are weak (i.e., the chains are a few beads apart), chains and needles possess virtually the same effective interaction. However, at short separation there is a remarkable hardening upon approaching two chains in registry in qualitative contrast to the needles case. PMID:27562832

  2. Natural 1,3-Dipolar Cycloadditions.

    PubMed

    Baunach, Martin; Hertweck, Christian

    2015-10-19

    [3+2] in the wild: Biomimetic natural product syntheses and theoretical considerations have indicated that 1,3-dipolar cycloadditions take place in nature. Now, the structure, biosynthesis, and function of a heavily modified prenylated flavin cofactor have been elucidated. In the azomethine ylide form, it undergoes [3+2] cycloadditions with aromatic acids and promotes their decarboxylation. PMID:26465651

  3. Dimensional Reduction in Quantum Dipolar Antiferromagnets.

    PubMed

    Babkevich, P; Jeong, M; Matsumoto, Y; Kovacevic, I; Finco, A; Toft-Petersen, R; Ritter, C; Månsson, M; Nakatsuji, S; Rønnow, H M

    2016-05-13

    We report ac susceptibility, specific heat, and neutron scattering measurements on a dipolar-coupled antiferromagnet LiYbF_{4}. For the thermal transition, the order-parameter critical exponent is found to be 0.20(1) and the specific-heat critical exponent -0.25(1). The exponents agree with the 2D XY/h_{4} universality class despite the lack of apparent two-dimensionality in the structure. The order-parameter exponent for the quantum phase transitions is found to be 0.35(1) corresponding to (2+1)D. These results are in line with those found for LiErF_{4} which has the same crystal structure, but largely different T_{N}, crystal field environment and hyperfine interactions. Our results therefore experimentally establish that the dimensional reduction is universal to quantum dipolar antiferromagnets on a distorted diamond lattice. PMID:27232040

  4. Quantum spin glass and the dipolar interaction.

    PubMed

    Schechter, Moshe; Laflorencie, Nicolas

    2006-09-29

    Anisotropic dipolar systems are considered. Such systems in an external magnetic field are expected to be a good experimental realization of the transverse field Ising model. With random interactions, this model yields a spin glass to paramagnet phase transition as a function of the transverse field. We show that the off-diagonal dipolar interaction, although effectively reduced, induces a finite correlation length and thus destroys the spin-glass order at any finite transverse field. We thus explain the behavior of the nonlinear susceptibility in the experiments on LiHo(x)Y(1-x)F(4), and argue that a crossover to the paramagnetic phase, and not quantum criticality, is observed.

  5. Nonequilibrium dynamics of an ultracold dipolar gas

    NASA Astrophysics Data System (ADS)

    Sykes, A. G.; Bohn, J. L.

    2015-01-01

    We study the relaxation and damping dynamics of an ultracold, but not quantum degenerate, gas consisting of dipolar particles. These simulations are performed using a direct simulation Monte Carlo method and employing the highly anisotropic differential cross section of dipoles in the Wigner threshold regime. We find that both cross-dimensional relaxation and damping of breathing modes occur at rates that are strongly dependent on the orientation of the dipole moments relative to the trap axis. The relaxation simulations are in excellent agreement with recent experimental results in erbium. The results direct our interest toward a less explored regime in dipolar gases where interactions are dominated by collision processes rather than mean-field interactions.

  6. Dimensional Reduction in Quantum Dipolar Antiferromagnets

    NASA Astrophysics Data System (ADS)

    Babkevich, P.; Jeong, M.; Matsumoto, Y.; Kovacevic, I.; Finco, A.; Toft-Petersen, R.; Ritter, C.; Mânsson, M.; Nakatsuji, S.; Rønnow, H. M.

    2016-05-01

    We report ac susceptibility, specific heat, and neutron scattering measurements on a dipolar-coupled antiferromagnet LiYbF4 . For the thermal transition, the order-parameter critical exponent is found to be 0.20(1) and the specific-heat critical exponent -0.25 (1 ) . The exponents agree with the 2D X Y /h4 universality class despite the lack of apparent two-dimensionality in the structure. The order-parameter exponent for the quantum phase transitions is found to be 0.35(1) corresponding to (2 +1 )D . These results are in line with those found for LiErF4 which has the same crystal structure, but largely different TN, crystal field environment and hyperfine interactions. Our results therefore experimentally establish that the dimensional reduction is universal to quantum dipolar antiferromagnets on a distorted diamond lattice.

  7. 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.

  8. Dark High Density Dipolar Liquid of Excitons

    NASA Astrophysics Data System (ADS)

    Cohen, Kobi; Shilo, Yehiel; West, Ken; Pfeiffer, Loren; Rapaport, Ronen

    2016-06-01

    The possible phases and the nano-scale particle correlations of two-dimensional interacting dipolar particles is a long-sought problem in many-body physics. Here we observe a spontaneous condensation of trapped two-dimensional dipolar excitons with internal spin degrees of freedom from an interacting gas into a high density, closely packed liquid state made mostly of dark dipoles. Another phase transition, into a bright, highly repulsive plasma is observed at even higher excitation powers. The dark liquid state is formed below a critical temperature $T_c \\approx 4.8K$, and it is manifested by a clear spontaneous spatial condensation to a smaller and denser cloud, suggesting an attractive part to the interaction which goes beyond the purely repulsive dipole-dipole forces. Contributions from quantum mechanical fluctuations are expected to be significant in this strongly correlated, long living dark liquid. This is a new example of a two-dimensional atomic-like interacting dipolar quantum liquid, but where the coupling of light to its internal spin degrees of freedom plays a crucial role in the dynamical formation and the nature of resulting ground state.

  9. Magnetic relaxation in dipolar magnetic nanoparticle clusters

    NASA Astrophysics Data System (ADS)

    Hovorka, Ondrej; Barker, Joe; Chantrell, Roy; Friedman, Gary; York-Drexel Collaboration

    2013-03-01

    Understanding the role of dipolar interactions on thermal relaxation in magnetic nanoparticle (MNP) systems is of fundamental importance in magnetic recording, for optimizing the hysteresis heating contribution in the hyperthermia cancer treatment in biomedicine, or for biological and chemical sensing, for example. In this talk, we discuss our related efforts to quantify the influence of dipolar interactions on thermal relaxation in small clusters of MNPs. Setting up the master equation and solving the associated eigenvalue problem, we identify the observable relaxation time scale spectra for various types of MNP clusters, and demonstrate qualitatively different spectral characteristics depending on the point group of symmetries of the particle arrangement within the cluster - being solely a dipolar interaction effect. Our findings provide insight into open questions related to magnetic relaxation in bulk MNP systems, and may prove to be also of practical relevance, e.g., for improving robustness of methodologies in biological and chemical sensing. OH gratefully acknowledges support from a Marie Curie Intra European Fellowship within the 7th European Community Framework Programme under grant agreement PIEF-GA-2010-273014

  10. Dark High Density Dipolar Liquid of Excitons.

    PubMed

    Cohen, Kobi; Shilo, Yehiel; West, Ken; Pfeiffer, Loren; Rapaport, Ronen

    2016-06-01

    The possible phases and the nanoscale particle correlations of two-dimensional interacting dipolar particles is a long-sought problem in many-body physics. Here we observe a spontaneous condensation of trapped two-dimensional dipolar excitons with internal spin degrees of freedom from an interacting gas into a high density, closely packed liquid state made mostly of dark dipoles. Another phase transition, into a bright, highly repulsive plasma, is observed at even higher excitation powers. The dark liquid state is formed below a critical temperature Tc ≈ 4.8 K, and it is manifested by a clear spontaneous spatial condensation to a smaller and denser cloud, suggesting an attractive part to the interaction which goes beyond the purely repulsive dipole-dipole forces. Contributions from quantum mechanical fluctuations are expected to be significant in this strongly correlated, long living dark liquid. This is a new example of a two-dimensional atomic-like interacting dipolar liquid, but where the coupling of light to its internal spin degrees of freedom plays a crucial role in the dynamical formation and the nature of resulting condensed dark ground state.

  11. 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.

  12. Aging solitons in photorefractive dipolar glasses.

    PubMed

    Parravicini, J; Pierangeli, D; Di Mei, F; Conti, C; Agranat, A J; DelRe, E

    2013-12-16

    We study experimentally the aging of optical spatial solitons in a dipolar glass hosted by a nanodisordered sample of photorefractive potassium-sodium-tantalate-niobate (KNTN). As the system ages, the waves erratically explore varying strengths of the nonlinear response, causing them to break up and scatter. We show that this process can still lead to solitons, but in a generalized form for which the changing response is compensated by changing the normalized wave size and intensity so as to maintain fixed the optical waveform.

  13. Anisotropic Superfluidity in a Dipolar Bose Gas

    SciTech Connect

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

    2011-02-11

    We study the superfluid character of a dipolar Bose-Einstein condensate (DBEC) in a quasi-two dimensional geometry. We consider the dipole polarization to have some nonzero projection into the plane of the condensate so that the effective interaction is anisotropic in this plane, yielding an anisotropic dispersion relation. By performing direct numerical simulations of a probe moving through the DBEC, we observe the sudden onset of drag or creation of vortex-antivortex pairs at critical velocities that depend strongly on the direction of the probe's motion. This anisotropy emerges because of the anisotropic manifestation of a rotonlike mode in the system.

  14. Two dipolar atoms in a harmonic trap

    NASA Astrophysics Data System (ADS)

    Ołdziejewski, Rafał; Górecki, Wojciech; Rzążewski, Kazimierz

    2016-05-01

    Two identical dipolar atoms moving in a harmonic trap without an external magnetic field are investigated. Using the algebra of angular momentum we reduce the problem to a simple numerics. We show that the internal spin-spin interactions between the atoms couple to the orbital angular momentum causing an analogue of the Einstein-de Haas effect. We show a possibility of adiabatically pumping our system from the s-wave to the d-wave relative motion. The effective spin-orbit coupling occurs at anti-crossings of the energy levels.

  15. Nonlocal order in elongated dipolar gases

    NASA Astrophysics Data System (ADS)

    Ruhman, J.; Dalla Torre, E. G.; Huber, S. D.; Altman, E.

    2012-03-01

    Dipolar particles in an elongated trap are expected to undergo a quantum phase transition from a linear to a zigzag structure with decreasing transverse confinement. We derive the low-energy effective theory of the transition showing that in the presence of quantum fluctuations the zigzag phase can be characterized by a long-ranged string order, while the local Ising correlations decay as a power law. This is also confirmed using density matrix renormalization group calculations on a microscopic model. The nonlocal order in the bulk gives rise to zero energy states localized at the interface between the ordered and disordered phases. Such an interface naturally arises when the particles are subject to a weak harmonic confinement along the tube axis. We compute the signature of the edge states in the single-particle tunneling spectra pointing to differences between a system with bosonic versus fermionic particles. Finally we assess the magnitude of the relevant quantum fluctuations in realistic systems of dipolar particles, including ultracold polar molecules as well as alkali atoms weakly dressed by a Rydberg excitation.

  16. Freezing in relaxor ferroelectrics and dipolar glasses

    NASA Astrophysics Data System (ADS)

    Pirc, Raša; Kutnjak, Zdravko

    2015-03-01

    A recently proposed semi-phenomenological model of freezing in relaxor ferroelectrics, based on the concept of polar nanoregions (PNRs) embedded in a polarizable medium, is reviewed. A generalized Landau-type free energy for the medium is discussed, where the medium polarization couples linearly to the PNR polarization. When the fourth-order Landau coefficient is negative (b < 0), the correlation radius rc, which measures the PNR size, depends on the temperature T and the applied field E. As T is lowered or E increased, rc increases and the volume of a cluster of PNRs grows until the percolation limit is reached. This leads to a generalized expression for the Vogel-Fulcher (VF) relaxation time with a field-dependent VF freezing temperature T0(E). The case b > 0, in which the percolation mechanism cannot be realized, is considered to be appropriate for dipolar glasses.

  17. Crystallization of a dilute atomic dipolar condensate

    NASA Astrophysics Data System (ADS)

    Bisset, Russell; Blakie, Blair

    2016-05-01

    A recent experiment found that a dilute BEC of highly-magnetic dysprosium atoms may spontaneously break up into a crystal of droplets, a process reminiscent of the Rosensweig instability [ArXiv:1508.05007]. We dynamically simulate this scenario and find that the standard dipolar Gross-Pitaevskii equation (GPE) cannot explain such a droplet crystal. Indeed, the GPE predicts too much heating during the violent droplet formation, and a droplet lifetime that is much shorter than observed in the experiment. We investigate the requisite properties of the unknown stabilization mechanism, and find that an effective repulsive interaction with a higher order density dependence than the usual two-body interactions is required to quantitatively reproduce the experimental results.

  18. Topological flat bands from dipolar spin systems.

    PubMed

    Yao, N Y; Laumann, C R; Gorshkov, A V; Bennett, S D; Demler, E; Zoller, P; Lukin, M D

    2012-12-28

    We propose and analyze a physical system that naturally admits two-dimensional topological nearly flat bands. Our approach utilizes an array of three-level dipoles (effective S=1 spins) driven by inhomogeneous electromagnetic fields. The dipolar interactions produce arbitrary uniform background gauge fields for an effective collection of conserved hard-core bosons, namely, the dressed spin flips. These gauge fields result in topological band structures, whose band gap can be larger than the corresponding bandwidth. Exact diagonalization of the full interacting Hamiltonian at half-filling reveals the existence of superfluid, crystalline, and supersolid phases. An experimental realization using either ultracold polar molecules or spins in the solid state is considered.

  19. 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.

  20. 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.

  1. Vortex Lattices in Rotating Atomic Bose Gases with Dipolar Interactions

    SciTech Connect

    Cooper, N.R.; Rezayi, E.H.; Simon, S.H.

    2005-11-11

    We show that dipolar interactions have dramatic effects on the ground states of rotating atomic Bose gases in the weak-interaction limit. With increasing dipolar interaction (relative to the net contact interaction), the mean field, or high filling factor, ground state undergoes a series of transitions between vortex lattices of different symmetries: triangular, square, 'stripe', and 'bubble' phases. We also study the effects of dipolar interactions on the quantum fluids at low filling factors. We show that the incompressible Laughlin state at filling factor {nu}=1/2 is replaced by compressible stripe and bubble phases.

  2. Free Expansion of a Weakly-Interacting Dipolar Fermi Gas

    NASA Astrophysics Data System (ADS)

    Takushi Nishimura,; Tomoyuki Maruyama,

    2010-08-01

    We theoretically investigate a polarized dipolar Fermi gas in free expansion. The inter-particle dipolar interaction deforms phase-space distribution in trap and also in the expansion. We exactly predict the minimal quadrupole deformation in the expansion for the high-temperature Maxwell-Boltzmann and zero-temperature Thomas-Fermi gases in the Hartree-Fock and Landau-Vlasov approaches. In conclusion, we provide a proper approach to develop the time-of-flight method for the weakly-interacting dipolar Fermi gas and also reveal a scaling law associated with the Liouville’s theorem in the long-time behaviors of the both gases.

  3. Diffraction cancellation over multiple wavelengths in photorefractive dipolar glasses.

    PubMed

    Parravicini, J; Di Mei, F; Conti, C; Agranat, A J; DelRe, E

    2011-11-21

    We report the simultaneous diffraction cancellation for beams of different wavelengths in out-of-equilibrium dipolar glass. The effect is supported by the photorefractive diffusive nonlinearity and scale-free optics, and can find application in imaging and microscopy.

  4. Soft modes, freezing, and nonlinear response of a dipolar glass

    SciTech Connect

    Lyons, K.B.; Fleury, P.A.; Chou, H.; Kjems, J.; Shapiro, S.; Rytz, D.; Brookhaven National Lab., Upton, NY; Hughes Research Labs., Malibu, CA )

    1989-01-01

    A careful study of the polarization dynamics near the dipolar glass transition, utilizing both neutron and light scattering reveals a dichotomy in the behavior, on the one hand suggesting ordered domains of macroscopic extent and on the other clearly indicating dynamic cluster behavior in the same temperature region. An examination of this evidence leads us to suggest a percolated cluster model for the dipolar glass phase in KTN. 13 refs., 4 figs., 1 tab.

  5. Artificial Kagome Arrays of Nanomagnets: A Frozen Dipolar Spin Ice

    NASA Astrophysics Data System (ADS)

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

    2011-02-01

    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.

  6. 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.

  7. 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.

  8. Self-replication with magnetic dipolar colloids

    NASA Astrophysics Data System (ADS)

    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.

  9. 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.

  10. Formation mechanisms of magnetotail dipolarization fronts

    NASA Astrophysics Data System (ADS)

    Fu, Huishan

    2016-07-01

    Dipolarization fronts (DFs) are frequently detected in the Earth's magnetotail. How these DFs are formed is still poorly understood. Three possible mechanisms have been suggested in previous simulations: (1) jet braking, (2) transient reconnection, and (3) spontaneous formation. Among these three mechanisms, the first has been verified by using spacecraft observation, while the second and third have not. In this study, we show Cluster observation of DFs inside reconnection diffusion region. This observation provides in situ evidence of the second mechanism: transient reconnection can produce DFs. We suggest that the DFs detected in the near-Earth region (XGSM > -10 RE) are primarily attributed to jet braking, while the DFs detected in the mid- or far-tail region (XGSM < -15 RE) are primarily attributed to transient reconnection or spontaneous formation. In the jet-braking mechanism, the high-speed flow 'pushes' the pre-existing plasmas to produce the DF, so that there is causality between high-speed flow and DF. In the transient-reconnection mechanism, there is no causality between high-speed flow and DF, because the frozen-in condition is violated.

  11. 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

  12. 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.

  13. Beliaev damping in quasi-two-dimensional dipolar condensates

    NASA Astrophysics Data System (ADS)

    Wilson, Ryan M.; Natu, Stefan

    2016-05-01

    We study the effects of quasiparticle interactions in a quasi-two-dimensional (quasi-2D), zero-temperature Bose-Einstein condensate of dipolar atoms, which can exhibit a roton-maxon feature in its quasiparticle spectrum. Our focus is the Beliaev damping process, in which a quasiparticle collides with the condensate and resonantly decays into a pair of quasiparticles. Remarkably, the rate for this process exhibits a highly nontrivial dependence on the quasiparticle momentum and the dipolar interaction strength. For weak interactions, low-energy phonons experience no damping, and higher-energy quasiparticles undergo anomalously weak damping. In contrast, the Beliaev damping rates become anomalously large for stronger dipolar interactions, as rotons become energetically accessible as final states. When the dipoles are tilted off the axis of symmetry, the damping rates acquire an anisotropic character. Surprisingly, this anisotropy does not simply track the anisotropy of the dipolar interactions, rather, the mechanisms for damping are qualitatively modified in the anisotropic case. Our study reveals the unconventional nature of Beliaev damping in dipolar condensates, and has important implications for ongoing studies of equilibrium and nonequilibrium dynamics in these systems. Further, our results are relevant for other 2D superfluids with roton excitations, including spin-orbit-coupled Bose gases, magnon condensates, and 4He films.

  14. Evidence for two types of dipolarization in the earth's magnetotail

    NASA Astrophysics Data System (ADS)

    Lui, A. T. Y.

    2014-08-01

    There is a long history in the study of current-disruptions/dipolarizations (CDDs) in the Earth's magnetotail. A recent trend for this topic is the focus on very transient (~1-2 min) positive pulses of the Bz component in the magnetotail coined as dipolarization fronts (DFs). We reviewed several salient features of CDDs reported previously and compare them with those of DFs. We find several major differences between them. First, their temporal profiles differ significantly-DFs have pulse-like form while CDDs have the sustained dipolarization lasting for many minutes. Second, CDDs are typically associated with initial large magnetic fluctuations having the characteristics of turbulence while DFs are not. Third, DFs typically propagate Earthward while CDDs spread tailward. Fourth, DFs are mainly spatial structures acting as discontinuities to separate the regions ahead and behind them with a north-south oriented thin current sheet. On the other hand, CDDs are mainly temporal manifestations of a local dynamic process that reduces the east-west cross-tail current near the neutral sheet. There is indication that CDDs in the near-Earth region (within the downstream distance of ~15 RE) occur prior to substorm onset and DFs are typically found in the midtail region after substorm onsets. These differences justify renaming DFs as dipolarization pulses so that the fronts of CDDs can be distinguished from dipolarization pulses without the confusion brought about by the present terminology.

  15. Dynamics of nematic order in ultracold dipolar gases

    NASA Astrophysics Data System (ADS)

    Ebling, Ulrich; Ueda, Masahito

    2016-05-01

    We study dynamcial properties of ultracold atoms with strong dipole-dipole interactions, such as rare-earth atoms like Erbium or Dysprosium. Dipole-dipole interactions are anisotropic and can lead to the appearance of two types of nematic order in such quantum gases. Orbital nematic order is related to spatial anisotropies such as the deformation of a Fermi surface of an ultracold dipolar Fermi gas. Spin nematic order is present only in systems with spin larger than 1/2 as a higher moment of the spin operators. We study the case of a not fully polarized dipolar gas, such that the intrinsic coupling of spin and orbital degrees of freedom can lead to an interplay between orbital and spin nematic order. We investigate how this interplay can lead to a transfer between orbital and spin nematicity, similar to the transfer of spin into orbital angular momentum predicted for dipolar gases.

  16. Quantum phases of dipolar soft-core bosons

    NASA Astrophysics Data System (ADS)

    Grimmer, D.; Safavi-Naini, A.; Capogrosso-Sansone, B.; Söyler, Ş. G.

    2014-10-01

    We study the phase diagram of a system of soft-core dipolar bosons confined to a two-dimensional optical lattice layer. We assume that dipoles are aligned perpendicular to the layer such that the dipolar interactions are purely repulsive and isotropic. We consider the full dipolar interaction and perform path-integral quantum Monte Carlo simulations using the worm algorithm. Besides a superfluid phase, we find various solid and supersolid phases. We show that, unlike what was found previously for the case of nearest-neighbor interaction, supersolid phases are stabilized by doping the solids not only with particles but with holes as well. We further study the stability of these quantum phases against thermal fluctuations. Finally, we discuss pair formation and the stability of the pair checkerboard phase formed in a bilayer geometry, and we suggest experimental conditions under which the pair checkerboard phase can be observed.

  17. Weyl superfluidity in a three-dimensional dipolar Fermi gas.

    PubMed

    Liu, Bo; Li, Xiaopeng; Yin, Lan; Liu, W Vincent

    2015-01-30

    Weyl superconductivity or superfluidity, a fascinating topological state of matter, features novel phenomena such as emergent Weyl fermionic excitations and anomalies. Here we report that an anisotropic Weyl superfluid state can arise as a low temperature stable phase in a 3D dipolar Fermi gas. A crucial ingredient of our model is a direction-dependent two-body effective attraction generated by a rotating external field. Experimental signatures are predicted for cold gases in radio-frequency spectroscopy. The finite temperature phase diagram of this system is studied and the transition temperature of the Weyl superfluidity is found to be within the experimental scope for atomic dipolar Fermi gases. PMID:25679898

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

    PubMed

    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.

  19. 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

  20. Magnetic order and energetics of dipolar coupling in magnetic superconductors

    PubMed Central

    Redi, Martha; Anderson, P. W.

    1981-01-01

    The exact (not just nearest-neighbor) dipolar coupling energy densities for the observed structures of the rare earth Chevrel compounds are calculated by the method of Luttinger and Tisza. The dipolar coupling energy density for the most probable spin configuration is comparable to the observed magnetic transition temperature, TM, but the most probable ground state is not found experimentally. The discrepancy between the observed magnetic ground state and that predicted from dipole coupling may arise from conduction electron effects or possibly from some strong crystal field effect and should be included in any electronic theory of the superconductive state below TM. PMID:16592947

  1. Realizing dipolar spin models with arrays of superconducting qubits

    NASA Astrophysics Data System (ADS)

    Dalmonte, M.; Mirzaei, S. I.; Muppalla, P. R.; Marcos, D.; Zoller, P.; Kirchmair, G.

    2015-11-01

    We propose a platform for quantum many body simulations of dipolar spin models using current circuit QED technology. Our basic building blocks are 3D transmon qubits where we use the naturally occurring dipolar interactions to realize interacting spin systems. This opens the way toward the realization of a broad class of tunable spin models in both two- and one-dimensional geometries. We illustrate the potential offered by these systems in the context of dimerized Majumdar-Ghosh-type phases, archetypical examples of quantum magnetism, showing how such phases are robust against disorder and decoherence and could be observed within state-of-the-art experiments.

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

    PubMed

    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

  3. 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.

  4. 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. PMID:24920153

  5. 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.

  6. 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

  7. 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.

  8. 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).

  9. Dipolar energy of Nd-Fe-B nanocrystalline magnets in magnetization reversal process

    NASA Astrophysics Data System (ADS)

    Ohtori, Hiroyuki; Iwano, Kaoru; Mitsumata, Chiharu; Yano, Masao; Kato, Akira; Shoji, Tetsuya; Manabe, Akira; Ono, Kanta

    2014-05-01

    We analyzed the dipolar energy of Nd-Fe-B nanocrystalline magnets in magnetization reversal process through visualizing magnetic dipolar interaction. We obtained magnetization distribution images experimentally by using scanning transmission X-ray microscopy (STXM). The magnetic dipolar interaction was calculated by the interaction between the magnetization at each point and those at the other points on the STXM image. We showed the dipolar energy in the nanocrystalline Nd-Fe-B magnets and compared it with the exchange energy at various applied fields. Our results indicated the significance of the dipolar energy in magnetization reversal process.

  10. Stability of a dipolar Bose-Einstein condensate in a one-dimensional lattice

    SciTech Connect

    Mueller, S.; Billy, J.; Henn, E. A. L.; Kadau, H.; Griesmaier, A.; Pfau, T.; Jona-Lasinio, M.; Santos, L.

    2011-11-15

    We show that in contrast with contact interacting gases, an optical lattice changes drastically the stability properties of a dipolar condensate, inducing a crossover from dipolar destabilization to dipolar stabilization for increasing lattice depths. Performing stability measurements on a {sup 52}Cr Bose-Einstein condensate in an interaction-dominated regime, repulsive dipolar interaction balances negative scattering lengths down to -17 Bohr radii. Our findings are in excellent agreement with mean-field calculations, revealing the important destabilizing role played by intersite dipolar interactions in deep lattices.

  11. Critical superfluid velocity in a trapped dipolar gas.

    PubMed

    Wilson, Ryan M; Ronen, Shai; Bohn, John L

    2010-03-01

    We investigate the superfluid properties of a dipolar Bose-Einstein condensate (BEC) in a fully three-dimensional trap. Specifically, we estimate a superfluid critical velocity for this system by applying the Landau criterion to its discrete quasiparticle spectrum. We test this critical velocity by direct numerical simulation of condensate depletion as a blue-detuned laser moves through the condensate. In both cases, the presence of the roton in the spectrum serves to lower the critical velocity beyond a critical particle number. Since the shape of the dispersion, and hence the roton minimum, is tunable as a function of particle number, we thereby propose an experiment that can simultaneously measure the Landau critical velocity of a dipolar BEC and demonstrate the presence of the roton in this system.

  12. Heat transfer through dipolar coupling: Sympathetic cooling without contact

    NASA Astrophysics Data System (ADS)

    Renklioglu, B.; Tanatar, B.; Oktel, M. Ã.-.

    2016-02-01

    We consider two parallel layers of dipolar ultracold Fermi gases at different temperatures and calculate the heat transfer between them. The effective interactions describing screening and correlation effects between the dipoles in a single layer are modeled within the Euler-Lagrange Fermi-hypernetted-chain approximation. The random-phase approximation is used for the interactions across the layers. We investigate the amount of transferred power between the layers as a function of the temperature difference. Energy transfer arises due to the long-range dipole-dipole interactions. A simple thermal model is established to investigate the feasibility of using the contactless sympathetic cooling of the ultracold polar atoms and molecules. Our calculations indicate that dipolar heat transfer is effective for typical polar molecule experiments and may be utilized as a cooling process.

  13. Cooling without contact in bilayer dipolar Fermi gases

    NASA Astrophysics Data System (ADS)

    Tanatar, Bilal; Renklioglu, Basak; Oktel, M. Ozgur

    2016-05-01

    We consider two parallel layers of dipolar ultracold Fermi gases at different temperatures and calculate the heat transfer between them. The effective interactions describing screening and correlation effects between the dipoles in a single layer are modelled within the Euler-Lagrange Fermi-hypernetted chain approximation. The random-phase approximation is employed for the interactions across the layers. We investigate the amount of transferred power between the layers as a function of the temperature difference. Energy transfer proceeds via the long-range dipole-dipole interactions. A simple thermal model is developed to investigate the feasibility of using the contactless sympathetic cooling of the ultracold polar atoms/molecules. Our calculations indicate that dipolar heat transfer is effective for typical polar molecule experiments and may be utilized as a cooling process. Supported by TUBA and TUBITAK (112T974).

  14. 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.

  15. Demixing in binary mixtures of apolar and dipolar hard spheres

    NASA Astrophysics Data System (ADS)

    Almarza, N. G.; Lomba, E.; Martín, C.; Gallardo, A.

    2008-12-01

    We study the demixing transition of mixtures of equal size hard spheres and dipolar hard spheres using computer simulation and integral equation theories. Calculations are carried out at constant pressure, and it is found that there is a strong correlation between the total density and the composition. The critical temperature and the critical total density are found to increase with pressure. The critical mole fraction of the dipolar component on the contrary decreases as pressure is augmented. These qualitative trends are reproduced by the theoretical approaches that on the other hand overestimate by far the value of the critical temperature. Interestingly, the critical parameters for the liquid-vapor equilibrium extrapolated from the mixture results in the limit of vanishing neutral hard sphere concentration agree rather well with recent estimates based on the extrapolation of charged hard dumbbell phase equilibria when dumbbell elongation shrinks to zero [G. Ganzenmüller and P. J. Camp, J. Chem. Phys. 126, 191104 (2007)].

  16. 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.

  17. 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.

  18. Current Driven Magnetic Damping in Dipolar-Coupled Spin System

    NASA Astrophysics Data System (ADS)

    Lee, Sung Chul; Pi, Ung Hwan; Kim, Keewon; Kim, Kwang Seok; Shin, Jaikwang; -in Chung, U.

    2012-07-01

    Magnetic damping of the spin, the decay rate from the initial spin state to the final state, can be controlled by the spin transfer torque. Such an active control of damping has given birth to novel phenomena like the current-driven magnetization reversal and the steady spin precession. The spintronic devices based on such phenomena generally consist of two separate spin layers, i.e., free and pinned layers. Here we report that the dipolar coupling between the two layers, which has been considered to give only marginal effects on the current driven spin dynamics, actually has a serious impact on it. The damping of the coupled spin system was greatly enhanced at a specific field, which could not be understood if the spin dynamics in each layer was considered separately. Our results give a way to control the magnetic damping of the dipolar coupled spin system through the external magnetic field.

  19. 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.

  20. Coherent manipulation of dipolar coupled spins in an anisotropic environment

    NASA Astrophysics Data System (ADS)

    Baibekov, E. I.; Gafurov, M. R.; Zverev, D. G.; Kurkin, I. N.; Malkin, B. Z.; Barbara, B.

    2014-11-01

    We study coherent dynamics in a system of dipolar coupled spin qubits diluted in a solid and subjected to a driving microwave field. In the case of rare earth ions, an anisotropic crystal background results in anisotropic g tensor and thus modifies the dipolar coupling. We develop a microscopic theory of spin relaxation in a transient regime for the frequently encountered case of axially symmetric crystal field. The calculated decoherence rate is nonlinear in the Rabi frequency. We show that the direction of a static magnetic field that corresponds to the highest spin g factor is preferable in order to obtain a higher number of coherent qubit operations. The results of calculations are in excellent agreement with our experimental data on Rabi oscillations recorded for a series of CaW O4 crystals with different concentrations of N d3 + ions.

  1. Quantum filaments in dipolar Bose-Einstein condensates

    NASA Astrophysics Data System (ADS)

    Wächtler, F.; Santos, L.

    2016-06-01

    Collapse in dipolar Bose-Einstein condensates may be arrested by quantum fluctuations. Due to the anisotropy of the dipole-dipole interactions, the dipole-driven collapse induced by soft excitations is compensated by the repulsive Lee-Huang-Yang contribution resulting from quantum fluctuations of hard excitations, in a similar mechanism as that recently proposed for Bose-Bose mixtures. The arrested collapse results in self-bound filamentlike droplets, providing an explanation for the intriguing results of recent dysprosium experiments. Arrested instability and droplet formation are general features directly linked to the nature of the dipole-dipole interactions, and should hence play an important role in all future experiments with strongly dipolar gases.

  2. Dipolar Bose-Einstein condensates with weak disorder

    SciTech Connect

    Krumnow, Christian; Pelster, Axel

    2011-08-15

    A homogeneous polarized dipolar Bose-Einstein condensate is considered in the presence of weak quenched disorder within mean-field theory at zero temperature. By first solving perturbatively the underlying Gross-Pitaevskii equation and then performing disorder ensemble averages for physical observables, it is shown that the anisotropy of the two-particle interaction is passed on to both the superfluid density and the sound velocity.

  3. Thermal entanglement and teleportation in a dipolar interacting system

    NASA Astrophysics Data System (ADS)

    Castro, C. S.; Duarte, O. S.; Pires, D. P.; Soares-Pinto, D. O.; Reis, M. S.

    2016-04-01

    Quantum teleportation, which depends on entangled states, is a fascinating subject and an important branch of quantum information processing. The present work reports the use of a dipolar spin thermal system as a noisy quantum channel to perform quantum teleportation. Non-locality, tested by violation of Bell's inequality and thermal entanglement, measured by negativity, shows that for the present model all entangled states, even those that do not violate Bell's inequality, are useful for teleportation.

  4. Band-selective homonuclear dipolar recoupling in rotating solids

    NASA Astrophysics Data System (ADS)

    Hohwy, M.; Rienstra, C. M.; Griffin, R. G.

    2002-09-01

    In this paper, we introduce approaches to band-selective homonuclear dipolar recoupling with the SPC-5 sequence described previously [Hohwy [et al.], J. Chem. Phys. 110, 7983 (1999)]. The technique, denoted SPC-53, restores the homonuclear dipolar coupling during magic angle spinning (MAS) and introduces a fifth-order residual offset term of controllable magnitude. The fifth order term truncates the dipolar coupling to spins that fall outside the operational bandwidth of the experiment. It is shown with high-order average Hamiltonian theory, multiple-spin simulations, and experiments, that polarization within a spin cluster can be propagated to destination spins with improved efficiency using this approach. Further, we show that a spin system subjected to band-selective recoupling obeys the equation of motion of the reduced spin cluster and that modeling of the polarization transfer process is simplified. Thus, in the important case of peptides and proteins, all of the backbone and side-chain carbonyl spins as well as aromatic spins can be neglected, leading to enhanced transfer efficiency among Calpha, Cbeta, Cgamma, etc. Experimental spectra of U-13C,15N-threonine and formyl-U-13C,15N-Met-Leu-Phe-OH, indicate that the backbone carbonyl and sidechain aromatic spins can be neglected in the polarization transfer equations. This leads to enhanced transfer efficiencies of up to a factor of approx2.

  5. Propagating Dipolarization Fronts Earthward of 6 Earth Radii

    NASA Astrophysics Data System (ADS)

    Malaspina, D.; Andersson, L.; Ergun, R.; Wygant, J. R.; Bonnell, J. W.; Kletzing, C.; Reeves, G. D.; Skoug, R. M.; Larsen, B.

    2014-12-01

    During geomagnetically active conditions, the Van Allen Probes observe magnetic dipolarizations associated with enhancements in > 1 keV electron energy flux and the presence of nonlinear electric field structures (e.g. double layers and phase space holes) in the inner magnetosphere (4-6 Re). These dipolarization events are observed most frequently between dusk and midnight, though some appear between midnight and dawn. In some cases, nonlinear electric field power shows abrupt onset that is nearly simultaneous with electron energy flux enhancements across a range of energies. By comparing magnetic field, electric field, and particle data from both spacecraft, recorded when the twin Van Allen Probes are in close proximity, it is found that some of these abrupt onset features can be identified as earthward-propagating fonts with speeds on the order of 30 km/s. The presence of coherent propagating dipolarization fronts well inside the nominal flow breaking region (9 - 12 Re) suggests that earthward plasma flows may influence the magnetospheric plasma environment at the radial distances associated with the ring current and radiation belts. Possible mechanisms for this influence include the localized injection of particles adiabatically energized by their earthward transport, and wave-particle interactions related to the high amplitude parallel electric fields associated with the nonlinear electric field structures observed near these propagating fronts.

  6. Quantum dynamics of a dipolar Fermi gas in free expansion

    NASA Astrophysics Data System (ADS)

    Nishimura, T.; Maruyama, T.

    2010-05-01

    We presented our theoretical study on quantum dynamics of a polarized dipolar Fermi gas in free expansion. The dipole-dipolar interparticle interaction induces axisymmetrical deformation of the expanding gas not only in the spatial space but also in the momentum space, so that, in order to obtain proper results in the time-of-flight method for the dipolar Fermi gas, it is necessary to deal with time-evolution of the deformation. To solve the free expansion problem, we develop the Hartree-Fock and Landau-Vlasov approaches and a new time-evolution ansatz for the quantum dynamics. In conclusion, we obtain exact predictions for the minimal quadrupole deformation of the high-temperature Maxwell-Boltzmann and zero-temperature Thomas-Fermi gases in the week-interaction and small-deformation regime, and also reveal a scaling law associated with the Liouville’s theorem in the long-time behaviors of the MB and TF gases.

  7. The sum rule for dipolar absorptions and rotational kinetic energy of wate and some dipolar molecules in condensed phases

    NASA Astrophysics Data System (ADS)

    Ikawa, Shun-ichi; Yamazaki, Shuichi; Kimura, Masao

    1981-06-01

    Another form of the sum rule for dipolar absorptions has been derived by means of quantum statistics. The difference between this and usually used form results from a quantum effect on the molecular rotational motion. By the joint use of the two forms, average rotational kinetic energies of water molec in the liquid and solid phases and some dipolar molecules in solutions have been estimated. It has been shown that the average rotational kinetic energ larger than the value expected from the classical equipartition rule, with an increase in the hindering potential for the rotational motion of the mole The dipole moments of water molecules in liquid and solid water have been estimated. These are considerably smaller than the gas-phase value.

  8. Coherent matter waves of a dipolar condensate in two-dimensional optical lattices

    SciTech Connect

    Zhang Aixia; Xue Jukui

    2010-07-15

    The coherent matter waves of a dipolar condensate in deep two-dimensional (2D) tilted and nontilted optical lattices are studied both analytically and numerically. It is shown that, in tilted lattices, by properly designing the sign and the magnitude of the contact interaction and the dipolar interaction, it is possible to control the decoherence of Bloch oscillations. Contrary to the usual short-range interacting Bose system, long-lived Bloch oscillations of the dipolar condensate are achieved when the dipolar interaction, the contact interaction, and the lattice dimension satisfy an analytical condition. Furthermore, we predict that, in untilted lattices, stable coherent 2D moving soliton and breather states of the dipolar condensate exist. This fact is very different from the purely short-range interacting Bose system (where the moving soliton cannot be stabilized in high-dimensional lattices). The dipolar interaction can lead to some novel phenomena that can not appear in short-range interacting BEC system.

  9. 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.

  10. A long-lived spin-orbit-coupled dipolar Fermi gas

    NASA Astrophysics Data System (ADS)

    Burdick, Nathaniel; Tang, Yijun; Kao, Wil; Lev, Benjamin

    2016-05-01

    We report on the demonstration of spin-orbit coupling in a quantum degenerate dipolar Fermi gas of dysprosium. The T /TF = 0 . 4 gas has a lifetime as large as 0.4 s under Raman dressing at densities exceeding 1013 cm-3. The lifetime is limited not by spontaneous emission but by dipolar relaxation loss, and the effect of the dipolar interaction is also observed in the dephasing of Rabi oscillations. This spin-orbit-coupled dipolar gas will allow future studies of fermionic systems in the presence of synthetic gauge fields wherein long lifetimes are essential to observing collective effects.

  11. 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.

  12. 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.

  13. Quantum Phases of a Two-Dimensional Dipolar Fermi Gas

    SciTech Connect

    Bruun, G. M.; Taylor, E.

    2008-12-12

    We examine the superfluid and collapse instabilities of a quasi-two-dimensional gas of dipolar fermions aligned by an orientable external field. It is shown that the interplay between the anisotropy of the dipole-dipole interaction, the geometry of the system, and the p-wave symmetry of the superfluid order parameter means that the effective interaction for pairing can be made very large without the system collapsing. This leads to a broad region in the phase diagram where the system forms a stable superfluid. Analyzing the superfluid transition at finite temperatures, we calculate the Berezinskii-Kosterlitz-Thouless temperature as a function of the dipole angle.

  14. Confocal shift interferometry of coherent emission from trapped dipolar excitons

    SciTech Connect

    Repp, J.; Schinner, G. J.; Schubert, E.; Rai, A. K.; Wieck, A. D.; Reuter, D.; Wurstbauer, U.; Holleitner, A. W.; and others

    2014-12-15

    We introduce a confocal shift-interferometer based on optical fibers. The presented spectroscopy allows measuring coherence maps of luminescent samples with a high spatial resolution even at cryogenic temperatures. We apply the spectroscopy onto electrostatically trapped, dipolar excitons in a semiconductor double quantum well. We find that the measured spatial coherence length of the excitonic emission coincides with the point spread function of the confocal setup. The results are consistent with a temporal coherence of the excitonic emission down to temperatures of 250 mK.

  15. Quantum melting of a crystal of dipolar bosons

    SciTech Connect

    Mora, Christophe; Parcollet, Olivier

    2007-08-01

    We investigate the behavior of dipolar bosons in two dimensions. We describe the large density crystalline limit analytically while we use quantum Monte Carlo to study the melting toward the Bose-Einstein condensate. We find strong evidence for a first order transition. We characterize the window of experimentally accessible parameters in the context of ultracold bosons and show that observing the quantum melting should be within grasp once one is able to form cold heteronuclear molecules. Close to the melting, we cannot conclude on the existence of a supersolid phase due to an insufficient overlap of our variational Bijl-Jastrow ansatz with the actual ground state.

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

    PubMed

    Tycko, Robert

    2007-11-01

    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.

  17. On the rigidity of polynorbornenes with dipolar pendant groups.

    PubMed

    Lin, Wei-Yu; Murugesh, Modachur G; Sudhakar, Sundarraj; Yang, Hsiao-Ching; Tai, Hwan-Ching; Chang, Chia-Seng; Liu, Yi-Hung; Wang, Yu; Chen, I-Wen Peter; Chen, Chun-Hsien; Luh, Tien-Yau

    2005-12-16

    A range of polynorbornenes (PNBs) with fused dipolar pendant groups at C-5,6 positions was synthesized by ring-opening metathesis polymerization catalyzed by a ruthenium carbene complex (Grubbs I). Photophysical studies, EFISH measurements, and atomic force microscopy images have been used to investigate the structures and morphology of these polymers. These results suggest that the polymers may adopt rigid rod-like structures. The presence of the double bonds in PNBs appeared to be indispensable for the rigidity of the polymers. Interaction between unsaturated pendant groups may result in coherent alignment leading to a rod-like structure.

  18. Freezing transition of a strongly dipolar simple fluid

    NASA Astrophysics Data System (ADS)

    Gao, G. T.; Zeng, X. C.

    2000-03-01

    The freezing transition of a strongly dipolar Lennard-Jones fluid is investigated using Monte Carlo simulation. It is found that the system undergoes a ferroelectric liquid-to-solid transition when cooled under a constant pressure. Near the triple point the stable solid phase is a body-centered orthorhombic ferroelectric crystal; a metastable ferroelectric solid phase with distorted hexagonal lattice structure is also discovered. To locate the freezing point, Gibbs free energies of the solid and liquid phase are determined using a thermodynamic integration method.

  19. Density functional theory for strongly-correlated ultracold dipolar gases

    NASA Astrophysics Data System (ADS)

    Malet Giralt, Francesc; Reimann, Stephanie; Gori-Giorgi, Paola; Lund University Collaboration

    2014-03-01

    We address quasi-one-dimensional strongly-correlated dipolar ultracold gases by means of density functional theory. We make use of an approximation for the Hartree-exchange-correlation that has been shown to be very accurate for electronic systems with coulombic interactions. We show that this approach allows to treat systems with very large particle numbers at relatively low computational cost. This work has been supported by a VIDI grant of the NWO and a Marie Curie grant within the FP7 programme.

  20. 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.

  1. 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

  2. Observation of Fermi surface deformation in a dipolar quantum gas

    NASA Astrophysics Data System (ADS)

    Aikawa, K.; Baier, S.; Frisch, A.; Mark, M.; Ravensbergen, C.; Ferlaino, F.

    2014-09-01

    In the presence of isotropic interactions, the Fermi surface of an ultracold Fermi gas is spherical. Introducing anisotropic interactions can deform the Fermi surface, but the effect is subtle and challenging to observe experimentally. Here, we report on the observation of a Fermi surface deformation in a degenerate dipolar Fermi gas of erbium atoms. The deformation is caused by the interplay between strong magnetic dipole-dipole interaction and the Pauli exclusion principle. We demonstrate the many-body nature of the effect and its tunability with the Fermi energy. Our observation provides a basis for future studies on anisotropic many-body phenomena in normal and superfluid phases.

  3. Spreading dynamics of 2D dipolar Langmuir monolayer phases.

    PubMed

    Heinig, P; Wurlitzer, S; Fischer, Th M

    2004-07-01

    We study the spreading of a liquid 2D dipolar droplet in a Langmuir monolayer. Interfacial tensions (line tensions) and microscopic contact angles depend on the scale on which they are probed and obey a scaling law. Assuming rapid equilibration of the microscopic contact angle and ideal slippage of the 2D solid/liquid and solid/gas boundary, the driving force of spreading is merely expressed by the shape-dependent long-range interaction integrals. We obtain good agreement between experiment and numerical simulations using this theory. PMID:15278693

  4. 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.

  5. Heisenberg-scaled magnetometer with dipolar spin-1 condensates

    NASA Astrophysics Data System (ADS)

    Xing, Haijun; Wang, Anbang; Tan, Qing-Shou; Zhang, Wenxian; Yi, Su

    2016-04-01

    We propose a scheme to realize a Heisenberg-scaled magnetometer using dipolar spin-1 condensates. The input state of magnetometer is prepared by slowly sweeping a transverse magnetic field to zero, which yields a highly entangled spin state of N atoms. We show that this process is protected by a parity symmetry such that the state preparation time is within the reach of the current experiment. We also propose a parity measurement with a Stern-Gerlach apparatus which is shown to approach the optimal measurement in the large atom number limit. Finally, we show that the phase estimation sensitivity of the proposed scheme roughly follows the Heisenberg scaling.

  6. Dynamical simulation of dipolar Janus colloids: dynamical properties.

    PubMed

    Hagy, Matthew C; Hernandez, Rigoberto

    2013-05-14

    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)]. 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. PMID:23676070

  7. Sensing with magnetic dipolar resonances in semiconductor nanospheres.

    PubMed

    García-Cámara, Braulio; Gómez-Medina, Raquel; Sáenz, Juan José; Sepúlveda, Borja

    2013-10-01

    In this work we propose two novel sensing principles of detection that exploit the magnetic dipolar Mie resonance in high-refractive-index dielectric nanospheres. In particular, we theoretically investigate the spectral evolution of the extinction and scattering cross sections of these nanospheres as a function of the refractive index of the external medium (next). Unlike resonances in plasmonic nanospheres, the spectral position of magnetic resonances in high-refractive-index nanospheres barely shifts as next changes. Nevertheless, there is a drastic reduction in the extinction cross section of the nanospheres when next increases, especially in the magnetic dipolar spectral region, which is accompanied with remarkable variations in the radiation patterns. Thanks to these changes, we propose two new sensing parameters, which are based on the detection of: i) the intensity variations in the transmitted or backscattered radiation by the dielectric nanospheres at the magnetic dipole resonant frequency, and ii) the changes in the radiation pattern at the frequency that satisfies Kerker's condition of near-zero forward radiation. To optimize the sensitivity, we consider several semiconductor materials and particles sizes.

  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. 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

  10. 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.

  11. Self-assembly of strongly dipolar molecules on metal surfaces

    NASA Astrophysics Data System (ADS)

    Kunkel, Donna A.; Hooper, James; Simpson, Scott; Miller, Daniel P.; Routaboul, Lucie; Braunstein, Pierre; Doudin, Bernard; Beniwal, Sumit; Dowben, Peter; Skomski, Ralph; Zurek, Eva; Enders, Axel

    2015-03-01

    The role of dipole-dipole interactions in the self-assembly of dipolar organic molecules on surfaces is investigated. As a model system, strongly dipolar model molecules, p-benzoquinonemonoimine zwitterions (ZI) of type C6H2(⋯ NHR)2(⋯ O)2 on crystalline coinage metal surfaces were investigated with scanning tunneling microscopy and first principles calculations. Depending on the substrate, the molecules assemble into small clusters, nano gratings, and stripes, as well as in two-dimensional islands. The alignment of the molecular dipoles in those assemblies only rarely assumes the lowest electrostatic energy configuration. Based on calculations of the electrostatic energy for various experimentally observed molecular arrangements and under consideration of computed dipole moments of adsorbed molecules, the electrostatic energy minimization is ruled out as the driving force in the self-assembly. The structures observed are mainly the result of a competition between chemical interactions and substrate effects. The substrate's role in the self-assembly is to (i) reduce and realign the molecular dipole through charge donation and back donation involving both the molecular HOMO and LUMO, (ii) dictate the epitaxial orientation of the adsorbates, specifically so on Cu(111), and (iii) inhibit attractive forces between neighboring chains in the system ZI/Cu(111), which results in regularly spaced molecular gratings.

  12. 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.

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

    NASA Astrophysics Data System (ADS)

    Steinbach, Gabi; Gemming, Sibylle; Erbe, Artur

    2016-09-01

    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.

  14. Visualization of magnetic dipolar interaction based on scanning transmission X-ray microscopy

    NASA Astrophysics Data System (ADS)

    Ohtori, Hiroyuki; Iwano, Kaoru; Mitsumata, Chiharu; Takeichi, Yasuo; Yano, Masao; Kato, Akira; Miyamoto, Noritaka; Shoji, Tetsuya; Manabe, Akira; Ono, Kanta

    2014-04-01

    Using scanning transmission X-ray microscopy (STXM), in this report we visualized the magnetic dipolar interactions in nanocrystalline Nd-Fe-B magnets and imaged their magnetization distributions at various applied fields. We calculated the magnetic dipolar interaction by analyzing the interaction between the magnetization at each point and those at the other points on the STXM image.

  15. Coherent zero-field magnetization resonance in a dipolar spin-1 Bose-Einstein condensate

    NASA Astrophysics Data System (ADS)

    Zhang, Wenxian; Yi, S.; Chapman, M. S.; You, J. Q.

    2015-08-01

    With current magnetic-field shielding and high-precision detection in dipolar spinor Bose-Einstein condensates, it is possible to experimentally detect the low- or zero-field nonsecular dipolar dynamics. Here we analytically investigate the zero-field nonsecular magnetic dipolar interaction effect, with an emphasis on magnetization dynamics in a spin-1 Bose-Einstein condensate under the single spatial mode approximation within the mean-field theory. Due to the biaxial nature of the dipolar interaction, a novel resonance occurs in the condensate magnetization oscillation, in contrast to the previous assumption of a conserved magnetization in strong magnetic fields. Furthermore, we propose a dynamical-decoupling detection method for such a resonance, which cancels the stray magnetic fields in experiment but restores the magnetization dynamics. Our results shed light on the dipolar systems and may find potential applications beyond cold atoms.

  16. Homonuclear dipolar recoupling techniques for structure determination in uniformly 13C-labeled proteins.

    PubMed

    Ladizhansky, Vladimir

    2009-11-01

    In solid-state NMR magic angle spinning is often used to remove line broadening associated with anisotropic interactions, such as chemical shift anisotropy and dipolar couplings. Dipolar recoupling refers to sequences of pulses designed to reintroduce dipolar interactions that are otherwise averaged by magic angle spinning. One of the key applications of homonuclear (and heteronuclear) dipolar recoupling is for the purpose of protein structure determination. Recoupling experiments, originally designed for applications in spin-pair labeled samples, have been revised in recent years for applications in samples with extensive or uniform incorporation of isotopic labels. In these samples multiple internuclear distances can in principle be probed simultaneously, but the dipolar truncation effects (i.e. attenuation of the effects of weak couplings by strong ones) circumvent such measurements. In this article we review some of the recent developments in homonuclear recoupling methods that allow overcoming this problem.

  17. Parameter maps of 1H residual dipolar couplings in tendon under mechanical load

    NASA Astrophysics Data System (ADS)

    Fechete, R.; Demco, D. E.; Blümich, B.

    2003-11-01

    Proton multipolar spin states associated with dipolar encoded longitudinal magnetization (DELM) and double-quantum (DQ) coherences of bound water are investigated for bovine and sheep Achilles tendon under mechanical load. DELM decay curves and DQ buildup and decay curves reveal changes of the 1H residual dipolar couplings for tendon at rest and under local compression forces. The multipolar spin states are used to design dipolar contrast filters for NMR 1H images of heterogeneous tendon. Heterogeneities in tendon samples were artificially generated by local compression parallel and perpendicular to the tendon plug axis. Quotient images obtained from DQ-filtered images by matched and mismatched excitation/reconversion periods are encoded only by the residual dipolar couplings. Semi-quantitative parameter maps of the residual dipolar couplings of bound water were obtained from these quotient images using a reference elastomer sample. This method can be used to quantify NMR imaging of injured ordered tissues.

  18. Quantum data bus in dipolar coupled nuclear spin qubits

    SciTech Connect

    Zhang Jingfu; Ditty, Michael; Ryan, Colm A.; Laforest, Martin; Moussa, Osama; Baugh, Jonathan; Burgarth, Daniel; Chandrashekar, C. M.; Laflamme, Raymond

    2009-07-15

    We implement an iterative quantum state transfer exploiting the natural dipolar couplings in a spin chain of a liquid-crystal NMR system. During each iteration, a finite part of the amplitude of the state is transferred and, by applying an external operation on only the last two spins, the transferred state is made to accumulate on the spin at the end point. The transfer fidelity reaches one asymptotically through increasing the number of iterations. We also implement the inverted version of the scheme which can transfer an arbitrary state from the end point to any other position of the chain and entangle any pair of spins in the chain, acting as a full quantum data bus.

  19. Time of flight transients in the dipolar glass model

    NASA Astrophysics Data System (ADS)

    Novikov, S. V.; Tyutnev, A. P.; Schein, L. B.

    2012-07-01

    Using Monte Carlo simulation we investigated time of flight current transients predicted by the dipolar glass model for a random spatial distribution of hopping centers. Behavior of the carrier drift mobility was studied at room temperature over a broad range of electric field and sample thickness. A flat plateau followed by j∝t-2 current decay is the most common feature of the simulated transients. Poole-Frenkel mobility field dependence was confirmed over 5-200 V/μm as well as its independence of the sample thickness. Universality of transients with respect to both field and sample thickness has been observed. A simple phenomenological model to describe simulated current transients has been proposed. Simulation results agree well with the reported Poole-Frenkel slope and shape of the transients for a prototype molecularly doped polymer.

  20. Resonance and localization effects at a dipolar organic semiconductor interface

    SciTech Connect

    Steele, Mary P.; Kelly, Leah L.; Ilyas, Nahid; Monti, Oliver L.A.

    2011-01-01

    The image state manifold of the dipolar organic semiconductor vanadyl naphthalocyanine (VONc) on highly oriented pyrolytic graphite is investigated by angle-resolved two-photon photoemission (AR-TPPE) spectroscopy in the 0 – 1 monolayer regimes. Interfacial charge-transfer from the image potential state of clean graphite populates a near-resonant VONc anion level, identifiable by the graphite image potential state by its distinct momentum dispersion obtained from AR-TPPE. This affinity level is subject to depolarization by the neighboring molecules, resulting in stabilization of this state with coverage. Near a coverage of one monolayer, a hybrid image potential/anion state is also formed, showing progressive localization with coverage. Intensities for all these features develop rather differently with molecular coverage, pointing towards the different types of charge-transfer interactions at play at this interface.

  1. 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.

  2. 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

  3. Fragmentation of magnetism in artificial kagome dipolar spin ice

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

    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.

  4. Scaling laws in NMR scattering via dipolar fields.

    PubMed

    Brown, S M; Sen, P N; Cory, D G

    2002-01-01

    Breaking translational symmetry in magnetostatics imparts a scale dependence that is commonly investigated in physics (W. Warren et al., 1993, Science 262, 2005-2008). An interesting and important example arises in nuclear magnetic resonance studies involving the dipolar mean field of adjacent nuclear spins where the scattering (transfer of spatial spin gratings) via intermolecular macroscopic fields carries a signature of the local spatial distribution of the spin density. For arbitrary geometry, the inverse problem of extracting this spin distribution from experiments is intractable. Here we point out a simple, universal crossover in the scaling behavior at the sample's characteristic length scale, xi, of the species fluctuations in the sample along the measurement direction. This behavior is observed experimentally in an oil-water emulsion, an important representation of complex, heterogeneous, soft matter. PMID:11820836

  5. 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.

  6. 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.

  7. Enhanced phase segregation induced by dipolar interactions in polymer blends

    SciTech Connect

    Kumar, Rajeev; Muthukumar, Murugappan; Sumpter, Bobby G

    2013-01-01

    We present a generalized theory for studying phase separation in polymer blends containing dipoles on their backbone. The theory is used to construct co-existence curves and study the effects of dipolar interactions on interfacial tension for a planar interface between the coexisting phases. It is shown that mismatch in monomeric dipole moments leads to destabilization of homogeneous phase. Corrections to the Flory-Huggins phase diagram are predicted using the theory. Furthermore, it is found that interfacial tension increases with an increase in the mismatch. Density profiles and interfacial tensions are constructed for diffuse and sharp polymer-polymer interfaces by extending Cahn-Hilliard and Helfand-Tagami-Sapse s treatment, respectively. Correlating dipole moments with the dielectric constant of pure phases, it is demonstrated that effects of mismatch between the dipole moments of the two monomers is equivalent to the dielectric mismatch between the polymers.

  8. 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.

  9. 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.

  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

    2016-01-01

    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

  11. Magnetic Orders and Fluctuations in the Dipolar Pyrochlore Antiferromagnet

    NASA Astrophysics Data System (ADS)

    Cepas, Olivier; Shastry, B. Sriram

    2005-03-01

    While the classical Heisenberg antiferromagnet on the pyrochlore lattice does not order, we will discuss, from a theoretical standpoint, possible magnetic phases induced by the dipole-dipole interactions. Such interactions play a role in systems such as Gd2Ti2O7 or Gd2Sn2O7 in stabilizing exotic forms of magnetic order, a subject of current debate. We will also argue that the external magnetic field induces multiple transitions, one of which is associated with no obvious broken symmetry, but can be characterized by a disorder parameter. Finally, Monte-Carlo simulations and Landau-Ginzburg expansion show that the dipolar Heisenberg model exhibits a fluctuation-induced first-order transition, thanks to the frustration and a continuous set of soft modes.

  12. 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

  13. Dipolar Physics in an Erbium Quantum Gas Microscope

    NASA Astrophysics Data System (ADS)

    Hebert, Anne; Krahn, Aaron; Phelps, Gregory; Dickerson, Susannah; Greiner, Markus; Erbium Lab Team

    2016-05-01

    Erbium offers exciting possibilities for extending the single-site imaging work of current quantum gas microscopes. With a magnetic dipole moment of 7μB, the dipole-dipole interaction of erbium is 50 times that of alkali atoms. The long-range and anisotropic nature of the dipole interaction adds richness to the short-range interactions that dominate the physics of the ground-state alkali atoms commonly used in ultracold experiments today. Erbium has several abundant isotopes, giving the added flexibility of studying both bosonic and fermionic systems. We present proposed avenues of research for the dipolar microscope being developed, including studies of magnetism, the Einstein-de Haas effect, and quantum phase transitions with fractional filling factors.

  14. 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.

  15. 1,3-Dipolar cycloadditions of azomethine imines.

    PubMed

    Nájera, Carmen; Sansano, José M; Yus, Miguel

    2015-08-28

    Azomethine imines are considered 1,3-dipoles of the aza-allyl type which are transient intermediates and should be generated in situ but can also be stable and isolable compounds. They react with electron-rich and electron-poor olefins as well as with acetylenic compounds and allenoates mainly by a [3 + 2] cycloaddition but they can also take part in [3 + 3], [4 + 3], [3 + 2 + 2] and [5 + 3] with different dipolarophiles. These 1,3-dipolar cycloadditions (1,3-DC) can be performed not only under thermal or microwave conditions but also using metallo- and organocatalytic systems. In recent years enantiocatalyzed 1,3-dipolar cycloadditions have been extensively considered and applied to the synthesis of a great variety of dinitrogenated heterocycles with biological activity. Acyclic azomethine imines derived from mono and disubstituted hydrazones could be generated by prototropy under heating or by using Lewis or Brønsted acids to give, after [3 + 2] cycloadditions, pyrazolidines and pyrazolines. Cyclic azomethine imines, incorporating a C-N bond in a ring, such as isoquinolinium imides are the most widely used dipoles in normal and inverse-electron demand 1,3-DC allowing the synthesis of tetrahydro-, dihydro- and unsaturated pyrazolo[1,5-a]isoquinolines in racemic and enantioenriched forms with interesting biological activity. Pyridinium and quinolinium imides give the corresponding pyrazolopyridines and indazolo[3,2-a]isoquinolines, respectively. In the case of cyclic azomethine imines with an N-N bond incorporated into a ring, N-alkylidene-3-oxo-pyrazolidinium ylides are the most popular stable and isolated dipoles able to form dinitrogen-fused saturated and unsaturated pyrazolopyrazolones as racemic or enantiomerically enriched compounds present in many pharmaceuticals, agrochemicals and other useful chemicals.

  16. 1,3-Dipolar cycloadditions of azomethine imines.

    PubMed

    Nájera, Carmen; Sansano, José M; Yus, Miguel

    2015-08-28

    Azomethine imines are considered 1,3-dipoles of the aza-allyl type which are transient intermediates and should be generated in situ but can also be stable and isolable compounds. They react with electron-rich and electron-poor olefins as well as with acetylenic compounds and allenoates mainly by a [3 + 2] cycloaddition but they can also take part in [3 + 3], [4 + 3], [3 + 2 + 2] and [5 + 3] with different dipolarophiles. These 1,3-dipolar cycloadditions (1,3-DC) can be performed not only under thermal or microwave conditions but also using metallo- and organocatalytic systems. In recent years enantiocatalyzed 1,3-dipolar cycloadditions have been extensively considered and applied to the synthesis of a great variety of dinitrogenated heterocycles with biological activity. Acyclic azomethine imines derived from mono and disubstituted hydrazones could be generated by prototropy under heating or by using Lewis or Brønsted acids to give, after [3 + 2] cycloadditions, pyrazolidines and pyrazolines. Cyclic azomethine imines, incorporating a C-N bond in a ring, such as isoquinolinium imides are the most widely used dipoles in normal and inverse-electron demand 1,3-DC allowing the synthesis of tetrahydro-, dihydro- and unsaturated pyrazolo[1,5-a]isoquinolines in racemic and enantioenriched forms with interesting biological activity. Pyridinium and quinolinium imides give the corresponding pyrazolopyridines and indazolo[3,2-a]isoquinolines, respectively. In the case of cyclic azomethine imines with an N-N bond incorporated into a ring, N-alkylidene-3-oxo-pyrazolidinium ylides are the most popular stable and isolated dipoles able to form dinitrogen-fused saturated and unsaturated pyrazolopyrazolones as racemic or enantiomerically enriched compounds present in many pharmaceuticals, agrochemicals and other useful chemicals. PMID:26140443

  17. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    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).

  19. 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

  20. Metastable States of a Gas of Dipolar Bosons in a 2D Optical Lattice

    SciTech Connect

    Menotti, C.; Trefzger, C.; Lewenstein, M.

    2007-06-08

    We investigate the physics of dipolar bosons in a two-dimensional optical lattice. It is known that due to the long-range character of dipole-dipole interaction, the ground state phase diagram of a gas of dipolar bosons in an optical lattice presents novel quantum phases, like checkerboard and supersolid phases. In this Letter, we consider the properties of the system beyond its ground state, finding that it is characterized by a multitude of almost degenerate metastable states, often competing with the ground state. This makes dipolar bosons in a lattice similar to a disordered system and opens possibilities of using them as quantum memories.

  1. Symmetry break in ferromagnetic electrocrystallization: the interplay between dipolar interactions and Laplacian growth

    NASA Astrophysics Data System (ADS)

    Alves, S. G.; Braga, F. L.; Martins, M. L.

    2007-10-01

    Electrochemical ferromagnetic deposits grown under a planar magnetic field exhibit a striking morphological symmetry breaking. The present paper demonstrate through two-dimensional off-lattice simulations of an extended diffusion-limited aggregation (DLA) model that the competition between magnetic dipolar interactions and electric forces can impose locally the experimentally observed angle selection in a two-dimensional extended DLA model. The long-range correlations in the orientation of dipoles interacting with the applied and dipolar fields preserve this order over a macroscopic scale. Hence, the magnetic dipolar interactions alone cannot impose the field-induced symmetry breaking observed in ferromagnetic electrochemical deposition (ECD).

  2. 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

  3. Measuring (13)C-(2)D dipolar couplings with a universal REDOR dephasing curve

    PubMed

    Gullion

    2000-09-01

    A (13)C-observe REDOR experiment is described which allows (13)C-(2)D dipolar couplings to be obtained by a universal dipolar dephasing curve. Previous (13)C-observe REDOR experiments on (13)C-(2)D spin pairs generally relied on numerical simulations to obtain the dipolar coupling. The REDOR experiment described in this article is based on a deuterium composite pulse, and the data analysis eliminates the need for numerical simulations and is the same as the traditional REDOR analysis performed on pairs of spin-12 nuclei. Copyright 2000 Academic Press. PMID:10968975

  4. The influence of dimensionality on the behavior of magnetic dipolar soft spheres: calculation of the pressure.

    PubMed

    Minina, E; Kantorovich, S

    2013-04-17

    We investigate the influence of dimensionality of a sample on the properties of magnetic dipolar soft spheres. Molecular dynamics simulations and diagram expansion are employed to analyze the pressure and microscopic structure of model monodisperse magnetic fluids in a bulk and in a monolayer. We found that, for a broad range of densities and dipolar interaction strengths, strong geometrical confinement weakens the influence of the dipole-dipole interaction on the pressure and, as a result, steric repulsion of dipolar particles provides the main contribution to the thermodynamic properties of ferrofluids in strong confinement. PMID:23515201

  5. 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.

  6. Probing the Dipolar Coupling in a Heterospin Endohedral Fullerene-Phthalocyanine Dyad.

    PubMed

    Zhou, Shen; Yamamoto, Masanori; Briggs, G Andrew D; Imahori, Hiroshi; Porfyrakis, Kyriakos

    2016-02-01

    Paramagnetic endohedral fullerenes and phthalocyanine (Pc) complexes are promising building blocks for molecular quantum information processing, for which tunable dipolar coupling is required. We have linked these two spin qubit candidates together and characterized the resulting electron paramagnetic resonance properties, including the spin dipolar coupling between the fullerene spin and the copper spin. Having interpreted the distance-dependent coupling strength quantitatively and further discussed the antiferromagnetic aggregation effect of the CuPc moieties, we demonstrate two ways of tuning the dipolar coupling in such dyad systems: changing the spacer group and adjusting the solution concentration. PMID:26745202

  7. ac susceptibility of an assembly of nanomagnets: Combined effects of surface anisotropy and dipolar interactions

    NASA Astrophysics Data System (ADS)

    Vernay, F.; Sabsabi, Z.; Kachkachi, H.

    2014-09-01

    We compute the ac susceptibility of a weakly dipolar-interacting monodisperse assembly of magnetic nanoclusters with oriented anisotropy. For this purpose, we first compute the relaxation rate in a longitudinal magnetic field of a single nanomagnet taking account of both dipolar interactions in the case of dilute assemblies and surface anisotropy. We then study the behavior of the real and imaginary components of the ac susceptibility as functions of temperature, frequency, surface anisotropy, and interparticle interactions. We find that the surface anisotropy induces an upward shift of the temperature at the maximum of the ac susceptibility components and that its effects may be tuned so as to screen out the effects of interactions. The phenomenological Vogel-Fulcher law for the effect of dipolar interaction on the relaxation rate is revisited within our formalism and a semianalytical expression is given for the effective temperature in terms of inter alia the applied field, surface anisotropy, and dipolar interaction.

  8. 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.

  9. 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.

  10. Chiral-glass transition in a diluted dipolar-interaction Heisenberg system

    NASA Astrophysics Data System (ADS)

    Zhang, Kai-Cheng; Liu, Gui-Bin; Zhu, Yan

    2011-05-01

    Recently, numerical simulations reveal that a spin-glass transition can occur in the three-dimensional diluted dipolar system. By defining the chirality of triple spins in a diluted dipolar Heisenberg spin glass, we study the chiral ordering in the system using parallel tempering algorithm and heat bath method. The finite-size scaling analysis reveals that the system undergoes a chiral-glass transition at finite temperature.

  11. 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

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

    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.

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

    PubMed

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

    2015-03-03

    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.

  14. 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

  15. 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.

  16. Ekman decay of a dipolar vortex in a rotating fluid

    NASA Astrophysics Data System (ADS)

    Zavala Sansón, L.; van Heijst, G. J. F.; Backx, N. A.

    2001-02-01

    The evolution of quasi-two-dimensional (2D) dipolar vortices over a flat bottom in a rotating fluid system is studied numerically, and the main results are experimentally verified. Our aim is to examine the dipole decay due to bottom friction effects. The numerical simulations are based on the 2D physical model derived by Zavala Sansón and van Heijst [J. Fluid Mech. 412, 75 (2000)], which contains nonlinear Ekman terms, associated with bottom friction, in the vorticity equation. In contrast, the conventional 2D model with bottom friction only retains a linear stretching term in the same equation. It is shown that the dipole trajectory is deflected towards the right (i.e., in the anticyclonic direction) when nonlinear Ekman terms are included. This effect is not observed in simulations based on the conventional model, where the dipole trajectory is a straight line. The basic reason for this behavior is the slower decay of the anticyclonic part of the dipole, with respect to the cyclonic one, due to nonlinear Ekman effects. Another important result is the exchange of fluid between the cyclonic part and the ambient, leaving a tail behind the dipole. By means of laboratory experiments in a rotating tank, these results are qualitatively verified.

  17. Ordered phases in a bilayer system of dipolar fermions

    NASA Astrophysics Data System (ADS)

    van Zyl, B. P.; Ferguson, W.

    2016-05-01

    The liquid-to-ordered phase transition in a bilayer system of fermions is studied within the context of our recently proposed density-functional theory [B. P. van Zyl, W. Kirkby, and W. Ferguson, Phys. Rev. A 92, 023614 (2015), 10.1103/PhysRevA.92.023614]. In each two-dimensional layer, the fermions interact via a repulsive, isotropic dipolar interaction. The presence of a second layer introduces an attractive interlayer interaction, thereby allowing the presence of inhomogeneous density phases which would otherwise be energetically unfavorable. For any fixed layer separation, we find an instability to a commensurate one-dimensional stripe phase in each layer, which always precedes the formation of a triangular Wigner crystal. However, at a certain fixed coupling, tuning the separation can lead to the system favoring a commensurate triangular Wigner crystal, or one-dimensional stripe phase, completely bypassing the Fermi liquid state. While other crystalline symmetries, with energies lower than the liquid phase can be found, they are never allowed to form owing to their high energetic cost relative to the triangular Wigner crystal and stripe phase.

  18. 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.

  19. Probing of susceptibility structures through the distant dipolar field effect.

    PubMed

    Wong, Chung Ki

    2013-07-01

    In this paper, the utilization of the distant dipolar field (DDF) signal to extract the properties of susceptibility structures over a subvoxel length scale is investigated. Numerical simulations are performed to study a system of randomly distributed blood vessels with a susceptibility offset inside a voxel. It is shown that the DDF signal of the system as a function of the strength of the correlation gradient field manifests a peak that depends on the volume ratio, size, and susceptibility offset of the blood vessels. In particular, the location of the signal peak is found to vary as powers of these parameters. As a result, by varying the strength of the correlation gradient field, the characteristic properties of the blood vessels can be extracted from the peak position of the DDF signal. It is also found that, for a given volume ratio of the blood vessels, a smaller size of the blood vessels can be probed when the susceptibility offset is increased. Nevertheless, it is demonstrated that, owing to the broad width of the signal peak, the DDF effect generally cannot be used for the preferential selection of the signal arising from the blood vessels on the length scale determined by the correlation length. PMID:23643159

  20. Quantum dynamics and topological excitations in interacting dipolar particles

    NASA Astrophysics Data System (ADS)

    Rey, Ana

    2016-05-01

    Dipole-dipole interactions, long-range and anisotropic interactions that arise due to the virtual exchange of photons, are of fundamental importance in optical physics, and are enabling a range of new quantum technologies including quantum networks and optical lattice atomic clocks. In this talk I will first discuss how arrays of dipolar particles with a simple J = 0- J = 1 internal level structure can naturally host topological and chiral excitations including Weyl quasi-particles. Weyl fermions were first predicted to exist in the context of high energy physics but only recently have been observed in solid state systems. I will discuss a proposal of using Mott insulators of Sr atoms to observe and probe the Weyl excitation spectrum and its non-trivial chirality. Finally I will report on a recent experiment done at JILA which validates the underlying microscopic model that predicts the existence of these excitations. The experiment measured the collective emission from a coherently driven gas of ultracold 88 Sr atoms and observed a highly directional and anisotropic emission intensity and a substantial broadening of the atomic spectral lines. All of the measurements are well reproduced by the theoretical model. These investigations open the door for the exploration of novel quantum many-body systems involving strongly interacting atoms and photons, and are useful guides for further developments of optical atomic clocks and other applications involving dense atomic ensembles. AFOSR, MURI-AFOSR, ARO,NSF-PHY-1521080, JILA-NSF-PFC-1125844.

  1. Selective coherence transfers in homonuclear dipolar coupled spin systems

    SciTech Connect

    Ramanathan, Chandrasekhar; Sinha, Suddhasattwa; Havel, Timothy F.; Cory, David G.; Baugh, Jonathan

    2005-02-01

    Controlling the dynamics of a dipolar coupled spin system is critical to the development of solid-state spin-based quantum information processors. Such control remains challenging, as every spin is coupled to a large number of surrounding spins. Here we demonstrate that in an ensemble of spin pairs it is possible to decouple the weaker interactions (weak coupling {omega}{sub D}{sup w}) between different pairs and extend the coherence lifetimes within the two-spin system from 19 {mu}s to 11.1 ms, a factor of 580. This is achieved without decoupling the stronger interaction (strong coupling {omega}{sub D}{sup S}) between the two spins within a pair. An amplitude modulated rf field is applied on resonance with the Larmor frequency of the spins, with amplitude {omega}{sub 1}, and frequency of the modulation matched to the strong coupling. The spin pairs appear isolated from each other in the regime where the rf power satisfies {omega}{sub D}{sup w}<<{omega}{sub 1}<<{omega}{sub D}{sup S}.

  2. 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

  3. 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.

  4. 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.

  5. Dynamical stability of dipolar Bose-Einstein condensates with temporal modulation of the s-wave scattering length.

    PubMed

    Sabari, S; Jisha, Chandroth P; Porsezian, K; Brazhnyi, Valeriy A

    2015-09-01

    We study the stabilization properties of dipolar Bose-Einstein condensate by temporal modulation of short-range two-body interaction. Through both analytical and numerical methods, we analyze the mean-field Gross-Pitaevskii equation with short-range two-body and long-range, nonlocal, dipolar interaction terms. We derive the equation of motion and effective potential of the dipolar condensate by variational method. We show that there is an enhancement of the condensate stability due to the inclusion of dipolar interaction in addition to the two-body contact interaction. We also show that the stability of the dipolar condensate increases in the presence of time varying two-body contact interaction; the temporal modification of the contact interaction prevents the collapse of dipolar Bose-Einstein condensate. Finally we confirm the semi-analytical prediction through the direct numerical simulations of the governing equation.

  6. 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.

  7. Wave-particle interaction during a dipolarization front event

    NASA Astrophysics Data System (ADS)

    Goldstein, M. L.; Hwang, K.; Klimas, A. J.; Schriver, D.; Ashour-Abdalla, M.; Vinas, A. F.

    2013-12-01

    We present Cluster observations of wave-particle interactions during an earthward-propagating dipolarization front (DF) and associated fast plasma bulk flows detected at the central current sheet in Earth's magnetotail. During this period, flux tubes behind a DF frequently contain more energetic or hotter ions than did the pre-existing flux tubes ahead of the DF. On the other hand, electrons within the DF flux tubes heat less, or are even colder, than were the pre-existing populations, and are often accompanied by superposed isolated beams. At the same time, electrostatic emissions are strongly enhanced over a wide range of frequencies (up to several times the electron cyclotron frequency). The lower-frequency (below about several tenths of the electron cyclotron frequency) electrostatic wave power is well correlated with ion energization. From linear theory, we find two wave modes: a high-frequency beam mode and a low-frequency whistler mode that are associated with the electron beam component. We attribute the generation of whistlers to electron beams that persist for a while before undergoing rapid thermalization. The existence of isolated beam components behind DFs detected during the 4-sec Cluster spin period indicates that DFs either provide a continuous source of electron beams or facilitate a physical process that maintains the beams against rapid thermalization. Our analysis suggests that the earthward motion of the DF flux tube, via Fermi acceleration related to a shortening of the magnetic field lines, leads to the generation or sustenance of the electron beams that can generate whistler mode waves, which can in turn heat ions. This scenario, by which free energy in electron beams generates waves that then heat ions, accounts for Cluster observations of the different energization behaviors between electrons and ions behind DFs. Our PIC simulations qualitatively reproduce the Cluster observations.

  8. 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.

  9. 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.

  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. 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

  12. 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

    2016-01-01

    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

  13. 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).

  14. A refined solution structure of hen lysozyme determined using residual dipolar coupling data.

    PubMed

    Schwalbe, H; Grimshaw, S B; Spencer, A; Buck, M; Boyd, J; Dobson, C M; Redfield, C; Smith, L J

    2001-04-01

    A high resolution NMR structure of hen lysozyme has been determined using 209 residual 1H-15N dipolar coupling restraints from measurements made in two different dilute liquid crystalline phases (bicelles) in conjunction with a data set of 1632 NOE distance restraints, 110 torsion angle restraints, and 60 hydrogen bond restraints. The ensemble of 50 low-energy calculated structures has an average backbone RMSD of 0.50+/-0.13A to the mean structure and of 1.49+/-0.10A to the crystal structure of hen lysozyme. To assess the importance of the dipolar coupling data in the structure determination, the final structures are compared with an ensemble calculated using an identical protocol but excluding the dipolar coupling restraints. The comparison shows that structures calculated with the dipolar coupling data are more similar to the crystal structure than those calculated without, and have better stereochemical quality. The structures also show improved quality factors when compared with additional dipolar coupling data that were not included in the structure calculations, with orientation-dependent 15N chemical shift changes measured in the bicelle solutions, and with T1/T2 values obtained from 15N relaxation measurements. Analysis of the ensemble of NMR structures and comparisons with crystal structures, 15N relaxation data, and molecular dynamics simulations of hen lysozyme provides a detailed description of the solution structure of this protein and insights into its dynamical behavior.

  15. 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.

  16. Exotic vortex lattices in a rotating binary dipolar Bose-Einstein condensate

    NASA Astrophysics Data System (ADS)

    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.

  17. 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.

  18. 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.

  19. 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.

  20. Three-dimensional vortex structures in a rotating dipolar Bose–Einstein condensate

    NASA Astrophysics Data System (ADS)

    Kishor Kumar, Ramavarmaraja; Sriraman, Thangarasu; Fabrelli, Henrique; Muruganandam, Paulsamy; Gammal, Arnaldo

    2016-08-01

    We study three-dimensional vortex lattice structures in purely dipolar Bose–Einstein condensate (BEC). By using the mean-field approximation, we obtain a stability diagram for the vortex states in purely dipolar BECs as a function of harmonic trap aspect ratio (λ) and dipole–dipole interaction strength (D) under rotation. Rotating the condensate within the unstable region leads to collapse while in the stable region furnishes stable vortex lattices of dipolar BECs. We analyse stable vortex lattice structures by solving the three-dimensional time-dependent Gross–Pitaevskii equation in imaginary time. Further, the stability of vortex states is examined by evolution in real-time. We also investigate the distribution of vortices in a fully anisotropic trap by increasing eccentricity of the external trapping potential. We observe the breaking up of the condensate in two parts with an equal number of vortices on each when the trap is sufficiently weak, and the rotation frequency is high.

  1. On the formation of dipolar magnetic fields in the central regions of active galaxies

    NASA Astrophysics Data System (ADS)

    Andreasyan, R. R.

    A model of the formation of large-scale magnetic fields of dipolar configuration in the central regions of active galaxies is studied. It is assumed that these regions contain a rapidly rotating partly ionized gas. Ionized matter escapes with a high velocity from the center of this region and is entrained by the rotation of the surrounding medium. Biermann's "battery" effect (L.Biermann, Z. Naturforsch., 5a, 65, 1950) operates under such conditions, and circular electric curents are generated in the medium, which amplify the dipolar magnetic fields. Dipolar magnetic fields of opposite orientation with respect to the angular momentum of the central engine can be amplified where there is accretion of gaseous matter onto the rotating central part of a galaxy. The direction of the "Halo" magnetic field of our Galaxy is in accordance with the first model.

  2. Energy landscapes, structural topologies and rearrangement mechanisms in clusters of dipolar particles

    NASA Astrophysics Data System (ADS)

    Farrell, James D.; Lines, Christabel; Shepherd, James J.; Chakrabarti, Dwaipayan; Miller, Mark A.; Wales, David J.

    Clusters of spherical particles with isotropic attraction favour compact structures that maximise the number of energetically optimal nearest-neighbour interactions. In contrast, dipolar interactions lead to the formation of chains with a low coordination number. When both isotropic and dipolar interactions are present, the competition between them can lead to intricate knot, link and coil structures. Here, we investigate how these structures may self-organise and interconvert in clusters bound by the Stockmayer potential (Lennard-Jones plus point dipole). We map out the low-lying region of the energy landscape using disconnectivity graphs to follow how it evolves as the strength of the dipolar interactions increases. From comprehensive surveys of isomerisation pathways, we identify a number of rearrangement mechanisms that allow the topology of chain-like structures to interconvert.

  3. Vortices of a rotating two-component dipolar Bose-Einstein condensate in an optical lattice

    NASA Astrophysics Data System (ADS)

    Wang, Lin-Xue; Dong, Biao; Chen, Guang-Ping; Han, Wei; Zhang, Shou-Gang; Shi, Yu-Ren; Zhang, Xiao-Fei

    2016-01-01

    We consider a two-component Bose-Einstein condensate, which consists of both dipolar and scalar bosonic atoms, in a confinement that is composed of a harmonic oscillator and an underlying optical lattice set rotation. When the dipoles are polarized along the symmetry axis of the harmonic potential, the ground-state density distributions of such a system are investigated as a function of the relative strength between the dipolar and contact interactions, and of the rotation frequency. Our results show that the number of vortices and its related vortex structures of such a system depend strongly on such system parameters. The special two-component system considered here opens up alternate ways for exploring the rich physics of dipolar quantum gases.

  4. 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.

  5. Measurement of Heteronuclear Dipolar Coupling by Transferred-Echo Double-Resonance NMR

    NASA Astrophysics Data System (ADS)

    Hing, A. W.; Vega, S.; Schaefer, J.

    A magic-angle spinning experiment called transferred-echo double resonance (TEDOR) has been introduced recently to measure the I-S dipolar coupling of heteronuclear I-S pairs of spin- {1}/{2} nuclei while eliminating unwanted background signals from uncoupled I and S spins via a coherence-transfer process. In this paper, a quantitative description of the TEDOR experiment is given in terms of the evolution of the density matrix for a pair of heteronuclear spins. The resulting equations provide a theoretical basis for evaluating the selectivity and sensitivity of TEDOR and suggest strategies for determining dipolar coupling constants directly from TEDOR data. Experimental examples illustrating these aspects of TEDOR are provided by studies performed on a range of 13C- 15N dipolar couplings found in double-labeled asparagine, alanine, glycine, and the linear peptide antibiotic, gramicidin.

  6. Numerical method for evolving the dipolar projected Gross-Pitaevskii equation

    NASA Astrophysics Data System (ADS)

    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.

  7. Antiferromagnetism and superfluidity of a dipolar Fermi gas in a two-dimensional optical lattice

    SciTech Connect

    Liu Bo; Yin Lan

    2011-10-15

    In a dipolar Fermi gas, the dipole-dipole interaction between fermions can be turned into a dipolar Ising interaction between pseudospins in the presence of an ac electric field. When trapped in a two-dimensional optical lattice, this dipolar Fermi gas has a very rich phase diagram at zero temperature, due to the competition between antiferromagnetism and superfluidity. At half-filling, the antiferromagnetic state is the favored ground state. The superfluid state appears as the ground state at a smaller filling factor. In between there is a phase-separated region. The order parameter of the superfluid state can display different symmetries depending on the filling factor and interaction strength, including the d-wave (d), the extended s-wave (xs), or their linear combination (xs+id). Implications for the current experiment are discussed.

  8. 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.

  9. Ion and electron kinetic physics associated with magnetotail dipolarization fronts

    NASA Astrophysics Data System (ADS)

    Eastwood, Jonathan; Goldman, Martin; Newman, David; Zhang, Xiao-Jia; Hietala, Heli; Krupar, Vratislav; Mistry, Rishi; Lapenta, Giovanni; Angelopoulos, Vassilis

    2016-04-01

    Magnetic reconnection plays an important role in controlling the dynamics of the Earth's magnetotail. In particular, a dipolarization front (DF) may form at the leading edge of the reconnection exhaust as a consequence of its interaction with the pre-existing plasma sheet. Earthward moving DFs typically exhibit a rapid increase in the northward component of the magnetic field which divides the pre-existing plasma sheet from the hotter, high speed and lower density reconnection exhaust. Extensive observations have been made of DFs at Earth with multi-point missions such as Cluster, THEMIS/ARTEMIS and now Magnetospheric Multi-Scale (MMS). In this invited contribution we will first review previous work showing that DFs are often relatively thin and locations where significant particle acceleration and heating can occur in a variety of ways. The dynamics and kinematics of ions and electrons at DFs are very different, as a result of their different particle masses. The reflection of ions by DFs leads to acceleration and heating, and we show that via kinetic effects, some part of the pre-existing plasma sheet ion population is entrained and accelerated into the exhaust. This interaction in fact occurs over a macroscopic region, rather than simply being limited to the thin DF interface. This leads to a more general consequence which is that reconnection exhausts are not necessarily simply fed by plasma inflow across the separatrices, but also by plasma from the region into which the jet is propagating; the implications of this finding are discussed. In contrast, electron acceleration and thermalisation is more related to the presence of instabilities in particular associated with temperature anisotropy and the growth of whistler waves. We discuss the observational evidence and also explore the possibility of the role that Cherenkov emission of whistlers by electron holes could play in this process. Finally we will briefly highlight recent new work in this area, and

  10. 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

  11. Theoretical studies of excited state 1,3 dipolar cycloadditions

    NASA Astrophysics Data System (ADS)

    Belluccci, Michael A.

    The 1,3 dipolar photocycloaddition reaction between 3-hydroxy-4',5,7-trimethoxyflavone (3-HTMF) and methyl cinnamate is investigated in this work. Since its inception in 2004 [JACS, 124, 13260 (2004)], this reaction remains at the forefront in the synthetic design of the rocaglamide natural products. The reaction is multi-faceted in that it involves multiple excited states and is contingent upon excited state intramolecular proton transfer (ESIPT) in 3-HTMF. Given the complexity of the reaction, there remain many questions regarding the underlying mechanism. Consequently, throughout this work we investigate the mechanism of the reaction along with a number of other properties that directly influence it. To investigate the photocycloaddition reaction, we began by studying the effects of different solvent environments on the ESIPT reaction in 3-hydroxyflavone since this underlying reaction is sensitive to the solvent environment and directly influences the cycloaddition. To study the ESIPT reaction, we developed a parallel multi-level genetic program to fit accurate empirical valence bond (EVB) potentials to ab initio data. We found that simulations with our EVB potentials accurately reproduced experimentally determined reaction rates, fluorescence spectra, and vibrational frequency spectra in all solvents. Furthermore, we found that the ultrafast ESIPT process results from a combination of ballistic transfer and intramolecular vibrational redistribution. To investigate the cycloaddition reaction mechanism, we utilized the string method to obtain minimum energy paths on the ab initio potential. These calculations demonstrated that the reaction can proceed through formation of an exciplex in the S1 state, followed by a non-adiabatic transition to the ground state. In addition, we investigated the enantioselective catalysis of the reaction using alpha,alpha,alpha',alpha'-tetraaryl-1,3-dioxolan-4,5-dimethanol alcohol (TADDOL). We found that TADDOL lowered the energy

  12. Quantum Monte Carlo study of dipolar lattice bosons in the presence of random diagonal disorder

    NASA Astrophysics Data System (ADS)

    Zhang, Chao; Safavi-Naini, Arghavan; Capogrosso-Sansone, Barbara

    2015-05-01

    We report the results of our study of dipolar bosons in a two dimensional optical lattice in the presence of random diagonal disorders using Path Integral Quantum Monte Carlo simulations. We study the phase diagram at half filling which features three phases: superfluid, checkerboard solid and bose glass. We observe that, in contrast to the standard Bose-Hubbard model in presence of diagonal disorder, superfluidity is destroyed at considerable lower disorder strengths in favor of the Bose glass phase. Additionally we find that as the disorder strength increases, larger dipolar interaction is required in order to stabilize a checkerboard solid.

  13. Rotational properties of dipolar Bose-Einstein condensates confined in anisotropic harmonic potentials

    SciTech Connect

    Malet, F.; Reimann, S. M.; Kristensen, T.; Kavoulakis, G. M.

    2011-03-15

    We study the rotational properties of a dipolar Bose-Einstein condensate confined in a quasi-two-dimensional anisotropic trap for an arbitrary orientation of the dipoles with respect to their plane of motion. Within the mean-field approximation, we find that the lowest-energy state of the system depends strongly on the relative strength between the dipolar and the contact interactions, as well as on the size and the orientation of the dipoles and the size and the orientation of the deformation of the trapping potential.

  14. Meron ground state of Rashba spin-orbit-coupled dipolar bosons.

    PubMed

    Wilson, Ryan M; Anderson, Brandon M; Clark, Charles W

    2013-11-01

    We study the effects of dipolar interactions on a Bose-Einstein condensate with synthetically generated Rashba spin-orbit coupling. The dipolar interaction we consider includes terms that couple spin and orbital angular momentum in a way perfectly congruent with the single-particle Rashba coupling. We show that this internal spin-orbit coupling plays a crucial role in the rich ground-state phase diagram of the trapped condensate. In particular, we predict the emergence of a thermodynamically stable ground state with a meron spin configuration.

  15. 1,3-Dipolar Cycloadditions of Diazo Compounds in the Presence of Azides.

    PubMed

    Aronoff, Matthew R; Gold, Brian; Raines, Ronald T

    2016-04-01

    The diazo group has untapped utility in chemical biology. The tolerance of stabilized diazo groups to cellular metabolism is comparable to that of azido groups. However, chemoselectivity has been elusive, as both groups undergo 1,3-dipolar cycloadditions with strained alkynes. Removing strain and tuning dipolarophile electronics yields diazo group selective 1,3-dipolar cycloadditions that can be performed in the presence of an azido group. For example, diazoacetamide but not its azido congener react with dehydroalanine residues, as in the natural product nisin. PMID:26981746

  16. Ground-state candidate for the classical dipolar kagome Ising antiferromagnet

    NASA Astrophysics Data System (ADS)

    Chioar, I. A.; Rougemaille, N.; Canals, B.

    2016-06-01

    We have investigated the low-temperature thermodynamic properties of the classical dipolar kagome Ising antiferromagnet using Monte Carlo simulations, in the quest for the ground-state manifold. In spite of the limitations of a single-spin-flip approach, we managed to identify certain ordering patterns in the low-temperature regime and we propose a candidate for this unknown state. This configuration presents some intriguing features and is fully compatible with the extrapolations of the at-equilibrium thermodynamic behavior sampled so far, making it a very likely choice for the dipolar long-range ordered state of the classical kagome Ising antiferromagnet.

  17. Dipolar Order and Spin-Lattice Relaxation in a Liquid Entrapped into Nanosize Cavities

    NASA Astrophysics Data System (ADS)

    Furman, Gregory; Goren, Shaul

    2011-12-01

    It was shown that by means of the two-pulse sequence, the spin system of a liquid entrapped into nanosize cavities can be prepared in quasi-equilibrium states of high dipolar order, which relax to thermal equilibrium with the molecular environment with a relaxation time T1d. Measurements of the inverse dipolar temperature and spin-lattice relaxation time in the local fields provide an important information about the cavity size V, its shape F, and orientation θ (with respect to the external magnetic field) of the nanopores.

  18. Dipolar structures in colloidal dispersions of PbSe and CdSe quantum dots.

    PubMed

    Klokkenburg, Mark; Houtepen, Arjan J; Koole, Rolf; de Folter, Julius W J; Erné, Ben H; van Faassen, Ernst; Vanmaekelbergh, Daniël

    2007-09-01

    We show by cryogenic transmission electron microscopy that PbSe and CdSe nanocrystals of various shapes in a liquid colloidal dispersion self-assemble into equilibrium structures that have a pronounced dipolar character, to an extent that depends on particle concentration and size. Analyzing the cluster-size distributions with a one-dimensional (1D) aggregation model yields a dipolar pair attraction of 8-10 kBT at room temperature. This accounts for the long-range alignment of the crystal planes of individual nanocrystals in self-assembled superstructures and for anisotropic nanostructures grown via oriented attachment. PMID:17713960

  19. Proton Dipolar Recoupling in Resin-Bound Peptides under High-Resolution Magic Angle Spinning

    NASA Astrophysics Data System (ADS)

    Raya, Jésus; Bianco, Alberto; Furrer, Julien; Briand, Jean-Paul; Piotto, Martial; Elbayed, Karim

    2002-07-01

    Rotational resonance and radiofrequency-driven dipolar recoupling (RFDR) experiments have been used to recover the weak proton dipolar interaction present in peptides bound to swollen resins spun at the magic angle. The intensity of the correlation peaks obtained using these sequences is shown to be significantly stronger than the one obtained using the classical NOESY experiment. In addition, it is found that during the relatively long mixing times required to transfer magnetization in such soft materials, the RFDR sequence also achieves magnetization transfer via the scalar J-coupling.

  20. Dipolar Quinoidal Acene Analogues as Stable Isoelectronic Structures of Pentacene and Nonacene.

    PubMed

    Shi, Xueliang; Kueh, Weixiang; Zheng, Bin; Huang, Kuo-Wei; Chi, Chunyan

    2015-11-23

    Quinoidal thia-acene analogues, as the respective isoelectronic structures of pentacene and nonacene, were synthesized and an unusual 1,2-sulfur migration was observed during the Friedel-Crafts alkylation reaction. The analogues display a closed-shell quinoidal structure in the ground state with a distinctive dipolar character. In contrast to their acene isoelectronic structures, both compounds are stable because of the existence of more aromatic sextet rings, a dipolar character, and kinetic blocking. They exhibit unique packing in single crystals resulting from balanced dipole-dipole and [C-H⋅⋅⋅π]/[C-H⋅⋅⋅S] interactions. PMID:26447720

  1. Diffusion effects on the CPMG relaxation rate in a dipolar field.

    PubMed

    Ziener, C H; Kampf, T; Jakob, P M; Bauer, W R

    2010-01-01

    The diffusion in the magnetic dipolar field around a sphere is considered. The diffusion is restricted to the space between two concentric spheres, where the inner sphere is the source of the magnetic dipolar field. Analytical expressions for the CPMG transverse relaxation rate as well as the free induction decay and the spin echo time evolution are given in the Gaussian approximation. The influence of the inter-echo time is analyzed. The limiting cases of small and large inter-echo times as well as the short and long time behavior are evaluated.

  2. Stepwise π-extension of meso-alkylidenyl porphyrins through sequential 1,3-dipolar cycloaddition and redox reactions.

    PubMed

    Park, Dowoo; Jeong, Seung Doo; Ishida, Masatoshi; Lee, Chang-Hee

    2014-08-25

    Several regioselectively π-extended, pyrrole fused porphyrinoids have been synthesized by the 1,3-dipolar cycloaddition of meso-alkylidene-(benzi)porphyrins. Pd(II) complexes gave oxidation resistant, bis-pyrrole fused adducts. The repeated 1,3-dipolar cycloaddition followed by oxidation-reduction of pentaphyrin analogs afforded π-extended porphyrin analogs.

  3. Dipolar-coupling-mediated total correlation spectroscopy in solid-state 13C NMR: Selection of individual 13C- 13C dipolar interactions

    NASA Astrophysics Data System (ADS)

    Spano, Justin; Wi, Sungsool

    2010-06-01

    Herein is described a useful approach in solid-state NMR, for selecting homonuclear 13C- 13C spin pairs in a multiple- 13C homonuclear dipolar coupled spin system. This method builds upon the zero-quantum (ZQ) dipolar recoupling method introduced by Levitt and coworkers (Marin-Montesinos et al., 2006 [30]) by extending the originally introduced one-dimensional (1D) experiment into a two-dimensional (2D) method with selective irradiation scheme, while moving the 13C- 13C mixing scheme from the transverse to the longitudinal mode, together with a dramatic improvement in the proton decoupling efficiency. Selective spin-pair recoupling experiments incorporating Gaussian and cosine-modulated Gaussian pulses for inverting specific spins were performed, demonstrating the ability to detect informative, simplified/individualized, long-range 13C- 13C homonuclear dipolar coupling interactions more accurately by removing less informative, stronger, short-range 13C- 13C interactions from 2D correlation spectra. The capability of this new approach was demonstrated experimentally on uniformly 13C-labeled Glutamine and a tripeptide sample, GAL.

  4. 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.

  5. Improving dipolar recoupling for site-specific structural and dynamics studies in biosolids NMR: windowed RN-symmetry sequences.

    PubMed

    Lu, Xingyu; Zhang, Huilan; Lu, Manman; Vega, Alexander J; Hou, Guangjin; Polenova, Tatyana

    2016-02-01

    Experimental characterization of one-bond heteronuclear dipolar couplings is essential for structural and dynamics characterization of molecules by solid-state NMR. Accurate measurement of heteronuclear dipolar tensor parameters in magic-angle spinning NMR requires that the recoupling sequences efficiently reintroduce the desired heteronuclear dipolar coupling term, fully suppress other interactions (such as chemical shift anisotropy and homonuclear dipolar couplings), and be insensitive to experimental imperfections, such as radio frequency (rf) field mismatch. In this study, we demonstrate that the introduction of window delays into the basic elements of a phase-alternating R-symmetry (PARS) sequence results in a greatly improved protocol, termed windowed PARS (wPARS), which yields clean dipolar lineshapes that are unaffected by other spin interactions and are largely insensitive to experimental imperfections. Higher dipolar scaling factors can be attained in this technique with respect to PARS, which is particularly useful for the measurement of relatively small dipolar couplings. The advantages of wPARS are verified experimentally on model molecules N-acetyl-valine (NAV) and a tripeptide Met-Leu-Phe (MLF). The incorporation of wPARS into 3D heteronuclear or homonuclear correlation experiments permits accurate site-specific determination of dipolar tensors in proteins, as demonstrated on dynein light chain 8 (LC8). Through 3D wPARS recoupling based spectroscopy we have determined both backbone and side chain dipolar tensors in LC8 in a residue-resolved manner. We discuss these in the context of conformational dynamics of LC8. We have addressed the effect of paramagnetic relaxant Cu(ii)-EDTA doping on the dipolar coupling parameters in LC8 and observed no significant differences with respect to the neat sample permitting fast data collection. Our results indicate that wPARS is advantageous with respect to the windowless version of the sequence and is applicable

  6. Using “domino” model to study the secular variation of the geomagnetic dipolar moment

    NASA Astrophysics Data System (ADS)

    Duka, B.; Peqini, K.; De Santis, A.; Pavón-Carrasco, F. J.

    2015-05-01

    Aiming to understand the physical processes underneath the reversals events of geomagnetic field, different numerical models have been conceived. We considered here the so named “domino” model, an Ising-Heisenberg model of interacting magnetic macrospins aligned along a ring. This model was proposed by Mazaud and Laj (1989) and then applied by Mori et al. (2013) to study geomagnetic field reversals. The long series of the axial magnetic moment (dipolar moment or “magnetization”) generated by the “domino” model are empirically studied by varying all model parameters. We present here some results which are slightly different from those given by Mori et al. (2013), and will provide our explanation on the presence of these differences. We also define the set of parameters that supply the longest mean time between reversals. Using this set of parameters, a large number of time series of axial magnetic moment are also generated. After de-noising the fluctuation of these time series and averaging them, we compared the resulting averaged series with the series of axial dipolar magnetic moment values supplied by CALS7k.2, and CALS10k.1b models, finding similar behavior for the all time series. In a similar way, we also compared the averaged 14,000 years long series of dipolar moment with the dipolar magnetic moment obtained by the model SHA.DIF.14k.

  7. Expanding Stereochemical and Skeletal Diversity Using Petasis Reactions and 1,3-Dipolar Cycloadditions

    PubMed Central

    2010-01-01

    A short and modular synthetic pathway using intramolecular 1,3-dipolar cycloaddition reactions and yielding functionalized isoxazoles, isoxazolines, and isoxazolidines is described. The change in shape of previous compounds and those in this study is quantified and compared using principal moment-of-inertia shape analysis. PMID:20977261

  8. Stripe glass and stripe supersolid of two-dimensional dipolar bosons in an optical lattice

    NASA Astrophysics Data System (ADS)

    Roscilde, Tommaso; Boninsegni, Massimo

    2010-03-01

    Making use of mean-field theory and quantum Monte Carlo simulations, we investigate the zero-temperature phase diagram of dipolar bosons (with hardcore on-site interactions) on a square and triangular lattice. We consider dipoles forming an angle of 45 degrees with respect to the lattice plane, so that the dipolar interaction takes a spatially anisotropic nature, and it is attractive along the dipole direction and repulsive perpendicular to it. In the case of the square lattice, the attractive part of the interaction leads to the collapse of the dipolar gas and phase separation. On the contrary, in the case of the triangular lattice a stripe crystal is stabilized at most commensurate fillings of the form n/L, where 1 < n < L and L is the linear size. Yet, dislocations in the stripe crystal give rise to highly metastable states, which can be systematically studied at the mean-field level. Metastability is most pronounced close to half filling, and it leads to a strong tendency towards the formation of a ``stripe glass,'' which exhibits a characteristic signature in the structure factor. For higher fillings crystal phase exhibits strong quantum fluctuations, and it hosts a superfluid fraction for sufficiently low strength of the dipolar potential, resulting in a stripe supersolid phase.

  9. 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

    2015-05-01

    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.

  10. Modulation of Magnetic Heating via Dipolar Magnetic Interactions in Monodisperse and Crystalline Iron Oxide Nanoparticles

    DOE PAGES

    Salas, Gorka; Camarero, Julio; Cabrera, David; Takacs, Hélène; Varela, María; Ludwig, Robert; Dähring, Heidi; Hilger, Ingrid; Miranda, Rodolfo; Morales, María del Puerto; et al

    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

  11. Dynamics of spherical distributions of charge with small internal dipolar motion

    NASA Astrophysics Data System (ADS)

    Flammer, P. D.

    2016-04-01

    This paper extends the Lorentz-Abraham model of an electron (i.e., the equations of motion for a small spherical shell of charge, which is rigid in its proper frame) to treat a small, spherically symmetric charge distribution, allowing for small internal dipolar motion. This is done by dividing the distribution into thin spherical shells (in the continuum limit), and tracking the interactions between shells. Dipolar motion of each constituent spherical shell is allowed along the net dipole moment, but higher-order multipole moments are ignored. The amplitude of dipolar motion of each spherical shell is assumed to be linearly proportional to the net dipole moment. Under these assumptions, low-velocity equations of motion are determined for both the center-of-mass motion and net dipolar motion of the distribution. This is then generalized to arbitrary (relativistic) center-of-mass velocity and acceleration, assuming the motion of individual shells is completely in phase or out of phase with the net dipole moment.

  12. Second harmonic generation from small gold metallic particles: From the dipolar to the quadrupolar response

    NASA Astrophysics Data System (ADS)

    Nappa, J.; Russier-Antoine, I.; Benichou, E.; Jonin, Ch.; Brevet, P. F.

    2006-11-01

    Hyper Raleigh scattering, a common technique to investigate the second harmonic light scattered from a liquid suspension of molecular compounds and to determine their quadratic hyperpolarizability, has been used for aqueous suspensions of gold nanoparticles, the diameter of which ranges from 20 up to 150nm. The hyper Rayleigh signal intensity was recorded as a function of the angle of polarization of the incident fundamental wave. For the particles with a diameter smaller than 50nm, the response is dominated by the dipolar contribution arising from the deviation of the particle shape from that of a perfect sphere. For larger diameter particles, retardation effects in the interaction of the electromagnetic fields with the particles cannot be neglected any longer and the response deviates from the pure dipolar response, exhibiting a strong quadrupolar contribution. It is then shown that in order to quantify the relative magnitude of these two dipolar and quadrupolar contributions, a weighting parameter ζV which equals unity for a pure quadrupolar contribution and vanishes for a pure dipolar response, can be introduced.

  13. 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

    2015-05-01

    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. PMID:25835488

  14. 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

  15. Theory of stochastic dipolar recoupling in solid-state nuclear magnetic resonance.

    PubMed

    Tycko, Robert

    2008-05-15

    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 nonzero 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 f(max)) 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 f(max), with pairwise transfer rates that are proportional to the inverse sixth power of pairwise internuclear distances; (3) quantum mechanical interferences among noncommuting 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 f(max), provided that coupled nuclei have distinct NMR chemical shifts. PMID:18085769

  16. 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.

  17. 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. PMID:27139819

  18. Synthesis of demissidine by a ring fragmentation 1,3-dipolar cycloaddition approach

    PubMed Central

    Zhang, Zhe; Giampa, Geoffrey M.; Draghici, Cristian; Huang, Qiufeng

    2013-01-01

    A synthesis of the steroidal alkaloid demissidine from epiandrosterone is reported. A ring fragmentation reaction that efficiently ruptured the D-ring of a diazo ester derivative of epiandrosterone to provide an aldehyde tethered ynoate product was key to this sequence. Incorporation of the indolizidine framework was achieved by an azomethine ylide 1,3-dipolar cycloaddition. PMID:23586838

  19. 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

    2016-02-01

    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.

  20. Flagella as a novel alignment medium for the measurement of residual dipolar couplings in proteins.

    PubMed

    Singh, Himanshu; Shukla, Manish; Rao, Basuthkar J; Chary, Kandala V R

    2013-12-18

    The two flexible rod-like flagella (∼500 nm in diameter and 5-15 μm long) of Chlamydomonas reinhardtii, a unicellular green alga, can weakly align molecules in an external magnetic field, thereby enabling the measurement of various residual dipolar couplings in solution NMR spectroscopy. PMID:24165953

  1. 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.

  2. 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.

  3. Effect of dipolar ions on the entropy-driven polymerization of tobacco mosaic virus protein.

    PubMed

    Lauffer, M A; Shalaby, R A

    1985-11-01

    The effect of the dipolar ions, glycine, glycylglycine, and glycylglycylglycine on the polymerization of tobacco mosaic virus (TMV) protein has been studied by the methods of light scattering and ultracentrifugation. All three dipolar ions promote polymerization. The major reaction in the early stage is transition from the 4 S to the 20 S state. As in the absence of dipolar ions, the polymerization is enhanced by an increase in temperature; it is endothermic and therefore entropy-driven. The effect of the dipolar ions can be understood in terms of their action as salting-out agents; they increase the activity coefficient of TMV A protein, the 4 S material, and thus shift the equilibrium toward the 20 S state. The salting-out constants, K, for the reaction in 0.10 ionic strength phosphate buffer at pH 6.7 was found by the light scattering method to be 1.6 for glycine, 2.5 for glycylglycine, and 2.5 for glycylglycylglycine. A value of 2.7 was obtained by the ultracentrifugation method for glycylglycine in phosphate buffer at 0.1 ionic strength and pH 6.8 at 10 degrees C. For both glycine and glycylglycine, K increases when the ionic strength of the phosphate buffer is decreased. This result suggests that electrolytes decrease the activity coefficient of the dipolar ions, a salting-in phenomenon. However, the salting-in constants evaluated from these results are substantially higher than those previously determined by solubility measurements. The effect of glycine and glycylglycine on polymerization was studied at pH values between 6.2 and 6.8. The effectiveness of both dipolar ions is approximately 50% greater at pH 6.8 than at pH 6.2. The variation of the extent of polymerization with pH in the presence of the dipolar ions is consistent with the interpretation that approximately one hydrogen ion is bound for half of the polypeptide units in the polymerized A protein.

  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. Accurate determination of order parameters from 1H,15N dipolar couplings in MAS solid-state NMR experiments.

    PubMed

    Chevelkov, Veniamin; Fink, Uwe; Reif, Bernd

    2009-10-01

    A reliable site-specific estimate of the individual N-H bond lengths in the protein backbone is the fundamental basis of any relaxation experiment in solution and in the solid-state NMR. The N-H bond length can in principle be influenced by hydrogen bonding, which would result in an increased N-H distance. At the same time, dynamics in the backbone induces a reduction of the experimental dipolar coupling due to motional averaging. We present a 3D dipolar recoupling experiment in which the (1)H,(15)N dipolar coupling is reintroduced in the indirect dimension using phase-inverted CP to eliminate effects from rf inhomogeneity. We find no variation of the N-H dipolar coupling as a function of hydrogen bonding. Instead, variations in the (1)H,(15)N dipolar coupling seem to be due to dynamics of the protein backbone. This is supported by the observed correlation between the H(N)-N dipolar coupling and the amide proton chemical shift. The experiment is demonstrated for a perdeuterated sample of the alpha-spectrin SH3 domain. Perdeuteration is a prerequisite to achieve high accuracy. The average error in the analysis of the H-N dipolar couplings is on the order of +/-370 Hz (+/-0.012 A) and can be as small as 150 Hz, corresponding to a variation of the bond length of +/-0.005 A.

  6. Singlet and triplet superfluid competition in a mixture of two-component Fermi and one-component dipolar Bose gases

    SciTech Connect

    Kain, Ben; Ling, Hong Y.

    2011-06-15

    We consider a mixture of two-component Fermi and (one-component) dipolar Bose gases in which both dipolar interaction and s-wave scattering between fermions of opposite spins are tunable. We show that in the long-wavelength limit, the anisotropy in the Fermi-Fermi interaction induced by phonons of the dipolar condensate can strongly enhance the scattering in the triplet channel. We investigate in detail the conditions for achieving optimal critical temperature at which the triplet superfluid begins to compete with the singlet superfluid.

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

    PubMed

    Daschakraborty, Snehasis; Biswas, Ranjit

    2016-03-14

    A semi-molecular theory is developed here for studying dielectric relaxation (DR) in binary mixtures of ionic liquids (ILs) with common dipolar solvents. Effects of ion translation on DR time scale, and those of ion rotation on conductivity relaxation time scale are explored. Two different models for the theoretical calculations have been considered: (i) separate medium approach, where molecularities of both the IL and dipolar solvent molecules are retained, and (ii) effective medium approach, where the added dipolar solvent molecules are assumed to combine with the dipolar ions of the IL, producing a fictitious effective medium characterized via effective dipole moment, density, and diameter. Semi-molecular expressions for the diffusive DR times have been derived which incorporates the effects of wavenumber dependent orientational static correlations, ion dynamic structure factors, and ion translation. Subsequently, the theory has been applied to the binary mixtures of 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]) with water (H2O), and acetonitrile (CH3CN) for which experimental DR data are available. On comparison, predicted DR time scales show close agreement with the measured DR times at low IL mole fractions (x(IL)). At higher IL concentrations (x(IL) > 0.05), the theory over-estimates the relaxation times and increasingly deviates from the measurements with x(IL), deviation being the maximum for the neat IL by almost two orders of magnitude. The theory predicts negligible contributions to this deviation from the x(IL) dependent collective orientational static correlations. The drastic difference between DR time scales for IL/solvent mixtures from theory and experiments arises primarily due to the use of the actual molecular volume (V(mol)(dip)) for the rotating dipolar moiety in the present theory and suggests that only a fraction of V(mol)(dip) is involved at high x(IL). Expectedly, nice agreement between theory and experiments appears when

  8. 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

    A semi-molecular theory is developed here for studying dielectric relaxation (DR) in binary mixtures of ionic liquids (ILs) with common dipolar solvents. Effects of ion translation on DR time scale, and those of ion rotation on conductivity relaxation time scale are explored. Two different models for the theoretical calculations have been considered: (i) separate medium approach, where molecularities of both the IL and dipolar solvent molecules are retained, and (ii) effective medium approach, where the added dipolar solvent molecules are assumed to combine with the dipolar ions of the IL, producing a fictitious effective medium characterized via effective dipole moment, density, and diameter. Semi-molecular expressions for the diffusive DR times have been derived which incorporates the effects of wavenumber dependent orientational static correlations, ion dynamic structure factors, and ion translation. Subsequently, the theory has been applied to the binary mixtures of 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]) with water (H2O), and acetonitrile (CH3CN) for which experimental DR data are available. On comparison, predicted DR time scales show close agreement with the measured DR times at low IL mole fractions (xIL). At higher IL concentrations (xIL > 0.05), the theory over-estimates the relaxation times and increasingly deviates from the measurements with xIL, deviation being the maximum for the neat IL by almost two orders of magnitude. The theory predicts negligible contributions to this deviation from the xIL dependent collective orientational static correlations. The drastic difference between DR time scales for IL/solvent mixtures from theory and experiments arises primarily due to the use of the actual molecular volume ( Vmol dip ) for the rotating dipolar moiety in the present theory and suggests that only a fraction of Vmol dip is involved at high xIL. Expectedly, nice agreement between theory and experiments appears when experimental

  9. Stability and collapse of fermions in a binary dipolar boson-fermion 164Dy-161Dy mixture

    NASA Astrophysics Data System (ADS)

    Adhikari, S. K.

    2013-10-01

    We suggest a time-dependent mean-field hydrodynamic model for a binary dipolar boson-fermion mixture to study the stability and collapse of fermions in the 164Dy-161Dy mixture. The condition of stability of the dipolar mixture is illustrated in terms of phase diagrams. A collapse is induced in a disk-shaped stable binary mixture by jumping the interspecies contact interaction from repulsive to attractive by the Feshbach resonance technique. The subsequent dynamics is studied by solving the time-dependent mean-field model including three-body loss due to molecule formation in boson-fermion and boson-boson channels. Collapse and fragmentation in the fermions after subsequent explosions are illustrated. The anisotropic dipolar interaction leads to anisotropic fermionic density distribution during collapse. This study is carried out in three-dimensional space using realistic values of dipolar and contact interactions.

  10. 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.

  11. 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.

  12. NMR Detection Using Laser-Polarized Xenon as a DipolarSensor

    SciTech Connect

    Granwehr, Josef; Urban, Jeffry T.; Trabesinger, Andreas H.; Pines, Alexander

    2005-02-28

    Hyperpolarized Xe-129 can be used as a sensor to indirectly detect NMR spectra of heteronuclei that are neither covalently bound nor necessarily in direct contact with the Xe atoms, but coupled through long-range intermolecular dipolar couplings. In order to reintroduce long-range dipolar couplings the sample symmetry has to be broken. This can be done either by an asymmetric sample arrangement, or by breaking the symmetry of the spin magnetization with field gradient pulses. Experiments are performed where only a small fraction of the available Xe-129 magnetization is used for each point, so that a single batch of xenon suffices for the point-by-point acquisition of a heteronuclear NMR spectrum. Examples with H-1 as analyte nucleus show that these methods have the potential to obtain spectra with a resolution that is high enough to determine homonuclear J couplings. The applicability of this technique with remote detection is discussed.

  13. 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.

  14. Ferroelectric Coordination Polymers Self-Assembled from Mesogenic Zinc(II) Porphyrin and Dipolar Bridging Ligands.

    PubMed

    Hui, Joseph K-H; Kishida, Hiroyuki; Ishiba, Keita; Takemasu, Kenta; Morikawa, Masa-Aki; Kimizuka, Nobuo

    2016-09-26

    A new class of ferroelectric coordination-based polymers has been developed by the self-assembly of lipophilic zinc porphyrin (ZnP) and ditopic bridging ligands. The ligands contain dipolar benzothiadiazole or fluorobenzene units, which are axially coordinated to ZnP with the dipole moments oriented perpendicular to the coordination axes. The coordination-based polymers show ferroelectric characteristics in the liquid crystalline state, as revealed by distinctive hysteresis in the polarization-electric field (P-E) loops and inversion current peaks in current-voltage (I-V) loops. The observed ferroelectric properties are explainable by flip-flop rotation of the dipolar axle ligands induced by the applied electric field, as demonstrated by the positive-up-negative-down (PUND) measurements. The present system provides a new operating principle in supramolecular ferroelectrics.

  15. Phase locking of spin-torque nano-oscillator pairs with magnetic dipolar coupling

    NASA Astrophysics Data System (ADS)

    Chen, Hao-Hsuan; Lee, Ching-Ming; Zhang, Zongzhi; Liu, Yaowen; Wu, Jong-Ching; Horng, Lance; Chang, Ching-Ray

    2016-06-01

    A spin-torque nanopillar oscillator (STNO) that combines a perpendicular-to-plane polarizer (PERP) with an in-plane magnetized free layer is a good candidate for phase locking, which opens a potential approach to enhancement of the output power of STNOs. In this paper, the magnetic dipolar coupling effect is used as the driving force to synchronize two STNOs. We develop an approximation theory for synchronizing two identical and nonidentical pairs of PERP STNOs, by which the critical current of synchronization, dipolar coupling strength, phase-locking transient time, and frequency can be analytically predicted. These predictions are further confirmed by macrospin and micromagnetic simulations. Finally, we show the phase diagrams of the phase locking as a function of applied current and separation between two STNOs.

  16. 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.

  17. Anisotropic relaxation dynamics in a dipolar Fermi gas driven out of equilibrium.

    PubMed

    Aikawa, K; Frisch, A; Mark, M; Baier, S; Grimm, R; Bohn, J L; Jin, D S; Bruun, G M; Ferlaino, F

    2014-12-31

    We report on the observation of a large anisotropy in the rethermalization dynamics of an ultracold dipolar Fermi gas driven out of equilibrium. Our system consists of an ultracold sample of strongly magnetic 167Er fermions, spin polarized in the lowest Zeeman sublevel. In this system, elastic collisions arise purely from universal dipolar scattering. Based on cross-dimensional rethermalization experiments, we observe a strong anisotropy of the scattering, which manifests itself in a large angular dependence of the thermal relaxation dynamics. Our result is in good agreement with recent theoretical predictions. Furthermore, we measure the rethermalization rate as a function of temperature for different angles and find that the suppression of collisions by Pauli blocking is not influenced by the dipole orientation. PMID:25615326

  18. Exploring Strain-Promoted 1,3-Dipolar Cycloadditions of End Functionalized Polymers

    PubMed Central

    Ledin, Petr A.; Kolishetti, Nagesh; Hudlikar, Manish S.

    2014-01-01

    Strain-promoted 1,3-dipolar cycloaddition of cyclooctynes with 1,3-dipoles such as azides, nitrones, and nitrile oxides, are of interest for the functionalization of polymers. In this study, we have explored the use of a 4-dibenzocyclooctynol (DIBO)-containing chain transfer agent in reversible addition–fragmentation chain transfer polymerizations. The controlled radical polymerization resulted in well-defined DIBO-terminating polymers that could be modified by 1,3-dipolar cycloadditions using nitrones, nitrile oxides, and azides having a hydrophilic moiety. The self-assembly properties of the resulting block copolymers have been examined. The versatility of the methodology was further demonstrated by the controlled preparation of gold nanoparticles coated with the DIBO-containing polymers to produce materials that can be further modified by strain-promoted cyclo-additions. PMID:24906200

  19. Nonlinear localized modes in dipolar Bose-Einstein condensates in two-dimensional optical lattices

    NASA Astrophysics Data System (ADS)

    Rojas-Rojas, Santiago; Naether, Uta; Delgado, Aldo; Vicencio, Rodrigo A.

    2016-09-01

    We analyze the existence and properties of discrete localized excitations in a Bose-Einstein condensate loaded into a periodic two-dimensional optical lattice, when a dipolar interaction between atoms is present. The dependence of the Number of Atoms (Norm) on the energy of solutions is studied, along with their stability. Two important features of the system are shown, namely, the absence of the Norm threshold required for localized solutions to exist in finite 2D systems, and the existence of regions in the parameter space where two fundamental solutions are simultaneously unstable. This feature enables mobility of localized solutions, which is an uncommon feature in 2D discrete nonlinear systems. With attractive dipolar interaction, a non-trivial behavior of the Norm dependence is obtained, which is well described by an analytical model.

  20. Liquid crystal phases of two-dimensional dipolar gases and Berezinskii-Kosterlitz-Thouless melting.

    PubMed

    Wu, Zhigang; Block, Jens K; Bruun, Georg M

    2016-01-01

    Liquid crystals are phases of matter intermediate between crystals and liquids. Whereas classical liquid crystals have been known for a long time and are used in electro-optical displays, much less is known about their quantum counterparts. There is growing evidence that quantum liquid crystals play a central role in many electron systems including high temperature superconductors, but a quantitative understanding is lacking due to disorder and other complications. Here, we analyse the quantum phase diagram of a two-dimensional dipolar gas, which exhibits stripe, nematic and supersolid phases. We calculate the stiffness constants determining the stability of the nematic and stripe phases, and the melting of the stripes set by the proliferation of topological defects is analysed microscopically. Our results for the critical temperatures of these phases demonstrate that a controlled study of the interplay between quantum liquid and superfluid phases is within experimental reach for the first time, using dipolar gases. PMID:26750156

  1. Mean-field predictions for a dipolar Bose-Einstein condensate with 164Dy

    NASA Astrophysics Data System (ADS)

    Zajec, Damir; Wunner, Günter

    2015-11-01

    Dipolar Bose-Einstein condensates are systems well suited for the investigation of effects caused by the nonlocal and anisotropic dipole-dipole interaction. In this paper we are interested in properties which are directly connected to the realization of a condensate with 164Dy , such as stability and phase diagrams. Additionally, we study the expansion of dipolar condensates and find signatures of the dipole-dipole interaction in terms of structured states and a deviation of the well-known inversion of the aspect ratio of the cloud during a time of flight. Our analysis is based on the extended Gross-Pitaevskii equation, which we solve numerically exactly on a grid by means of an imaginary- and real-time evolution.

  2. 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

  3. 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.

  4. Ferroelectric Coordination Polymers Self-Assembled from Mesogenic Zinc(II) Porphyrin and Dipolar Bridging Ligands.

    PubMed

    Hui, Joseph K-H; Kishida, Hiroyuki; Ishiba, Keita; Takemasu, Kenta; Morikawa, Masa-Aki; Kimizuka, Nobuo

    2016-09-26

    A new class of ferroelectric coordination-based polymers has been developed by the self-assembly of lipophilic zinc porphyrin (ZnP) and ditopic bridging ligands. The ligands contain dipolar benzothiadiazole or fluorobenzene units, which are axially coordinated to ZnP with the dipole moments oriented perpendicular to the coordination axes. The coordination-based polymers show ferroelectric characteristics in the liquid crystalline state, as revealed by distinctive hysteresis in the polarization-electric field (P-E) loops and inversion current peaks in current-voltage (I-V) loops. The observed ferroelectric properties are explainable by flip-flop rotation of the dipolar axle ligands induced by the applied electric field, as demonstrated by the positive-up-negative-down (PUND) measurements. The present system provides a new operating principle in supramolecular ferroelectrics. PMID:27527513

  5. Anisotropic Relaxation Dynamics in a Dipolar Fermi Gas Driven Out of Equilibrium

    NASA Astrophysics Data System (ADS)

    Aikawa, K.; Frisch, A.; Mark, M.; Baier, S.; Grimm, R.; Bohn, J. L.; Jin, D. S.; Bruun, G. M.; Ferlaino, F.

    2014-12-01

    We report on the observation of a large anisotropy in the rethermalization dynamics of an ultracold dipolar Fermi gas driven out of equilibrium. Our system consists of an ultracold sample of strongly magnetic Er 167 fermions, spin polarized in the lowest Zeeman sublevel. In this system, elastic collisions arise purely from universal dipolar scattering. Based on cross-dimensional rethermalization experiments, we observe a strong anisotropy of the scattering, which manifests itself in a large angular dependence of the thermal relaxation dynamics. Our result is in good agreement with recent theoretical predictions. Furthermore, we measure the rethermalization rate as a function of temperature for different angles and find that the suppression of collisions by Pauli blocking is not influenced by the dipole orientation.

  6. Liquid crystal phases of two-dimensional dipolar gases and Berezinskii-Kosterlitz-Thouless melting

    PubMed Central

    Wu, Zhigang; Block, Jens K.; Bruun, Georg M.

    2016-01-01

    Liquid crystals are phases of matter intermediate between crystals and liquids. Whereas classical liquid crystals have been known for a long time and are used in electro-optical displays, much less is known about their quantum counterparts. There is growing evidence that quantum liquid crystals play a central role in many electron systems including high temperature superconductors, but a quantitative understanding is lacking due to disorder and other complications. Here, we analyse the quantum phase diagram of a two-dimensional dipolar gas, which exhibits stripe, nematic and supersolid phases. We calculate the stiffness constants determining the stability of the nematic and stripe phases, and the melting of the stripes set by the proliferation of topological defects is analysed microscopically. Our results for the critical temperatures of these phases demonstrate that a controlled study of the interplay between quantum liquid and superfluid phases is within experimental reach for the first time, using dipolar gases. PMID:26750156

  7. Partial alignment and measurement of residual dipolar couplings of proteins under high hydrostatic pressure

    PubMed Central

    Fu, Yinan; Wand, A. Joshua

    2013-01-01

    High-pressure NMR spectroscopy has emerged as a complementary approach for investigating various structural and thermodynamic properties of macromolecules. Noticeably absent from the array of experimental restraints that have been employed to characterize protein structures at high hydrostatic pressure is the residual dipolar coupling, which requires the partial alignment of the macromolecule of interest. Here we examine five alignment media that are commonly used at ambient pressure for this purpose. We find that the spontaneous alignment of Pf1 phage, d(GpG) and a C12E5/n-hexnanol mixture in a magnetic field is preserved under high hydrostatic pressure. However, DMPC/ DHPC bicelles and collagen gel are found to be unsuitable. Evidence is presented to demonstrate that pressure-induced structural changes can be identified using the residual dipolar coupling. PMID:23807390

  8. Non-dipolar gauge links for transverse-momentum-dependent pion wave functions

    NASA Astrophysics Data System (ADS)

    Wang, Yu-Ming

    2016-03-01

    I discuss the factorization-compatible definitions of transverse-momentumdependent (TMD) pion wave functions which are fundamental theory inputs entering QCD factorization formulae for many hard exclusive processes. I will first demonstrate that the soft subtraction factor introduced to remove both rapidity and pinch singularities can be greatly reduced by making the maximal use of the freedom to construct the Wilson-line paths when defining the TMD wave functions. I will then turn to show that the newly proposed TMD definition with non-dipolarWilson lines is equivalent to the one with dipolar gauge links and with a complicated soft function, to all orders of the perturbative expansion in the strong coupling, as far as the infrared behavior is concerned.

  9. 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.

  10. 1,3-Dipolar cycloaddition of sugar azides with benzyne: a novel synthesis of 1,2,3-benzotriazolyl glycoconjugates.

    PubMed

    Subba Reddy, Basi V; Praneeth, Karanam; Yadav, Jhillu S

    2011-06-01

    Glycosyl azides undergo smooth 1,3-dipolar cycloaddition with benzyne generated in situ from 2-(trimethylsilyl)phenyltrifluoromethanesulfonate and cesium fluoride under mild conditions to furnish 1,2,3-benzotriazole-linked glycoconjugates in excellent yields and with high stereoselectivity. This method provides a novel class of benzotriazole linked glycoconjugates in a single-step reaction. This is the first example of a fluoride- triggered 1,3-dipolar cycloaddition of benzyne with glycosyl azides.

  11. Scaling parallels in the non-Debye dielectric relaxation of ionic glasses and dipolar supercooled liquids

    SciTech Connect

    Sidebottom, D.L.; Green, P.F.; Brow, R.K.

    1997-07-01

    We compare the dielectric response of ionic glasses and dipolar liquids near the glass transition. Our work is divided into two parts. In the first section we examine ionic glasses and the two prominent approaches to analyzing the dielectric response. The conductivity of ion-conducting glasses displays a power law dispersion {sigma}({omega}){proportional_to}{omega}{sup n}, where n{approx}0.67, but frequently the dielectric response is analyzed using the electrical modulus M{sup {asterisk}}({omega})=1/{var_epsilon}{sup {asterisk}}({omega}), where {var_epsilon}{sup {asterisk}}({omega})={var_epsilon}({omega}){minus}i{sigma}({omega})/{omega} is the complex permittivity. We reexamine two specific examples where the shape of M{sup {asterisk}}({omega}) changes in response to changes in (a) temperature and (b) ion concentration, to suggest fundamental changes in ion dynamics are occurring. We show, however, that these changes in the shape of M{sup {asterisk}}({omega}) occur in the absence of changes in the scaling properties of {sigma}({omega}), for which n remains constant. In the second part, we examine the dielectric relaxation found in dipolar liquids, for which {var_epsilon}{sup {asterisk}}({omega}) likewise exhibits changes in shape on approach to the glass transition. Guided by similarities of M{sup {asterisk}}({omega}) in ionic glasses and {var_epsilon}{sup {asterisk}}({omega}) in dipolar liquids, we demonstrate that a recent scaling approach proposed by Dixon and co-workers for {var_epsilon}{sup {asterisk}}({omega}) of dipolar relaxation also appears valid for M{sup {asterisk}}({omega}) in the ionic case. While this suggests that the Dixon scaling approach is more universal than previously recognized, we demonstrate how the dielectric response can be scaled in a linear manner using an alternative data representation. {copyright} {ital 1997} {ital The American Physical Society}

  12. 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.

  13. 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.

  14. 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.

  15. 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

  16. Dipolar field effects on the critical current for spin transfer switch of iron and permalloy nanoelements

    SciTech Connect

    Oliveira, L. L.; Dantas, J. T. S.; Souza, R. M.; Carriço, A. S.; Dantas, Ana L.

    2014-05-07

    We report a theoretical study of dipolar effects on the switching current density of soft ferromagnetic elliptical nanoelements. Relevant changes on the critical current value are found according to the orientation of the magnetization and the spin polarization with the major axis. We show that the critical current density may be reduced by as much as 92% for thin nanoelements magnetized along the minor axis direction, using in-plane spin polarization parallel to the magnetization.

  17. Existence and stability results for thermoelastic dipolar bodies with double porosity

    NASA Astrophysics Data System (ADS)

    Marin, M.; Nicaise, S.

    2016-11-01

    This paper is concerned with the theory of thermoelastic dipolar bodies which have a double porosity structure. In contrast with previous papers dedicated to classical elastic bodies, in our context the double porosity structure of the body is influenced by the displacement field, which is consistent with real models. In this setting, we show instability of solution as the initial energy is negative while under an appropriated (and realistic) condition, we prove existence and uniqueness of solution using semi-group theory.

  18. Self-bound dipolar droplet: A localized matter wave in free space

    NASA Astrophysics Data System (ADS)

    Baillie, D.; Wilson, R. M.; Bisset, R. N.; Blakie, P. B.

    2016-08-01

    We demonstrate that a dipolar condensate can be prepared into a three-dimensional wave packet that remains localized when released in free space. Such self-bound states arise from the interplay of the two-body interactions and quantum fluctuations. We develop a phase diagram for the parameter regimes where these self-bound states are stable, examine their properties, and demonstrate how they can be produced in current experiments.

  19. 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. PMID:26014117

  20. Comparison of the dipolar magnetic field generated by two Ising-like models

    NASA Astrophysics Data System (ADS)

    Peqini, Klaudio; Duka, Bejo

    2015-04-01

    We consider two Ising-like models named respectively the "domino" model and the Rikitake disk dynamo model. Both models are based on some collective interactions that can generate a dipolar magnetic field which reproduces the well-known features of the geomagnetic field: the reversals and secular variation (SV). The first model considers the resultant dipolar magnetic field as formed by the superposition of the magnetic fields generated by the dynamo elements called macrospins, while the second one, starting from the two-disk dynamo action, takes in consideration the collective interactions of several disk dynamo elements. We will apply two versions of each model: the short-range and the long-range coupled dynamo elements. We will study the statistical properties of the time series generated by the simulation of all models. The comparison of these results with the paleomagnetic data series and long series of SV enables us to conclude which of these Ising-like models better match with the geomagnetic field time series. Key words: geomagnetic field, domino model, Rikitake disk dynamo, dipolar moment

  1. Applying "domino" model to study dipolar geomagnetic field reversals and secular variation

    NASA Astrophysics Data System (ADS)

    Peqini, Klaudio; Duka, Bejo

    2014-05-01

    Aiming to understand the physical processes underneath the reversals events of geomagnetic field, different numerical models have been conceived. We considered the so named "domino" model, an Ising-Heisenberg model of interacting magnetic spins aligned along a ring [Mazaud and Laj, EPSL, 1989; Mori et al., arXiv:1110.5062v2, 2012]. We will present here some results which are slightly different from the already published results, and will give our interpretation on the differences. Following the empirical studies of the long series of the axial magnetic moment (dipolar moment or "magnetization") generated by the model varying all model parameters, we defined the set of parameters that supply the longest mean time between reversals. Using this set of parameters, a short time series (about 10,000 years) of axial magnetic moment was generated. After de-noising the fluctuation of this time series, we compared it with the series of dipolar magnetic moment values supplied by CALS10K.1b model for the last 10000 years. We found similar behavior of the both series, even if the "domino" model could not supply a full explanation of the geomagnetic field SV. In a similar way we will compare a 14000 years long series with the dipolar magnetic moment obtained by the model SHA.DIF.14k [Pavón-Carrasco et al., EPSL, 2014].

  2. Effect of dipolar nanoparticle interaction on transverse magnetic susceptibility: particle pair model

    NASA Astrophysics Data System (ADS)

    Plowman, Elizabeth; Hovorka, Ondrej; Friedman, Gennady

    2014-03-01

    Determining nanoparticle dipolar interactions from experimental measurement of magnetic moments is a classical inverse problem in magnetism. It is important in a variety of applications including magnetic information storage and Magnetic Particle Imaging (MPI). Historically, magnetic moment relaxation has been used to characterize system parameters including dipolar interactions. However, the results are sensitive to particle size distribution. We demonstrate that dipolar coupling strength in a nanoparticle-pair can be determined from transverse magnetic susceptibility, a readily measured parameter. Moreover, we demonstrate that this method is insensitive to particle size, rendering it more robust for real-world experiments. We present both analytical and numerical models for transient and steady-state transverse magnetic susceptibility and resulting interaction strength of our two-particle system. In the analytical model master equation is employed. The particles are assumed to be immobile and the set of possible states is discrete. In the numerical models both master equation and Landau-Lifshitz-Gilbert dynamics are employed. In these models random particle anisotropy directions are taken into account. The results of each model are compared. National Science Foundation GRFP.

  3. 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.

  4. 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).

  5. 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).

  6. Tuning of magnetic dipolar interactions of maghemite nanoparticles embedded in polyelectrolyte layer-by-layer films.

    PubMed

    Paterno, Leonardo G; Sinnecker, Elis H C P; Soler, Maria A G; Sinnecker, João P; Novak, Miguel A; Morais, Paulo C

    2012-08-01

    In this study we report an experimental approach capable of tuning dipolar interactions in hybrid magnetic nanofilms produced via layer-by-layer assembly of positively-charged maghemite nanoparticles and sodium sulfonated polystyrene onto glass and silicon substrates. Morphological and magnetic properties of the as prepared nanofilms were determined by Raman spectroscopy, atomic force microscopy, conventional and SQUID magnetometry. Maghemite nanoparticles form densely packed layers with voids between particles being filled by polymeric material as observed in atomic force microscopy images. Magnetic hysteresis loops and zero-field-cooled/field-cooled magnetization curves reveal a superparamagnetic behavior at room temperature. The energy barrier for the magnetic moment reversal of the nanofilms has been determined from the frequency dependent ac susceptibility and is related to the gamma-Fe2O3 nanoparticles concentration used in the colloidal dispersion throughout film fabrication. Variations on the interparticle distances have a direct effect on the interparticle dipolar interactions. A less concentrated colloid gives rise to large separated nanoparticles inside the nanofilm with a consequent reduction on the energy barrier for the magnetic moment reversal. The fabrication process exploring the control of the nanoparticle concentration can thus be used to tune the magnetic dipolar interactions in the nanofilms.

  7. Fundamental measure density functional theory study of liquid-vapor interface of dipolar and quadrupolar fluids.

    PubMed

    Warshavsky, V B; Zeng, X C

    2013-10-01

    We have studied interfacial structure and properties of liquid-vapor interfaces of dipolar fluids and quadrupolar fluids, respectively, using the classical density functional theory (DFT). Towards this end, we employ the fundamental measure DFT for a reference hard-sphere (HS) part of free energy and the modified mean field approximation for the correlation function of dipolar or quadrupolar fluid. At low temperatures we find that both the liquid-vapor interfacial density profile and orientational order parameter profile exhibit weakly damped oscillatory decay into the bulk liquid. At high temperatures the decay of interfacial density and order parameter profiles is entirely monotonic. The scaled temperature τ = 1 - T/T(c) that separates the two qualitatively different interfacial structures is in the range 0.10-0.15. At a given (dimensionless) temperature, increasing the dipolar or quadrupolar moment enhances the density oscillations. Application of an electric field (normal to the interface) will damp the oscillations. Likewise, at the given temperature, increasing the strength of any multipolar moment also increases the surface tensions while increasing the strength of the applied electric field will reduce the surface tensions. The results are compared with those based on the local-density approximations (LDA) for the reference HS part of free energy as well as with results of numerical experiments.

  8. Scattering of a two-soliton molecule by Gaussian potentials in dipolar Bose–Einstein condensates

    NASA Astrophysics Data System (ADS)

    Umarov, B. A.; Aklan, N. A. B.; Baizakov, B. B.; Abdullaev, F. Kh

    2016-06-01

    Two bright solitons in a dipolar Bose–Einstein condensate (BEC) can form stable bound states, known as soliton molecules. In this paper we study the scattering of a two-soliton molecule by external potential, using the simplest and analytically tractable Gaussian potential barriers and wells, in one spatial dimension. Collisions of soliton molecules with single solitons are investigated, the latter playing the role of a localized defect. Due to the long-range character of dipolar forces solitons interact with each other even though their waveforms do not appreciably overlap. This is an essentially different feature of dipolar solitons compared to their counterparts in BECs with contact atomic interactions. The result of scattering significantly depends on the potential’s strength and velocity of collision. For weak potentials and/or low velocity the molecule preserves its coherence, meantime the internal modes are excited. Scattering by strong potentials at moderately high velocity ends up with dissociation of the molecule. The theoretical model is based on the variational approximation for the nonlocal Gross–Pitaevskii equation (GPE). Predictions of the mathematical model are compared with numerical simulations of the nonlocal GPE, and good qualitative agreement between them is demonstrated.

  9. Nuclear magnetic resonance signal dynamics of liquids in the presence of distant dipolar fields, revisited.

    PubMed

    Barros, Wilson; Gochberg, Daniel F; Gore, John C

    2009-05-01

    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.

  10. 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

  11. Thermodynamics of dipolar hard spheres with low-to-intermediate coupling constants.

    PubMed

    Elfimova, Ekaterina A; Ivanov, Alexey O; Camp, Philip J

    2012-08-01

    The thermodynamic properties of the dipolar hard-sphere fluid are studied using theory and simulation. A new theory is derived using a convenient mathematical approximation for the Helmholtz free energy relative to that for the hard-sphere fluid. The approximation is designed to give the correct low-density virial expansion. New theoretical and numerical results for the fourth virial coefficient are given. Predictions of thermodynamic functions for dipolar coupling constants λ=1 and 2 show excellent agreement with simulation results, even at the highest value of the particle volume fraction φ. For higher values of λ, there are deviations at high volume fractions, but the correct low-density behavior is retained. The theory is compared critically against the established thermodynamic perturbation theory; it gives significant improvements at low densities and is more convenient in terms of the required numerics. Dipolar hard spheres provide a basic model for ferrofluids, and the theory is accurate for typical experimental parameters λ

  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. Magnetic dipolar interaction between correlated triplets created by singlet fission in tetracene crystals

    PubMed Central

    Wang, Rui; Zhang, Chunfeng; Zhang, Bo; Liu, Yunlong; Wang, Xiaoyong; Xiao, Min

    2015-01-01

    Singlet fission can potentially break the Shockley–Queisser efficiency limit in single-junction solar cells by splitting one photoexcited singlet exciton (S1) into two triplets (2T1) in organic semiconductors. A dark multiexciton state has been proposed as the intermediate connecting S1 to 2T1. However, the exact nature of this multiexciton state, especially how the doubly excited triplets interact, remains elusive. Here we report a quantitative study on the magnetic dipolar interaction between singlet-fission-induced correlated triplets in tetracene crystals by monitoring quantum beats relevant to the multiexciton sublevels at room temperature. The resonances of multiexciton sublevels approached by tuning an external magnetic field are observed to be avoided, which agrees well with the theoretical predictions considering a magnetic dipolar interaction of ∼0.008 GHz. Our work quantifies the magnetic dipolar interaction in certain organic materials and marks an important step towards understanding the underlying physics of the multiexciton state in singlet fission. PMID:26456368

  14. Dipolarization in the inner magnetosphere during a geomagnetic storm on 7 October 2015

    NASA Astrophysics Data System (ADS)

    Matsui, H.; Erickson, P. J.; Foster, J. C.; Torbert, R. B.; Argall, M. R.; Anderson, B. J.; Blake, J. B.; Cohen, I. J.; Ergun, R. E.; Farrugia, C. J.; Khotyaintsev, Yu. V.; Korth, H.; Lindqvist, P.-A.; Magnes, W.; Marklund, G. T.; Mauk, B. H.; Paulson, K. W.; Russell, C. T.; Strangeway, R. J.; Turner, D. L.

    2016-09-01

    A dipolarization event was observed by the Magnetospheric Multiscale (MMS) spacecraft at L = 3.8 and 19.8 magnetic local time starting at ˜23:42:36 UT on 7 October 2015. The magnetic and electric fields showed initially coherent variations between the spacecraft. The sunward convection turned tailward after the dipolarization. The observation is interpreted in terms of the pressure balance or the momentum equation. This was followed by a region traversed where the fields were irregular. The scale length was of the order of the ion gyroradius, suggesting the kinetic nature of the fluctuations. Combination of the multi-instrument, multispacecraft data reveals a more detailed picture of the dipolarization event in the inner magnetosphere. Conjunction ionosphere-plasmasphere observations from DMSP, two-dimensional GPS total electron content, the Millstone Hill midlatitude incoherent scatter radar, and AMPERE measurements imply that MMS observations are located on the poleward edge of the ionospheric trough where Region 2 field-aligned currents flow.

  15. Catalytic enantioselective 1,3-dipolar cycloadditions of azomethine ylides for biology-oriented synthesis.

    PubMed

    Narayan, Rishikesh; Potowski, Marco; Jia, Zhi-Jun; Antonchick, Andrey P; Waldmann, Herbert

    2014-04-15

    Cycloaddition reactions are among the most powerful methods for the synthesis of complex compounds. In particular, the development and application of the 1,3-dipolar cycloaddition, an important member of this reaction class, has grown immensely due to its powerful ability to efficiently build various five-membered heterocycles. Azomethine ylides are commonly used as dipoles for the synthesis of the pyrrolidine scaffold, which is an important motif in natural products, pharmaceuticals, and biological probes. The reaction between azomethine ylides and cyclic dipolarophiles allows access to polycyclic products with considerable complexity. The extensive application of the 1,3-dipolar cycloaddition is based on the fact that the desired products can be obtained with high yield in a regio- and stereocontrolled manner. The most attractive feature of the 1,3-dipolar cycloaddition of azomethine ylides is the possibility to generate pyrrolidines with multiple stereocenters in a single step. The development of enantioselective cycloadditions became a subject of intensive and impressive studies in recent years. Among many modes of stereoinduction, the application of chiral metal-ligand complexes has emerged as the most viable option for control of enantioselectivity. In chemical biology research based on the principle of biology-oriented synthesis (BIOS), compound collections are prepared inspired by natural product scaffolds. In BIOS, biological relevance is employed as the key criterion to generate hypotheses for the design and synthesis of focused compound libraries. In particular, the underlying scaffolds of natural product classes provide inspiration for BIOS because they define the areas of chemical space explored by nature, and therefore, they can be regarded as "privileged". The scaffolds of natural products are frequently complex and rich in stereocenters, which necessitates the development of efficient enantioselective methodologies. This Account highlights examples

  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. 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

  18. Nuclear magnetic resonance proton dipolar order relaxation in thermotropic liquid crystals: A quantum theoretical approach

    NASA Astrophysics Data System (ADS)

    Zamar, R. C.; Mensio, O.

    2004-12-01

    By means of the Jeener-Broekaert nuclear magnetic resonance pulse sequence, the proton spin system of a liquid crystal can be prepared in quasiequilibrium states of high dipolar order, which relax to thermal equilibrium with the molecular environment with a characteristic time (T1D). Previous studies of the Larmor frequency and temperature dependence of T1D in thermotropic liquid crystals, that included field cycling and conventional high-field experiments, showed that the slow hydrodynamic modes dominate the behavior of T1D, even at high Larmor frequencies. This noticeable predominance of the cooperative fluctuations (known as order fluctuations of the director, OFD) could not be explained by standard models based on the spin-lattice relaxation theory in the limit of high temperature (weak order). This fact points out the necessity of investigating the role of the quantum terms neglected in the usual high temperature theory of dipolar order relaxation. In this work, we present a generalization of the proton dipolar order relaxation theory for highly correlated systems, which considers all the spins belonging to correlated domains as an open quantum system interacting with quantum bath. As starting point, we deduce a formulation of the Markovian master equation of relaxation for the statistical spin operator, valid for all temperatures, which is suitable for introducing a dipolar spin temperature in the quantum regime, without further assumptions about the form of the spin-lattice Hamiltonian. In order to reflect the slow dynamics occurring in correlated systems, we lift the usual short-correlation-time assumption by including the average over the motion of the dipolar Hamiltonian together with the Zeeman Hamiltonian into the time evolution operator. In this way, we calculate the time dependence of the spin operators in the interaction picture in a closed form, valid for high magnetic fields, bringing into play the spin-spin interactions within the microscopic time

  19. 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.

  20. Simulations of dipolar fluids using effective many-body isotropic interactions.

    PubMed

    Sindt, Julien O; Camp, Philip J

    2015-07-14

    The partition function of a system with pairwise-additive anisotropic dipole-dipole interactions is equal to that of a hypothetical system with many-body isotropic interactions [G. Stell, Phys. Rev. Lett. 32, 286 (1974)]. The effective many-body interactions contain n-body contributions of all orders. Each contribution is known as an expansion in terms of the particle-particle distances r, and the coefficients are temperature dependent. The leading-order two-body term is the familiar -r(-6) attraction, and the leading-order three-body term is equivalent to the Axilrod-Teller interaction. In this work, a fluid of particles with the leading-order two-body and three-body interactions is compared to an equivalent dipolar soft-sphere fluid. Molecular simulations are used to determine the conditions under which the effective many-body interactions reproduce the fluid-phase structures of the dipolar system. The effective many-body interaction works well at moderately high temperatures but fails at low temperatures where particle chaining is expected to occur. It is shown that an adjustment of the coefficients of the two-body and three-body terms leads to a good description of the structure of the dipolar fluid even in the chaining regime, due primarily to the ground-state linear configuration of the three-body Axilrod-Teller interaction. The vapor-liquid phase diagrams of systems with different Axilrod-Teller contributions are determined. As the strength of the three-body interaction is increased, the critical temperature and density both decrease and disappear completely above a threshold strength, where chaining eventually suppresses the condensation transition. PMID:26178112

  1. 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.

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

    PubMed

    Chang, Zhiwei; Halle, Bertil

    2016-07-21

    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. PMID:27448879

  3. Pair-Supersolid Phase in a Bilayer System of Dipolar Lattice Bosons

    SciTech Connect

    Trefzger, C.; Menotti, C.; Lewenstein, M.

    2009-07-17

    The competition between tunneling and interactions in bosonic lattice models generates a whole variety of different quantum phases. While, in the presence of a single species interacting via on site interaction, the phase diagram presents only superfluid or Mott insulating phases, for long-range interactions or multiple species, exotic phases such as supersolid or pair-superfluid appear. In this Letter, we show for the first time that the coexistence of effective multiple species and long-range interactions leads to the formation of a novel pair-supersolid phase, namely, a supersolid of composites. We propose a possible implementation with dipolar bosons in a bilayer two-dimensional optical lattice.

  4. 1,3-Dipolar Cycloaddition Reactions of Azomethine Ylides with Carbonyl Dipolarophiles Yielding Oxazolidine Derivatives.

    PubMed

    Meyer, Adam G; Ryan, John H

    2016-01-01

    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. PMID:27455230

  5. Biological colloid engineering: Self-assembly of dipolar ferromagnetic chains in a functionalized biogenic ferrofluid

    NASA Astrophysics Data System (ADS)

    Ruder, Warren C.; Hsu, Chia-Pei D.; Edelman, Brent D.; Schwartz, Russell; LeDuc, Philip R.

    2012-08-01

    We have studied the dynamic behavior of nanoparticles in ferrofluids consisting of single-domain, biogenic magnetite (Fe3O4) 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.

  6. 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. PMID:27391706

  7. Influence of dipolar interaction on magnetic properties of ultrafine ferromagnetic particles

    PubMed

    Garcia-Otero; Porto; Rivas; Bunde

    2000-01-01

    We use Monte Carlo simulations to study the influence of dipolar interaction and polydispersity on the magnetic properties of single-domain ultrafine ferromagnetic particles. From the zero field cooling (ZFC)/field cooling (FC) simulations we observe that the blocking temperature T(B) clearly increases with increasing strength of interaction, but it is almost not effected by a broadening of the distribution of particle sizes. While the dependence of the ZFC/FC curves on interaction and cooling rate are reminiscent of a spin glass transition at T(B), the relaxational behavior of the magnetic moments below T(B) is not in accordance with the picture of cooperative freezing.

  8. Relaxation spectra and dipolar correlations for flexible polymers with bulky side groups

    SciTech Connect

    Diaz-Calleja, R.; Riande, E.; Roman, J.S.

    1992-08-06

    This paper discusses how relaxation spectra and dipolar correlations for flexible polymers with bulky side groups (PBPA chains) suggest that intermolecular correlations are not very important in this polymer and that {alpha}, {beta}, and {gamma} absorptions exist. TSDC techniques reveal that the {gamma} peak has a smaller activation energy than the {beta}, and the coupling scheme is used to interpret the complex dielectric and mechanical {alpha} relaxations. The anomalous temperature dependence of the glass-rubber relaxation is discussed in terms of the bulkiness of the side group. 23 refs., 8 figs., 3 tabs.

  9. Topological order-by-disorder in orbitally degenerate dipolar bosons on a zigzag lattice

    NASA Astrophysics Data System (ADS)

    Sun, G.; Vekua, T.

    2014-09-01

    Spinor bosons offer a conceptually simple picture of macroscopic quantum behavior of topological order-by-disorder: The paramagnetic state of two-component dipolar bosons in an orbitally degenerate zigzag lattice is unstable against infinitesimal quantum fluctuations of orbitals, λ, towards developing nonlocal hidden order. Adjacent to the topological state a locally correlated exact ground state with spontaneously a quadrupoled lattice constant is realized for the broad parameter regime. The topological order is extremely robust surviving the λ →∞ limit where the ground state evolves into the Majumdar-Ghosh state of a frustrated spin-1/2 chain.

  10. Density-wave instability in a two-dimensional dipolar Fermi gas

    SciTech Connect

    Yamaguchi, Yasuhiro; Sogo, Takaaki; Ito, Toru; Miyakawa, Takahiko

    2010-07-15

    We consider a uniform dipolar Fermi gas in two dimensions (2D) where the dipole moments of fermions are aligned by an orientable external field. We obtain the ground state of the gas in the Hartree-Fock approximation and investigate random-phase-approximation stability against density fluctuations of finite momentum. It is shown that the density-wave instability takes place in a broad region where the system is stable against collapse. We also find that the critical temperature can be a significant fraction of Fermi temperature for a realistic system of polar molecules.

  11. Quantum gases. Observation of Fermi surface deformation in a dipolar quantum gas.

    PubMed

    Aikawa, K; Baier, S; Frisch, A; Mark, M; Ravensbergen, C; Ferlaino, F

    2014-09-19

    In the presence of isotropic interactions, the Fermi surface of an ultracold Fermi gas is spherical. Introducing anisotropic interactions can deform the Fermi surface, but the effect is subtle and challenging to observe experimentally. Here, we report on the observation of a Fermi surface deformation in a degenerate dipolar Fermi gas of erbium atoms. The deformation is caused by the interplay between strong magnetic dipole-dipole interaction and the Pauli exclusion principle. We demonstrate the many-body nature of the effect and its tunability with the Fermi energy. Our observation provides a basis for future studies on anisotropic many-body phenomena in normal and superfluid phases. PMID:25237096

  12. Transition Structures of Diastereoselective 1,3-Dipolar Cycloadditions of Nitrile Oxides to Chiral Homoallylic Alcohols

    PubMed Central

    Luft, Jennifer A. R.; Meleson, Kieche; Houk, K. N.

    2008-01-01

    Transition structures of the 1,3-dipolar cycloaddition of substituted nitrile oxides with chiral homoallylic alcohols were explored with density functional theory (B3LYP/6-311+G(d,p)+CPCM(dichloromethane)//B3LYP/6-31+G(d)). The diastereoselectivity observed in these reactions was explained. The anti product is favored in both the thermal and magnesium-mediated reactions. Selectivity is predicted to increase in the presence of magnesium, in agreement with experimental results. The energetics of the magnesium-mediated reaction are similar to those previously found for allylic alcohols. PMID:17253700

  13. Interaction-driven Lifshitz transition with dipolar fermions in optical lattices

    NASA Astrophysics Data System (ADS)

    van Loon, E. G. C. P.; Katsnelson, M. I.; Chomaz, L.; Lemeshko, M.

    2016-05-01

    Anisotropic dipole-dipole interactions between ultracold dipolar fermions break the symmetry of the Fermi surface and thereby deform it. Here we demonstrate that such a Fermi surface deformation induces a topological phase transition—the so-called Lifshitz transition—in the regime accessible to present-day experiments. We describe the impact of the Lifshitz transition on observable quantities such as the Fermi surface topology, the density-density correlation function, and the excitation spectrum of the system. The Lifshitz transition in ultracold atoms can be controlled by tuning the dipole orientation and, in contrast to the transition studied in crystalline solids, is completely interaction driven.

  14. Dipolar vortices and collisional instability in rotating electron-positron-ion plasmas

    SciTech Connect

    Haque, Q.

    2011-11-15

    Linear dispersion relation of electrostatic waves is derived for rotating electron-positron-ion (e-p-i) plasmas. The role of the rotational plasma frequency on drift wave through Coriolis force in the pulsar magnetosphere is discussed. This wave can couple with acoustic mode. In the nonlinear regime, stationary solution in the form of dipolar vortices is obtained. At the end we have also found the collisional instability in the presence of neutral-ion collisions for this rotating e-p-i plasma. The importance of the study with respect to astrophysical plasmas is also pointed out.

  15. 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.

  16. 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.

  17. No evidence of gas-liquid coexistence in dipolar hard spheres.

    PubMed

    Rovigatti, Lorenzo; Russo, John; Sciortino, Francesco

    2011-12-01

    We report accurate calculations of the particle density of states in the dipolar hard-sphere fluid. Implementing efficient and tailored Monte Carlo algorithms, we are able to explore, in equilibrium, the low temperature region where a phase separation between a dilute gas of chain ends and a high-density liquid of chain junctions has been predicted to occur. Our data clearly show that the density of states remains always single peaked, definitively excluding the possibility of critical phenomena in the investigated temperature and density region. The analysis of the low temperature configurations shows that at low densities particles preferentially self-assemble into closed rings, strongly suppressing the chain ends concentration.

  18. Field-driven transitions in the dipolar pyrochlore antiferromagnet Gd2Ti2O7

    NASA Astrophysics Data System (ADS)

    Cépas, Olivier; Shastry, B. Sriram

    2004-05-01

    We present a mean-field theory for magnetic-field-driven transitions in dipolar coupled gadolinium titanate Gd2Ti2O7 pyrochlore system. Low-temperature neutron scattering yields a phase that can be regarded as a eight sublattice antiferromagnet, in which long-ranged ordered moments and fluctuating moments coexist. Our theory gives parameter regions where such a phase is realized, and predicts several other phases, with transitions amongst them driven by magnetic field as well as temperature. We find several instances of local disorder parameters describing the transitions.

  19. Correlations of a quasi-two-dimensional dipolar ultracold gas at finite temperatures

    NASA Astrophysics Data System (ADS)

    Pawłowski, Krzysztof; Bienias, Przemysław; Pfau, Tilman; Rzążewski, Kazimierz

    2013-04-01

    We study a quasi-two-dimensional dipolar gas at finite, but ultralow, temperatures using the classical field approximation. The method, already used for a contact interacting gas, is extended here to samples with a weakly interacting long-range interatomic potential. We present statistical properties of the system for the current experiment with chromium [Müller, Billy, Henn, Kadau, Griesmaier, Jona-Lasinio, Santos, and Pfau, Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.84.053601 84, 053601 (2011)] and compare them with statistics for atoms with larger magnetic dipole moments. Significant enhancement of the third-order correlation function, relevant for the particle losses, is found.

  20. 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

  1. Stability of Superfluid and Supersolid Phases of Dipolar Bosons in Optical Lattices

    SciTech Connect

    Danshita, Ippei; Sa de Melo, Carlos A. R.

    2009-11-27

    We perform a stability analysis of superfluid (SF) and supersolid (SS) phases of polarized dipolar bosons in two-dimensional optical lattices at high filling factors and zero temperature, and obtain the phase boundaries between SF, checkerboard SS (CSS), striped SS (SSS), and collapse. We show that the phase diagram can be explored through the application of an external field and the tuning of its direction with respect to the optical lattice plane. In particular, we find a transition between the CSS and SSS phases.

  2. Phase separation of two-dimensional Coulombic crystals of mesoscale dipolar particles from mesoscale polarizable ``solvent''

    NASA Astrophysics Data System (ADS)

    Kaufman, George K.; Reches, Meital; Thomas, Samuel W.; Feng, Ji; Shaw, Bryan F.; Whitesides, George M.

    2009-01-01

    This letter describes the formation of two-dimensional (2D) crystals of dipolar particles (TN) made of electrostatically charged, joined, millimeter-scale Teflon (T) and nylon-6,6 (N) spheres, and the separation of these crystals, as a distinct phase, from a mixture of TN and similar, capacitively charged particles that were coated with gold (Au2). The extent of separation increased with increasing amplitude of agitation, and with decreasing density of particles. Above a threshold in the amplitude of agitation, the crystals broke apart and the particles remixed. This system is a 2D model of the nucleation of crystals of polar molecules in a polarizable liquid.

  3. 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.

  4. 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.

  5. Electrostatic potential topography for exploring electronic reorganizations in 1,3 dipolar cycloadditions.

    PubMed

    Balanarayan, P; Kavathekar, Ritwik; Gadre, Shridhar R

    2007-04-12

    Topographical analysis of the molecular electrostatic potential (MESP) along a reaction path is employed for bringing out sequential electronic reorganizations for 1,3-dipolar cycloadditions of ethyne to fulminic acid as well as diazomethane. A simple and consistent set of rules for portraying electronic mechanisms of chemical reactions using the MESP topography is applied for this purpose. The MESP topography at each point on the concerted reaction path is associated with a classical electronic structure yielding a clear picture of the electronic reorganization along the reaction path.

  6. Investigating protein conformational energy landscapes and atomic resolution dynamics from NMR dipolar couplings: a review.

    PubMed

    Salmon, Loïc; Blackledge, Martin

    2015-12-01

    Nuclear magnetic resonance spectroscopy is exquisitely sensitive to protein dynamics. In particular inter-nuclear dipolar couplings, that become measurable in solution when the protein is dissolved in a dilute liquid crystalline solution, report on all conformations sampled up to millisecond timescales. As such they provide the opportunity to describe the Boltzmann distribution present in solution at atomic resolution, and thereby to map the conformational energy landscape in unprecedented detail. The development of analytical methods and approaches based on numerical simulation and their application to numerous biologically important systems is presented. PMID:26517337

  7. Dipolar Self-Assembling in Mixtures of Propylene Carbonate and Dimethyl Sulfoxide as Revealed by the Orientational Entropy.

    PubMed

    Płowaś, Iwona; Świergiel, Jolanta; Jadżyn, Jan

    2016-08-18

    This article presents the results of static dielectric studies performed on mixtures of two strongly polar liquids important from a technological point of view: propylene carbonate (PC) and dimethyl sulfoxide (DMSO). The dielectric data were analyzed in terms of the molar orientational entropy increment induced by the probing electric field. It was found that the two polar liquids in the neat state reveal quite different molecular organization in terms of dipole-dipole self-assembling: PC exhibits a dipolar coupling of the head-to-tail type, whereas in DMSO one observes extreme restriction of dipolar association in any form. In PC + DMSO mixtures, the disintegration of the dipolar ensembles of PC molecules takes place and the progress of that process is strictly proportional to the concentration of DMSO. The static permittivity of mixtures of such differently self-organized liquids exhibits a positive deviation from the additive rule and the deviation develops symmetrically within the concentration scale. PMID:27458791

  8. Dipolarization, current sheet flapping motion and periodic particle flux enhancements observed during the Galaxy 15 spacecraft anomaly

    NASA Astrophysics Data System (ADS)

    Loto'aniu, Paul; Rodriguez, Juan; Redmon, Robert

    2016-04-01

    On 5 April 2010, the Galaxy 15 spacecraft, orbiting at geosynchronous altitudes experienced an anomaly near local midnight when it stopped responding to any ground commands. Galaxy 15 spacecraft encountered severe plasma conditions while it was in eclipse and during the subsequent anomaly interval and these conditions included a massive magnetic field dipolarization that injected energetic particles from the magnetotail during a substorm. This anomaly was interesting for many reasons including that multiple spacecraft (GOES and THEMIS probes) were well located in the nightside to observe the substorm. At the time of the field line stretching and dipolarization some of the satellites observed magnetic variations together with particle flux enhancements with periodicities of a few minutes. In this study, we detail characteristics of this dipolarization, which was one of the strongest ever observed by a GOES spacecraft, as well as discuss perturbations in the magnetic field and particle fluxes that are indicative of magnetotail current sheet flapping motion.

  9. Communication: influence of nanosecond-pulsed electric fields on water and its subsequent relaxation: dipolar effects and debunking memory.

    PubMed

    Avena, Massimiliano; Marracino, Paolo; Liberti, Micaela; Apollonio, Francesca; English, Niall J

    2015-04-14

    Water has many intriguing and anomalous physical properties that have puzzled and titillated the scientific community for centuries, perhaps none more so than the proposition that water may retain some (permanent) "memory" of conditions (e.g., dilution) or electric fields to which it has been subject. Here, we have performed non-equilibrium molecular dynamics simulations of liquid water in external electric-field nanosecond pulses, at 260-310 K, and gauged significant non-thermal field effects in terms of dipolar response. Response of both system- and individual-dipoles has been investigated, and autocorrelation functions of both show more significant effects in stronger fields, with more sluggish relaxation. Crucially, we show that once the field is removed, the dipoles relax, exhibiting no memory or permanent dipolar alignment. We also quantify the time scales for system dynamical-dipolar properties to revert to zero-field equilibrium behaviour.

  10. Synthesis of BF2 complexes of prodigiosin type oligopyrroles.

    PubMed

    Rao, M Rajeswara; Tiwari, Manu D; Bellare, Jayesh R; Ravikanth, M

    2011-09-01

    We developed a simple, facile route for the synthesis of BF(2) complexes of prodigiosin type oligopyrroles and their cholesterol conjugates. This route gives an access to synthesize any desired meso-aryl-substituted 3-pyrrolyl BODIPYs which were not easily accessible earlier.

  11. Multispacecraft analysis of dipolarization fronts and associated whistler wave emissions using MMS data

    NASA Astrophysics Data System (ADS)

    Breuillard, H.; Le Contel, O.; Retino, A.; Chasapis, A.; Chust, T.; Mirioni, L.; Graham, D. B.; Wilder, F. D.; Cohen, I.; Vaivads, A.; Khotyaintsev, Yu. V.; Lindqvist, P.-A.; Marklund, G. T.; Burch, J. L.; Torbert, R. B.; Ergun, R. E.; Goodrich, K. A.; Macri, J.; Needell, J.; Chutter, M.; Rau, D.; Dors, I.; Russell, C. T.; Magnes, W.; Strangeway, R. J.; Bromund, K. R.; Plaschke, F.; Fischer, D.; Leinweber, H. K.; Anderson, B. J.; Le, G.; Slavin, J. A.; Kepko, E. L.; Baumjohann, W.; Mauk, B.; Fuselier, S. A.; Nakamura, R.

    2016-07-01

    Dipolarization fronts (DFs), embedded in bursty bulk flows, play a crucial role in Earth's plasma sheet dynamics because the energy input from the solar wind is partly dissipated in their vicinity. This dissipation is in the form of strong low-frequency waves that can heat and accelerate energetic electrons up to the high-latitude plasma sheet. However, the dynamics of DF propagation and associated low-frequency waves in the magnetotail are still under debate due to instrumental limitations and spacecraft separation distances. In May 2015 the Magnetospheric Multiscale (MMS) mission was in a string-of-pearls configuration with an average intersatellite distance of 160 km, which allows us to study in detail the microphysics of DFs. Thus, in this letter we employ MMS data to investigate the properties of dipolarization fronts propagating earthward and associated whistler mode wave emissions. We show that the spatial dynamics of DFs are below the ion gyroradius scale in this region (˜500 km), which can modify the dynamics of ions in the vicinity of the DF (e.g., making their motion nonadiabatic). We also show that whistler wave dynamics have a temporal scale of the order of the ion gyroperiod (a few seconds), indicating that the perpendicular temperature anisotropy can vary on such time scales.

  12. Dipolar motions and ionic conduction in an ibuprofen derived ionic liquid.

    PubMed

    Viciosa, M T; Santos, G; Costa, A; Danède, F; Branco, L C; Jordão, N; Correia, N T; Dionísio, M

    2015-10-01

    It was demonstrated that the combination of the almost water insoluble active pharmaceutical ingredient (API) ibuprofen with the biocompatible 1-ethanol-3-methylimidazolium [C2OHMIM] cation of an ionic liquid (IL) leads to a highly water miscible IL-API with a solubility increased by around 5 orders of magnitude. Its phase transformations, as crystallization and glass transition, are highly sensitive to the water content, the latter shifting to higher temperatures upon dehydration. By dielectric relaxation spectroscopy the dynamical behavior of anhydrous [C2OHMIM][Ibu] and with 18.5 and 3% of water content (w/w) was probed from well below the calorimetric glass transition (Tg) up to the liquid state. Multiple reorientational dipolar processes were detected which become strongly affected by conductivity and electrode polarization near above Tg. Therefore [C2OHMIM][Ibu] exhibits mixed behavior of a conventional molecular glass former and an ionic conductor being analysed in this work through conductivity, electrical modulus and complex permittivity. The dominant process, σα-process, originates by a coupling between both charge transport and dipolar mechanisms. The structural relaxation times were derived from permittivity analysis and confirmed by temperature modulated differential scanning calorimetry. The temperature dependence of the β-secondary relaxation is coherent with a Johari-Goldstein (βJG) process as detected in conventional glass formers.

  13. Charge carrier transport in molecularly doped polycarbonate as a test case for the dipolar glass model.

    PubMed

    Novikov, S V; Tyutnev, A P

    2013-03-14

    We present the results of Monte Carlo simulations of the charge carrier transport in a disordered molecular system containing spatial and energetic disorders using the dipolar glass model. Model parameters of the material were chosen to fit a typical polar organic photoconductor polycarbonate doped with 30% of aromatic hydrazone, whose transport properties are well documented in literature. Simulated carrier mobility demonstrates a usual Poole-Frenkel field dependence and its slope is very close to the experimental value without using any adjustable parameter. At room temperature transients are universal with respect to the electric field and transport layer thickness. At the same time, carrier mobility does not depend on the layer thickness and transients develop a well-defined plateau where the current does not depend on time, thus demonstrating a non-dispersive transport regime. Tails of the transients decay as power law with the exponent close to -2. This particular feature indicates that transients are close to the boundary between dispersive and non-dispersive transport regimes. Shapes of the simulated transients are in very good agreement with the experimental ones. In summary, we provide a first verification of a self-consistency of the dipolar glass transport model, where major transport parameters, extracted from the experimental transport data, are then used in the transport simulation, and the resulting mobility field dependence and transients are in very good agreement with the initial experimental data.

  14. Charge carrier transport in molecularly doped polycarbonate as a test case for the dipolar glass model

    NASA Astrophysics Data System (ADS)

    Novikov, S. V.; Tyutnev, A. P.

    2013-03-01

    We present the results of Monte Carlo simulations of the charge carrier transport in a disordered molecular system containing spatial and energetic disorders using the dipolar glass model. Model parameters of the material were chosen to fit a typical polar organic photoconductor polycarbonate doped with 30% of aromatic hydrazone, whose transport properties are well documented in literature. Simulated carrier mobility demonstrates a usual Poole-Frenkel field dependence and its slope is very close to the experimental value without using any adjustable parameter. At room temperature transients are universal with respect to the electric field and transport layer thickness. At the same time, carrier mobility does not depend on the layer thickness and transients develop a well-defined plateau where the current does not depend on time, thus demonstrating a non-dispersive transport regime. Tails of the transients decay as power law with the exponent close to -2. This particular feature indicates that transients are close to the boundary between dispersive and non-dispersive transport regimes. Shapes of the simulated transients are in very good agreement with the experimental ones. In summary, we provide a first verification of a self-consistency of the dipolar glass transport model, where major transport parameters, extracted from the experimental transport data, are then used in the transport simulation, and the resulting mobility field dependence and transients are in very good agreement with the initial experimental data.

  15. Micro-mutual-dipolar model for rapid calculation of forces between paramagnetic colloids.

    PubMed

    Du, Di; Biswal, Sibani Lisa

    2014-09-01

    Typically, the force between paramagnetic particles in a uniform magnetic field is calculated using either dipole-based models or the Maxwell stress tensor combined with Laplace's equation for magnetostatics. Dipole-based models are fast but involve many assumptions, leading to inaccuracies in determining forces for clusters of particles. The Maxwell stress tensor yields an exact force calculation, but solving Laplace's equation is very time consuming. Here, we present a more elaborate dipole-based model: the micro-mutual-dipolar model. Our model has a time complexity that is similar to that of other dipole-based models but is much more accurate especially when used to calculate the force of small aggregates. Using this model, we calculate the force between two paramagnetic spheres in a uniform magnetic field and a circular rotational magnetic field and compare our results with those of other models. The forces for three-particle and ten-particle systems dispersed in two-dimensional (2D) space are examined using the same model. We also apply this model to calculate the force between two paramagnetic disks dispersed in 2D space. The micro-mutual-dipolar model is demonstrated to be useful for force calculations in dynamic simulations of small clusters of particles for which both accuracy and efficiency are desirable. PMID:25314567

  16. Strong Dipolar Effects on an Octupolar Luminiscent Chromophore: Implications on their Linear and Nonlinear Optical Properties.

    PubMed

    Jiménez-Sánchez, Arturo; Isunza-Manrique, Itzel; Ramos-Ortiz, Gabriel; Rodríguez-Romero, Jesús; Farfán, Norberto; Santillan, Rosa

    2016-06-30

    Design parameters derived from structure-property relationships play a very important role in the development of efficient molecular-based functional materials with optical properties. Here, we report on the linear and nonlinear optical properties of a fluorene-derived dipolar system (DS) and its octupolar analogue (OS), in which donor and acceptor groups are connected by a phenylacetylene linkage, as a strategy to increase the number of delocalized electrons in the π-conjugated system. The optical nonlinear response was analyzed in detail by experimental and theoretical methods, showing that, in the octupolar system OS, the dipolar effects induced a strong two-photon absorption process whose magnitude is as large as 2210 GM at infrared wavelengths. Solvatochromism studies were implemented to obtain further insight on the charge transfer process. We found that the triple bond plays a fundamental role in the linear and nonlinear optical responses. The strong solvatochromism behavior in DS and OS was analyzed by using four empirical solvent scales, namely Lippert-Mataga, Kamlet-Taft, Catalán, and the recently proposed scale of Laurence et al., finding consistent results of strong solvent polarizability and viscosity dependence. Finally, the role of the acceptor groups was further studied by synthesizing the analogous compound 2DS, having no acceptor group.

  17. Dipolar motions and ionic conduction in an ibuprofen derived ionic liquid.

    PubMed

    Viciosa, M T; Santos, G; Costa, A; Danède, F; Branco, L C; Jordão, N; Correia, N T; Dionísio, M

    2015-10-01

    It was demonstrated that the combination of the almost water insoluble active pharmaceutical ingredient (API) ibuprofen with the biocompatible 1-ethanol-3-methylimidazolium [C2OHMIM] cation of an ionic liquid (IL) leads to a highly water miscible IL-API with a solubility increased by around 5 orders of magnitude. Its phase transformations, as crystallization and glass transition, are highly sensitive to the water content, the latter shifting to higher temperatures upon dehydration. By dielectric relaxation spectroscopy the dynamical behavior of anhydrous [C2OHMIM][Ibu] and with 18.5 and 3% of water content (w/w) was probed from well below the calorimetric glass transition (Tg) up to the liquid state. Multiple reorientational dipolar processes were detected which become strongly affected by conductivity and electrode polarization near above Tg. Therefore [C2OHMIM][Ibu] exhibits mixed behavior of a conventional molecular glass former and an ionic conductor being analysed in this work through conductivity, electrical modulus and complex permittivity. The dominant process, σα-process, originates by a coupling between both charge transport and dipolar mechanisms. The structural relaxation times were derived from permittivity analysis and confirmed by temperature modulated differential scanning calorimetry. The temperature dependence of the β-secondary relaxation is coherent with a Johari-Goldstein (βJG) process as detected in conventional glass formers. PMID:26315452

  18. 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.

  19. Tunable negligible-loss energy transfer between dipolar-coupled magnetic disks by stimulated vortex gyration.

    PubMed

    Jung, Hyunsung; Lee, Ki-Suk; Jeong, Dae-Eun; Choi, Youn-Seok; Yu, Young-Sang; Han, Dong-Soo; Vogel, Andreas; Bocklage, Lars; Meier, Guido; Im, Mi-Young; Fischer, Peter; Kim, Sang-Koog

    2011-01-01

    A wide variety of coupled harmonic oscillators exist in nature. Coupling between different oscillators allows for the possibility of mutual energy transfer between them and the information-signal propagation. Low-energy input signals and their transport with negligible energy loss are the key technological factors in the design of information-signal processing devices. Here, utilizing the concept of coupled oscillators, we experimentally demonstrated a robust new mechanism for energy transfer between spatially separated dipolar-coupled magnetic disks - stimulated vortex gyration. Direct experimental evidence was obtained by a state-of-the-art experimental time-resolved soft X-ray microscopy probe. The rate of energy transfer from one disk to the other was deduced from the two normal modes' frequency splitting caused by dipolar interaction. This mechanism provides the advantages of tunable energy transfer rates, low-power input signals and negligible energy loss in the case of negligible intrinsic damping. Coupled vortex-state disks might be implemented in applications for information-signal processing.

  20. Long-Lived Spin-Orbit-Coupled Degenerate Dipolar Fermi Gas

    NASA Astrophysics Data System (ADS)

    Burdick, Nathaniel Q.; Tang, Yijun; Lev, Benjamin L.

    2016-07-01

    We describe the creation of a long-lived spin-orbit-coupled gas of quantum degenerate atoms using the most magnetic fermionic element, dysprosium. Spin-orbit coupling arises from a synthetic gauge field created by the adiabatic following of degenerate dressed states composed of optically coupled components of an atomic spin. Because of dysprosium's large electronic orbital angular momentum and large magnetic moment, the lifetime of the gas is limited not by spontaneous emission from the light-matter coupling, as for gases of alkali-metal atoms, but by dipolar relaxation of the spin. This relaxation is suppressed at large magnetic fields due to Fermi statistics. We observe lifetimes up to 400 ms, which exceeds that of spin-orbit-coupled fermionic alkali atoms by a factor of 10-100 and is close to the value obtained from a theoretical model. Elastic dipolar interactions are also observed to influence the Rabi evolution of the spin, revealing an interacting fermionic system. The long lifetime of this weakly interacting spin-orbit-coupled degenerate Fermi gas will facilitate the study of quantum many-body phenomena manifest at longer time scales, with exciting implications for the exploration of exotic topological quantum liquids.

  1. Salt-Excluding Artificial Water Channels Exhibiting Enhanced Dipolar Water and Proton Translocation.

    PubMed

    Licsandru, Erol; Kocsis, Istvan; Shen, Yue-Xiao; Murail, Samuel; Legrand, Yves-Marie; van der Lee, Arie; Tsai, Daniel; Baaden, Marc; Kumar, Manish; Barboiu, Mihail

    2016-04-27

    Aquaporins (AQPs) are biological water channels known for fast water transport (∼10(8)-10(9) molecules/s/channel) with ion exclusion. Few synthetic channels have been designed to mimic this high water permeability, and none reject ions at a significant level. Selective water translocation has previously been shown to depend on water-wires spanning the AQP pore that reverse their orientation, combined with correlated channel motions. No quantitative correlation between the dipolar orientation of the water-wires and their effects on water and proton translocation has been reported. Here, we use complementary X-ray structural data, bilayer transport experiments, and molecular dynamics (MD) simulations to gain key insights and quantify transport. We report artificial imidazole-quartet water channels with 2.6 Å pores, similar to AQP channels, that encapsulate oriented dipolar water-wires in a confined chiral conduit. These channels are able to transport ∼10(6) water molecules/s, which is within 2 orders of magnitude of AQPs' rates, and reject all ions except protons. The proton conductance is high (∼5 H(+)/s/channel) and approximately half that of the M2 proton channel at neutral pH. Chirality is a key feature influencing channel efficiency. PMID:27063409

  2. 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

  3. 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.

  4. Reversible Switching of Liquid Crystalline Order Permits Synthesis of Homogeneous Populations of Dipolar Patchy Microparticles

    PubMed Central

    Wang, Xiaoguang; Miller, Daniel S.; de Pablo, Juan J.

    2014-01-01

    The spontaneous positioning of colloids on the surfaces of micrometer-sized liquid crystalline 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 liquid crystal (LC) droplets and result in heterogeneous populations of patchy microparticles. To address this issue, here we demonstrate 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. By using magnetic colloids, we illustrate the utility of the approach 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. PMID:25484850

  5. Tunable negligible-loss energy transfer between dipolar-coupled magnetic disks by stimulated vortex gyration

    PubMed Central

    Jung, Hyunsung; Lee, Ki-Suk; Jeong, Dae-Eun; Choi, Youn-Seok; Yu, Young-Sang; Han, Dong-Soo; Vogel, Andreas; Bocklage, Lars; Meier, Guido; Im, Mi-Young; Fischer, Peter; Kim, Sang-Koog

    2011-01-01

    A wide variety of coupled harmonic oscillators exist in nature. Coupling between different oscillators allows for the possibility of mutual energy transfer between them and the information-signal propagation. Low-energy input signals and their transport with negligible energy loss are the key technological factors in the design of information-signal processing devices. Here, utilizing the concept of coupled oscillators, we experimentally demonstrated a robust new mechanism for energy transfer between spatially separated dipolar-coupled magnetic disks - stimulated vortex gyration. Direct experimental evidence was obtained by a state-of-the-art experimental time-resolved soft X-ray microscopy probe. The rate of energy transfer from one disk to the other was deduced from the two normal modes' frequency splitting caused by dipolar interaction. This mechanism provides the advantages of tunable energy transfer rates, low-power input signals and negligible energy loss in the case of negligible intrinsic damping. Coupled vortex-state disks might be implemented in applications for information-signal processing. PMID:22355578

  6. 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.

  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. 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.

  9. Search Coil and Fluxgate Data Merging on MMS: Examples on Dipolarization Event Cases

    NASA Astrophysics Data System (ADS)

    Plaschke, F.; Fischer, D.; Magnes, W.; Valavanoglou, A.; Le Contel, O.; Nakamura, R.; Andriopoulou, M.; Schmid, D.; Baumjohann, W.; Torbert, R. B.; Russell, C.; Strangeway, R. J.; Leinweber, H. K.; Bromund, K. R.; Anderson, B. J.; Le, G.; Chutter, M.; Needell, J.; Dors, I.; Slavin, J. A.; Kepko, L.; Mirioni, L.

    2015-12-01

    The instrument suite of MMS mission includes one search coil and two fluxgate magnetometers on each observatory and can therefore provide the possibility to study events that cross the sensitive frequency range of both instrument types. It is therefore desirable to have a common merged data product that combines the best parts of both instruments. Extensive ground based test measurements have been performed to identify the properties of the instruments. New models for compensating time and frequency properties were created and the difference to existing calibrations is analyzed. Considerations for application as well as signal processing constraints are discussed and the resulting method is applied on data from the mission. Dipolarization events can serve as suitable example, since they contain a variety of disturbances with different characteristic scales: transient filamentary properties, sharp fronts, reconfiguration of the current sheet, wave signatures on kinetic as well as fluid scales, thus requiring highest sensitivity data in a wide frequency range. We show these different signatures relevant to the dipolarization events based on the analysis of these newly produced data.

  10. 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.

  11. Strong Dipolar Effects on an Octupolar Luminiscent Chromophore: Implications on their Linear and Nonlinear Optical Properties.

    PubMed

    Jiménez-Sánchez, Arturo; Isunza-Manrique, Itzel; Ramos-Ortiz, Gabriel; Rodríguez-Romero, Jesús; Farfán, Norberto; Santillan, Rosa

    2016-06-30

    Design parameters derived from structure-property relationships play a very important role in the development of efficient molecular-based functional materials with optical properties. Here, we report on the linear and nonlinear optical properties of a fluorene-derived dipolar system (DS) and its octupolar analogue (OS), in which donor and acceptor groups are connected by a phenylacetylene linkage, as a strategy to increase the number of delocalized electrons in the π-conjugated system. The optical nonlinear response was analyzed in detail by experimental and theoretical methods, showing that, in the octupolar system OS, the dipolar effects induced a strong two-photon absorption process whose magnitude is as large as 2210 GM at infrared wavelengths. Solvatochromism studies were implemented to obtain further insight on the charge transfer process. We found that the triple bond plays a fundamental role in the linear and nonlinear optical responses. The strong solvatochromism behavior in DS and OS was analyzed by using four empirical solvent scales, namely Lippert-Mataga, Kamlet-Taft, Catalán, and the recently proposed scale of Laurence et al., finding consistent results of strong solvent polarizability and viscosity dependence. Finally, the role of the acceptor groups was further studied by synthesizing the analogous compound 2DS, having no acceptor group. PMID:27281172

  12. Micro-mutual-dipolar model for rapid calculation of forces between paramagnetic colloids

    NASA Astrophysics Data System (ADS)

    Du, Di; Biswal, Sibani Lisa

    2014-09-01

    Typically, the force between paramagnetic particles in a uniform magnetic field is calculated using either dipole-based models or the Maxwell stress tensor combined with Laplace's equation for magnetostatics. Dipole-based models are fast but involve many assumptions, leading to inaccuracies in determining forces for clusters of particles. The Maxwell stress tensor yields an exact force calculation, but solving Laplace's equation is very time consuming. Here, we present a more elaborate dipole-based model: the micro-mutual-dipolar model. Our model has a time complexity that is similar to that of other dipole-based models but is much more accurate especially when used to calculate the force of small aggregates. Using this model, we calculate the force between two paramagnetic spheres in a uniform magnetic field and a circular rotational magnetic field and compare our results with those of other models. The forces for three-particle and ten-particle systems dispersed in two-dimensional (2D) space are examined using the same model. We also apply this model to calculate the force between two paramagnetic disks dispersed in 2D space. The micro-mutual-dipolar model is demonstrated to be useful for force calculations in dynamic simulations of small clusters of particles for which both accuracy and efficiency are desirable.

  13. Supra Arcade Downflows with XRT Informed by Dipolarization Fronts with THEMIS

    NASA Technical Reports Server (NTRS)

    Kobelski, Adam; Savage, Sabrina Leah; Malaspina, David

    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.

  14. 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.

  15. Quantum hexatic order in two-dimensional dipolar and charged fluids

    NASA Astrophysics Data System (ADS)

    Bruun, Georg M.; Nelson, David R.

    2014-03-01

    Recent advances in cold atom experimentation suggest that studies of quantum two-dimensional melting of dipolar molecules, with dipoles aligned perpendicular to ordering plane, may be on the horizon. An intriguing aspect of this problem is that two-dimensional classical aligned dipoles (already studied in great detail in soft matter experiments on magnetic colloids) are known to melt via a two-stage process, with an intermediate hexatic phase separating the usual crystal and isotropic fluid phases. We estimate here the effect of quantum fluctuations on this hexatic phase, for both dipolar systems and charged Wigner crystals. Our approximate phase diagrams rely on a pair of Lindemann criteria, suitably adapted to deal with the effects of thermal fluctuations in two dimensions. As part of our analysis, we determine the phonon spectra of quantum particles on a triangular lattice interacting with repulsive 1/r3 and 1/r potentials. A large softening of the transverse and longitudinal phonon frequencies, due to both lattice effects and quantum fluctuations, plays a significant role in our analysis. The hexatic phase is predicted to survive down to very low temperatures.

  16. Spontaneous formation of magnetotail bursty bulk flows, dipolarization fronts, and corresponding changes of magnetic topology

    NASA Astrophysics Data System (ADS)

    Spence, H. E.; Boyd, A. J.; Huang, C. L.; Smith, S. S.; Henderson, M. G.; Friedel, R. H. W.; Larsen, B.; Reeves, G. D.; Blake, J. B.; Claudepierre, S. G.; Fennell, J.; Baker, D. N.; Kanekal, S.

    2014-12-01

    It is commonly assumed that magnetotail transients are caused by either changes of magnetic topology or buoyancy-driven ballooning/interchange processes. However, observations and 3D particle-in-cell simulations show that the primary process in the formation of dipolarization fronts, new X-lines, interchange fingers and flapping motions may be the spontaneous formation of bulk earthward plasma flows. It appears in tearing-unstable configurations with a tailward gradient of the normal magnetic field Bz. The earthward motion arising in these regions results in the formation of dipolarization fronts (DFs). While monopolar Bz variations in DFs can be explained by the MHD snowplow compression of plasma ahead of the front, the formation of new X-lines ahead of and behind the front occurs as a part of the kinetic process of the plasma bubble formation. This process enhances (initially mild) buoyancy of the magnetotail plasma sheet and thus instigates ballooning/interchange and flapping instabilities. We compare the properties of reconnection, buoyancy and flapping transients at the front, ahead and behind it as well as the corresponding energy conversion and plasma heating.

  17. Spontaneous formation of magnetotail bursty bulk flows, dipolarization fronts, and corresponding changes of magnetic topology

    NASA Astrophysics Data System (ADS)

    Sitnov, M. I.; Merkin, V. G.; Runov, A.

    2015-12-01

    It is commonly assumed that magnetotail transients are caused by either changes of magnetic topology or buoyancy-driven ballooning/interchange processes. However, observations and 3D particle-in-cell simulations show that the primary process in the formation of dipolarization fronts, new X-lines, interchange fingers and flapping motions may be the spontaneous formation of bulk earthward plasma flows. It appears in tearing-unstable configurations with a tailward gradient of the normal magnetic field Bz. The earthward motion arising in these regions results in the formation of dipolarization fronts (DFs). While monopolar Bz variations in DFs can be explained by the MHD snowplow compression of plasma ahead of the front, the formation of new X-lines ahead of and behind the front occurs as a part of the kinetic process of the plasma bubble formation. This process enhances (initially mild) buoyancy of the magnetotail plasma sheet and thus instigates ballooning/interchange and flapping instabilities. We compare the properties of reconnection, buoyancy and flapping transients at the front, ahead and behind it as well as the corresponding energy conversion and plasma heating.

  18. Design amphiphilic dipolar π-systems for stimuli-responsive luminescent materials using metastable states

    NASA Astrophysics Data System (ADS)

    Yagai, Shiki; Okamura, Satoru; Nakano, Yujiro; Yamauchi, Mitsuaki; Kishikawa, Keiki; Karatsu, Takashi; Kitamura, Akihide; Ueno, Akira; Kuzuhara, Daiki; Yamada, Hiroko; Seki, Tomohiro; Ito, Hajime

    2014-06-01

    π-Conjugated compounds that exhibit tunable luminescence in the solid state under external mechanical stimuli have potential applications in sensors and imaging devices. However, no rational designs have been proposed that impart these mechano-responsive luminescent properties to π-conjugated compounds. Here we demonstrate a strategy for mechano-responsive luminescent materials by imparting amphiphilic and dipolar characteristics to a luminescent π-conjugated system. The oligo(p-phenylenevinylene) luminophore with a didodecylamino group at one end and a tri(ethylene glycol) ester group at the other end yields segregated solid structures by separately aggregating its hydrophobic and hydrophilic moieties. The segregated structures force the molecules to align in the same direction, thereby generating a conflict between the side-chain aggregation and dipolar stabilization of the π-system. Consequently, these metastable solid structures can be transformed through mechanical stimulation to a more stable structure, from a π-π stacked aggregate to a liquid crystal and further to a crystalline phase with variable luminescence.

  19. Investigations of polymer dynamics in nanoporous media by field cycling NMR relaxometry and the dipolar correlation effect.

    PubMed

    Kausik, Ravinath; Fatkullin, Nail; Hüsing, Nicola; Kimmich, Rainer

    2007-05-01

    The chain dynamics of short-chain perfluoropolyether melts confined in Vycor nanoporous media has been characterized by field cycling nuclear magnetic resonance relaxometry and the dipolar correlation effect. The slowdown of motions under confinement, leading to larger residual dipolar couplings, has been probed by looking at the quotient of stimulated and primary echoes. Using field cycling relaxometry, it has been shown that there is strong evidence of reptation-like motion, even for such short-chain polymers as shown by the frequency and molecular weight dependences of the spin-lattice relaxation time.

  20. Effect of anisotropic exchange interactions and short-range phenomena on superfluidity in a homogeneous dipolar Fermi gas

    NASA Astrophysics Data System (ADS)

    Corro, I.; Martin, A. M.

    2016-08-01

    We develop a simple numerical method that allows us to calculate the BCS superfluid transition temperature Tc precisely for any interaction potential. We apply it to a polarized, ultracold Fermi gas with long-range, anisotropic, dipolar interactions and include the effects of anisotropic exchange interactions. We pay particular attention to the short-range behavior of dipolar gases and reexamine current renormalization methods. In particular, we find that dimerization of both atoms and molecules significantly hampers the formation of a superfluid. The end result is that at high density or interaction strengths, we find Tc is orders of magnitude lower than previous calculations.

  1. Paramagnetic Effects on Nuclear Relaxation in Enzyme-Bound Co(II)-Adenine Nucleotide Complexes: Relative Contributions of Dipolar and Scalar Interactions

    NASA Astrophysics Data System (ADS)

    Ray, Bruce D.; Jarori, Gotam K.; Nageswara Rao, B. D.

    1999-01-01

    31P NMR measurements on CoADP bound to creatine kinase designed to estimate the relative contribution of scalar and dipolar interactions to31P spin relaxation rates show that these rates are primarily due to distance-dependent dipolar interactions and that the contribution of the scalar interaction is negligible.

  2. 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

  3. Pre-onset Azimuthal Pressure Gradient and Associated Auroral Intensifications Related to Dipolarization Fronts

    NASA Astrophysics Data System (ADS)

    Xing, X.; Lyons, L. R.; Angelopoulos, V.; Zhou, X.; Donovan, E.; Larson, D. E.; Carlson, C. W.; Auster, U.

    2011-12-01

    The plasma pressure spatial distribution and the magnetic field in force balance with it determine the distribution of the Field-Aligned Current (FAC) in the quasi-static near-Earth plasma sheet. The time evolution of the azimuthal plasma pressure gradient during undisturbed periods is of particular importance in leading to the evolution of FACs, which strongly affect the ionospheric current circulation and the aurora formation before dynamical processes strike, e.g., substorms. Xing et al. (2011) demonstrated by case study that the plasma sheet pressure gradient at ~11 RE near the substorm onset meridian undergoes a substantial duskward enhancement shortly before the onset as identified from the auroral poleward expansion. The increased upward FAC driven by this pressure gradient enhancement leads to the thin onset arc intensification from which the poleward expansion initiates. The mechanism of the formation of such a transient duskward pressure gradient is still an open question. In the present study, we employ the multi-THEMIS spacecraft in azimuthal conjunction -at ~-11 RE and examine the ion flux and distributions during the period of pressure gradient enhancement. Strong field-aligned ion flux enhancements covering the energy range from several KeV to above 25KeV were observed by the spacecraft identifying the higher pressure increase, while at the same time the ion distributions show substantial field-aligned, mushroom-like shift in velocity space. These resemble the ion acceleration ahead of earthward moving dipolarization fronts in a highly stretched magnetic field during the late growth phase. The local plasma develops strong transient parallel anisotropy due to the ion acceleration. On the other hand, the spacecraft observing the lower pressure increase found weaker or no ion flux enhancements and had nearly isotropic distributions. Due to these spatial differences, similar transient pressure gradient enhancements in the dawnward direction were also

  4. Beyond Molecular Wires: Design Molecular Electronic Functions Based on Dipolar Effect.

    PubMed

    Lo, Wai-Yip; Zhang, Na; Cai, Zhengxu; Li, Lianwei; Yu, Luping

    2016-09-20

    investigated the rectification effect of different types of p-n junction diodes and its modification by structural and external effects. Through a combination of structural modifications, low temperature study, and quantum mechanical calculations, we showed that the origin of the rectification in these molecules can be attributed to the effect of dipolar field. Further studies on charge transport through transition metal complexes and anchoring group effect supported this conclusion. Most recently, a model system of molecular transistor was synthesized and demonstrated by STM-BJ technique. The gating effect in the molecular wire originated from the tuning of the energy levels via dipolar field and can be turned on/off by dipolar field and chemical stimulation. This is the first example of gated charge transport in molecular electronics.

  5. Beyond Molecular Wires: Design Molecular Electronic Functions Based on Dipolar Effect.

    PubMed

    Lo, Wai-Yip; Zhang, Na; Cai, Zhengxu; Li, Lianwei; Yu, Luping

    2016-09-20

    investigated the rectification effect of different types of p-n junction diodes and its modification by structural and external effects. Through a combination of structural modifications, low temperature study, and quantum mechanical calculations, we showed that the origin of the rectification in these molecules can be attributed to the effect of dipolar field. Further studies on charge transport through transition metal complexes and anchoring group effect supported this conclusion. Most recently, a model system of molecular transistor was synthesized and demonstrated by STM-BJ technique. The gating effect in the molecular wire originated from the tuning of the energy levels via dipolar field and can be turned on/off by dipolar field and chemical stimulation. This is the first example of gated charge transport in molecular electronics. PMID:27575979

  6. 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

  7. 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

  8. An improved synthesis of 1,2-benzisoxazoles: TBAF mediated 1,3-dipolar cycloaddition of nitrile oxides and benzyne.

    PubMed

    Spiteri, Christian; Sharma, Pallavi; Zhang, Fengzhi; Macdonald, Simon J F; Keeling, Steve; Moses, John E

    2010-02-28

    An efficient synthesis of a range of 1,2-benzisoxazoles using an improved 1,3-dipolar cycloaddition of nitrile oxides and benzyne is described. Key to the procedure is the in situ generation of the reactive nitrile oxide and benzyne reaction partners mediated by TBAF. Reactions are complete within 30 s, giving the target products in good to excellent yield.

  9. Multicomponent Dipolar Cycloaddition Strategy: Combinatorial Synthesis of Novel Spiro-Tethered Pyrazolo[3,4-b]quinoline Hybrid Heterocycles.

    PubMed

    Sumesh, Remani Vasudevan; Muthu, Muthumani; Almansour, Abdulrahman I; Suresh Kumar, Raju; Arumugam, Natarajan; Athimoolam, S; Jeya Yasmi Prabha, E Arockia; Kumar, Raju Ranjith

    2016-05-01

    The stereoselective syntheses of a library of novel spiro-tethered pyrazolo[3,4-b]quinoline-pyrrolidine/pyrrolothiazole/indolizine-oxindole/acenaphthene hybrid heterocycles have been achieved through the 1,3-dipolar cycloaddition of azomethine ylides generated in situ from α-amino acids and 1,2-diketones to dipolarophiles derived from pyrazolo[3,4-b]quinoline derivatives.

  10. Intramolecular 1,3-dipolar cycloaddition reactions in the synthesis of complex annelated quinolines, α-carbolines and coumarins.

    PubMed

    Majumder, Swarup; Borah, Pallabi; Bhuyan, Pulak J

    2012-05-01

    In this study, we report the synthesis of several novel dihydroisoxazole-, tetrahydroisoxazole- and dihydropyrazole-fused pyrido[2,3-b]quinolines, α-carbolines, and pyrido[2,3-c]coumarins, respectively, from simple precursors and by exploring intramolecular 1,3-dipolar cycloaddition reactions involving nitrile oxides, nitrones, and nitrile imines as 1,3-dipoles. PMID:22374452

  11. High-density limit of quasi-two-dimensional dipolar Bose gas

    NASA Astrophysics Data System (ADS)

    Pastukhov, Volodymyr

    2016-09-01

    We consider a simple model of the quasi-two-dimensional dipolar Bose gas confined in the one-dimensional square well potential. All dipoles are assumed to be oriented along the confining axis. By means of hydrodynamic approach it is shown that the general structure of the low-lying excitations can be analyzed exactly. We demonstrate that the problem significantly simplifies in the high-density limit for which the density profile in the confined direction as well as the leading-order contribution to the ground-state energy and spectrum of elementary excitations are calculated. The low-temperature result for the damping rate of the phonon mode is also presented.

  12. 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.

  13. Measuring Residual Dipolar Couplings in Excited Conformational States of Nucleic Acids by CEST NMR Spectroscopy.

    PubMed

    Zhao, Bo; Zhang, Qi

    2015-10-28

    Nucleic acids undergo structural transitions to access sparsely populated and transiently lived conformational states--or excited conformational states--that play important roles in diverse biological processes. Despite ever-increasing detection of these functionally essential states, 3D structure determination of excited states (ESs) of RNA remains elusive. This is largely due to challenges in obtaining high-resolution structural constraints in these ESs by conventional structural biology approaches. Here, we present nucleic-acid-optimized chemical exchange saturation transfer (CEST) NMR spectroscopy for measuring residual dipolar couplings (RDCs), which provide unique long-range angular constraints in ESs of nucleic acids. We demonstrate these approaches on a fluoride riboswitch, where one-bond (13)C-(1)H RDCs from both base and sugar moieties provide direct structural probes into an ES of the ligand-free riboswitch.

  14. A Dipolar Anthracene Dye: Synthesis, Optical Properties and Two-photon Tissue Imaging.

    PubMed

    Moon, Hyunsoo; Jun, Yong Woong; Kim, Dokyoung; Ryu, Hye Gun; Wang, Taejun; Kim, Ki Hean; Huh, Youngbuhm; Jung, Junyang; Ahn, Kyo Han

    2016-09-20

    Two-photon microscopy is a powerful tool for studying biological systems. In search of novel two-photon absorbing dyes for bioimaging, we synthesized a new anthracene-based dipolar dye (anthradan) and evaluated its two-photon absorbing and imaging properties. The new anthradan, 9,10-bis(o-dimethoxy-phenyl)-anthradan, absorbs and emits at longer wavelengths than acedan, a well-known two-photon absorbing dye. It is also stable under two-photon excitation conditions and biocompatible, and thus used for two-photon imaging of mouse organ tissues to show bright, near-red fluorescence along with negligible autofluorescence. Such an anthradan thus holds promise as a new class of two-photon absorbing dyes for the development of fluorescent probes and tags for biological systems. PMID:27535006

  15. Observation of a Rosensweig Instability and Stable Quantum Droplets in a Dipolar Bose Gas

    NASA Astrophysics Data System (ADS)

    Pfau, Tilman; Ferrier Barbut, Igor; Kadau, Holger; Schmitt, Matthias; Wenzel, Matthias

    2016-05-01

    Ferrofluids show unusual hydrodynamic effects due to the magnetic nature of their constituents. For increasing magnetization a classical ferrofluid undergoes a Rosensweig instability and creates self-organized ordered surface structures or droplet crystals. We observe a related instability in a Bose-Einstein condensate with strong dipolar interactions resulting in surprisingly stable droplet crystals. We find that quantum fluctuations which are the origin of genuine quantum many-body effects cannot be neglected and provide a stabilizing mechanism. We study experimentally individual stable quantum droplets containing about 800 atoms which are expected to collapse at the mean-field level due to the essentially attractive interaction. By systematic measurements on individual droplets we demonstrate quantitatively that quantum fluctuations stabilize them against the mean-field collapse. We observe in addition interference of several droplets indicating that this stable many-body state is phase coherent.

  16. Magnetic Dipolar Interaction in a Bose-Einstein Condensate Atomic Interferometer

    SciTech Connect

    Fattori, M.; Roati, G.; D'Errico, C.; Inguscio, M.; Modugno, G.; Deissler, B.; Zaccanti, M.; Jona-Lasinio, M.; Santos, L.

    2008-11-07

    We study the role played by the magnetic dipole interaction in the decoherence of a lattice-based interferometer that employs an alkali Bose-Einstein condensate with a tunable scattering length. The different behavior we observe for two different orientations of the dipoles gives us evidence of the anisotropic character of the interaction. The experiment is correctly reproduced by a model we develop only if the long-range interaction between different lattice sites is taken into account. Our model indicates that dipolar interaction can be compensated by a proper choice of the scattering length and that the magnetic dipole interaction should not represent an obstacle for atom interferometry with Bose-Einstein condensates with a tunable interaction.

  17. Influence of the dipolar interactions in the magnetization reversal asymmetry of hard-soft magnetic ribbons

    SciTech Connect

    Rivas, M.; Garcia, J.A.; Tejedor, M.; Bertran, E.; Cespedes, J.G.

    2005-01-15

    Partial crystallization of the metallic glass Co{sub 66}Si{sub 16}B{sub 12}Fe{sub 4}Mo{sub 2} was performed by annealing at temperatures between 500 and 540 deg. C for 10-20 min, resulting in crystallite volume fractions of (0.7-5)x10{sup -3} and sizes of 50-100 nm. This two-phase alloy presents a remarkable feature: a hysteresis loop shift that can be tailored by simply premagnetizing the sample in the adequate magnetic field. Shifts as large as five times the coercive field have been obtained which make them interesting for application as magnetic cores in dc pulse transformers. The asymetrical magnetic reversal is explained in terms of the magnetic dipolar field interaction and the observed hysteresis loops have been satisfactorily simulated by a modification of Stoner-Wohlfarth's model of coherent rotations.

  18. 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.

  19. Monte Carlo study of the two-dimensional site-diluted dipolar Ising model

    NASA Astrophysics Data System (ADS)

    Alonso, Juan J.; Allés, B.

    2010-08-01

    By tempered Monte Carlo simulations, we study two-dimensional site-diluted dipolar Ising systems. Dipoles are randomly placed on a fraction x of all L2 sites in a square lattice and point along a common crystalline axis. For xc0 range. Our results enable us to obtain an estimate of the critical exponent associated to the correlation length at T=0 , 1/ν=0.35(10) .

  20. Dynamical Properties of a Diluted Dipolar-Interaction Heisenberg Spin Glass

    NASA Astrophysics Data System (ADS)

    Zhang, Kai-Cheng; Liu, Yong; Chi, Feng

    2014-02-01

    Up to now the chirality is seldom studied in the diluted spin glass although many investigations have been performed on the site-ordered Edwards—Anderson model. By simulation, we investigate the dynamical properties of both the spin-glass and the chiral-glass phases in a diluted dipolar system, which was manifested to have a spin-glass transition by recent numerical study. By scaling we find that both phases have the same aging behavior and closer aging parameter μ. Similarly, the domains grow in the same way and both phases have a closer barrier exponent Ψ. It means that both the spins and the chirality have the same dynamical properties and they may freeze at the same temperature.

  1. Study of dipolar many-body system in a one-dimensional zig-zag chain

    NASA Astrophysics Data System (ADS)

    Ghimire, Niraj R.; Yelin, Susanne F.

    2016-05-01

    The goal is to understand the many-body properties of a one-dimensional zig-zag chain of a fixed number of classical dipolar spins. This is a system that could potentially be modeled by ultracold polar molecules, and be extended such that topological quantities in triangular or hexagonal lattices can be studied. In order to achieve this, we use the density-matrix renormalization group (DMRG) method and find the ground state of the spin S = 1 / 2 model. For this purpose, we will take into account nearest-neighbor (NN) and next-nearest-neighbor (NNN) hopping and interactions which can be expressed as functions of angles between the dipoles.

  2. Half-Quantum Vortex Molecules in a Binary Dipolar Bose Gas

    NASA Astrophysics Data System (ADS)

    Shirley, Wilbur E.; Anderson, Brandon M.; Clark, Charles W.; Wilson, Ryan M.

    2014-10-01

    We study the ground state phases of a rotating two-component, or binary, Bose-Einstein condensate, wherein one component possesses a large permanent magnetic dipole moment. A variety of nontrivial phases emerge in this system, including a half-quantum vortex (HQV) chain phase and a HQV molecule phase, where HQVs bind at short distances. We attribute these phases to the development of a minimum in the HQV interaction potential, which emerges without coherent coupling or attractive interactions between the components. Thus, we show that the presence of dipolar interactions in this system provides a unique mechanism for the formation of HQV molecules and results in a rich ground state phase diagram.

  3. Half-Quantum Vortex Molecules in a Binary Dipolar Bose Gas

    NASA Astrophysics Data System (ADS)

    Wilson, Ryan; Shirley, Wilbur; Anderson, Brandon; Clark, Charles

    2015-03-01

    We discuss the ground state phases of a rotating two-component, or binary Bose-Einstein condensate, wherein one component possesses a large permanent magnetic dipole moment. A variety of non-trivial phases emerge in this system, including a half-quantum vortex (HQV) chain phase and a HQV molecule phase, where HQVs bind at short distances. We attribute these phases to the development of a minimum in the HQV interaction potential, which emerges without coherent coupling or attractive interactions between the components. Thus, we show that the presence of dipolar interactions in this system provides a unique mechanism for the formation of HQV molecules and results in a rich ground state phase diagram.

  4. Half-quantum vortex molecules in a binary dipolar Bose gas.

    PubMed

    Shirley, Wilbur E; Anderson, Brandon M; Clark, Charles W; Wilson, Ryan M

    2014-10-17

    We study the ground state phases of a rotating two-component, or binary, Bose-Einstein condensate, wherein one component possesses a large permanent magnetic dipole moment. A variety of nontrivial phases emerge in this system, including a half-quantum vortex (HQV) chain phase and a HQV molecule phase, where HQVs bind at short distances. We attribute these phases to the development of a minimum in the HQV interaction potential, which emerges without coherent coupling or attractive interactions between the components. Thus, we show that the presence of dipolar interactions in this system provides a unique mechanism for the formation of HQV molecules and results in a rich ground state phase diagram.

  5. 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.

  6. Quantum Levy Flights and Multifractality of Dipolar Excitations in a Random System.

    PubMed

    Deng, X; Altshuler, B L; Shlyapnikov, G V; Santos, L

    2016-07-01

    We consider dipolar excitations propagating via dipole-induced exchange among immobile molecules randomly spaced in a lattice. The character of the propagation is determined by long-range hops (Levy flights). We analyze the eigenenergy spectra and the multifractal structure of the wave functions. In 1D and 2D, all states are localized, although in 2D the localization length can be extremely large leading to an effective localization-delocalization crossover in realistic systems. In 3D, all eigenstates are extended but not always ergodic, and we identify the energy intervals of ergodic and nonergodic states. The reduction of the lattice filling induces an ergodic to nonergodic transition, and the excitations are mostly nonergodic at low filling. PMID:27447492

  7. Biological colloid engineering: Self-assembly of dipolar ferromagnetic chains in a functionalized biogenic ferrofluid

    PubMed Central

    Ruder, Warren C.; Hsu, Chia-Pei D.; Edelman, Brent D.; Schwartz, Russell; LeDuc, Philip R.

    2012-01-01

    We have studied the dynamic behavior of nanoparticles in ferrofluids consisting of single-domain, biogenic magnetite (Fe3O4) 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. PMID:22952408

  8. 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

  9. 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.

  10. Long-range orientation correlation in dipolar liquids probed by hyper-Rayleigh scattering.

    PubMed

    Shelton, David P

    2015-10-01

    Hyper-Rayleigh scattering (HRS) is sensitive to long-range molecular orientation correlation in isotropic liquids composed of dipolar molecules. The correlation functions that appear in the calculation of HRS mediated by the vector part of the first hyperpolarizability β are the same as the correlation functions for the homogeneous isotropic random vector fields that appear in the description of fluid turbulence. Recent experiments measuring the angle and polarization dependence of HRS from water find a dominant transverse mode contribution with amplitude independent of the scattering wavevector, and this observation of transverse mode HRS strongly constrains the form of the orientation correlation function. Analysis of these HRS results for water determines that the long-range molecular orientation correlation function varies as r(-3±ε) with |ε| < 0.03 on spatial scales up to 2000 nm. PMID:26450319

  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. Effect of dipolar interactions on the phase behavior of the Gay-Berne liquid crystal model

    NASA Astrophysics Data System (ADS)

    Houssa, Mohammed; Rull, Luis F.; McGrother, Simon C.

    1998-12-01

    A computer simulation study of the phase behavior of the dipolar Gay-Berne liquid crystal model is presented. The phase transitions are determined with isothermal-isobaric (NPT) Monte Carlo simulations, utilizing the reaction field method. The electrostatic forces are found to have a considerable effect on the nature of the observed phases, but the density at which the isotropic fluid becomes unstable with respect to partially ordered phases is seen to be remarkably insensitive to the strength of the dipole. We pay particular attention to the structure of the mesophases, combining information from several singlet and pair distribution functions to build up an accurate picture of the molecular arrangement of the systems.

  13. 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

  14. Parametric amplification of matter waves in dipolar spinor Bose-Einstein condensates

    SciTech Connect

    Deuretzbacher, F.; Gebreyesus, G.; Santos, L.; Topic, O.; Scherer, M.; Luecke, B.; Ertmer, W.; Klempt, C.; Arlt, J.

    2010-11-15

    Spin-changing collisions may lead under proper conditions to the parametric amplification of matter waves in spinor Bose-Einstein condensates. Magnetic dipole-dipole interactions, although typically very weak in alkali-metal atoms, are shown to play a very relevant role in the amplification process. We show that these interactions may lead to a strong dependence of the amplification dynamics on the angle between the trap axis and the magnetic-field orientation. We analyze as well the important role played by magnetic-field gradients, which also modify strongly the amplification process. Magnetic-field gradients, hence, must be carefully controlled in future experiments, in order to observe clearly the effects of the dipolar interactions in the amplification dynamics.

  15. Comment on "Origin of tilted-phase generation in systems of ellipsoidal molecules with dipolar interactions''

    NASA Astrophysics Data System (ADS)

    Madhusudana, N. V.

    2014-04-01

    In this Comment, I point out that the physical origin of molecular tilt in the smectic phase, found in the Monte Carlo simulations of systems of rodlike molecules with two terminal antiparallel transverse dipole moments by Bose and Saha [Phys. Rev. E 86, 050701(R) (2012), 10.1103/PhysRevE.86.050701], is similar to the one proposed by McMillan. In particular, unlike in smectic-C liquid crystals, in which the molecules are known to have practically free rotations about their long axes, the molecular rotations are found to be partially frozen in the simulations. Further, I suggest that the attractive interaction between correlated splay fluctuations of the antiparallel polarized sublayers which lie close to each other in adjacent molecular layers give rise to the tilting, rather than a reduced attractive interaction between dipoles belonging to the two dipolar sublayers within one molecular layer, as proposed by the authors.

  16. Coexistence, Interfacial Energy and the Fate of Microemulsions of 2D Dipolar Bosons

    NASA Astrophysics Data System (ADS)

    Boninsegni, Massimo

    The superfluid-crystal quantum phase transition of a system of purely repulsive dipolar bosons in two dimensions has been the subject of a lot of theoretical study, mainly because of some intriguing predictions by Spivak and Kivelson (2004) regarding an exotic, intermediate ''microemulsion'' that should appear at low temperature between the crystal and the superfluid. We investigated this scenario by means of Quantum Monte Carlo simulations at zero temperature, determined freezing and melting densities, and estimated the energy per unit length of a macroscopic interface separating the coexisting crystal and superfluid phases. The results rule out quantitatively the microemulsion scenario for any physical realization of this system, given the exceedingly large predicted size of the bubbles. Reference: S. Moroni and M. Boninsegni, Phys. Rev. Lett. 113, 240407 (2014)

  17. Tunable defect interactions and supersolidity in dipolar quantum gases on a lattice potential

    NASA Astrophysics Data System (ADS)

    Lechner, Wolfgang; Cinti, Fabio; Pupillo, Guido

    2015-11-01

    Point defects in self-assembled crystals, such as vacancies and interstitials, attract each other and form stable clusters. This leads to a phase separation between perfect crystalline structures and defect conglomerates at low temperatures. We propose a method that allows one to tune the effective interactions between point defects from attractive to repulsive by means of external periodic fields. In the quantum regime, this allows one to engineer strongly correlated many-body phases. We exemplify the microscopic mechanism by considering dipolar quantum gases of ground-state polar molecules and weakly bound molecules of strongly magnetic atoms trapped in a weak optical lattice in a two-dimensional configuration. By tuning the lattice depth, defect interactions turn repulsive, which allows us to deterministically design a novel supersolid phase in the continuum limit.

  18. 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.

  19. Proterozoic low orbital obliquity and axial-dipolar geomagnetic field from evaporite palaeolatitudes.

    PubMed

    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.

  20. High-Q polariton modes in heterostructures with traps for dipolar excitons

    SciTech Connect

    Kalinin, Petr A; Kocharovsky, Vitalii V; Kocharovskii, Vladimir V

    2009-11-30

    Polariton modes are studied in two-dimensional traps based on quantum-well heterostructures allowing the production of a Bose - Einstein condensate of indirect excitons. The characteristic equation for the modes is derived using the boundary conditions on the exciton layer located inside a resonator formed by such a trap. The spectrum and the structure of high-Q modes are found analytically and numerically. It is shown that some of these modes become unstable at the high exciton density and long polarisation relaxation time. According to the estimates, this instability can take place in experiments on the Bose condensation of dipolar excitons, thus explaining the origin of their coherent emission. (laser applications and other topics in quantum electronics)

  1. 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

  2. Collective motion of polarized dipolar Fermi gases in the hydrodynamic regime

    SciTech Connect

    Lima, Aristeu R. P.; Pelster, Axel

    2010-02-15

    Recently, a seminal stimulated Raman adiabatic passage (STIRAP) experiment allowed the creation of {sup 40}K{sup 87}Rb molecules in the rovibrational ground state [K.-K. Ni et al., Science 322, 231 (2008)]. To describe such a polarized dipolar Fermi gas in the hydrodynamic regime, we work out a variational time-dependent Hartree-Fock approach. With this we calculate dynamical properties of such a system, for instance, the frequencies of the low-lying excitations and the time-of-flight expansion. We find that the dipole-dipole interaction induces anisotropic breathing oscillations in momentum space. In addition, after release from the trap, the momentum distribution becomes asymptotically isotropic, while the particle density becomes anisotropic.

  3. Efficient dipolar double quantum filtering under magic angle spinning without a (1)H decoupling field.

    PubMed

    Courtney, Joseph M; Rienstra, Chad M

    2016-08-01

    We present a systematic study of dipolar double quantum (DQ) filtering in (13)C-labeled organic solids over a range of magic-angle spinning rates, using the SPC-n recoupling sequence element with a range of n symmetry values from 3 to 11. We find that efficient recoupling can be achieved for values n⩾7, provided that the (13)C nutation frequency is on the order of 100kHz or greater. The decoupling-field dependence was investigated and explicit heteronuclear decoupling interference conditions identified. The major determinant of DQ filtering efficiency is the decoupling interference between (13)C and (1)H fields. For (13)C nutation frequencies greater than 75kHz, optimal performance is observed without an applied (1)H field. At spinning rates exceeding 20kHz, symmetry conditions as low as n=3 were found to perform adequately.

  4. Efficient dipolar double quantum filtering under magic angle spinning without a 1H decoupling field

    NASA Astrophysics Data System (ADS)

    Courtney, Joseph M.; Rienstra, Chad M.

    2016-08-01

    We present a systematic study of dipolar double quantum (DQ) filtering in 13C-labeled organic solids over a range of magic-angle spinning rates, using the SPC-n recoupling sequence element with a range of n symmetry values from 3 to 11. We find that efficient recoupling can be achieved for values n ⩾ 7, provided that the 13C nutation frequency is on the order of 100 kHz or greater. The decoupling-field dependence was investigated and explicit heteronuclear decoupling interference conditions identified. The major determinant of DQ filtering efficiency is the decoupling interference between 13C and 1H fields. For 13C nutation frequencies greater than 75 kHz, optimal performance is observed without an applied 1H field. At spinning rates exceeding 20 kHz, symmetry conditions as low as n = 3 were found to perform adequately.

  5. 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.

  6. High- and low-frequency phonon modes in dipolar quantum gases trapped in deep lattices

    NASA Astrophysics Data System (ADS)

    Maluckov, Aleksandra; Gligorić, Goran; Hadžievski, Ljupčo; Malomed, Boris A.; Pfau, Tilman

    2013-02-01

    We study normal modes propagating on top of the stable uniform background in arrays of dipolar Bose-Einstein condensate (BEC) droplets trapped in a deep optical lattice. Both the on-site mean-field dynamics of the droplets and their displacement due to the repulsive dipole-dipole interactions (DDIs) are taken into account. Dispersion relations for two modes, viz., high- and low- frequency counterparts of optical and acoustic phonon modes in condensed matter, are derived analytically and verified by direct simulations, for both cases of the repulsive and attractive contact interactions. The (counterpart of the) optical-phonon branch does not exist without the DDIs. These results are relevant in the connection to emerging experimental techniques enabling real-time imaging of the condensate dynamics and direct experimental measurement of phonon dispersion relations in BECs.

  7. Interplay between magnetic anisotropy and dipolar interaction in one-dimensional nanomagnets: Optimized magnetocaloric effect

    NASA Astrophysics Data System (ADS)

    Serantes, D.; Vega, V.; Rosa, W. O.; Prida, V. M.; Hernando, B.; Pereiro, M.; Baldomir, D.

    2012-09-01

    The magnetocaloric effect (MCE) in one-dimensional (1D) magnetic nanostructures is optimized for a specific value of the magnetic field H* when applied perpendicularly to the longitudinal direction of the system. Our results reveal that H* corresponds to the saturation field, slightly above the transition from a magnetically stable dipolar-coupled configuration to an unstable one. This MCE-optimizing field explicitly depends on the characteristic magnetic parameters of the system, namely, saturation magnetization (MS) and anisotropy constant (K): H* is directly proportional to MS2, and the anisotropy contribution is equal to the anisotropy field of the particles HA=2K/MS. Accordingly, the MCE in 1D nanomagnets can be directly tuned by a proper choice of the characteristic MS and K values of the materials.

  8. A Dipolar Anthracene Dye: Synthesis, Optical Properties and Two-photon Tissue Imaging.

    PubMed

    Moon, Hyunsoo; Jun, Yong Woong; Kim, Dokyoung; Ryu, Hye Gun; Wang, Taejun; Kim, Ki Hean; Huh, Youngbuhm; Jung, Junyang; Ahn, Kyo Han

    2016-09-20

    Two-photon microscopy is a powerful tool for studying biological systems. In search of novel two-photon absorbing dyes for bioimaging, we synthesized a new anthracene-based dipolar dye (anthradan) and evaluated its two-photon absorbing and imaging properties. The new anthradan, 9,10-bis(o-dimethoxy-phenyl)-anthradan, absorbs and emits at longer wavelengths than acedan, a well-known two-photon absorbing dye. It is also stable under two-photon excitation conditions and biocompatible, and thus used for two-photon imaging of mouse organ tissues to show bright, near-red fluorescence along with negligible autofluorescence. Such an anthradan thus holds promise as a new class of two-photon absorbing dyes for the development of fluorescent probes and tags for biological systems.

  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

    2012-08-01

    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. PMID:22952408

  10. Formation of Bose-Einstein magnon condensate via dipolar and exchange thermalization channels

    NASA Astrophysics Data System (ADS)

    Bozhko, D. A.; Clausen, P.; Chumak, A. V.; Kobljanskyj, Yu. V.; Hillebrands, B.; Serga, A. A.

    2015-10-01

    Thermalization of a parametrically driven magnon gas leading to the formation of a Bose-Einstein condensate at the bottom of a spin-wave spectrum was studied by time- and wavevector-resolved Brillouin light scattering spectroscopy. Two distinct channels of the thermalization process related on dipolar and exchange parts of a magnon gas spectrum are clearly determined. It has been found that the magnon population in these thermalization channels strongly depends on applied microwave pumping power. The observed magnon redistribution between the channels is caused by the downward frequency shift of the magnon gas spectrum due to the decrease of the saturation magnetization in the course of injection of parametrically pumped magnons.

  11. Simulation study of localization of electromagnetic waves in two-dimensional random dipolar systems.

    PubMed

    Wang, Ken Kang-Hsin; Ye, Zhen

    2003-12-01

    We study the propagation and scattering of electromagnetic waves by random arrays of dipolar cylinders in a uniform medium. A set of self-consistent equations, incorporating all orders of multiple scattering of the electromagnetic waves, is derived from first principles and then solved numerically for electromagnetic fields. For certain ranges of frequencies, spatially localized electromagnetic waves appear in such a simple but realistic disordered system. Dependence of localization on the frequency, radiation damping, and filling factor is shown. The spatial behavior of the total, coherent, and diffusive waves is explored in detail, and found to comply with a physical intuitive picture. A phase diagram characterizing localization is presented, in agreement with previous investigations on other systems.

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

    PubMed

    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

    2015-11-26

    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.

  13. QUANTUM SIMULATION. Localization-delocalization transition in the dynamics of dipolar-coupled nuclear spins.

    PubMed

    Álvarez, Gonzalo A; Suter, Dieter; Kaiser, Robin

    2015-08-21

    Nonequilibrium dynamics of many-body systems are important in many scientific fields. Here, we report the experimental observation of a phase transition of the quantum coherent dynamics of a three-dimensional many-spin system with dipolar interactions. Using nuclear magnetic resonance (NMR) on a solid-state system of spins at room-temperature, we quench the interaction Hamiltonian to drive the evolution of the system. Depending on the quench strength, we then observe either localized or extended dynamics of the system coherence. We extract the critical exponents for the localized cluster size of correlated spins and diffusion coefficient around the phase transition separating the localized from the delocalized dynamical regime. These results show that NMR techniques are well suited to studying the nonequilibrium dynamics of complex many-body systems. PMID:26293957

  14. 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.

  15. Proterozoic low orbital obliquity and axial-dipolar geomagnetic field from evaporite palaeolatitudes.

    PubMed

    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. PMID:17080082

  16. Electromagnetic disturbances observed near the dip region ahead of dipolarization front

    NASA Astrophysics Data System (ADS)

    Zhao, D.; Fu, S. Y.; Sun, W. J.; Parks, G. K.; Zong, Q. G.; Shi, Q. Q.; Pu, Z. Y.; Cui, Y. B.; Wu, T.; Liu, J.; Zhou, X. Z.

    2016-04-01

    Dipolarization front (DF) is a thin magnetic structure embedded in fast flows in the magnetotail, which plays an important role in particle acceleration, flow braking, wave excitation, and other related processes. Electromagnetic disturbances near the magnetic dip region in front of DFs are investigated using Time History of Events and Macroscale Interactions during Substorms probe observations in this paper. Strong magnetic field and electric field fluctuations, with several wave bands below and around the lower hybrid frequency, are found in an event on 21 March 2008. The properties of the wave are similar to that of magnetosonic wave. Detailed analyses show that the phase space density for ions in the perpendicular direction has a positive slope near the local Alfvén speed, which is a possible free-energy source for the generation of the wave. This type of ion distribution could result from the earthward reflected ions ahead of DF, though other forming mechanism could not be fully ruled out.

  17. Efficient dipolar double quantum filtering under magic angle spinning without a (1)H decoupling field.

    PubMed

    Courtney, Joseph M; Rienstra, Chad M

    2016-08-01

    We present a systematic study of dipolar double quantum (DQ) filtering in (13)C-labeled organic solids over a range of magic-angle spinning rates, using the SPC-n recoupling sequence element with a range of n symmetry values from 3 to 11. We find that efficient recoupling can be achieved for values n⩾7, provided that the (13)C nutation frequency is on the order of 100kHz or greater. The decoupling-field dependence was investigated and explicit heteronuclear decoupling interference conditions identified. The major determinant of DQ filtering efficiency is the decoupling interference between (13)C and (1)H fields. For (13)C nutation frequencies greater than 75kHz, optimal performance is observed without an applied (1)H field. At spinning rates exceeding 20kHz, symmetry conditions as low as n=3 were found to perform adequately. PMID:27314744

  18. Quantum Levy Flights and Multifractality of Dipolar Excitations in a Random System

    NASA Astrophysics Data System (ADS)

    Deng, X.; Altshuler, B. L.; Shlyapnikov, G. V.; Santos, L.

    2016-07-01

    We consider dipolar excitations propagating via dipole-induced exchange among immobile molecules randomly spaced in a lattice. The character of the propagation is determined by long-range hops (Levy flights). We analyze the eigenenergy spectra and the multifractal structure of the wave functions. In 1D and 2D, all states are localized, although in 2D the localization length can be extremely large leading to an effective localization-delocalization crossover in realistic systems. In 3D, all eigenstates are extended but not always ergodic, and we identify the energy intervals of ergodic and nonergodic states. The reduction of the lattice filling induces an ergodic to nonergodic transition, and the excitations are mostly nonergodic at low filling.

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

    PubMed

    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. 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.

  1. Magnetic-dipolar-mode Fano resonances for microwave spectroscopy of high absorption matter

    NASA Astrophysics Data System (ADS)

    Vaisman, G.; Kamenetskii, E. O.; Shavit, R.

    2015-03-01

    The interaction between high absorption matter and microwave radiated energy is a subject of great importance. In particular, this concerns the microwave spectroscopic characterization of biological liquids. The use of effective testing methods to obtain information about physical properties of different liquids on the molecular level is one of the most important problems in biophysics. However, the standard methods based on microwave resonant techniques are not sufficiently suitable for biological liquids because the resonance peak in a resonator with high-loss liquids is so broad that the material parameters cannot be measured correctly. Although molecular vibrations of biomolecules may have microwave frequencies, it is not thought that such resonant coupling is significant due to their low energy compared with thermal energy and the strongly dampening aqueous environment. This paper presents an innovative microwave sensing technique for different types of lossy materials, including biological liquids. The technique is based on the combination of the microwave perturbation method and the Fano resonance effects observed recently in microwave structures with embedded magnetic-dipolar quantum dots. When the frequency of the magnetic dipolar mode (MDM) resonance is not equal to the cavity resonance frequency, one gets Fano transmission intensity. When the MDM resonance frequency is tuned to the cavity resonance frequency, by a bias magnetic field, one observes a Lorentzian line shape. Use of an extremely narrow Lorentzian peak allows exact probing of the resonant frequency of a cavity loaded by a highly lossy material sample. For different kinds of samples, one has different frequencies of Lorentzian peaks. This presents a picture of precise spectroscopic characterization of high absorption matter in microwaves.

  2. Sub-Tg relaxations due to dipolar solutes in nonpolar glass-forming solvents.

    PubMed

    Shahin, Md; Murthy, S S N

    2005-01-01

    It is well known that rigid dipolar solutes (in smaller quantity) dispersed in a nonpolar glassy matrix exhibit a sub-T(g) (or beta(s)) relaxation due to the solute often designated as Johari-Goldstein (JG) relaxation, which is intermolecular in nature. In this article, we report the results of our study of such a sub-T(g) process in a wide variety of dipolar solutes in different glassy systems using dielectric spectroscopy over a frequency range of 20-10(6) Hz down to a temperature of 77 K. The T(g) of these solutions are determined using differential scanning calorimetry. The solvents used in this study are o-terphenyl (OTP), isopropylbenzene (IPB), and methylcyclohexane. In the case of rigid molecular solutes, like mono-halogen benzenes, the activation energy (DeltaE(beta)) of the beta(s) process is found to increase with decreasing T(g) of the solvent, with a corresponding decrease in the magnitude of the beta(s) process. In the case of more symmetrical molecular solute, for example, tert-butylchloride, the change in DeltaE(beta) is not very appreciable. These results emphasize the importance of the size of the cage of the host matrix in the relaxation of the solute molecules. We have also studied the sub-T(g) relaxation(s) due to some flexible molecular solutes, viz., 1butylbromide, 1hexylbromide, 1butylacetate, and benzylacetate. These solutes in IPB matrix exhibit only one relaxation, whereas in OTP matrix they exhibit an additional sub-T(g) process, which may be identified with a JG type of relaxation. These observations lead us to the conclusion that the beta process observed in the glassy states of these pure solutes is predominantly intramolecular in nature.

  3. 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.

  4. Pulsed EPR dipolar spectroscopy at Q- and G-band on a trityl biradical.

    PubMed

    Akhmetzyanov, D; Schöps, P; Marko, A; Kunjir, N C; Sigurdsson, S Th; Prisner, T F

    2015-10-01

    Pulsed electron paramagnetic resonance (EPR) spectroscopy is a valuable technique for the precise determination of distances between paramagnetic spin labels that are covalently attached to macromolecules. Nitroxides have commonly been utilised as paramagnetic tags for biomolecules, but trityl radicals have recently been developed as alternative spin labels. Trityls exhibit longer electron spin relaxation times and higher stability than nitroxides under in vivo conditions. So far, trityl radicals have only been used in pulsed EPR dipolar spectroscopy (PDS) at X-band (9.5 GHz), Ku-band (17.2 GHz) and Q-band (34 GHz) frequencies. In this study we investigated a trityl biradical by PDS at Q-band (34 GHz) and G-band (180 GHz) frequencies. Due to the small spectral width of the trityl (30 MHz) at Q-band frequencies, single frequency PDS techniques, like double-quantum coherence (DQC) and single frequency technique for refocusing dipolar couplings (SIFTER), work very efficiently. Hence, Q-band DQC and SIFTER experiments were performed and the results were compared; yielding a signal to noise ratio for SIFTER four times higher than that for DQC. At G-band frequencies the resolved axially symmetric g-tensor anisotropy of the trityl exhibited a spectral width of 130 MHz. Thus, pulsed electron electron double resonance (PELDOR/DEER) obtained at different pump-probe positions across the spectrum was used to reveal distances. Such a multi-frequency approach should also be applicable to determine structural information on biological macromolecules tagged with trityl spin labels.

  5. Stacking of purines in water: the role of dipolar interactions in caffeine.

    PubMed

    Tavagnacco, L; Di Fonzo, S; D'Amico, F; Masciovecchio, C; Brady, J W; Cesàro, A

    2016-05-11

    During the last few decades it has been ascertained that base stacking is one of the major contributions stabilizing nucleic acid conformations. However, the understanding of the nature of the interactions involved in the stacking process remains under debate and it is a subject of theoretical and experimental studies. Structural similarity between purine bases (guanine and adenine) in DNA and the caffeine molecule makes caffeine an excellent model for the purine bases. The present study clearly shows that dipolar interactions play a fundamental role in determining stacking of purine molecules in solution. In order to reach this achievement, polarized ultraviolet Raman resonant scattering experiments have been carried out on caffeine aqueous solutions as a function of concentration and temperature. The investigation pointed out at the aggregation and solvation properties, particularly at elevated temperatures. Kubo-Anderson theory was used as a framework to investigate the non-coincidence effect (NCE) occurring in the totally symmetric breathing modes of the purine rings, and in the bending modes of the methyl groups of caffeine. The NCE concentration dependence shows that caffeine aggregation at 80 °C occurs by planar stacking of the hydrophobic faces. The data clearly indicate that dipolar interactions determine the reorientational motion of the molecules in solution and are the driving force for the stacking of caffeine. In parallel, the observed dephasing times imply a change in caffeine interactions as a function of temperature and concentration. A decrease, at low water content, of the dephasing time for the ring breathing vibration mode indicates that self-association alters the solvation structure that is detectable at low concentration. These results are in agreement with simulation predictions and serve as an important validation of the models used in those calculations. PMID:27127808

  6. Stacking of purines in water: the role of dipolar interactions in caffeine.

    PubMed

    Tavagnacco, L; Di Fonzo, S; D'Amico, F; Masciovecchio, C; Brady, J W; Cesàro, A

    2016-05-11

    During the last few decades it has been ascertained that base stacking is one of the major contributions stabilizing nucleic acid conformations. However, the understanding of the nature of the interactions involved in the stacking process remains under debate and it is a subject of theoretical and experimental studies. Structural similarity between purine bases (guanine and adenine) in DNA and the caffeine molecule makes caffeine an excellent model for the purine bases. The present study clearly shows that dipolar interactions play a fundamental role in determining stacking of purine molecules in solution. In order to reach this achievement, polarized ultraviolet Raman resonant scattering experiments have been carried out on caffeine aqueous solutions as a function of concentration and temperature. The investigation pointed out at the aggregation and solvation properties, particularly at elevated temperatures. Kubo-Anderson theory was used as a framework to investigate the non-coincidence effect (NCE) occurring in the totally symmetric breathing modes of the purine rings, and in the bending modes of the methyl groups of caffeine. The NCE concentration dependence shows that caffeine aggregation at 80 °C occurs by planar stacking of the hydrophobic faces. The data clearly indicate that dipolar interactions determine the reorientational motion of the molecules in solution and are the driving force for the stacking of caffeine. In parallel, the observed dephasing times imply a change in caffeine interactions as a function of temperature and concentration. A decrease, at low water content, of the dephasing time for the ring breathing vibration mode indicates that self-association alters the solvation structure that is detectable at low concentration. These results are in agreement with simulation predictions and serve as an important validation of the models used in those calculations.

  7. Zero-quantum stochastic dipolar recoupling in solid state nuclear magnetic resonance

    PubMed Central

    Qiang, Wei; Tycko, Robert

    2012-01-01

    We present the theoretical description and experimental demonstration of a zero-quantum stochastic dipolar recoupling (ZQ-SDR) technique for solid state nuclear magnetic resonance (NMR) studies of 13C-labeled molecules, including proteins, under magic-angle spinning (MAS). The ZQ-SDR technique combines zero-quantum recoupling pulse sequence blocks with randomly varying chemical shift precession periods to create randomly amplitude- and phase-modulated effective homonuclear magnetic dipole-dipole couplings. To a good approximation, couplings between different 13C spin pairs become uncorrelated under ZQ-SDR, leading to spin dynamics (averaged over many repetitions of the ZQ-SDR sequence) that are fully described by an orientation-dependent N × N polarization transfer rate matrix for an N-spin system, with rates that are inversely proportional to the sixth power of internuclear distances. Suppression of polarization transfers due to non-commutivity of pairwise couplings (i.e., dipolar truncation) does not occur under ZQ-SDR, as we show both analytically and numerically. Experimental demonstrations are reported for uniformly 13C-labeled L-valine powder (at 14.1 T and 28.00 kHz MAS), uniformly 13C-labeled protein GB1 in microcrystalline form (at 17.6 T and 40.00 kHz MAS), and partially labeled 13C-labeled protein GB1 (at 14.1 T and 40.00 kHz MAS). The experimental results verify that spin dynamics under ZQ-SDR are described accurately by rate matrices and suggest the utility of ZQ-SDR in structural studies of 13C-labeled solids. PMID:22979851

  8. Zero-quantum stochastic dipolar recoupling in solid state nuclear magnetic resonance

    NASA Astrophysics Data System (ADS)

    Qiang, Wei; Tycko, Robert

    2012-09-01

    We present the theoretical description and experimental demonstration of a zero-quantum stochastic dipolar recoupling (ZQ-SDR) technique for solid state nuclear magnetic resonance (NMR) studies of 13C-labeled molecules, including proteins, under magic-angle spinning (MAS). The ZQ-SDR technique combines zero-quantum recoupling pulse sequence blocks with randomly varying chemical shift precession periods to create randomly amplitude- and phase-modulated effective homonuclear magnetic dipole-dipole couplings. To a good approximation, couplings between different 13C spin pairs become uncorrelated under ZQ-SDR, leading to spin dynamics (averaged over many repetitions of the ZQ-SDR sequence) that are fully described by an orientation-dependent N × N polarization transfer rate matrix for an N-spin system, with rates that are inversely proportional to the sixth power of internuclear distances. Suppression of polarization transfers due to non-commutivity of pairwise couplings (i.e., dipolar truncation) does not occur under ZQ-SDR, as we show both analytically and numerically. Experimental demonstrations are reported for uniformly 13C-labeled L-valine powder (at 14.1 T and 28.00 kHz MAS), uniformly 13C-labeled protein GB1 in microcrystalline form (at 17.6 T and 40.00 kHz MAS), and partially labeled 13C-labeled protein GB1 (at 14.1 T and 40.00 kHz MAS). The experimental results verify that spin dynamics under ZQ-SDR are described accurately by rate matrices and suggest the utility of ZQ-SDR in structural studies of 13C-labeled solids.

  9. Dipolarization fronts as a signature of transient reconnection in the magnetotail

    NASA Astrophysics Data System (ADS)

    Sitnov, M. I.; Swisdak, M.; Divin, A. V.

    2009-04-01

    Dipolarization fronts (DFs), characterized by a strong and steep increase of the tail magnetic field component B z normal to the neutral plane and preceded by a much less negative dip of B z , are reported in many observations of bursty bulk flows and substorm activations throughout the whole Earth's magnetotail. It is shown that similar structures appear in full-particle simulations with open boundaries in a transient regime before the steady reconnection in the original Harris current sheet driven out of the equilibrium by the initial X-line perturbation is established. Being secondary reconnection structures propagating with the Alfvén speed, DFs are different from the magnetic field pileup regions reported in earlier simulations with closed boundaries. They also differ from the secondary plasmoids with bipolar B z changes reported in earlier fluid simulations and particle simulations with open boundaries. In spite of their transient nature, DFs are found to form when the force balance is already restored in the system, which justifies their interpretation as a nonlinear stage of the tearing instability developing in two magnetotail-like structures on the left and on the right of the initial central X-line. 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 E × B drift, whereas electrons either follow that drift being completely magnetized or move faster, forming super-Alfvénic jets. In spite of the different motions of electrons and ions, the growth of the front is not accompanied by the corresponding growth of the electrostatic field and the energy dissipation in fronts is dominated by ions.

  10. A Bis-Manganese(II)-DOTA Complex for Pulsed Dipolar Spectroscopy.

    PubMed

    Demay-Drouhard, Paul; Ching, H Y Vincent; Akhmetzyanov, Dmitry; Guillot, Régis; Tabares, Leandro C; Bertrand, Hélène C; Policar, Clotilde

    2016-07-01

    High-spin gadolinium(III) and manganese(II) complexes have emerged as alternatives to standard nitroxide radical spin labels for measuring nanometric distances by using pulsed electron-electron double resonance (PELDOR or DEER) at high fields/frequencies. For certain complexes, particularly those with relatively small zero-field splitting (ZFS) and short distances between the two metal centers, the pseudosecular term of the dipolar coupling Hamiltonian is non-negligible. However, in general, the contribution from this term during conventional data analysis is masked by the flexibility of the molecule of interest and/or the long tethers connecting them to the spin labels. The efficient synthesis of a model system consisting of two [Mn(dota)](2-) (MnDOTA; DOTA(4-) =1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate) directly connected to the ends of a central rodlike oligo(phenylene-ethynylene) (OPE) spacer is reported. The rigidity of the OPE is confirmed by Q-band PELDOR measurements on a bis-nitroxide analogue. The Mn(II) -Mn(II) distance distribution profile determined by W-band PELDOR is in reasonable agreement with one simulated by using a simple rotamer analysis. The small degree of flexibility arising from the linking MnDOTA arm appears to outweigh the contribution from the pseudosecular term at this interspin distance. This study illustrates the potential of MnDOTA-based spin labels for measuring fairly short nanometer distances, and also presents an interesting candidate for in-depth studies of pulsed dipolar spectroscopy methods on Mn(II) -Mn(II) systems. PMID:27017296

  11. The effect of noncollinearity of 15N-1H dipolar and 15N CSA tensors and rotational anisotropy on 15N relaxation, CSA/dipolar cross correlation, and TROSY.

    PubMed

    Fushman, D; Cowburn, D

    1999-02-01

    Current approaches to 15N relaxation in proteins assume that the 15N-1H dipolar and 15N CSA tensors are collinear. We show theoretically that, when there is significant anisotropy of molecular rotation, different orientations of the two tensors, experimentally observed in proteins, nucleic acids, and small peptides, will result in differences in site-specific correlation functions and spectral densities. The standard treatments of the rates of longitudinal and transverse relaxation of amide 15N nuclei, of the 15N CSA/15N-1H dipolar cross correlation, and of the TROSY experiment are extended to account for the effect of noncollinearity of the 15N-1H dipolar and 15N CSA (chemical shift anisotropy) tensors. This effect, proportional to the degree of anisotropy of the overall motion, (D parallel/D perpendicular - 1), is sensitive to the relative orientation of the two tensors and to the orientation of the peptide plane with respect to the diffusion coordinate frame. The effect is negligible at small degrees of anisotropy, but is predicted to become significant for D parallel/D perpendicular > or = 1.5, and at high magnetic fields. The effect of noncollinearity of 15N CSA and 15N-1H dipolar interaction is sensitive to both gross (hydrodynamic) properties and atomic-level details of protein structure. Incorporation of this effect into relaxation data analysis is likely to improve both precision and accuracy of the derived characteristics of protein dynamics, especially at high magnetic fields and for molecules with a high degree of anisotropy of the overall motion. The effect will also make TROSY efficiency dependent on local orientation in moderately anisotropic systems.

  12. Probing a single dipolar interaction between a pair of two-level quantum system by scatterings of single photons in an aside waveguide

    NASA Astrophysics Data System (ADS)

    Li, Xingmin; Wei, L. F.

    2016-05-01

    Weak dipolar interactions exist widely in various atomic, nuclear and molecular systems, and could be utilized to implement the desired quantum information processings. However, these interactions are relatively weak and hard to be measured precisely. Here, we propose an approach to detect such a weak interaction by probing the transport of a single waveguide-photon scattered by two aside qubits with a single dipolar exchange-interaction. By a full quantum theory of photon transports in optical waveguide, we show that the dipolar interaction between the aside two qubits significantly influence the transmitted spectra of the photon traveling along the one-dimensional waveguide. Thus, probing the relevant changes in the transmitted spectra and the transmission probability distribution specifically for the resonant photons, compared with those scattered by the two individual qubits, the information of the single dipolar interaction between the qubits could be extracted. The feasibility of the proposal is also discussed.

  13. A Theoretical Study on Stepwise- and Concertedness of the Mechanism of 1,3-Dipolar Cycloaddition Reaction Between Tetra Amino Ethylene and Trifluoro Methyl Azide.

    PubMed

    Siadati, Seyyed Amir

    2016-01-01

    The order of reaction, especially in 1,3-dipolar cycloadditions directly affects the products' stereo selectivity. Due to this fact that a wide range of heterocyclic rings of natural products and biologically active molecules are synthesizing via this valuable procedure, understanding about the order of this reaction is so useful in designing the synthesis of different types of heterocyclic species. Therefore, the order of 1, 3-dipolar reaction has been carefully studied by many researchers but it seems that this question is still open despite many valuable answers. Considering this, in the present work, it is attempted to pursue this subject by theoretical investigation of any possible pathway of 1, 3-dipolar reaction of tetra amino ethylene as a highly electron rich dipolarophile and trifluoro methyl azide as an electron poor 1,3-dipole. During the calculations, one, two, and three step mechanism(s) have been found to be possible for the present 1, 3-dipolar reaction.

  14. Nuclear magnetic resonance studies of quadrupolar nuclei and dipolar field effects

    SciTech Connect

    Urban, Jeffry Todd

    2004-01-01

    Experimental and theoretical research conducted in two areas in the field of nuclear magnetic resonance (NMR) spectroscopy is presented: (1) studies of the coherent quantum-mechanical control of the angular momentum dynamics of quadrupolar (spin I > 1/2) nuclei and its application to the determination of molecular structure; and (2) applications of the long-range nuclear dipolar field to novel NMR detection methodologies.The dissertation is organized into six chapters. The first two chapters and associated appendices are intended to be pedagogical and include an introduction to the quantum mechanical theory of pulsed NMR spectroscopy and the time dependent theory of quantum mechanics. The third chapter describes investigations of the solid-state multiple-quantum magic angle spinning (MQMAS) NMR experiment applied to I = 5/2 quadrupolar nuclei. This work reports the use of rotary resonance-matched radiofrequency irradiation for sensitivity enhancement of the I = 5/2 MQMAS experiment. These experiments exhibited certain selective line narrowing effects which were investigated theoretically.The fourth chapter extends the discussion of multiple quantum spectroscopy of quadrupolar nuclei to a mostly theoretical study of the feasibility of enhancing the resolution of nitrogen-14 NMR of large biomolecules in solution via double-quantum spectroscopy. The fifth chapter continues to extend the principles of multiple quantum NMR spectroscopy of quadrupolar nuclei to make analogies between experiments in NMR/nuclear quadrupolar resonance (NQR) and experiments in atomic/molecular optics (AMO). These analogies are made through the Hamiltonian and density operator formalism of angular momentum dynamics in the presence of electric and magnetic fields.The sixth chapter investigates the use of the macroscopic nuclear dipolar field to encode the NMR spectrum of an analyte nucleus indirectly in the magnetization of a sensor nucleus. This technique could potentially serve as an

  15. Non-dipolar magnetic field models and patterns of radio emission: Uranus and Neptune compared

    NASA Technical Reports Server (NTRS)

    Evans, D. R.

    1994-01-01

    The magnetic field geometries of Uranus and Neptune are superficially similar, and are similarly unlike those of other planets: the field strengths are similar, and they contain extraordinarily large non-dipolar components. As a corollary, the best dipolar field models of each of the two planets comprises a dipole that is considerably offset from the planetary center and tilted away from the rotational axis. However, in other respects the best field models of the two planets are quite different. Uranus has a quadrupole model in which all the terms are well determined and in which none of the higher order terms is determined. To represent the magnetometer data acquired during Voyager's Neptune encounter requires a model of order 8 (instead of Uranus' order 2), yet many of the coefficients are poorly determined. A second model, an octupole model comprising the terms up to order three of the order 8 model, has been suggested by the magnetometer team as being useful; its use, however, is limited only to the region outside of about 2R(exp N), whereas planetary radio emissions have their sources well inside this surface. Computer code has been written that permits an analysis of the detailed motion of low energy charged particles moving in general planetary magnetic fields. At Uranus, this code reveals the existence of an isolated region of the inner magnetosphere above the day side in which particles may be trapped, separate from the more general magnetospheric trapping. An examination of the so-call ordinary mode uranian radio emissions leads us to believe that these emissions are in fact extraordinary mode emissions coming from particles trapped in this isolated region. A similar attempt to discover trapping regions at Neptune has proved, unfortunately, to be impossible. This arises from three factors: (1) the computation needed to track particles in an eighth order field is more than an order of magnitude greater than that needed to perform a similar calculation in a

  16. The aluminum ordering in aluminosilicates: a dipolar 27Al NMR spectroscopy study.

    PubMed

    Gee, Becky A

    2004-01-01

    The spatial ordering of aluminum atoms in CsAl(SiO3)2 and 3Al2O3.2SiO2 was probed by 27Al dipolar solid-state NMR spectroscopy. The 27Al response to a Hahn spin-echo pulse sequence in a series of aluminum-containing model crystalline compounds demonstrates that quantitative 27Al homonuclear dipolar second moments can be obtained to within +/-20% of the theoretical values, if evaluation of the spin-echo response curve is limited to short evolution periods (2t1 < or = 0.10 ms). Additionally, selective excitation of the central transition m = 1/2 --> -1/2 is necessary in order to ensure quantitative results. Restriction of spin exchange affecting the dephasing of the magnetization may decelerate the spin-echo decay at longer evolution periods. Considering these restraints, the method was used to probe the spatial distribution of aluminum atoms among the tetrahedral sites in two aluminosilicate materials. Experimental 27Al spin-echo response data for the aluminosilicates CsAl(SiO3)2 (synthetic pollucite) and 3Al2O3.2SiO2 (mullite) are compared with theoretical data based on (I) various degrees of aluminum-oxygen-aluminum bond formation among tetrahedrally coordinated aluminum atoms (Al(T(d) )-O-Al(T(d) )) and (II) the maximum avoidance of Al(T(d) )-O-Al(T(d) ) bonding. Analysis of the second moment values and resulting echo decay responses suggests that partial suppression of spin exchange among aluminum atoms in crystallographically distinct sites may contribute to the 27Al spin echo decay in 3Al2O3.2SiO2, thus complicating quantitative analysis of the data. Silicon-29 and aluminum-27 magic angle spinning (MAS) NMR spectra of 3Al2O3.2SiO2 are consistent with those previously reported. The experimental 27Al spin-echo response behavior of CsAl(SiO3)2 differs from the theoretical response behavior based on the maximum avoidance of Al-O-Al bonding between tetrahedral aluminum sites in CsAl(SiO3)2. A single unresolved resonance is observed in both the silicon-29 and

  17. Challenging the presence of scalar charge and dipolar radiation in binary pulsars

    NASA Astrophysics Data System (ADS)

    Yagi, Kent; Stein, Leo C.; Yunes, Nicolás

    2016-01-01

    Corrections to general relativity that introduce long-ranged scalar fields which are nonminimally coupled to curvature typically predict that neutron stars possess a nontrivial scalar field profile anchored to the star. An observer far from a star is most sensitive to the spherically symmetric piece of this profile that decays linearly with the inverse of the distance to the source, the so-called scalar monopole charge, which is related to the emission of dipolar radiation from compact binary systems. The presence of dipolar radiation has the potential to rule out or very strongly constrain extended theories of gravity. These facts may lead people to believe that gravitational theories that introduce long-ranged scalar fields have already been constrained strongly from binary pulsar observations. Here we challenge this "lore" by investigating the decoupling limit of Gauss-Bonnet gravity as an example, in which the scalar field couples linearly to the Gauss-Bonnet density in the action. We prove a theorem that neutron stars in this theory cannot possess a scalar charge, due to the topological nature of the Gauss-Bonnet density. Thus Gauss-Bonnet gravity evades the strong binary pulsar constraints on dipole radiation. We discuss the astrophysical systems which will yield the best constraints on Gauss-Bonnet gravity and related quadratic gravity theories. To achieve this we compute the scalar charge in quadratic gravity theories by performing explicit analytic and numerical matching calculations for slowly rotating neutron stars. In generic quadratic gravity theories, either neutron star-binary or neutron star-black hole systems can be used to constrain the theory, but because of the vanishing charge, Gauss-Bonnet gravity evades the neutron star-binary constraints. However, in contrast to neutron stars, black holes in Gauss-Bonnet gravity do anchor scalar charge, because of the difference in topology. The best constraints on Gauss-Bonnet gravity will thus come from

  18. Incorporating Dipolar Solvents with Variable Density in Poisson-Boltzmann Electrostatics

    PubMed Central

    Azuara, Cyril; Orland, Henri; Bon, Michael; Koehl, Patrice; Delarue, Marc

    2008-01-01

    We describe a new way to calculate the electrostatic properties of macromolecules that goes beyond the classical Poisson-Boltzmann treatment with only a small extra CPU cost. The solvent region is no longer modeled as a homogeneous dielectric media but rather as an assembly of self-orienting interacting dipoles of variable density. The method effectively unifies both the Poisson-centric view and the Langevin Dipole model. The model results in a variable dielectric constant \\documentclass[10pt]{article} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{pmc} \\usepackage[Euler]{upgreek} \\pagestyle{empty} \\oddsidemargin -1.0in \\begin{document} \\begin{equation*}{\\epsilon}({\\vec{r}})\\end{equation*}\\end{document} in the solvent region and also in a variable solvent density \\documentclass[10pt]{article} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{pmc} \\usepackage[Euler]{upgreek} \\pagestyle{empty} \\oddsidemargin -1.0in \\begin{document} \\begin{equation*}{\\rho}({\\vec{r}})\\end{equation*}\\end{document} that depends on the nature of the closest exposed solute atoms. The model was calibrated using small molecules and ions solvation data with only two adjustable parameters, namely the size and dipolar moment of the solvent. Hydrophobicity scales derived from the solvent density profiles agree very well with independently derived hydrophobicity scales, both at the atomic or residue level. Dimerization interfaces in homodimeric proteins or lipid-binding regions in membrane proteins clearly appear as poorly solvated patches on the solute accessible surface. Comparison of the thermally averaged solvent density of this model with the one derived from molecular dynamics simulations shows qualitative agreement on a coarse-grained level. Because this calculation is much more

  19. Asymmetric Formal Total Synthesis of the Stemofoline Alkaloids: The Evolution, Development and Application of a Catalytic Dipolar Cycloaddition Cascade

    PubMed Central

    Shanahan, Charles S.; Fang, Chao; Paull, Daniel H.; Martin, Stephen F.

    2013-01-01

    A formal synthesis of didehydrostemofoline and isodidehydrostemofoline has been accomplished by preparing an intermediate in the Overman synthesis of these alkaloids from commercially available 2-deoxy-D-ribose. The work presented in this account chronicles the evolution of our explorations to identify the optimal steric and electronic control elements necessary to generate the tricyclic core structure of these alkaloids in a single operation from an acyclic precursor. The key step in the synthesis is a novel dipolar cycloaddition cascade sequence that is initiated by cyclization of a rhodium-derived carbene onto the nitrogen atom of a proximal imine group to generate an azomethine ylide that then undergoes spontaneous cyclization via dipolar cycloaddition. The synthesis features several other interesting reactions, including a Boord elimination to prepare a chiral allylic alcohol, a highly diastereoselective Hirama-Itô cyclization, and a useful modification of the Barton decarboxylation protocol. PMID:24072939

  20. Effects of inter- and intra-aggregate magnetic dipolar interactions on the magnetic heating efficiency of iron oxide nanoparticles.

    PubMed

    Ovejero, J G; Cabrera, D; Carrey, J; Valdivielso, T; Salas, G; Teran, F J

    2016-04-28

    Iron oxide nanoparticles have found an increasing number of biomedical applications as sensing or trapping platforms and therapeutic and/or diagnostic agents. Most of these applications are based on their magnetic properties, which may vary depending on the nanoparticle aggregation state and/or concentration. In this work, we assess the effect of the inter- and intra-aggregate magnetic dipolar interactions on the heat dissipation power and AC hysteresis loops upon increasing the nanoparticle concentration and the hydrodynamic aggregate size. We observe different effects produced by inter- (long distance) and intra-aggregate (short distance) interactions, resulting in magnetizing and demagnetizing effects, respectively. Consequently, the heat dissipation power under alternating magnetic fields strongly reflects such different interacting phenomena. The intra-aggregate interaction results were successfully modeled by numerical simulations. A better understanding of magnetic dipolar interactions is mandatory for achieving a reliable magnetic hyperthermia response when nanoparticles are located into biological matrices.

  1. Phase diagram of dipolar hard and soft spheres: manipulation of colloidal crystal structures by an external field.

    PubMed

    Hynninen, Antti-Pekka; Dijkstra, Marjolein

    2005-04-01

    Phase diagrams of hard and soft spheres with a fixed dipole moment are determined by calculating the Helmholtz free energy using simulations. The pair potential is given by a dipole-dipole interaction plus a hard-core and a repulsive Yukawa potential for soft spheres. Our system models colloids in an external electric or magnetic field, with hard spheres corresponding to uncharged and soft spheres to charged colloids. The phase diagram of dipolar hard spheres shows fluid, face-centered-cubic (fcc), hexagonal-close-packed (hcp), and body-centered-tetragonal (bct) phases. The phase diagram of dipolar soft spheres exhibits, in addition to the above mentioned phases, a body-centered-orthorhombic (bco) phase, and it agrees well with the experimental phase diagram [Nature (London) 421, 513 (2003)]. Our results show that bulk hcp, bct, and bco crystals can be realized experimentally by applying an external field. PMID:15904046

  2. New metal phthalocyanines/metal simple hydroxide multilayers: experimental evidence of dipolar field-driven magnetic behavior.

    PubMed

    Bourzami, Riadh; Eyele-Mezui, Séraphin; Delahaye, Emilie; Drillon, Marc; Rabu, Pierre; Parizel, Nathalie; Choua, Sylvie; Turek, Philippe; Rogez, Guillaume

    2014-01-21

    A series of new hybrid multilayers has been synthesized by insertion-grafting of transition metal (Cu(II), Co(II), Ni(II), and Zn(II)) tetrasulfonato phthalocyanines between layers of Cu(II) and Co(II) simple hydroxides. The structural and spectroscopic investigations confirm the formation of new layered hybrid materials in which the phthalocyanines act as pillars between the inorganic layers. The magnetic investigations show that all copper hydroxide-based compounds behave similarly, presenting an overall antiferromagnetic behavior with no ordering down to 1.8 K. On the contrary, the cobalt hydroxide-based compounds present a ferrimagnetic ordering around 6 K, regardless of the nature of the metal phthalocyanine between the inorganic layers. The latter observation points to strictly dipolar interactions between the inorganic layers. The amplitude of the dipolar field has been evaluated from X-band and Q-band EPR spectroscopy investigation (Bdipolar ≈ 30 mT).

  3. New metal phthalocyanines/metal simple hydroxide multilayers: experimental evidence of dipolar field-driven magnetic behavior.

    PubMed

    Bourzami, Riadh; Eyele-Mezui, Séraphin; Delahaye, Emilie; Drillon, Marc; Rabu, Pierre; Parizel, Nathalie; Choua, Sylvie; Turek, Philippe; Rogez, Guillaume

    2014-01-21

    A series of new hybrid multilayers has been synthesized by insertion-grafting of transition metal (Cu(II), Co(II), Ni(II), and Zn(II)) tetrasulfonato phthalocyanines between layers of Cu(II) and Co(II) simple hydroxides. The structural and spectroscopic investigations confirm the formation of new layered hybrid materials in which the phthalocyanines act as pillars between the inorganic layers. The magnetic investigations show that all copper hydroxide-based compounds behave similarly, presenting an overall antiferromagnetic behavior with no ordering down to 1.8 K. On the contrary, the cobalt hydroxide-based compounds present a ferrimagnetic ordering around 6 K, regardless of the nature of the metal phthalocyanine between the inorganic layers. The latter observation points to strictly dipolar interactions between the inorganic layers. The amplitude of the dipolar field has been evaluated from X-band and Q-band EPR spectroscopy investigation (Bdipolar ≈ 30 mT). PMID:24400974

  4. Effects of inter- and intra-aggregate magnetic dipolar interactions on the magnetic heating efficiency of iron oxide nanoparticles.

    PubMed

    Ovejero, J G; Cabrera, D; Carrey, J; Valdivielso, T; Salas, G; Teran, F J

    2016-04-28

    Iron oxide nanoparticles have found an increasing number of biomedical applications as sensing or trapping platforms and therapeutic and/or diagnostic agents. Most of these applications are based on their magnetic properties, which may vary depending on the nanoparticle aggregation state and/or concentration. In this work, we assess the effect of the inter- and intra-aggregate magnetic dipolar interactions on the heat dissipation power and AC hysteresis loops upon increasing the nanoparticle concentration and the hydrodynamic aggregate size. We observe different effects produced by inter- (long distance) and intra-aggregate (short distance) interactions, resulting in magnetizing and demagnetizing effects, respectively. Consequently, the heat dissipation power under alternating magnetic fields strongly reflects such different interacting phenomena. The intra-aggregate interaction results were successfully modeled by numerical simulations. A better understanding of magnetic dipolar interactions is mandatory for achieving a reliable magnetic hyperthermia response when nanoparticles are located into biological matrices. PMID:27041536

  5. The Relationship Between Dipolarization Fronts and Pi2 Pulsations in the Near-Earth Magnetotail - A MHD Case Study

    NASA Astrophysics Data System (ADS)

    Ream, J. B.; Walker, R. J.; Ashour-Abdalla, M.; El-Alaoui, M.

    2011-12-01

    We performed a global MHD simulation of a substorm event on 14 September 2004 in order to investigate the link between Pi2 generation and dipolarization fronts. Pi2 pulsations (T = 40-150 s) measured by ground-based instruments are typically used as an indicator of substorm onset, therefore, understanding how and where they are generated is vital to understanding the series of events leading up to onset. Kepko et al. [1999] suggested that the compression regions and velocity variations associated with earthward propagating dipolarization fronts directly drive Pi2 pulsations. Similarly, Panov et al. [2011] suggested that Pi2 pulsations are generated by the overshoot and rebound of bursty bulk flows. Dipolarization fronts are step-wise enhancements in Bz which are associated with fast (>100km/s) earthward flows and are followed by tailward expansion due to pile-up at the high pressure region where the magnetic field lines transition from a stretched to a dipolar configuration. Cao et al. [2009] have presented observations from Double Star (TC1), Cluster 4 and Polar of a substorm with onset at 18:22 UT. During this event a dipolarization front was observed by Double Star at ~18:25, and dipolarization associated expansion was observed by Cluster 4 at ~18:50 and Polar at ~18:55 UT. The spacecraft were positioned at (-10.2, -1.6, 1.2), (-16.4, 1.6, 2.2) and (-7.5, -1.8, -4.9) RE in GSM coordinates respectively. The simulation was carried out with the UCLA global MHD code [El-Alaoui (2001), Raeder (1998)], using Geotail, located near the bow shock at ~24 RE, as the solar wind monitor. The solar wind magnetic field data were rotated into a minimum variance frame to be used as input for the simulation. The results from the simulation have been compared to observations and do a good job reproducing the structures observed by all three satellites. Around the time of onset, we have identified a dipolarization front near midnight which originates at ~12 RE. We show that as the

  6. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

    We report a Phase-Alternating R-Symmetry (PARS) dipolar recoupling scheme for accurate measurement of heteronuclear 1H-X (X = 13C, 15N, 31P, 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 1H CSA interaction persists and thereby introduces considerable errors in the dipolar measurements. In PARS, phase-shifted RN symmetry pulse blocks applied on the 1H spins combined with π pulses applied on the X spins at the end of each RN block efficiently suppress the effect from 1H chemical shift anisotropy, while keeping the 1H-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, [15N]-N-acetyl-valine and [U-13C,15N]-N-formyl-Met-Leu-Phe tripeptide. The application of PARS for site-resolved measurement of accurate 1H-15N dipolar couplings in the context of 3D experiments is presented on U-13C,15N-enriched dynein light chain protein LC8.

  8. Competing orders in a dipolar Bose-Fermi mixture on a square optical lattice: mean-field perspective

    NASA Astrophysics Data System (ADS)

    Scaramazza, Jasen A.; Kain, Ben; Ling, Hong Y.

    2016-07-01

    We consider a mixture of a two-component Fermi gas and a single-component dipolar Bose gas in a square optical lattice and reduce it into an effective Fermi system where the Fermi-Fermi interaction includes the attractive interaction induced by the phonons of a uniform dipolar Bose-Einstein condensate. Focusing on this effective Fermi system in the parameter regime that preserves the symmetry of D4, the point group of a square, we explore, within the Hartree-Fock-Bogoliubov mean-field theory, the phase competition among density wave orderings and superfluid pairings. We construct the matrix representation of the linearized gap equation in the irreducible representations of D4. We show that in the weak coupling regime, each matrix element, which is a four-dimensional (4D) integral in momentum space, can be put in a separable form involving a 1D integral, which is only a function of temperature and the chemical potential, and a pairing-specific "effective" interaction, which is an analytical function of the parameters that characterize the Fermi-Fermi interactions in our system. We analyze the critical temperatures of various competing orders as functions of different system parameters in both the absence and presence of the dipolar interaction. We find that close to half filling, the dx2 - y2-wave pairing with a critical temperature in the order of a fraction of Fermi energy (at half filling) may dominate all other phases, and at a higher filling factor, the p-wave pairing with a critical temperature in the order of a hundredth of Fermi energy may emerge as a winner. We find that tuning a dipolar interaction can dramatically enhance the pairings with dxy- and g-wave symmetries but not enough for them to dominate other competing phases.

  9. Structure determination using the method of continuous variation: lithium phenolates solvated by protic and dipolar aprotic ligands.

    PubMed

    Tomasevich, Laura L; Collum, David B

    2013-08-01

    The method of continuous variation (MCV) was used in conjunction with (6)Li NMR spectroscopy to characterize four lithium phenolates solvated by a range of solvents, including N,N,N',N'-tetramethylethylenediamine, Et2O, pyridine, protic amines, alcohols, and highly dipolar aprotic solvents. Dimers, trimers, and tetramers were observed, depending on the precise lithium phenolate-solvent combinations. Competition experiments (solvent swaps) provide insights into the relative propensities toward mixed solvation.

  10. Reply to "Comment on 'Origin of tilted-phase generation in systems of ellipsoidal molecules with dipolar interactions' "

    NASA Astrophysics Data System (ADS)

    Bose, Tushar Kanti; Saha, Jayashree

    2014-04-01

    In a recent article [T. K. Bose and J. Saha, Phys. Rev. E 86, 050701 (2012), 10.1103/PhysRevE.86.050701], we have presented the results of a Monte Carlo simulation study of the systems of dipolar Gay-Berne ellipsoids where two terminal antiparallel dipoles are placed symmetrically on the long axis of each ellipsoid, and the results revealed the combined contribution of dipolar separation and transverse orientations in controlling the tilt angle in the tilted hexatic smectic phase. The tilt angle changed from zero to a significant value, in the case of transverse dipoles, with a change in the dipolar separation. In the related comment, Madhusudana [preceding Comment, Phys. Rev. E 89, 046501 (2014), 10.1103/PhysRevE.89.046501] has claimed that the physical origin of the molecular tilt in the significantly tilted phases found in the simulations is similar to that proposed by McMillan [Phys. Rev. A 8, 1921 (1973), 10.1103/PhysRevA.8.1921]. Here, we explain that the claim is not correct and make it clear that the two compared pictures are quite different. In the preceding Comment, Madhusudana has also suggested an alternative explanation for tilt generation in the simulations by criticizing the original one proposed by us. We argue here in support of the original explanation and clarify that his explanation does not follow the simulation results.

  11. Structural phase transition in perovskite metal-formate frameworks: a Potts-type model with dipolar interactions.

    PubMed

    Šimėnas, Mantas; Balčiūnas, Sergejus; Ma Combining Cedilla Czka, Mirosław; Banys, Jūras; Tornau, Evaldas E

    2016-07-21

    We propose a combined experimental and numerical study to describe an order-disorder structural phase transition in perovskite-based [(CH3)2NH2][M(HCOO)3] (M = Zn(2+), Mn(2+), Fe(2+), Co(2+) and Ni(2+)) dense metal-organic frameworks (MOFs). The three-fold degenerate orientation of the molecular (CH3)2NH2(+) (DMA(+)) cation implies a selection of the statistical three-state model of the Potts type. It is constructed on a simple cubic lattice where each lattice point can be occupied by a DMA(+) cation in one of the available states. In our model the main interaction is the nearest-neighbor Potts-type interaction, which effectively accounts for the H-bonding between DMA(+) cations and M(HCOO)3(-) cages. The model is modified by accounting for the dipolar interactions which are evaluated for the real monoclinic lattice using density functional theory. We employ the Monte Carlo method to numerically study the model. The calculations are supplemented with the experimental measurements of electric polarization. The obtained results indicate that the three-state Potts model correctly describes the phase transition order in these MOFs, while dipolar interactions are necessary to obtain better agreement with the experimental polarization. We show that in our model with substantial dipolar interactions the ground state changes from uniform to the layers with alternating polarization directions. PMID:27341447

  12. Competing Orders in a Dipolar Bose - Fermi Mixture on a Square Optical Lattice: Mean-Field Perspective

    NASA Astrophysics Data System (ADS)

    Ling, Hong; Scaramaazza, Jasen; Kain, Ben

    2015-05-01

    We study superfluid pairings of two-component fermions interacting by exchanging virtual phonons of a dipolar condensate in an optical lattice that preserves the symmetry of D4. We construct, within the Hartree-Fock-Bogoliubov theory, the matrix representation of the linearized gap equation in the irreducible representations of D4. We find that each matrix element, which is a four-dimensional (4D) integral in momentum space, can be put in a separable form involving a 1D integral, which is only a function of temperature and the chemical potential, and a pairing-specific ``effective'' interaction, which is an analytical function of the parameters that characterize Fermi-Fermi interactions. We analyze the critical temperatures of various competing orders (superfluids with s-, dx2-y2-, dxy-, and g-wave symmetries and density waves) as functions of different system parameters in both the absence and presence of the dipolar interaction. We find that tuning a dipolar interaction can dramatically enhance various unconventional pairings. KITP, University of Santa Barbara; ITAMP, Harvard-Smithsonian Center for Astrophysics.

  13. Reply to "Comment on 'Origin of tilted-phase generation in systems of ellipsoidal molecules with dipolar interactions' ".

    PubMed

    Bose, Tushar Kanti; Saha, Jayashree

    2014-04-01

    In a recent article [T. K. Bose and J. Saha, Phys. Rev. E 86, 050701 (2012)], we have presented the results of a Monte Carlo simulation study of the systems of dipolar Gay-Berne ellipsoids where two terminal antiparallel dipoles are placed symmetrically on the long axis of each ellipsoid, and the results revealed the combined contribution of dipolar separation and transverse orientations in controlling the tilt angle in the tilted hexatic smectic phase. The tilt angle changed from zero to a significant value, in the case of transverse dipoles, with a change in the dipolar separation. In the related comment, Madhusudana [preceding Comment, Phys. Rev. E 89, 046501 (2014)] has claimed that the physical origin of the molecular tilt in the significantly tilted phases found in the simulations is similar to that proposed by McMillan [Phys. Rev. A 8, 1921 (1973)]. Here, we explain that the claim is not correct and make it clear that the two compared pictures are quite different. In the preceding Comment, Madhusudana has also suggested an alternative explanation for tilt generation in the simulations by criticizing the original one proposed by us. We argue here in support of the original explanation and clarify that his explanation does not follow the simulation results. PMID:24827369

  14. Experimental study of quasi-2D dipolar vortex streets generated by a moving momentum source in a stratified fluid

    NASA Astrophysics Data System (ADS)

    Chen, K.; You, Y.; Noblesse, F.

    2016-07-01

    Experiments are conducted in a linear stratified fluid with a momentum source modeled via a nozzle jet moving horizontally. The generation mechanism of the quasi-two-dimensional dipolar vortex streets is investigated and their evolution characteristics are analyzed. Observation shows that the formation of a dipolar vortex street requires a nonzero motion of the nozzle in addition to conditions of the Reynolds and Froude number (Re, Fr). The (Re, Fr) condition that the dipolar vortex streets can be generated is determined via experimental measurements. The explanation for the absence of such a vortex street can be the low energy of the jet and the strong body-effect disturbance of the solid nozzle. The dependence of the vortex street dimensionless formation time τ and the Strouhal number St on the Froude number Fr or the Reynolds number Re is analyzed. This analysis shows that τ and St appear to be independent of Re and approximately have power-law relations with Fr via data fitting. The exponents of Fr in the two power-law functions are -0.27 for τ and -0.21 for St, while the constant coefficients are 65 and 0.21.

  15. Theoretical studies to elucidate the influence of magnetic dipolar interactions occurring in the magnetic nanoparticle systems, for biomedical applications

    NASA Astrophysics Data System (ADS)

    Osaci, M.; Cacciola, M.

    2016-02-01

    In recent years, the study of magnetic nanoparticles has been intensively developed not only for their fundamental theoretical interest, but also for their many technological applications, especially biomedical applications, ranging from contrast agents for magnetic resonance imaging to the deterioration of cancer cells via hyperthermia treatment. The theoretical and experimental research has shown until now that the magnetic dipolar interactions between nanoparticles can have a significant influence on the magnetic behaviour of the system. But, this influence is not well understood. It is clear that the magnetic dipolar interaction intensity is correlated with the nanoparticle concentration, volume fraction and magnetic moment orientations. In this paper, we try to understand the influence of magnetic dipolar interactions on the behaviour of magnetic nanoparticle systems, for biomedical applications. For the model, we considered spherical nanoparticles with uniaxial anisotropy and lognormal distribution of the sizes. The model involves a simulation stage of the spatial distribution and orientation of the nanoparticles and their easy axes of magnetic anisotropy, and an evaluation stage of the Néel relaxation time. To assess the Néel relaxation time, we are going to discretise and adapt, to the local magnetic field, the Coffey analytical solution for the equation Fokker-Planck describing the dynamics of magnetic moments of nanoparticles in oblique external magnetic field. There are three fundamental aspects of interest in our studies on the magnetic nanoparticles: their spatial & orientational distributions, concentrations and sizes.

  16. Near-earth injection of MeV electrons associated with intense dipolarization electric fields: Van Allen Probes observations

    DOE PAGES

    Dai, Lei; Wang, Chi; Duan, Suping; He, Zhaohai; Wygant, John R.; Cattell, Cynthia A.; Tao, Xin; Su, Zhenpeng; Kletzing, Craig; Baker, Daniel N.; et al

    2015-08-10

    Substorms generally inject tens to hundreds of keV electrons, but intense substorm electric fields have been shown to inject MeV electrons as well. An intriguing question is whether such MeV electron injections can populate the outer radiation belt. Here we present observations of a substorm injection of MeV electrons into the inner magnetosphere. In the premidnight sector at L~5.5, Van Allen Probes (Radiation Belt Storm Probes)-A observed a large dipolarization electric field (50 mV/m) over ~40 s and a dispersionless injection of electrons up to ~3 MeV. Pitch angle observations indicated betatron acceleration of MeV electrons at the dipolarization front.more » Corresponding signals of MeV electron injection were observed at LANL-GEO, THEMIS-D, and GOES at geosynchronous altitude. Through a series of dipolarizations, the injections increased the MeV electron phase space density by 1 order of magnitude in less than 3 h in the outer radiation belt (L > 4.8). Our observations provide evidence that deep injections can supply significant MeV electrons.« less

  17. Near-earth injection of MeV electrons associated with intense dipolarization electric fields: Van Allen Probes observations

    SciTech Connect

    Dai, Lei; Wang, Chi; Duan, Suping; He, Zhaohai; Wygant, John R.; Cattell, Cynthia A.; Tao, Xin; Su, Zhenpeng; Kletzing, Craig; Baker, Daniel N.; Li, Xinlin; Malaspina, David; Blake, J. Bernard; Fennell, Joseph; Claudepierre, Seth; Turner, Drew L.; Reeves, Geoffrey D.; Funsten, Herbert O.; Spence, Harlan E.; Angelopoulos, Vassilis; Fruehauff, Dennis; Chen, Lunjin; Thaller, Scott; Breneman, Aaron; Tang, Xiangwei

    2015-08-10

    Substorms generally inject tens to hundreds of keV electrons, but intense substorm electric fields have been shown to inject MeV electrons as well. An intriguing question is whether such MeV electron injections can populate the outer radiation belt. Here we present observations of a substorm injection of MeV electrons into the inner magnetosphere. In the premidnight sector at L~5.5, Van Allen Probes (Radiation Belt Storm Probes)-A observed a large dipolarization electric field (50 mV/m) over ~40 s and a dispersionless injection of electrons up to ~3 MeV. Pitch angle observations indicated betatron acceleration of MeV electrons at the dipolarization front. Corresponding signals of MeV electron injection were observed at LANL-GEO, THEMIS-D, and GOES at geosynchronous altitude. Through a series of dipolarizations, the injections increased the MeV electron phase space density by 1 order of magnitude in less than 3 h in the outer radiation belt (L > 4.8). Our observations provide evidence that deep injections can supply significant MeV electrons.

  18. Tunable dipolar resonances and Einstein-de Haas effect in a {sup 87}Rb-atom condensate

    SciTech Connect

    Swislocki, Tomasz; Sowinski, Tomasz; Pietraszewicz, Joanna; Gajda, Mariusz; Lewenstein, Maciej; Zakrzewski, Jakub

    2011-06-15

    We theoretically study a spinor condensate of {sup 87}Rb atoms in a F=1 hyperfine state confined in an optical dipole trap. Putting initially all atoms in an m{sub F}=1, component we observe a significant transfer of atoms to other, initially empty Zeeman states exclusively due to dipolar forces. Because of conservation of a total angular momentum the atoms going to other Zeeman components acquire an orbital angular momentum and circulate around the center of the trap. This is a realization of the Einstein-de Haas effect in a system of cold gases. We show that the transfer of atoms via dipolar interactions is possible only when the energies of the initial and the final sates are equal. This condition can be fulfilled utilizing a resonant external magnetic field, which tunes energies of involved states via the linear Zeeman effect. We found that there are many final states of different spatial density, which can be tuned selectively to the initial state. We show a simple model explaining high selectivity and controllability of weak dipolar interactions in the condensate of {sup 87}Rb atoms.

  19. Determination of peptide backbone torsion angles using double-quantum dipolar recoupling solid-state NMR spectroscopy.

    PubMed

    Mehta, Manish A; Eddy, Matthew T; McNeill, Seth A; Mills, Frank D; Long, Joanna R

    2008-02-20

    Several approaches for utilizing dipolar recoupling solid-state NMR (ssNMR) techniques to determine local structure at high resolution in peptides and proteins have been developed. However, many of these techniques measure only one torsion angle or are accurate for only certain classes of secondary structure. Additionally, the efficiency with which these dipolar recoupling experiments suppress the deleterious effects of chemical shift anisotropy (CSA) at high magnetic field strengths varies. Dipolar recoupling with a windowless sequence (DRAWS) has proven to be an effective pulse sequence for exciting double-quantum (DQ) coherences between adjacent carbonyl carbons along the peptide backbone. By allowing this DQ coherence to evolve, it is possible to measure the relative orientations of the CSA tensors and subsequently use this information to determine the Ramachandran torsion angles phi and psi. Here, we explore the accuracies of the assumptions made in interpreting DQ-DRAWS data and demonstrate their fidelity in measuring torsion angles corresponding to a variety of secondary structures irrespective of hydrogen-bonding patterns. It is shown how a simple choice of isotopic labels and experimental conditions allows accurate measurement of backbone secondary structures without any prior knowledge. This approach is considerably more sensitive for determining structure in helices and has comparable accuracy for beta-sheet and extended conformations relative to other methods. We also illustrate the ability of DQ-DRAWS to distinguish between structures in heterogeneous samples.

  20. Theory of noise in high-gain surface plasmon-polariton amplifiers incorporating dipolar gain media.

    PubMed

    De Leon, Israel; Berini, Pierre

    2011-10-10

    A theoretical analysis of noise in high-gain surface plasmon-polariton amplifiers incorporating dipolar gain media is presented. An expression for the noise figure is obtained in terms of the spontaneous emission rate into the amplified surface plasmon-polariton taking into account the different energy decay channels experienced by dipoles in close proximity to the metallic surface. Two amplifier structures are examined: a single-interface between a metal and a gain medium and a thin metal film bounded by identical gain media on both sides. A realistic configuration is considered where the surface plasmon-polariton undergoing amplification has a Gaussian field profile in the plane of the metal and paraxial propagation along the amplifier's length. The noise figure of these plasmonic amplifiers is studied considering three prototypical gain media with different permittivities. It is shown that the noise figure exhibits a strong dependance on the real part of the permittivities of the metal and gain medium, and that its minimum value is 4/π(∼3.53 dB). The origin of this minimum value is discussed. It is also shown that amplifier configurations supporting strongly confined surface plasmon-polaritons suffer from a large noise figure, which follows from an enhanced spontaneous emission rate due to the Purcell effect.

  1. 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

  2. A colloidal model system with an interaction tunable from hard sphere to soft and dipolar.

    PubMed

    Yethiraj, Anand; van Blaaderen, Alfons

    2003-01-30

    Monodisperse colloidal suspensions of micrometre-sized spheres are playing an increasingly important role as model systems to study, in real space, a variety of phenomena in condensed matter physics--such as glass transitions and crystal nucleation. But to date, no quantitative real-space studies have been performed on crystal melting, or have investigated systems with long-range repulsive potentials. Here we demonstrate a charge- and sterically stabilized colloidal suspension--poly(methyl methacrylate) spheres in a mixture of cycloheptyl (or cyclohexyl) bromide and decalin--where both the repulsive range and the anisotropy of the interparticle interaction potential can be controlled. This combination of two independent tuning parameters gives rise to a rich phase behaviour, with several unusual colloidal (liquid) crystalline phases, which we explore in real space by confocal microscopy. The softness of the interaction is tuned in this colloidal suspension by varying the solvent salt concentration; the anisotropic (dipolar) contribution to the interaction potential can be independently controlled with an external electric field ranging from a small perturbation to the point where it completely determines the phase behaviour. We also demonstrate that the electric field can be used as a pseudo-thermodynamic temperature switch to enable real-space studies of melting transitions. We expect studies of this colloidal model system to contribute to our understanding of, for example, electro- and magneto-rheological fluids.

  3. Antiferromagnetic dipolar ordering in [Co{sub 2}MnGe/V]{sub N} multilayers

    SciTech Connect

    Bergmann, A.; Grabis, J.; Zabel, H.; Westerholt, K.; Toperverg, B.P.; Leiner, V.; Wolff, M.

    2005-12-01

    We have studied [Co{sub 2}MnGe/V]{sub N} multilayers with a thickness of the V layers t{sub V} between 1.5 and 10 nm and a fixed thickness of the Heusler layer t{sub Co{sub 2}}{sub MnGe}=3 nm by x-ray scattering, neutron reflectivity, and magnetization measurements. In the thickness range t{sub V}{<=}3 nm neutron reflectivity results provide clear evidence for an antiferromagnetic (af) interlayer long-range order below a Neel temperature T{sub N}. The interlayer long range order does not show an oscillating character and is stabilized by a weak af coupling field H{sub af}{approx_equal}100 Oe. We attribute the af coupling to magnetic dipolar stray fields originating from magnetically rough surfaces of a granular Co{sub 2}MnGe microstructure. In the thickness range t{sub V}{>=}4 nm the multilayers undergo a cluster glass transition at T{sub f}{approx_equal}150 K. At high temperatures above T{sub N} or T{sub f} the mutilayers are superparamagnetic with a huge cluster magnetic moment {mu}{sub c}{>=}10{sup 5}{mu}{sub B}.

  4. Assembly-mediated interplay of dipolar interactions and surface spin disorder in colloidal maghemite nanoclusters.

    PubMed

    Kostopoulou, A; Brintakis, K; Vasilakaki, M; Trohidou, K N; Douvalis, A P; Lascialfari, A; Manna, L; Lappas, A

    2014-04-01

    Controlled assembly of single-crystal, colloidal maghemite nanoparticles is facilitated via a high-temperature polyol-based pathway. Structural characterization shows that size-tunable nanoclusters of 50 and 86 nm diameters (D), with high dispersibility in aqueous media, are composed of ∼13 nm (d) crystallographically oriented nanoparticles. The interaction effects are examined against the increasing volume fraction, φ, of the inorganic magnetic phase that goes from individual colloidal nanoparticles (φ = 0.47) to clusters (φ = 0.72). The frozen-liquid dispersions of the latter exhibit weak ferrimagnetic behaviour at 300 K. Comparative Mössbauer spectroscopic studies imply that intra-cluster interactions come into play. New insight emerges from the clusters' temperature-dependent ac susceptibility that displays two maxima in χ''(T), with strong frequency dispersion. Scaling-law analysis together with the observed memory effects suggests that a superspin-glass state settles-in at TB ∼ 160-200 K, while at lower-temperatures, surface spin-glass freezing is established at Tf ∼ 40-70 K. In such nanoparticle-assembled systems, with increased φ, Monte Carlo simulations corroborate the role of the inter-particle dipolar interactions and that of the constituent nanoparticles' surface spin disorder in the emerging spin-glass dynamics.

  5. Dipolar magnets and glasses: Neutron-scattering, dynamical, and calorimetric studies of randomly distributed Ising spins

    SciTech Connect

    Reich, D.H.; Ellman, B.; Yang, J.; Rosenbaum, T.F. . James Franck Institute University of Chicago, Chicago, IL . Department of Physics); Aeppli, G. ); Belanger, D.P. )

    1990-09-01

    We have measured the magnetic correlations, susceptibility, specific heat, and thermal relaxation in the dipolar-coupled Ising system LiHo{sub {ital x}}Y{sub 1{minus}{ital x}}F{sub 4}. The material is ferromagnetic for spin concentrations at least as low as {ital x}=0.46, with a Curie temperature obeying mean-field scaling relative to that of pure LiHoF{sub 4}. In contrast, an {ital x}=0.167 sample behaves as a spin glass above its transition temperature, while an {ital x}=0.045 crystal shows very different glassy properties characterized by decreasing barriers to relaxation and nonexponential thermal relaxation as {ital T}{r arrow}0. We find the properties of the {ital x}=0.045 system to be consistent with a single low-degeneracy ground state with a large gap for excitations. The {ital x}=0.167 sample, however, supports a complex ground state with no appreciable gap, in accordance with prevailing theories of spin glasses. The underlying causes of such disparate behavior are discussed in terms of random clusters as probed by neutron studies of the {ital x}=0.167 sample.

  6. Low-temperature spin-glass behavior in a diluted dipolar Ising system

    NASA Astrophysics Data System (ADS)

    Alonso, Juan J.

    2015-03-01

    Using Monte Carlo simulations, we study the character of the spin-glass (SG) state of a site-diluted dipolar Ising model. We consider systems of dipoles randomly placed on a fraction x of all L3 sites of a simple cubic lattice that point up or down along a given crystalline axis. For x ≲0.65 these systems are known to exhibit an equilibrium spin-glass phase below a temperature Tsg∝x . At high dilution and very low temperatures, well deep in the SG phase, we find spiky distributions of the overlap parameter q that are strongly sample dependent. We focus on spikes associated with large excitations. From cumulative distributions of q and a pair correlation function averaged over several thousands of samples we find that, for the system sizes studied, the average width of spikes, and the fraction of samples with spikes higher than a certain threshold, does not vary appreciably with L . This is compared with the behavior found for the Sherrington-Kirkpatrick model.

  7. Contribution of spin pairs to the magnetic response in a dilute dipolar ferromagnet

    NASA Astrophysics Data System (ADS)

    Gannarelli, C. M. S.; Silevitch, D. M.; Rosenbaum, T. F.; Aeppli, G.; Fisher, A. J.

    2012-07-01

    We simulate the dc magnetic response of the diluted dipolar-coupled Ising magnet LiHo0.045Y0.955F4 in a transverse field, using exact diagonalization of a two-spin Hamiltonian averaged over nearest-neighbor configurations. The pairwise model, incorporating hyperfine interactions, accounts for the observed drop-off in the longitudinal (c -axis) susceptibility with increasing transverse field; with the inclusion of a small tilt in the transverse field, it also accounts for the behavior of the off-diagonal magnetic susceptibility. The hyperfine interactions do not appear to lead to qualitative changes in the pair susceptibilities, although they do renormalize the crossover fields between different regimes. The comparison with experiment indicates that antiferromagnetic correlations are more important than anticipated based on simple pair statistics and our first-principles calculations of the pair response. This means that larger clusters will be needed for a full description of the reduction in the diagonal response at small transverse fields.

  8. Protein structure validation and identification from unassigned residual dipolar coupling data using 2D-PDPA.

    PubMed

    Fahim, Arjang; Mukhopadhyay, Rishi; Yandle, Ryan; Prestegard, James H; Valafar, Homayoun

    2013-08-22

    More than 90% of protein structures submitted to the PDB each year are homologous to some previously characterized protein structure. The extensive resources that are required for structural characterization of proteins can be justified for the 10% of the novel structures, but not for the remaining 90%. This report presents the 2D-PDPA method, which utilizes unassigned residual dipolar coupling in order to address the economics of structure determination of routine proteins by reducing the data acquisition and processing time. 2D-PDPA has been demonstrated to successfully identify the correct structure of an array of proteins that range from 46 to 445 residues in size from a library of 619 decoy structures by using unassigned simulated RDC data. When using experimental data, 2D-PDPA successfully identified the correct NMR structures from the same library of decoy structures. In addition, the most homologous X-ray structure was also identified as the second best structural candidate. Finally, success of 2D-PDPA in identifying and evaluating the most appropriate structure from a set of computationally predicted structures in the case of a previously uncharacterized protein Pf2048.1 has been demonstrated. This protein exhibits less than 20% sequence identity to any protein with known structure and therefore presents a compelling and practical application of our proposed work.

  9. Quantum Correlations of Few Dipolar Bosons in a Double-Well Trap

    NASA Astrophysics Data System (ADS)

    Pizzardo, Michele; Mazzarella, Giovanni; Salasnich, Luca

    2016-10-01

    We consider N interacting dipolar bosonic atoms at zero temperature in a double-well potential. This system is described by the two-space-mode extended Bose-Hubbard Hamiltonian which includes (in addition to the familiar BH terms) the nearest-neighbor interaction, correlated hopping and bosonic-pair hopping. For systems with N=2 and N=3 particles, we calculate analytically both the ground state and the Fisher information, the coherence visibility, and the entanglement entropy that characterize the correlations of the lowest energy state. The structure of the ground state crucially depends on the correlated hopping K_c. On one hand, we find that this process makes possible the occurrence of Schrödinger-cat states even if the onsite interatomic attraction is not strong enough to guarantee the formation of such states. On the other hand in the presence of a strong onsite attraction, sufficiently large values of |K_c| destroy the cat-like state in favor of a delocalized atomic coherent state.

  10. Two-dimensional solitons in dipolar Bose-Einstein condensates with spin-orbit coupling

    NASA Astrophysics Data System (ADS)

    Jiang, Xunda; Fan, Zhiwei; Chen, Zhaopin; Pang, Wei; Li, Yongyao; Malomed, Boris A.

    2016-02-01

    We report families of two-dimensional (2D) composite solitons in spinor dipolar Bose-Einstein condensates, with two localized components linearly mixed by the spin-orbit coupling (SOC), and the intrinsic nonlinearity represented by the dipole-dipole interaction (DDI) between atomic magnetic moments polarized in plane by an external magnetic field. Recently, stable solitons were predicted in the form of semivortices (composites built of coupled fundamental and vortical components) in the 2D system combining the SOC and contact attractive interactions. Replacing the latter by the anisotropic long-range DDI, we demonstrate that, for a fixed norm of the soliton, the system supports a continuous family of stable spatially asymmetric vortex solitons (AVSs), parameterized by an offset of the pivot of the vortical component relative to its fundamental counterpart. The offset is limited by a certain maximum value, while the energy of the AVS practically does not depend on the offset. At small values of the norm, the vortex solitons are subject to a weak oscillatory instability. In the present system, with the Galilean invariance broken by the SOC, the composite solitons are set in motion by a kick the strength of which exceeds a certain depinning value. The kicked solitons feature a negative effective mass, drifting along a spiral trajectory opposite to the direction of the kick. A critical angular velocity, up to which the semivortices may follow rotation of the polarizing magnetic field, is found too.

  11. Ground-state properties and elementary excitations of quantum droplets in dipolar Bose-Einstein condensates

    NASA Astrophysics Data System (ADS)

    Wächtler, F.; Santos, L.

    2016-10-01

    Recent experiments have revealed the formation of stable droplets in dipolar Bose-Einstein condensates. This surprising result has been explained by the stabilization given by quantum fluctuations. We study in detail the properties of a Bose-Einstein condensate in the presence of quantum stabilization. The ground-state phase diagram presents three main regimes: mean-field regime, in which the quantum correction is perturbative; droplet regime, in which quantum stabilization is crucial; and a multistable regime. In the absence of a multistable region, the condensate undergoes a crossover from the mean-field to the droplet solution marked by a characteristic growth of the peak density that may be employed to clearly distinguish quantum stabilization from other stabilization mechanisms. Interestingly, quantum stabilization allows for three-dimensionally self-bound condensates. We characterized these self-bound solutions, and discuss their realization in experiments. We conclude with a discussion of the lowest-lying excitations both for trapped condensates, and for self-bound solutions.

  12. Dynamics of a coupled spin-vortex pair in dipolar spinor Bose-Einstein condensates

    NASA Astrophysics Data System (ADS)

    Li, Tiantian; Yi, Su; Zhang, Yunbo

    2016-05-01

    The collisional and magnetic field quench dynamics of a coupled spin-vortex pair in dipolar spinor Bose-Einstein condensates in a double-well potential are numerically investigated in the mean-field theory. Upon a sudden release of the potential barrier the two layers of condensates collide with each other in the trap center with the chirality of the vortex pair exchanged after each collision, showing the typical signature of in-phase collision for the parallel spin-vortex phase, and out-of-phase collision for the antiparallel phase. When quenching the transverse magnetic field, the vortex center in the single-layered condensate starts to make a helical motion with oval-shaped trajectories and the displacement of the center position is found to exhibit a damped simple harmonic oscillation with an intrinsic frequency and damping rate. The oscillation mode of the spin-vortex pair may be tuned by the initial magnetic field and the height of the Gaussian barrier; e.g., the gyrotropic motions for a parallel spin-vortex pair are out of sync with each other in the two layers, while those for the antiparallel pair exhibit a double-helix structure with the vortex centers moving opposite to each other with the same amplitude.

  13. Phase transitions and multicritical behavior in the Ising model with dipolar interactions

    NASA Astrophysics Data System (ADS)

    Bab, M. A.; Horowitz, C. M.; Rubio Puzzo, M. L.; Saracco, G. P.

    2016-10-01

    In this work, the phase diagram of the ferromagnetic Ising model with dipole interactions is revisited with the aim of determining the nature of the phase transition between stripe-ordered phases with width n (hn) and tetragonal liquid (TL) phases. Extensive Monte Carlo simulations are performed in order to study the short-time dynamic behavior of the observables for selected values of the ratio between the ferromagnetic exchange and dipolar constants δ . The obtained results indicate that the h1-TL phase transition line is continuous up to δ =1.2585 , while for the h2-TL line a weak first-order character is found in the interval 1.2585 ≤δ ≤1.36 and becomes continuous for 1.37 ≤δ ≤1.9 . This result suggests the existence of a tricritical point close to δ =1.37 . When it is appropriate, the complete set of critical exponents is obtained, and in all the studied cases they depend on δ but do not belong to the Ising universality class. Furthermore, short-time dynamic studies reveal that at the point where the mentioned lines meet the h1-h2 line, i.e., at δ =1.2585 , the critical phase corresponding to the h1-TL transition coexists with the h2 phase.

  14. Open Boundary Particle-in-Cell Simulation of Dipolarization Front Propagation

    NASA Technical Reports Server (NTRS)

    Klimas, Alex; Hwang, Kyoung-Joo; Vinas, Adolfo F.; Goldstein, Melvyn L.

    2014-01-01

    First results are presented from an ongoing open boundary 2-1/2D particle-in-cell simulation study of dipolarization front (DF) propagation in Earth's magnetotail. At this stage, this study is focused on the compression, or pileup, region preceding the DF current sheet. We find that the earthward acceleration of the plasma in this region is in general agreement with a recent DF force balance model. A gyrophase bunched reflected ion population at the leading edge of the pileup region is reflected by a normal electric field in the pileup region itself, rather than through an interaction with the current sheet. We discuss plasma wave activity at the leading edge of the pileup region that may be driven by gradients, or by reflected ions, or both; the mode has not been identified. The waves oscillate near but above the ion cyclotron frequency with wavelength several ion inertial lengths. We show that the waves oscillate primarily in the perpendicular magnetic field components, do not propagate along the background magnetic field, are right handed elliptically (close to circularly) polarized, exist in a region of high electron and ion beta, and are stationary in the plasma frame moving earthward. We discuss the possibility that the waves are present in plasma sheet data, but have not, thus far, been discovered.

  15. Microscopic description of anisotropic low-density dipolar Bose gases in two dimensions

    NASA Astrophysics Data System (ADS)

    Macia, A.; Mazzanti, F.; Boronat, J.; Zillich, R. E.

    2011-09-01

    A microscopic description of the zero-energy two-body ground state and many-body static properties of anisotropic homogeneous gases of bosonic dipoles in two dimensions at low densities is presented and discussed. By changing the polarization angle with respect to the plane, we study the impact of the anisotropy, present in the dipole-dipole interaction, on the energy per particle, comparing the results with mean-field predictions. We restrict the analysis to the regime where the interaction is always repulsive, although the strength of the repulsion depends on the orientation with respect to the polarization field. We present a series expansion of the solution of the zero-energy two-body problem, which allows us to find the scattering length of the interaction and to build a suitable Jastrow factor that we use as a trial wave function for both a variational and diffusion Monte Carlo simulation of the infinite system. We find that the anisotropy has an almost negligible impact on the ground-state properties of the many-body system in the universal regime where the scattering length governs the physics of the system. We also show that scaling in the gas parameter persists in the dipolar case up to values where other isotropic interactions with the same scattering length yield different predictions.

  16. Creation of an Ultracold Gas of Ground-State Dipolar 23Na 87 Molecules

    NASA Astrophysics Data System (ADS)

    Guo, Mingyang; Zhu, Bing; Lu, Bo; Ye, Xin; Wang, Fudong; Vexiau, Romain; Bouloufa-Maafa, Nadia; Quéméner, Goulven; Dulieu, Olivier; Wang, Dajun

    2016-05-01

    We report the successful production of an ultracold sample of absolute ground-state 23Na 87Rb molecules. Starting from weakly bound Feshbach molecules formed via magnetoassociation, the lowest rovibrational and hyperfine level of the electronic ground state is populated following a high-efficiency and high-resolution two-photon Raman process. The high-purity absolute ground-state samples have up to 8000 molecules and densities of over 1011 cm-3 . By measuring the Stark shifts induced by external electric fields, we determined the permanent electric dipole moment of the absolute ground-state 23Na 87Rb and demonstrated the capability of inducing an effective dipole moment over 1 D. Bimolecular reaction between ground-state 23Na 87Rb molecules is endothermic, but we still observed a rather fast decay of the molecular sample. Our results pave the way toward investigation of ultracold molecular collisions in a fully controlled manner and possibly to quantum gases of ultracold bosonic molecules with strong dipolar interactions.

  17. Creation of an Ultracold Gas of Ground-State Dipolar ^{23}Na^{87}Rb Molecules.

    PubMed

    Guo, Mingyang; Zhu, Bing; Lu, Bo; Ye, Xin; Wang, Fudong; Vexiau, Romain; Bouloufa-Maafa, Nadia; Quéméner, Goulven; Dulieu, Olivier; Wang, Dajun

    2016-05-20

    We report the successful production of an ultracold sample of absolute ground-state ^{23}Na^{87}Rb molecules. Starting from weakly bound Feshbach molecules formed via magnetoassociation, the lowest rovibrational and hyperfine level of the electronic ground state is populated following a high-efficiency and high-resolution two-photon Raman process. The high-purity absolute ground-state samples have up to 8000 molecules and densities of over 10^{11}  cm^{-3}. By measuring the Stark shifts induced by external electric fields, we determined the permanent electric dipole moment of the absolute ground-state ^{23}Na^{87}Rb and demonstrated the capability of inducing an effective dipole moment over 1 D. Bimolecular reaction between ground-state ^{23}Na^{87}Rb molecules is endothermic, but we still observed a rather fast decay of the molecular sample. Our results pave the way toward investigation of ultracold molecular collisions in a fully controlled manner and possibly to quantum gases of ultracold bosonic molecules with strong dipolar interactions. PMID:27258875

  18. 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.

  19. Thiophenes as traps for benzyne. 3. Diaryl sulfides and the role of dipolar intermediates.

    PubMed

    Reinecke, Manfred G; Del Mazza, Dario; Obeng, Marcus

    2003-01-10

    The reactions of seven thiophenes with benzyne generated from diphenyliodonium-2-carboxylate (DPIC) under a standard set of conditions led among other products to the formation of alpha- and beta-naphthyl phenyl sulfides 2a and 2b from thiophene (1a) and of 2c and 2d from 2-methylthiophene (1b). Dithienyl sulfides 4a-f were produced from the halothiophenes 1c-g. The structures of the naphthyl sulfides were proven by comparison with authentic samples of 2a-f, thus eliminating one of two possible mechanisms of formation. The remaining mechanism involves [4+2]-cycloaddition of benzyne to thiophene or to an S-phenylthiophenium ylide 10 to give the dipolar 2:1 benzyne/thiophene adduct 8 followed by ring-opening. Stevens-like rearrangements of 11, formed from 10 by proton transfer, may also explain the origin of arylated thiophenes such as 12 and 3 found in some reactions of benzynes with thiophene.

  20. 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.

  1. Dipolar matter-wave solitons in two-dimensional anisotropic discrete lattices

    NASA Astrophysics Data System (ADS)

    Chen, Huaiyu; Liu, Yan; Zhang, Qiang; Shi, Yuhan; Pang, Wei; Li, Yongyao

    2016-05-01

    We numerically demonstrate two-dimensional (2D) matter-wave solitons in the disk-shaped dipolar Bose-Einstein condensates (BECs) trapped in strongly anisotropic optical lattices (OLs) in a disk's plane. The considered OLs are square lattices which can be formed by interfering two pairs of plane waves with different intensities. The hopping rates of the condensates between two adjacent lattices in the orthogonal directions are different, which gives rise to a linearly anisotropic system. We find that when the polarized orientation of the dipoles is parallel to disk's plane with the same direction, the combined effects of the linearly anisotropy and the nonlocal nonlinear anisotropy strongly influence the formations, as well as the dynamics of the lattice solitons. Particularly, the isotropy-pattern solitons (IPSs) are found when these combined effects reach a balance. Motion, collision, and rotation of the IPSs are also studied in detail by means of systematic simulations. We further find that these IPSs can move freely in the 2D anisotropic discrete system, hence giving rise to an anisotropic effective mass. Four types of collisions between the IPSs are identified. By rotating an external magnetic field up to a critical angular velocity, the IPSs can still remain localized and play as a breather. Finally, the influences from the combined effects between the linear and the nonlocal nonlinear anisotropy with consideration of the contact and/or local nonlinearity are discussed too.

  2. The Role of Localized Inductive Electric Fields in Electron Injections Around Dipolarizing Flux Bundles

    NASA Astrophysics Data System (ADS)

    Gabrielse, C.; Harris, C.; Angelopoulos, V.; Runov, A.

    2015-12-01

    We study energetic electron injections using an analytical model that describes self-consistent electric and magnetic field perturbations of a transient, localized dipolarizing flux bundle (DFB). This simple model can reproduce most injection signatures at multiple locations simultaneously, reaffirming earlier findings that an earthward-traveling DFB can both transport and accelerate electrons to suprathermal energies, and can thus be considered as the primary driver of short-lived (~<10 min) injections. We find that energetic electron drift paths are greatly influenced by the sharp magnetic field gradients around the localized DFB. If the gradients are weak the energetic electrons initiating at reconnection will drift out of the flow channel such that the observed injection is comprised mostly of plasma sheet electrons. However, if the duskward magnetic field gradients on the DFB's dawn flank are strong they can cause electrons to drift further earthward from the reconnection site than due to E x B alone. Similarly, strong dawnward magnetic field gradients on the DFB's dusk flank can extract energetic electrons from the inner magnetosphere out to the plasma sheet, where they can either be recirculated earthward or remain at higher L-shells. Therefore, the source of electrons observed during injection depends sensitively on the spacecraft location relative to the DFB and on the DFB's properties.

  3. Vortices in dipolar Bose-Einstein condensates in synthetic magnetic field

    NASA Astrophysics Data System (ADS)

    Qiang, Zhao; Qiang, Gu

    2016-01-01

    We study the formation of vortices in a dipolar Bose-Einstein condensate in a synthetic magnetic field by numerically solving the Gross-Pitaevskii equation. The formation process depends on the dipole strength, the rotating frequency, the potential geometry, and the orientation of the dipoles. We make an extensive comparison with vortices created by a rotating trap, especially focusing on the issues of the critical rotating frequency and the vortex number as a function of the rotating frequency. We observe that a higher rotating frequency is needed to generate a large number of vortices and the anisotropic interaction manifests itself as a perceptible difference in the vortex formation. Furthermore, a large dipole strength or aspect ratio also can increase the number of vortices effectively. In particular, we discuss the validity of the Feynman rule. Project supported by the National Natural Science Foundation of China (Grant No. 11274039), the National Basic Research Program of China (Grant No. 2013CB922002), and the Fundamental Research Funds for the Central Universities of China.

  4. Structural and dipolar properties of the voltage-dependent pore former alamethicin in octanol/dioxane.

    PubMed Central

    Schwarz, G; Savko, P

    1982-01-01

    Dielectric constant and loss of the membrane-active peptide alamethicin in octanol/dioxane mixtures have been measured at frequencies between 5 kHz and 50 MHz. On the basis of a rotational mechanism of dipolar orientation, the observed dispersion provides information regarding size, shape, and dipole moment of the structural entities which the solute may assume in media of diverse lipophilicity. Particularly detailed results are obtained in a pure octanol solvent where an apparent molecular weight of alamethicin could be determined. It turns out that in this quite lipophilic medium most of the peptide material exists as a monomer particle that has approximate length and diameter of 35 and 13 A, respectively. It carries a dipole moment of approximately 75 Debye units (directed nearly parallel to the long axis). At our concentrations of a few milligrams per milliliters, appreciable formation of dimers by head-to-tail linkage is indicated. When the octanol content is reduced by adding greater amounts of dioxane, larger particles are encountered. This is accompanied by a decrease of the effective polarity. The inherent increase of hydrophilicity in the dioxane-enriched solvent apparently favors another monomer conformation that has a low dipole moment and easily aggregates to some kind of micelle. PMID:7115881

  5. Spectral diffusion and dipolar flip-flop in spin-based solid state quantum computers

    NASA Astrophysics Data System (ADS)

    de Sousa, Rogerio; Das Sarma, S.

    2002-03-01

    We estimate phase coherence times for spins in two quantum computer architectures, where the qubit is either an electron spin bound to a P donor impurity in Si or a GaAs quantum dot. Since the magnetic resonance line in both these systems is inhomogeneously broadened, a natural way to probe these coherence times is to measure the decay time of a two pulse spin echo envelope. Based on spin echo experiments performed on Si:P we consider three mechanisms for this decay: (1) Spin-lattice relaxation (T1 processes), (2) flip-flop between qubits mediated by dipolar interaction, and (3) spectral diffusion caused by nearby flip-flopping nuclear spins. Our estimates indicate that mechanism (3) dominates in both architectures, except for isotopically pure Si-28 samples where mechanism (2) dominates due to the fact that the line is not inhomogeneously broadened and more spin qubits can flip-flop. We acknowledge support from ARDA, DARPA and the US-ONR.

  6. MMS Observations of magnetospheric fast ion flows and magnetic dipolarization near the dusk-meridian flank

    NASA Astrophysics Data System (ADS)

    Pollock, Craig; Chen, Li-Jen; Wang, Shan; Torbert, Roy; Russell, Christopher; Reiff, Patricia; Giles, Barbara; Burch, James

    2016-04-01

    The concept of a magnetic dipolarization front propagating earthward through Earth's magnetotail and accompanied by fast earthward ion flows, both as consequences of magnetic reconnection occurring tail-ward of an observation point, is well known. Examples of this phenomenology have recently been referred to as reconnection fronts. It is less common to imagine similar signature sets in contexts other than the imagined noon-midnight magnetotail configuration. Nevertheless, signatures of 800 km/s earthward ion flows were observed contemporaneously with distinct but temporary increases in the GSE-z component of the magnetic field at a geocentric distance of the order of 10 RE, in the vicinity (but somewhat tail-ward) of Earth's equatorial dusk terminator on August 12, 2015. These observations were obtained using the Fast Plasma Investigation (FPI) and the Fields electric fields experiment on NASA's Magnetospheric Multiscale (MMS) mission. Several interesting questions arise as to the nature of the observed plasma and field signatures and their drivers in cases such as this. To what degree are they analogous to the magnetotail reconnection fronts previously alluded to? And, to the degree that they are, what kind of reconnection geometry can we envision as giving rise to these signatures at such a location? We will present sample observations and discuss their significance from this point of view.

  7. A physical explanation for the magnetic decrease ahead of dipolarization fronts

    NASA Astrophysics Data System (ADS)

    Yao, Z. H.; Liu, J.; Owen, C. J.; Forsyth, C.; Rae, I. J.; Pu, Z. Y.; Fu, H. S.; Zhou, X.-Z.; Shi, Q. Q.; Du, A. M.; Guo, R. L.; Chu, X. N.

    2015-10-01

    Recent studies have shown that the ambient plasma in the near-Earth magnetotail can be compressed by the arrival of a dipolarization front (DF). In this paper we study the variations in the characteristics of currents flowing in this compressed region ahead of the DF, particularly the changes in the cross-tail current, using observations from the THEMIS satellites. Since we do not know whether the changes in the cross-tail current lead to a field-aligned current formation or just form a current loop in the magnetosphere, we thus use redistribution to represent these changes of local current density. We found that (1) the redistribution of the cross-tail current is a common feature preceding DFs; (2) the redistribution of cross-tail current is caused by plasma pressure gradient ahead of the DF and (3) the resultant net current redistributed by a DF is an order of magnitude smaller than the typical total current associated with a moderate substorm current wedge (SCW). Moreover, our results also suggest that the redistributed current ahead of the DF is closed by currents on the DF itself, forming a closed current loop around peaks in plasma pressure, what is traditionally referred to as a banana current.

  8. Protein structure validation and identification from unassigned residual dipolar coupling data using 2D-PDPA.

    PubMed

    Fahim, Arjang; Mukhopadhyay, Rishi; Yandle, Ryan; Prestegard, James H; Valafar, Homayoun

    2013-01-01

    More than 90% of protein structures submitted to the PDB each year are homologous to some previously characterized protein structure. The extensive resources that are required for structural characterization of proteins can be justified for the 10% of the novel structures, but not for the remaining 90%. This report presents the 2D-PDPA method, which utilizes unassigned residual dipolar coupling in order to address the economics of structure determination of routine proteins by reducing the data acquisition and processing time. 2D-PDPA has been demonstrated to successfully identify the correct structure of an array of proteins that range from 46 to 445 residues in size from a library of 619 decoy structures by using unassigned simulated RDC data. When using experimental data, 2D-PDPA successfully identified the correct NMR structures from the same library of decoy structures. In addition, the most homologous X-ray structure was also identified as the second best structural candidate. Finally, success of 2D-PDPA in identifying and evaluating the most appropriate structure from a set of computationally predicted structures in the case of a previously uncharacterized protein Pf2048.1 has been demonstrated. This protein exhibits less than 20% sequence identity to any protein with known structure and therefore presents a compelling and practical application of our proposed work. PMID:23973992

  9. A new dipolar potential for numerical simulations of polar fluids on the 4D hypersphere

    NASA Astrophysics Data System (ADS)

    Caillol, Jean-Michel; Trulsson, Martin

    2014-09-01

    We present a new method for Monte Carlo or Molecular Dynamics numerical simulations of three-dimensional polar fluids. The simulation cell is defined to be the surface of the northern hemisphere of a four-dimensional (hyper)sphere. The point dipoles are constrained to remain tangent to the sphere and their interactions are derived from the basic laws of electrostatics in this geometry. The dipole-dipole potential has two singularities which correspond to the following boundary conditions: when a dipole leaves the northern hemisphere at some point of the equator, it reappears at the antipodal point bearing the same dipole moment. We derive all the formal expressions needed to obtain the thermodynamic and structural properties of a polar liquid at thermal equilibrium in actual numerical simulation. We notably establish the expression of the static dielectric constant of the fluid as well as the behavior of the pair correlation at large distances. We report and discuss the results of extensive numerical Monte Carlo simulations for two reference states of a fluid of dipolar hard spheres and compare these results with previous methods with a special emphasis on finite size effects.

  10. Protein Structure Validation and Identification from Unassigned Residual Dipolar Coupling Data Using 2D-PDPA

    PubMed Central

    Fahim, Arjang; Mukhopadhyay, Rishi; Yandle, Ryan; Prestegard, James H.; Valafar, Homayoun

    2014-01-01

    More than 90% of protein structures submitted to the PDB each year are homologous to some previously characterized protein structure. The extensive resources that are required for structural characterization of proteins can be justified for the 10% of the novel structures, but not for the remaining 90%. This report presents the 2D-PDPA method, which utilizes unassigned residual dipolar coupling in order to address the economics of structure determination of routine proteins by reducing the data acquisition and processing time. 2D-PDPA has been demonstrated to successfully identify the correct structure of an array of proteins that range from 46 to 445 residues in size from a library of 619 decoy structures by using unassigned simulated RDC data. When using experimental data, 2D-PDPA successfully identified the correct NMR structures from the same library of decoy structures. In addition, the most homologous X-ray structure was also identified as the second best structural candidate. Finally, success of 2D-PDPA in identifying and evaluating the most appropriate structure from a set of computationally predicted structures in the case of a previously uncharacterized protein Pf2048.1 has been demonstrated. This protein exhibits less than 20% sequence identity to any protein with known structure and therefore presents a compelling and practical application of our proposed work. PMID:23973992

  11. Parafermion excitations in superfluid of quasi-molecular chains formed by dipolar molecules or indirect excitons

    NASA Astrophysics Data System (ADS)

    Kuklov, Anatoly; Tsvelik, Alexei

    2013-03-01

    We study a quantum phase transition in a system of dipoles confined in a stack of N identical 1D lattices (tubes) polarized perpendicularly to the lattices. The dipoles may represent polar molecules or indirect excitons. The transition separates two phases; in one of them superfluidity takes place in each individual lattice, in the other (chain superfluid) the order parameter is the product of bosonic operators from all lattices. We argue that in the presence of finite inter-lattice tunneling the transition belongs to the universality class of the q = N two-dimensional classical Potts model. For N = 2 , 3 , 4 the corresponding low energy field theory is the model of ZN parafermions perturbed by the thermal operator. Results of Monte Carlo simulations are consistent with these predictions. The detection schemes for the chain superfluid of dipolar molecules and indirect excitons are outlined. ABK was supported by the NSF under Grant No.PHY1005527; AMT acknowledges a support from US DOE under contract DE-AC02-98 CH108

  12. Microscopic description of anisotropic low-density dipolar Bose gases in two dimensions

    SciTech Connect

    Macia, A.; Mazzanti, F.; Boronat, J.; Zillich, R. E.

    2011-09-15

    A microscopic description of the zero-energy two-body ground state and many-body static properties of anisotropic homogeneous gases of bosonic dipoles in two dimensions at low densities is presented and discussed. By changing the polarization angle with respect to the plane, we study the impact of the anisotropy, present in the dipole-dipole interaction, on the energy per particle, comparing the results with mean-field predictions. We restrict the analysis to the regime where the interaction is always repulsive, although the strength of the repulsion depends on the orientation with respect to the polarization field. We present a series expansion of the solution of the zero-energy two-body problem, which allows us to find the scattering length of the interaction and to build a suitable Jastrow factor that we use as a trial wave function for both a variational and diffusion Monte Carlo simulation of the infinite system. We find that the anisotropy has an almost negligible impact on the ground-state properties of the many-body system in the universal regime where the scattering length governs the physics of the system. We also show that scaling in the gas parameter persists in the dipolar case up to values where other isotropic interactions with the same scattering length yield different predictions.

  13. Characterization of alkyl carbon in forest soils by CPMAS 13C NMR spectroscopy and dipolar dephasing

    USGS Publications Warehouse

    Kogel-Knabner, I.; Hatcher, P.G.

    1989-01-01

    Samples obtained from forest soils at different stages of decomposition were treated sequentially with chloroform/methanol (extraction of lipids), sulfuric acid (hydrolysis), and sodium chlorite (delignification) to enrich them in refractory alkyl carbon. As revealed by NMR spectroscopy, this treatment yielded residues with high contents of alkyl carbon. In the NMR spectra of residues obtained from litter samples, resonances for carbohydrates are also present, indicating that these carbohydrates are tightly bound to the alkyl carbon structures. During decomposition in the soils this resistant carbohydrate fraction is lost almost completely. In the litter samples the alkyl carbon shows a dipolar dephasing behavior indicative of two structural components, a rigid and a more mobile component. As depth and decomposition increase, only the rigid component is observed. This fact could be due to selective degradation of the mobile component or to changes in molecular mobility during decomposition, e.g., because of an increase in cross linking or contact with the mineral matter of the soil.

  14. Manipulation and control of the interfacial polarization in organic light-emitting diodes by dipolar doping

    NASA Astrophysics Data System (ADS)

    Jäger, Lars; Schmidt, Tobias D.; Brütting, Wolfgang

    2016-09-01

    Most of the commonly used electron transporting materials in organic light-emitting diodes exhibit interfacial polarization resulting from partially aligned permanent dipole moments of the molecules. This property modifies the internal electric field distribution of the device and therefore enables an earlier flat band condition for the hole transporting side, leading to improved charge carrier injection. Recently, this phenomenon was studied with regard to different materials and degradation effects, however, so far the influence of dilution has not been investigated. In this paper we focus on dipolar doping of the hole transporting material 4,4-bis[N-(1-naphthyl)-N-phenylamino]-biphenyl (NPB) with the polar electron transporting material tris-(8-hydroxyquinolate) aluminum (Alq3). Impedance spectroscopy reveals that changes of the hole injection voltage do not scale in a simple linear fashion with the effective thickness of the doped layer. In fact, the measured interfacial polarization reaches a maximum value for a 1:1 blend. Taking the permanent dipole moment of Alq3 into account, an increasing degree of dipole alignment is found for decreasing Alq3 concentration. This observation can be explained by the competition between dipole-dipole interactions leading to dimerization and the driving force for vertical orientation of Alq3 dipoles at the surface of the NPB layer.

  15. A new dipolar potential for numerical simulations of polar fluids on the 4D hypersphere

    SciTech Connect

    Caillol, Jean-Michel; Trulsson, Martin

    2014-09-28

    We present a new method for Monte Carlo or Molecular Dynamics numerical simulations of three-dimensional polar fluids. The simulation cell is defined to be the surface of the northern hemisphere of a four-dimensional (hyper)sphere. The point dipoles are constrained to remain tangent to the sphere and their interactions are derived from the basic laws of electrostatics in this geometry. The dipole-dipole potential has two singularities which correspond to the following boundary conditions: when a dipole leaves the northern hemisphere at some point of the equator, it reappears at the antipodal point bearing the same dipole moment. We derive all the formal expressions needed to obtain the thermodynamic and structural properties of a polar liquid at thermal equilibrium in actual numerical simulation. We notably establish the expression of the static dielectric constant of the fluid as well as the behavior of the pair correlation at large distances. We report and discuss the results of extensive numerical Monte Carlo simulations for two reference states of a fluid of dipolar hard spheres and compare these results with previous methods with a special emphasis on finite size effects.

  16. Assembly-mediated interplay of dipolar interactions and surface spin disorder in colloidal maghemite nanoclusters

    NASA Astrophysics Data System (ADS)

    Kostopoulou, A.; Brintakis, K.; Vasilakaki, M.; Trohidou, K. N.; Douvalis, A. P.; Lascialfari, A.; Manna, L.; Lappas, A.

    2014-03-01

    Controlled assembly of single-crystal, colloidal maghemite nanoparticles is facilitated via a high-temperature polyol-based pathway. Structural characterization shows that size-tunable nanoclusters of 50 and 86 nm diameters (D), with high dispersibility in aqueous media, are composed of ~13 nm (d) crystallographically oriented nanoparticles. The interaction effects are examined against the increasing volume fraction, ϕ, of the inorganic magnetic phase that goes from individual colloidal nanoparticles (ϕ = 0.47) to clusters (ϕ = 0.72). The frozen-liquid dispersions of the latter exhibit weak ferrimagnetic behaviour at 300 K. Comparative Mössbauer spectroscopic studies imply that intra-cluster interactions come into play. New insight emerges from the clusters' temperature-dependent ac susceptibility that displays two maxima in χ''(T), with strong frequency dispersion. Scaling-law analysis together with the observed memory effects suggests that a superspin-glass state settles-in at TB ~ 160-200 K, while at lower-temperatures, surface spin-glass freezing is established at Tf ~ 40-70 K. In such nanoparticle-assembled systems, with increased ϕ, Monte Carlo simulations corroborate the role of the inter-particle dipolar interactions and that of the constituent nanoparticles' surface spin disorder in the emerging spin-glass dynamics.Controlled assembly of single-crystal, colloidal maghemite nanoparticles is facilitated via a high-temperature polyol-based pathway. Structural characterization shows that size-tunable nanoclusters of 50 and 86 nm diameters (D), with high dispersibility in aqueous media, are composed of ~13 nm (d) crystallographically oriented nanoparticles. The interaction effects are examined against the increasing volume fraction, ϕ, of the inorganic magnetic phase that goes from individual colloidal nanoparticles (ϕ = 0.47) to clusters (ϕ = 0.72). The frozen-liquid dispersions of the latter exhibit weak ferrimagnetic behaviour at 300 K. Comparative

  17. 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.

  18. Magnetostatic dipolar domain-wall pinning in chains of permalloy triangular rings.

    SciTech Connect

    Vavassori, P.; Bisero, D.; Bonanni, V.; Busato, A.; Grimsditch, M.; Lebecki, K. M.; Metlushko, V.; Ilic, B.; Materials Science Division; CIC nanoGUNE Consolider; Univ. di Ferrara; CNR-INFM National Research Centre; Polish Academy of Science; Univ. of Illinois at Chicago; Cornell Univ.

    2008-01-01

    In a combined experimental and numerical study, we investigated the details of the motion and pinning of domain walls in isolated and interacting permalloy triangular rings (side 2 {micro}m, width 250 nm, and thickness 25 nm). To induce interaction between the rings, they were arranged either in vertical chains with an apex of each triangle in proximity to the edge center of the triangle above it or in horizontal chains where the proximity is between the adjacent corners of the triangles. Using longitudinal and diffraction magneto-optic Kerr effects, magnetic force microscopy, and micromagnetic simulations, we determined the field dependence of the spin structure in the rings. In all cases the remnant state of each ring is an 'onion' state characterized by two domain walls - one head to head the other tail to tail - pinned at the apexes. In isolated rings the magnetization reversal occurs between two onion states via the formation of an intermediate vortex state, which arises from the motion and annihilation of the two domain walls. In the case of the horizontal chains the reversal mechanism is unchanged except that the dipolar interaction affects the field range in which the rings are in the vortex state. In the case of vertical chains an additional intermediate state is observed during reversal. The new state involves a domain wall pinned at the center of the edge that is in close proximity to the apex of its neighbor. We show that the domain-wall motion in this last case can be modeled by a triple potential well. Because the new state requires that a domain wall be pinned at the neighboring apex, our observations can be viewed as a very elementary form of magnetic logic.

  19. Magnetic dipolar coupling and collective effects for binary information codification in cost-effective logic devices

    NASA Astrophysics Data System (ADS)

    Chiolerio, Alessandro; Allia, Paolo; Graziano, Mariagrazia

    2012-09-01

    Physical limitations foreshadow the eventual end to traditional Complementary Metal Oxide Semiconductor (CMOS) scaling. Therefore, interest has turned to various materials and technologies aimed to succeed to traditional CMOS. Magnetic Quantum dot Cellular Automata (MQCA) are one of these technologies. Working MQCA arrays require very complex techniques and an excellent control on the geometry of the nanomagnets and on the quality of the magnetic thin film, thus limiting the possibility for MQCA of representing a definite solution to cost-effective, high density and low power consumption device demand. Counter-intuitively, moving towards bigger sizes and lighter technologies it is still possible to develop multi-state logic devices, as we demonstrated, whose main advantage is cost-effectiveness. Applications may be seen in low cost logic devices where integration and computational power are not the main issue, eventually using flexible substrates and taking advantage of the intrinsic mechanical toughness of systems where long range interactions do not need wirings. We realized cobalt micrometric MQCA arrays by means of Electron Beam Lithography, exploiting cost-effective processes such as lift-off and RF sputtering that usually are avoided due to their low control on array geometry and film roughness. Information relative to the magnetic configuration of MQCA elements including their eventual magnetic interactions was obtained from Magnetic Force Microscope (MFM) images, enhanced by means of a numerical procedure and presented in differential maps. We report the existence of bi-stable magnetic patterns, as detected by MFM while sampling the z-component of magnetic induction field, arising from dipolar inter-element magnetostatic coupling, able to store and propagate binary information. This is achieved despite the array quality and element magnetic state, which are low and multi-domain, respectively. We discuss in detail shape, inter-element spacing and dot profile

  20. Influence of dipolar interactions on the magnetic susceptibility spectra of ferrofluids.

    PubMed

    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)1744-683X10.1039/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 χ_{L}. The theory is in quantitative agreement with the simulation results as long as χ_{L}≲1. PMID:27415368

  1. Photocurrent enhancement in diketopyrrolopyrrole solar cells by manipulating dipolar anchoring terminals on alkyl-chain spacers.

    PubMed

    Tang, Ailing; Lu, Zhenhuan; Bai, Shuming; Huang, Jianhua; Chen, Yuxia; Shi, Qiang; Zhan, Chuanlang; Yao, Jiannian

    2014-03-01

    We chose DPP-BDT-DPP {DPP=diketopyrrolopyrrole, BDT=4,8-di-[2-(2-ethylhexyl)-thienyl]benzo[1,2-b:4,5-b']dithiophene} as a model backbone and varied the anchoring groups [C5 H11 , COOCH3 , and SiCH3 (OSiCH3 )2 ] terminated on the N-substituted alkyl-chain spacer of the DPP units to study the effect of anchoring terminals on the morphology of blend film and on the device performances of bulk heterojunction solar cells. By replacing the nonpolar C5 H11 anchoring terminal with the polar COOCH3 anchoring terminal leads to an enhancement in the short-circuit current density (Jsc ) (4.62 vs. 9.32 mA cm(-2) ), whereas the value of Jsc sharply decreases to 0.45 mA cm(-2) if the C5 H11 anchoring terminal is replaced by a SiCH3 (OSiCH3 )2 group. The changes in Jsc are associated with changes in the π-π stacking distance (3.39→3.34 Å vs. 3.39→3.45 Å) and the phase size (50→20 nm vs. 50→>250 nm) through alteration of the anchoring group from C5 H11 to COOCH3 versus from C5 H11 to SiCH3 (OSiCH3 )2 . Interestingly, the anchoring terminals bring about drastic changes in molecular orientations, which result in different out-of-plane hole transport. This is the first time this effect has been systemically demonstrated to improve photocurrent generation by manipulating the dipolar anchoring groups terminated on the alkyl-chain spacer.

  2. Low temperatures shear viscosity of a two-component dipolar Fermi gas with unequal population

    NASA Astrophysics Data System (ADS)

    Darsheshdar, E.; Yavari, H.; Zangeneh, Z.

    2016-07-01

    By using the Green's functions method and linear response theory we calculate the shear viscosity of a two-component dipolar Fermi gas with population imbalance (spin polarized) in the low temperatures limit. In the strong-coupling Bose-Einstein condensation (BEC) region where a Feshbach resonance gives rise to tightly bound dimer molecules, a spin-polarized Fermi superfluid reduces to a simple Bose-Fermi mixture of Bose-condensed dimers and the leftover unpaired fermions (atoms). The interactions between dimer-atom, dimer-dimer, and atom-atom take into account to the viscous relaxation time (τη) . By evaluating the self-energies in the ladder approximation we determine the relaxation times due to dimer-atom (τDA) , dimer-dimer (τcDD ,τdDD) , and atom-atom (τAA) interactions. We will show that relaxation rates due to these interactions τDA-1 ,τcDD-1, τdDD-1, and τAA-1 have T2, T4, e - E /kB T (E is the spectrum of the dimer atoms), and T 3 / 2 behavior respectively in the low temperature limit (T → 0) and consequently, the atom-atom interaction plays the dominant role in the shear viscosity in this rang of temperatures. For small polarization (τDA ,τAA ≫τcDD ,τdDD), the low temperatures shear viscosity is determined by contact interaction between dimers and the shear viscosity varies as T-5 which has the same behavior as the viscosity of other superfluid systems such as superfluid neutron stars, and liquid helium.

  3. The breakdown of dipolar magnetic field generation in planetary dynamo models (Invited)

    NASA Astrophysics Data System (ADS)

    Soderlund, K. M.; King, E. M.; Aurnou, J. M.

    2013-12-01

    Magnetic field measurements show that each dynamo in our solar system is distinct with field strengths that differ by many orders of magnitude and morphologies that range from titled dipoles to nearly axisymmetric dipole-quadrupoles to non-axisymmetric multipoles. The characteristics of stellar and astrophysical magnetic fields are similarly wide-ranging. Towards understanding the diversity of this dynamo zoo, we investigate the breakdown of dipole-dominated magnetic fields in a suite of planetary dynamo and otherwise identical non-magnetic simulations where the convective vigor and rotation rate are varied systematically. This survey considers models with Prandtl number Pr=1, magnetic Prandtl numbers up to Pm = 5, Ekman numbers in the range 1e-3 <= E <= 1e-5, and Rayleigh numbers from near onset to more than 1000 times critical. A sharp transition from dipolar to multipolar dynamos is observed in models with moderate to high Ekman numbers. This breakdown of the dipole happens when inertial and viscous forces become comparable and coincides with a degradation of helicity in the flow, which also occurs when no magnetic field is present. Large-scale poloidal magnetic fields in these models then appear to be generated by a viscously controlled, macro-scale alpha-effect. Our lowest Ekman number cases, however, suggest that the dynamics may be changing as the viscous force decreases. Since viscosity is expected to be negligible in planetary and stellar interiors, an extrapolation of our results implies that moderate Ekman number models may not simulate the physical mechanisms of magnetic field generation in these bodies correctly.

  4. 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 .

  5. A Tailward Moving Current Sheet Normal Magnetic Field Front Followed by an Earthward Moving Dipolarization Front

    NASA Technical Reports Server (NTRS)

    Hwang, K.-J.; Goldstein, M. L.; Moore, T. E.; Walsh, B. M.; Baishev, D. G.; Moiseyev, A. V.; Shevtsov, B. M.; Yumoto, K.

    2014-01-01

    A case study is presented using measurements from the Cluster spacecraft and ground-based magnetometers that show a substorm onset propagating from the inner to outer plasma sheet. On 3 October 2005, Cluster, traversing an ion-scale current sheet at the near-Earth plasma sheet, detected a sudden enhancement of Bz, which was immediately followed by a series of flux rope structures. Both the local Bz enhancement and flux ropes propagated tailward. Approximately 5 min later, another Bz enhancement, followed by a large density decrease, was observed to rapidly propagate earthward. Between the two Bz enhancements, a significant removal of magnetic flux occurred, possibly resulting from the tailward moving Bz enhancement and flux ropes. In our scenario, this flux removal caused the magnetotail to be globally stretched so that the thinnest sheet formed tailward of Cluster. The thinned current sheet facilitated magnetic reconnection that quickly evolved from plasma sheet to lobe and generated the later earthward moving dipolarization front (DF) followed by a reduction in density and entropy. Ground magnetograms located near the meridian of Cluster's magnetic foot points show two-step bay enhancements. The positive bay associated with the first Bz enhancement indicates that the substorm onset signatures propagated from the inner to the outer plasma sheet, consistent with the Cluster observation. The more intense bay features associated with the later DF are consistent with the earthward motion of the front. The event suggests that current disruption signatures that originated in the near-Earth current sheet propagated tailward, triggering or facilitating midtail reconnection, thereby preconditioning the magnetosphere for a later strong substorm enhancement.

  6. Experimental quantification of decoherence via the Loschmidt echo in a many spin system with scaled dipolar Hamiltonians

    SciTech Connect

    Buljubasich, Lisandro; Dente, Axel D.; Levstein, Patricia R.; Chattah, Ana K.; Pastawski, Horacio M.; Sánchez, Claudia M.

    2015-10-28

    We performed Loschmidt echo nuclear magnetic resonance experiments to study decoherence under a scaled dipolar Hamiltonian by means of a symmetrical time-reversal pulse sequence denominated Proportionally Refocused Loschmidt (PRL) echo. The many-spin system represented by the protons in polycrystalline adamantane evolves through two steps of evolution characterized by the secular part of the dipolar Hamiltonian, scaled down with a factor |k| and opposite signs. The scaling factor can be varied continuously from 0 to 1/2, giving access to a range of complexity in the dynamics. The experimental results for the Loschmidt echoes showed a spreading of the decay rates that correlate directly to the scaling factors |k|, giving evidence that the decoherence is partially governed by the coherent dynamics. The average Hamiltonian theory was applied to give an insight into the spin dynamics during the pulse sequence. The calculations were performed for every single radio frequency block in contrast to the most widely used form. The first order of the average Hamiltonian numerically computed for an 8-spin system showed decay rates that progressively decrease as the secular dipolar Hamiltonian becomes weaker. Notably, the first order Hamiltonian term neglected by conventional calculations yielded an explanation for the ordering of the experimental decoherence rates. However, there is a strong overall decoherence observed in the experiments which is not reflected by the theoretical results. The fact that the non-inverted terms do not account for this effect is a challenging topic. A number of experiments to further explore the relation of the complete Hamiltonian with this dominant decoherence rate are proposed.

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

    PubMed

    Chang, Zhiwei; Halle, Bertil

    2016-02-28

    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

  8. Experimental quantification of decoherence via the Loschmidt echo in a many spin system with scaled dipolar Hamiltonians

    NASA Astrophysics Data System (ADS)

    Buljubasich, Lisandro; Sánchez, Claudia M.; Dente, Axel D.; Levstein, Patricia R.; Chattah, Ana K.; Pastawski, Horacio M.

    2015-10-01

    We performed Loschmidt echo nuclear magnetic resonance experiments to study decoherence under a scaled dipolar Hamiltonian by means of a symmetrical time-reversal pulse sequence denominated Proportionally Refocused Loschmidt (PRL) echo. The many-spin system represented by the protons in polycrystalline adamantane evolves through two steps of evolution characterized by the secular part of the dipolar Hamiltonian, scaled down with a factor |k| and opposite signs. The scaling factor can be varied continuously from 0 to 1/2, giving access to a range of complexity in the dynamics. The experimental results for the Loschmidt echoes showed a spreading of the decay rates that correlate directly to the scaling factors |k|, giving evidence that the decoherence is partially governed by the coherent dynamics. The average Hamiltonian theory was applied to give an insight into the spin dynamics during the pulse sequence. The calculations were performed for every single radio frequency block in contrast to the most widely used form. The first order of the average Hamiltonian numerically computed for an 8-spin system showed decay rates that progressively decrease as the secular dipolar Hamiltonian becomes weaker. Notably, the first order Hamiltonian term neglected by conventional calculations yielded an explanation for the ordering of the experimental decoherence rates. However, there is a strong overall decoherence observed in the experiments which is not reflected by the theoretical results. The fact that the non-inverted terms do not account for this effect is a challenging topic. A number of experiments to further explore the relation of the complete Hamiltonian with this dominant decoherence rate are proposed.

  9. Experimental quantification of decoherence via the Loschmidt echo in a many spin system with scaled dipolar Hamiltonians.

    PubMed

    Buljubasich, Lisandro; Sánchez, Claudia M; Dente, Axel D; Levstein, Patricia R; Chattah, Ana K; Pastawski, Horacio M

    2015-10-28

    We performed Loschmidt echo nuclear magnetic resonance experiments to study decoherence under a scaled dipolar Hamiltonian by means of a symmetrical time-reversal pulse sequence denominated Proportionally Refocused Loschmidt (PRL) echo. The many-spin system represented by the protons in polycrystalline adamantane evolves through two steps of evolution characterized by the secular part of the dipolar Hamiltonian, scaled down with a factor |k| and opposite signs. The scaling factor can be varied continuously from 0 to 1/2, giving access to a range of complexity in the dynamics. The experimental results for the Loschmidt echoes showed a spreading of the decay rates that correlate directly to the scaling factors |k|, giving evidence that the decoherence is partially governed by the coherent dynamics. The average Hamiltonian theory was applied to give an insight into the spin dynamics during the pulse sequence. The calculations were performed for every single radio frequency block in contrast to the most widely used form. The first order of the average Hamiltonian numerically computed for an 8-spin system showed decay rates that progressively decrease as the secular dipolar Hamiltonian becomes weaker. Notably, the first order Hamiltonian term neglected by conventional calculations yielded an explanation for the ordering of the experimental decoherence rates. However, there is a strong overall decoherence observed in the experiments which is not reflected by the theoretical results. The fact that the non-inverted terms do not account for this effect is a challenging topic. A number of experiments to further explore the relation of the complete Hamiltonian with this dominant decoherence rate are proposed.

  10. Free energy landscapes of electron transfer system in dipolar environment below and above the rotational freezing temperature

    SciTech Connect

    Suzuki, Yohichi; Tanimura, Yoshitaka

    2007-02-07

    Electron transfer reaction in a polar solvent is modeled by a solute dipole surrounded by dipolar molecules with simple rotational dynamics posted on the three-dimensional distorted lattice sites. The interaction energy between the solute and solvent dipoles as a reaction coordinate is adopted and free energy landscapes are calculated by generating all possible states for a 26 dipolar system and by employing Wang-Landau sampling algorithm for a 92 dipolar system. For temperatures higher than the energy scale of dipole-dipole interactions, the free energy landscapes for the small reaction coordinate region have quadratic shape as predicted by Marcus [Rev. Mod. Phys. 65, 599 (1993)] whereas for the large reaction coordinate region, the landscapes exhibit a nonquadratic shape. When the temperature drops, small notched structures appear on the free energy profiles because of the frustrated interactions among dipoles. The formation of notched structure is analyzed with statistical approach and it is shown that the amplitude of notched structure depend upon the segment size of the reaction coordinate and is characterized by the interaction energy among the dipoles. Using simulated free energy landscapes, the authors calculate the reaction rates as a function of the energy gap for various temperatures. At high temperature, the reactions rates follow a bell shaped (inverted parabolic) energy gap law in the small energy gap regions, while it becomes steeper than the parabolic shape in a large energy gap regions due to the nonquadratic shape of the free energy landscape. The peak position of parabola also changes as the function of temperature. At low temperature, the profile of the reaction rates is no longer smooth because of the many local minima of the free energy landscape.

  11. Effect of Dipolar Cross Correlation on Model-Free Motional Parameters Obtained from 13C Relaxation in AX 2 Systems

    NASA Astrophysics Data System (ADS)

    Zhu, L. Y.; Kemple, M. D.; Landy, S. B.; Buckley, P.

    The importance of dipolar cross correlation in 13C relaxation studies of molecular motion in AX 2 spin systems (A = 13C, X = 1H) was examined. Several different models for the internal motion, including two restricted-diffusion, and two-site jump models, the Kinosita model [K. Kinosita, Jr., S. Kawato, and A. Ikegami, Biophys. J.20, 289 (1977)], and an axially symmetric model, were applied through the Lipari and Szabo [ J. Am. Chem. Soc.104, 4546 (1982)] formalism to calculate errors in 13C T1, obtained from inversion-recovery measurements under proton saturation, and NOE when dipolar cross correlation is neglected. Motional parameters in the Lipari and Szabo formalism, τ m, S2, and τ e, were then determined from T1 and NOE (including the errors) and compared with parameters initially used to simulate the relaxation data. The resulting differences in the motional parameters, while model dependent, were generally small for plausible motions. At larger S2 values (≥ 0.6), the errors in both τ m and S2 were <5%. Errors in τ e increased with S2 but were usually less than 10%. Larger errors in the parameters were found for an axially symmetric model, but with τ m fixed even those were >5% only for the τ m = 1 ns, τ e = 10 ps case. Furthermore, it was observed that deviations in a given motional parameter were mostly of the same sign, which allows bounds to be set on experimentally derived parameters. Relaxation data for the peptide melittin synthesized with gly enriched with 13C at the backbone cu position and with lys enriched with 13C in the side chain were examined in light of the results of the simulations. All in all, it appears that neglect of dipolar cross correlation in 13C T1 (With proton saturation) and NOE measurements in AX 2 systems does not lead to major problems in interpretation of the results in terms of molecular motion.

  12. Overcoming artificial broadening in Gd(3+)-Gd(3+) distance distributions arising from dipolar pseudo-secular terms in DEER experiments.

    PubMed

    Cohen, Marie Ramirez; Frydman, Veronica; Milko, Petr; Iron, Mark A; Abdelkader, Elwy H; Lee, Michael D; Swarbrick, James D; Raitsimring, Arnold; Otting, Gottfried; Graham, Bim; Feintuch, Akiva; Goldfarb, Daniella

    2016-05-14

    By providing accurate distance measurements between spin labels site-specifically attached to bio-macromolecules, double electron-electron resonance (DEER) spectroscopy provides a unique tool to probe the structural and conformational changes in these molecules. Gd(3+)-tags present an important family of spin-labels for such purposes, as they feature high chemical stability and high sensitivity in high-field DEER measurements. The high sensitivity of the Gd(3+) ion is associated with its high spin (S = 7/2) and small zero field splitting (ZFS), resulting in a narrow spectral width of its central transition at high fields. However, under the conditions of short distances and exceptionally small ZFS, the weak coupling approximation, which is essential for straightforward DEER data analysis, becomes invalid and the pseudo-secular terms of the dipolar Hamiltonian can no longer be ignored. This work further explores the effects of pseudo-secular terms on Gd(3+)-Gd(3+) DEER measurements using a specifically designed ruler molecule; a rigid bis-Gd(3+)-DOTA model compound with an expected Gd(3+)-Gd(3+) distance of 2.35 nm and a very narrow central transition at the W-band (95 GHz). We show that the DEER dipolar modulations are damped under the standard W-band DEER measurement conditions with a frequency separation, Δν, of 100 MHz between the pump and observe pulses. Consequently, the DEER spectrum deviates considerably from the expected Pake pattern. We show that the Pake pattern and the associated dipolar modulations can be restored with the aid of a dual mode cavity by increasing Δν from 100 MHz to 1.09 GHz, allowing for a straightforward measurement of a Gd(3+)-Gd(3+) distance of 2.35 nm. The increase in Δν increases the contribution of the |-5/2〉→|-3/2〉 and |-7/2〉→|-5/2〉 transitions to the signal at the expense of the |-3/2 〉→|-1/2〉 transition, thus minimizing the effect of dipolar pseudo-secular terms and restoring the validity of the weak

  13. Spin dynamics in the frozen state of the dipolar spin ice material Dy2Ti2O7

    NASA Astrophysics Data System (ADS)

    Yaraskavitch, L. R.; Revell, H. M.; Meng, S.; Ross, K. A.; Noad, H. M. L.; Dabkowska, H. A.; Gaulin, B. D.; Kycia, J. B.

    2012-01-01

    Low-temperature magnetic ac susceptibility measurements of single-crystal dipolar spin ice Dy2Ti2O7 are presented. The relaxation is found to exhibit thermally activated Arrhenius behavior with an activation energy of 9.79 K (˜9Jeff), which is not consistent with a simple scaling of 6Jeff, as previously found for Ho2Ti2O7. There are distinct quantifiable differences between Dy2Ti2O7 and Ho2Ti2O7 absorption spectra. The measured dynamics does not agree with simulations based on current magnetic monopole theory nor thermal relaxation measurements, but instead freezes out at a faster rate.

  14. Overcoming artificial broadening in Gd(3+)-Gd(3+) distance distributions arising from dipolar pseudo-secular terms in DEER experiments.

    PubMed

    Cohen, Marie Ramirez; Frydman, Veronica; Milko, Petr; Iron, Mark A; Abdelkader, Elwy H; Lee, Michael D; Swarbrick, James D; Raitsimring, Arnold; Otting, Gottfried; Graham, Bim; Feintuch, Akiva; Goldfarb, Daniella

    2016-05-14

    By providing accurate distance measurements between spin labels site-specifically attached to bio-macromolecules, double electron-electron resonance (DEER) spectroscopy provides a unique tool to probe the structural and conformational changes in these molecules. Gd(3+)-tags present an important family of spin-labels for such purposes, as they feature high chemical stability and high sensitivity in high-field DEER measurements. The high sensitivity of the Gd(3+) ion is associated with its high spin (S = 7/2) and small zero field splitting (ZFS), resulting in a narrow spectral width of its central transition at high fields. However, under the conditions of short distances and exceptionally small ZFS, the weak coupling approximation, which is essential for straightforward DEER data analysis, becomes invalid and the pseudo-secular terms of the dipolar Hamiltonian can no longer be ignored. This work further explores the effects of pseudo-secular terms on Gd(3+)-Gd(3+) DEER measurements using a specifically designed ruler molecule; a rigid bis-Gd(3+)-DOTA model compound with an expected Gd(3+)-Gd(3+) distance of 2.35 nm and a very narrow central transition at the W-band (95 GHz). We show that the DEER dipolar modulations are damped under the standard W-band DEER measurement conditions with a frequency separation, Δν, of 100 MHz between the pump and observe pulses. Consequently, the DEER spectrum deviates considerably from the expected Pake pattern. We show that the Pake pattern and the associated dipolar modulations can be restored with the aid of a dual mode cavity by increasing Δν from 100 MHz to 1.09 GHz, allowing for a straightforward measurement of a Gd(3+)-Gd(3+) distance of 2.35 nm. The increase in Δν increases the contribution of the |-5/2〉→|-3/2〉 and |-7/2〉→|-5/2〉 transitions to the signal at the expense of the |-3/2 〉→|-1/2〉 transition, thus minimizing the effect of dipolar pseudo-secular terms and restoring the validity of the weak

  15. Resonance activation and collision-induced-dissociation of ions using rectangular wave dipolar potentials in a digital ion trap mass spectrometer.

    PubMed

    Xu, Fuxing; Wang, Liang; Dai, Xinhua; Fang, Xiang; Ding, Chuan-Fan

    2014-04-01

    Collision-induced dissociation (CID) of ions by resonance activation in a quadrupole ion trap is usually accomplished by resonance exciting the ions to higher kinetic energy, whereby the high kinetic energy ions collide with a bath gas, such as helium or argon, inside the trap and dissociate to fragments. A new ion activation method using a well-defined rectangular wave dipolar potential formed by dividing down the trapping rectangular waveform is developed and examined herein. The mass-selected parent ions are resonance excited to high kinetic energies by simply changing the frequency of the rectangular wave dipolar potential and dissociation proceeds. A relationship between the ion mass and the activation waveform frequency is also identified and described. This highly efficient (CID) procedure can be realized by simply changing the waveform frequency of the dipolar potential, which could certainly simplify tandem mass spectrometry analysis methods.

  16. Dipolar effective interaction in a fluid of charged spheres near a dielectric plate.

    PubMed

    Aqua, J-N; Cornu, F

    2003-08-01

    Static correlations in a classical fluid of charged spheres at equilibrium are studied in the vicinity of an insulating wall characterized by its dielectric constant. It is well known that the deformations of screening clouds induced by the presence of the wall result into an effective f(alphaalpha('))(x,x('))/y(3) interaction in the pair distribution function between two charges e(alpha) and e(alpha(')) located at distances x and x(') from the wall and separated by a large distance y along the wall. We investigate the structure of f(alphaalpha('))(x,x(')). The method is based on systematic resummations in the Mayer diagrammatics, which are valid both in the bulk and in an inhomogeneous situation. The screened potential phi arising in the formalism happens to coincide with the linearized mean-field approximation for the immersion free energy of two external unit charges. Phi is shown to decay as a repulsive f(phi)(x,x('))/y(3) interaction, whatever the density profiles may be. f(phi)(x,x(')) takes a factorized dipolar structure f(phi)(x,x('))=D(phi)(x)D(phi)(x(')) for distances x and x(') larger than the maximum of the closest approach distances b(alpha)'s to the wall for every species alpha. Moreover, we devise a reorganization of resummed diagrammatics, which is adequate for the determination of the large-distance behavior of correlations, and we prove that, when all species have the same approach distance b to the wall, f(alphaalpha('))(x,x(');b)=D(alpha)(x)D(alpha('))(x(')). In this case, the leading tail of the effective electrostatic interaction between two like charges at the same distance x from a single wall is repulsive. Results are independent of charge magnitudes, of excluded-volume sphere sizes, and of the existence of a surface charge on the wall. It holds whether charges are concentrated at sphere centers or uniformly spread over their surfaces. Comparison is made with an experiment about dilute colloids where the linearized mean-field approximation

  17. 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

  18. Dipolarization fronts as earthward propagating flux ropes: A three-dimensional global hybrid simulation

    NASA Astrophysics Data System (ADS)

    Lu, S.; Lu, Q.; Lin, Y.; Wang, X.; Ge, Y.; Wang, R.; Zhou, M.; Fu, H.; Huang, C.; Wu, M.; Wang, S.

    2015-12-01

    Dipolarization fronts (DFs) as earthward propagating flux ropes (FRs) in the Earth's magnetotail are presented and investigated with a three-dimensional (3-D) global hybrid simulation for the first time. In the simulation, several small-scale earthward propagating FRs are found to be formed by multiple X-line reconnection in the near-tail. During their earthward propagation, the magnetic field Bz of the FRs becomes highly asymmetric due to the imbalance of the reconnection rates between the multiple X-lines. At the later stage, when the FRs approach the near-Earth dipole-like region, the anti-reconnection between the southward/negative Bz of the FRs and the northward geomagnetic field leads to the erosion of the southward magnetic flux of the FRs, which further aggravates the Bz asymmetry. Eventually, the FRs merge into the near-Earth region through the anti-reconnection. These earthward propagating FRs can fully reproduce the observational features of the DFs, e.g., a sharp enhancement of Bz preceded by a smaller amplitude Bz dip, an earthward flow enhancement, the presence of the electric field components in the normal and dawn-dusk directions, and ion energization. Our results show that the earthward propagating FRs can be used to explain the DFs observed in the magnetotail. The thickness of the DFs is on the order of several ion inertial lengths, and the electric field normal to the front is found to be dominated by the Hall physics. During the earthward propagation from the near-tail to the near-Earth region, the speed of the FR/DFs increases from ~150km/s to ~1000km/s. The FR/DFs can be tilted in the GSM xy plane with respect to the y (dawn-dusk) axis and only extend several RE in this direction. Moreover, the structure and evolution of the FRs/DFs are non-uniform in the dawn-dusk direction, which indicates that the DFs are essentially 3-D.

  19. Plane-strain crack problems in microstructured solids governed by dipolar gradient elasticity

    NASA Astrophysics Data System (ADS)

    Gourgiotis, P. A.; Georgiadis, H. G.

    2009-11-01

    The present study aims at determining the elastic stress and displacement fields around the tips of a finite-length crack in a microstructured solid under remotely applied plane-strain loading (mode I and II cases). The material microstructure is modeled through the Toupin-Mindlin generalized continuum theory of dipolar gradient elasticity. According to this theory, the strain-energy density assumes the form of a positive-definite function of the strain tensor (as in classical elasticity) and the gradient of the strain tensor (additional term). A simple but yet rigorous version of the theory is employed here by considering an isotropic linear expression of the elastic strain-energy density that involves only three material constants (the two Lamé constants and the so-called gradient coefficient). First, a near-tip asymptotic solution is obtained by the Knein-Williams technique. Then, we attack the complete boundary value problem in an effort to obtain a full-field solution. Hypersingular integral equations with a cubic singularity are formulated with the aid of the Fourier transform. These equations are solved by analytical considerations on Hadamard finite-part integrals and a numerical treatment. The results show significant departure from the predictions of standard fracture mechanics. In view of these results, it seems that the classical theory of elasticity is inadequate to analyze crack problems in microstructured materials. Indeed, the present results indicate that the stress distribution ahead of the crack tip exhibits a local maximum that is bounded. Therefore, this maximum value may serve as a measure of the critical stress level at which further advancement of the crack may occur. Also, in the vicinity of the crack tip, the crack-face displacement closes more smoothly as compared to the standard result and the strain field is bounded. Finally, the J-integral (energy release rate) in gradient elasticity was evaluated. A decrease of its value is noticed

  20. Monte Carlo simulations of the LiHoxY1-xF4 diluted dipolar magnet

    NASA Astrophysics Data System (ADS)

    Andresen, Juan Carlos; Schechter, Moshe; Katzgraber, Helmut G.

    2012-02-01

    Recent intriguing experimental results on LiHoxY1-xF4, a diluted dipolar magnet, along with new analytical insights, suggest that neither a mean-field treatment nor simulations using simplified versions of the underlying Hamiltonian adequately describe these materials. Not only does this imply that novel disordering mechanism might be present, it requires a detailed numerical analysis that incorporates all terms in the Hamiltonian. We present large-scale Monte Carlo simulations of the diluted dipolar magnet with competing interactions on a LiHo lattice with the inclusion of a random field term. For low concentrations of Ho atoms we reproduce the peculiar linear dependence of the transition temperature as a function of the random-field strength found in recent experimental results by Silevich et al. [Nature 448, 567 (2007)]. We then find a zero-temperature phase transition between the ferromagnetic and quasi-spin-glass phases, suggesting that it is the underlying spin-glass phase that dictates the above linear dependence of Tc on the random field. For large concentrations we recover the quadratic dependence of the critical temperature as a function of the random field strength.