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.
Rotational ratchets with dipolar interactions.
Jäger, Sebastian; Klapp, Sabine H L
2012-12-01
We report results from a computer simulation study on the rotational ratchet effect in systems of magnetic particles interacting via dipolar interactions. The ratchet effect consists of directed rotations of the particles in an oscillating magnetic field, which lacks a net rotating component. Our investigations are based on Brownian dynamics simulations of such many-particle systems. We investigate the influence of both the random and deterministic contributions to the equations of motion on the ratchet effect. As a main result, we show that dipolar interactions can have an enhancing as well as a dampening effect on the ratchet behavior depending on the dipolar coupling strength of the system under consideration. The enhancement is shown to be caused by an increase in the effective field on a particle generated by neighboring magnetic particles, while the dampening is due to restricted rotational motion in the effective field. Moreover, we find a nontrivial influence of the short-range, repulsive interaction between the particles.
Ion acceleration in dipolarization fronts
NASA Astrophysics Data System (ADS)
Birn, J.; Hesse, M.
2014-12-01
The electric field associated with flow bursts and dipolarization fronts has been shown to be an efficient mechanism for producing energetic ions and electrons. Using an MHD simulation of magnetotail reconnection, flow bursts and dipolarization, we investigate the acceleration of test particles to suprathermal energies. Particular emphasis of this presentation is on spatial, temporal, and angular variations of the modeled energetic ion fluxes. The test particle simulations reproduce characteristic features of observed injection events, such as a fast rise of energetic particle fluxes, limitations in energy, and demonstrate the large variability of energetic ion features.
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.
Studying electric fields in dipolarization fronts
NASA Astrophysics Data System (ADS)
Balcerak, Ernie
2014-11-01
In Earth's magnetotail, sharp increases in the magnetic field known as dipolarization fronts are associated with high-speed plasma flows that connect Earth's ionosphere via electric currents. Some aspects of these dipolarization fronts have puzzled scientists; in particular, the dip in magnetic field that occurs just ahead of the dipolarization front layer is not well understood. Sun et al. analyze observations made using the Cluster satellites to elucidate the details of electric fields associated with dipolarization fronts. The study shows that a type of electric current known as a Hall current dominates in the dipolarization front region and in the region where the magnetic field dips, but this current flows in opposite directions in these two regions.
Control of dipolar relaxation in external fields
NASA Astrophysics Data System (ADS)
Pasquiou, B.; Bismut, G.; Beaufils, Q.; Crubellier, A.; Maréchal, E.; Pedri, P.; Vernac, L.; Gorceix, O.; Laburthe-Tolra, B.
2010-04-01
We study dipolar relaxation in both ultracold thermal and Bose-condensed Cr atom gases. We show three different ways to control dipolar relaxation, making use of either a static magnetic field, an oscillatory magnetic field, or an optical lattice to reduce the dimensionality of the gas from three-dimensional (3D) to two-dimensional (2D). Although dipolar relaxation generally increases as a function of a static magnetic-field intensity, we find a range of nonzero magnetic-field intensities where dipolar relaxation is strongly reduced. We use this resonant reduction to accurately determine the S=6 scattering length of Cr atoms: a6=103±4a0. We compare this new measurement to another new determination of a6, which we perform by analyzing the precise spectroscopy of a Feshbach resonance in d-wave collisions, yielding a6=102.5±0.4a0. These two measurements provide, by far, the most precise determination of a6 to date. We then show that, although dipolar interactions are long-range interactions, dipolar relaxation only involves the incoming partial wave l=0 for large enough magnetic-field intensities, which has interesting consequences on the stability of dipolar Fermi gases. We then study ultracold Cr gases in a one-dimensional (1D) optical lattice resulting in a collection of independent 2D gases. We show that dipolar relaxation is modified when the atoms collide in reduced dimensionality at low magnetic-field intensities, and that the corresponding dipolar relaxation rate parameter is reduced by a factor up to 7 compared to the 3D case. Finally, we study dipolar relaxation in the presence of rf oscillating magnetic fields, and we show that both the output channel energy and the transition amplitude can be controlled by means of the rf frequency and Rabi frequency.
Reorientation of a dipolar monolayer and dipolar solvent.
Yi, Taeil; Lichter, Seth
2014-06-01
The reliable persistence of an adhered monolayer film on a substrate is critical for film function. The process by which monolayers degrade or disperse remains unclear. Our study investigates the properties and dynamics of a solute of dipolar molecules initially adhered as a monolayer on a substrate in a water-like Stockmayer solvent. We find that for a rigid solute, both the solute and solvent show qualitatively different dynamics than for a flexible solute and its solvent. For the rigid solute, spreading is hindered and solvent orientation is more pronounced. We formulate a simple kinetic model that shows qualitatively similar results to the molecular dynamics simulations of the time evolution of the monolayer. Simple kinetics of molecules on substrates is a starting point for understanding important industrial monolayer applications and complex interactions on membranes.
Dipolar excitation in the third stability region.
Konenkov, Nikolai V; Chernyak, Eugenii Ya; Stepanov, Vladimir A
2016-01-01
Dipole resonant excitation of ions creates instability bands which follow iso-β lines where β is the characteristic exponent (stability parameter). Instability bands are exited most effectively on the fundamental frequency π= βΩ/2. Here π is the angle resonance frequency of the dipolar voltage applied to x or y pair rods of the analyzer, and Ω is the angle frequency of the main drive voltage. Our goal is to study the mass peak shape in the third stability region with dipolar resonance excitation of the instability band with respect to the resonance frequency π and the dipolar potential amplitude. Numerical integration of the ion motion equations with a given ion source emittance is used to investigate peak shapes and ion transmission. We show that it is possible to vary the resolution power at any part of the third stability region. A change of the dipolar potential phase leads to a periodical variation of the resolution with period π.The most effective dipolar excitation in the y direction is along βy near the stability boundary. The mass peak shape is calculated also for a quadrupole with round rods. The best peak shape (small tails and high resolution) takes place for the rod set with r/r0=1.130. Dipolar excitation increases the transmission by approximately 5-10% at a given resolution.
Dipolar correlations in liquid water
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.
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.
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.
Second virial coefficients of dipolar hard spheres.
Philipse, Albert P; Kuipers, Bonny W M
2010-08-18
An asymptotic formula is reported for the second virial coefficient B(2) of a dipolar hard-sphere (DHS) fluid, in zero external field, for strongly coupled dipolar interactions. This simple formula, together with the one for the weak-coupling B(2), provides an accurate prediction of the second virial coefficient for a wide range of dipole moments, including those that are experimentally accessible in magnetite ferrofluids. The weak-coupling B(2) also yields an estimate of the magnetic moment minimally needed for isotropic gas-liquid phase-separation, if any, in the DHS fluid.
Nonlinear dielectric effect of dipolar fluids.
Szalai, I; Nagy, S; Dietrich, S
2009-10-21
The nonlinear dielectric effect for dipolar fluids is studied within the framework of the mean spherical approximation (MSA) of hard core dipolar Yukawa fluids. Based on earlier results for the electric field dependence of the polarization our analytical results show so-called normal saturation effects, which are in good agreement with corresponding NVT ensemble Monte Carlo (MC) simulation data. The linear and the nonlinear dielectric permittivities obtained from MC simulations are determined from the fluctuations of the total dipole moment of the system in the absence of an applied electric field. We compare the MSA based theoretical results with the corresponding Langevin and Debye-Weiss behaviors and with actual experimental data.
Concertedness of 1,3-Dipolar Cycloadditions.
ERIC Educational Resources Information Center
Haque, M. Serajul
1984-01-01
There are two conflicting views about the mechanism of 1,3-dipolar cycloadditions to multibonds. To reconcile these viewpoints a concerted, spin-paired, diradical mechanism, based on valence bond theory, is proposed. Each of these three mechanisms is discussed. (JN)
Toroidal dipolar responses in a planar metamaterial
NASA Astrophysics Data System (ADS)
Guo, Linyan; Li, Minhua; Yang, Helin; Huang, Xiaojun; Wu, Song
2014-10-01
Both the magnetic toroidal dipolar (MTD) response and electric toroidal dipolar (ETD) response have been achieved and studied in the microwave region by designing a feasible planar metamaterial. By changing the polarized direction of a normally incident wave, two different coupling modes are observed, and therefore MTD and ETD responses can be achieved accordingly. It is also confirmed by scattered powers for various multipole moments and field distributions that they dominate over other traditional multipole responses at 5.69 GHz and 11.69 GHz, respectively. In view of the design feasibility of planar metamaterial, these resonance-enhanced MTD and ETD responses could provide an avenue for various interesting phenomena associated with the elusive toroidal moments.
Dimensional crossover in dipolar magnetic layers
NASA Astrophysics Data System (ADS)
Bulenda, M.; Täuber, U. C.; Schwabl, F.
2000-01-01
We investigate the static critical behaviour of a uniaxial magnetic layer, with finite thickness L in one direction, yet infinitely extended in the remaining d dimensions. The magnetic dipole-dipole interaction is taken into account. We apply a variant of Wilson's momentum shell renormalization group approach to describe the crossover between the critical behaviour of the 3D Ising, 2D Ising, 3D uniaxial dipolar, and the 2D uniaxial dipolar universality classes. The corresponding renormalization group fixed points are in addition to different effective dimensionalities characterized by distinct analytic structures of the propagator, and are consequently associated with varying upper critical dimensions. While the limiting cases can be discussed by means of dimensional icons/Journals/Common/epsilon" ALT="epsilon" ALIGN="TOP"/> expansions with respect to the appropriate upper critical dimensions, respectively, the crossover features must be addressed in terms of the renormalization group flow trajectories at fixed dimensionality d .
Zero sound in dipolar Fermi gases
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.
Theory of substorm onset and dipolarization
NASA Astrophysics Data System (ADS)
Cheng, C. Z.; Zaharia, S.
2003-04-01
We present a theory of substorm onset and dipolarization. At the end of the substorm growth phase, the plasma pressure profile steepens and a thin current sheet is formed in the near-Earth plasma sheet around the local midnight with a finite radial and azimuthal domain. In the current sheet the plasma beta becomes about 50 or larger and magnetic field curvature is enhanced, and the kinetic ballooning instability (KBI) is excited with amplitude localized at the maximum plasma beta region. The KBI explains the low frequency (about 1 min period) instability observed by AMPTE/CCE with period on the order of 1 min is observed about 2-3 minutes before the substorm onset [Cheng and Lui, GRL, 1998]. The KBI is responsible for substorm onset because as it grows to a large amplitude with Δ B/B > 01, it causes an enhanced westward ion drift during the explosive growth phase that lasts about 30 sec. The KBI then excites higher frequency instabilities, and the plasma and magnetic field become strongly turbulent. The plasma transport in both radial and azimuthal direction caused by the turbulence relaxes the steep plasma pressure profile during the expansion phase. As the plasma pressure profile relaxes, the magnetic field configuration dipolarizes and returns to the pre-substorm more dipole-like geometry. Theories of current sheet formation, KBI mechanism and dipolarization will be presented along with numerical solutions of 3D magnetospheric structure.
NASA Astrophysics Data System (ADS)
Chen, Zhi-De; Liang, J.-Q.; Shen, Shun-Qing
2002-09-01
Renormalized tunnel splitting with a finite distribution in the biaxial spin model for molecular magnets is obtained by taking into account the dipolar interaction of enviromental spins. Oscillation of the resonant tunnel splitting with a transverse magnetic field along the hard axis is smeared by the finite distribution, which subsequently affects the quantum steps of the hysteresis curve evaluated in terms of the modified Landau-Zener model of spin flipping induced by the sweeping field. We conclude that the dipolar-dipolar interaction drives decoherence of quantum tunneling in the molecular magnet Fe8, which explains why the quenching points of tunnel splitting between odd and even resonant tunneling predicted theoretically were not observed experimentally.
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.
Influence of dipolar interactions on hyperthermia properties of ferromagnetic particles
NASA Astrophysics Data System (ADS)
Serantes, D.; Baldomir, D.; Martinez-Boubeta, C.; Simeonidis, K.; Angelakeris, M.; Natividad, E.; Castro, M.; Mediano, A.; Chen, D.-X.; Sanchez, A.; Balcells, LI.; Martínez, B.
2010-10-01
We show both experimental evidences and Monte Carlo modeling of the effects of interparticle dipolar interactions on the hysteresis losses. Results indicate that an increase in the intensity of dipolar interactions produce a decrease in the magnetic susceptibility and hysteresis losses, thus diminishing the hyperthermia output. These findings may have important clinical implications for cancer treatment.
Current system associated with small dipolarization fronts
NASA Astrophysics Data System (ADS)
Palin, Laurianne; Jacquey, Christian; Opgenoorth, Hermann; Connors, Martin; Sergeev, Victor; Sauvaud, Jean-André; Nakamura, Rumi; Reeves, Geoffrey D.; Singer, Howard; Angelopoulos, Vassilis; Turc, Lucile
2015-04-01
We present a case study of eight successive Plasma Sheet (PS) activations (usually referred to as « Bursty Bulk Flows » or « Dipolarisation Fronts ») associated with small individual BZGSM increases on 31 March 2009 (0200 - 0900 UT). This series of events happens during generally very quiet SW conditions, over a period of 7 hours preceding a substorm onset at 1230 UT. The amplitude of the dipolarizations increases with time. The low amplitude dipolarization fronts are associated with few (1 or 2) Rapid Flux Transfer events (Eh > 2mV/m), whereas the large amplitude ones engulf many more RFT events. All PS activations are associated with a small and localised current wedge(« wedgelet ») which seems to be the consequence of RFT arrival in the near tail. Ground magnetic perturbations affect a larger part of the contracted auroral oval for the events with more RTF event embedded (> 5). Dipolarisation Fronts with very low amplitude, a type usually not included in statistical studies, are of particular interest because we found them associated with clear wedgelets and particle injections at geosynchronous orbit. This exceptional dataset highlights the role of flow bursts in the magnetotail and brings up the question: are we in this case observing the smallest form of a substorm ?
Particle energization by a substorm dipolarization
NASA Astrophysics Data System (ADS)
Kabin, K.; Kalugin, G.; Donovan, E.; Spanswick, E.
2017-01-01
Magnetotail dipolarizations, often associated with substorms, produce significant energetic particle enhancements in the nighttime magnetosphere. In this paper, we apply our recently developed magnetotail dipolarization model to the problem of energizing electrons and ions. Our model is two-dimensional in the meridional plane and is characterized by the ability to precisely control the location of the transition from the dipole-like to tail-like magnetic fields. Both magnetic and electric fields are calculated, self-consistently, as the transition zone retreats farther into the tail and the area around the Earth occupied by dipole-like lines increases in size. These fields are used to calculate the motion of electrons and ions and changes in their energies. We consider the energizing effects of the fields restricted to ±15° and ±30° sectors around the midnight meridian, as well the axisymmetric case. Energies of some electrons increase by a factor of 25, which is more than enough to produce observable ionospheric signatures. Electrons are treated using the Guiding Center approximation, while protons and heavier particles generally require description based on the Lorentz equations.
Specific heat anomaly in relaxor ferroelectrics and dipolar glasses
NASA Astrophysics Data System (ADS)
Kutnjak, Z.; Pirc, R.
2017-03-01
The temperature and electric field dependence of the specific heat of relaxor ferroelectrics and dipolar glasses is investigated by means of a Landau-type theoretical model. It is shown that the dipolar specific heat, which is due to the randomly interacting polar nanoregions in relaxors and electric dipoles in dipolar glasses, is negative in a temperature region below the permittivity maximum. Also, it follows that for sufficiently low values of the field, where the induced polarization shows a quasi linear field dependence, the dipolar specific heat is proportional to the second temperature derivative of the dielectric polarization. This quantity can be extracted from the experimental temperature profile of the polarization, thus enabling an indirect experimental estimate of the negative specific heat, which is demonstrated for a set of representative relaxor and dipolar glass systems.
Orientational structure of dipolar hard-spherical colloids.
Alarcón-Waess, O; Diaz-Herrera, E; Gil-Villegas, A
2002-03-01
We have studied the orientational structure of a dipolar hard-spherical colloid on a homogeneous isotropic phase. The results are expressed as a function of the dipolar strength mu and volume fraction phi of dipolar colloids, and the refractive index of the scattering medium, n(s). The study is based on the self-correlation of the orientation density of the dipolar colloids, which is the static orientational structure factor [F(q)], where q is the wave vector. The importance of this quantity is that for very low phi values, it can be probed in a depolarized light scattering experiment. We have found that the structure of the suspension is better observed for high n(s). F(q) presents a different behavior for dilute and dense concentrations, it is also observed that the position of its minimum depends on phi. The response of a dipolar colloid due to its collective orientational behavior is also studied, using as an "ordering parameter" the static orientational structure factor at q=0[F(q=0)]. The study is performed for isochores as a function of mu. We have divided the analysis into five regimes, from very low to very high phi; values, i.e., phi=0.005 24, 0.1, 0.2, 0.35, and 0.45. Our analysis suggests that the dipolar colloid evolves to an orientationally ordered phase when the dipolar strength is increased, for all concentrations except for the lowest value case, phi=0.005 24. When phi=0.1 the dipolar colloid reaches the transition suddenly, whereas for the very low regime, the slope of F(q=0) first increases as if the dipolar colloid would evolve to an orientationally ordered phase; but near the transition the slope is inverted, resulting in a no global orientational order. Thus, our results suggest that in the very low regime a dipolar colloid may have a reentrant transition.
Self-replicating devices with dipolar colloids
NASA Astrophysics Data System (ADS)
Dempster, Joshua; Zhang, Rui; Olvera de La Cruz, Monica
2014-03-01
Ubiquitous in nature, self-replication on the nano-scale has been challenging to produce in the laboratory. Recent efforts with DNA tiles have shown great success in correctly replicating tile-sequence templates but require frequent manipulation by the experimenter. We propose a scheme for achieving self-replication with dipolar colloids. Dimers in these systems replicate exponentially over millisecond time scales with no intervention other than periodic energy pulses supplied by external fields. We develop a general formalism governing the rate of self-replication as a function of the interval between pulses. Results from kinetic Monte Carlo simulations show good agreement with the growth rates predicted by simple models of the replication process. We thank the Office of the Director of Defense Research and Engineering (DDR&E) and Air Force Office of Scientific Research (AFOSR) for their support under Award FA9550-10-1-0167.
Electric fields associated with dipolarization fronts
NASA Astrophysics Data System (ADS)
Sun, Wei-Jie; Fu, Suiyan; Parks, George K.; Pu, Zuyin; Zong, Qiu-Gang; Liu, Jiang; Yao, Zhonghua; Fu, Huishan; Shi, Quanqi
2014-07-01
Electric fields associated with dipolarization fronts (DFs) have been investigated in the magnetotail plasma sheet using Cluster observations. We have studied each term in the generalized Ohm's law using data obtained from the multispacecraft Cluster. Our results show that in the plasma flow frame, electric fields are directed normal to the DF in the magnetic dip region ahead of the DF as well as in the DF layer but in opposite directions. Case and statistical studies show that the Hall electric field is important while the electron pressure gradient term is much smaller. The ions decouple from the magnetic field in the DF layer and dip region (E + Vi×B ≠ 0), whereas electrons remain frozen-in (E + Ve×B=∇pe/nee).
Droplets of Trapped Quantum Dipolar Bosons
NASA Astrophysics Data System (ADS)
Macia, A.; Sánchez-Baena, J.; Boronat, J.; Mazzanti, F.
2016-11-01
Strongly interacting systems of dipolar bosons in three dimensions confined by harmonic traps are analyzed using the exact path integral ground-state Monte Carlo method. By adding a repulsive two-body potential, we find a narrow window of interaction parameters leading to stable ground-state configurations of droplets in a crystalline arrangement. We find that this effect is entirely due to the interaction present in the Hamiltonian without resorting to additional stabilizing mechanisms or specific three-body forces. We analyze the number of droplets formed in terms of the Hamiltonian parameters, relate them to the corresponding s -wave scattering length, and discuss a simple scaling model for the density profiles. Our results are in qualitative agreement with recent experiments showing a quantum Rosensweig instability in trapped Dy atoms.
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.
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.
Slow spin relaxation in dipolar spin ice.
NASA Astrophysics Data System (ADS)
Orendac, Martin; Sedlakova, Lucia; Orendacova, Alzbeta; Vrabel, Peter; Feher, Alexander; Pajerowski, Daniel M.; Cohen, Justin D.; Meisel, Mark W.; Shirai, Masae; Bramwell, Steven T.
2009-03-01
Spin relaxation in dipolar spin ice Dy2Ti2O7 and Ho2Ti2O7 was investigated using the magnetocaloric effect and susceptibility. The magnetocaloric behavior of Dy2Ti2O7 at temperatures where the orientation of spins is governed by ``ice rules`` (T < Tice) revealed thermally activated relaxation; however, the resulting temperature dependence of the relaxation time is more complicated than anticipated by a mere extrapolation of the corresponding high temperature data [1]. A susceptibility study of Ho2Ti2O7 was performed at T > Tice and in high magnetic fields, and the results suggest a slow relaxation of spins analogous to the behavior reported in a highly polarized cooperative paramagnet [2]. [1] J. Snyder et al., Phys. Rev. Lett. 91 (2003) 107201. [2] B. G. Ueland et al., Phys. Rev. Lett. 96 (2006) 027216.
Angular momentum conservation in dipolar energy transfer.
Guo, Dong; Knight, Troy E; McCusker, James K
2011-12-23
Conservation of angular momentum is a familiar tenet in science but has seldom been invoked to understand (or predict) chemical processes. We have developed a general formalism based on Wigner's original ideas concerning angular momentum conservation to interpret the photo-induced reactivity of two molecular donor-acceptor assemblies with physical properties synthetically tailored to facilitate intramolecular energy transfer. Steady-state and time-resolved spectroscopic data establishing excited-state energy transfer from a rhenium(I)-based charge-transfer state to a chromium(III) acceptor can be fully accounted for by Förster theory, whereas the corresponding cobalt(III) adduct does not undergo an analogous reaction despite having a larger cross-section for dipolar coupling. Because this pronounced difference in reactivity is easily explained within the context of the angular momentum conservation model, this relatively simple construct may provide a means for systematizing a broad range of chemical reactions.
Heating and acceleration of charged particles during magnetic dipolarizations
NASA Astrophysics Data System (ADS)
Grigorenko, E. E.; Kronberg, E. A.; Daly, P. W.
2017-01-01
In this paper, we analyzed the thermal and energy characteristics of the plasma components observed during the magnetic dipolarizations in the near tail by the Cluster satellites. It was previously found that the first dipolarization the ratio of proton and electron temperatures ( T p/ T e) was 6-7. At the time of the observation of the first dipolarization front T p/ T e decreases by up to 3-4. The minimum value T p/ T e ( 2.0) is observed behind the front during the turbulent dipolarization phase. Decreases in T p/ T e observed at this time are associated with an increase in T e, whereas the proton temperature either decreases or remains unchanged. Decreases of the value T p/ T e during the magnetic dipolarizations coincide with increase in wave activity in the wide frequency band up to electron gyrofrequency f ce. High-frequency modes can resonantly interact with electrons causing their heating. The acceleration of ions with different masses up to energies of several hundred kiloelectron-volts is also observed during dipolarizations. In this case, the index of the energy spectrum decreases (a fraction of energetic ions increases) during the enhancement of low-frequency electromagnetic fluctuations at frequencies that correspond to the gyrofrequency of this ion component. Thus, we can conclude that the processes of the interaction between waves and particles play an important role in increasing the energy of plasma particles during magnetic dipolarizations.
Bose-Einstein condensation of dipolar excitons in quantum wells
NASA Astrophysics Data System (ADS)
Timofeev, V. B.; Gorbunov, A. V.
2009-02-01
The experiments on Bose-Einstein condensation (BEC) of dipolar (spatially-indirect) excitons in the lateral traps in GaAs/AlGaAs Schottky-diode heterostructures with double and single quantum wells are presented. The condensed part of dipolar excitons under detection in the far zone is placed in k-space in the range which is almost two orders of magnitude less than thermal exciton wave vector. BEC occurs spontaneously in a reservoir of thermalized excitons. Luminescence images of Bose-condensate of dipolar excitons exhibit along perimeter of circular trap axially symmetrical spatial structures of equidistant bright spots which strongly depend on excitation power and temperature. By means of two-beam interference experiments with the use of cw and pulsed photoexcitation it was found that the state of dipolar exciton Bose-condensate is spatially coherent and the whole patterned luminescence configuration in real space is described by a common wave function.
Artificial kagome arrays of nanomagnets: a frozen dipolar spin ice.
Rougemaille, N; Montaigne, F; Canals, B; Duluard, A; Lacour, D; Hehn, M; Belkhou, R; Fruchart, O; El Moussaoui, S; Bendounan, A; Maccherozzi, F
2011-02-04
Magnetic frustration effects in artificial kagome arrays of nanomagnets are investigated using x-ray photoemission electron microscopy and Monte Carlo simulations. Spin configurations of demagnetized networks reveal unambiguous signatures of long range, dipolar interaction between the nanomagnets. As soon as the system enters the spin ice manifold, the kagome dipolar spin ice model captures the observed physics, while the short range kagome spin ice model fails.
Dipolar dark matter with massive bigravity
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.
Dipolar dark matter with massive bigravity
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.
Self-replication with magnetic dipolar colloids.
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.
Pal, Tamisra; Biswas, Ranjit
2014-10-28
A semi-molecular theory for studying composition dependent Stokes shift dynamics of a dipolar solute in binary mixtures of (non-dipolar ionic liquid + common dipolar solvent) is developed here. The theory provides microscopic expressions for solvation response functions in terms of static and dynamic structure factors of the mixture components and solute-solvent static correlations. In addition, the theory provides a framework for examining the interrelationship between the time dependent solvation response in and frequency dependent dielectric relaxation of a binary mixture containing electrolyte. Subsequently, the theory has been applied to predict ionic liquid (IL) mole fraction dependent dynamic Stokes shift magnitude and solvation energy relaxation for a dipolar solute, C153, in binary mixtures of an ionic liquid, trihexyltetradecylphosphonium chloride ([P(14,666)][Cl]) with a common dipolar solvent, methanol (MeOH). In the absence of suitable experimental data, necessary input parameters have been obtained from approximate methods. Dynamic shifts calculated for these mixtures exhibit a linear increase with IL mole fraction for the most part of the mixture composition, stressing the importance of solute-IL dipole-ion interaction. Average solvation rates, on the other hand, show a nonlinear IL mole fraction dependence which is qualitatively similar to what has been observed for such binary mixtures with imidazolium (dipolar) ILs. These predictions should be re-examined in suitable experiments.
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
OBSERVATION OF DIPOLAR FERROMAGNETISM BY TEM TECHNIQUES.
BELEGGIA, M.ZHU,Y.TANDON,S.ET AL.
2004-08-01
Magnetostatic interactions play a central role in determining the magnetic response of an array of patterned magnetic elements or magnetized nanoparticles of given shape. The Fourier space approach recently introduced for the analytical computation of the demagnetizing tensor, field and energy for particles of arbitrary shape [1], has been recently extended to cover interactions between elements [2]. The main achievement has been the definition of a generalized dipole-dipole interaction for cylindrical objects, which takes into account the influence of shape anisotropy without resorting to,any kind of approximations [3]. Once the interaction energy is available, it becomes possible to evaluate the minimum energy state of the system for a given set of external parameters (such as applied field, aspect ratio, distance between elements). It turns out that, below a critical combination of aspect ratios and distances, the system undergoes a phase transition, changing abruptly from a closure domain state, with zero net magnetization, to a dipolar ferromagnetic state with a net magnetization which depends on the interaction strength between the elements. In order to observe this phenomenon by TEM, it is necessary to estimate the feasibility of the experiment by a series of simulations. Figure 1 shows the electron optical phase shifts for the system of three weakly (a-c) and strongly (d) interacting disks. The elements have a radius of 50 nm, a thickness of 5 nm (aspect ratio 1/20), and are uniformly magnetized at 2 T. By comparing Fig.1 (c) and (d), it can be seen that the fingerprint of the transition is the presence of fringing fields around the elements, revealed by the cosine fringes which resemble a dipole-like field in (d). When the system is in the closure-domain state, as in (a-c), no fringing field can be observed on a large scale. Figure 2 shows a set of Fresnel images, calculated for the same configurations as in Fig.1. As the Fresnel technique is scarcely
Cluster Observations of Multiple Dipolarization Fronts
NASA Technical Reports Server (NTRS)
Hwang, Kyoung-Joo; Goldstein, Melvyn L.; Lee, Ensang; Pickett, Jolene S.
2011-01-01
We present Cluster observations of a series of dipolarization fronts (DF 1 to 6) at the central current sheet in Earth's magnetotail. The velocities of fast earthward flow following behind each DF 1-3, are comparable to the Alfven velocity, indicating that the flow bursts might have been generated by bursty reconnection that occurred tailward of the spacecraft. Based on multi-spacecraft timing analysis, DF normals are found to propagate mainly earthward at $160-335$ km/s with a thickness of 900-1500 km, which corresponds to the ion inertial length or gyroradius scale. Each DF is followed by significant fluctuations in the $x$ and $y$ components of the magnetic field whose peaks are found 1-2 minutes after the DF passage. These $(B_{x},B_{y} )$-fluctuations propagate dawnward (mainly) and earthward. Strongly enhanced field-aligned beams are observed coincidently with $(B_{x},B_{y})$ fluctuations, while an enhancement of cross-tail currents is associated with the DFs. From the observed pressure imbalance and flux-tube entropy changes between the two regions separated by the DF, we speculate that interchange instability destabilizes the DFs and causes the deformation of the mid-tail magnetic topology. This process generates significant field-aligned currents, and might power the auroral brightening in the ionosphere. However, this event is neither associated with the main substorm auroral breakup nor the poleward expansion, which might indicate that the observed multiple DFs have been dissipated before they reach the inner plasma sheet boundary.
Cluster Observations of Multiple Dipolarization Fronts
NASA Technical Reports Server (NTRS)
Hwang, K.-J.; Goldstein, M. L.; Lee, E.; Pickett, J. S.
2011-01-01
We present Cluster observations of a series of dipolarization fronts (DF 1 to 6) at the central current sheet in Earth's magnetotail. The velocities of fast earthward flow following behind each DF 1.3 are comparable to the Alfven velocity, indicating that the flow bursts might have been generated by bursty reconnection that occurred tailward of the spacecraft. Based on multispacecraft timing analysis, DF normals are found to propagate mainly earthward at 160.335 km/s with a thickness of 900-1500 km, which corresponds to the ion inertial length or gyroradius scale. Each DF is followed by significant fluctuations in the x and y components of the magnetic field whose peaks are found 1.2 min after the DF passage. These (B(sub x), B(sub y)) fluctuations propagate dawnward (mainly) and earthward. Strongly enhanced field-aligned beams are observed coincidently with (B(sub x), B(sub y)) fluctuations, while an enhancement of cross-tail currents is associated with the DFs. From the observed pressure imbalance and flux tube entropy changes between the two regions separated by the DF, we speculate that interchange instability destabilizes the DFs and causes the deformation of the midtail magnetic topology. This process generates significant field-aligned currents and might power the auroral brightening in the ionosphere. However, this event is associated with neither the main substorm auroral breakup nor the poleward expansion, which might indicate that the observed multiple DFs have been dissipated before they reach the inner plasma sheet boundary.
Jet Dipolarity: Top Tagging with Color Flow
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.
Characterization of slow conformational dynamics in solids: dipolar CODEX.
Li, Wenbo; McDermott, Ann E
2009-09-01
A solid state NMR experiment is introduced for probing relatively slow conformational exchange, based on dephasing and refocusing dipolar couplings. The method is closely related to the previously described Centerband-Only Detection of Exchange or CODEX experiment. The use of dipolar couplings for this application is advantageous because their values are known a priori from molecular structures, and their orientations and reorientations relate in a simple way to molecular geometry and motion. Furthermore the use of dipolar couplings in conjunction with selective isotopic enrichment schemes is consistent with selection for unique sites in complex biopolymers. We used this experiment to probe the correlation time for the motion of (13)C, (15)N enriched urea molecules within their crystalline lattice.
Second virial coefficient for the dipolar hard sphere fluid.
Henderson, Douglas
2011-07-28
The dipolar hard sphere fluid is a useful model for a polar fluid. Some years ago, the second virial coefficient, B(2), of this fluid was obtained as a series expansion in the inverse temperature or (dipole strength) by Keesom. Little work on this problem seems to have been done since that time. Using a result of Chan and Henderson for the spherical average of the Boltzmann factor of this fluid, more complete results are obtained for B(2). The more complete results are more negative than the Keesom series, as one would expect, but his expansion is remarkably accurate. This method can be used to obtain the second virial coefficient of the dipolar Lennard-Jones (Stockmayer) or dipolar Yukawa fluids.
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.
Nonlocal and nonlinear electrostatics of a dipolar Coulomb fluid.
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.
Engineering bright matter-wave solitons of dipolar condensates
NASA Astrophysics Data System (ADS)
Edmonds, M. J.; Bland, T.; Doran, R.; Parker, N. G.
2017-02-01
We present a comprehensive analysis of the form and interaction of dipolar bright solitons across the full parameter space afforded by dipolar Bose–Einstein condensates, revealing the rich behavior introduced by the non-local nonlinearity. Working within an effective one-dimensional description, we map out the existence of the soliton solutions and show three collisional regimes: free collisions, bound state formation and soliton fusion. Finally, we examine the solitons in their full three-dimensional form through a variational approach; along with regimes of instability to collapse and runaway expansion, we identify regimes of stability which are accessible to current experiments.
Anisotropic Expansion of a Thermal Dipolar Bose Gas.
Tang, Y; Sykes, A G; Burdick, N Q; DiSciacca, J M; Petrov, D S; Lev, B L
2016-10-07
We report on the anisotropic expansion of ultracold bosonic dysprosium gases at temperatures above quantum degeneracy and develop a quantitative theory to describe this behavior. The theory expresses the postexpansion aspect ratio in terms of temperature and microscopic collisional properties by incorporating Hartree-Fock mean-field interactions, hydrodynamic effects, and Bose-enhancement factors. Our results extend the utility of expansion imaging by providing accurate thermometry for dipolar thermal Bose gases. Furthermore, we present a simple method to determine scattering lengths in dipolar gases, including near a Feshbach resonance, through observation of thermal gas expansion.
Infrared Behavior of Dipolar Bose Systems at Low Temperatures
NASA Astrophysics Data System (ADS)
Pastukhov, Volodymyr
2017-01-01
We rigorously discuss the infrared behavior of the uniform three-dimensional dipolar Bose systems. In particular, it is shown that low-temperature physics of the system is controlled by two parameters, namely isothermal compressibility and intensity of the dipole-dipole interaction. By using a hydrodynamic approach, we calculate the spectrum and damping of low-lying excitations and analyze the infrared behavior of the one-particle Green's function. The low-temperature corrections to the anisotropic superfluid density as well as condensate depletion are found. Additionally, we derive equations of the two-fluid hydrodynamics for dipolar Bose systems and calculate velocities of first and second sound.
Evanescent Wave-Assisted Symmetry Breaking of Gold Dipolar Nanoantennas
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
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.
Strongly correlated quasi-two-dimensional dipolar fermions
NASA Astrophysics Data System (ADS)
Babadi, Mehrtash; Skinner, Brian; Fogler, Michael; Demler, Eugene
2013-03-01
We study the collective oscillations of strongly correlated quasi-two-dimensional dipolar fermions at zero temperature. The correlation energy of the quasi-two-dimensional gas is obtained using a novel variational method based on the fixed-node diffusion Monte-Carlo analysis of strictly two-dimensional dipolar Fermi gas. As an application, we predict the dependence of the Wigner crystal transition point on the thickness of the layer, as well as the shift of the monopole oscillation frequency in harmonic traps.
Anisotropic superfluidity in a dipolar Bose gas
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
Fermionized Dipolar Bosons Trapped in a Harmonic Trap
NASA Astrophysics Data System (ADS)
Kościk, Przemysław
2017-03-01
We explore entanglement properties of systems of identical dipolar bosons confined in a 1D harmonic trap by using explicitly correlated Jastrow-type wavefunctions. Results for the linear entropy in dependence on the dimensionless coupling and the number of particles are provided and discussed.
Two-dimensional dipolar scattering with a tilt
Ticknor, Christopher
2011-09-15
We study two-body dipolar scattering in two dimensions with a tilted polarization axis. This tilt reintroduces the anisotropic interaction in a controllable manner. As a function of this polarization angle, we present the scattering rates in both the threshold and semiclassical regimes. Additionally, we study the properties of the molecular bound states as a function of the polarization angle.
Non-dipolar Wilson Links for Parton Densities
NASA Astrophysics Data System (ADS)
Li, Hsiang-nan
We propose a new definition of a transverse-momentum-dependent wave function with simpler soft subtraction. The unsubtracted wave function involves two pieces of non-light-like Wilson links oriented in different directions, so that the rapidity singularity appearing in usual kT factorization is regularized, and the pinched singularity from Wilson-link self-energy corrections is alleviated to a logarithmic one. We show explicitly at one-loop level that the simpler definition with the non-dipolar Wilson links exhibits the same infrared behavior as the one with the dipolar Wilson links. The non-dipolar Wilson links are also introduced to the quasi-parton distribution function (QPDF) with an equal-time correlator in the large momentum limit, which can remove the involved linear divergence, and allow perturbative matching to the standard light-cone parton distribution function. The latter can then be extracted reliably from Euclidean lattice data for the QPDF with the non-dipolar Wilson links.
Stability of solid phases in the dipolar hard sphere system
NASA Astrophysics Data System (ADS)
Levesque, D.; Weis, J.-J.
2011-12-01
Free energy differences between solid phases of dipolar hard spheres are estimated by Monte Carlo simulation using a nonequilibrium work method. These calculations allow one to determine which of the considered phases has the minimum free energy. The phase diagram which we obtain is confirmed by simulations in the isothermal-isobaric ensemble over a wide region of the density and temperature domain.
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).
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.
Tuning ultracold collisions of excited rotational dipolar molecules
NASA Astrophysics Data System (ADS)
Quéméner, Goulven
2015-05-01
Ultracold molecular dipolar gases often suffer from losses due to chemical reactions (or eventual sticky collisions for non-reactive molecules). Loss suppression for both bosonic and fermionic dipolar species can be obtained in a one-dimensional optical lattice but this requires usually strong confinements to get into a pure two-dimensional collision regime. An alternative way can be found without confinement using rotationally excited molecules. In this talk I will explore the ultracold collisions of rotationally excited dipolar molecules in free space. I will focus on electric dipolar molecules of KRb and electric and magnetic dipolar molecules of RbSr. I will show that we can sharply tune the elastic, inelastic and reactive rate coefficients of lossy molecular collisions when a second rotationally excited colliding channel crosses the threshold of the initial colliding channel, with the help of an applied electric field. We can increase or decrease the loss processes whether the second channel is above or below the initial channel. This could lead to favorable conditions for evaporative cooling. Additionally, we include the electric quadrupole and octopole moment to the dipole moment in the expression of the long-range multipole-multipole interaction. For processes mediated by the incident channel like elastic and loss collisions, the inclusion of quadrupole and octopole moments are not important at ultralow energies. They are important for processes mediated by state-to-state transitions like inelastic collisions. I acknowledge the financial support of the COPOMOL project (ANR-13-IS04-0004) from Agence Nationale de la Recherche.
Vidadala, Srinivasa Rao; Golz, Christopher; Strohmann, Carsten; Daniliuc, Constantin-G; Waldmann, Herbert
2015-01-07
Enantioselective catalytic intermolecular 1,3-dipolar cycloadditions are powerful methods for the synthesis of heterocycles. In contrast, intramolecular enantioselective 1,3-dipolar cycloadditions are virtually unexplored. A highly enantioselective synthesis of natural-product-inspired pyrrolidino-piperidines by means of an intramolecular 1,3-dipolar cycloaddition with azomethine ylides is now reported. The method has a wide scope and yields the desired cycloadducts with four tertiary stereogenic centers with up to 99% ee. Combining the enantioselective catalytic intramolecular 1,3-dipolar cycloaddition with a subsequent diastereoselective intermolecular 1,3-dipolar cycloaddition yielded complex piperidino-pyrrolizidines with very high stereoselectivity in a one-pot tandem reaction.
Manipulating microwaves with magnetic-dipolar-mode vortices
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.
Triplet superfluidity on a triangular ladder with dipolar fermions
NASA Astrophysics Data System (ADS)
Pandey, Bradraj; Pati, Swapan K.
2017-02-01
Motivated by recent experimental progress in the field of dipolar-Fermi gases, we investigate the quantum phases of dipolar fermions on a triangular ladder at half filling. Using density matrix renormalization group method, in the presence of onsite repulsion and intersite attractive interaction, we find an exotic spin-triplet superfluid phase in addition to the usual spin-density and charge-density waves. We examine the stability of the spin-triplet superfluid phase by varying hopping along the rungs of the triangle. The possibility of fermionic supersolidity has also been discussed, by considering three-body interaction in the Hamiltonian. We also study the effect of spin-dependent hopping on the stability of the spin-triplet superfluid phase.
Magnetization plateaus of dipolar spin ice on kagome lattice
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.
Noncommutative geometry and the primordial dipolar imaginary power spectrum
NASA Astrophysics Data System (ADS)
Jain, Pankaj; Rath, Pranati K.
2015-03-01
We argue that noncommutative space-times lead to an anisotropic dipolar imaginary primordial power spectrum. We define a new product rule, which allows us to consistently extract the power spectrum in such space-times. The precise nature of the power spectrum depends on the model of noncommutative geometry. We assume a simple dipolar model which has a power dependence on the wave number, , with a spectral index, . We show that such a spectrum provides a good description of the observed dipole modulation in the cosmic microwave background radiation (CMBR) data with . We extract the parameters of this model from the data. The dipole modulation is related to the observed hemispherical anisotropy in the CMBR data, which might represent the first signature of quantum gravity.
Spinor condensate of {sup 87}Rb as a dipolar gas
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.
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.
Modulated magnetization depth profile in dipolarly coupled magnetic multilayers
Bedanta, S.; Petracic, O.; Kleemann, W.; Kentzinger, E.; Ruecker, U.; Brueckel, Th.; Paul, A.; Cardoso, S.; Freitas, P. P.
2006-08-01
Polarized neutron reflectivity (PNR) and magnetometry studies have been performed on the metal-insulator multilayer [Co{sub 80}Fe{sub 20}(1.6 nm)/Al{sub 2}O{sub 3}(3 nm)]{sub 9} which exhibits dominant dipolar coupling between the ferromagnetic layers. Our PNR measurements at the coercive field reveal a novel and unexpected magnetization state of the sample, exhibiting an oscillating magnetization depth profile from CoFe layer to CoFe layer with a period of five bilayers along the multilayer stack. With the help of micromagnetic simulations we demonstrate that competition between long- and short-ranged dipolar interactions apparently gives rise to this unprecedented phenomenon.
Properties of strongly dipolar Bose gases beyond the Born approximation
NASA Astrophysics Data System (ADS)
Ołdziejewski, Rafał; Jachymski, Krzysztof
2016-12-01
Strongly dipolar Bose gases can form liquid droplets stabilized by quantum fluctuations. In a theoretical description of this phenomenon, the low-energy scattering amplitude is utilized as an effective potential. We show that for magnetic atoms, corrections with respect to the Born approximation arise, and we derive a modified pseudopotential using a realistic interaction model. We discuss the resulting changes in collective mode frequencies and droplet stability diagrams. Our results are relevant to recent experiments with erbium and dysprosium atoms.
Random acoustic metamaterial with a subwavelength dipolar resonance.
Duranteau, Mickaël; Valier-Brasier, Tony; Conoir, Jean-Marc; Wunenburger, Régis
2016-06-01
The effective velocity and attenuation of longitudinal waves through random dispersions of rigid, tungsten-carbide beads in an elastic matrix made of epoxy resin in the range of beads volume fraction 2%-10% are determined experimentally. The multiple scattering model proposed by Luppé, Conoir, and Norris [J. Acoust. Soc. Am. 131(2), 1113-1120 (2012)], which fully takes into account the elastic nature of the matrix and the associated mode conversions, accurately describes the measurements. Theoretical calculations show that the rigid particles display a local, dipolar resonance which shares several features with Minnaert resonance of bubbly liquids and with the dipolar resonance of core-shell particles. Moreover, for the samples under study, the main cause of smoothing of the dipolar resonance of the scatterers and the associated variations of the effective mass density of the dispersions is elastic relaxation, i.e., the finite time required for the shear stresses associated to the translational motion of the scatterers to propagate through the matrix. It is shown that its influence is governed solely by the value of the particle to matrix mass density contrast.
Anisotropic dynamics of dipolar liquids in narrow slit pores.
Froltsov, Vladimir A; Klapp, Sabine H L
2006-04-07
We report molecular dynamics simulation results for Stockmayer fluids confined to narrow slitlike pores with structureless, nonconducting walls. The translational and rotational dynamics of the dipolar particles have been investigated by calculating autocorrelation functions, diffusion coefficients, and relaxation times for various pore widths (five or less particle diameters) and directions parallel and perpendicular to the walls. The dynamic properties of the confined systems are compared to bulk properties, where corresponding bulk and pore states at the same temperature and chemical potential are determined in parallel grand canonical Monte Carlo simulations. We find that the dynamic behavior inside the pore depends on the distance from the walls and can be strongly anisotropic even in globally isotropic systems. This concerns especially the particles in the surface layers close to the walls, where the single particle and collective dipolar relaxation resemble that of true two-dimensional dipolar fluids with different in-plane and out-of-plane relaxations. On the other hand, bulklike relaxation is observed in the pore center of sufficiently wide pores.
Phase diagram of split 2D dipolar spin ice
NASA Astrophysics Data System (ADS)
Roscilde, Tommaso; Henry, Louis-Paul
2013-03-01
Long-ranged dipolar interactions, which are very natural in artificial square-lattice spin ice, can mask some of the most relevant aspects of spin-ice physics, as they remove the extensive degeneracy of the ground state manifold to give a unique ground state, and they bind monopole pairs into localized spin flips. Following an earlier idea of G. Möller and R. Moessner [Phys. Rev. Lett. 96, 237202 (2006)] we investigate how adding a third direction to square ice allows to recover fundamental traits of spin-ice physics even in the presence of dipolar interactions. Using Monte Carlo simulations based on a generalized loop algorithm, we explore the phase diagram of square dipolar spin ice in which horizontal and vertical dipoles are spatially separated in a third direction (split 2D spin ice). As a function of the splitting we recover a two-fold degenerate staggered state for coplanar dipoles, and a four-fold degenerate ``Manhattan'' state for strongly split dipoles, separated by a first order transition. The competition between the two states at intermediate splitting leads to a strong suppression of the ordering transition temperatures, and makes space for the observation of a hallmark of spin-ice physics in the paramagnetic phase: pinch points in the static structure factor.
Magnetic Reversal of an Artificial Square Ice: Dipolar Correlation and Charge Ordering
Stein A.; Morgan J.P.; Langridge S.; Marrows C.H.
2011-10-13
Magnetic reversal of an artificial square ice pattern subject to a sequence of magnetic fields applied slightly off the diagonal axis is investigated via magnetic force microscopy of the remanent states that result. Sublattice independent reversal is observed via correlated incrementally pinned flip cascades along parallel dipolar chains, as evident from analysis of vertex populations and dipolar correlation functions. Weak dipolar interactions between adjacent chains favour antialignment and give rise to weak charge ordering of 'monopole' vertices during the reversal process.
Analytical polarization and coherence transfer functions for three dipolar coupled spins 12.
Luy, B; Glaser, S J
2000-02-01
Analytical polarization and coherence transfer functions are presented for a spin system consisting of three dipolar coupled homonuclear spins 12 under energy matched conditions. Based on these transfer functions, optimal durations of Hartmann-Hahn mixing periods can be determined for arbitrary dipolar coupling constants D(12), D(13), and D(23). In addition, the dependence of the transfer efficiency on the relative size of the dipolar coupling constants is illustrated.
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.
Magnetic hysteresis based on dipolar interactions in granular magnetic systems
NASA Astrophysics Data System (ADS)
Allia, Paolo; Coisson, Marco; Knobel, Marcelo; Tiberto, Paola; Vinai, Franco
1999-11-01
The magnetic hysteresis of granular magnetic systems is investigated in the high-temperature limit (T>> blocking temperature of magnetic nanoparticles). Measurements of magnetization curves have been performed at room temperature on various samples of granular bimetallic alloys of the family Cu100-xCox (x=5-20 at. %) obtained in ribbon form by planar flow casting in a controlled atmosphere, and submitted to different thermal treatments. The loop amplitude and shape, which are functions of sample composition and thermal history, are studied taking advantage of a novel method of graphical representation, particularly apt to emphasize the features of thin, elongated loops. The hysteresis is explained in terms of the effect of magnetic interactions of the dipolar type among magnetic-metal particles, acting to hinder the response of the system of moments to isothermal changes of the applied field. Such a property is accounted for in a mean-field scheme, by introducing a memory term in the argument of the Langevin function which describes the anhysteretic behavior of an assembly of noninteracting superparamagnetic particles. The rms field arising from the cumulative effect of dipolar interactions is linked by the theory to a measurable quantity, the reduced remanence of a major symmetric hysteresis loop. The theory's self-consistence and adequacy have been properly tested at room temperature on all examined systems. The agreement with experimental results is always striking, indicating that at high temperatures the magnetic hysteresis of granular systems is dominated by interparticle, rather than single-particle, effects. Dipolar interactions seem to fully determine the magnetic hysteresis in the high-temperature limit for low Co content (x<=10). For higher concentrations of magnetic metal, the experimental results indicate that additional hysteretic mechanisms have to be introduced.
Stochastic dipolar recoupling in nuclear magnetic resonance of solids
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
Synchronization of spin torque nano-oscillators through dipolar interactions
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.
Phases of dipolar bosons in a bilayer geometry
NASA Astrophysics Data System (ADS)
Cinti, Fabio; Wang, Daw-Wei; Boninsegni, Massimo
2017-02-01
We study, by first-principles computer simulations, the low-temperature phase diagram of bosonic dipolar gases in a bilayer geometry as a function of the two control parameters, i.e., the in-plane density and the interlayer distance. We observe four distinct phases, namely, paired and decoupled superfluids, as well as a crystal of dimers and one consisting of two aligned crystalline layers. A direct quantum phase transition from a dimer crystal to two independent superfluids is observed in a relatively wide range of parameters. No supersolid phase is predicted for this system.
Field-induced layer formation in dipolar nanofilms.
Jordanovic, Jelena; Klapp, Sabine H L
2008-07-18
Using molecular dynamics simulations, we demonstrate that the layering of confined colloidal particles with dipolar interactions, such as ferrofluids, in slablike geometries can be controlled by homogeneous external fields. For suitable surface separations, strong fields directed perpendicular to the film plane do not only align the particles but create additional layers in the system. The reverse effect occurs with an in-plane field which can induce a collapse of layers. Both effects are accompanied by pronounced particle rearrangements in lateral directions. Our simulation results are consistent with recent experiments of ferrofluids at surfaces.
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.
Exact second virial coefficient for dipolar hard spheres.
Virga, Epifanio G
2013-11-20
The second virial coefficient B2 for a fluid of dipolar hard spheres has been given several approximate forms valid in the limits of weak and strong interactions. They have been formulated as asymptotic expressions in a dimensionless interaction parameter λ. In this paper, B2 is determined exactly for all values of λ in both the three-dimensional case, where spheres may access the whole space and their dipole moments may be oriented in all directions, and in the quasi-two-dimensional case, where spheres have their centres bound to glide on a plane, while their dipole moments are still freely orientable in space.
Stochastic dipolar recoupling in nuclear magnetic resonance of solids.
Tycko, Robert
2007-11-02
I describe a nuclear magnetic resonance (NMR) technique, called stochastic dipolar recoupling (SDR), that permits continuous experimental control of the character of spin dynamics between coherent and incoherent limits in a system of magnetic dipole-coupled nuclei. In the fully incoherent limit of SDR, spin polarization transfers occur at distance-dependent rates without the quantum mechanical interferences among pairwise dipole-dipole couplings that often limit the feasibility or precision of structural studies of solids by NMR. In addition to facilitating structural studies, SDR represents a possible route to experimental studies of effects of decoherence on the dynamics of quantum many-body systems.
Stochastic Dipolar Recoupling in Nuclear Magnetic Resonance of Solids
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.
Model independence in two dimensions and polarized cold dipolar molecules.
Volosniev, A G; Fedorov, D V; Jensen, A S; Zinner, N T
2011-06-24
We calculate the energy and wave functions of two particles confined to two spatial dimensions interacting via arbitrary anisotropic potentials with negative or zero net volume. The general rigorous analytic expressions are given in the weak coupling limit where universality or model independence are approached. The monopole part of anisotropic potentials is crucial in the universal limit. We illustrate the universality with a system of two arbitrarily polarized cold dipolar molecules in a bilayer. We discuss the transition to universality as a function of polarization and binding energy and compare analytic and numerical results obtained by the stochastic variational method. The universal limit is essentially reached for experimentally accessible strengths.
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.
Characterization of ionic, dipolar and molecular mobility in polymer systems
NASA Astrophysics Data System (ADS)
Guo, Zhenrong
Changes in the ionic and dipolar molecular mobility in a polymer system are the basis for the changes in the dielectric mechanical properties of polymer materials. Frequency Dependent Dielectric Measurements (FDEMS) and Ion Time-of-Flight (ITOF) are two important techniques to investigate ionic and dipolar molecular mobility in polymer systems. The results can be related to the macro- and molecular dielectric, electrical and dynamic properties of polymeric materials. The combination of these two methods provides a full view of electric, dielectric and dynamic behavior for the systems as they undergo chemical and/or physical changes during polymerization crystallization, vitrification, and/or phase separation. The research on microscopic mass mobility in polymer systems was done on three aspects: (1) ion mobility in an epoxy-amine reaction system; (2) dipolar mobility and relaxation during dimethacrylate resin cure and (3) dye molecule migration and diffusion in polymer films. In the ion mobility study, we separately monitor the changes in the ion mobility and the number of charge carriers during the epoxy-amine polymerization with FDEMS and ITOF measurements. The isolation of the number of carriers and their mobility allows significant improvement in monitoring changes in the state and structure of a material as it cures. For the dipolar mobility and relaxation study, FDEMS measurements were used to detect structural evolution and spatial heterogeneity formation during the polymerization process of dimethacrylate resins. The dielectric spectra, glass transition (Tg) profiles and dynamic mechanical measurements were used to investigate the existence of two cooperative regions of sufficient size to create two alpha-relaxation processes representing oligomer rich and polymer microgel regions during the polymerization. For the dye migration research, we tried to develop a visually color changing paper (VCP) due to dye molecule migration in polymer films. The mobility
Stability spectroscopy of rotons in a dipolar Bose gas
NASA Astrophysics Data System (ADS)
Corson, John P.; Wilson, Ryan M.; Bohn, John L.
2013-05-01
We study the stability of a quasi-one-dimensional dipolar Bose-Einstein condensate that is perturbed by a weak lattice potential along its axis. Our numerical simulations demonstrate that systems exhibiting a roton-maxon structure destabilize readily when the lattice wavelength equals either half the roton wavelength or a low roton subharmonic. We apply perturbation theory to the Gross-Pitaevskii and Bogoliubov-de Gennes equations to illustrate the mechanisms behind the instability threshold. The features of our stability diagram may be used as a direct measurement of the roton wavelength for quasi-one-dimensional geometries.
Stability Spectroscopy of Rotons in a Dipolar Bose Gas
NASA Astrophysics Data System (ADS)
Corson, John; Wilson, Ryan; Bohn, John
2013-05-01
We study the stability of a quasi-one-dimensional dipolar Bose-Einstein condensate that is perturbed by a weak lattice potential along its axis. Our numerical simulations demonstrate that systems exhibiting a roton-maxon structure destabilize readily when the lattice wavelength equals either half the roton wavelength or a low roton subharmonic. We apply perturbation theory to the Gross-Pitaevskii and Bogoliubov de Gennes equations to illustrate the mechanisms behind the instability threshold. The features of our stability diagram are a novel signature of roton physics, and their experimental observation would constitute a direct measurement of the roton wavelength for quasi-one-dimensional geometries.
Vertical shift register using dipolar interaction in magnetic multilayers
NASA Astrophysics Data System (ADS)
Chin, Shin-Liang; Fernández-Pacheco, Amalio; Petit, Dorothée C. M. C.; Cowburn, Russell P.
2015-12-01
A vertical shift register consisting of multi-layered ferromagnetic bars with in-plane magnetization is investigated numerically using macrospin simulations. These layers are anti-ferromagnetically coupled via dipolar interactions and their in-plane aspect ratio determines their anisotropy. A single data bit is represented by a magnetic kink soliton, which forms at the boundary of two anti-parallel domains with opposite phases. It can be propagated bi-directionally using an externally applied rotating magnetic field. The soliton propagation is dependent on the applied field strength, the magnetic anisotropy of the ferromagnetic layers, and the dipolar coupling energies. For the device investigated here, the largest field range for soliton propagation is found to be from 35 Oe to 235 Oe at a lateral aspect ratio of 1.33. The soliton is also subjected to edge effects where it can be either pinned or reflected rather than being expelled from the stack. It is found that by reducing the thickness of the edge layer, these effects can be reduced substantially. By reducing the thickness of the edge layer by 20%, the field range in which the soliton is expelled increases by more than a factor of two.
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.
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.
Transfer of dipolar gas through the discrete localized mode
NASA Astrophysics Data System (ADS)
Bai, Xiao-Dong; Zhang, Ai-Xia; Xue, Ju-Kui
2013-12-01
By considering the discrete nonlinear Schrödinger model with dipole-dipole interactions for dipolar condensate, the existence, the types, the stability, and the dynamics of the localized modes in a nonlinear lattice are discussed. It is found that the contact interaction and the dipole-dipole interactions play important roles in determining the existence, the type, and the stability of the localized modes. Because of the coupled effects of the contact interaction and the dipole-dipole interactions, rich localized modes and their stability nature can exist: when the contact interaction is larger and the dipole-dipole interactions is smaller, a discrete bright breather occurs. In this case, while the on-site interaction can stabilize the discrete breather, the dipole-dipole interactions will destabilize the discrete breather; when both the contact interaction and the dipole-dipole interactions are larger, a discrete kink appears. In this case, both the on-site interaction and the dipole-dipole interactions can stabilize the discrete kink, but the discrete kink is more unstable than the ordinary discrete breather. The predicted results provide a deep insight into the dynamics of blocking, filtering, and transfer of the norm in nonlinear lattices for dipolar condensates.
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.
Dipolar clusters and ferroelectricity in high Tc superconductors
NASA Astrophysics Data System (ADS)
Kusmartsev, F. V.; Saarela, M.
2015-08-01
In this paper, we show that doping of hole charge carriers induces formation of resonance plaquettes (RPs) having electric dipolar moments and fluctuating stripes in cuprates. A single RP is created by many-body interactions between the dopant ion or a charge fluctuation outside and holes inside the CuO plane. In such a process, Coulomb interacting holes in the CuO plane are self-organized into four-particles resonance valence bond plaquettes bound with dopants or polarons located in the spacer layer between CuO planes. Such RPs have ordered and disordered phases. They are ordered into charge density waves (CDW) or stripes only at certain conditions. The lowest energy of the ordered phase corresponds to a local antiferroelectric ordering. The RPs mobility is very low at low temperatures and they are bound into dipole-dipole pairs. Electromagnetic radiation interacts strongly with RPs electric dipoles and when the sample is subjected to it, the mobility changes significantly. This leads to a fractal growth of dipolar RP clusters. The existence of electric dipoles and CDW reveal a series of new phenomena such as ferroelectricity, strong light and microwave absorption and the field induced superconductivity.
Rotational friction of dipolar colloids measured by driven torsional oscillations
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
Dynamical simulation of dipolar Janus colloids: Dynamical properties
NASA Astrophysics Data System (ADS)
Hagy, Matthew C.; Hernandez, Rigoberto
2013-05-01
The dynamical properties of dipolar Janus particles are studied through simulation using our previously-developed detailed pointwise (PW) model and an isotropically coarse-grained (CG) model [M. C. Hagy and R. Hernandez, J. Chem. Phys. 137, 044505 (2012), 10.1063/1.4737432]. The CG model is found to have accelerated dynamics relative to the PW model over a range of conditions for which both models have near identical static equilibrium properties. Physically, this suggests dipolar Janus particles have slower transport properties (such as diffusion) in comparison to isotropically attractive particles. Time rescaling and damping with Langevin friction are explored to map the dynamics of the CG model to that of the PW model. Both methods map the diffusion constant successfully and improve the velocity autocorrelation function and the mean squared displacement of the CG model. Neither method improves the distribution of reversible bond durations f(tb) observed in the CG model, which is found to lack the longer duration reversible bonds observed in the PW model. We attribute these differences in f(tb) to changes in the energetics of multiple rearrangement mechanisms. This suggests a need for new methods that map the coarse-grained dynamics of such systems to the true time scale.
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.
CHARGED TORI IN SPHERICAL GRAVITATIONAL AND DIPOLAR MAGNETIC FIELDS
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.
Nonequilibrium condensation and coarsening of field-driven dipolar colloids
NASA Astrophysics Data System (ADS)
Jäger, Sebastian; Schmidle, Heiko; Klapp, Sabine H. L.
2012-07-01
In colloidal suspensions, self-organization processes can be easily fueled by external fields. Here we consider monolayers of particles with permanent dipole moments that are driven by rotating external fields. In recent experiments, it has been shown that the particles in such systems self-organize into two-dimensional clusters. Here we report results from a computer simulation study of these pattern forming systems. Specifically, we employ Langevin dynamics simulations, Brownian dynamics simulations that include hydrodynamic interactions, and Wang-Landau Monte Carlo simulations of soft spheres interacting via dipolar potentials. We investigate at which field strengths and frequencies clusters form and explore the influence of hydrodynamic interactions. We also examine the phase behavior of the equilibrium system resulting from a time average of the colloidal interactions in the rotating field. In this way we demonstrate that the clustering described in the driven system arises from a first-order phase transition between a vapor and a condensed phase.
Fibonacci anyon excitations of one-dimensional dipolar lattice bosons
NASA Astrophysics Data System (ADS)
Äńurić, Tanja; Biedroń, Krzysztof; Zakrzewski, Jakub
2017-02-01
We study a system of dipolar bosons in a one-dimensional optical lattice using exact diagonalization and density matrix renormalization group methods. In particular, we analyze low energy properties of the system at an average filling of 3/2 atoms per lattice site. We identify the region of the parameter space where the system has non-Abelian Fibonacci anyon excitations that correspond to fractional domain walls between different charge-density waves. When such one-dimensional systems are combined into a two-dimensional network, braiding of Fibonacci anyon excitations has potential application for fault tolerant, universal, topological quantum computation. Contrary to previous calculations, our results also demonstrate that super-solid phases are not present in the phase diagram for the discussed 3/2 average filling. Instead, decreasing the value of the nearest-neighbor tunneling strength leads to a direct, Berezinskii-Kosterlitz-Thouless, superfluid to charge-density-wave quantum phase transition.
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.
Optical force and torque on dipolar dual chiral particles
NASA Astrophysics Data System (ADS)
Rahimzadegan, A.; Fruhnert, M.; Alaee, R.; Fernandez-Corbaton, I.; Rockstuhl, C.
2016-09-01
On the one hand, electromagnetic dual particles preserve the helicity of light upon interaction. On the other hand, chiral particles respond differently to light of opposite helicity. These two properties on their own constitute a source of fascination. Their combined action, however, is less explored. Here, we study on analytical grounds the force and torque as well as the optical cross sections of dual chiral particles in the dipolar approximation exerted by a particular wave of well-defined helicity: A circularly polarized plane wave. We put emphasis on particles that possess a maximally electromagnetic chiral and hence dual response. Besides the analytical insights, we also investigate the exerted optical force and torque on a real particle using the example of a metallic helix that is designed to approach the maximal electromagnetic chirality condition. Various applications in the context of optical sorting but also nanorobotics can be foreseen considering the particles studied in this contribution.
Nonequilibrium condensation and coarsening of field-driven dipolar colloids.
Jäger, Sebastian; Schmidle, Heiko; Klapp, Sabine H L
2012-07-01
In colloidal suspensions, self-organization processes can be easily fueled by external fields. Here we consider monolayers of particles with permanent dipole moments that are driven by rotating external fields. In recent experiments, it has been shown that the particles in such systems self-organize into two-dimensional clusters. Here we report results from a computer simulation study of these pattern forming systems. Specifically, we employ Langevin dynamics simulations, Brownian dynamics simulations that include hydrodynamic interactions, and Wang-Landau Monte Carlo simulations of soft spheres interacting via dipolar potentials. We investigate at which field strengths and frequencies clusters form and explore the influence of hydrodynamic interactions. We also examine the phase behavior of the equilibrium system resulting from a time average of the colloidal interactions in the rotating field. In this way we demonstrate that the clustering described in the driven system arises from a first-order phase transition between a vapor and a condensed phase.
Dipolar bilayer with antiparallel polarization: A self-bound liquid
NASA Astrophysics Data System (ADS)
Hebenstreit, Martin; Rader, Michael; Zillich, Robert E.
2016-01-01
Dipolar bilayers with antiparallel polarization, i.e., opposite polarization in the two layers, exhibit liquidlike rather than gaslike behavior. In particular, even without external pressure, a self-bound liquid droplet of constant density will form. We investigate the symmetric case of two identical layers, corresponding to a two-component Bose system with equal partial densities. The zero-temperature equation of state E (ρ )/N , where ρ is the total density, has a minimum, with an equilibrium density that can be adjusted by the distance d between the layers (decreasing with increasing d ). The attraction necessary for a self-bound liquid comes from the interlayer dipole-dipole interaction that leads to a mediated intralayer attraction. We investigate the regime of negative pressure towards the spinodal instability, where the bilayer is unstable against infinitesimal fluctuations of the total density, confirmed by calculations of the speed of sound of total density fluctuations.
Strongly dipolar fluids at low densities compared to living polymers
NASA Astrophysics Data System (ADS)
Tavares, J. M.; Weis, J. J.; Telo da Gama, M. M.
1999-04-01
We carried out extensive canonical Monte Carlo (MC) simulations of the dipolar hard-sphere (DHS) fluid, with N=1024 particles at fixed reduced density ρ*=0.05, in order to investigate the chainlike structure that occurs at low densities, for sufficiently large reduced dipole moments μ*. The dissociation and recombination of chains during equilibrium runs suggest an analogy between the DHS's and a system of living polymers. This was checked quantitatively by comparing the results of the simulations with those of a theory for living polymers taking into account the indistinguishability of the particles in self-assembled chains. Quantitative agreement between theoretical and simulated mean chain lengths and number of monomers, was found for particular choices of the parameters used in the working definition of the MC chains.
Plasmonic Toroidal Dipolar Response under Radially Polarized Excitation
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
Tunnel Splitting Distributions and Dipolar Shuffling in Mn12-acetate
NASA Astrophysics Data System (ADS)
Mertes, K. M.; Suzuki, Yoko; Sarachik, M. P.; Rumberger, E. M.; Hendrickson, D. N.; Christou, G.; Myasoedov, Y.; Shtrikman, H.; Zeldov, E.
2003-03-01
In magnetic fields applied parallel to the anisotropy axis, the magnetization of Mn12 has been measured in response to a field that is swept back and forth across each of the ground state energy resonances corresponding to steps N=4...9, which provides a means of more directly [1] determining the distribution of tunnel splittings. The analysis of the data in terms of a distribution of tunnel splittings will be presented. Deviations from the expected curves at slow sweep rates are attributed to dipolar shuffling [2] which results in a redistribution of internal magnetic fields whenever a molecule tunnels. [1] K. M. Mertes, Yoko Suzuki, M. P. Sarachik, Y. Paltiel, H. Shtrikman, E. Zeldov, E. M. Rumberger, D. N. Hendrickson and G. Christou, Phys. Rev. Lett. 87, 227205 (2001) [2] Jie Liu, Biao Wu, Libin Fu, R. B. Diener and Qian Niu, Phys. Rev. B, 65 224401 (2002)
Fragmentation of magnetism in artificial kagome dipolar spin ice
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
Strongly Correlated States of Ultracold Rotating Dipolar Fermi Gases
Osterloh, Klaus; Barberan, Nuria; Lewenstein, Maciej
2007-10-19
We study strongly correlated ground and excited states of rotating quasi-2D Fermi gases constituted of a small number of dipole-dipole interacting particles with dipole moments polarized perpendicular to the plane of motion. As the number of atoms grows, the system enters an intermediate regime, where ground states are subject to a competition between distinct bulk-edge configurations. This effect obscures their description in terms of composite fermions and leads to the appearance of novel quasihole ground states. In the presence of dipolar interactions, the principal Laughlin state at filling {nu}=1/3 exhibits a substantial energy gap for neutral (total angular momentum conserving) excitations and is well-described as an incompressible Fermi liquid. Instead, at lower fillings, the ground state structure favors crystalline order.
Fragmentation of magnetism in artificial kagome dipolar spin ice.
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.
Properties of a dipolar condensate with three-body interactions
NASA Astrophysics Data System (ADS)
Blakie, Peter
2016-05-01
We discuss the properties of a harmonically trapped dilute dipolar condensate with a short ranged conservative three-body interaction. We show that this system supports two distinct fluid states: a usual condensate state and a self-cohering droplet state. We develop a simple model to quantify the energetics of these states, which we verify with full numerical calculations. Based on our simple model we develop a phase diagram showing that there is a first order phase transition between the states. Using dynamical simulations we explore the phase transition dynamics, revealing that the droplet crystal observed in previous work is an excited state that arises from heating as the system crosses the phase transition. Utilising our phase diagram we show it is feasible to produce a single droplet by dynamically adjusting the confining potential. We acknowledge support from the Marsden Fund of New Zealand.
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.
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.
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.
Two states of magnetotail dipolarization fronts: A statistical study
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
Ordering and short-time orientational diffusion in dipolar hard-spherical colloids.
Alarcón-Waess, O; Diaz-Herrera, E
2002-03-01
Orientational hydrodynamic functions and short-time, self-orientational and collective orientational diffusion coefficients of dipolar hard-spherical colloids are performed on a homogeneous isotropic phase, as functions of the wave vector q, for various values of the volume fraction and the dipolar strength of the macroparticles. The calculation is based on the dynamic orientational structure factor, which is the time-dependent self-correlation of the orientation density. We assume that the time evolution of the orientation density is given by the Smoluchoswki's equation, taking into account the hydrodynamic interactions as well as the dipolar interaction. The former are considered assuming pairwise additivity. The importance of the dynamic orientational structure factor is that its initial slope can be measured in a depolarized light scattering experiment. The results predict a different behavior for dilute and for dense dipolar colloids. The ordering phenomena are studied via the ordering coefficients, which are the orientational hydrodynamic functions at q=0. The results show that as the dipolar colloid evolves to the instability line, the translational ordering velocity increases while the rotational one reduces. The short-time orientational diffusion coefficients at q=0 are also performed. They predict that near to the instability line, the dipolar colloid diffuses translationally more than rotationally. At very dilute concentration the dipolar colloid presents an unexpected dynamical behavior, which seems to indicate that the colloid could be evolving to a reentrant phase.
Fermion production in dipolar electric field on de Sitter expanding universe
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.
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
Thermal 1,3-dipolar cycloaddition reaction of azomethine imines with active esters.
He, Liwenze; Liu, Lin; Han, Runfeng; Zhang, Weiwei; Xie, Xingang; She, Xuegong
2016-07-12
An efficient method for the 1,3-dipolar cycloaddition of azomethine imines with active esters under thermal conditions has been described in good to high yields. This method offers a straightforward pathway to synthesize bioactive pyrazolidinones.
Modification of roton instability due to the presence of a second dipolar Bose-Einstein condensate
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.
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.
Spectral collocation and a two-level continuation scheme for dipolar Bose-Einstein condensates
NASA Astrophysics Data System (ADS)
Jeng, B.-W.; Chien, C.-S.; Chern, I.-L.
2014-01-01
We exploit the high accuracy of spectral collocation methods in the context of a two-level continuation scheme for computing ground state solutions of dipolar Bose-Einstein condensates (BEC), where the first kind Chebyshev polynomials and Fourier sine functions are used as the basis functions for the trial function space. The governing Gross-Pitaevskii equation (or Schrödinger equation) can be reformulated as a Schrödinger-Poisson (SP) type system [13]. The two-level continuation scheme is developed for tracing the first solution curves of the SP system, which in turn provide an appropriate initial guess for the Newton method to compute ground state solutions for 3D dipolar BEC. Extensive numerical experiments on 3D dipolar BEC and dipolar BEC in optical lattices are reported.
Mollica, Giulia; Dekhil, Myriam; Ziarelli, Fabio; Thureau, Pierre; Viel, Stéphane
2015-02-01
The relationship between the crystal packing of powder samples and long-range (13)C-(13)C homonuclear dipolar couplings is presented and illustrated for the case of uniformly (13)C-enriched L-alanine and L-histidine·HCl·H2O. Dipolar coupling measurement is based on the partial reintroduction of dipolar interactions by spinning the sample slightly off-magic-angle, while the coupling of interest for a given spin pair is isolated with a frequency-selective pulse. A cost function is used to correlate the so-derived dipolar couplings to trial crystal structures of the samples under study. This procedure allowed for the investigation of the l-alanine space group and L-histidine·HCl·H2O space group and unit-cell parameters.
Many-Body Dynamics of Dipolar Molecules in an Optical Lattice
NASA Astrophysics Data System (ADS)
Hazzard, Kaden R. A.; Gadway, Bryce; Foss-Feig, Michael; Yan, Bo; Moses, Steven A.; Covey, Jacob P.; Yao, Norman Y.; Lukin, Mikhail D.; Ye, Jun; Jin, Deborah S.; Rey, Ana Maria
2014-11-01
We use Ramsey spectroscopy to experimentally probe the quantum dynamics of disordered dipolar-interacting ultracold molecules in a partially filled optical lattice, and we compare the results to theory. We report the capability to control the dipolar interaction strength. We find excellent agreement between our measurements of the spin dynamics and theoretical calculations with no fitting parameters, including the dynamics' dependence on molecule number and on the dipolar interaction strength. This agreement verifies the microscopic model expected to govern the dynamics of dipolar molecules, even in this strongly correlated beyond-mean-field regime, and represents the first step towards using this system to explore many-body dynamics in regimes that are inaccessible to current theoretical techniques.
Many-body dynamics of dipolar molecules in an optical lattice.
Hazzard, Kaden R A; Gadway, Bryce; Foss-Feig, Michael; Yan, Bo; Moses, Steven A; Covey, Jacob P; Yao, Norman Y; Lukin, Mikhail D; Ye, Jun; Jin, Deborah S; Rey, Ana Maria
2014-11-07
We use Ramsey spectroscopy to experimentally probe the quantum dynamics of disordered dipolar-interacting ultracold molecules in a partially filled optical lattice, and we compare the results to theory. We report the capability to control the dipolar interaction strength. We find excellent agreement between our measurements of the spin dynamics and theoretical calculations with no fitting parameters, including the dynamics' dependence on molecule number and on the dipolar interaction strength. This agreement verifies the microscopic model expected to govern the dynamics of dipolar molecules, even in this strongly correlated beyond-mean-field regime, and represents the first step towards using this system to explore many-body dynamics in regimes that are inaccessible to current theoretical techniques.
How to Observe Dipolar Effects in Spinor Bose-Einstein Condensates
Gawryluk, Krzysztof; Brewczyk, Miroslaw; Bongs, Kai
2011-04-08
We propose an experiment which proves the possibility of spinning gaseous media via dipolar interactions in the spirit of the famous Einstein-de Haas effect for ferromagnets. The main idea is to utilize resonances that we find in spinor condensates of alkali atoms while these systems are placed in an oscillating magnetic field. A significant transfer of angular momentum from spin to motional degrees of freedom observed on resonance is a spectacular manifestation of dipolar effects in spinor condensates.
Two-component dipolar Bose-Einstein condensate in concentrically coupled annular traps
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
Vertical Phase Segregation Induced by Dipolar Interactions in Planar Polymer Brushes
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
Vertical Phase Segregation Induced by Dipolar Interactions in Planar Polymer Brushes
Mahalik, Jyoti P.; Sumpter, Bobby G.; Kumar, Rajeev
2016-09-13
In this paper, we present a generalized theory for studying structural properties of a planar dipolar polymer brush immersed in a polar solvent. We show that an explicit treatment of the dipolar interactions yields a macroscopic concentration dependent effective “chi” (the Flory–Huggins-like interaction) parameter. Furthermore, it is shown that the concentration dependent chi parameter promotes phase segregation in polymer solutions and brushes so that the polymer-poor phase consists of a finite/nonzero polymer concentration. Such a destabilization of the homogeneous phase by the dipolar interactions appears as vertical phase segregation in a planar polymer brush. In a vertically phase segregated polymer brush, the polymer-rich phase near the grafting surface coexists with the polymer-poor phase at the other end. Predictions of the theory are directly compared with prior reported experimental results for dipolar polymers in polar solvents. Excellent agreements with the experimental results are found, hinting that the dipolar interactions play a significant role in vertical phase segregation of planar polymer brushes. We also compare our field theoretical approach with the two-state and other models invoking ad hoc concentration dependence of the chi parameter. Interplay between the short-ranged excluded volume interactions and long-ranged dipolar interactions is shown to play an important role in affecting the vertical phase separation. Finally, effects of mismatch between the dipole moments of the polymer segments and the solvent molecules are investigated in detail.
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.
Plasma Entry from Tail into the Dipolar Magnetosphere During Substorms
NASA Astrophysics Data System (ADS)
Haerendel, Gerhard
Plasma entering the dipolar magnetosphere from the tail has to overcome the obstacle presented by the conductivity enhancements caused by the poleward arc(s). While the arcs move poleward, the plasma proceeds equatorward as testified by the existence of a westward electric field. The arcs break into smaller-scale structures and loops with a tendency of eastward growth and expansion, although the basic driving force is directed earthward/equatorward. The likely reason is that the arc-related conductivity enhancements act as flow barriers and convert normal into shear stresses. The energy derived from the release of the shear stresses and dissipated in the arcs lowers the entropy content of the flux tubes and enables their earthward progression. In addition, poleward jumps of the breakup arcs are quite common. They result from refreshments of the generator plasma by the sequential arrival of flow bursts from the near-Earth neutral line. Once inside the oval, the plasma continues to move equatorward as manifested through north-south aligned auroral forms. Owing to the existence of an inner border of the oval, marked by the Region 2 currents, all flows are eventually diverted sunward.
Dynamical Properties of Surface-mounted Dipolar Molecular Rotators
NASA Astrophysics Data System (ADS)
Underwood, Jason; Price, John; Caskey, Douglas; Michl, Josef
2007-03-01
We use dielectric relaxation spectroscopy (DRS) to study the rotational dynamics of dipolar molecules mounted on fused SiO2 surfaces. Each ``molecular rotor'' consists of three parts: 1) a mounting group for attachment to the substrate, 2) a rotating group having a permanent dipole moment, and 3) an axis connecting the rotor to the attachment group. Attachment is facilitated either by covalent bonding through reaction of silane groups with surface hydroxyls or by van der Waals interactions. Fused SiO2 substrates are patterned with interdigitated electrode Au capacitors (C ˜ 1 pF), and rotor molecule dynamics are characterized by measurement of the capacitance C and loss tangent δ≡ReZ/ImZ. We employ a ratio-transformer bridge technique to measure these quantities, with sensitivities in C and δ of 1 aF and 1 ppm, respectively. A unique aspect of this work is the experimental apparatus, which allows us to prepare sub-monolayer films, determine coverage via two independent methods (DRS and XPS), and study molecule rotational motion, in-situ in ultra-high vacuum. Results will be presented on the kinetics of rotor adsorption/desorption, barrier height and asymmetry of the rotational potential of the molecules, and the effects of varying rotor coverages and adventitious H2O.
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.
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.
Conformations of a dipolar solute in a Stockmayer solvent channel.
Yi, Taeil; Wang, Qian; Lichter, Seth
2012-10-30
A wide range of molecules, from inorganic to biological, self-assemble on surfaces. Previous studies have elucidated many features of solute reorganization on surfaces using coarse-grained modeling, implicit solvents, and constraints such as chemically bonding the solute to the surface. Using molecular dynamics simulations under various combinations of interaction parameters, solute fractions, and solute dipole moment, we study the redistribution of freely-rotating dipolar solute molecules solvated by a water-like Stockmayer solvent initially adhered to a face-centered cubic substrate. The balance of attractive and repulsive forces is essential for acquiring a particular stable conformation. Here we show that the adsorbed molecules redistribute into different conformations--wetting film, nonwetting, partial wetting, and pseudopartial wetting drops--depending on the parameter values. We observe that the pseudopartial wetting drop is transient and its rate of spreading fluctuates, slowing to nearly zero as it passes through particular conformations before reaching an equilibrium thin film. Strong attraction between solute molecules yields a droplet with a net dipole moment. A high solute fraction leads to a pancake-like conformation arising from a balance of surface tension and van der Waals forces. This study augments our understanding of the evolution of aggregates in biological systems and also the design of polymers for self-assembled monolayers for industrial applications.
Rapid acceleration of protons upstream of earthward propagating dipolarization fronts
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
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.
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.
NASA Astrophysics Data System (ADS)
Kamenetskii, E. O.; Joffe, R.; Shavit, R.
2011-08-01
A coupled state of an electromagnetic field with an electric or magnetic dipole-carrying excitation is well known as a polariton. Such a state is the result of the mixing of a photon with the excitation of a material. The most discussed types of polaritons are phonon polaritons, exciton polaritons, and surface-plasmon polaritons. Recently, it was shown that, in microwaves, strong magnon-photon coupling can be achieved due to magnetic-dipolar-mode (MDM) vortices in small thin-film ferrite disks. These coupled states can be specified as MDM-vortex polaritons. In this paper, we study the properties of MDM-vortex polaritons. We numerically analyze a variety of topological structures of MDM-vortex polaritons. Based on analytical studies of the MDM spectra, we give theoretical insight into a possible origin for the observed topological properties of the fields. We show that the MDM-vortex polaritons are characterized by helical-mode resonances. We demonstrate the PT-invariance properties of MDM oscillations in a quasi-two-dimensional ferrite disk and show that such properties play an essential role in the physics of the observed topologically distinctive states with the localization or cloaking of electromagnetic fields. We may suppose that one of the useful implementations of the MDM-vortex polaritons could be microwave metamaterial structures and microwave near-field sensors.
Statistical and superposed epoch study of dipolarization events using data from Wind perigee passes
NASA Astrophysics Data System (ADS)
Sigsbee, K.; Slavin, J. A.; Lepping, R. P.; Szabo, A.; Øieroset, M.; Kaiser, M. L.; Reiner, M. J.; Singer, H. J.
2005-03-01
From 1995 to 2000, the Wind spacecraft spent over 500h in the magnetotail, much of it within ~2x104km of the predicted location of the neutral sheet. Wind passed through the near magnetotail at distances of -15 RE
NASA Astrophysics Data System (ADS)
Pruski, M.; Bailly, A.; Lang, D. P.; Amoureux, J.-P.; Fernandez, C.
1999-06-01
A new technique for measurements of dipolar interactions in rotating solids is presented that combines the capabilities of multiple quantum magic angle spinning (MQMAS) with the rotational echo double resonance (REDOR). It employs the dipolar recoupling between spin-1/2 ( I) and quadrupolar ( S) nuclei by applying a series of π pulses to the I spins. In contrast to the previously reported MQ-REDOR method, the recoupling sequence is applied during the triple quantum, rather than single quantum evolution. As the dipolar effect is enhanced by the MQ coherence order, this new technique exhibits improved sensitivity toward weak dipolar interactions.
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.
Physics of Substorm Growth Phase, Onset, and Dipolarization
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.
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.
Multi-dipolar microwave plasmas and their application to negative ion production
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.
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.
Exotic vortex lattices in a rotating binary dipolar Bose-Einstein condensate
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
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.
NASA Astrophysics Data System (ADS)
Batalov, L. A.; Syromyatnikov, A. V.
2015-06-01
Using 1 /S expansion, we discuss the magnon spectrum of Heisenberg antiferromagnet (AF) on a simple cubic lattice with small dipolar interaction at small temperature T ≪TN , where TN is the Néel temperature. Similar to three-dimensional and two-dimensional ferromagnets, quantum and thermal fluctuations renormalize greatly the bare gapless spectrum leading to a gap Δ ˜ω0 , where ω0 is the characteristic dipolar energy. This gap is accompanied by anisotropic corrections to the free energy which make the cube edges easy directions for the staggered magnetization (dipolar anisotropy). In accordance with previous results, we find that dipolar forces split the magnon spectrum into two branches. This splitting makes possible two types of processes which lead to a considerable enhancement of the damping compared to the Heisenberg AF: a magnon decay into two other magnons and a confluence of two magnons. It is found that magnons are well defined quasiparticles in quantum AF. We demonstrate however that a small fraction of long-wavelength magnons can be overdamped in AFs with S ≫1 and in quantum AFs with a single-ion anisotropy competing with the dipolar anisotropy. Particular materials are pointed out which can be suitable for experimental observation of this long-wavelength magnons breakdown that contradicts expectation of the quasiparticle concept.
Exotic vortex lattices in a rotating binary dipolar Bose-Einstein condensate.
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.
AC susceptibility as a tool to probe the dipolar interaction in magnetic nanoparticles
NASA Astrophysics Data System (ADS)
Landi, Gabriel T.; Arantes, Fabiana R.; Cornejo, Daniel R.; Bakuzis, Andris F.; Andreu, Irene; Natividad, Eva
2017-01-01
The dipolar interaction is known to substantially affect the properties of magnetic nanoparticles. This is particularly important when the particles are kept in a fluid suspension or packed within nano-carriers. In addition to its usual long-range nature, in these cases the dipolar interaction may also induce the formation of clusters of particles, thereby strongly modifying their magnetic anisotropies. In this paper we show how AC susceptibility may be used to obtain information regarding the influence of the dipolar interaction in a sample. We develop a model which includes both aspects of the dipolar interaction and may be fitted directly to the susceptibility data. The usual long-range nature of the interaction is implemented using a mean-field approximation, whereas the particle-particle aggregation is modeled using a distribution of anisotropy constants. The model is then applied to two samples studied at different concentrations. One consists of spherical magnetite nanoparticles dispersed in oil and the other of cubic magnetite nanoparticles embedded on polymeric nanospheres. We also introduce a simple technique to address the presence of the dipolar interaction in a given sample, based on the height of the AC susceptibility peaks for different driving frequencies.
Forces driving fast flow channels, dipolarizations, and turbulence in the magnetotail
NASA Astrophysics Data System (ADS)
El-Alaoui, Mostafa; Richard, Robert L.; Nishimura, Yukitoshi; Walker, Raymond J.
2016-11-01
Fast flow channels are a major contributor to earthward transport in the magnetotail. Fast flow channels originate at reconnection sites in the magnetotail and terminate with dipolarizations, earthward moving regions of enhanced magnetic field. We have used a global magnetohydrodynamic simulation of magnetotail dynamics during a substorm on 7 February 2009 to investigate the stresses in the plasma sheet. In particular, we present an analysis of forces in and around flow channels and dipolarizations. Earthward of the dipolarization magnetic and thermal pressure forces are nearly in equilibrium. Tailward of the dipolarization the pattern of stresses is complex, but several general features are evident. In the earthward flow channel the magnetic tension force dominates. In the dipolarization a tailward magnetic force is partially balanced by the earthward pressure force. The stresses in azimuth (y) are variable. In some places they cause the flow stream to meander, while in others they cause the stream to become wider or narrower. A major consequence of fast earthward flow channels is that they drive large-scale vortices that initiate turbulence.
Mixing, demixing, and structure formation in a binary dipolar Bose-Einstein condensate
NASA Astrophysics Data System (ADS)
Young-S., Luis E.; Adhikari, S. K.
2012-12-01
We study the static properties of disk-shaped binary dipolar Bose-Einstein condensates of 168Er-164Dy and 52Cr-164Dy mixtures under the action of interspecies and intraspecies contact and dipolar interactions and demonstrate the effect of dipolar interaction using the mean-field approach. Throughout this study we use realistic values of interspecis and intraspecies dipolar interactions and the intraspecies scattering lengths and consider the interspecies scattering length as a parameter. The stability of the binary mixture is illustrated through phase plots involving a number of atoms of the species. The binary system always becomes unstable as the number of atoms increases beyond a certain limit. As the interspecies scattering length increases corresponding to more repulsion, an overlapping mixed state of the two species changes to a separated demixed configuration. During the transition from a mixed to a demixed configuration as the interspecies scattering length is increased for parameters near the stability line, the binary condensate shows special transient structures in density in the form of red-blood-cell-like biconcave and Saturn-ring-like shapes, which are direct manifestations of the dipolar interaction.
Performance of RINEPT is amplified by dipolar couplings under ultrafast MAS conditions.
Zhang, Rongchun; Ramamoorthy, Ayyalusamy
2014-06-01
The refocused insensitive nuclei enhanced by polarization transfer (RINEPT) technique is commonly used for heteronuclear polarization transfer in solution and solid-state NMR spectroscopy. Suppression of dipolar couplings, either by fast molecular motions in solution or by a combination of MAS and multiple pulse sequences in solids, enables the polarization transfer via scalar couplings. However, the presence of unsuppressed dipolar couplings could alter the functioning of RINEPT, particularly under fast/ultrafast MAS conditions. In this study, we demonstrate, through experiments on rigid solids complemented by numerical simulations, that the polarization transfer efficiency of RINEPT is dependent on the MAS frequency. In addition, we show that heteronuclear dipolar coupling is the dominant factor in the polarization transfer, which is strengthened by the presence of (1)H-(1)H dipolar couplings. In fact, the simultaneous presence of homonuclear and heteronuclear dipolar couplings is the premise for the polarization transfer by RINEPT, whereas the scalar coupling plays an insignificant role under ultrafast MAS conditions on rigid solids. Our results additionally reveal that the polarization transfer efficiency decreases with the increasing duration of RF pulses used in the RINEPT sequence.
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).
Model energy landscapes of low-temperature fluids: Dipolar hard spheres.
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.
NASA Astrophysics Data System (ADS)
Yang, Lianyun; Zhu, Lei
2014-03-01
The leakage current, ion migration, and dipolar orientational polarization are major losses in ferroelectric polymers. The loss from the leakage current originates from electronic conduction and its behavior could be significantly affected by the internal electric field, which is induced by the dipolar orientational polarization. In this work, the leakage current in the corona charged PVDF electrets is studied under different external electric fields. Under low applied electric field, when no or very few dipoles could flip, the conductivity from the leakage direct current increases upon increasing the electric field. Under higher electric field, the aligned dipole-induced internal field would prevent the electrons from going through so that the conductivity decreases. After all the dipoles are aligned with the external electric field, the conductivity can increase again. This study will help us better understand the interplay between electronic conduction and dipolar orientation in ferroelectric materials.
Quantum Monte Carlo study of entanglement entropy for dipolar hardcore bosons in optical lattices
NASA Astrophysics Data System (ADS)
Wang, Wei; Safavi-Naini, Arghavan; Capogrosso-Sansone, Barbara
2016-05-01
Entanglement entropy and its scaling with system size provide an alternative way to characterize quantum phases and phase transitions, and can be used to probe topological order. Motivated by the recent theoretical investigation of entanglement properties of the ground-states of hard-core lattice bosons, we use Quantum Monte Carlo simulations, well suited to studying equilibrium properties, to calculate the Renyi entropy and topological entanglement entropy of the ground state of dipolar lattice bosons. In contrast to the traditional observables, these probes allow us to study the emergence of long-range entanglement in the ground state, as well as its dependence on the dipolar coupling. Additionally, in light of recent experimental success in creating low entropy dipolar lattice gases we discuss the possibility of observing these phases experimentally.
Topological defect formation in rotating binary dipolar Bose-Einstein condensate
NASA Astrophysics Data System (ADS)
Zhang, Xiao-Fei; Han, Wei; Jiang, Hai-Feng; Liu, Wu-Ming; Saito, Hiroki; Zhang, Shou-Gang
2016-12-01
We investigate the topological defects and spin structures of a rotating binary Bose-Einstein condensate, which consists of both dipolar and scalar bosonic atoms confined in spin-dependent optical lattices, for an arbitrary orientation of the dipoles with respect to their plane of motion. Our results show that the tunable dipolar interaction, especially the orientation of the dipoles, can be used to control the direction of stripe phase and its related half-vortex sheets. In addition, it can also be used to obtain a regular arrangement of various topological spin textures, such as meron, circular and cross disgyration spin structures. We point out that such topological defects and regular arrangement of spin structures arise primarily from the long-range and anisotropic nature of dipolar interaction and its competition with the spin-dependent optical lattices and rotation.
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.
Numerical method for evolving the dipolar projected Gross-Pitaevskii equation.
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.
Numerical method for evolving the dipolar projected Gross-Pitaevskii equation
Blakie, P. B.; Bradley, A. S.; Ticknor, C.; Martin, A. M.; Davis, M. J.; Kawaguchi, Y.
2009-07-15
We describe a method for evolving the projected Gross-Pitaevskii equation (PGPE) for an interacting Bose gas in a harmonic-oscillator potential, with the inclusion of a long-range dipolar interaction. The central difficulty in solving this equation is the requirement that the field is restricted to a small set of prescribed modes that constitute the low-energy c-field region of the system. We present a scheme, using a Hermite-polynomial-based spectral representation, which precisely implements this mode restriction and allows an efficient and accurate solution of the dipolar PGPE. We introduce a set of auxiliary oscillator states to perform a Fourier transform necessary to evaluate the dipolar interaction in reciprocal space. We extensively characterize the accuracy of our approach and derive Ehrenfest equations for the evolution of the angular momentum.
Stability spectroscopy: recurring roton signatures in a dipolar-BEC phase diagram
NASA Astrophysics Data System (ADS)
Corson, John; Wilson, Ryan; Bohn, John
2015-05-01
When a strongly-dipolar Bose-Einstein condensate (BEC) is tightly confined in either one or two dimensions, the excitation spectrum is predicted to exhibit a nontrivial local minimum, termed ``roton.'' Rotons have proven to be elusive in dipolar-BEC experiments, and it is therefore of interest to devise a straightforward scheme whereby rotons may be measured. We propose observing the stability of a dipolar BEC that is perturbed by a tunable optical lattice. When the stability is mapped in terms of lattice depth s and spacing λ, we find regularly-spaced features whose positions and periodicity are determined by the roton wavelength. In this sense, a measurement of the phase diagram represents a spectroscopic measurement of the roton itself. In quasi-two-dimensional geometry, the polarization tilt plays an important role in determining which features appear in the stability diagram.
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
Improved narrowband dipolar recoupling for homonuclear distance measurements in rotating solids.
Goobes, G; Vega, S
2002-02-01
Recovery of the magnetic dipolar interaction between nuclei bearing the same gyromagnetic ratio in rotating solids can be promoted by synchronous rf irradiation. Determination of the dipolar interaction strength can serve as a tool for structural elucidation in polycrystalline powders. Spinning frequency dependent narrow-band (nb) RFDR and SEDRA experiments are utilized as simple techniques for the determination of dipolar interactions between the nuclei in coupled homonuclear spin pairs. The magnetization exchange and coherence dephasing due to a fixed number of rotor-synchronously applied pi-pulses is monitored at spinning frequencies in the vicinity of the rotational resonance (R(2)) conditions. The powder nbRFDR and nbSEDRA decay curves of spin magnetizations and coherences, respectively, as a function of the spinning frequency can be measured and analyzed using simple rate equations providing a quantitative measure of the dipolar coupling. The effects of the phenomenological relaxation parameters in these rate equations are discussed and an improved methodology is suggested for analyzing nbRFDR data for small dipolar couplings. The distance between the labeled nuclei in the 1,3-(13)C(2)-hydroxybutyric acid molecule is rederived using existing nbRFDR results and the new simulation procedure. A nbSEDRA experiment has been performed successfully on a powder sample of singly labeled 1-(13)C-L-leucine measuring the dipolar interaction between the labeled carboxyl carbon and the natural abundant beta-carbon. Both narrowband techniques are employed for the determination of the nuclear distances between the side-chain carbons of leucine and its carbonyl carbon in a tripeptide Leu-Gly-Phe that is singly (13)C-labeled at the leucine carbonyl carbon position.
Improved Narrowband Dipolar Recoupling for Homonuclear Distance Measurements in Rotating Solids
NASA Astrophysics Data System (ADS)
Goobes, G.; Vega, S.
2002-02-01
Recovery of the magnetic dipolar interaction between nuclei bearing the same gyromagnetic ratio in rotating solids can be promoted by synchronous rf irradiation. Determination of the dipolar interaction strength can serve as a tool for structural elucidation in polycrystalline powders. Spinning frequency dependent narrow-band (nb) RFDR and SEDRA experiments are utilized as simple techniques for the determination of dipolar interactions between the nuclei in coupled homonuclear spin pairs. The magnetization exchange and coherence dephasing due to a fixed number of rotor-synchronously applied π-pulses is monitored at spinning frequencies in the vicinity of the rotational resonance (R2) conditions. The powder nbRFDR and nbSEDRA decay curves of spin magnetizations and coherences, respectively, as a function of the spinning frequency can be measured and analyzed using simple rate equations providing a quantitative measure of the dipolar coupling. The effects of the phenomenological relaxation parameters in these rate equations are discussed and an improved methodology is suggested for analyzing nbRFDR data for small dipolar couplings. The distance between the labeled nuclei in the 1,3-13C2-hydroxybutyric acid molecule is rederived using existing nbRFDR results and the new simulation procedure. A nbSEDRA experiment has been performed successfully on a powder sample of singly labeled 1-13C-L-leucine measuring the dipolar interaction between the labeled carboxyl carbon and the natural abundant β-carbon. Both narrowband techniques are employed for the determination of the nuclear distances between the side-chain carbons of leucine and its carbonyl carbon in a tripeptide Leu-Gly-Phe that is singly 13C-labeled at the leucine carbonyl carbon position.
Luy, B; Glaser, S J
2001-01-01
The superposition of scalar and residual dipolar couplings gives rise to so-called cylindrical mixing Hamiltonians in dipolar coupling spectroscopy. General analytical polarization and coherence transfer functions are presented for three cylindrically coupled spins 12 under energy-matched conditions. In addition, the transfer efficiency is analyzed as a function of the relative coupling constants for characteristic special cases.
Consequences of rotating off-centred dipolar electromagnetic field in vacuum around Pulsars
NASA Astrophysics Data System (ADS)
Kundu, A.; Pétri, J.
2016-12-01
Studying the electromagnetic field of pulsars is one of the key themes in neutron star physics. While most of the works assume a standard central dipolar electromagnetic field model, recently some efforts had been made in explaining how inclusion of higher field components produces drastic consequences in our understanding of these objects. We put forward the effects of a unique recently presented approach in which the magnetic axis is shifted off from the centre. It is found that the rotating off-centred dipolar electromagnetic field itself reveals the presence of the higher components within. The consequences of this approach on the shape of the polar caps and the emission diagrams are discussed.
Crossover from normal to anomalous diffusion in systems of field-aligned dipolar particles.
Jordanovic, Jelena; Jäger, Sebastian; Klapp, Sabine H L
2011-01-21
Using molecular dynamics simulations we investigate the translational dynamics of particles with dipolar interactions in homogenous external fields. For a broad range of concentrations, we find that the anisotropic, yet normal diffusive behavior characterizing weakly coupled systems becomes anomalous both parallel and perpendicular to the field at sufficiently high dipolar coupling and field strength. After the ballistic regime, chain formation first yields cagelike motion in all directions, followed by transient, mixed diffusive-superdiffusive behavior resulting from cooperative motion of the chains. The enhanced dynamics disappears only at higher densities close to crystallization.
Acoustic-excitonic effects in a two-dimensional gas of dipolar excitons
NASA Astrophysics Data System (ADS)
Boev, M. V.; Kovalev, V. M.; Chaplik, A. V.
2016-08-01
The theory of the interaction of a two-dimensional gas of indirect dipolar excitons with Rayleigh surface elastic waves has been developed. The absorption and renormalization of the phase velocity of a surface wave, as well as the drag of excitons by the surface acoustic wave and the generation of bulk acoustic waves by a twodimensional gas of dipolar excitons irradiated by external electromagnetic radiation, have been considered. These effects have been studied both in a normal phase at high temperatures and in a condensed phase of the exciton gas. The calculations have been performed in the ballistic and diffusion limits for both phases.
Review: Use of residual dipolar couplings to determine the structure of carbohydrates.
Canales, A; Jiménez-Barbero, J; Martín-Pastor, M
2012-12-01
Solution nuclear magnetic resonance spectroscopy is especially useful in the carbohydrate field. The measurement of residual dipolar couplings provides long-range structural information, a valuable complement for the structural study of carbohydrates either in its free form or in the bound state to proteins. They permit to deduce the geometry and the flexibility of the glycosidic linkages, which have a major influence on the conformation of carbohydrates and their overall shape. This article reviews the current application of the residual dipolar couplings methodology to carbohydrates.
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.
Salas, Gorka; Camarero, Julio; Cabrera, David; ...
2014-07-23
Here, we report on the study of heat dissipation power in monodisperse and crystalline magnetite nanoparticles as function of particle and aggregate sizes, magnetic field frequencies (up to 435 kHz) and amplitudes (up to 50 mT), media viscosity and particle concentration. These nanoparticles display specific absorption rate values of few hundreds of WgFe-1 at moderate frequencies (~100 kHz), increasing up to 3632 WgFe-1 at more extreme field conditions (430 kHz and 40 mT) for the largest size. We have found that Néelian relaxation processes are dominant for all nanoparticle sizes, whereas Brownian contribution dominates only for the largest size (22more » nm) at high particle concentrations when dipolar interactions enhance the effective magnetic anisotropy. Besides, the particle concentration dependence of the specific absorption rate reflects the importance of magnetic dipolar interactions which strongly depend on aggregate and particle size. Our results show that dipolar interactions tune the effective magnetic anisotropy determining the Néelian and Brownian contributions into SAR values. The possibility of switching between heating mechanisms via dipolar interactions is of great importance towards controlling the heat exposure supplied by IONP as intracellular heating mediators.« less
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 Wg_{Fe}^{-1} at moderate frequencies (~100 kHz), increasing up to 3632 Wg_{Fe}^{-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.
Theory of Stochastic Dipolar Recoupling in Solid State Nuclear Magnetic Resonance
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
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.
Dong, Zhenghao; Zhu, Yuanyuan; Li, Boyu; Wang, Cui; Yan, Wenjin; Wang, Kairong; Wang, Rui
2017-02-28
The optically active α-trifluoromethyl pyrrolidines have been achieved through organocatalyzed 1, 3-dipolar cycloaddition reaction firstly. With diphenyl- prolinol trimethylsilyl ether as catalyst and in the presence of 3, 5-dinitrobenzoic acid, the reaction of trifluoroethylamine-derived ketimine with 2-enals gave α-trifluoro-methyl pyrrolidines bearing three contiguous stereogenic centers in excellent diastereoselectivies, stereoselectivities and yields.
Effect of Nanoclustering and Dipolar Interactions in Heat Generation for Magnetic Hyperthermia.
Coral, Diego F; Zélis, Pedro Mendoza; Marciello, Marzia; Morales, María del Puerto; Craievich, Aldo; Sánchez, Francisco H; van Raap, Marcela B Fernández
2016-02-09
Biomedical magnetic colloids commonly used in magnetic hyperthermia experiments often display a bidisperse structure, i.e., are composed of stable nanoclusters coexisting with well-dispersed nanoparticles. However, the influence of nanoclusters in the optimization of colloids for heat dissipation is usually excluded. In this work, bidisperse colloids are used to analyze the effect of nanoclustering and long-range magnetic dipolar interaction on the magnetic hyperthermia efficiency. Two kinds of colloids, composed of magnetite cores with mean sizes of around 10 and 18 nm, coated with oleic acid and dispersed in hexane, and coated with meso-2,3-dimercaptosuccinic acid and dispersed in water, were analyzed. Small-angle X-ray scattering was applied to thoroughly characterize nanoparticle structuring. We proved that the magnetic hyperthermia performances of nanoclusters and single nanoparticles are distinctive. Nanoclustering acts to reduce the specific heating efficiency whereas a peak against concentration appears for the well-dispersed component. Our experiments show that the heating efficiency of a magnetic colloid can increase or decrease when dipolar interactions increase and that the colloid concentration, i.e., dipolar interaction, can be used to improve magnetic hyperthermia. We have proven that the power dissipated by an ensemble of dispersed magnetic nanoparticles becomes a nonextensive property as a direct consequence of the long-range nature of dipolar interactions. This knowledge is a key point in selecting the correct dose that has to be injected to achieve the desired outcome in intracellular magnetic hyperthermia therapy.
Lorentz microscopy sheds light on the role of dipolar interactions in magnetic hyperthermia.
Campanini, M; Ciprian, R; Bedogni, E; Mega, A; Chiesi, V; Casoli, F; de Julián Fernández, C; Rotunno, E; Rossi, F; Secchi, A; Bigi, F; Salviati, G; Magén, C; Grillo, V; Albertini, F
2015-05-07
Monodispersed Fe3O4 nanoparticles with comparable size distributions have been synthesized by two different synthesis routes, co-precipitation and thermal decomposition. Thanks to the different steric stabilizations, the described samples can be considered as a model system to investigate the effects of magnetic dipolar interactions on the aggregation states of the nanoparticles. Moreover, the presence of magnetic dipolar interactions can strongly affect the nanoparticle efficiency as a hyperthermic mediator. In this paper, we present a novel way to visualize and map the magnetic dipolar interactions in different kinds of nanoparticle aggregates by the use of Lorentz microscopy, an easy and reliable in-line electron holographic technique. By exploiting Lorentz microscopy, which is complementary to the magnetic measurements, it is possible to correlate the interaction degrees of magnetic nanoparticles with their magnetic behaviors. In particular, we demonstrate that Lorentz microscopy is successful in visualizing the magnetic configurations stabilized by dipolar interactions, thus paving the way to the comprehension of the power loss mechanisms for different nanoparticle aggregates.
Dipolarization Front: A Distinctive Feature of the Reconnection Onset in the Magnetotail
NASA Astrophysics Data System (ADS)
Sitnov, M. I.; Swisdak, M.; Divin, A. V.
2008-12-01
Recent particle simulations with open boundaries revealed interesting new effects in collisionless magnetic reconnection, including its intermittent regimes with the formation of the secondary plasmoids in the outflow regions. In this presentation we show that, apart from rather conventional plasmoids forming near the electron diffusion region of the central X-line, there is another group of the secondary reconnection structures that strongly resemble the dipolarization fronts, reported in Geotail, Cluster, and Themis observations of bursty bulk flows and substorm activations in the terrestrial magnetotail. These structures are characterized by a strong and quick increase of the original tail field Bz, normal to the neutral plane, up a half of the lobe field, in contrast to a relatively small and shallow negative dip of Bz in the front precursor, comparable in amplitude to the field Bz prior to the dipolarization onset. Both electrons and ions are magnetized at the front of the dipolarization wave. In contrast, in its trail, ions are unmagnetized and move slower compared to the ExB drift, whereas the magnetized electrons either follow that drift or move even faster, forming super-Alfvenic jets. In spite of drastically different motions of electrons and ions, the formation and growth of the dipolarization front is not accompanied by the corresponding growth of the electrostatic field. This suggests that the electron compressibility effect, stabilizing the ion tearing mode in the tail-like systems with trapped magnetized electrons [Lembege and Pellat, 1982], is strongly attenuated in open systems.
Synthesis of 2H-indazoles by the [3 + 2] dipolar cycloaddition of sydnones with arynes.
Fang, Yuesi; Wu, Chunrui; Larock, Richard C; Shi, Feng
2011-11-04
A rapid and efficient synthesis of 2H-indazoles has been developed using a [3 + 2] dipolar cycloaddition of sydnones and arynes. A series of 2H-indazoles have been prepared in good to excellent yields using this protocol, and subsequent Pd-catalyzed coupling reactions can be applied to the halogenated products to generate a structurally diverse library of indazoles.
Dipolar interactions between domains in lipid monolayers at the air-water interface.
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.
Observational test of the interchange stability associated with near-tail dipolarizations
NASA Astrophysics Data System (ADS)
Lee, D.; Kim, K.; Ohtani, S.; Park, M.
2010-12-01
The interchange instability is a pressure gradient-driven instability. Formally speaking, the interchange mode can be considered to be a special case of the more general ballooning mode in the sense that the perpendicular displacement (as multiplied by the magnetic field strength) of the interchange mode is defined to be constant along the magnetic field line while that of a ballooning mode can be localized to the “bad curvature” region (i.e. the equatorial plane). Since the radial pressure profile in the near-earth tail is expected to become steeper prior to the substorm onset, instability of either interchange or ballooning type mode may be expected to occur. An observational test is generally non-trivial and difficult for the ballooning mode. For the interchange mode, however, the classic analytic criterion has long been known and thus using this criterion an observational test of the instability can be more feasible. The only difficulty has been how to evaluate the flux tube volume, for which Wolf et al. [2006] have suggested a useful formula. Using the formula, we have evaluated the interchange criterion for a set of pair-dipolarization events that are radially aligned. We found that the near-tail configuration before and during a dipolarization is likely stable against the interchange mode. Using a number of more dipolarizations, we have performed an analysis on evaluating the interchange criterion in a statistical manner and reached the results that support the conclusion of the interchange stability. This seems to suggest to us that the interchange instability is unlikely a candidate to trigger dipolarizations in association with substorms. But, the ballooning instability, the mode structure of which can be localized near the equatorial plane, remains a possibility responsible for dipolarizations.
Temperature dependence of contact and dipolar NMR chemical shifts in paramagnetic molecules
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.
Temperature dependence of contact and dipolar NMR chemical shifts in paramagnetic molecules.
Martin, Bob; Autschbach, Jochen
2015-02-07
Using a recently proposed equation for NMR nuclear magnetic shielding for molecules with unpaired electrons [A. Soncini and W. Van den Heuvel, J. Chem. Phys. 138, 021103 (2013)], equations for the temperature (T) dependent isotropic shielding for multiplets with an effective spin S equal to 1/2, 1, 3/2, 2, and 5/2 in terms of electron paramagnetic resonance spin Hamiltonian parameters are derived and then expanded in powers of 1/T. One simplifying assumption used is that a matrix derived from the zero-field splitting (ZFS) tensor and the Zeeman coupling matrix (g-tensor) share the same principal axis system. The influence of the rhombic ZFS parameter E is only investigated for S = 1. Expressions for paramagnetic contact shielding (from the isotropic part of the hyperfine coupling matrix) and pseudo-contact or dipolar shielding (from the anisotropic part of the hyperfine coupling matrix) are considered separately. The leading order is always 1/T. A temperature dependence of the contact shielding as 1/T and of the dipolar shielding as 1/T(2), which is sometimes assumed in the assignment of paramagnetic chemical shifts, is shown to arise only if S ≥ 1 and zero-field splitting is appreciable, and only if the Zeeman coupling matrix is nearly isotropic (Δg = 0). In such situations, an assignment of contact versus dipolar shifts may be possible based only on linear and quadratic fits of measured variable-temperature chemical shifts versus 1/T. Numerical data are provided for nickelocene (S = 1). Even under the assumption of Δg = 0, a different leading order of contact and dipolar shifts in powers of 1/T is not obtained for S = 3/2. When Δg is not very small, dipolar and contact shifts both depend in leading order in 1/T in all cases, with sizable contributions in order 1/T(n) with n = 2 and higher.
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
Dielectric relaxation in ionic liquid/dipolar solvent binary mixtures: A semi-molecular theory.
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
Narayanarao, Manjunatha; Koodlur, Lokesh; Revanasiddappa, Vijayakumar G; Gopal, Subramanya
2016-01-01
A new series of spiropyrrolidine compounds containing indole/indazole moieties as side chains have been accomplished via a one-pot multicomponent synthesis. The method uses the 1,3-dipolar cycloaddition reaction between N-alkylvinylindole/indazole and azomethine ylides, prepared in situ from cyclic/acyclic amino acids. The 1,3-dipolar cycloaddition proceeds efficiently under thermal conditions to afford the regio- and stereospecific cyclic adducts. PMID:28144362
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.
Narayanarao, Manjunatha; Koodlur, Lokesh; Revanasiddappa, Vijayakumar G; Gopal, Subramanya; Kamila, Susmita
2016-01-01
A new series of spiropyrrolidine compounds containing indole/indazole moieties as side chains have been accomplished via a one-pot multicomponent synthesis. The method uses the 1,3-dipolar cycloaddition reaction between N-alkylvinylindole/indazole and azomethine ylides, prepared in situ from cyclic/acyclic amino acids. The 1,3-dipolar cycloaddition proceeds efficiently under thermal conditions to afford the regio- and stereospecific cyclic adducts.
Collective excitations of dipolar gases based on local tunneling in superlattices
NASA Astrophysics Data System (ADS)
Cao, Lushuai; Mistakidis, Simeon I.; Deng, Xing; Schmelcher, Peter
2017-01-01
The collective dynamics of a dipolar fermionic quantum gas confined in a one-dimensional double-well superlattice is explored. The fermionic gas resides in a paramagnetic-like ground state in the weak interaction regime, upon which a new type of collective dynamics is found when applying a local perturbation. This dynamics is composed of the local tunneling of fermions in separate supercells, and is a pure quantum effect, with no classical counterpart. Due to the presence of the dipolar interactions the local tunneling transports through the entire superlattice, giving rise to a collective dynamics. A well-defined momentum-energy dispersion relation is identified in the ab-initio simulations demonstrating the phonon-like behavior. The phonon-like characteristic is also confirmed by an analytical description of the dynamics within a semiclassical picture.
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.
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.
NASA Astrophysics Data System (ADS)
Ţifrea, Ionel; Flatté, Michael E.
2011-10-01
We investigate the dynamic nuclear polarization (DNP) caused by hyperfine coupling between nonequilibrium electronic spins and nuclear spins in semiconductor nanostructures. We derive the time and position dependence of the resulting hyperfine and dipolar magnetic fields. In GaAs quantum wells the induced nuclear spin polarization greatly exceeds the polarization of the electronic system that causes the DNP. The induced magnetic fields vary between tens of tesla for the electronic hyperfine field acting on nuclei, to hundreds of gauss for the nuclear hyperfine field acting on electrons, to a few gauss for the induced nuclear dipolar fields that act on both nuclei and electrons. The field strengths should be measurable via optically induced nuclear magnetic resonance or time-resolved Faraday rotation experiments. We discuss the implications of our calculations for low-dimensional semiconductor nanostructures.
Coherence Transfer in Dipolar-Coupled Homonuclear Spin Systems in Solids Rotating at the Magic Angle
NASA Astrophysics Data System (ADS)
Weintraub, O.; Vega, S.; Hoelger, C.; Limbach, H. H.
Two routes for the exploitation of the t-SEDRA pulse scheme, which induces coherence transfer in dipolar-coupled homonuclear spin systems in rotating samples, are demonstrated and discussed. This sequence is utilized to deduce intramolecular connectivities by creating an initial coherence of one spin only, applying the t-SEDRA sequence, and monitoring the signal enhancement of the coupled spin. Probing the signal amplitude variations of the two spins and comparing them to simulations can also yield molecular distances. Using 2D spectroscopy, t-SEDRA can also be utilized to establish spin correlations. In this case, the t-SEDRA sequence is applied during the mixing time of a 2D dipolar-correlation experiment. These two approaches are demonstrated by performing 15N CPMAS NMR experiments on a 15N-doubly labeled sample of 3(5)-methyl-5(3)-phenylpyrazole.
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.
Arrays of dipolar molecular rotors in Tris(o-phenylenedioxy) cyclotriphosphazene.
Zhao, Ke; Dron, Paul I; Kaleta, Jiří; Rogers, Charles T; Michl, Josef
2014-01-01
Regular two-dimensional or three-dimensional arrays of mutually interacting dipolar molecular rotors represent a worthy synthetic objective. Their dielectric properties, including possible collective behavior, will be a sensitive function of the location of the rotors, the orientation of their axes, and the size of their dipoles. Host-guest chemistry is one possible approach to gaining fine control over these factors. We describe the progress that has been achieved in recent years using tris (o-phenylenedioxy)cyclotriphosphazene as a host and a series of rod-shaped dipolar molecular rotors as guests. Structures of both surface and bulk inclusion compounds have been established primarily by solid-state nuclear magnetic resonance (NMR) and powder X-ray diffraction (XRD) techniques. Low-temperature dielectric spectroscopy revealed rotational barriers as low as 1.5 kcal/mol, but no definitive evidence for collective behavior has been obtained so far.
Rotating colloids in rotating magnetic fields: Dipolar relaxation and hydrodynamic coupling
NASA Astrophysics Data System (ADS)
Coughlan, Anna C. H.; Bevan, Michael A.
2016-10-01
Video microscopy (VM) experiments and Brownian dynamics (BD) simulations were used to measure and model superparamagnetic colloidal particles in rotating magnetic fields for interaction energies on the order of the thermal energy, kT . Results from experiments and simulations were compared for isolated particle rotation, particle rotation within doublets, doublet rotation, and separation within doublets vs field rotation frequency. Agreement between VM and BD results was obtained at all frequencies and amplitudes only by including exact two-body hydrodynamic interactions and relevant relaxation times of magnetic dipoles. Frequency-dependent particle forces and torques cause doublets to rotate at low frequencies via dipolar interactions and at high frequencies via hydrodynamic translation-rotation coupling. By matching measurements and simulations for a range of conditions, our findings unambiguously demonstrate the quantitative forms of dipolar and hydrodynamic interactions necessary to capture nonequilibrium, steady-state dynamics of Brownian colloids in magnetic fields.
Liu, Yu; Begin-Colin, Sylvie; Pichon, Benoît P; Leuvrey, Cedric; Ihiawakrim, Dris; Rastei, Mircea; Schmerber, Guy; Vomir, Mircea; Bigot, Jean Yves
2014-10-21
The dimensionality of assembled nanoparticles plays an important role in their optical and magnetic properties, via dipolar effects and the interaction with their environment. In this work we develop a methodology for distinguishing between two (2D) and three (3D) dimensional collective interactions on the surface plasmon resonance of assembled metal nanoparticles. Towards that goal, we elaborate different sets of Au and Ag nanoparticles as suspensions, random 3D arrangements and well organized 2D arrays. Then we model their scattering cross-section using effective field methods in dimension n, including interparticle as well as particle-substrate dipolar interactions. For this modelling, two effective field medium approaches are employed, taking into account the filling factors of the assemblies. Our results are important for realizing photonic amplifier devices.
Dielectric antennas--a suitable platform for controlling magnetic dipolar emission.
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.
Determination of residual dipolar couplings in homonuclear MOCCA-SIAM experiments.
Möglich, Andreas; Wenzler, Michael; Kramer, Frank; Glaser, Steffen J; Brunner, Eike
2002-07-01
In solutions with partial molecular alignment, anisotropic magnetic interactions such as the chemical shift anisotropy, the electric quadrupole interaction, and the magnetic dipole-dipole interaction are no longer averaged out to zero in contrast to isotropic solutions. The resulting residual anisotropic magnetic interactions are increasingly used in biological NMR studies for the determination of 3D structures of proteins and other biomolecules. In the present paper we propose a new approach allowing the measurement of residual HN-H(alpha) dipolar couplings of non-isotope enriched proteins based on the application of the MOCCA-SIAM experiment. This experiment allows the measurement of homonuclear coupling constants with an accuracy of ca. +/- 0.2 Hz and is therefore particularly well suited to determine residual dipolar couplings at relatively low degrees of molecular orientation. The agreement between experimentally determined residual HN-H(alpha) couplings and calculated values is demonstrated for BPTI.
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.
Monte Carlo simulations of a kagome lattice with magnetic dipolar interactions
NASA Astrophysics Data System (ADS)
Holden, M. S.; Plumer, M. L.; Saika-Voivod, I.; Southern, B. W.
2015-06-01
The results of extensive Monte Carlo simulations of classical spins on the two-dimensional kagome lattice with only dipolar interactions are presented. In addition to revealing the sixfold-degenerate ground state, the nature of the finite-temperature phase transition to long-range magnetic order is discussed. Low-temperature states consisting of mixtures of degenerate ground-state configurations separated by domain walls can be explained as a result of competing exchange-like and shape-anisotropy-like terms in the dipolar coupling. Fluctuations between pairs of degenerate spin configurations are found to persist well into the ordered state as the temperature is lowered until locking in to a low-energy state.
A combined discontinuous Galerkin method for the dipolar Bose-Einstein condensation
NASA Astrophysics Data System (ADS)
Li, Xiang-Gui; Zhu, Jiang; Zhang, Rong-Pei; Cao, Shengshan
2014-10-01
In this work, a combined discontinuous Galerkin (DG) method, which is a hybridized mixed discontinuous Galerkin (HMDG) method combined with the direct discontinuous Galerkin (DDG) method, is proposed to compute ground states and dynamics of dipolar Bose-Einstein condensates (BECs) described by a multi-dimensional Gross-Pitaevskii equation (GPE) coupled with a first-order velocity system. Due to the adaption of the first-order velocity system instead of dipolar interactions, the proposed combined DG method avoids to evaluate integrals with high singularity. Additionally, this method keeps the conservation of the particle number. The Krylov semi-implicit method is applied to the time discretization. Finally, numerical examples are presented to demonstrate the accuracy and capability of the proposed method.
Mean-field regime of trapped dipolar Bose-Einstein condensates in one and two dimensions
Cai Yongyong; Rosenkranz, Matthias; Lei Zhen; Bao Weizhu
2010-10-15
We derive rigorous one- and two-dimensional mean-field equations for cigar- and pancake-shaped dipolar Bose-Einstein condensates with arbitrary polarization angle. We show how the dipolar interaction modifies the contact interaction of the strongly confined atoms. In addition, our equations introduce a nonlocal potential, which is anisotropic for pancake-shaped condensates. We propose to observe this anisotropy via measurement of the condensate aspect ratio. We also derive analytically approximate density profiles from our equations. Both the numerical solutions of our reduced mean-field equations and the analytical density profiles agree well with numerical solutions of the full Gross-Pitaevskii equation while being more efficient to compute.
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
Quantum non-Markovian reservoirs of atomic condensates engineered via dipolar interactions
NASA Astrophysics Data System (ADS)
Yuan, Ji-Bing; Xing, Hai-Jun; Kuang, Le-Man; Yi, Su
2017-03-01
We investigate the quantum dephasing dynamics of an impurity qubit immersed in a quasi-two-dimensional dipolar Bose-Einstein condensate whose collective excitations act as a reservoir for the qubit. We show that the properties of the environment are highly engineerable through the relative strength of the dipolar and contact interactions such that qubit's dephasing dynamics could be Markovian, weak non-Markovian, or even highly non-Markovian. It is also revealed that the appearance of the roton excitation is responsible for the highly non-Markovian dephasing dynamics. Since rotonlike dispersions also appear in condensates placed in cavities or with spin-orbit couplings, our results pave the way for searching for systems that are suitable environment engineering.
NASA Astrophysics Data System (ADS)
Martin, A. D.; Blakie, P. B.
2012-11-01
We study theoretically Bose-Einstein condensates with polarized dipolar interactions in anisotropic traps. We map the parameter space by varying the trap frequencies and dipolar interaction strengths and find an irregular-shaped region of parameter space in which density-oscillating condensate states occur, with maximum density away from the trap center. These density-oscillating states may be biconcave (red-blood-cell-shaped), or have two or four peaks. For all trap frequencies, the condensate becomes unstable to collapse for sufficiently large dipole interaction strength. The collapse coincides with the softening of an elementary excitation. When the condensate mode is density oscillating, the character of the softening excitation is related to the structure of the condensate. We classify these excitations by linear and angular characteristics. We also find excited solutions to the Gross-Pitaevskii equation, which are always unstable.
Geometric stability spectra of dipolar Bose gases in tunable optical lattices
NASA Astrophysics Data System (ADS)
Corson, John P.; Wilson, Ryan M.; Bohn, John L.
2013-07-01
We examine the stability of quasi-two-dimensional dipolar Bose-Einstein condensates in the presence of weak optical lattices of various geometries. We find that when the condensate possesses a roton-maxon quasiparticle dispersion, the conditions for stability exhibit a strong dependence both on the lattice geometry and the polarization tilt. This results in rich structures in the system's stability diagram akin to spectroscopic signatures. We show how these structures originate from the mode matching of rotons to the perturbing lattice. In the case of a one-dimensional lattice, some of the features emerge only when the polarization axis is tilted into the plane of the condensate. Our results suggest that the stability diagram may be used as a novel means to spectroscopically measure rotons in dipolar condensates.
Spin squeezing of a dipolar Bose gas in a double-well potential
NASA Astrophysics Data System (ADS)
Tan, Qing-Shou; Lu, Hai-Yan; Yi, Su
2016-01-01
The spin-squeezing dynamics of a quasi-one-dimensional dipolar Bose gas trapped in a double-well potential is studied by employing the method of the multiconfigurational time-dependent Hartree for bosons. We find that optimal squeezing generated by the dipolar interaction can be improved over the one-axis twisting limit, and this squeezing is much stronger than that obtained by the contact interaction. Moreover, natural orbital-related squeezing can be controlled by the direction of the dipole moment, which provides control for storing the optimal spin squeezing. The origin of the squeezing as well as the relationship between spin squeezing and the two-order correlation function are also discussed.
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.
Synthesis of 2H-Indazoles by the [3 + 2] Dipolar Cycloaddition of Sydnones with Arynes
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
Ionic liquid crystals as alignment medium to measure residual dipolar couplings for carbohydrates.
Dama, Murali; Berger, Stefan
2013-08-09
Ionic liquids consisting of N-dodecyl-N-methyl pyrrolidinium bromide [C12MPB] in a mixture with D2O, decanol, and DMSO were for the first time found to give anisotropic molecular alignment in magnetic fields and are useful to measure residual dipolar couplings (RDCs) from polar analytes, for example, glucose. The system shows less quadrupolar splitting of the deuterated solvent signal compared with other liquid crystal systems and hence less undesired line broadening.
1,3-Dipolar cycloaddition of diazomethane to element-substituted (Si, Ge, Sn)-alkoxyacetylenes
Kostyuk, A.S.; Knyaz'kov, K.A.; Ponomarev, S.V.; Lutsenko, I.F.
1986-03-10
1,3-Dipolar cycloaddition of diazomethane to the triple bond of trialkylsilyl-, trialkylgermyl-, and trialkylstannylalkoxyacetylenes proceeds regioselectivity and is a convenient method for synthesis of the previously not described 3(5)-element-substituted 4-alkoxypyrazoles. When heated in methanol in the presence of an acid, 3(5)-silyl(germyl)-4-alkoxypyrazoles are slowly hydrolyzed with cleavage of the element-carbon bond.
Chiral phosphoric acid catalyzed enantioselective 1,3-dipolar cycloaddition reaction of azlactones.
Zhang, Zhenhua; Sun, Wangsheng; Zhu, Gongming; Yang, Junxian; Zhang, Ming; Hong, Liang; Wang, Rui
2016-01-25
The first chiral phosphoric acid catalyzed highly diastereo- and enantioselective 1,3-dipolar cycloaddition reaction of azlactones and methyleneindolinones was disclosed. By using a BINOL-derived chiral phosphoric acid as the catalyst, azlactones were activated as chiral anti N-protonated 1,3-dipoles to react with methyleneindolinones to yield biologically important 3,3'-pyrrolidonyl spirooxindole scaffolds in high yields, with good-to-excellent diastereo- and enantioselectivity.
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.
Collection of NMR Scalar and Residual Dipolar Couplings Using a Single Experiment.
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.
Improving resolution in proton solid-state NMR by removing nitrogen-14 residual dipolar broadening
NASA Astrophysics Data System (ADS)
Stein, Robin S.; Elena, Bénédicte; Emsley, Lyndon
2008-06-01
Residual dipolar coupling between quadrupolar and other nuclei under MAS has not usually been thought to be important in high field NMR spectroscopy. We show that coupling to 14N broadens 1H lineshapes significantly even at 11.7 T, and that we can decouple 14N from 1H during 1H homonuclear decoupling to successfully improve 1H resolution. The method used for decoupling is the application of evenly spaced pulses to the quadrupolar nucleus.
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.
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.
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).
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).
Dipolar Magnetism in Ordered and Disordered Low-Dimensional Nanoparticle Assemblies
Varón, M.; Beleggia, M.; Kasama, T.; Harrison, R. J.; Dunin-Borkowski, R. E.; Puntes, V. F.; Frandsen, C.
2013-01-01
Magnetostatic (dipolar) interactions between nanoparticles promise to open new ways to design nanocrystalline magnetic materials and devices if the collective magnetic properties can be controlled at the nanoparticle level. Magnetic dipolar interactions are sufficiently strong to sustain magnetic order at ambient temperature in assemblies of closely-spaced nanoparticles with magnetic moments of ≥ 100 μB. Here we use electron holography with sub-particle resolution to reveal the correlation between particle arrangement and magnetic order in self-assembled 1D and quasi-2D arrangements of 15 nm cobalt nanoparticles. In the initial states, we observe dipolar ferromagnetism, antiferromagnetism and local flux closure, depending on the particle arrangement. Surprisingly, after magnetic saturation, measurements and numerical simulations show that overall ferromagnetic order exists in the present nanoparticle assemblies even when their arrangement is completely disordered. Such direct quantification of the correlation between topological and magnetic order is essential for the technological exploitation of magnetic quasi-2D nanoparticle assemblies. PMID:23390584
Barros, Wilson; Gochberg, Daniel F; Gore, John C
2009-05-07
The description of the nuclear magnetic resonance magnetization dynamics in the presence of long-range dipolar interactions, which is based upon approximate solutions of Bloch-Torrey equations including the effect of a distant dipolar field, has been revisited. New experiments show that approximate analytic solutions have a broader regime of validity as well as dependencies on pulse-sequence parameters that seem to have been overlooked. In order to explain these experimental results, we developed a new method consisting of calculating the magnetization via an iterative formalism where both diffusion and distant dipolar field contributions are treated as integral operators incorporated into the Bloch-Torrey equations. The solution can be organized as a perturbative series, whereby access to higher order terms allows one to set better boundaries on validity regimes for analytic first-order approximations. Finally, the method legitimizes the use of simple analytic first-order approximations under less demanding experimental conditions, it predicts new pulse-sequence parameter dependencies for the range of validity, and clarifies weak points in previous calculations.
Decoherence of multiple quantum coherences generated from a dipolar ordered state
NASA Astrophysics Data System (ADS)
González, C. E.; Segnorile, H. H.; Zamar, R. C.
2011-01-01
Starting from the hypothesis that the decay of coherent signals observed in H1 NMR experiments is driven by quantum interference, irreversible decoherence, and nonidealities in the experiment, we design an experiment to isolate and identify the irreversible attenuation of multiple-quantum coherences toward quasiequilibrium states of dipolar order in nematic liquid crystals (LCs). The experiment combines the well-known “magic sandwich” pulse sequence with preparation of dipolar ordered states and encoding of multiple-quantum coherences. The spin system composed of the dipole-coupled protons of a LC molecule provides an example of a small cluster of strongly interacting spins. We study decoherence rates under a sequence that reverses time evolution with the secular dipolar Hamiltonian to compensate coherent evolution of a closed quantum system. In this way, the time scale is made evident where irreversible decoherence takes place, providing insight into the nature of the processes responsible for the attainment of quasiequilibrium. The behavior of single- and double-quantum-coherence amplitudes with reversal time is interpreted as evidence of the quantum character (as opposed to stochastic character) of the processes that drive irreversible decoherence. The experimental method proposed is useful for probing the action of the environment on materials with quantum information processing potential.
New cofactor supports α,β-unsaturated acid decarboxylation via 1,3-dipolar cycloaddition.
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.
Kechrakos, D; Trohidou, K N
2008-06-01
Assemblies of magnetic nanoparticles exhibit interesting physical properties arising from the competition of intraparticle dynamics and interparticle interactions. In ordered arrays of magnetic nanoparticles magnetostatic interparticle interactions introduce collective dynamics acting competitively to random anisotropy. Basic understanding, characterization and control of dipolar interaction effects in arrays of magnetic nanoparticles is an issue of central importance. To this end, numerical simulation techniques offer an indispensable tool. We report on Monte Carlo studies of the magnetic hysteresis and spin-dependent transport in thin films formed by ordered arrays of magnetic nanoparticles. Emphasis is given to the modifications of the single-particle behavior due to interparticle dipolar interactions as these arise in quantities of experimental interest, such as, the magnetization, the susceptibility and the magnetoresistance. We investigate the role of the structural parameters of an array (interparticle separation, number of stacked monolayers) and the role of the internal structure of the nanoparticles (single phase, core-shell). Dipolar interactions are responsible for anisotropic magnetic behavior between the in-plane and out-of-plane directions of the sample, which is reflected on the investigated magnetic properties (magnetization, transverse susceptibility and magnetoresistance) and the parameters of the array (remanent magnetization, coercive field, and blocking temperature). Our numerical results are compared to existing measurements on self-assembled arrays of Fe-based and Co nanoparticles is made.
Magnetotail dipolarization and associated current systems observed by Cluster and Double Star
NASA Astrophysics Data System (ADS)
Volwerk, M.; Lui, A. T. Y.; Lester, M.; Walsh, A. P.; Alexeev, I.; Cao, X.; Dunlop, M. W.; Fazakerley, A. N.; Grocott, A.; Kistler, L.; Lun, X.; Mouikis, C.; Pu, Z.; Shen, C.; Shi, J. K.; Taylor, M. G. G. T.; Baumjohann, W.; Nakamura, R.; Runov, A.; VöRöS, Z.; Zhang, T. L.; Takada, T.; RèMe, H.; Klecker, B.; Carr, C. M.
2008-08-01
A dipolarization and its associated current systems are studied using Cluster, Double Star TC1, and ground-based observations. The Cluster spacecraft are located approximately 16 RE downtail near 0030 LT. The Double Star TC1 spacecraft is located more earthward at approximately 7 RE just before local midnight. Auroral observations by the Wideband Imaging Camera on the Imager for Magnetopause-to-Aurora Global Exploration spacecraft are used to determine the onset times of substorms. It is shown that the magnetic phenomena at the earthward site of a magnetic reconfiguration region are governed by field-aligned currents, which in their turn generate auroral brightenings near the foot points of the spacecraft. It is also shown that the inward and outward motion of the dipolarization front near Cluster has a direct influence on the parallel plasma flow at TC1, indicating a piston mechanism. Just like a piston, the inward moving dipolarization at Cluster pushes in plasma along with the flux transport, which turns to parallel plasma flow at TC1. When the flow reverses at Cluster, i.e., outgoing flux transport, the plasma gets "sucked out" again, which is directly reflected in the plasma data from TC1.
Dipolar condensates with tilted dipoles in a pancake-shaped confinement
NASA Astrophysics Data System (ADS)
Mishra, Chinmayee; Nath, Rejish
2016-09-01
The effect of dipolar orientation with respect to the condensate plane on the mean-field dynamics of dipolar Bose-Einstein condensates in a pancake-shaped confinement is discussed. The stability of a quasi-two-dimensional condensate, with respect to the tilting angle, is found to be different from a two-dimensional layer of dipoles, indicating the relevance of the transverse extension while characterizing two-dimensional dipolar systems. An anisotropic excitation spectrum exhibiting a highly tunable, rotonlike minimum can arise entirely from the dipole-dipole interactions, by tilting the dipoles. At the magic angle and in the absence of contact interactions, the long-wavelength excitations are not phononlike and always unstable. The post-roton-instability dynamics, in contrast to phonon instability, in a uniform condensate, is featured by a transient, defect-free, stripe pattern, which eventually undergoes local collapses, and driving the condensate back into the stable regime can make them sustained for longer. Hopping between stripes has been observed before it melts into a uniform state in the presence of dissipation. Finally, we discuss a class of solutions, in which a quasi-two-dimensional condensate is self-trapped in one direction, as well as a regime of interaction parameters, including attractive short-range interactions, at which a two-dimensional anisotropic soliton can be stabilized, and we show that a chromium condensate with a relatively small number of atoms is well suited for this.
Constraining the dipolar magnetic field of M82 X-2 by the accretion model
NASA Astrophysics Data System (ADS)
Chen, Wen-Cong
2017-02-01
Recently, ultraluminous X-ray source (ULX) M82 X-2 has been identified to be an accreting neutron star, which has a P = 1.37 s spin period, and is spinning up at a rate dot{P}=-2.0× 10^{-10} s s^{-1}. Interestingly, its isotropic X-ray luminosity Liso = 1.8 × 1040 erg s- 1 during outbursts is 100 times the Eddington limit for a 1.4 M⊙ neutron star. In this Letter, based on the standard accretion model we attempt to constrain the dipolar magnetic field of the pulsar in ULX M82 X-2. Our calculations indicate that the accretion rate at the magnetospheric radius must be super-Eddington during outbursts. To support such a super-Eddington accretion, a relatively high multipole field ( ≳ 1013 G) near the surface of the accretor is invoked to produce an accreting gas column. However, our constraint shows that the surface dipolar magnetic field of the pulsar should be in the range of 1.0-3.5 × 1012 G. Therefore, our model supports that the neutron star in ULX M82 X-2 could be a low-magnetic-field magnetar (proposed by Tong) with a normal dipolar field (˜1012 G) and relatively strong multipole field. For the large luminosity variations of this source, our scenario can also present a self-consistency interpretation.
Theoretical Study of Dual-Direction Dipolar Excitation of Ions in Linear Ion Traps.
Dang, Qiankun; Xu, Fuxing; Wang, Liang; Huang, Xiaohua; Dai, Xinhua; Fang, Xiang; Wang, Rizhi; Ding, Chuan-Fan
2016-04-01
The ion enhanced activation and collision-induced dissociation (CID) by simultaneous dipolar excitation of ions in the two radial directions of linear ion trap (LIT) have been recently developed and tested by experiment. In this work, its detailed properties were further studied by theoretical simulation. The effects of some experimental parameters such as the buffer gas pressure, the dipolar excitation signal phases, power amplitudes, and frequencies on the ion trajectory and energy were carefully investigated. The results show that the ion activation energy can be significantly increased by dual-direction excitation using two identical dipolar excitation signals because of the addition of an excitation dimension and the fact that the ion motion radius related to ion kinetic energy can be greater than the field radius. The effects of higher-order field components, such as dodecapole field on the performance of this method are also revealed. They mainly cause ion motion frequency shift as ion motion amplitude increases. Because of the frequency shift, there are different optimized excitation frequencies in different LITs. At the optimized frequency, ion average energy is improved significantly with relatively few ions lost. The results show that this method can be used in different kinds of LITs such as LIT with 4-fold symmetric stretch, linear quadrupole ion trap, and standard hyperbolic LIT, which can significantly increase the ion activation energy and CID efficiency, compared with the conventional method.
Nonlinear localized modes in dipolar Bose-Einstein condensates in optical lattices
Rojas-Rojas, S.; Vicencio, R. A.; Molina, M. I.; Abdullaev, F. Kh.
2011-09-15
Modulational instability and discrete matter wave solitons in dipolar BECs, loaded into a deep optical lattice, are investigated analytically and numerically. The process of modulational instability of nonlinear plane matter waves in a dipolar nonlinear lattice is studied and the regions of instability are established. The existence and stability of bulk discrete solitons are analyzed analytically and confirmed by numerical simulations. In marked contrast with the usual discrete nonlinear Schroedinger behavior (no dipolar interactions), we found a region where the two fundamental modes are simultaneously unstable, allowing enhanced mobility across the lattice for large norm values. To study the existence and properties of surface discrete solitons, an analysis of the dimer configuration is performed. The properties of symmetric and antisymmetric modes including stability diagrams and bifurcations are investigated in closed form. For the case of a bulk medium, properties of fundamental on-site and intersite localized modes are analyzed. On-site and intersite surface localized modes are studied, and we find that they do not exist when nonlocal interactions predominate with respect to local ones.
Impurity modes in Frenkel exciton systems with dipolar interactions and cubic symmetry.
Avgin, I; Huber, D L
2013-04-28
We introduce a continuum model for impurity modes of Frenkel excitons in fully occupied face-centered and body-centered cubic lattices with dipole-dipole interactions and parallel moments. In the absence of impurities, the model reproduces the small-k behavior found in numerical calculations of dipolar lattice sums. The exciton densities of states near the upper and lower band edges are calculated and compared with the corresponding results for a random array of dipoles. The Green function obtained with the continuum model, together with a spherical approximation to the Brillouin zone, is used to determine the conditions for the formation of a localized exciton mode associated with a shift in the transition energy of a single chromophore. The dependence of the local mode energy on the magnitude of the shift is ascertained. The formation of impurity bands at high concentrations of perturbed sites is investigated using the coherent potential approximation. The contribution of the impurity bands to the optical absorption is calculated in the coherent potential approximation. The locations of the optical absorption peaks of the dipolar system are shown to depend on the direction of propagation of the light relative to the dipolar axis, a property that is maintained in the presence of short-range interactions.
The effect of bottom friction on tidal dipolar vortices and the associated transport
NASA Astrophysics Data System (ADS)
Duran-Matute, Matias; Kamp, Leon; van Heijst, Gertjan
2016-11-01
Tidal dipolar vortices can be formed in a semi-enclosed basin as the tides flow in and out through an inlet. If they are strong enough to overcome the opposing tidal currents, these vortices can travel away from the inlet due to their self-propelling mechanism, and hence, act as an efficient transport agent for suspended material. We present results of two-dimensional numerical simulations of the flow through an idealized tidal inlet, with either a linear or a nonlinear parameterization of the bottom friction. We then quantify the effect of the bottom friction on the propagation of the dipolar vortex and on its ability as a transport agent by computing the flushing and residence times of passive particles. Bottom friction is detrimental to the ability of tidal dipolar vortices to propagate and hinders transport away from the inlet. The magnitude of this effect is related to the relative duration of the tidal period as compared to the typical decay time scale of the vortex dipole. This research is funded by NWO (the Netherlands) through the VENI Grant 863.13.022.
NASA Astrophysics Data System (ADS)
Vinther, Joachim M.; Khaneja, Navin; Nielsen, Niels Chr.
2013-01-01
Refocused continuous wave (rCW) decoupling is presented as an efficient and robust means to obtain well-resolved magic-angle-spinning solid-state NMR spectra of low-γ spins, such as 13C dipolar coupled to fluorine. The rCW decoupling sequences, recently introduced for 1H decoupling, are very robust towards large isotropic and anisotropic shift ranges as often encountered for 19F spins. In rCW decoupling, the so-called refocusing pulses inserted into the CW irradiation eliminate critical residual second- and third-order dipolar coupling and dipolar-coupling against chemical shielding anisotropy cross-terms in the effective Hamiltonian through time-reversal (i.e. refocusing). As important additional assets, the rCW decoupling sequences are robust towards variations in rf amplitudes, operational at low to high spinning speeds, and easy to set-up for optimal performance experimentally. These aspects are demonstrated analytically/numerically and experimentally in comparison to state-of-the-art decoupling sequences such as TPPM, SPINAL-64, and frequency-swept variants of these.
Chain-based order and quantum spin liquids in dipolar spin ice
NASA Astrophysics Data System (ADS)
McClarty, P. A.; Sikora, O.; Moessner, R.; Penc, K.; Pollmann, F.; Shannon, N.
2015-09-01
Recent experiments on the spin-ice material Dy2Ti2O7 suggest that the Pauling "ice entropy," characteristic of its classical Coulombic spin-liquid state, may be lost at low temperatures [Pomaranski et al., Nat. Phys. 9, 353 (2013), 10.1038/nphys2591]. However, despite nearly two decades of intensive study, the nature of the equilibrium ground state of spin ice remains uncertain. Here we explore how long-range dipolar interactions D , short-range exchange interactions, and quantum fluctuations combine to determine the ground state of dipolar spin ice. We identify the organizational principle that ordered ground states are selected from a set of "chain states" in which dipolar interactions are exponentially screened. Using both quantum and classical Monte Carlo simulation, we establish phase diagrams as a function of quantum tunneling g and temperature T , and find that only a very small gc≪D is needed to stabilize a quantum spin liquid ground state. We discuss the implications of these results for Dy2Ti2O7 .
EPR-correlated dipolar spectroscopy by Q-band chirp SIFTER.
Doll, Andrin; Jeschke, Gunnar
2016-08-17
While two-dimensional correlation spectra contain more information as compared to one-dimensional spectra, typical spectral widths encountered in electron paramagnetic resonance (EPR) spectroscopy largely restrict the applicability of correlation techniques. In essence, the monochromatic excitation pulses established in pulsed EPR often cannot uniformly excite the entire spectrum. Here, this restriction is alleviated for nitroxide spin labels at Q-band microwave frequencies around 35 GHz. This is achieved by substitution of monochromatic pulses by frequency-swept chirp pulses tailored for uniform excitation. Unwanted interference effects brought by this substitution are analyzed for a pair of electron spins with secular dipolar coupling. Experimentally, the dipole-dipole interaction can be separated from other interactions by a constant-time Zeeman-compensated solid echo sequence called SIFTER. Such SIFTER experiments usually yield a one-dimensional dipolar spectrum. EPR-correlated dipolar spectra can be obtained when the four pulses are replaced by chirp pulses. These two-dimensional spectra encode additional information on the geometrical arrangement of the two spin labels. With the excitation parameters achieved by a home-built Q-band spectrometer capable of frequency-swept excitation, unwanted interference effects can be largely neglected for the examined model compound with a spin-spin distance of 4 nm. The experimentally obtained correlation pattern conforms to the expectation based on the inter-spin geometry of the investigated rigid model compound.
New cofactor supports α,β-unsaturated acid decarboxylation via 1,3-dipolar cycloaddition
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
Phase transitions to dipolar clusters and charge density waves in high Tc superconductors
NASA Astrophysics Data System (ADS)
Saarela, M.; Kusmartsev, F. V.
2017-02-01
We show that doping of hole charge carriers leads to formation of electric dipolar clusters in cuprates. They are created by many-body interactions between the dopant ion outside and holes inside the CuO planes. Because of the two-fold degeneracy holes in the CuO plane cluster into four-particles resonance valence bond plaquettes bound with dopant ions. Such dipoles may order into charge-density waves (CDW) or stripes or form a disordered state depending on doping and temperature. The lowest energy of the ordered system corresponds to a local anti-ferroelectric ordering. The mobility of individual disordered dipoles is very low at low temperatures and they prefer first to bind into dipole-dipole pairs. Electromagnetic radiation interacts strongly with electric dipoles and when the sample is subjected to it the mobility changes significantly. This leads to a fractal growth of dipolar clusters. The existence of electric dipoles and CDW induce two phase transitions with increasing temperature, melting of the ordered state and disappearance of the dipolar state. Ferroelectricity at low doping is a natural consequence of such dipole moments. We develop a theory based on two-level systems and dipole-dipole interaction to explain the behavior of the polarization as a function of temperature and electric field.
Theoretical Study of Dual-Direction Dipolar Excitation of Ions in Linear Ion Traps
NASA Astrophysics Data System (ADS)
Dang, Qiankun; Xu, Fuxing; Wang, Liang; Huang, Xiaohua; Dai, Xinhua; Fang, Xiang; Wang, Rizhi; Ding, Chuan-Fan
2016-04-01
The ion enhanced activation and collision-induced dissociation (CID) by simultaneous dipolar excitation of ions in the two radial directions of linear ion trap (LIT) have been recently developed and tested by experiment. In this work, its detailed properties were further studied by theoretical simulation. The effects of some experimental parameters such as the buffer gas pressure, the dipolar excitation signal phases, power amplitudes, and frequencies on the ion trajectory and energy were carefully investigated. The results show that the ion activation energy can be significantly increased by dual-direction excitation using two identical dipolar excitation signals because of the addition of an excitation dimension and the fact that the ion motion radius related to ion kinetic energy can be greater than the field radius. The effects of higher-order field components, such as dodecapole field on the performance of this method are also revealed. They mainly cause ion motion frequency shift as ion motion amplitude increases. Because of the frequency shift, there are different optimized excitation frequencies in different LITs. At the optimized frequency, ion average energy is improved significantly with relatively few ions lost. The results show that this method can be used in different kinds of LITs such as LIT with 4-fold symmetric stretch, linear quadrupole ion trap, and standard hyperbolic LIT, which can significantly increase the ion activation energy and CID efficiency, compared with the conventional method.
Statics and dynamics of a self-bound dipolar matter-wave droplet
NASA Astrophysics Data System (ADS)
Adhikari, S. K.
2017-02-01
We study the statics and dynamics of a stable, mobile, self-bound three-dimensional dipolar matter-wave droplet created in the presence of a tiny repulsive three-body interaction. In frontal collision with an impact parameter and in angular collision at large velocities along all directions two droplets behave like quantum solitons. Such a collision is found to be quasi elastic and the droplets emerge undeformed after collision without any change of velocity. However, in a collision at small velocities the axisymmeric dipolar interaction plays a significant role and the collision dynamics is sensitive to the direction of motion. For an encounter along the z direction at small velocities, two droplets, polarized along the z direction, coalesce to form a larger droplet—a droplet molecule. For an encounter along the x direction at small velocities, the same droplets stay apart and never meet each other due to the dipolar repulsion. The present study is based on an analytic variational approximation and a numerical solution of the mean-field Gross-Pitaevskii equation using the parameters of 52Cr atoms.
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
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
NASA Astrophysics Data System (ADS)
Kumar, R. Kishor; Young-S., Luis E.; Vudragović, Dušan; Balaž, Antun; Muruganandam, Paulsamy; Adhikari, S. K.
2015-10-01
Many of the static and dynamic properties of an atomic Bose-Einstein condensate (BEC) are usually studied by solving the mean-field Gross-Pitaevskii (GP) equation, which is a nonlinear partial differential equation for short-range atomic interaction. More recently, BEC of atoms with long-range dipolar atomic interaction are used in theoretical and experimental studies. For dipolar atomic interaction, the GP equation is a partial integro-differential equation, requiring complex algorithm for its numerical solution. Here we present numerical algorithms for both stationary and non-stationary solutions of the full three-dimensional (3D) GP equation for a dipolar BEC, including the contact interaction. We also consider the simplified one- (1D) and two-dimensional (2D) GP equations satisfied by cigar- and disk-shaped dipolar BECs. We employ the split-step Crank-Nicolson method with real- and imaginary-time propagations, respectively, for the numerical solution of the GP equation for dynamic and static properties of a dipolar BEC. The atoms are considered to be polarized along the z axis and we consider ten different cases, e.g., stationary and non-stationary solutions of the GP equation for a dipolar BEC in 1D (along x and z axes), 2D (in x- y and x- z planes), and 3D, and we provide working codes in Fortran 90/95 and C for these ten cases (twenty programs in all). We present numerical results for energy, chemical potential, root-mean-square sizes and density of the dipolar BECs and, where available, compare them with results of other authors and of variational and Thomas-Fermi approximations.
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.
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.
NASA Astrophysics Data System (ADS)
Pergamenshchik, V. M.; Uzunova, V. A.
2011-02-01
In spite of the analogy to the electrostatics, the three-dimensional colloidal nematostatics is substantially different in both its mathematical structure and its physical implications. The general tensorial structure of elastic multipoles derived in V. M. Pergamenshchik and V. O. Uzunova [Eur. Phys. J. EEPJSFH1292-894110.1140/epje/i2006-10169-x 23, 161 (2007); Phys. Rev. EEPJSFH1539-375510.1103/PhysRevE.76.011707 76, 011707 (2007)] allows for a classification of different types of colloids in the nematostatics. In comparison to their electrostatic counterparts, the elastic multipoles have one extra tensorial index. Based on this structure, we identify possible types of elastic dipoles. An elastic dipole is characterized by three coefficients—isotropic strength, anisotropy, and chirality—and a two-component vector along the unperturbed director. The relationship between the dipole type and symmetry groups is established and sketches of various representative types of dipolar colloids are given. Instead of a single electric dipole, in the nematostatics there are four different pure types (dipolar singlets) and eight mixed types of elastic dipoles (one quintet, one quartet, two triplets, and four doublets). It is shown that the full symmetry of the colloid-induced director field and the colloid’s shape (body) symmetry determine different dipole components. For instance, a helicoidal component of the anchoring easy axes can make a chiral elastic dipole of a colloid with the quadrupolar shape symmetry. The interaction potentials for different singlet and doublet dipoles are derived and illustrated in terms of the dipolar dyads and elastic Coulomb law. We argue that multipole parameters must be found by pure numerical means, as from ansatz director distributions one can find only orders of their magnitudes.
NASA Astrophysics Data System (ADS)
Moscoso-Londoño, O.; Tancredi, P.; Muraca, D.; Mendoza Zélis, P.; Coral, D.; Fernández van Raap, M. B.; Wolff, U.; Neu, V.; Damm, C.; de Oliveira, C. L. P.; Pirota, K. R.; Knobel, M.; Socolovsky, L. M.
2017-04-01
Controlled magnetic granular materials with different concentrations of magnetite nanoparticles immersed in a non-conducting polymer matrix were synthesized and, their macroscopic magnetic observables analyzed in order to advance towards a better understanding of the magnetic dipolar interactions and its effects on the obtained magnetic parameters. First, by means of X-ray diffraction, transmission electron microscopy, small angle X-ray scattering and X-ray absorption fine structure an accurate study of the structural properties was carried out. Then, the magnetic properties were analyzed by means of different models, including those that consider the magnetic interactions through long-range dipolar forces as: the Interacting Superparamagnetic Model (ISP) and the Vogel-Fulcher law (V-F). In systems with larger nanoparticle concentrations, magnetic results clearly indicate that the role played by the dipolar interactions affects the magnetic properties, giving rise to obtaining magnetic and structural parameters without physical meaning. Magnetic parameters as the effective anisotropic constant, magnetic moment relaxation time and mean blocking temperature, extracted from the application of the ISP model and V-F Law, were used to simulate the zero-field-cooling (ZFC) and field-cooling curves (FC). A comparative analysis of the simulated, fitted and experimental ZFC/FC curves suggests that the current models depict indeed our dilute granular systems. Notwithstanding, for concentrated samples, the ISP model infers that clustered nanoparticles are being interpreted as single entities of larger magnetic moment and volume, effect that is apparently related to a collective and complex magnetic moment dynamics within the cluster.
NASA Astrophysics Data System (ADS)
Wood, A. A.; McKellar, B. H. J.; Martin, A. M.
2016-06-01
We show that the He-McKellar-Wilkens effect can induce a persistent flow in a Bose-Einstein condensate of polar molecules confined in a toroidal trap, with the dipolar interaction mediated via an electric dipole moment. For Bose-Einstein condensates of atoms with a magnetic dipole moment, we show that although it is theoretically possible to induce persistent flow via the Aharonov-Casher effect, the strength of the electric field required is prohibitive. We also outline an experimental geometry tailored specifically for observing the He-McKellar-Wilkens effect in toroidally trapped condensates.
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.
Influence of the black hole spin on the chaotic particle dynamics within a dipolar halo
NASA Astrophysics Data System (ADS)
Nag, Sankhasubhra; Sinha, Siddhartha; Ananda, Deepika B.; Das, Tapas K.
2017-04-01
We investigate the role of the spin angular momentum of astrophysical black holes in controlling the special relativistic chaotic dynamics of test particles moving under the influence of a post-Newtonian pseudo-Kerr black hole potential, along with a perturbative potential created by an asymmetrically placed (dipolar) halo. Proposing a Lyapunov-like exponent to be the effective measure of the degree of chaos observed in the system under consideration, it has been found that black hole spin anti-correlates with the degree of chaos for the aforementioned dynamics. Our findings have been explained applying the general principles of dynamical systems analysis.
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.
Dipolar field-induced spin-wave waveguides for spin-torque magnonics
Demidov, V. E.; Urazhdin, S.; Zholud, A.; Sadovnikov, A. V.; Demokritov, S. O.
2015-01-12
We use high-resolution imaging to study the propagation of spin waves in magnonic waveguides created by the dipolar magnetic fields of microscopic patterns. We show that the characteristics of spin-wave modes in such waveguides depend strongly on their geometry. In particular, by tuning the geometrical parameters, field-induced confinement for both the edge and the center waveguide modes can be achieved, enabling control over the spin-wave transmission characteristics. The studied waveguiding structures are particularly promising for the implementation of magnonic devices utilizing spin-torque phenomena.
s -wave scattering lengths of the strongly dipolar bosons 162Dy and 164Dy
NASA Astrophysics Data System (ADS)
Tang, Yijun; Sykes, Andrew; Burdick, Nathaniel Q.; Bohn, John L.; Lev, Benjamin L.
2015-08-01
We report the measurement of the deca-heptuplet s -partial-wave scattering length a of two bosonic isotopes of the highly magnetic element dysprosium: a =112 (10 ) a0 for 162Dy and a =92 (8 ) a0 for 164Dy, where a0 is the Bohr radius. The scattering lengths are determined by the cross-dimensional relaxation of ultracold gases of these Dy isotopes at temperatures above quantum degeneracy. In this temperature regime, the measured rethermalization dynamics can be compared to simulations of the Boltzmann equation using a direct-simulation Monte Carlo method employing the anisotropic differential scattering cross section of dipolar particles.
Triazol-substituted titanocenes by strain-driven 1,3-dipolar cycloadditions
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
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.
Ruder, Warren C; Hsu, Chia-Pei D; Edelman, Brent D; Schwartz, Russell; Leduc, Philip R
2012-08-06
We have studied the dynamic behavior of nanoparticles in ferrofluids consisting of single-domain, biogenic magnetite (Fe(3)O(4)) isolated from Magnetospirillum magnetotacticum (MS-1). Although dipolar chains form in magnetic colloids in zero applied field, when dried upon substrates, the solvent front disorders nanoparticle aggregation. Using avidin-biotin functionalization of the particles and substrate, we generated self-assembled, linear chain motifs that resist solvent front disruption in zero-field. The engineered self-assembly process we describe here provides an approach for the creation of ordered magnetic structures that could impact fields ranging from micro-electro-mechanical systems development to magnetic imaging of biological structures.
Conditions for the spin wave nonreciprocity in an array of dipolarly coupled magnetic nanopillars
NASA Astrophysics Data System (ADS)
Verba, Roman; Tiberkevich, Vasil; Bankowski, Elena; Meitzler, Thomas; Melkov, Gennadiy; Slavin, Andrei
2013-08-01
It is demonstrated that collective spin waves (SWs) propagating in complex periodic arrays of dipolarly coupled magnetic nanopillars existing in a saturated (single-domain) ground state in a zero bias magnetic field could be nonreciprocal. To guarantee the SW nonreciprocity, two conditions should be fulfilled: (i) existence of a nonzero out-of-plane component of the pillars' static magnetization and (ii) a complex periodicity of array's ground state with at least two elements per a primitive cell, if the elements are different, and at least three elements per a primitive cell, if the elements are identical.
Meyer, Adam G; Ryan, John H
2016-07-23
We provide a comprehensive account of the 1,3-dipolar cycloaddition reactions of azomethine ylides with carbonyl dipolarophiles. Many different azomethine ylides have been studied, including stabilized and non-stabilized ylides. Of the carbonyl dipolarophiles, aldehydes including formaldehyde are the most studied, although there are now examples of cycloadditions with ketones, ketenes and carboxyl systems, in particular isatoic anhydrides and phthalic anhydrides. Intramolecular cycloadditions with esters can also occur under certain circumstances. The oxazolidine cycloadducts undergo a range of reactions triggered by the ring-opening of the oxazolidine ring system.
Three-body interacting dipolar bosons and the fate of lattice supersolidity
NASA Astrophysics Data System (ADS)
Singh, Manpreet; Mishra, Tapan
2016-12-01
We investigate a system of dipolar bosons in an optical lattice with local two- and three-body interactions. Using the mean-field-theory approach, we obtain the ground-state phase diagram of the extended Bose-Hubbard model with both repulsive and attractive three-body interactions. We show that the additional three-body on-site interaction has strong effects on the phase diagram, especially on the supersolid phase. Positive values of the three-body interaction lead to the enhancement of the gapped phases at densities larger than unity by reducing the supersolid region. However, a small attractive three-body interaction enhances the supersolid phase.
Theoretical Study of 1,3-Dipolar Cycloaddition of Hydrazoic Acid to Substituted Ynamines
NASA Astrophysics Data System (ADS)
Chen, Xiao-fang; Yang, Kun; Han, Ke-li
2009-04-01
The 1,3-dipolar cycloaddition reactions of various substituted ynamines with hydrazoic acid were theoretically investigated with the high-accuracy CBS-QB3 method. Two regioisomers, 4-amine, and 5-amine substituted adducts, were obtained, with the former as the preferred yield. This regioselectivity is rationalized by the frontier molecular orbital theory. The reactivity and synchronicity are enhanced with the increase of the electron-withdrawing character of the substitute on ynamine fragment. The calculations also show that the effect of solvent increases the activation energy, and the reaction becomes even harder in polar solvent.
Multiple Field Induced Transitions in the Dipolar Pyrochlore Gd2 Ti2 O_7
NASA Astrophysics Data System (ADS)
Shastry, B. Sriram
2003-03-01
Pyrochlore frustrated magnetic systems have received considerable attention after the experiment by Ramirez and coworkers on the ``Spin Ice'' compound DTO or Dy2 Ti2 O_7, a magnetic realization of entropic Ice originally studied by Pauling, Bernal and Fowler. DTO consists of effective spin half moments residing on the Pyrochlore lattice, but by changing the rare earth, one has realizations of the XY and also Heisenberg models. GTO, or Gd2 Ti2 O7 is a Heisenberg system, where the interactions are predominantly dipolar with a weak isotropic superexchange. This enables one to study almost for the first time, the rich and novel behavior of spins living on undistorted cubic systems with dipolar interactions, in contrast to the well understood spin flop transition in uniaxial magnets. The thermodynamics in the presence of a magnetic field of (powder) GTO shows a remarkably rich phase diagram[1], with several phase transitions occurring at a given temperature as the field is varied. In an effort to understand this, we have studied a 4- sublattice mean field theory[1] wherein the spins interact via a dipolar interaction plus superexchange. This mean field theory is intriguingly non trivial and reproduces the observed transitions with only one free parameter (J). The magnetic field partially lifts the degeneracy of the six zero field states in a specific ways depending on the direction of the field, signaling the transitions. The nature of some of the transitions is best described in terms of a nematic type order parameter T^α, β=1/4 sum_i=1^4 m^αi m^βi where mi is the sublattice magnetization vector. This talk describes the above experiment and theory, its recent extensions, and also some more recent experiments on GTO. [1] "Multiple Phase Transitions in a Geometrically-Frustrated Dipolar Spin System Gd_2Ti_2O_7, (A P Ramirez, B S Shastry , A Hayashi, J J Krajewski, D A Huse, and R J Cava), Phys. Rev. Letts. 89, 067202 (2002).
Computer-Assisted 3D Structure Elucidation of Natural Products using Residual Dipolar Couplings.
Troche-Pesqueira, Eduardo; Anklin, Clemens; Gil, Roberto R; Navarro-Vázquez, Armando
2017-03-20
An enhanced computer-assisted procedure for the determination of the relative configuration of natural products, which starts from the molecular formula and uses a combination of conventional 1D and 2D NMR spectra, and residual dipolar couplings (RDCs), is reported. Having already the data acquired (1D/2D NMR and RDCs), the procedure begins with the determination of the molecular constitution using standard computer-assisted structure elucidation (CASE) and is followed by fully automated determination of relative configuration through RDC analysis. In the case of moderately flexible molecules the simplest data-explaining conformational model is selected by the use of the Akaike information criterion.
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.
NASA Astrophysics Data System (ADS)
Kindervater, J.; Säubert, S.; Böni, P.
2017-01-01
Iron is one of the archetypical ferromagnets to study the critical fluctuations at a continuous phase transition thus serving as a model system for the application of scaling theory. We report a comprehensive study of the critical dynamics at the transition from the ferro- to the paramagnetic phase in Fe, employing the high-resolution neutron spin-echo technique, modulated intensity of zero effort (MIEZE). The results show that the dipolar interactions lead to an additional damping of the critical spin fluctuations at small momentum transfers q . The results agree essentially with scaling theory if the dipolar interactions are taken into account by means of the mode-coupling equations. However, in contrast to expectations, the dipolar wave number qD that plays a central role in the scaling function f (κ /q ,qD/κ ) becomes temperature dependent. In the limit of small q the critical exponent z crosses over from 2.5 to 2.0.
The dipolar interaction in CoFeB/MgO/CoFeB perpendicular magnetic tunnel junction
NASA Astrophysics Data System (ADS)
Tsai, C. C.; Cheng, Chih-Wei; Weng, Yi-Chien; Chern, G.
2014-05-01
Ultrathin CoFeB/MgO/CoFeB system with perpendicular magnetic anisotropy is a promising candidate for the high density magnetic random access memory. However, a dipolar interaction between the CoFeB layers may introduce a minor loop shift (Hs) and causes uncertainty during the operation. In this report, we systematically studied the dipolar effect in these structures and found that the coupling may be either ferromagnetic or antiferromagnetic (15 Oe > Hs > -15 Oe) depending upon the CoFeB thickness (0.9-1.4 nm). A modified Fabry-Perot model, which accounts the Bloch wave interference, may explain the present observations of the dipolar effect in the perpendicular junctions of CoFeB/MgO/CoFeB.
Ground-state properties of few dipolar bosons in a quasi-one-dimensional harmonic trap
Deuretzbacher, F.; Cremon, J. C.; Reimann, S. M.
2010-06-15
We study the ground state of few bosons with repulsive dipole-dipole interaction in a quasi-one-dimensional harmonic trap by means of the exact diagonalization method. Up to three interaction regimes are found, depending on the strength of the dipolar interaction and the ratio of transverse to axial oscillator lengths: a regime where the dipolar Bose gas resembles a system of weakly {delta}-interacting bosons, a second regime where the bosons are fermionized, and a third regime where the bosons form a Wigner crystal. In the first two regimes, the dipole-dipole potential can be replaced by a {delta} potential. In the crystalline state, the overlap between the localized wave packets is strongly reduced and all the properties of the boson system equal those of its fermionic counterpart. The transition from the Tonks-Girardeau gas to the solidlike state is accompanied by a rapid increase of the interaction energy and a considerable change of the momentum distribution, which we trace back to the different short-range correlations in the two interaction regimes.
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.
Ground-state and dynamical properties of two-dimensional dipolar Fermi liquids
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.
Low density mesostructures of confined dipolar particles in an external field.
Richardi, J; Weis, J-J
2011-09-28
Mesostructures formed by dipolar particles confined between two parallel walls and subjected to an external field are studied by Monte Carlo simulations. The main focus of the work is the structural behavior of the Stockmayer fluid in the low density regime. The dependence of cluster thickness and ordering is estimated as a function of density and wall separation, the two most influential parameters, for large dipole moments and high field strengths. The great sensitivity of the structure to details of the short-range part of the interactions is pointed out. In particular, the attractive part of the Lennard-Jones potential is shown to play a major role in driving chain aggregation. The effect of confinement, evaluated by comparison with results for a bulk system, is most pronounced for a short range hard sphere potential. No evidence is found for a novel "gel-like" phase recently uncovered in low density dipolar colloidal suspensions [A. K. Agarwal and A. Yethiraj, Phys. Rev. Lett. 102, 198301 (2009)].
Dipolar Effects in an Ultracold Gas of LiCs Molecules
NASA Astrophysics Data System (ADS)
Weidemueller, Matthias
2011-05-01
Recently, there has been important progress in the investigation of ultracold polar molecules in the absolute ground state, thus opening intriguing perspectives for strongly correlated quantum systems under the influence of long-range dipolar forces. We have studied the formation of LiCs molecules via photoassociation (PA) in a double-species magneto-optical trap. The LiCs dimer is a particularly promising candidate for observing dipolar effects, as it possesses the largest dipole moment of all alkali dimers (5.5 Debye in the ground state). Ultracold LiCs molecules in the absolute rovibrational ground state are formed by a single photo-association step. The dipole moment of ground state levels is determined by Stark spectroscopy and was found to be in excellent agreement with the theoretical predictions. Vibrational redistribution due to spontaneous emission and blackbody radiation is observed and compared a rate-equation model.In collaboration with Johannes Deiglmayr, Marc Repp, University of Heidelberg; Roland Wester, University of Innsbruck; and Olivier Dulieu, Laboratoire Aime Cotton. Work was supported by DFG and ESF in the framework of the Eurocores EuroQUAM as well as the Heidelberg Center for Quantum Dynamics.
1,3-Dipolar cycloaddition of organic azides to alkynes by a dicopper-substituted silicotungstate.
Kamata, Keigo; Nakagawa, Yoshinao; Yamaguchi, Kazuya; Mizuno, Noritaka
2008-11-19
The dicopper-substituted gamma-Keggin silicotungstate TBA 4[gamma-H2SiW10O36Cu2(mu-1,1-N3)2] (I, TBA = tetra- n-butylammonium) could act as an efficient precatalyst for the regioselective 1,3-dipolar cycloaddition of organic azides to alkynes. Various combinations of substrates (four azides and eight alkynes) were efficiently converted to the corresponding 1,2,3-triazole derivatives in excellent yields without any additives. The present system was applicable to a larger-scale cycloaddition of benzyl azide to phenylacetylene under solvent-free conditions (100 mmol scale) in which 21.5 g of the analytically pure corresponding triazole could be isolated. In this case, the turnover frequency and the turnover number reached up to 14,800 h(-1) and 91,500, respectively, and these values were the highest among those reported for the copper-mediated systems so far. In addition, I could be applied to the one-pot synthesis of 1-benzyl-4-phenyl-1H-1,2,3-triazole from benzyl chloride, sodium azide, and phenylacetylene. The catalyst effect, kinetic, mechanistic, and computational studies show that the reduced dicopper core plays an important role in the present 1,3-dipolar cycloaddition.
NASA Astrophysics Data System (ADS)
Chan, Jerry C. C.; Eckert, Hellmut
2000-12-01
Anexperimental strategy has been developed for measuring multiple dipole-dipole interactions in inorganic compounds using the technique of rotational echo double resonance (REDOR) NMR. Geometry-independent information about the dipole couplings between the observe nuclear species S (arbitrary quantum number) and the heteronuclear species I (spin-{1}/{2}) can be conveniently obtained from the experimental curve of ΔS/S0 versus dipolar evolution time by limiting the analysis to the initial data range 0 < ΔS/S0 < 0.30. Numerical simulations have been carried out on a three-spin system of type SI2 in order to assess the effect of the I-I homonuclear dipole-dipole coupling and the influence of experimental imperfections such as finite pulse length and misadjustments of the 180° pulses applied to the I-spin species. The simulations show further that within the initial data range the effects of such misadjustments can be internally compensated by a modified sequence having an additional 180° pulse on the I channel in the middle of the dipolar evolution periods. Experimental 27Al{31P} REDOR results on the multispin systems Al(PO3)3, AlPO4, [AlPO4]12(C3H7)4NF, and Na3PO4 confirm the general utility of this approach. Thus, for applications to unknown systems the compensation strategy obviates calibration procedures with model compounds.
Asymmetric 1,3-Dipolar Cycloaddition Reactions Catalyzed by Heterocycle-Based Metal Complexes
NASA Astrophysics Data System (ADS)
Suga, Hiroyuki
Highly enantioselective 1,3-dipolar cycloaddition reactions of several 1,3-dipoles, such as nitrones, nitrile oxides, nitrile imines, diazoalkanes, azomethine imines and carbonyl ylides, catalyzed by heterocyclic supramolecular type of metal complexes consisting of chiral heterocyclic compounds and metal salts were described in terms of their ability of asymmetric induction and enantioface differentiation. The scope and limitations of each cycloaddition reactions were also briefly described. Of the chiral hererocycle-based ligands, chiral bisoxazoline, 2,6-bis(oxazolinyl)pyridine, and related oxazoline ligands are shown to be quite effective in obtaining high levels of asymmtric induction. The combination of the bisoxazoline ligand derived from (1S,2R)-cis-1-amino-2-indanol and metal salts was especially efficient for asymmetric cycloaddition reactions of a number of 1,3-dipoles, such as nitrones, nitrile oxide, nitrile imines, diazoacetates and azomethine imines. The metals utilized for the heterocycle-based complexes show a crucial role for degree of asymmetric induction depending upon the 1,3-dipole used. High levels of enantioselectivity were achieved in 1,3-dipolar cycloaddition reactions of unstable carbonyl ylides with benzyloxyacetaldehyde derivatives, α-keto esters, 3-(2-alkenoyl)-2-oxazolidinones, and even vinyl ethers, which were catalyzed by Pybox-lanthanoid metal complexes.
Khaneja, Navin; Kehlet, Cindie; Glaser, Steffen J; Nielsen, Niels Chr
2006-03-21
The efficiency of dipole-dipole coupling driven coherence transfer experiments in solid-state nuclear magnetic resonance (NMR) spectroscopy of powder samples is limited by dispersion of the orientation of the internuclear vectors relative to the external magnetic field. Here we introduce general design principles and resulting pulse sequences that approach full polarization transfer efficiency for all crystallite orientations in a powder in magic-angle-spinning experiments. The methods compensate for the defocusing of coherence due to orientation dependent dipolar coupling interactions and inhomogeneous radio-frequency fields. The compensation scheme is very simple to implement as a scaffold (comb) of compensating pulses in which the pulse sequence to be improved may be inserted. The degree of compensation can be adjusted and should be balanced as a compromise between efficiency and length of the overall pulse sequence. We show by numerical and experimental data that the presented compensation protocol significantly improves the efficiency of known dipolar recoupling solid-state NMR experiments.
Spectroscopy of dipolar fermions in layered two-dimensional and three-dimensional lattices
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.
Wang, Xiaoguang; Miller, Daniel S.; de Pablo, Juan J.; Abbott, Nicholas L.
2014-08-15
The spontaneous positioning of colloids on the surfaces of micrometer-sized liquid crystal (LC) droplets and their subsequent polymerization offers the basis of a general and facile method for the synthesis of patchy microparticles. The existence of multiple local energetic minima, however, can generate kinetic traps for colloids on the surfaces of the LC droplets and result in heterogeneous populations of patchy microparticles. To address this issue, in this paper it is demonstrated that adsorbate-driven switching of the internal configurations of LC droplets can be used to sweep colloids to a single location on the LC droplet surfaces, thus resulting in the synthesis of homogeneous populations of patchy microparticles. The surface-driven switching of the LC can be triggered by addition of surfactant or salts, and permits the synthesis of dipolar microparticles as well as “Janus-like” microparticles. Finally, by using magnetic colloids, the utility of the approach is illustrated by synthesizing magnetically responsive patchy microdroplets of LC with either dipolar or quadrupolar symmetry that exhibit distinct optical responses upon application of an external magnetic field.
Wang, Xiaoguang; Miller, Daniel S.; de Pablo, Juan J.; ...
2014-08-15
The spontaneous positioning of colloids on the surfaces of micrometer-sized liquid crystal (LC) droplets and their subsequent polymerization offers the basis of a general and facile method for the synthesis of patchy microparticles. The existence of multiple local energetic minima, however, can generate kinetic traps for colloids on the surfaces of the LC droplets and result in heterogeneous populations of patchy microparticles. To address this issue, in this paper it is demonstrated that adsorbate-driven switching of the internal configurations of LC droplets can be used to sweep colloids to a single location on the LC droplet surfaces, thus resulting inmore » the synthesis of homogeneous populations of patchy microparticles. The surface-driven switching of the LC can be triggered by addition of surfactant or salts, and permits the synthesis of dipolar microparticles as well as “Janus-like” microparticles. Finally, by using magnetic colloids, the utility of the approach is illustrated by synthesizing magnetically responsive patchy microdroplets of LC with either dipolar or quadrupolar symmetry that exhibit distinct optical responses upon application of an external magnetic field.« less
Transport of dipolar excitons in (Al,Ga)N/GaN quantum wells
NASA Astrophysics Data System (ADS)
Fedichkin, F.; Andreakou, P.; Jouault, B.; Vladimirova, M.; Guillet, T.; Brimont, C.; Valvin, P.; Bretagnon, T.; Dussaigne, A.; Grandjean, N.; Lefebvre, P.
2015-05-01
We investigate the transport of dipolar indirect excitons along the growth plane of polar (Al,Ga)N/GaN quantum well structures by means of spatially and time-resolved photoluminescence spectroscopy. The transport in these strongly disordered quantum wells is activated by dipole-dipole repulsion. The latter induces an emission blue shift that increases linearly with exciton density, whereas the radiative recombination rate increases exponentially. Under continuous, localized excitation, we observe continuously decreasing emission energy, as excitons propagate away from the excitation spot. This corresponds to a steady-state gradient of exciton density, measured over several tens of micrometers. Time-resolved microphotoluminescence experiments provide information on the dynamics of recombination and transport of dipolar excitons. We account for the ensemble of experimental results by solving the nonlinear drift-diffusion equation. Quantitative analysis suggests that in such structures, exciton propagation on the scale of 10 to 20 μ m is mainly driven by diffusion, rather than by drift, due to the strong disorder and the presence of nonradiative defects. Secondary exciton creation, most probably by the intense higher-energy luminescence, guided along the sample plane, is shown to contribute to the exciton emission pattern on the scale up to 100 μ m . The exciton propagation length is strongly temperature dependent, the emission being quenched beyond a critical distance governed by nonradiative recombination.
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.
Supra Arcade Downflows with XRT Informed by Dipolarization Fronts with THEMIS
NASA Technical Reports Server (NTRS)
Kobelski, Adam; Savage, Sabrina L.; Malaspina, David M.
2016-01-01
Magnetic reconnection can rapidly reconfigure the magnetic field of the corona, accelerating plasma through the site of reconnection. Ambiguities due to the nature of remote sensing have complicated the interpretation of observations of the inflowing and outflowing plasma in reconnecting regions. In particular, the interpretation of sunward moving density depletions above flare arcades (known as Supra Arcade Downflows - SADs) is still debated. Hinode/XRT has provided a wealth of observations for SADs and helped inform our current understanding of these structures. SADs have been interpreted as wakes behind newly reconnected and outflowing loops (Supra Arcade Downflowing Loops - SADLs). Models have shown the plausibility of this interpretation, though this interpretation has not yet been fully accepted. We present here observations of newly reconnected outflowing loops observed via in situ instruments in the magnetosphere. These observations, provided by five THEMIS spacecraft, show that around retracting loops (dipolarization fronts in this context) similar dynamic temperature and density structures are found as seen in SADs. We compare data from multiple SADs and dipolarization fronts to show that the observational signatures implied in the corona can be directly observed in similar plasma regimes in the magnetosphere, strongly favoring the interpretation of SADs as wakes behind retracting loops.
Supramolecular Magnetic Brushes: The Impact of Dipolar Interactions on the Equilibrium Structure
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
SOLAR MICRO-TYPE III BURST STORMS AND LONG DIPOLAR MAGNETIC FIELD IN THE OUTER CORONA
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.
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.
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.
Washburn, Kathryn E; Cheng, Yuesheng
2017-03-04
The mechanism behind surface relaxivity within organic porosity in shales has been an unanswered question. Here, we present results that confirm the existence of intermolecular homonuclear dipolar coupling between solid and liquid phases in sedimentary organic matter. Transverse magnetization exchange measurements were performed on an organic-rich shale saturated with liquid hydrocarbon. Liquid and solid constituents were identified through both sample resaturation and through their T1/T2 ratios. Extensive cross peaks are observed in the T2-T2 exchange spectra between the solid and liquid constituents, indicating an exchange of magnetization between the two phases. This result cannot arise from physical molecular diffusion, and the dissolution energies are too high for chemical exchange, such that the magnetization exchange must arise from intermolecular homonuclear dipolar coupling. These results both confirm a possible source of surface relaxivity in organic matter and emphasize caution in the use of standard porous media interpretations of relaxation results in shales because of coupling between different magnetization environments.
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
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
NASA Astrophysics Data System (ADS)
Spöler, C.; Klapp, S. H. L.
2004-11-01
Using replica integral equations in the reference hypernetted-chain (RHNC) approximation we calculate vapor-liquid spinodals, chemical potentials, and compressibilities of fluids with angle-averaged dipolar interactions adsorbed to various disordered porous media. Comparison with previous RHNC results for systems with true angle-dependent Stockmayer (dipolar plus Lennard-Jones) interactions [C. Spöler and S. H. L. Klapp, J. Chem. Phys. 118, 3628 (2003); ibid.120, 6734 (2004)] indicate that, for a dilute hard sphere matrix, the angle-averaged fluid-fluid (ff) potential is a reasonable alternative for reduced fluid dipole moments m*2=μ2/(ɛ0σ3)⩽2.0. This range is comparable to that estimated in bulk fluids, for which RHNC results are presented as well. Finally, results for weakly polar matrices suggest that angle-averaged fluid-matrix (fm) interactions can reproduce main features observed for true dipolar (fm) interactions such as the shift of the vapor-liquid spinodals towards lower temperatures and higher densities. However, the effective attraction induced by dipolar (fm) interaction is underestimated rather than overestimated as in the case of angle-averaged ff interactions.
P-wave superfluid in a quasi-two-dimensional dipolar Bose-Fermi quantum gas mixture
NASA Astrophysics Data System (ADS)
Kain, Ben; Ling, Hong
2013-03-01
The p-wave (px + ipy) superfluid has attracted significant attention in recent years mainly because its vortex core supports a Majorana fermion which, due to its non-Abelian statistics, can be explored for implementing topological quantum computation (TQC). Mixing in bosons may lead to p-wave pairing in a Fermi gas. In a dipolar condensate, the dipole-dipole interaction represents a control knob inaccessible to nondipolar Bosons. Thus, mixing dipolar bosons with fermions opens up new possibilities. We consider a mixture of a spin-polarized Fermi gas and a dipolar Bose-Einstein condensate in a quasi-two-dimensional trap setting. We take the Hartree-Fock-Bogoliubov mean-field approach and develop a theory for studying the stability of the mixture and estimating the critical temperature of the p-wave superfluid. We use this theory to identify the experimentally accessible parameter space in which the mixture is stable against phase separation and the p-wave superfluid pairing can be resonantly enhanced. An enhanced p-wave superfluid order parameter can make the fault tolerant TQC less susceptible to thermal fluctuations. This work aims to stimulate experimental activity in creating dipolar Bose-Fermi mixtures. This work is supported by the US National Science Foundation and the US Army Research Office
Brioche, Julien; Meyer, Christophe; Cossy, Janine
2015-06-05
Electron-deficient ynamides, possessing an ynoate or an ynone moiety, have been successfully involved for the first time in a 1,3-dipolar cycloaddition with stabilized pyridinium ylides. These reactions afford an efficient and general access toward a variety of substituted 2-aminoindolizines which can serve as useful precursors for the synthesis of other more complex nitrogen heterocycles.
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
Xu, Qin; Wang, De; Wei, Yin; Shi, Min
2014-06-01
A highly regio- and stereoselective synthesis of bispirooxindoles by 1,3-dipolar cycloaddition of in situ generated azomethine ylides from isatin and proline to different electron-deficient alkenes has been developed. The synthesis affords the desired bispiro scaffold compounds in excellent yields with high regioselectivity under mild conditions. The stereochemistry was determined by single-crystal X-ray analysis.
Pietrzik, Nikolas; Schmollinger, Daniel
2008-01-01
Summary Copper-catalyzed, thermal or microwave promoted 1,3-dipolar cycloaddition (Click Reaction) of 2-propynyl and 3-butynyl 2,3,4-tri-O-acetyl-6-azido-6-deoxy-glycopyranosides in the D-gluco, D-galacto and D-manno series afford the corresponding dimeric cycloaddition products. PMID:18941499
Tosner, Zdenek; Glaser, Steffen J; Khaneja, Navin; Nielsen, Niels Chr
2006-11-14
We report the use of optimal control algorithms for tailoring the effective Hamiltonians in nuclear magnetic resonance (NMR) spectroscopy through sophisticated radio-frequency (rf) pulse irradiation. Specifically, we address dipolar recoupling in solid-state NMR of powder samples for which case pulse sequences offering evolution under planar double-quantum and isotropic mixing dipolar coupling Hamiltonians are designed. The pulse sequences are constructed numerically to cope with a range of experimental conditions such as inhomogeneous rf fields, spread of chemical shifts, the intrinsic orientation dependencies of powder samples, and sample spinning. While the vast majority of previous dipolar recoupling sequences are operating through planar double-or zero-quantum effective Hamiltonians, we present here not only improved variants of such experiments but also for the first time homonuclear isotropic mixing sequences which transfers all I(x), I(y), and I(z) polarizations from one spin to the same operators on another spin simultaneously and with equal efficiency. This property may be exploited to increase the signal-to-noise ratio of two-dimensional experiments by a factor of square root 2 compared to conventional solid-state methods otherwise showing the same efficiency. The sequences are tested numerically and experimentally for a powder of (13)C(alpha),(13)C(beta)-L-alanine and demonstrate substantial sensitivity gains over previous dipolar recoupling experiments.
NASA Astrophysics Data System (ADS)
Vinther, Joachim M.; Nielsen, Anders B.; Bjerring, Morten; van Eck, Ernst R. H.; Kentgens, Arno P. M.; Khaneja, Navin; Nielsen, Niels Chr.
2012-12-01
A novel strategy for heteronuclear dipolar decoupling in magic-angle spinning solid-state nuclear magnetic resonance (NMR) spectroscopy is presented, which eliminates residual static high-order terms in the effective Hamiltonian originating from interactions between oscillating dipolar and anisotropic shielding tensors. The method, called refocused continuous-wave (rCW) decoupling, is systematically established by interleaving continuous wave decoupling with appropriately inserted rotor-synchronized high-power π refocusing pulses of alternating phases. The effect of the refocusing pulses in eliminating residual effects from dipolar coupling in heteronuclear spin systems is rationalized by effective Hamiltonian calculations to third order. In some variants the π pulse refocusing is supplemented by insertion of rotor-synchronized π/2 purging pulses to further reduce the residual dipolar coupling effects. Five different rCW decoupling sequences are presented and their performance is compared to state-of-the-art decoupling methods. The rCW decoupling sequences benefit from extreme broadbandedness, tolerance towards rf inhomogeneity, and improved potential for decoupling at relatively low average rf field strengths. In numerical simulations, the rCW schemes clearly reveal superior characteristics relative to the best decoupling schemes presented so far, which we to some extent also are capable of demonstrating experimentally. A major advantage of the rCW decoupling methods is that they are easy to set up and optimize experimentally.
Baez, M L; Borzi, R A
2017-02-08
We study the three-dimensional Kasteleyn transition in both nearest neighbours and dipolar spin ice models using an algorithm that conserves the number of excitations. We first limit the interactions range to nearest neighbours to test the method in the presence of a field applied along [Formula: see text], and then focus on the dipolar spin ice model. The effect of dipolar interactions, which is known to be greatly self screened at zero field, is particularly strong near full polarization. It shifts the Kasteleyn transition to lower temperatures, which decreases ≈0.4 K for the parameters corresponding to the best known spin ice materials, [Formula: see text] and [Formula: see text]. This shift implies effective dipolar fields as big as 0.05 T opposing the applied field, and thus favouring the creation of 'strings' of reversed spins. We compare the reduction in the transition temperature with results in previous experiments, and study the phenomenon quantitatively using a simple molecular field approach. Finally, we relate the presence of the effective residual field to the appearance of string-ordered phases at low fields and temperatures, and we check numerically that for fields applied along [Formula: see text] there are only three different stable phases at zero temperature.
NASA Astrophysics Data System (ADS)
Baez, M. L.; Borzi, R. A.
2017-02-01
We study the three-dimensional Kasteleyn transition in both nearest neighbours and dipolar spin ice models using an algorithm that conserves the number of excitations. We first limit the interactions range to nearest neighbours to test the method in the presence of a field applied along ≤ft[1 0 0\\right] , and then focus on the dipolar spin ice model. The effect of dipolar interactions, which is known to be greatly self screened at zero field, is particularly strong near full polarization. It shifts the Kasteleyn transition to lower temperatures, which decreases ≈0.4 K for the parameters corresponding to the best known spin ice materials, \\text{D}{{\\text{y}}2}\\text{T}{{\\text{i}}2}{{\\text{O}}7} and \\text{H}{{\\text{o}}2}\\text{T}{{\\text{i}}2}{{\\text{O}}7} . This shift implies effective dipolar fields as big as 0.05 T opposing the applied field, and thus favouring the creation of ‘strings’ of reversed spins. We compare the reduction in the transition temperature with results in previous experiments, and study the phenomenon quantitatively using a simple molecular field approach. Finally, we relate the presence of the effective residual field to the appearance of string-ordered phases at low fields and temperatures, and we check numerically that for fields applied along ≤ft[1 0 0\\right] there are only three different stable phases at zero temperature.
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.
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.
NASA Astrophysics Data System (ADS)
Tan, Kong Ooi; Rajeswari, M.; Madhu, P. K.; Ernst, Matthias
2015-02-01
We show a theoretical framework, based on triple-mode Floquet theory, to analyze recoupling sequences derived from symmetry-based pulse sequences, which have a non-vanishing effective field and are not rotor synchronized. We analyze the properties of one such sequence, a homonuclear double-quantum recoupling sequence derived from the C72 1 sequence. The new asynchronous sequence outperforms the rotor-synchronized version for spin pairs with small dipolar couplings in the presence of large chemical-shift anisotropy. The resonance condition of the new sequence is analyzed using triple-mode Floquet theory. Analytical calculations of second-order effective Hamiltonian are performed to compare the efficiency in suppressing second-order cross terms. Experiments and numerical simulations are shown to corroborate the results of the theoretical analysis.
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.
Evans, David A D
2006-11-02
Palaeomagnetism of climatically sensitive sedimentary rock types, such as glacial deposits and evaporites, can test the uniformitarianism of ancient geomagnetic fields and palaeoclimate zones. Proterozoic glacial deposits laid down in near-equatorial palaeomagnetic latitudes can be explained by 'snowball Earth' episodes, high orbital obliquity or markedly non-uniformitarian geomagnetic fields. Here I present a global palaeomagnetic compilation of the Earth's entire basin-scale evaporite record. Magnetic inclinations are consistent with low orbital obliquity and a geocentric-axial-dipole magnetic field for most of the past two billion years, and the snowball Earth hypothesis accordingly remains the most viable model for low-latitude Proterozoic ice ages. Efforts to reconstruct Proterozoic supercontinents are strengthened by this demonstration of a consistently axial and dipolar geomagnetic reference frame, which itself implies stability of geodynamo processes on billion-year timescales.
Fractional quantum Hall states of dipolar fermions in a strained optical lattice
NASA Astrophysics Data System (ADS)
Fujita, Hiroyuki; Nakagawa, Yuya O.; Ashida, Yuto; Furukawa, Shunsuke
2016-10-01
We study strongly correlated ground states of dipolar fermions in a honeycomb optical lattice with spatial variations in hopping amplitudes. Similar to strained graphene, such nonuniform hopping amplitudes produce valley-dependent pseudomagnetic fields for fermions near the two Dirac points, resulting in the formation of Landau levels. The dipole moments aligned perpendicular to the honeycomb plane yield a long-range repulsive interaction. By exact diagonalization in the zeroth-Landau-level basis, we show that this repulsive interaction stabilizes a variety of valley-polarized fractional quantum Hall states such as Laughlin and composite-fermion states. The present system thus offers an intriguing platform for emulating fractional quantum Hall physics in a static optical lattice. We calculate the energy gaps above these incompressible states and discuss the temperature scales required for their experimental realization.
Robustness of fractional quantum Hall states with dipolar atoms in artificial gauge fields
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.
NASA Astrophysics Data System (ADS)
Borkar, Aditi N.; De Simone, Alfonso; Montalvao, Rinaldo W.; Vendruscolo, Michele
2013-06-01
We describe a method of determining the conformational fluctuations of RNA based on the incorporation of nuclear magnetic resonance (NMR) residual dipolar couplings (RDCs) as replica-averaged structural restraints in molecular dynamics simulations. In this approach, the alignment tensor required to calculate the RDCs corresponding to a given conformation is estimated from its shape, and multiple replicas of the RNA molecule are simulated simultaneously to reproduce in silico the ensemble-averaging procedure performed in the NMR measurements. We provide initial evidence that with this approach it is possible to determine accurately structural ensembles representing the conformational fluctuations of RNA by applying the reference ensemble test to the trans-activation response element of the human immunodeficiency virus type 1.
Efficient Synchronization of Dipolarly Coupled Vortex-Based Spin Transfer Nano-Oscillators
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
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.
Suprathermal particle energization in dipolarization fronts: Particle-in-cell simulations
NASA Astrophysics Data System (ADS)
Lu, San; Angelopoulos, V.; Fu, Huishan
2016-10-01
Within dipolarization fronts (DFs) in the Earth's magnetotail, significant magnetic energy is converted to plasma energy, and a significant portion of the electrons and ions therein are accelerated to suprathermal energies. The mechanism that produces these suprathermal particles while simultaneously reducing magnetic field energy is poorly understood, however. We use two-dimensional particle-in-cell simulations to explore this process in conventional flux bundle-type DFs, which are formed by single X line reconnection and connected to the Earth, and in newly proposed flux rope-type DFs, which are formed and bracketed by two X lines. In flux bundle-type DFs, electrons are betatron accelerated near the Bz peak, and ions are energized through reflection at the front. In flux rope-type DFs, most suprathermal electrons and ions are confined to the flux rope's magnetic structure and are accelerated through repeated reflections at the structure's two ends.
Testing physical models for dipolar asymmetry: From temperature to k space to lensing
NASA Astrophysics Data System (ADS)
Zibin, J. P.; Contreras, D.
2017-03-01
One of the most intriguing hints of a departure from the standard cosmological model is a large-scale dipolar power asymmetry in the cosmic microwave background (CMB). If not a statistical fluke, its origins must lie in the modulation of the position-space fluctuations via a physical mechanism, which requires the observation of new modes to confirm or refute. We introduce an approach to describe such a modulation in k space and calculate its effects on the CMB temperature and lensing. We fit the k -space modulation parameters to Planck 2015 temperature data and show that CMB lensing will not provide us with enough independent information to confirm or refute such a mechanism. However, our approach elucidates some poorly understood aspects of the asymmetry, in particular that it is weakly constrained. Also, it will be particularly useful in predicting the effectiveness of polarization in testing a physical modulation.
Long-range transverse Ising model built with dipolar condensates in two-well arrays
NASA Astrophysics Data System (ADS)
Li, Yongyao; Pang, Wei; Xu, Jun; Lee, Chaohong; Malomed, Boris A.; Santos, Luis
2017-01-01
Dipolar Bose–Einstein condensates in an array of double-well potentials realize an effective transverse Ising model with peculiar inter-layer interactions, that may result under proper conditions in an anomalous first-order ferromagnetic–antiferromagnetic phase transition, and non-trivial phases due to frustration. The considered setup allows as well for the study of Kibble–Zurek defect formation, whose kink statistics follows that expected from the universality class of the mean-field one-dimensional transverse Ising model. Furthermore, random occupation of each layer of the stack leads to random effective Ising interactions and local transverse fields, that may lead to the Anderson-like localization of imbalance perturbations.
Quantum control of spin-nematic squeezing in a dipolar spin-1 condensate.
Huang, Yixiao; Xiong, Heng-Na; Yang, Yang; Hu, Zheng-Da; Xi, Zhengjun
2017-02-24
Versatile controllability of interactions and magnetic field in ultracold atomic gases ha now reached an era where spin mixing dynamics and spin-nematic squeezing can be studied. Recent experiments have realized spin-nematic squeezed vacuum and dynamic stabilization following a quench through a quantum phase transition. Here we propose a scheme for storage of maximal spin-nematic squeezing, with its squeezing angle maintained in a fixed direction, in a dipolar spin-1 condensate by applying a microwave pulse at a time that maximal squeezing occurs. The dynamic stabilization of the system is achieved by manipulating the external periodic microwave pulses. The stability diagram for the range of pulse periods and phase shifts that stabilize the dynamics is numerical simulated and agrees with a stability analysis. Moreover, the stability range coincides well with the spin-nematic vacuum squeezed region which indicates that the spin-nematic squeezed vacuum will never disappear as long as the spin dynamics are stabilized.
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.
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
Uranyl triazolate formation via an in situ Huisgen 1,3-dipolar cycloaddition reaction
Knope, Karah E.; Cahill, Christopher L.
2010-08-27
A two dimensional UO_{2}^{2+} coordination polymer, (UO_{2})_{3}(C_{10}H_{5}N_{3}O_{4})_{2}(OH)_{2}(H_{2}O)_{2}, has been synthesized under solvothermal conditions. The triazolate ligand, 1-(4-carboxyphenyl)-1H-1,2,3-triazole-4-carboxylic acid (CPTAZ) has been generated via a 1,3-dipolar cycloaddition of 4-azidobenzoic acid and propiolic acid. Reactions of the UO_{2}^{2+} cation with both the in situ generated triazolate ligand and the presynthesized ligand have been explored. The structure, fluorescent and thermal behaviour of this material are presented, as is a discussion of the utility of in situ ligand formation versus direct assembly.
Efficient Synchronization of Dipolarly Coupled Vortex-Based Spin Transfer Nano-Oscillators
NASA Astrophysics Data System (ADS)
Locatelli, Nicolas; Hamadeh, Abbass; Abreu Araujo, Flavio; Belanovsky, Anatoly D.; Skirdkov, Petr N.; Lebrun, Romain; Naletov, Vladimir V.; Zvezdin, Konstantin A.; Muñoz, Manuel; Grollier, Julie; Klein, Olivier; Cros, Vincent; de Loubens, Grégoire
2015-11-01
Due to their nonlinear properties, spin transfer nano-oscillators can easily adapt their frequency to external stimuli. This makes them interesting model systems to study the effects of synchronization and brings some opportunities to improve their microwave characteristics in view of their applications in information and communication technologies and/or to design innovative computing architectures. So far, mutual synchronization of spin transfer nano-oscillators through propagating spinwaves and exchange coupling in a common magnetic layer has been demonstrated. Here we show that the dipolar interaction is also an efficient mechanism to synchronize neighbouring oscillators. We experimentally study a pair of vortex-based spin transfer nano-oscillators, in which mutual synchronization can be achieved despite a significant frequency mismatch between oscillators. Importantly, the coupling efficiency is controlled by the magnetic configuration of the vortices, as confirmed by an analytical model and micromagnetic simulations highlighting the physics at play in the synchronization process.
Spin-wave edge modes in finite arrays of dipolarly coupled magnetic nanopillars
NASA Astrophysics Data System (ADS)
Lisenkov, Ivan; Tyberkevych, Vasyl; Slavin, Andrei; Bondarenko, Pavel; Ivanov, Boris A.; Bankowski, Elena; Meitzler, Thomas; Nikitov, Sergey
2014-09-01
The frequency spectrum of spin-wave edge modes localized near the boundaries of a finite array of dipolarly coupled magnetic nanopillars is calculated theoretically. Two mechanisms of edge mode formation are revealed: inhomogeneity of the internal static magnetic field existing near the array boundaries and time-reversal symmetry breaking of the dipole-dipole interaction. The latter mechanism is analogous to the formation mechanism of a surface Damon-Eschbach mode in continuous in-plane magnetized magnetic films and is responsible for the nonreciprocity of edge modes in finite-width nanopillar arrays. The number of edge modes in nanopillar arrays depends on the spatial profile of the internal static magnetic field near the array boundaries and several edge modes are formed if a substantial field inhomogeneity extends over several rows of nanopillars.
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.
Dipolar colloids in apolar media: direct microscopy of two-dimensional suspensions
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
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.
Reentrant superfluidity and pair density wave in single-component dipolar Fermi gases
NASA Astrophysics Data System (ADS)
Che, Yanming; Wang, Jibiao; Chen, Qijin
2016-06-01
We study the superfluidity of single-component dipolar Fermi gases in three dimensions using a pairing fluctuation theory, within the context of BCS-BEC crossover. The transition temperature Tc for the dominant pz wave superfluidity exhibits a remarkable reentrant behavior as a function of the pairing strength induced by the dipole-dipole interaction (DDI), which leads to an anisotropic pair dispersion. The anisotropy and the long-range nature of the DDI cause Tc to vanish for a narrow range of intermediate interaction strengths, where a pair density wave emerges as the ground state. The superfluid density and thermodynamics below Tc, along with the density profiles in a harmonic trap, are investigated as well. Implications for experiments are discussed.
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.
Dipolar order by disorder in the classical Heisenberg antiferromagnet on the kagome lattice.
Chern, Gia-Wei; Moessner, R
2013-02-15
Ever since the experiments which founded the field of highly frustrated magnetism, the kagome Heisenberg antiferromagnet has been the archetypical setting for the study of fluctuation induced exotic ordering. To this day the nature of its classical low-temperature state has remained a mystery: the nonlinear nature of the fluctuations around the exponentially numerous harmonically degenerate ground states has not permitted a controlled theory, while its complex energy landscape has precluded numerical simulations at low temperature, T. Here we present an efficient Monte Carlo algorithm which removes the latter obstacle. Our simulations detect a low-temperature regime in which correlations asymptote to a remarkably small value as T→0. Feeding these results into an effective model and analyzing the results in the framework of an appropriate field theory implies the presence of long-range dipolar spin order with a tripled unit cell.
Beyond mean-field properties of binary dipolar Bose mixtures at low temperatures
NASA Astrophysics Data System (ADS)
Pastukhov, Volodymyr
2017-02-01
We rigorously analyze the low-temperature properties of homogeneous three-dimensional two-component Bose mixture with dipole-dipole interaction. For such a system the effective hydrodynamic action that governs the behavior of low-energy excitations is derived. The infrared structure of the exact single-particle Green's functions is obtained in terms of macroscopic parameters, namely the inverse compressibility and the superfluid density matrices. Within the one-loop approximation we calculate some of the most relevant observable quantities and give the beyond mean-field stability condition for the binary dipolar Bose gas in the dilute limit. A brief variational derivation of the coupled equations that describe macroscopic hydrodynamics of the system in the external nonuniform potential at zero temperature is presented.
Awan, Z A
2015-04-10
An analytical theory for the dipolar scattering characteristics of uncoated or coated sphere with different materials is presented. These materials are magnetodielectric, single negative, single near zero, and double near zero (DNZ) materials. It is shown that an uncoated magnetodielectric sphere has nearly identical E- and H-plane scattered intensities. It is further observed that for an epsilon near zero (ENZ) sphere, the intensity of scattered field in the E plane is nearly isotropic. For a coated sphere, it is shown that a magnetodielectric sphere coated with ENZ and mu near zero materials have nearly identical E-plane scattered intensities in the forward and backward scattering (BS) directions. Likewise, it is also shown that a finite sized magnetodielectric sphere coated with a DNZ layer can be made hidden to the incoming wave in the BS direction.
Preparation of chromophoric dipolar dendrons as second-order nonlinear optical material
Yokoyama, S.; Mashiko, S.
1998-07-01
Dendritic macromolecules, called dendrons, having a branching structure modified with an electron donor/acceptor functionalized azobenzene chromophore have been synthesized. The structurally different dendrons possess different numbers, 1, 3, 7, and 15, of chromophore units. The second harmonic generation (SHG) of dendrons was measured in the molecular oriented thin films prepared by the Langmuir-Blodgett film transfer technique. In such structurally organized thin films, individual chromophores coherently contribute to the increase in the molecular hyperpolarizability of dendrons. The SHG activity became large as the numbers of branching units of dendrons increased. The highest molecular hyperpolarizability was found to be >8,000 x 10{sup {minus}}30 esu for dendron containing 15 chromophoric units. The SHG results suggest that the structure of dendrons synthesized is uniaxially dipolar, and that there is a particular merit in this structure for the generation of SHG.
Karakatsani, Eirini K; Economou, Ioannis G
2006-05-11
The perturbed chain statistical associating fluid theory (PC-SAFT) is extended to polar molecular fluids, namely dipolar and quadrupolar fluids. The extension is based on the perturbation theory for polar fluids by Stell and co-workers. Appropriate expressions are proposed for dipole-dipole, quadrupole-quadrupole, and dipole-quadrupole interactions. Furthermore, induced dipole interactions are calculated explicitly in the model. The new polar PC-SAFT model is relatively complex; for this purpose, a truncated polar PC-SAFT model is proposed using only the leading term in the polynomial expansion for polar interactions. The new model is used for the calculation of thermodynamic properties of various quadrupolar pure fluids. In all cases, the agreement between experimental data and model predictions is very good.
Pitchfork bifurcations in blood-cell-shaped dipolar Bose-Einstein condensates
Rau, Stefan; Main, Joerg; Koeberle, Patrick; Wunner, Guenter
2010-03-15
We demonstrate that the method of coupled Gaussian wave packets is a full-fledged alternative to direct numerical solutions of the Gross-Pitaevskii equation of condensates with electromagnetically induced attractive 1/r interaction or with dipole-dipole interaction. Moreover, Gaussian wave packets are superior in that they are capable of producing both stable and unstable stationary solutions and thus of giving access to yet unexplored regions of the space of solutions of the Gross-Pitaevskii equation. We apply the method to clarify the theoretical nature of the collapse mechanism of blood-cell-shaped dipolar condensates: On the route to collapse the condensate passes through a pitchfork bifurcation, where the ground state itself turns unstable, before it finally vanishes in a tangent bifurcation.
Variational calculations for anisotropic solitons in dipolar Bose-Einstein condensates
Eichler, Ruediger; Main, Joerg; Wunner, Guenter
2011-05-15
We present variational calculations using a Gaussian trial function to calculate the ground state of the Gross-Pitaevskii equation (GPE) and to describe the dynamics of the quasi-two-dimensional solitons in dipolar Bose-Einstein condensates (BECs). Furthermore, we extend the ansatz to a linear superposition of Gaussians, improving the results for the ground state to exact agreement with numerical grid calculations using imaginary time and the split-operator method. We are able to give boundaries for the scattering length at which stable solitons may be observed in an experiment. By dynamic calculations with coupled Gaussians, we are able to describe the rather complex behavior of the thermally excited solitons. The discovery of dynamically stabilized solitons indicates the existence of such BECs at experimentally accessible temperatures.
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.
Protein dynamics from chemical shift and dipolar rotational spin-echo sup 15 N NMR
Garbow, J.R.; Jacob, G.S.; Stejskal, E.O.; Schaefer, J. )
1989-02-07
The partial collapse of dipolar and chemical shift tensors for peptide NH and for the amide NH at cross-link sites in cell wall peptidoglycan, of intact lyophilized cells of Aerococcus viridans, indicates NH vector root-mean-square fluctuations of 23{degree}. This result is consistent with the local mobility calculated in typical picosecond regime computer simulations of protein dynamics in the solid state. The experimental root-mean-square angular fluctuations for both types of NH vectors increase to 37{degree} for viable wet cells at 10{degree}C. The similarity in mobilities for both general protein and cell wall peptidoglycan suggests that one additional motion in wet cells involves cooperative fluctuations of segments of cell walls, attached proteins, and associated cytoplasmic proteins.
Compressibility, zero sound, and effective mass of a fermionic dipolar gas at finite temperature
Kestner, J. P.; Das Sarma, S.
2010-09-15
The compressibility, zero-sound dispersion, and effective mass of a gas of fermionic dipolar molecules is calculated at finite temperature for one-, two-, and three-dimensional uniform systems, and in a multilayer quasi-two-dimensional system. The compressibility is nonmonotonic in the reduced temperature, T/T{sub F}, exhibiting a maximum at finite temperature. This effect might be visible in a quasi-low-dimensional experiment, providing a clear signature of the onset of many-body quantum degeneracy effects. The collective mode dispersion and effective mass show similar nontrivial temperature and density dependence. In a quasi-low-dimensional system, the zero-sound mode may propagate at experimentally attainable temperatures.
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.
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)
Wirz, Lukas N; Allison, Jane R
2017-02-20
Residual dipolar couplings (RDCs), unlike most other types of NMR observables, provide orientational information, reporting on the alignment of inter-spin vectors (ISVs) relative to the magnetic field. A great challenge in using experimental RDCs to restrain molecular dynamics (MD) simulations is how to represent this alignment. An alignment tensor is often used to parameterise the contribution of molecular alignment to the angular dependence of RDCs. All ISVs that share the same tensor have fixed relative alignment, i.e. if just one tensor is used, the molecule is internally rigid. Here we propose and illustrate a method for subdividing molecules into individually aligned blocks during MD simulations restrained to fit RDCs. This allows the relative orientation of each block to vary during the simulation, which in turn ensures that the internal structure of each block is more realistically reproduced.
NASA Astrophysics Data System (ADS)
Stamate, E.; Draghici, M.
2012-04-01
A large area plasma source based on 12 multi-dipolar ECR plasma cells arranged in a 3 × 4 matrix configuration was built and optimized for silicon etching by negative ions. The density ratio of negative ions to electrons has exceeded 300 in Ar/SF6 gas mixture when a magnetic filter was used to reduce the electron temperature to about 1.2 eV. Mass spectrometry and electrostatic probe were used for plasma diagnostics. The new source is free of density jumps and instabilities and shows a very good stability for plasma potential, and the dominant negative ion species is F-. The magnetic field in plasma volume is negligible and there is no contamination by filaments. The etching rate by negative ions measured in Ar/SF6/O2 mixtures was almost similar with that by positive ions reaching 700 nm/min.
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.
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.
Stacking of purines in water: the role of dipolar interactions in caffeine.
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.
Photoinduced charge recombination in dipolar D-A-A photonic liquid crystal polymorphs.
Mazza, Mercedes M A; Yamazaki, Shiori; Mai, Dieu X; Padgaonkar, Suyog; Peurifoy, Samuel; Goncalves, Ariane; Wu, Yi-Lin; Hu, Qiaoyu; Scott, Amy M
2017-02-08
A hexylalkoxy dipolar D-A-A molecule [7-(4-N,N-(bis(4-hexyloxyphenyl)amino)phenyl)-2,1,3-(benzothia-diazol-4-yl)methylene]propane-dinitrile, (C6-TPA-BT-CN) has been synthesized and the photophysics studied via femtosecond transient absorption spectroscopy (FsTA) in toluene and in amorphous and liquid crystalline spherulite thin films. Two spherulite macromolecular crystalline phases (banded, and non-banded) were observed through concentration dependent, solution processing techniques and are birefringent with a negative sign of elongation. A dramatic change in the electronic absorption from blue in amorphous films to green in spherulites was observed, and the molecular orientation was determined through the combined analysis of polarized light microscopy, X-ray diffraction, and scanning electron microscopy. FsTA was performed on amorphous films and show complex charge recombination dynamics, and a Stark effect, characterized from the combined TPA+˙ and [BT-CN]-˙ spectroscopic signatures at 450 nm and 510 nm and identified through spectroelectrochemistry. Radical cation dynamics of TPA+˙ was observed selectively at 750 nm with >503.3 ps (18%) recombination kinetics resulting in a rather significant yield of free charge carriers in amorphous films and consistent with previous reports on energetically disordered blend films. However, photoexcitation on large, non-banded spherulites areas (>250 μm) reveal average monoexponential charge recombination lifetimes of 169.2 ps from delocalized states similar to those observed in amorphous films and are 5× longer-lived than previous reports [Chang et al., J. Am. Chem. Soc., 2013, 135, 8790] of a related methyl-DPAT-BT-CN whose amorphous thin films were prepared through vapor deposition. Thus, the correlation between the microstructure of the blend film and the photoinduced radical pair dynamics described here is critical for developing a fundamental understanding of how dipolar states contribute to the charge carrier
Terenziani, Francesca; Mongin, Olivier; Katan, Claudine; Bhatthula, Bharath Kumar Goud; Blanchard-Desce, Mireille
2006-04-03
Interchromophore interactions in flexible multidipolar structures for nonlinear optics were addressed by a combined experimental and theoretical study on two series of one-, two-, and three-chromophore systems in which identical push-pull chromophores are assembled through covalent and flexible linkers in close proximity. The photophysical and nonlinear optical properties (quadratic hyperpolarizability) of the multichromophore systems were investigated and compared to those of the monomeric chromophores. Multimers have larger dipole moments than their monomeric analogues, that is, the dipolar subchromophores self-orientate within the multimeric structures. This effect was found to depend on the intersubchromophore distance in a nontrivial manner, which confirms that molecular engineering of such flexible systems is more complex than in completely geometrically controlled systems. Electric-field-induced second-harmonic generation (EFISHG) measurements in solution revealed increased figures of merit as compared to the monomeric analogue. This effect increases with increasing number and polarity of the individual subchromophores in the nanoassembly and increasing spacing between dipolar subchromophores. Experimental results are interpreted by a theoretical model for interacting polar and polarizable chromophores. The properties of multidipolar assemblies are shown to be related to the relative orientation of chromophores, which is imposed by interchromophore interactions. The supramolecular structure is thus a result of self-organization. The proposed theoretical model was also used to predict the properties of multichromophore structures made up of more polar and polarizable push-pull chromophores, and showed that stronger interchromophore interactions can heavily affect the individual optical responses. This suggests new routes for engineering highly NLO responsive multichromophore systems.
The effect of charge separation on the phase behavior of dipolar colloidal rods.
Rutkowski, David M; Velev, Orlin D; Klapp, Sabine H L; Hall, Carol K
2016-06-14
Colloids with anisotropic shape and charge distribution can assemble into a variety of structures that could find use as novel materials for optical, photonic, electronic and structural applications. Because experimental characterization of the many possible types of multi-shape and multipolar colloidal particles that could form useful structures is difficult, the search for novel colloidal materials can be enhanced by simulations of colloidal particle assembly. We have simulated a system of dipolar colloidal rods at fixed aspect ratio using discontinuous molecular dynamics (DMD) to investigate how the charge separation of an embedded dipole affects the types of assemblies that occur. Each dipolar rod is modeled as several overlapping spheres fixed in an elongated shape to represent excluded volume and two smaller, embedded spheres to represent the charges that make up the extended dipole. Large charge separations predominately form structures where the rods link head-to-tail while small charge separations predominately form structures where the rods stack side-by-side. Rods with small charge separations tend to form dense aggregates while rods with large charge separations tend to form coarse gel-like structures. Structural phase boundaries between fluid, string-fluid, and "gel" (networked) phases are mapped out and characterized as to whether they have global head-to-tail or global side-by-side order. A structural coarsening transition is observed for particles with large charge separations in which the head-tail networks thicken as temperature is lowered due to an increased tendency to form side-by-side structures. Triangularly connected networks form at small charge separations; these may be useful for encapsulating smaller particles.
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.
NASA Astrophysics Data System (ADS)
Franco, Alfredo; García-Macedo, Jorge; Brusatin, Giovanna; Guglielmi, Massimo
2013-04-01
The technological implementation of hybrid organic-inorganic materials in second order nonlinear optical photonic devices depends strongly on the ability of the host matrixes to contain high loads of dipolar molecules without aggregation. Some organic molecules are often used to diminish the attracting interactions between dipolar molecules in such kind of materials, but their efficiency as inhibitors of molecular aggregation is limited by their polarizability. In this work, we report the use of silver nanoparticles as inhibitors of molecular aggregation in hybrid organic-inorganic films doped with dipolar molecules. The large polarizability of the silver nanoparticles makes them ideal moieties for the inhibition of the electrostatic interactions between dipolar nonlinear optical molecules. The average size of the silver nanoparticles in this work was 70.5 nm in diameter, they were synthesized using silver nitrate (AgNO3) as precursor and aminoethylaminopropyltrimethoxysilane as reducing agent. These nanoparticles were immersed in SiO2 hybrid organic-inorganic sol-gel films doped with dipolar chromophores to study their effect as inhibitors of dipolar chromophores aggregation. The presence of the silver nanoparticles in the solid films was confirmed by transmission electronic microscopy and UV-Visible spectroscopy. UV-Visible spectroscopy was also used to monitor the dipolar chromophores aggregation in the SiO2 films. We found that, at room temperature, silver nanoparticles are good inhibiting chromophores aggregation in comparison with the performance of organic inhibitors.
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.
Zhou, Xiao; Xu, Xianhong; Shi, Zhenyan; Liu, Kun; Gao, Hua; Li, Wenjun
2016-06-21
TMG-catalyzed [3 + 2] organocatalytic 1,3-dipolar cycloaddition reactions of β-functionalized ketones with nitrile oxides have been developed. This strategy could generate 3,4,5-trisubstituted isoxazoles in high yields and regioselectivities.
NASA Astrophysics Data System (ADS)
Soh, Wee Tee; Tay, Z. J.; Yakovlev, N. L.; Peng, Bin; Ong, C. K.
2017-03-01
The characteristics of the static and dynamic components of the dipolar fields originating from a bulk polycrystalline yttrium iron garnet (YIG) substrate are probed by depositing a NiFe (Permalloy) layer on it, which acts as a detector. By measuring dc voltages generated via spin rectification effect (SRE) within the NiFe layer under microwave excitation, we characterize the influence of dipolar fields from bulk YIG on the NiFe layer. It is found that the dynamic YIG dipolar fields modify the self-SRE of NiFe, driving its own rectification voltages within the NiFe layer, an effect we term as non-local SRE. This non-local SRE only occurs near the simultaneous resonance of both YIG and NiFe. On the other hand, the static dipolar field from YIG manifests itself as a negative anisotropy in the NiFe layer which shifts the latter's ferromagnetic resonance frequency.
NASA Astrophysics Data System (ADS)
Perng, Baw-Ching; Newton, Marshall D.; Raineri, Fernando O.; Friedman, Harold L.
1996-05-01
porphyrin-quinone (PQ) ``dyad'' recently studied by Mataga and co-workers, we examine the ability of the molecular theories to explain the dependence of charge-transfer energetics on dipolar and nondipolar solvents. We find that the solvatochromic effect on the absorption energy of betaine-30, which forms the basis of the ET(30) empirical solvent polarity scale, is reproduced reasonably well by the RST, RDT, and HXA theories for solvents ranging from carbon tetrachloride to water. In the case of the PQ dyad, we find that the calculated values of λ in dipolar and nondipolar solvents are in good agreement with experimental estimates. Our results indicate that the molecular theories of solvation discussed in this paper can explain the observation that a solvent with vanishing molecular dipole moment, like benzene, can show unmistakable ``polarity,'' as reflected by its influence on the energetics of CT reactions. We also present calculations that corroborate the suggestion (Sec. VII of paper I) that, compared with the behavior in dipolar solvents, in nondipolar solvents the dependence of λ with the donor-acceptor separation distance is practically negligible.
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.
Hou, Guangjin; Lu, Xingyu; Vega, Alexander J; Polenova, Tatyana
2014-09-14
We report a Phase-Alternating R-Symmetry (PARS) dipolar recoupling scheme for accurate measurement of heteronuclear (1)H-X (X = (13)C, (15)N, (31)P, etc.) dipolar couplings in MAS NMR experiments. It is an improvement of conventional C- and R-symmetry type DIPSHIFT experiments where, in addition to the dipolar interaction, the (1)H CSA interaction persists and thereby introduces considerable errors in the dipolar measurements. In PARS, phase-shifted RN symmetry pulse blocks applied on the (1)H spins combined with π pulses applied on the X spins at the end of each RN block efficiently suppress the effect from (1)H chemical shift anisotropy, while keeping the (1)H-X dipolar couplings intact. Another advantage over conventional DIPSHIFT experiments, which require the signal to be detected in the form of a reduced-intensity Hahn echo, is that the series of π pulses refocuses the X chemical shift and avoids the necessity of echo formation. PARS permits determination of accurate dipolar couplings in a single experiment; it is suitable for a wide range of MAS conditions including both slow and fast MAS frequencies; and it assures dipolar truncation from the remote protons. The performance of PARS is tested on two model systems, [(15)N]-N-acetyl-valine and [U-(13)C,(15)N]-N-formyl-Met-Leu-Phe tripeptide. The application of PARS for site-resolved measurement of accurate (1)H-(15)N dipolar couplings in the context of 3D experiments is presented on U-(13)C,(15)N-enriched dynein light chain protein LC8.
NASA Astrophysics Data System (ADS)
Wu, Shan; Burlingame, Quinn; Cheng, Zhao-Xi; Lin, Minren; Zhang, Q. M.
2014-12-01
Dielectric materials with high electric energy density and low loss are of great importance for applications in modern electronics and electrical systems. Strongly dipolar materials have the potential to reach relatively higher dielectric constants than the widely used non-polar or weakly dipolar polymers, as well as a much lower loss than that of nonlinear high K polymer dielectrics or polymer-ceramic composites. To realize the high energy density while maintaining the low dielectric loss, aromatic polythioureas and polyureas with high dipole moments, high dipole densities, tunable molecular structures and dielectric properties were investigated. High energy density (>24 J/cm3), high breakdown strength (>800 MV/m), and high charge-discharge efficiency (>90%) can be achieved in the new polymers. The molecular structure and film surface morphology were also studied; it is of great importance to optimize the fabrication process to make high-quality thin films.
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.
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
Landau damping in a dipolar Bose-Fermi mixture in the Bose-Einstein condensation (BEC) limit
NASA Astrophysics Data System (ADS)
Moniri, S. M.; Yavari, H.; Darsheshdar, E.
2016-12-01
By using a mean-field approximation which describes the coupled oscillations of condensate and noncondensate atoms in the collisionless regime, Landau damping in a dilute dipolar Bose-Fermi mixture in the BEC limit where Fermi superfluid is treated as tightly bounded molecules, is investigated. In the case of a uniform quasi-two-dimensional (2D) case, the results for the Landau damping due to the Bose-Fermi interaction are obtained at low and high temperatures. It is shown that at low temperatures, the Landau damping rate is exponentially suppressed. By increasing the strength of dipolar interaction, and the energy of boson quasiparticles, Landau damping is suppressed over a broader temperature range.
NASA Astrophysics Data System (ADS)
Chomaz, L.; Baier, S.; Petter, D.; Mark, M. J.; Wächtler, F.; Santos, L.; Ferlaino, F.
2016-10-01
In a joint experimental and theoretical effort, we report on the formation of a macrodroplet state in an ultracold bosonic gas of erbium atoms with strong dipolar interactions. By precise tuning of the s -wave scattering length below the so-called dipolar length, we observe a smooth crossover of the ground state from a dilute Bose-Einstein condensate to a dense macrodroplet state of more than 2 ×104 atoms . Based on the study of collective excitations and loss features, we prove that quantum fluctuations stabilize the ultracold gas far beyond the instability threshold imposed by mean-field interactions. Finally, we perform expansion measurements, showing that although self-bound solutions are prevented by losses, the interplay between quantum stabilization and losses results in a minimal time-of-flight expansion velocity at a finite scattering length.
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).
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
NASA Astrophysics Data System (ADS)
Wang, Yuan-Sheng; Li, Zhen-Yu; Zhou, Zhu-Wen; Diao, Xin-Feng
2014-01-01
We investigate the properties of a three-dimensional (3D) dipolar Bose-Einstein condensate (BEC) in a double-well potential (DWP). The symmetry breaking and self-trapping (SBST) phenomena that the original symmetric ground state is replaced by a new asymmetric one and localized in one of the wells are demonstrated for Dy164 atoms in the 3D DWP by means of numerical solutions of the Gross-Pitaevskii (GP) equation. The results show that the SBST properties are affected dramatically by the magnetization direction for purely dipolar BEC. The SBST under various scattering lengths are also studied. In addition, the dynamical picture of the SBST induced by a gradual transformation of the single-well potential into a double-well is also illustrated.
NASA Astrophysics Data System (ADS)
Wang, Yuansheng; Zhou, Zhuwen; Li, Zhenyu; Liu, Gaofu
2014-06-01
We investigate the properties of a three-dimensional (3D) dipolar Bose-Einstein condensate (BEC) in a triple-well potential. Symmetry breaking and self-trapping (SBST) phenomena are demonstrated for 52Cr atoms in the 3D triple-well potential using numerical solutions of the Gross-Pitaevskii (GP) equation. The results show that the ground-state density distributions are affected markedly by the long-range nature and anisotropy of the dipolar interaction and the isotropic s-wave contact interaction. In addition, the dynamical picture of the SBST induced by a gradual transformation of the single-well potential into a triple-well one is also illustrated. SBST phenomena are also presented by adjusting the height of the middle potential well when the dipole orientation is aligned in the dipole axis.
Coherence of Bose-Einstein condensates of dipolar excitons in GaAs/AlGaAs heterostructures
NASA Astrophysics Data System (ADS)
Gorbunov, A. V.; Timofeev, V. B.
2016-05-01
Experiments relating to studies of the coherence of Bose condensates of dipolar excitons in GaAs/AlGaAs heterostructures with a wide, single quantum well and a Schottky gate are analyzed. Dipolar excitons were excited by light in an annular trap formed along the perimeter of a window in a metal gate with an applied electric voltage. A dual-beam interference technique involving interference combination of the amplitudes of the luminescence light field, together with subsequent analysis of first order correlators, is used to study the temporal (longitudinal) and spatial (transverse) coherence of the exciton condensates. It is found that the transverse coherence length of an exciton condensate is considerably longer than its thermal De Broglie wavelength. Experimental studies of the luminescence intensity correlator also confirm the coherence of the exciton Bose condensate.
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
Nuclear magnetic resonance studies of quadrupolar nuclei and dipolar field effects
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
NASA Astrophysics Data System (ADS)
Miyakawa, Takahiko; Nakamura, Shin; Yabu, Hiroyuki
2017-03-01
We study the ground state of a two-component dipolar Fermi gas in a spherically symmetric harmonic trap at zero temperature. On the basis of the Thomas-Fermi-von Weizsäcker approximation, we obtain a phase diagram of the system with equal but opposite values of the magnetic moment. We find that a phase-separated state, which spontaneously breaks the spherical symmetry of the system, emerges.
Basch, Corey H; Brinck, Jameson A; Ramos, Joaquin E; Habay, Stephen A; Yap, Glenn P A
2012-11-16
A concise method for the diastereoselective synthesis of octahydroindoles is presented. The products contain 2-amido and 7-hydroxyl substituents. A series of 2-acyl-5-aminooxazoles were prepared in one step. Upon methylation of the oxazole nitrogen atom, the substrates underwent rapid intramolecular 1,3-dipolar cycloaddition with a tethered alkene and, after reduction with excess hydride, produced octahydroindoles with excellent diastereoselectivity. The method allows for the installation of α-quaternary stereogenic carbon atoms.
D'Souza, Asha M; Spiccia, Nadia; Basutto, Jose; Jokisz, Pawel; Wong, Leon S-M; Meyer, Adam G; Holmes, Andrew B; White, Jonathan M; Ryan, John H
2011-02-04
A nonstabilized azomethine ylide reacts with a wide range of substituted isatoic anhydrides to afford novel 1,3-benzodiazepin-5-one derivatives, which are generally isolated in high yield. The transformations involve 1,3-dipolar cycloaddition reactions of the ylide with the anhydrides to give transient, and in a representative case spectroscopically observable, oxazolidine intermediates that undergo ring-opening-decarboxylation-ring-closing reaction cascades to yield the 1,3-benzodiazepin-5-one products.
Dürr, Ulrich H N; Afonin, Sergii; Hoff, Barbara; de Luca, Giuseppina; Emsley, James W; Ulrich, Anne S
2012-04-26
Solid-state (19)F-NMR spectroscopy is frequently used to analyze the structure and dynamics of lipophilic drugs and peptides embedded in biomembranes. The homonuclear dipolar couplings of trifluoromethyl (CF3) labels can provide valuable parameters such as orientational constraints and/or distances. To characterize the complex dipolar patterns of multiple (19)F spin interactions, three different model compounds carrying two CF3 groups in meta-position on a phenyl ring were incorporated in macroscopically aligned DMPC bilayers. The dipolar patterns obtained with the CPMG (Carr-Purcell-Meiboom-Gill) multipulse sequence were analyzed to yield simultaneously the intra-CF3 and intergroup dipolar coupling values. The fluorine-fluorine distances were predicted by a density functional calculation, and the alignment of the labeled molecular segment could be determined from these distances and the dipolar coupling values. The different compounds were found to align in the lipid bilayer according to their amphiphilic properties, though with a weak anisotropic preference that is typical of solutes in liquid crystals. The residual dipolar couplings were used to calculate Saupe order parameters. For the least complex molecule, (CF3)2-BA, an orientational probability function for the solute in the lipid matrix could be derived. The overall description of how (CF3)2-BA is embedded in the bilayer was independently assessed by molecular dynamics simulations, and compared in structural and dynamical terms with the results of the NMR experiments.
NASA Astrophysics Data System (ADS)
Li, Yueqiu; Wei, Peijun
2017-02-01
Reflection and transmission of an incident plane wave at five types of possible interfaces between two dipolar gradient elastic solids are studied in this paper. First, the explicit expressions of monopolar tractions and dipolar tractions are derived from the postulated function of strain energy density. Then, the displacements, the normal derivative of displacements, monopolar tractions, and dipolar tractions are used to create the nontraditional interface conditions. There are five types of possible interfaces based on all possible combinations of the displacements and the normal derivative of displacements. These interfacial conditions with consideration of microstructure effects are used to determine the amplitude ratio of the reflection and transmission waves with respect to the incident wave. Further, the energy ratios of the reflection and transmission waves with respect to the incident wave are calculated. Some numerical results of the reflection and transmission coefficients are given in terms of energy flux ratio for five types of possible interfaces. The influences of the five types of possible interfaces on the energy partition between the refection waves and the transmission waves are discussed, and the concept of double channels of energy transfer is first proposed to explain the different influences of five types of interfaces.
Dai, Lei; Wang, Chi; Duan, Suping; ...
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
NASA Astrophysics Data System (ADS)
Barzoukas, Marguerite; Blanchard-Desce, Mireille H.
2001-12-01
Recent reports of push-pull dipolar and quadrupolar chromophores with enhanced two-photon absorption have generated considerable interest in these two molecular systems. Two photon absorption is related to the imaginary part of the two-photon resonant cubic hyperpolarizability Im[(gamma) ((omega) )]. In this work, we have described both push-pull dipolar and quadrupolar chromophores using multi valence-bond states models based on measurable parameters of the valence-bond forms. We have derived analytical expressions of their non-resonant static cubic hyperpolarizability (gamma) (0) and of Im[(gamma) ((omega) )]. Comparison between the transparency / Im[(gamma) ((omega) )] trade-off and Im[(gamma) ((omega) )] / (gamma) (0) correlation helps understand the advantages and drawbacks of each of these two push-pull systems. Furthermore by understanding how the valence-bond parameters are related to the molecular structure and its environment, it is possible to predict how Im[(gamma) ((omega) )] will be affected by changing either the conjugation size, the donor-acceptor pair or the solvent polarity for both of these push-pull systems. The results of this study suggest common guidelines for the molecular engineering of both the push-pull dipolar and quadrupolar chromophores.
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.
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.
Tunable dipolar resonances and Einstein-de Haas effect in a {sup 87}Rb-atom condensate
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.
Frank, Andreas O; Freudenberger, J Christoph; Shaytan, Alexey K; Kessler, Horst; Luy, Burkhard
2015-03-01
Residual dipolar couplings are highly useful NMR parameters for calculating and refining molecular structures, dynamics, and interactions. For some applications, however, it is inevitable that the preferred orientation of a molecule in an alignment medium is calculated a priori. Several methods have been developed to predict molecular orientations and residual dipolar couplings. Being beneficial for macromolecules and selected small-molecule applications, such approaches lack sufficient accuracy for a large number of organic compounds for which the fine structure and eventually the flexibility of all involved molecules have to be considered or are limited to specific, well-studied liquid crystals. We introduce a simplified model for detailed all-atom molecular dynamics calculations with a polymer strand lined up along the principal axis as a new approach to simulate the preferred orientation of small to medium-sized solutes in polymer-based, gel-type alignment media. As is shown by a first example of strychnine in a polystyrene/CDCl3 gel, the simulations potentially enable the accurate prediction of residual dipolar couplings taking into account structural details and dynamic averaging effects of both the polymer and the solute.
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.
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
2015-08-16
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 MeVelectron 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.
Wang, Jun; Apte, Pankaj A; Morris, James R; Zeng, Xiao Cheng
2013-09-21
Stockmayer fluids are a prototype model system for dipolar fluids. We have computed the freezing temperatures of Stockmayer fluids at zero pressure using three different molecular-dynamics simulation methods, namely, the superheating-undercooling method, the constant-pressure and constant-temperature two-phase coexistence method, and the constant-pressure and constant-enthalpy two-phase coexistence method. The best estimate of the freezing temperature (in reduced unit) for the Stockmayer (SM) fluid with the dimensionless dipole moment μ*=1, √2, √3 is 0.656 ± 0.001, 0.726 ± 0.002, and 0.835 ± 0.005, respectively. The freezing temperature increases with the dipolar strength. Moreover, for the first time, the solid-liquid interfacial free energies γ of the fcc (111), (110), and (100) interfaces are computed using two independent methods, namely, the cleaving-wall method and the interfacial fluctuation method. Both methods predict that the interfacial free energy increases with the dipole moment. Although the interfacial fluctuation method suggests a weaker interfacial anisotropy, particularly for strongly dipolar SM fluids, both methods predicted the same trend of interfacial anisotropy, i.e., γ100 > γ110 > γ111.
Franco, A F; Kachkachi, H
2013-08-07
We investigate the effect of coupling (intensity and nature), applied field, and anisotropy on the spin dynamics of a multi-layer system composed of a hard magnetic layer coupled to a soft magnetic layer through a nonmagnetic spacer. The soft layer is modeled as a stack of several atomic planes while the hard layer, of a different material, is either considered as a pinned macroscopic magnetic moment or again as a stack of atomic planes. We compute the magnetization profile and hysteresis loop of the whole multi-layer system by solving the Landau-Lifshitz equations for the net magnetic moment of each (atomic) plane. We study the competition between the intra-layer anisotropy and exchange interaction, applied magnetic field, and the interface exchange, dipolar or Dzyalozhinski-Moriya interaction. Compared with the exchange coupling, the latter two couplings present peculiar features in the magnetization profile and hysteresis loop that may help identify the nature of the interface coupling in multi-layer magnetic systems.
Enhancement of oxygen in the magnetic island associated with dipolarization fronts
NASA Astrophysics Data System (ADS)
Wang, J.; Cao, J. B.; Fu, H. S.; Liu, W. L.; Lu, S.
2017-01-01
A significant enhancement of O+ is observed by Cluster inside an earthward propagating magnetic island behind a dipolarization front (DF). Such enhancement, from 0.005 to 0.03 cm-3, makes the O+ flux inside the magnetic island 20 times larger than that outside the magnetic island. In the meantime, the H+ density is nearly a constant, 0.1 cm-3, during the magnetic-island encounter. This results in a dramatic increase of the density ratio, nO
Theory of noise in high-gain surface plasmon-polariton amplifiers incorporating dipolar gain media.
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.
Reactions of dipolar bio-molecules in nano-capsules--example of folding-unfolding process.
Sanfeld, A; Sefiane, K; Steinchen, A
2011-11-14
The confinement of chemical reactions in nano-capsules can lead to a dramatic effect on the equilibrium constant of these latter. Indeed, capillary effects due to the curvature and surface energy of nano-capsules can alter in a noticeable way the evolution of reactions occurring within. Nano-encapsulation of bio-materials has attracted lately wide interest from the scientific community because of the great potential of its applications in biomedical areas and targeted therapies. The present paper focuses one's attention on alterations of conformation mechanisms due to extremely confining and interacting solvated dipolar macromolecules at their isoelectric point. As a specific example studied here, the folding-unfolding reaction of proteins (particularly RNase A and creatine kinase CK) is drastically changed when encapsulated in solid inorganic hollow nano-capsules. The effects demonstrated in this work can be extended to a wide variety of nano-encapsulation situations. The design and sizing of nano-capsules can even make use of the effects shown in the present study to achieve better and more effective encapsulation.
Roton-maxon excitation spectrum for Q2D weakly interacted dipolar excitons
NASA Astrophysics Data System (ADS)
Fedorov, Aleksey; Kurbakov, Igor; Lozovik, Yurii
2014-03-01
Remarkable progress was achieved in investigation of collective properties and BEC of quasiparticles, e.g., excitons and polaritons. As it well known their small effective mass provides sufficiently high BEC temperature. However, in reality excitons lifetime is not enough to achieve thermodynamical equilibrium. Spatial separation of electrons and holes in semiconductor layer suppresses recombination process, and exciton lifetime increases sufficiently. Moreover, the separation results in appearance of excitons dipole moments. We predict generation of roton-maxon excitation spectrum for BEC of dipolar excitons in weak correlation regime in Q2D geometry of semiconductor layer. The effect of roton-maxon spectrum is the result of attraction and anisotropy of dipole-dipole interaction in Q2D geometry, and it can be viewed as residual phenomena of phonon collapse for 3D dipoles. According to our estimation effects of BEC and roton-maxon spectrum are principally observable experimentally for excitons in crossed electromagnetic fields in GaAs heterostructures. The work was supported by the RFBR (14-02-00937, 14-08-00606). A.K.F. is an RQC fellow.
Residual dipolar coupling constants and structure determination of large DNA duplexes.
Mauffret, Olivier; Tevanian, Georges; Fermandjian, Serge
2002-12-01
Several NMR works have shown that long-range information provided by residual dipolar couplings (RDCs) significantly improve the global structure definition of RNAs and DNAs. Most of these are based on the use of a large set of RDCs, the collect of which requires samples labeled with (13)C, (15)N, and sometimes, (2)H. Here, we carried out torsion-angle dynamics simulations on a non-self complementary DNA fragment of 17 base-pairs, d(GGAAAATATCTAGCAGT).(ACTGCTAGAGATTTTCC). This reproduces the U5 LTR distal end of the HIV-1 cDNA that contains the enzyme integrase binding site. Simulations aimed at evaluating the impact of RDCs on the structure definition of long oligonucleotides, were performed in incorporating (i) nOe-distances at both < 4.5 A and < 5 A; (ii) a small set of (13)C-(1)H RDCs, easily detectable at the natural abundance, and (iii) a larger set of RDCs only accessible through the (13)C labeling of DNAs. Agreement between a target structure and a simulated structure was measured in terms of precision and accuracy. Results allowed to define conditions in which accurate DNA structures can be determined. We confirmed the strong impact of RDCs on the structure determination, and, above all, we found that a small set of RDC constraints (ca. 50) detectable at the natural abundance is sufficient to accurately derive the global and local DNA duplex structures when used in conjunction with nOe-distances < 5 A.
Phase transitions of two-dimensional dipolar fluids in external fields.
Schmidle, Heiko; Klapp, Sabine H L
2011-03-21
In this work, we study condensation phase transitions of two-dimensional Stockmayer fluids under additional external fields using Monte-Carlo (MC) simulations in the grand-canonical ensemble. We employ two recently developed methods to determine phase transitions in fluids, namely Wang-Landau (WL) MC simulations and successive-umbrella (SU) sampling. Considering first systems in zero field (and dipolar coupling strengths μ(2)∕εσ(3) ≤ 6), we demonstrate that the two techniques yield essentially consistent results but display pronounced differences in terms of efficiency. Indeed, comparing the computation times for these systems on a qualitative level, the SU sampling turns out to be significantly faster. In the presence of homogeneous external fields, however, the SU method becomes plagued by pronounced sampling difficulties, yielding the calculation of coexistence lines essentially impossible. Employing the WL scheme, on the other hand, we find phase coexistence even for strongly field-aligned systems. The corresponding critical temperatures are significantly shifted relative to the zero-field case.
NASA Astrophysics Data System (ADS)
Zyss, J.; Brasselet, S.; Thalladi, V. R.; Desiraju, G. R.
1998-07-01
A new type of crystalline structure for nonlinear optics whereby octupolar symmetry features are displayed at both molecular and crystalline levels is exemplified by the prototype 2,4,6-triaryloxy-1,3,5-triazine (TPOT) crystal and analyzed in terms of both individual molecular responses and crystal packing features. Polarized harmonic light scattering permits the full determination of the molecular β hyperpolarizability tensor and confirms the octupolar trigonal symmetry of the TPOT molecule. An oriented gas model is used to infer therefrom an estimate of the crystalline nonlinear d tensor which is predicted to be of the same order as that of the reference dipolar N-4-nitrophenyl-(L)-prolinol crystal. The concept of optimal packing toward quadratic nonlinear optics, which had been initially introduced in the realm of quasi-one-dimensional structures, is revisited and enlarged to encompass more isotropic uniaxial structures potentially amenable, in the case of octupoles, to larger optimal values than in the one-dimensional case. Moreover, considerations pertaining to phase matching which had been left aside in the earlier one-dimensional optimization framework are now considered and the various type I and type II configurations compared for both one-dimensional and octupolar uniaxial structures. Application perspectives of octupolar structures toward short pulse nonlinear optics are discussed: their structurally built-in polarization independence is outlined as a major asset in contrast with the more traditional one-dimensional structures.
Measuring membrane protein bond orientations in nanodiscs via residual dipolar couplings
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
Atomic-scale sensing of the magnetic dipolar field from single atoms.
Choi, Taeyoung; Paul, William; Rolf-Pissarczyk, Steffen; Macdonald, Andrew J; Natterer, Fabian D; Yang, Kai; Willke, Philip; Lutz, Christopher P; Heinrich, Andreas J
2017-03-06
Spin resonance provides the high-energy resolution needed to determine biological and material structures by sensing weak magnetic interactions. In recent years, there have been notable achievements in detecting and coherently controlling individual atomic-scale spin centres for sensitive local magnetometry. However, positioning the spin sensor and characterizing spin-spin interactions with sub-nanometre precision have remained outstanding challenges. Here, we use individual Fe atoms as an electron spin resonance (ESR) sensor in a scanning tunnelling microscope to measure the magnetic field emanating from nearby spins with atomic-scale precision. On artificially built assemblies of magnetic atoms (Fe and Co) on a magnesium oxide surface, we measure that the interaction energy between the ESR sensor and an adatom shows an inverse-cube distance dependence (r(-3.01±0.04)). This demonstrates that the atoms are predominantly coupled by the magnetic dipole-dipole interaction, which, according to our observations, dominates for atom separations greater than 1 nm. This dipolar sensor can determine the magnetic moments of individual adatoms with high accuracy. The achieved atomic-scale spatial resolution in remote sensing of spins may ultimately allow the structural imaging of individual magnetic molecules, nanostructures and spin-labelled biomolecules.
Ground-state and dynamical properties of two-dimensional dipolar Fermi liquids
NASA Astrophysics Data System (ADS)
Abedinpour, Saeed H.; Asgari, Reza; Tanatar, B.; Polini, Marco
2014-01-01
We study the ground-state properties of a two-dimensional spin-polarized fluid of dipolar fermions within the Euler-Lagrange Fermi-hypernetted-chain approximation. Our method is based on the solution of a scattering Schrödinger equation for the "pair amplitude" g(r), where g(r) is the pair distribution function. A key ingredient in our theory is the effective pair potential, which includes a bosonic term from Jastrow-Feenberg correlations and a fermionic contribution from kinetic energy and exchange, which is tailored to reproduce the Hartree-Fock limit at weak coupling. Very good agreement with recent results based on quantum Monte Carlo simulations is achieved over a wide range of coupling constants up to the liquid-to-crystal quantum phase transition. Using the fluctuation-dissipation theorem and a static approximation for the effective inter-particle interactions, we calculate the dynamical density-density response function, and furthermore demonstrate that an undamped zero-sound mode exists for any value of the interaction strength, down to infinitesimally weak couplings.
Phase transitions and multicritical behavior in the Ising model with dipolar interactions.
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 (h_{n}) 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 h_{1}-TL phase transition line is continuous up to δ=1.2585, while for the h_{2}-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 h_{1}-h_{2} line, i.e., at δ=1.2585, the critical phase corresponding to the h_{1}-TL transition coexists with the h_{2} phase.
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.
Spin correlations in the dipolar pyrochlore antiferromagnet Gd2Sn2O7
NASA Astrophysics Data System (ADS)
Paddison, Joseph A. M.; Ehlers, Georg; Petrenko, Oleg A.; Wildes, Andrew R.; Gardner, Jason S.; Stewart, J. Ross
2017-04-01
We investigate spin correlations in the dipolar Heisenberg antiferromagnet Gd2Sn2O7 using polarised neutron-scattering measurements in the correlated paramagnetic regime. Using Monte Carlo methods, we show that our data are sensitive to weak further-neighbour exchange interactions of magnitude ∼0.5% of the nearest-neighbour interaction, and are compatible with either antiferromagnetic next-nearest-neighbour interactions, or ferromagnetic third-neighbour interactions that connect spins across hexagonal loops. Calculations of the magnetic scattering intensity reveal rods of diffuse scattering along [1 1 1] reciprocal-space directions, which we explain in terms of strong antiferromagnetic correlations parallel to the set of < 1 1 0> directions that connect a given spin with its nearest neighbours. Finally, we demonstrate that the spin correlations in Gd2Sn2O7 are highly anisotropic, and correlations parallel to third-neighbour separations are particularly sensitive to critical fluctuations associated with incipient long-range order.
Characterization of alkyl carbon in forest soils by CPMAS 13C NMR spectroscopy and dipolar dephasing
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.
Chiral spin-wave edge modes in dipolar magnetic thin films
NASA Astrophysics Data System (ADS)
Shindou, Ryuichi; Ohe, Jun-ichiro; Matsumoto, Ryo; Murakami, Shuichi; Saitoh, Eiji
2013-05-01
Based on a linearized Landau-Lifshitz equation, we show that two-dimensional periodic allay of ferromagnetic particles coupled with magnetic dipole-dipole interactions supports chiral spin-wave edge modes, when subjected under the magnetic field applied perpendicular to the plane. The mode propagates along a one-dimensional boundary of the system in a unidirectional way and it always has a chiral dispersion within a band gap for spin-wave volume modes. Contrary to the well-known Damon-Eshbach surface mode, the sense of the rotation depends not only on the direction of the field but also on the strength of the field; its chiral direction is generally determined by the sum of the so-called Chern integers defined for spin-wave volume modes below the band gap. Using simple tight-binding descriptions, we explain how the magnetic dipolar interaction endows spin-wave volume modes with nonzero Chern integers and how their values will be changed by the field.
Dipolar order by disorder in the classical Heisenberg antiferromagnet on the kagome lattice
NASA Astrophysics Data System (ADS)
Chern, Gia-Wei
2014-03-01
The first experiments on the ``kagome bilayer'' SCGO triggered a wave of interest in kagome antiferromagnets in particular, and frustrated systems in general. A cluster of early seminal theoretical papers established kagome magnets as model systems for novel ordering phenomena, discussing in particular spin liquidity, partial order, disorder-free glassiness and order by disorder. Despite significant recent progress in understanding the ground state for the quantum S = 1 / 2 model, the nature of the low-temperature phase for the classical kagome Heisenberg antiferromagnet has remained a mystery: the non-linear nature of the fluctuations around the exponentially numerous harmonically degenerate ground states has not permitted a controlled theory, while its complex energy landscape has precluded numerical simulations at low temperature. Here we present an efficient Monte Carlo algorithm which removes the latter obstacle. Our simulations detect a low-temperature regime in which correlations saturate at a remarkably small value. Feeding these results into an effective model and analyzing the results in the framework of an appropriate field theory implies the presence of long-range dipolar spin order with a tripled unit cell.
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.
Phase transitions of two-dimensional dipolar fluids in external fields
NASA Astrophysics Data System (ADS)
Schmidle, Heiko; Klapp, Sabine H. L.
2011-03-01
In this work, we study condensation phase transitions of two-dimensional Stockmayer fluids under additional external fields using Monte-Carlo (MC) simulations in the grand-canonical ensemble. We employ two recently developed methods to determine phase transitions in fluids, namely Wang-Landau (WL) MC simulations and successive-umbrella (SU) sampling. Considering first systems in zero field (and dipolar coupling strengths μ2/ɛσ3 ⩽ 6), we demonstrate that the two techniques yield essentially consistent results but display pronounced differences in terms of efficiency. Indeed, comparing the computation times for these systems on a qualitative level, the SU sampling turns out to be significantly faster. In the presence of homogeneous external fields, however, the SU method becomes plagued by pronounced sampling difficulties, yielding the calculation of coexistence lines essentially impossible. Employing the WL scheme, on the other hand, we find phase coexistence even for strongly field-aligned systems. The corresponding critical temperatures are significantly shifted relative to the zero-field case.
Observation of discrete time-crystalline order in a disordered dipolar many-body system
NASA Astrophysics Data System (ADS)
Choi, Soonwon; Choi, Joonhee; Landig, Renate; Kucsko, Georg; Zhou, Hengyun; Isoya, Junichi; Jelezko, Fedor; Onoda, Shinobu; Sumiya, Hitoshi; Khemani, Vedika; von Keyserlingk, Curt; Yao, Norman Y.; Demler, Eugene; Lukin, Mikhail D.
2017-03-01
Understanding quantum dynamics away from equilibrium is an outstanding challenge in the modern physical sciences. Out-of-equilibrium systems can display a rich variety of phenomena, including self-organized synchronization and dynamical phase transitions. More recently, advances in the controlled manipulation of isolated many-body systems have enabled detailed studies of non-equilibrium phases in strongly interacting quantum matter; for example, the interplay between periodic driving, disorder and strong interactions has been predicted to result in exotic ‘time-crystalline’ phases, in which a system exhibits temporal correlations at integer multiples of the fundamental driving period, breaking the discrete time-translational symmetry of the underlying drive. Here we report the experimental observation of such discrete time-crystalline order in a driven, disordered ensemble of about one million dipolar spin impurities in diamond at room temperature. We observe long-lived temporal correlations, experimentally identify the phase boundary and find that the temporal order is protected by strong interactions. This order is remarkably stable to perturbations, even in the presence of slow thermalization. Our work opens the door to exploring dynamical phases of matter and controlling interacting, disordered many-body systems.
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.
Microscopic description of anisotropic low-density dipolar Bose gases in two dimensions
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.
NASA Astrophysics Data System (ADS)
Nakamura, R.; Torkar, K.; Andriopoulou, M.; Jeszenszky, H.; Plaschke, F.; Baumjohann, W.; Magnes, W.; Fischer, D.; Schmid, D.; Steller, M.; Nakamura, T.; Scharlemann, C.; Torbert, R. B.; Burch, J. L.; Ergun, R. E.; Lindqvist, P. A.; Marklund, G. T.; Khotyaintsev, Y. V.; Russell, C. T.; Strangeway, R. J.; Leinweber, H. K.; Anderson, B. J.; Le, G.; Bromund, K. R.; Fuselier, S. A.; Chutter, M.; Slavin, J. A.; Kepko, L.; Le Contel, O.; Pollock, C. J.; Dorelli, J.; Gershman, D. J.; Mauk, B.; Vaith, H.; Kletzing, C.; Bounds, S. R.; Sigsbee, K. M.
2015-12-01
With the successful launch of Magnetospheric Multiscale Misssion (MMS), it becomes possible to observe the dynamic signatures of magnetospheric transients with high-time resolution measurements of electromagnetic fields and plasma. The Active Spacecraft Potential Control (ASPOC) neutralizes the spacecraft potential by releasing positive charge produced by indium and thereby controlling the spacecraft potential in order to enable accurate measurements also in sparse plasma environments essential to study properties of reconnection. Since the current balance around the spacecraft is maintained by contribution also from the ambient plasma, predominantly electrons, ASPOC beam current values combined with spacecraft potential data from FIELDS instruments enable to deduce the ambient electron plasma parameters . Particularly, using data from multi-spacecraft measurements with different ASPOC current levels and FIELDS data, parameters on ambient electron temperature and density can be deduced. Monitoring the environmental plasma parameters are essential to determine the accurate scales of the structure or wave length relative to plasma scales and hence to understand the physical processes. In this study we investigate the changes of the electron parameters in the transient structures such as the magnetic field disturbance forming at the front of BBF/flow bursts, called dipolarization front (DF), and reconnection jets in thin current sheets obtained by MMS mainly during the commissioning phase when the spacecraft traversed the near-Earth tail.
Abu-Labdeh, A M; MacIsaac, A B; De'Bell, K
2011-07-27
The effects of a uniform magnetic field on the phase diagram of the dipolar Heisenberg model with a dominant antiferromagnetic exchange interaction have been investigated. The model consists of a square lattice of classical spin vectors, where the spins interact through an antiferromagnetic exchange interaction of strength J and a dipole-dipole interaction of strength g. The spins couple to a magnetic surface anisotropy of strength κ and to an applied external magnetic field of strength H. The external field is applied perpendicular to the plane of the lattice. From extensive Monte Carlo simulations, representative magnetic phase diagrams have been determined as a function of the ratios κ/g and T/g, where T is temperature, and at three different ratios of H/g (H/g = 10, 20, 27). These results are compared to the previously investigated case of H/g = 0 and to analytic calculations for the ground state energies. The nature of the equilibrium phases and order of the phase boundaries separating them are considered and changes due to the strength of the applied field are highlighted.
Asymptotic analysis of dipolar mixed modes of oscillations in red giant stars
NASA Astrophysics Data System (ADS)
Takata, Masao
2016-12-01
Dipolar modes of solar-like oscillations of red giant stars are analyzed asymptotically. Because of the high mass concentration in the helium core, the oscillations of the stars are composed of internal gravity waves in the core and acoustic waves in the envelope. The two types of oscillations interact with each other through a thin intermediate evanescent region to form an eigenmode of the mixed character. The process of the eigenmode formation is analyzed by assuming that the wavelength of the oscillations is much shorter than the scale height of the equilibrium stellar structure. Special care is paid to the following two points: (1) the effect of the perturbation to the gravitational potential is fully taken into account; (2) the interaction between the gravity waves in the core and the acoustic waves in the envelope can be strong. The condition that every eigenfrequency of the oscillations should satisfy is formulated. Also discussed are the amplitude ratio between the core and the envelope, and the transmission and reflection of the progressive-wave solutions at the intermediate evanescent region. The analysis should be of fundamental use in the interpretation of the observed solar-like oscillations in red giant stars.
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.
Effect of long- and short-range interactions on the thermodynamics of dipolar spin ice
NASA Astrophysics Data System (ADS)
Shevchenko, Yuriy; Makarov, Aleksandr; Nefedev, Konstantin
2017-02-01
The thermodynamic properties of dipolar spin ice on square, honeycomb and shakti lattices in the long-range and short-range dipole interaction models are studied. Exact solutions for the density of states, temperature dependencies of heat capacity, and entropy are obtained for these lattices with a finite number of point dipoles by means of complete enumeration. The magnetic susceptibility and average size of the largest low-energy cluster are calculated for square spin ice by means of Wang-Landau and Metropolis methods. We show that the long-range interaction leads to a blurring of the energy spectrum for all considered lattices. The inclusion of the long-range interaction leads to a significant change in the thermodynamic behaviour. An additional peak of heat capacity appears in the case of the honeycomb lattice. The critical temperature shifts in the direction of low or high temperatures; the direction depends on the lattice geometry. The critical temperature of the phase transition of square spin ice in the long-range model with frustrated ground states is obtained with the Wang-Landau and Metropolis methods independently.
Bolag, Altan; Sakai, Naomi; Matile, Stefan
2016-06-20
Push-pull aromatics are not popular as optoelectronic materials because their supramolecular organization is difficult to control. However, recent progress with synthetic methods has suggested that the directional integration of push-pull components into multicomponent photosystems should become possible. In this study, we report the design, synthesis, and evaluation of double- or triple-channel architectures that contain π stacks with push-pull components in parallel or mixed orientation. Moreover, the parallel push-pull stacks were uniformly oriented with regard to co-axial stacks, either with inward or outward oriented push-pull dipoles. Hole-transporting (p) aminoperylenemonoimides (APIs) and aminonaphthalimides (ANIs) are explored for ordered push-pull stacks. For the co-axial electron-transporting (n) stacks, naphthalenediimides (NDIs) are used. In double-channel photosystems, mixed push-pull stacks are overall less active than parallel push-pull stacks. The orientation of the parallel push-pull stacks with regard to the co-axial NDI stacks has little influence on activity. In triple-channel photosystems, outward-directed dipoles in bridging stacks between peripheral p and central n channels show higher activity than inward-directed dipolar stacks. Higher activities in response to direct irradiation of outward-directed parallel stacks reveal the occurrence of quite remarkable optical gating.
Non-Gaussianity in the cosmic microwave background induced by dipolar dark matter
Blanchet, Luc; Marsat, Sylvain; Langlois, David; Tiec, Alexandre Le E-mail: langlois@iap.fr E-mail: marsat@iap.fr
2013-02-01
In previous work [L. Blanchet and A. Le Tiec, Phys. Rev. D 80 (2009) 023524], motivated by the phenomenology of dark matter at galactic scales, a model of dipolar dark matter (DDM) was introduced. At linear order in cosmological perturbations, the dynamics of the DDM was shown to be identical to that of standard cold dark matter (CDM). In this paper, the DDM model is investigated at second order in cosmological perturbation theory. We find that the internal energy of the DDM fluid modifies the curvature perturbation generated by CDM with a term quadratic in the dipole field. This correction induces a new type of non-Gaussianity in the bispectrum of the curvature perturbation with respect to standard CDM. Leaving unspecified the primordial amplitude of the dipole field, which could in principle be determined by a more fundamental description of DDM, we find that, in contrast with usual models of primordial non-Gaussianities, the non-Gaussianity induced by DDM increases with time after the radiation-matter equality on super-Hubble scales. This distinctive feature of the DDM model, as compared with standard CDM, could thus provide a specific signature in the CMB and large-scale structure probes of non-Gaussianity.
Ground states of dipolar gases in quasi-one-dimensional ring traps
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.
Emergent structure in a dipolar Bose gas in a one-dimensional lattice
Wilson, Ryan M.; Bohn, John L.
2011-02-15
We consider an ultracold dipolar Bose gas in a one-dimensional lattice. For a sufficiently large lattice recoil energy, such a system becomes a series of nonoverlapping Bose-Einstein condensates that interact via the long-range dipole-dipole interaction (ddi). We model this system via a coupled set of nonlocal Gross-Pitaevskii equations (GPEs) for lattices of both infinite and finite extent. We find significantly modified stability properties in the lattice due to the softening of a discrete roton-like mode, as well as ''islands'' in parameter space where biconcave densities are predicted to exist and that only exist in the presence of the other condensates on the lattice. We solve for the elementary excitations of the system to check the dynamical stability of these solutions and to uncover the nature of their collapse. By solving a coupled set of GPEs exactly on a full numeric grid, we show that this emergent biconcave structure can be realized in a finite lattice with atomic {sup 52}Cr.
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.
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.
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.
Quantum control of spin-nematic squeezing in a dipolar spin-1 condensate
Huang, Yixiao; Xiong, Heng-Na; Yang, Yang; Hu, Zheng-Da; Xi, Zhengjun
2017-01-01
Versatile controllability of interactions and magnetic field in ultracold atomic gases ha now reached an era where spin mixing dynamics and spin-nematic squeezing can be studied. Recent experiments have realized spin-nematic squeezed vacuum and dynamic stabilization following a quench through a quantum phase transition. Here we propose a scheme for storage of maximal spin-nematic squeezing, with its squeezing angle maintained in a fixed direction, in a dipolar spin-1 condensate by applying a microwave pulse at a time that maximal squeezing occurs. The dynamic stabilization of the system is achieved by manipulating the external periodic microwave pulses. The stability diagram for the range of pulse periods and phase shifts that stabilize the dynamics is numerical simulated and agrees with a stability analysis. Moreover, the stability range coincides well with the spin-nematic vacuum squeezed region which indicates that the spin-nematic squeezed vacuum will never disappear as long as the spin dynamics are stabilized. PMID:28233786
Chou, Tom
2004-01-01
A discrete multistate kinetic model for water-wire proton transport is constructed and analyzed using Monte Carlo simulations. In the model, each water molecule can be in one of three states: oxygen lone-pairs pointing leftward, pointing rightward, or protonated (H3O+). Specific rules for transitions among these states are defined as protons hop across successive water oxygens. Our model also includes water-channel interactions that preferentially align the water dipoles, nearest-neighbor dipolar coupling interactions, and Coulombic repulsion. Extensive Monte Carlo simulations were performed and the observed qualitative physical behaviors discussed. We find the parameters that allow the model to exhibit superlinear and sublinear current-voltage relationships, and show why alignment fields, whether generated by interactions with the pore interior or by membrane potentials, always decrease the proton current. The simulations also reveal a “lubrication” mechanism that suppresses water dipole interactions when the channel is multiply occupied by protons. This effect can account for an observed sublinear-to-superlinear transition in the current-voltage relationship. PMID:15111400
A new dipolar potential for numerical simulations of polar fluids on the 4D hypersphere
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.
NASA Astrophysics Data System (ADS)
Park, M.; Lee, D.; Ohtani, S.; Kim, K.
2010-12-01
In this work we examined a number of magnetic dipolarizations that occurred at X > ~ -11 RE in the near-Earth plasma sheet. These dipolarization events were observed by the three near-tail THEMIS spacecraft. By employing the continuous wavelet transform technique, we found several interesting features. First, for the low frequency regime that we conveniently defined here, 0.005Hz to 0.03Hz (typically well below local proton gyro-frequency), we found that a significant percentage of dipolarizations indicate that the fluctuations are predominantly localized at one or more discrete frequencies. Many of them grow with growth time less than 2 min across onset time. Statistically, f ~ 0.012-0.014Hz is the dominant frequency, which is similar to frequency that has been referred to as “ballooning mode frequency” (e.g., Cheng and Lui, 1998; Horton et al., 1999). So, many of the dipolarizations can be viewed as manifestation of low frequency instability phenomenon. Further, we analyzed the polarization features (instability mode structure) of the dipolarization fluctuations in the low frequency domain, and found that the compressional component of magnetic fluctuations is significant for most of the studied events. It implies that the instability inevitably involves “compression” effect to a large extent. But it was also found that the relative significance of the perpendicular component of the fluctuations (so, the field line bending effect) increases with plasma beta which is thought to be proportional to the degree of field line stretching. When a perpendicular component is non-negligible, many events indicate that the magnetic oscillation on the perpendicular plane is mostly linearly polarized, and it is mostly in pshi direction, which is perpendicular to the azimuthal direction. This mode structure seems to be consistent with the conventional ballooning limit. Lastly, we have also studied the fluctuation features in the high frequency regime which we defined
Estimation of interdomain flexibility of N-terminus of factor H using residual dipolar couplings†
Maciejewski, Mateusz; Tjandra, Nico; Barlow, Paul N.
2011-01-01
Characterization of segmental flexibility is needed to understand the biological mechanisms of the very large category of functionally diverse proteins, exemplified by the regulators of complement activation, that consist of numerous compact modules or domains linked by short, potentially flexible, sequences of amino acid residues. The use of NMR-derived residual dipolar couplings (RDCs), in magnetically aligned media, to evaluate interdomain motion is established but only for two-domain proteins. We focused on the three N-terminal domains (called CCPs or SCRs) of the important complement regulator, human factor H (i.e. FH1-3). These domains cooperate to facilitate cleavage of the key complement activation-specific protein fragment, C3b, forming iC3b that no longer participates in the complement cascade. We refined a three-dimensional solution structure of recombinant FH1-3 based on nuclear Overhauser effects and RDCs. We then employed a rudimentary series of RDC datasets, collected in media containing magnetically aligned bicelles (disk-like particles formed from phospholipids) under three different conditions, to estimate interdomain motions. This circumvents a requirement of previous approaches for technically difficult collection of five independent RDC datasets. More than 80% of conformers of this predominantly extended three-domain molecule exhibit flexions of < 40 °. Such segmental flexibility (together with the local dynamics of the hypervariable loop within domain 3), could facilitate recognition of C3b via initial anchoring and eventual reorganization of modules to the conformation captured in the previously solved crystal structure of a C3b:FH1-4 complex. PMID:21793561
Magnetostatic dipolar domain-wall pinning in chains of permalloy triangular rings
NASA Astrophysics Data System (ADS)
Vavassori, P.; Bisero, D.; Bonanni, V.; Busato, A.; Grimsditch, M.; Lebecki, K. M.; Metlushko, V.; Ilic, B.
2008-11-01
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 2μm , 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.
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.
Magnetostatic dipolar domain-wall pinning in chains of permalloy triangular rings.
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.
Impact of Heavy Ions on Reconnection Rate and Dipolarization Fronts during Magnetotail Reconnection
NASA Astrophysics Data System (ADS)
Liang, H.; Ashour-Abdalla, M.; Lapenta, G.; Walker, R. J.
2015-12-01
Spacecraft observations show that near a magnetotail X-line, the concentration of oxygen (O+) ions varies greatly between storm-time and non-storm substorms. While O+ is a minor ion species during the non-storm substorms, it can become a major ion species during some storm-time substorms. It is important to understand how such a significant amount of O+ influences the onset of reconnection, the reconnection rate and the subsequent energy transfer at propagating dipolarization fronts (or reconnection jet fronts). In this work, we have studied the effects of O+ on the reconnection rate and DFs during magnetotail reconnection. We used a 2.5D implicit Particle-in-Cell simulation in a 2D Harris current sheet in the presence of H+ and O+ ions. We carried out a simulation with equal number densities of O+ and H+ (O+ Run) and compared the results with a simulation run using only H+ ions (H+ Run). We found that the reconnection rate in the O+ Run is much less than that in the H+ Run and identified two factors that contribute to this difference: (1) the O+ drag on the convective magnetic flux via an ambipolar electric field in O+ diffusion region; (2) the current sheet O+ inertia, which reduces the DF speed and delays the fast reconnection phase in the O+ Run. For factor (2) the O+ ions provide the main force contributions at the DFs and thereby determine the thickness of DFs provided the concentration of O+ is large enough. The velocity distribution functions of O+ have several peaks that result from ion reflection and acceleration near the DFs. These results illustrate some of the differences between the storm-time and non-storm substorms due to a significant concentration of heavy ions. They also are directly related to the expected observations by the Magnetospheric Multiscale (MMS) mission.
Pulse dipolar ESR of doubly labeled mini TAR DNA and its annealing to mini TAR RNA.
Sun, Yan; Borbat, Peter P; Grigoryants, Vladimir M; Myers, William K; Freed, Jack H; Scholes, Charles P
2015-02-17
Pulse dipolar electron-spin resonance in the form of double electron electron resonance was applied to strategically placed, site-specifically attached pairs of nitroxide spin labels to monitor changes in the mini TAR DNA stem-loop structure brought on by the HIV-1 nucleocapsid protein NCp7. The biophysical structural evidence was at Ångstrom-level resolution under solution conditions not amenable to crystallography or NMR. In the absence of complementary TAR RNA, double labels located in both the upper and the lower stem of mini TAR DNA showed in the presence of NCp7 a broadened distance distribution between the points of attachment, and there was evidence for several conformers. Next, when equimolar amounts of mini TAR DNA and complementary mini TAR RNA were present, NCp7 enhanced the annealing of their stem-loop structures to form duplex DNA-RNA. When duplex TAR DNA-TAR RNA formed, double labels initially located 27.5 Å apart at the 3'- and 5'-termini of the 27-base mini TAR DNA relocated to opposite ends of a 27 bp RNA-DNA duplex with 76.5 Å between labels, a distance which was consistent with the distance between the two labels in a thermally annealed 27-bp TAR DNA-TAR RNA duplex. Different sets of double labels initially located 26-27 Å apart in the mini TAR DNA upper stem, appropriately altered their interlabel distance to ~35 Å when a 27 bp TAR DNA-TAR RNA duplex formed, where the formation was caused either through NCp7-induced annealing or by thermal annealing. In summary, clear structural evidence was obtained for the fraying and destabilization brought on by NCp7 in its biochemical function as an annealing agent and for the detailed structural change from stem-loop to duplex RNA-DNA when complementary RNA was present.
Heteronuclear dipolar couplings, total spin coherence, and bilinear rotations in NMR spectroscopy
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.
NASA Astrophysics Data System (ADS)
Gabrielse, Christine; Harris, Camilla; Angelopoulos, Vassilis; Artemyev, Anton; Runov, Andrei
2016-10-01
We study energetic electron injections by using an analytical model that self-consistently describes electric and magnetic field perturbations of a transient, localized dipolarizing flux bundle (DFB). This simple model reproduces 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 an important driver of short-lived ( < 10 min) injections. We find that energetic electron drift paths are greatly influenced by the sharp magnetic field gradients around a localized DFB. Because a DFB is so localized (only a few RE wide across the tail), there are strong duskward magnetic field gradients on the DFB's dawn flank and strong dawnward magnetic field gradients on its dusk flank. Electrons on the DFB's dawnside therefore ∇B drift farther earthward from the reconnection site, whereas electrons on its duskside can potentially evacuate the inner magnetosphere by ∇B drifting tailward. This results in flux decrease at the front's duskside. As a result, the source of electrons observed during injection depends sensitively on the spacecraft location relative to the DFB and on the DFB's properties. We similarly find that the process of electron energization depends on how the electrons interact with the DFB. The initial injection signature is from electrons that interact with the front and gain the majority of their energy from the increasing magnetic field (∂B/∂t), whereas populations that arrive later gain most of their energy from ∇B drifting across the flow channel and against the DFB's electric fields.
Dipolar nuclear spin relaxation in liquids and plane fluids undergoing chemical reactions
NASA Astrophysics Data System (ADS)
Fries, P. H.
We describe the correlated translational and rotational relative brownian motions of two reacting groups of atoms, alternatively bound and free, by the normalized solutions of a set of coupled diffusion equations. Under equilibrium conditions we calculate the spectral densities j(ω) characteristic of the fluctuations of the intermolecular dipolar coupling between spins of these diffusing groups of atoms. When ωτ << 1, where τ is the translational correlation time, the form of the spectral density j2(ω) in three-dimensional liquids is j2(0) - α3ω1/2. The coefficient α3 is independent of the molecular local order, of the diffusional rotation speed of the spin-carrying groups of atoms and of their association and dissociation rates. In plane fluids, when ωτ << 1, the spectral density j(0)(ω) may be written as -a2 ln (ωτ) where the dependence of a2 on the average relative distribution of the interacting spins varies with the rate of the chemical reactions. In both three- and two-dimensional fluids spectral densities show an ω-3/2 or ω-2 behaviour for ωτ >> 1 according to the magnitude of the association rate of the reacting groups of atoms. In liquid glycerol we analyse the low- and high-frequency limits of the experimental proton relaxation rate 1/T1 and 1/T1ρ measured by Harmon, Harmon and Burnett, and Lenk. We also discuss the proton spin-lattice relaxation times measured by Kleinberg and Silbernagel in layered intercalation compounds TiS2-NH3 and TaS2-NH3.
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 .
Observation of the hot electron interchange instability in a high beta dipolar confined plasma
NASA Astrophysics Data System (ADS)
Ortiz, Eugenio Enrique
In this thesis the first study of the high beta, hot electron interchange (HEI) instability in a laboratory, dipolar confined plasma is presented. The Levitated Dipole Experiment (LDX) is a new research facility that explores the confinement and stability of plasma created within the dipole field produced by a strong superconducting magnet. In initial experiments long-pulse, quasi-steady state microwave discharges lasting more than 10 sec have been produced with equilibria having peak beta values of 20%. Creation of high-pressure, high beta plasma is possible only when intense HEI instabilities are stabilized by sufficiently high background plasma density. LDX plasma exist within one of three regimes characterized by its response to heating and fueling. The observed HEI instability depends on the regime and can take one of three forms: as quasiperiodic bursts during the low density, low beta plasma regime, as local high beta relaxation events in the high beta plasma regime, and as global, intense energy relaxation bursts, both in the high beta and afterglow plasma regimes. Measurements of the HEI instability are made using high-impedance, floating potential probes and fast Mirnov coils. Analysis of these signals reveals the extent of the transport during high beta plasmas. During intense high beta HEI instabilities, fluctuations at the edge significantly exceed the magnitude of the equilibrium field generated by the high beta electrons and energetic electron confinement ends in under 100 musec. For heated plasmas, one of the consequences of the observed high beta transport is the presence of hysteresis in the neutral gas fueling required to stabilize and maintain the high beta plasma. Finally, a nonlinear, self-consistent numerical simulation of the growth and saturation of the HEI instability has been adapted for LDX and compared to experimental observations.
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.
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.
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.
NASA Astrophysics Data System (ADS)
Chang, Zhiwei; Halle, Bertil
2016-02-01
In aqueous systems with immobilized macromolecules, including biological tissue, the longitudinal spin relaxation of water protons is primarily induced by exchange-mediated orientational randomization (EMOR) of intra- and intermolecular magnetic dipole-dipole couplings. We have embarked on a systematic program to develop, from the stochastic Liouville equation, a general and rigorous theory that can describe relaxation by the dipolar EMOR mechanism over the full range of exchange rates, dipole coupling strengths, and Larmor frequencies. Here, we present a general theoretical framework applicable to spin systems of arbitrary size with symmetric or asymmetric exchange. So far, the dipolar EMOR theory is only available for a two-spin system with symmetric exchange. Asymmetric exchange, when the spin system is fragmented by the exchange, introduces new and unexpected phenomena. Notably, the anisotropic dipole couplings of non-exchanging spins break the axial symmetry in spin Liouville space, thereby opening up new relaxation channels in the locally anisotropic sites, including longitudinal-transverse cross relaxation. Such cross-mode relaxation operates only at low fields; at higher fields it becomes nonsecular, leading to an unusual inverted relaxation dispersion that splits the extreme-narrowing regime into two sub-regimes. The general dipolar EMOR theory is illustrated here by a detailed analysis of the asymmetric two-spin case, for which we present relaxation dispersion profiles over a wide range of conditions as well as analytical results for integral relaxation rates and time-dependent spin modes in the zero-field and motional-narrowing regimes. The general theoretical framework presented here will enable a quantitative analysis of frequency-dependent water-proton longitudinal relaxation in model systems with immobilized macromolecules and, ultimately, will provide a rigorous link between relaxation-based magnetic resonance image contrast and molecular parameters.
Arigela, Rajesh K; Mandadapu, Anil K; Sharma, Sudhir K; Kumar, Brijesh; Kundu, Bijoy
2012-04-06
A rapid one-pot protocol for the synthesis of indole-based polyheterocycles via a sequential Lewis acid catalyzed intermolecular Michael addition and an intramolecular azide/internal alkyne 1,3-dipolar cycloaddition reaction has been described. The generality of the method has been demonstrated by treating a series of aromatic/aliphatic 2-alkynyl indoles with substituted (E)-1-azido-2-(2-nitrovinyl)benzenes to furnish annulated tetracyclic indolo[2,3-c][1,2,3]triazolo[1,5-a][1]benzazepines in good yields.
NASA Astrophysics Data System (ADS)
Saito, Hiroki
2016-05-01
Motivated by recent experiments [H. Kadau et al., http://doi.org/10.1038/nature16485, Nature (London) 530, 194 (2016); I. Ferrier-Barbut et al., http://arxiv.org/abs/1601.03318, arXiv:1601.03318] and theoretical prediction (F. Wächtler and L. Santos, http://arxiv.org/abs/1601.04501, arXiv:1601.04501), the ground state of a dysprosium Bose-Einstein condensate with strong dipole-dipole interaction is studied by the path-integral Monte Carlo method. It is shown that quantum fluctuation can stabilize the condensate against dipolar collapse.
NASA Astrophysics Data System (ADS)
Varga, Szabolcs; Szalai, István; Liszi, János; Jackson, George
2002-05-01
We present a density-functional approach to describe the orientational ordering of nonpolar and dipolar Gay-Berne fluids. The first-order perturbation theory developed by Velasco et al. [J. Chem. Phys. 102, 8107 (1995)] for a Gay-Berne fluid is simplified and tested for molecules with a length to breath ratio of κ=3 and energy anisotropies of κ'=1, 1.25, 2.5, and 5. The theory is found to be in fair agreement with existing simulation data for the location of the isotopic-nematic phase transition, but it overestimates the vapor-liquid critical point of the fluid due to a description of the free energy at the mean-field level. The effect on the phase behavior of including a central longitudinal point dipole within the Gay-Berne molecule is studied using a correct treatment of the long-range dipolar contribution at the level of a second-order virial theory [B. Groh and S. Dietrich, Phys. Rev. E 50, 3814 (1994)]. For a given energy anisotropy of κ'=5 and reduced dipole moment μ*=0.5 we search for a stable ferroelectric nematic phase by changing the length to breath ratio κ. We do not find any evidence of ferroelectric nematic ordering for κ>1.5; the system only exhibits vapor-liquid and isotropic-nematic phase transitions for these values of the aspect ratios. For a slightly elongated and oblate shaped potential (e.g., κ=0.5), regions of stable isotropic-ferroelectric nematic and nematic-ferroelectric nematic phase coexistences are observed. The results of the theory indicate that a ferroelectic nematic fluid phase may be stabilized with respect to the positional ordering in the fluid of oblate dipolar particles. Comparison are made, where appropriate, with the existing results of Monte Carlo simulations for dipolar Gay-Berne fluids (Rull and co-workers, Molec. Phys. 94, 439 (1998); J. Chem. Phys. 109, 9529 (1998)).
Schmidts, Volker
2017-01-01
This perspective article aims to review the general methodology in the application of residual dipolar couplings (RDCs) in the structure elucidation of small molecules and give the author's view on challenges for future applications. Recent improvements in the availability of alignment media, new pulse sequences for the measurement of couplings and improvements in the analysis software have garnered widespread interest in the technique. However, further generalization is needed in order to make RDC analysis into a truly "routine" method. Copyright © 2016 John Wiley & Sons, Ltd.
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.
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
Dynamics of dipolar defects in rare earth-doped alkaline-earth fluoride crystals
NASA Astrophysics Data System (ADS)
Charnock, Forrest Taylor
Alkaline-earth fluoride crystals such as SrF2 provide an excellent sample material for investigating the physics of point defects in crystal lattices. High quality crystals are easily grown, and they readily accept many dopant ions into the lattice, particularly rare earth ions. Rare earth dopant ions (typically trivalent) occupy substitutional sites in the lattice by replacing a Sr2+ ion. Due to the extra charge of the rare earth ion, charge compensation is often provided by an extra fluoride ion (F--) located in a nearby interstitial position. If located in the nearest-neighbor (nn) interstitial position, it forms a defect with C4n symmetry; if located in the next-nearest-neighbor (nnn) intersitial position, it forms a defect with C3n symmetry. Given sufficient thermal energy, this interstitial F ion can move to adjacent interstitial sites and hence reorient the defect. The rate w at which the ion moves from one interstitial site to another is well described by a simple Arrhenius expression: w=n0e-E/kT , where n0 is the attack frequency of the F-- and E is the activation energy. This motion can profoundly affect both the electronic polarizability of the material and the polarization of light emitted or absorbed by the rare earth ion. This thesis describes the normal mode motion of interstitial ions which may occupy either nn or nnn interstitial sites. Using electron paramagnetic resonance (EPR), I observed the relative populations of nn and nnn defects in SrF2 doped with Gd3+ as a function of temperature. These measurements show that dipolar reorientation of the nnn F occurs through the nn interstitial position. Not all interstitial F-- motion is thermally driven. Fluorescence depolarization measurements of SrF2:Pr3+ indicate that optically stimulating a Pr3+ may induce interstitial motion of a nn F--. Such motion was confirmed by showing that nn defects in SrF2:Pr3+ may be polarized at very low temperatures when the sample is illuminated with resonant light. I
AQUASOL: An efficient solver for the dipolar Poisson–Boltzmann–Langevin equation
Koehl, Patrice; Delarue, Marc
2010-01-01
The Poisson–Boltzmann (PB) formalism is among the most popular approaches to modeling the solvation of molecules. It assumes a continuum model for water, leading to a dielectric permittivity that only depends on position in space. In contrast, the dipolar Poisson–Boltzmann–Langevin (DPBL) formalism represents the solvent as a collection of orientable dipoles with nonuniform concentration; this leads to a nonlinear permittivity function that depends both on the position and on the local electric field at that position. The differences in the assumptions underlying these two models lead to significant differences in the equations they generate. The PB equation is a second order, elliptic, nonlinear partial differential equation (PDE). Its response coefficients correspond to the dielectric permittivity and are therefore constant within each subdomain of the system considered (i.e., inside and outside of the molecules considered). While the DPBL equation is also a second order, elliptic, nonlinear PDE, its response coefficients are nonlinear functions of the electrostatic potential. Many solvers have been developed for the PB equation; to our knowledge, none of these can be directly applied to the DPBL equation. The methods they use may adapt to the difference; their implementations however are PBE specific. We adapted the PBE solver originally developed by Holst and Saied [J. Comput. Chem. 16, 337 (1995)] to the problem of solving the DPBL equation. This solver uses a truncated Newton method with a multigrid preconditioner. Numerical evidences suggest that it converges for the DPBL equation and that the convergence is superlinear. It is found however to be slow and greedy in memory requirement for problems commonly encountered in computational biology and computational chemistry. To circumvent these problems, we propose two variants, a quasi-Newton solver based on a simplified, inexact Jacobian and an iterative self-consistent solver that is based directly on
Nuclear magnetic resonance dephasing effects in a spherical pore with a magnetic dipolar field
NASA Astrophysics Data System (ADS)
Valckenborg, R. M. E.; Huinink, H. P.; Kopinga, K.
2003-02-01
The NMR dephasing behavior of the nuclear spins of a fluid confined in a porous material can be investigated by Hahn spin echoes. Previous experimental results on water in a magnetically doped clay have shown a nonmonoexponentially decaying magnetization, which can be understood neither by the known dephasing rate of freely diffusing spins in a uniform gradient nor by spins diffusing in a restricted geometry. For a better understanding of NMR measurements on these systems, a systematic survey was performed of the various length scales that are involved. The standard length scales for the situation of a uniform gradient are diffusing length, structure length, and dephasing length. We show that for a nonuniform gradient, a new length scale has to be introduced: the magnetic-field curvature length. When a particle diffuses less than this length scale, it experiences a local uniform gradient. In that case the spin-echo decay can be described by the so-called local gradient approximation (LGA). When a particle diffuses over a longer distance than the structure length, the spin-echo decay can be described by the motional averaging regime. For both regimes, scaling laws are derived. In this paper, a random-walk model is used to simulate the dephasing effect of diffusing spins in a spherical pore in the presence of a magnetic dipole field. By varying the dipole magnitude, situations can be created in which the dephasing behavior scales according to the motional averaging regime or according to the LGA regime, for certain ranges of echo times. Two model systems are investigated: a spherical pore in the vicinity of a magnetic point dipole and a spherical pore adjacent to a magnetic dipolar grain of the same size as the pore. The simulated magnetization decay curves of both model systems confirm the scaling laws. The LGA, characterized by a nonmonoexponential magnetization decay, is also investigated by calculating the spatially resolved magnetization in the pore. For this
Pulse Dipolar ESR of Doubly Labeled Mini TAR DNA and Its Annealing to Mini TAR RNA
Sun, Yan; Borbat, Peter P.; Grigoryants, Vladimir M.; Myers, William K.; Freed, Jack H.; Scholes, Charles P.
2015-01-01
Pulse dipolar electron-spin resonance in the form of double electron electron resonance was applied to strategically placed, site-specifically attached pairs of nitroxide spin labels to monitor changes in the mini TAR DNA stem-loop structure brought on by the HIV-1 nucleocapsid protein NCp7. The biophysical structural evidence was at Ångstrom-level resolution under solution conditions not amenable to crystallography or NMR. In the absence of complementary TAR RNA, double labels located in both the upper and the lower stem of mini TAR DNA showed in the presence of NCp7 a broadened distance distribution between the points of attachment, and there was evidence for several conformers. Next, when equimolar amounts of mini TAR DNA and complementary mini TAR RNA were present, NCp7 enhanced the annealing of their stem-loop structures to form duplex DNA-RNA. When duplex TAR DNA-TAR RNA formed, double labels initially located 27.5 Å apart at the 3′- and 5′-termini of the 27-base mini TAR DNA relocated to opposite ends of a 27 bp RNA-DNA duplex with 76.5 Å between labels, a distance which was consistent with the distance between the two labels in a thermally annealed 27-bp TAR DNA-TAR RNA duplex. Different sets of double labels initially located 26–27 Å apart in the mini TAR DNA upper stem, appropriately altered their interlabel distance to ∼35 Å when a 27 bp TAR DNA-TAR RNA duplex formed, where the formation was caused either through NCp7-induced annealing or by thermal annealing. In summary, clear structural evidence was obtained for the fraying and destabilization brought on by NCp7 in its biochemical function as an annealing agent and for the detailed structural change from stem-loop to duplex RNA-DNA when complementary RNA was present. PMID:25692594
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
Wang, Huapei; Kent, Dennis V.; Rochette, Pierre
2015-01-01
The geomagnetic field is predominantly dipolar today, and high-fidelity paleomagnetic mean directions from all over the globe strongly support the geocentric axial dipole (GAD) hypothesis for the past few million years. However, the bulk of paleointensity data fails to coincide with the axial dipole prediction of a factor-of-2 equator-to-pole increase in mean field strength, leaving the core dynamo process an enigma. Here, we obtain a multidomain-corrected Pliocene–Pleistocene average paleointensity of 21.6 ± 11.0 µT recorded by 27 lava flows from the Galapagos Archipelago near the Equator. Our new result in conjunction with a published comprehensive study of single-domain–behaved paleointensities from Antarctica (33.4 ± 13.9 µT) that also correspond to GAD directions suggests that the overall average paleomagnetic field over the past few million years has indeed been dominantly dipolar in intensity yet only ∼60% of the present-day field strength, with a long-term average virtual axial dipole magnetic moment of the Earth of only 4.9 ± 2.4 × 1022 A⋅m2. PMID:26598664
NASA Astrophysics Data System (ADS)
Liu, J.; Angelopoulos, V.; Zhang, X. J.; Turner, D. L.; Gabrielse, C.; Runov, A.; Funsten, H. O.; Spence, H. E.
2015-12-01
Dipolarizing flux bundles (DFBs) are small flux tubes (typically < 3 RE in XGSM and YGSM) in the nightside magnetosphere that have magnetic field more dipolar than the background field. Although DFBs are known to accelerate particles to create energetic particle injections, their acceleration mechanism and importance in generating injections inside geosynchronous orbit remain open questions. To answer these questions, we investigate DFBs in the inner magnetosphere by conducting a statistical study with data from the Van Allen Probes. The results show that just like DFBs outside geosynchronous orbit, those inside that orbit occur most often in the pre-midnight sector. Half the DFBs are accompanied by energetic particle injection. Statistically, DFBs with injection have an electric field three times that of those without. All the injections accompanying DFBs appear dispersionless within the temporal and energy resolution considered. These findings suggest that the injections are ushered or locally produced by the DFB, and the DFB's strong electric field is an important aspect of the injection generation mechanism.
NASA Astrophysics Data System (ADS)
Elfimova, Ekaterina A.; Karavaeva, Tatyana E.; Ivanov, Alexey O.
2014-12-01
A method for calculation of the free energy of dipolar hard spheres under the presence of an applied magnetic field is presented. The method is based on the virial expansion in terms of density as well as the dipolar coupling constant λ, and it uses diagram technique. The formulas and the diagrams, needed to calculate the second B2 and third B3 virial coefficients, are derived up to the order of ˜λ3, and compared to the zero-field case. The formula for B2 is the same as in the zero-field case; the formula for B3, however, is different in an applied field, and a derivation is presented. This is a surprising result which is not emphasized in standard texts, but which has been noticed before in the virial expansion for flexible molecules (Caracciolo et al., 2006; Caracciolo et al., 2008). To verify the correctness of the obtained formulas, B2 and B3 were calculated within the accuracy of λ2, which were applied to initial magnetic susceptibility. The obtained expression fully coincides with the well-known theories (Morozov and Lebedev, 1990; Huke and Lücke, 2000; Ivanov and Kuznetsova, 2001), which used different methods to calculate the initial magnetic susceptibility.
Kharkov, B. B.; Chizhik, V. I.; Dvinskikh, S. V.
2016-01-21
Dipolar recoupling is an essential part of current solid-state NMR methodology for probing atomic-resolution structure and dynamics in solids and soft matter. Recently described magic-echo amplitude- and phase-modulated cross-polarization heteronuclear recoupling strategy aims at efficient and robust recoupling in the entire range of coupling constants both in rigid and highly dynamic molecules. In the present study, the properties of this recoupling technique are investigated by theoretical analysis, spin-dynamics simulation, and experimentally. The resonance conditions and the efficiency of suppressing the rf field errors are examined and compared to those for other recoupling sequences based on similar principles. The experimental data obtained in a variety of rigid and soft solids illustrate the scope of the method and corroborate the results of analytical and numerical calculations. The technique benefits from the dipolar resolution over a wider range of coupling constants compared to that in other state-of-the-art methods and thus is advantageous in studies of complex solids with a broad range of dynamic processes and molecular mobility degrees.
Brody, D A; Mirvis, D M; Ideker, R E; Cox, J W; Keller, F W; Larsen, R A; Bandura, J P
1977-03-01
We studied the relative dipolar and nondipolar content of signal energy throughout ventricular excitation and recovery in 34 isolated, perfused rabbit hearts, suspended in an electrolyte-filled spherical chamber. Computer-processed signals were derived from 20 evenly spaced tank-surface electrodes, and a single, moving, equivalent cardiac dipole generator was optimally fitted to the recorded potentials for each 1-msec sampling interval. Superimposed, time-based plots of signal energy for the 34 preparations showed ventricular excitation to be strikingly more nondipolar than was recovery. In terms of the summed square ratio of nondipolar residual energies, overall nondipolarity of QRS exceed that of ST-T by 41%. Furthermore, the maximum instantaneous ratio during QRS was considerably greater than during the ST-T. Evaluation of paired differences, comparing nondipolar behavior throughout QRS with all of ST-T, proved highly significant (P less than .005). We also found that in contrast to the considerable mobility exhibited by the equivalent QRS dipole, the ST-T dipole locus remained nearly stationary during most of ventricular recovery. Presumably because repolarization is temporally and spatially a relatively diffuse process, it may generate electrical fields which are notably more dipolar than those caused by depolarization.
NASA Astrophysics Data System (ADS)
Fu, S.; Sun, W.; Zhou, X.; Zhao, D.; Zong, Q.; Yao, Z.; Pu, Z.; Parks, G. K.
2015-12-01
Dipolarization front (DF) is characterized by a strong increase of magnetic field Bz component often observed before the arrival of high-speed flows in the Earth's plasma sheet. The DF interfaces between the high-speed flowing transient plasma and the ambient plasma. Ahead of the DFs, magnetic field Bz decreases and it is, called the "dip region." However, unlike in the high-speed flow and the ambient plasma which can be described by MHD theory, kinetic effects are important in the dip region because the spatial scale is less than the ion gyroradius. Observation and simulation have demonstrated that the dip region is formed by the reflecting ions at the sharp front. Short lived electromagnetic waves are also observed here generated by the reflected ions. In addition, Hall electric field observed in this region is in the opposite direction of the electric field inside the DF. The dipolarization front and the dip region ahead of it formed a set of current systems and they are fundamentally important for understanding the cause of flow braking in the plasma sheet.
NASA Astrophysics Data System (ADS)
Kharkov, B. B.; Chizhik, V. I.; Dvinskikh, S. V.
2016-01-01
Dipolar recoupling is an essential part of current solid-state NMR methodology for probing atomic-resolution structure and dynamics in solids and soft matter. Recently described magic-echo amplitude- and phase-modulated cross-polarization heteronuclear recoupling strategy aims at efficient and robust recoupling in the entire range of coupling constants both in rigid and highly dynamic molecules. In the present study, the properties of this recoupling technique are investigated by theoretical analysis, spin-dynamics simulation, and experimentally. The resonance conditions and the efficiency of suppressing the rf field errors are examined and compared to those for other recoupling sequences based on similar principles. The experimental data obtained in a variety of rigid and soft solids illustrate the scope of the method and corroborate the results of analytical and numerical calculations. The technique benefits from the dipolar resolution over a wider range of coupling constants compared to that in other state-of-the-art methods and thus is advantageous in studies of complex solids with a broad range of dynamic processes and molecular mobility degrees.
NASA Astrophysics Data System (ADS)
Capsal, Jean-Fabien; Lallart, Mickaël; Galineau, Jeremy; Cottinet, Pierre-Jean; Sebald, Gaël; Guyomar, Daniel
2012-05-01
Electrostrictive polymers, as an important category of electroactive polymers, are known to have non-linear response in terms of actuation that strongly affects their dynamic performance and limits their applications. Very few models exist in the literature, and even fewer are capable of making reliable predictions under an electric field. In this paper, electrostrictive strain of dipolar polymeric systems is discussed through constitutive equations derived from the Boltzmann statistics and Debye/Langevin formalism. Macroscopic polarization is expressed as a function of the inherent microscopic parameters of the dielectric material. Electrostrictive strain, polarization and dielectric permittivity are described well by the model in terms of dipole moment and saturation of dipole orientation, allowing the physical definition of the electrostrictive coefficient Q. Maxwell forces generated by dipolar orientation inducing surface charges are also used to explain the electrostrictive strain of polymers. The assessment of this analysis through a comparison with experimental data shows good agreement between reported values and theoretical predictions. These materials are generally used in low-frequency applications, thus the interfacial phenomena that are responsible for low saturation electric field should not be omitted so as not to underestimate or overestimate the low electric field response of the electrostrictive strain.
Rana, Malay Kumar; Chandra, Amalendu
2015-01-21
Atomistic simulations of model nonpolar nanotubes in a Stockmayer liquid are carried out for varying nanotube diameter and nanotube-solvent interactions to investigate solvophobic interactions in generic dipolar solvents. We have considered model armchair type single-walled nonpolar nanotubes with increasing radii from (5,5) to (12,12). The interactions between solute and solvent molecules are modeled by the well-known Lennard-Jones and repulsive Weeks-Chandler-Andersen potentials. We have investigated the density profiles and microscopic arrangement of Stockmayer molecules, orientational profiles of their dipole vectors, time dependence of their occupation, and also the translational and rotational motion of solvent molecules in confined environments of the cylindrical nanopores and also in their external peripheral regions. The present results of structural and dynamical properties of Stockmayer molecules inside and near atomistically rough nonpolar surfaces including their wetting and dewetting behavior for varying interactions provide a more generic picture of solvophobic effects experienced by simple dipolar liquids without any specific interactions such as hydrogen bonds.
BaZr0.5Ti0.5O3 : Lead-free relaxor ferroelectric or dipolar glass
NASA Astrophysics Data System (ADS)
Filipič, C.; Kutnjak, Z.; Pirc, R.; Canu, G.; Petzelt, J.
2016-06-01
Glassy freezing dynamics was investigated in BaZr0.5Ti0.5O3 (BZT50) ceramic samples by means of dielectric spectroscopy in the frequency range 0.001 Hz-1 MHz at temperatures 10
NASA Astrophysics Data System (ADS)
Garbuio, Luca; Zimmermann, Kaspar; Häussinger, Daniel; Yulikov, Maxim
2015-10-01
Spectral parameters of Gd(III) complexes are intimately linked to the performance of the Gd(III)-nitroxide or Gd(III)-Gd(III) double electron-electron resonance (DEER or PELDOR) techniques, as well as to that of relaxation induced dipolar modulation enhancement (RIDME) spectroscopy with Gd(III) ions. These techniques are of interest for applications in structural biology, since they can selectively detect site-to-site distances in biomolecules or biomolecular complexes in the nanometer range. Here we report relaxation properties, echo detected EPR spectra, as well as the magnitude of the echo reduction effect in Gd(III)-nitroxide DEER for a series of Gadolinium(III) complexes with chelating agents derived from tetraazacyclododecane. We observed that solvent deuteration does not only lengthen the relaxation times of Gd(III) centers but also weakens the DEER echo reduction effect. Both of these phenomena lead to an improved signal-to-noise ratios or, alternatively, longer accessible distance range in pulse EPR measurements. The presented data enrich the knowledge on paramagnetic Gd(III) chelate complexes in frozen solutions, and can help optimize the experimental conditions for most types of the pulse measurements of the electron-electron dipolar interactions.
Kharkov, B B; Chizhik, V I; Dvinskikh, S V
2016-01-21
Dipolar recoupling is an essential part of current solid-state NMR methodology for probing atomic-resolution structure and dynamics in solids and soft matter. Recently described magic-echo amplitude- and phase-modulated cross-polarization heteronuclear recoupling strategy aims at efficient and robust recoupling in the entire range of coupling constants both in rigid and highly dynamic molecules. In the present study, the properties of this recoupling technique are investigated by theoretical analysis, spin-dynamics simulation, and experimentally. The resonance conditions and the efficiency of suppressing the rf field errors are examined and compared to those for other recoupling sequences based on similar principles. The experimental data obtained in a variety of rigid and soft solids illustrate the scope of the method and corroborate the results of analytical and numerical calculations. The technique benefits from the dipolar resolution over a wider range of coupling constants compared to that in other state-of-the-art methods and thus is advantageous in studies of complex solids with a broad range of dynamic processes and molecular mobility degrees.
Rana, Malay Kumar; Chandra, Amalendu
2015-01-21
Atomistic simulations of model nonpolar nanotubes in a Stockmayer liquid are carried out for varying nanotube diameter and nanotube-solvent interactions to investigate solvophobic interactions in generic dipolar solvents. We have considered model armchair type single-walled nonpolar nanotubes with increasing radii from (5,5) to (12,12). The interactions between solute and solvent molecules are modeled by the well-known Lennard-Jones and repulsive Weeks-Chandler-Andersen potentials. We have investigated the density profiles and microscopic arrangement of Stockmayer molecules, orientational profiles of their dipole vectors, time dependence of their occupation, and also the translational and rotational motion of solvent molecules in confined environments of the cylindrical nanopores and also in their external peripheral regions. The present results of structural and dynamical properties of Stockmayer molecules inside and near atomistically rough nonpolar surfaces including their wetting and dewetting behavior for varying interactions provide a more generic picture of solvophobic effects experienced by simple dipolar liquids without any specific interactions such as hydrogen bonds.
Waratchareeyakul, Watcharee; Hellemann, Erich; Gil, Roberto R; Chantrapromma, Kan; Langat, Moses K; Mulholland, Dulcie A
2017-02-24
Nine triterpenoid derivatives were isolated from the heartwood of Xylocarpus rumphii and were identified as xylorumphiins E (1), C (2), L (3), and M-R (4-9). Compounds 4-9 have a hemiacetal group in the triterpenoid side chain, making them impossible to purify. Purification was achieved after acetylation and subsequent separation of the epimeric mixtures of acetates; however differentiaition of the R and S epimers was not possible using standard NMR techniques. In one case, the relative configuration of a remotely located stereocenter with respect to the stereocenters in the main skeleton was unambiguously determined using residual dipolar couplings. Dipolar couplings were collected from the sample oriented in compressed poly(methyl methacrylate) gels swollen in CDCl3. In another case, the relative configuration was determined using 1D selective quantitative NOE experiments. Xylorumphiin K (10), xyloccensin E, taraxer-14-en-3β-ol, (22S)-hydroxytirucalla-7,24-diene-3,23-dione, and 25-hydroxy-(20S,24S)-epoxydammaran-3-one were isolated from the bark of the same plant. Compounds 3-10 are new compounds. Compounds 1-6 and xyloccensin E were tested at one concentration, 1 × 10(-5) M, in the NCI59 cell one-dose screen but did not show significant activity.
Wang, Huapei; Kent, Dennis V; Rochette, Pierre
2015-12-08
The geomagnetic field is predominantly dipolar today, and high-fidelity paleomagnetic mean directions from all over the globe strongly support the geocentric axial dipole (GAD) hypothesis for the past few million years. However, the bulk of paleointensity data fails to coincide with the axial dipole prediction of a factor-of-2 equator-to-pole increase in mean field strength, leaving the core dynamo process an enigma. Here, we obtain a multidomain-corrected Pliocene-Pleistocene average paleointensity of 21.6 ± 11.0 µT recorded by 27 lava flows from the Galapagos Archipelago near the Equator. Our new result in conjunction with a published comprehensive study of single-domain-behaved paleointensities from Antarctica (33.4 ± 13.9 µT) that also correspond to GAD directions suggests that the overall average paleomagnetic field over the past few million years has indeed been dominantly dipolar in intensity yet only ∼ 60% of the present-day field strength, with a long-term average virtual axial dipole magnetic moment of the Earth of only 4.9 ± 2.4 × 10(22) A ⋅ m(2).
Pure dipolar-interacted CoFe{sub 2}O{sub 4} nanoparticles and their magnetic properties
Xu, Shi-tao; Ma, Yong-qing; Xu, Yuan-feng; Sun, Xiao; Geng, Bing-qian; Zheng, Gan-hong; Dai, Zhen-xiang
2015-02-15
Graphical abstract: The mono-dispersed CoFe{sub 2}O{sub 4} nanoparticles with the uniform size of 10.5 ± 2 nm were first synthesized and then they were embedded in amorphous SiO{sub 2} matrix with different CoFe{sub 2}O{sub 4} nanoparticles’ concentrations. The large coercivity (3056 Oe) and the remanence ratio (0.63) were obtained by suitably diluting CoFe{sub 2}O{sub 4} nanoparticles into the SiO{sub 2} matrix. The reciprocal of the absolute maximum of δm and the M{sub r}/M{sub s} ratio behave in the same trend (as shown in (e)), indicating that the M{sub r}/M{sub s} ratio was dominated by the interparticle dipolar interaction. The present work is meaningful for revealing the underlying mechanism in nano-scaled magnetic system and improving the magnetic performance. - Highlights: • The mono-dispersed CoFe{sub 2}O{sub 4} nanoparticles with the uniform size of 10.5 ± 2 nm were synthesized by the thermal decomposition of metals acetylacetonates in solvents with high boiling point. • The large coercivity (3056 Oe) and the remanence ratio (0.63) were obtained by diluting CoFe{sub 2}O{sub 4} nanoparticles into the SiO{sub 2} matrix with a suitable concentration. • The surface anisotropy and interparticle dipolar interaction affect the magnetic performance and magnetic ordering state. • It was observed that the M{sub r}/M{sub s} ratio was dominated by the interparticle dipolar interaction. - Abstract: The mono-dispersed and uniform CoFe{sub 2}O{sub 4} nanoparticles were synthesized by the thermal decomposition of Fe(acac){sub 3} and Co(acac){sub 2}. Then the CoFe{sub 2}O{sub 4} nanoparticles were diluted in amorphous SiO{sub 2} matrix with different CoFe{sub 2}O{sub 4} nanoparticles’ concentrations. All samples show the positive or negative exchange bias behavior, indicating the presence of canted spin layer at the CoFe{sub 2}O{sub 4} nanoparticles’ surface. The large effective anisotropy constant (3.38 × 10{sup 6} erg/cm{sup 3}) was observed, which
Li, Feng; Gao, Na; Xu, Hai; Liu, Wei; Shang, Hui; Yang, Wenjun; Zhang, Ming
2014-08-04
Five 9,10-bis((4-N,N-dialkylamino)styryl) anthracene derivatives (DSA-C1-DSA-C7) with different length alkyl chains were synthesized. They showed the same color in dilute solutions but different colors in crystals. The absorption, photoluminescence, and fluorescence decay indicate that there exist both excitonic and dipolar coupling in crystals of DSA-C1-DSA-C7. X-ray crystallographic analysis revealed that all the crystals belong to the triclinic space group P1 with one molecule per unit cell and that the molecules in every crystal have the identical orientation. This offers ideal samples to investigate the impact of the molecular stacking on the optical properties of the crystals. For the first time, the cooperation of excitonic and dipolar coupling has been comprehensively studied, and the contribution to the spectral shift from the excitonic and dipolar couplings quantitatively obtained. The experiments of amplified spontaneous emission (ASE) together with measurements of the quantum efficiency further confirmed this interpretation. The results suggest that the excitonic and dipolar couplings between the adjacent molecules are both important and jointly induce the spectral shifts of the crystals.
Dedola, Simone; Nepogodiev, Sergey A; Field, Robert A
2007-04-07
This article surveys recent applications of Cu(I)-catalysed 1,3-dipolar cycloaddition of azides and alkynes in carbohydrate chemistry, highlighting developments in the preparation of simple glycoside and oligosaccharide mimetics, glyco-macrocycles, glycopeptides, glyco-clusters and carbohydrate arrays.
Spiteri, Christian; Keeling, Steve; Moses, John E
2010-08-06
A new synthesis of 1-substituted-1H-indazoles via 1,3-dipolar cycloaddition of nitrile imines to benzyne is described. The reaction is completed within 5 min, affording the corresponding N(1)-C(3) disubstituted indazoles in moderate to excellent yields.
Eliav, U; Navon, G
1999-04-01
The effect of proton exchange on the measurement of 1H-1H, 1H-2H, and 2H-2H residual dipolar interactions in water molecules in bovine Achilles tendons was investigated using double-quantum-filtered (DQF) NMR and new pulse sequences based on heteronuclear and homonuclear multiple-quantum filtering (MQF). Derivation of theoretical expressions for these techniques allowed evaluation of the 1H-1H and 1H-2H residual dipolar interactions and the proton exchange rate at a temperature of 24 degrees C and above, where no dipolar splitting is evident. The values obtained for these parameters at 24 degrees C were 300 and 50 Hz and 3000 s-1, respectively. The results for the residual dipolar interactions were verified by repeating the above measurements at a temperature of 1.5 degrees C, where the spectra of the H2O molecules were well resolved, so that the 1H-1H dipolar interaction could be determined directly from the observed splitting. Analysis of the MQF experiments at 1.5 degrees C, where the proton exchange was in the intermediate regime for the 1H-2H dipolar interaction, confirmed the result obtained at 24 degrees C for this interaction. A strong dependence of the intensities of the MQF signals on the proton exchange rate, in the intermediate and the fast exchange regimes, was observed and theoretically interpreted. This leads to the conclusion that the MQF techniques are mostly useful for tissues where the residual dipolar interaction is not significantly smaller than the proton exchange rate. Dependence of the relaxation times and signal intensities of the MQF experiments on the orientation of the tendon with respect to the magnetic field was observed and analyzed. One of the results of the theoretical analysis is that, in the fast exchange regime, the signal decay rates in the MQF experiments as well as in the spin echo or CPMG pulse sequences (T2) depend on the orientation as the square of the second-rank Legendre polynomial.
Vugmeyster, Liliya; Ostrovsky, Dmitry; Fu, Riqiang
2015-10-01
In this work, we assess the usefulness of static (15)N NMR techniques for the determination of the (15)N chemical shift anisotropy (CSA) tensor parameters and (15)N-(1)H dipolar splittings in powder protein samples. By using five single labeled samples of the villin headpiece subdomain protein in a hydrated lyophilized powder state, we determine the backbone (15)N CSA tensors at two temperatures, 22 and -35 °C, in order to get a snapshot of the variability across the residues and as a function of temperature. All sites probed belonged to the hydrophobic core and most of them were part of α-helical regions. The values of the anisotropy (which include the effect of the dynamics) varied between 130 and 156 ppm at 22 °C, while the values of the asymmetry were in the 0.32-0.082 range. The Leu-75 and Leu-61 backbone sites exhibited high mobility based on the values of their temperature-dependent anisotropy parameters. Under the assumption that most differences stem from dynamics, we obtained the values of the motional order parameters for the (15)N backbone sites. While a simple one-dimensional line shape experiment was used for the determination of the (15)N CSA parameters, a more advanced approach based on the "magic sandwich" SAMMY pulse sequence (Nevzorov and Opella, 2003) was employed for the determination of the (15)N-(1)H dipolar patterns, which yielded estimates of the dipolar couplings. Accordingly, the motional order parameters for the dipolar interaction were obtained. It was found that the order parameters from the CSA and dipolar measurements are highly correlated, validating that the variability between the residues is governed by the differences in dynamics. The values of the parameters obtained in this work can serve as reference values for developing more advanced magic-angle spinning recoupling techniques for multiple labeled samples.
NASA Astrophysics Data System (ADS)
Teymoori, Gholamhasan; Pahari, Bholanath; Edén, Mattias
2015-12-01
We provide an experimental, numerical, and high-order average Hamiltonian evaluation of an open-ended series of homonuclear dipolar recoupling sequences, SR2 2p 1 with p = 1, 2, 3, … . While operating at a very low radio-frequency (rf) power, corresponding to a nutation frequency of 1/2 of the magic-angle spinning (MAS) rate (ωnut =ωr / 2), these recursively generated double-quantum (2Q) dipolar recoupling schemes offer a progressively improved compensation to resonance offsets and rf inhomogeneity for increasing pulse-sequence order p. The excellent recoupling robustness to these experimental obstacles, as well as to CSA, is demonstrated for 2Q filtering (2QF) experiments and for driving magnetization transfers in 2D NMR correlation spectroscopy, where the sequences may provide either double or zero quantum dipolar Hamiltonians during mixing. Experimental and numerical demonstrations, which mostly target conditions of "ultra-fast" MAS (≳50 kHz) and high magnetic fields, are provided for recoupling of 13C across a wide range of isotropic and anisotropic chemical shifts, as well as dipolar coupling constants, encompassing [2,3-13C2 ]alanine, [1,3-13C2 ]alanine, diammonium [1,4-13C2 ]fumarate, and [U-13 C]tyrosine. When compared at equal power levels, a superior performance is observed for the SR2p 1 sequences with p ⩾ 3 relative to existing and well-established 2Q recoupling techniques. At ultra-fast MAS, proton decoupling is redundant during the homonuclear dipolar recoupling of dilute spins in organic solids, which renders the family of SR2p 1 schemes the first efficient 2Q recoupling option for general applications, such as 2Q-1Q correlation NMR and high-order multiple-quantum excitation, under truly low-power rf conditions.
Teymoori, Gholamhasan; Pahari, Bholanath; Edén, Mattias
2015-12-01
We provide an experimental, numerical, and high-order average Hamiltonian evaluation of an open-ended series of homonuclear dipolar recoupling sequences, SR [Formula: see text] with p=1,2,3,…. While operating at a very low radio-frequency (rf) power, corresponding to a nutation frequency of 1/2 of the magic-angle spinning (MAS) rate (ωnut=ωr/2), these recursively generated double-quantum (2Q) dipolar recoupling schemes offer a progressively improved compensation to resonance offsets and rf inhomogeneity for increasing pulse-sequence order p. The excellent recoupling robustness to these experimental obstacles, as well as to CSA, is demonstrated for 2Q filtering (2QF) experiments and for driving magnetization transfers in 2D NMR correlation spectroscopy, where the sequences may provide either double or zero quantum dipolar Hamiltonians during mixing. Experimental and numerical demonstrations, which mostly target conditions of "ultra-fast" MAS (≳50kHz) and high magnetic fields, are provided for recoupling of (13)C across a wide range of isotropic and anisotropic chemical shifts, as well as dipolar coupling constants, encompassing [2,3-(13)C2]alanine, [1,3-(13)C2]alanine, diammonium [1,4-(13)C2]fumarate, and [U-(13)C]tyrosine. When compared at equal power levels, a superior performance is observed for the SR [Formula: see text] sequences with p⩾3 relative to existing and well-established 2Q recoupling techniques. At ultra-fast MAS, proton decoupling is redundant during the homonuclear dipolar recoupling of dilute spins in organic solids, which renders the family of SR [Formula: see text] schemes the first efficient 2Q recoupling option for general applications, such as 2Q-1Q correlation NMR and high-order multiple-quantum excitation, under truly low-power rf conditions.
Zong, Wen; Li, Gao-Wei; Cao, Jiang-Ming; Lei, Xinxiang; Hu, Mao-Lin; Sun, Han; Griesinger, Christian; Tan, Ren Xiang
2016-03-07
Residual dipolar couplings (RDCs) have attracted attention in light of their great impact on the structural elucidation of organic molecules. However, the effectiveness of RDC measurements is limited by the shortage of alignment media compatible with widely used organic solvents, such as DMSO. Herein, we present the first liquid crystal (LC) based alignment medium that is compatible with pure DMSO, thus enabling RDC measurements of polar and intermediate polarity molecules. The liquid crystals were obtained by grafting polymer brushes onto graphene oxide (GO) using free radical polymerization. The resulting new medium offers several advantages, such as absence of background signals, narrow line shapes, and tunable alignment. Importantly, this medium is compatible with π-conjugated molecules. Moreover, sonication-induced fragmentation can reduce the size of GO sheets. The resulting anisotropic medium has moderate alignment strength, which is a prerequisite for an accurate RDC measurement.
Acousto-exciton interaction in a gas of 2D indirect dipolar excitons in the presence of disorder
NASA Astrophysics Data System (ADS)
Kovalev, V. M.; Chaplik, A. V.
2016-03-01
A theory for the linear and quadratic responses of a 2D gas of indirect dipolar excitons to an external surface acoustic wave perturbation in the presence of a static random potential is considered. The theory is constructed both for high temperatures, definitely greater than the exciton gas condensation temperature, and at zero temperature by taking into account the Bose-Einstein condensation effects. The particle Green functions, the density-density correlation function, and the quadratic response function are calculated by the "cross" diagram technique. The results obtained are used to calculate the absorption of Rayleigh surface waves and the acoustic exciton gas drag by a Rayleigh wave. The damping of Bogoliubov excitations in an exciton condensate due to theirs scattering by a random potential has also been determined.
Yavari, Issa; Baoosi, Leila; Halvagar, Mohammad R
2017-01-13
An efficient synthesis of tetraalkyl 6a-hydroxy-3-alkyl-3H,6aH-acenaphtho[1,2-g] pyrrolizine-1,2,5,6-tetracarboxylates via the 1,3-dipolar cycloaddition reaction of azomethine ylides (generated in situ from [Formula: see text]-amino acids and acenaphthylene-1,2-dione) with dialkyl acetylenedicarboxylates is described. When glycine was used instead of alanine, phenylalanine, valine, or isoleucine, dialkyl (E)-1[Formula: see text]-(1,4-dialkoxy-1,4-dioxobut-2-en-2-yl)-2-oxo-[Formula: see text],5[Formula: see text]-dihydro-2H-spiro [acenaphthylene-1,2[Formula: see text]-pyrrole]-3[Formula: see text],4[Formula: see text]-dicarboxylates were obtained. The steric effects of the [Formula: see text]-amino acids side chains may be responsible for their different behaviors.
AC Susceptibility of the Dipolar Spin Ice Dy2Ti2O7: Experiments and Monte Carlo Simulations
NASA Astrophysics Data System (ADS)
Takatsu, Hiroshi; Goto, Kazuki; Otsuka, Hiromi; Higashinaka, Ryuji; Matsubayashi, Kazuyuki; Uwatoko, Yoshiya; Kadowaki, Hiroaki
2013-10-01
Experimental data of the frequency-dependent ac susceptibility [χac(ω)] for the dipolar spin ice Dy2Ti2O7 has been analyzed by Monte Carlo simulations on the basis of the single-spin-flip Metropolis algorithm. We have directly evaluated χac(ω) by applying an ac magnetic field. We found that this simulation reasonably reproduces the experimental behavior of χac(ω) in the temperature range from 0.6 to 1.0 K, where dilute magnetic monopoles diffusively move. The conversion factor from simulation time to real time, i.e., the rate of hopping of monopoles to nearest-neighbor sites, strongly depends on temperature.
NASA Astrophysics Data System (ADS)
Chevelkov, Veniamin; Habenstein, Birgit; Loquet, Antoine; Giller, Karin; Becker, Stefan; Lange, Adam
2014-05-01
Proton-detected solid-state NMR was applied to a highly deuterated insoluble, non-crystalline biological assembly, the Salmonella typhimurium type iii secretion system (T3SS) needle. Spectra of very high resolution and sensitivity were obtained at a low protonation level of 10-20% at exchangeable amide positions. We developed efficient experimental protocols for resonance assignment tailored for this system and the employed experimental conditions. Using exclusively dipolar-based interspin magnetization transfers, we recorded two sets of 3D spectra allowing for an almost complete backbone resonance assignment of the needle subunit PrgI. The additional information provided by the well-resolved proton dimension revealed the presence of two sets of resonances in the N-terminal helix of PrgI, while in previous studies employing 13C detection only a single set of resonances was observed.
NASA Astrophysics Data System (ADS)
Lončar, Vladimir; Balaž, Antun; Bogojević, Aleksandar; Škrbić, Srdjan; Muruganandam, Paulsamy; Adhikari, Sadhan K.
2016-03-01
In this paper we present new versions of previously published numerical programs for solving the dipolar Gross-Pitaevskii (GP) equation including the contact interaction in two and three spatial dimensions in imaginary and in real time, yielding both stationary and non-stationary solutions. New versions of programs were developed using CUDA toolkit and can make use of Nvidia GPU devices. The algorithm used is the same split-step semi-implicit Crank-Nicolson method as in the previous version (Kishor Kumar et al., 2015), which is here implemented as a series of CUDA kernels that compute the solution on the GPU. In addition, the Fast Fourier Transform (FFT) library used in the previous version is replaced by cuFFT library, which works on CUDA-enabled GPUs. We present speedup test results obtained using new versions of programs and demonstrate an average speedup of 12-25, depending on the program and input size.
NASA Astrophysics Data System (ADS)
Edén, Mattias; Annersten, Hans; Zazzi, Åsa
2005-07-01
We demonstrate numerically and experimentally that zero-quantum homonuclear dipolar recoupling techniques employing rotor-synchronized 180° pulses, previously introduced for spin-1/2 applications, are useful also for magnetization transfers between half-integer quadrupolar nuclei in rotating solids. The recoupling sequences are incorporated as mixing periods in two-dimensional experimental protocols, that correlate either single-quantum coherences of coupled spins, or triple-quantum with single-quantum coherences for improving spectral resolution. We present 23Na and 27Al NMR experiments on powders of sodium sulphite [Na 2SO 3], YAG [Y 3Al 5O 12] and a synthetic chlorite mineral [Mg 4.5Al 3Si 2.5O 10(OH) 8].
Polarimetry-based analysis of dipolar transitions of single colloidal CdSe/CdS dot-in-rods
NASA Astrophysics Data System (ADS)
Lethiec, C.; Pisanello, F.; Carbone, L.; Bramati, A.; Coolen, L.; Maître, A.
2014-09-01
We use polarization resolved micro-photoluminescence to analyze the dipolar nature of single core/shell cadmium selenide/cadmium sulfide (CdSe/CdS) dot-in-rods. Polarization analysis, anisotropy measurements on more than 400 nanoparticles, and defocused imaging suggest that these nanoparticles behave as linear dipoles. The same methods were also used to determine the three-dimensional orientation of the emission dipole, which proved to be consistent with the hypothesis of a linear dipole tilted with respect to the rod axis. Moreover, we observe that for high-energy pumping, the excitation transition of the dot-in-rod cannot be approximated by a single linear dipole, contrary to the emission transition.
NASA Astrophysics Data System (ADS)
Nielsen, N. C.; Bildsøe, H.; Jakobsen, H. J.; Levitt, M. H.
1994-08-01
We describe an efficient method for the recovery of homonuclear dipole-dipole interactions in magic-angle spinning NMR. Double-quantum homonuclear rotary resonance (2Q-HORROR) is established by fulfilling the condition ωr=2ω1, where ωr is the sample rotation frequency and ω1 is the nutation frequency around an applied resonant radio frequency (rf) field. This resonance can be used for double-quantum filtering and measurement of homonuclear dipolar interactions in the presence of magic-angle spinning. The spin dynamics depend only weakly on crystallite orientation allowing good performance for powder samples. Chemical shift effects are suppressed to zeroth order. The method is demonstrated for singly and doubly 13C labeled L-alanine.
Li, Zhong’an; Zhu, Zonglong; Chueh, Chu -Chen; ...
2016-08-23
In this paper, an electron donor-acceptor (D-A) substituted dipolar chromophore (BTPA-TCNE) is developed to serve as an efficient dopant-free hole-transporting material (HTM) for perovskite solar cells (PVSCs). BTPA-TCNE is synthesized via a simple reaction between a triphenylamine-based Michler’s base and tetracyanoethylene. This chromophore possesses a zwitterionic resonance structure in the ground state, as evidenced by X-ray crystallography and transient absorption spectroscopies. Moreover, BTPA-TCNE shows an antiparallel molecular packing (i.e., centrosymmetric dimers) in its crystalline state, which cancels out its overall molecular dipole moment to facilitate charge transport. Finally, BTPA-TCNE can be employed as an effective dopant-free HTM to realize anmore » efficient (PCE ≈ 17.0%) PVSC in the conventional n-i-p configuration, outperforming the control device with doped spiro-OMeTAD HTM.« less
Li, Zhong’an; Zhu, Zonglong; Chueh, Chu -Chen; Jo, Sae Byeok; Luo, Jingdong; Jang, Sei -Hum; Jen, Alex K. -Y.
2016-08-23
In this paper, an electron donor-acceptor (D-A) substituted dipolar chromophore (BTPA-TCNE) is developed to serve as an efficient dopant-free hole-transporting material (HTM) for perovskite solar cells (PVSCs). BTPA-TCNE is synthesized via a simple reaction between a triphenylamine-based Michler’s base and tetracyanoethylene. This chromophore possesses a zwitterionic resonance structure in the ground state, as evidenced by X-ray crystallography and transient absorption spectroscopies. Moreover, BTPA-TCNE shows an antiparallel molecular packing (i.e., centrosymmetric dimers) in its crystalline state, which cancels out its overall molecular dipole moment to facilitate charge transport. Finally, BTPA-TCNE can be employed as an effective dopant-free HTM to realize an efficient (PCE ≈ 17.0%) PVSC in the conventional n-i-p configuration, outperforming the control device with doped spiro-OMeTAD HTM.
Vögeli, Beat; Olsson, Simon; Riek, Roland; Güntert, Peter
2015-12-01
We compiled an NMR data set consisting of exact nuclear Overhauser enhancement (eNOE) distance limits, residual dipolar couplings (RDCs) and scalar (J) couplings for GB3, which forms one of the largest and most diverse data set for structural characterization of a protein to date. All data have small experimental errors, which are carefully estimated. We use the data in the research article Vogeli et al., 2015, Complementarity and congruence between exact NOEs and traditional NMR probes for spatial decoding of protein dynamics, J. Struct. Biol., 191, 3, 306-317, doi:10.1016/j.jsb.2015.07.008 [1] for cross-validation in multiple-state structural ensemble calculation. We advocate this set to be an ideal test case for molecular dynamics simulations and structure calculations.
NASA Astrophysics Data System (ADS)
Zhang, Kecong; Song, Jiancheng; Wang, Min; Fang, Changshui; Lu, Mengkai
1987-04-01
TGS crystals doped with aniline-family dipolar molecules (aniline, 2-aminobenzoic acid, 3-aminobenzoic acid, 3-aminobenzene-sulphonic acid, 4-aminobenzenesulphonic acid and 4-nitroraniline) have been grown by the slow-cooling solution method. The influence of these dopants on the growth habits, crystal morphology pyroelectric properties, and structure parameters of TGS crystals has been systematically investigated. The effects of the domain structure of the seed crystal on the pyroelectric properties of the doped crystals have been studied. It is found that the spontaneous polarization (P), pyroelectric coefficient (lambda), and internal bias field of the doped crystals are slightly higher than those of the pure TGS, and the larger the dipole moment of the dopant molecule, the higher the P and lambda of the doped TGS crystal.
Isse, B; Fidelio, G; Farías, R N
2003-02-01
The surface balance technique was employed to study the interactions of 3,5,3',5' tetraiodo L-thyronine, 3,5,3' triiodo L-thyronine, and 3,5-diiodothyronine with monomolecular phospholipid monolayers spread at the air-water interface. With this technique the insertion of thyroid hormones into egg yolk phosphatidylcholine was investigated. An increase of surface pressure and a substantial decrement in surface potential were observed after the injection of these hormones beneath a phospholipid monolayer. The negative dipole contribution upon hormone interaction opposes the well-known positive contribution of phospholipids. These effects correlated with iodo content of the thyroid molecule analogues 3,5,3',5' tetraiodo L-thyronine >3,5,3' triiodo L-thyronine >3,5-diiodothyronine. To our knowledge, these observations suggest a new and surprising effect of thyroid hormones on the regulation of transmembrane dipolar organization.
Mahanti, S D; Jha, Sudhanshu S
2007-12-01
We obtain the best upper bound for the ground-state energy of a system of chargeless fermions of mass m, spin s=1/2 , and magnetic moment mus[over ] as a function of its density in the fully spin-polarized Hartree-Fock determinantal state, specified by a prolate spheroidal plane-wave single-particle occupation function n_(k[over ]) , by minimizing the total energy E at each density with respect to the variational spheroidal deformation parameter beta(2),0< or =beta(2)< or =1 . We find that at high densities, this spheroidal ferromagnetic state is the most likely ground state of the system, but it is still unstable towards the infinite-density collapse. This optimized ferromagnetic state is shown to be a stable ground state of the dipolar system at high densities, if one has an additional repulsive short-range hardcore interaction of sufficient strength and nonvanishing range.
Guizzetti, Leonardo; McGirr, Rebecca; Dhanvantari, Savita
2014-05-23
Proglucagon is expressed in pancreatic α cells, intestinal L cells, and some hypothalamic and brainstem neurons. Tissue-specific processing of proglucagon yields three major peptide hormones as follows: glucagon in the α cells and glucagon-like peptides (GLP)-1 and -2 in the L cells and neurons. Efficient sorting and packaging into the secretory granules of the regulated secretory pathway in each cell type are required for nutrient-regulated secretion of these proglucagon-derived peptides. Our previous work suggested that proglucagon is directed into granules by intrinsic sorting signals after initial processing to glicentin and major proglucagon fragment (McGirr, R., Guizzetti, L., and Dhanvantari, S. (2013) J. Endocrinol. 217, 229-240), leading to the hypothesis that sorting signals may be present in multiple domains. In the present study, we show that the α-helices within glucagon and GLP-1, but not GLP-2, act as sorting signals by efficiently directing a heterologous secretory protein to the regulated secretory pathway. Biophysical characterization of these peptides revealed that glucagon and GLP-1 each encode a nonamphipathic, dipolar α-helix, whereas the helix in GLP-2 is not dipolar. Surprisingly, glicentin and major proglucagon fragment were sorted with different efficiencies, thus providing evidence that proglucagon is first sorted to granules prior to processing. In contrast to many other prohormones in which sorting is directed by ordered prodomains, the sorting determinants of proglucagon lie within the ordered hormone domains of glucagon and GLP-1, illustrating that each prohormone has its own sorting "signature."
Martin, Jeffrey W; Yan, Anthony K; Bailey-Kellogg, Chris; Zhou, Pei; Donald, Bruce R
2011-06-01
High-resolution structure determination of homo-oligomeric protein complexes remains a daunting task for NMR spectroscopists. Although isotope-filtered experiments allow separation of intermolecular NOEs from intramolecular NOEs and determination of the structure of each subunit within the oligomeric state, degenerate chemical shifts of equivalent nuclei from different subunits make it difficult to assign intermolecular NOEs to nuclei from specific pairs of subunits with certainty, hindering structural analysis of the oligomeric state. Here, we introduce a graphical method, DISCO, for the analysis of intermolecular distance restraints and structure determination of symmetric homo-oligomers using residual dipolar couplings. Based on knowledge that the symmetry axis of an oligomeric complex must be parallel to an eigenvector of the alignment tensor of residual dipolar couplings, we can represent distance restraints as annuli in a plane encoding the parameters of the symmetry axis. Oligomeric protein structures with the best restraint satisfaction correspond to regions of this plane with the greatest number of overlapping annuli. This graphical analysis yields a technique to characterize the complete set of oligomeric structures satisfying the distance restraints and to quantitatively evaluate the contribution of each distance restraint. We demonstrate our method for the trimeric E. coli diacylglycerol kinase, addressing the challenges in obtaining subunit assignments for distance restraints. We also demonstrate our method on a dimeric mutant of the immunoglobulin-binding domain B1 of streptococcal protein G to show the resilience of our method to ambiguous atom assignments. In both studies, DISCO computed oligomer structures with high accuracy despite using ambiguously assigned distance restraints.
NASA Astrophysics Data System (ADS)
Komath, Sneha Sudha; Bagchi, Biman
1993-06-01
Several recent theoretical and computer simulation studies have considered solvation dynamics in a Brownian dipolar lattice which provides a simple model solvent for which detailed calculations can be carried out. In this article a fully microscopic calculation of the solvation dynamics of an ion in a Brownian dipolar lattice is presented. The calculation is based on the non-Markovian molecular hydrodynamic theory developed recently. The main assumption of the present calculation is that the two-particle orientational correlation functions of the solid can be replaced by those of the liquid state. It is shown that such a calculation provides an excellent agreement with the computer simulation results. More importantly, the present calculations clearly demonstrate that the frequency-dependent dielectric friction plays an important role in the long time decay of the solvation time correlation function. We also find that the present calculation provides somewhat better agreement than either the dynamic mean spherical approximation (DMSA) or the Fried-Mukamel theory which use the simulated frequency-dependent dielectric function. It is found that the dissipative kernels used in the molecular hydrodynamic approach and in the Fried-Mukamel theory are vastly different, especially at short times. However, in spite of this disagreement, the two theories still lead to comparable results in good agreement with computer simulation, which suggests that even a semiquantitatively accurate dissipative kernel may be sufficient to obtain a reliable solvation time correlation function. A new wave vector and frequency-dependent dissipative kernel (or memory function) is proposed which correctly goes over to the appropriate expressions in both the single particle and the collective limits. This form is expected to lead to better results than all the existing descriptions.
[Synthesis of asymmetric tetraarylporphyrins and its ytterbium complexes].
Rumiantseva, V D; Roshchina, N V; Fedorova, L D; Mironov, A F; Markushev, V M; Shilov, I P
2011-01-01
The synthesis of asymmetric meso-aryl-substituted porphyrins containing three 4-methoxycarbonylphenyl groups, and as a forth substituent 4-hydroxyphenyl or 4-hydroxy-3- methoxyphenyl radicals, or the isomeric 3- and 4-pyridyl substituents is described. O-alkyl derivatives of 4-hydroxyl residue are obtained. The ytterbium complexes ofthese porphyrins were synthesized and studied their luminescence spectral properties were studied. A significant difference in the lifetimes of the excited state ofytterbium complexes of esters and acids of asymmetric porphyrins is demonstrated.
Mondal, Mukulesh; Puranik, Vedavati G; Argade, Narshinha P
2007-03-16
The complex bioactive natural and unnatural benzopyran congeners have been synthesized using one-/two-step approaches in very good yields from the reactions of two different dihydroxyphthalides, natural resorcyclic acid derivative, and trihydroxybenzophenone with citral and/or farnesal, via the phenol-driven intramolecular diastereoselective thermal/base-catalyzed dipolar [2+2] cycloaddition reactions and three different thermal intramolecular cyclization reactions. The effects of the nature and the position of phenolic groups in the starting materials on the course of these cycloaddition reactions have also been described. Depending upon the absence or presence of intramolecular hydrogen bonding of the phenolic group with the carbonyl moiety in the starting materials, these phenol-driven intramolecular thermal/base-catalyzed dipolar [2+2] cycloaddition reactions either furnished the kinetically controlled products or directly formed the thermodynamically controlled rearranged products, respectively.
NASA Astrophysics Data System (ADS)
Adhikari, S. K.
2016-08-01
We study the statics and dynamics of anisotropic, stable, bright and dark-in-bright dipolar quasi-two-dimensional Bose-Einstein condensate (BEC) solitons on a one-dimensional (1D) optical-lattice (OL) potential. These solitons mobile in a plane perpendicular to a 1D OL trap can have both repulsive and attractive contact interactions. Dark-in-bright solitons are the excited states of bright solitons. The solitons, when subjected to a small perturbation, exhibit sustained breathing oscillation. Dark-in-bright solitons can be created by phase imprinting a bright soliton. At medium velocities the collision between two solitons is found to be quasi-elastic. Results are demonstrated by a numerical simulation of the three-dimensional mean-field Gross-Pitaevskii equation in three spatial dimensions employing realistic interaction parameters for a dipolar 164Dy BEC.
NASA Astrophysics Data System (ADS)
Weiss, Volker C.; Leroy, Frédéric
2016-06-01
More than two decades ago, the elusiveness of a liquid-vapor equilibrium and a corresponding critical point in simulations of the supposedly simple model of dipolar hard spheres came as a surprise to many liquid matter theorists. van Leeuwen and Smit [Phys. Rev. Lett. 71, 3991 (1993)] showed that a minimum of attractive dispersion interactions among the dipolar particles may be needed to observe regular fluid behavior. Here, we adopt their approach and use an only slightly modified model, in which the original point dipole is replaced by a dipole moment produced by charges that are separated in space, to study the influence of dispersion interactions of variable strength on the coexistence and interfacial properties of a polar fluid. The thermophysical properties are discussed in terms of Guggenheim's corresponding-states approach. In this way, the coexistence curve, the critical compressibility factor, the surface tension, Guggenheim's ratio, and modifications of Guldberg's and Trouton's rules (related to the vapor pressure and the enthalpy of vaporization) are analyzed. As the importance of dispersion is decreased, a crossover from simple-fluid behavior to that characteristic of strongly dipolar systems takes place; for some properties, this transition is monotonic, but for others it occurs non-monotonically. For strongly dipolar systems, the reduced surface tension is very low, whereas Guggenheim's ratio and Guldberg's ratio are found to be high. The critical compressibility factor is smaller, and the coexistence curve is wider and more skewed than for simple fluids. For very weak dispersion, liquid-vapor equilibrium is still observable, but the interfacial tension is extremely low and may, eventually, vanish marking the end of the existence of a liquid phase. We discuss the implications of our findings for real fluids, in particular, for hydrogen fluoride.
Varma, G; Girard, O M; Prevost, V H; Grant, A K; Duhamel, G; Alsop, D C
2015-11-01
Comparison of off-resonance saturation with single and dual frequency irradiation indicates a contribution of inhomogeneously broadened lines to magnetization transfer in tissues. This inhomogeneous magnetization transfer (ihMT) phenomenon can be exploited to produce images that highlight tissues containing myelin, in vivo. Here, a model for ihMT is described that includes dipolar order effects from magnetization associated with motion-restricted macromolecules. In this model, equal irradiation at positive and negative frequency offsets eliminates dipolar order and achieves greater saturation than irradiation at a single offset frequency using the same power. Fitting of mouse and human volunteer brain data at different irradiation powers and offset frequencies was performed to assess the relevance of the model and approximate tissue parameters. A key parameter in determining ihMT signal was found to be the relaxation time T1D associated with the dipolar order reservoir and the fraction f of the semi-solid, bound magnetization that possessed a nonzero T1D. Indeed, better fits of myelinated tissue were achieved when assuming f≠1. From such fits, estimated T1Ds of mice in the white matter, (34±14) ms, were much longer than in muscle, T1D=(1±1) ms and the average f from white matter volunteer data was 2.2 times greater than that in grey matter. The combination of f and longer T1Ds was primarily responsible for the much higher ihMT in myelinated tissues, and provided explanation for the species variation. This dipolar order ihMT model should help guide future research, pulse sequence optimization, and clinical applications.
NASA Astrophysics Data System (ADS)
Ohtani, S.; Nose, M.; Miyashita, Y.; Lui, A.
2014-12-01
We investigate the responses of different ion species (H+, He+, He++, and O+) to fast plasma flows and local dipolarization in the plasma sheet in terms of energy density. We use energetic (9-210 keV) ion composition measurements made by the Geotail satellite at r = 10~31 RE. The results are summarized as follows: (1) whereas the O+-to-H+ ratio decreases with earthward flow velocity, it increases with tailward flow velocity with Vx dependence steeper for perpendicular flows than for parallel flows; (2) for fast earthward flows, the energy density of each ion species increases without any clear preference for heavy ions; (3) for fast tailward flows the ion energy density increases initially, then it decreases to below pre-flow levels except for O+; (4) the O+-to-H+ ratio does not increase through local dipolarization irrespective of dipolarization amplitude, background BZ, X distance, and VX; (5) in general, the H+ and He++ ions behave similarly. Result (1) can be attributed to radial transport along with the earthward increase of the background O+-to-H+ ratio. Results (2) and (4) indicate that ion energization associated with local dipolarization is not mass-dependent possibly because in the energy range of our interest the ions are not magnetized irrespective of species. In the tailward outflow region of reconnection, where the plasma sheet becomes thinner, the H+ ions escape along the field line more easily than the O+ ions, which possibly explains result (3). Result (5) suggests that the solar wind is the primary source of the high-energy H+ ions.
Auzinsh, M; Dashevskaya, E I; Litvin, I; Nikitin, E E; Troe, J
2013-10-14
Within the general axially nonadiabatic channel approach described in Paper I of this series [M. Auzinsh, E. I. Dashevskaya, I. Litvin, E. E. Nikitin, and J. Troe, J. Chem. Phys. 139, 084311 (2013)], the present article analyzes the simultaneous manifestation of electrostatic and gyroscopic interactions in the quantum capture of dipolar polarizable symmetric top molecules by ions. As a demonstration, the rate coefficients for capture of CH3D and CD3H by H(+), D(+), and H3(+) are calculated.
An, Peng; Yu, Zhipeng; Lin, Qing
2013-11-01
The design and synthesis of a new class of laser light activatable tetrazoles with extended π-systems is reported. Upon 405 nm laser light irradiation, these bithiophene-substituted tetrazoles underwent extremely fast 1,3-dipolar cycloaddition reactions with dimethyl fumarate with second-order rate constants approaching 4000 M(-1) s(-1). The resulting pyrazoline cycloadducts exhibited solvent-dependent red fluorescence, making these tetrazoles potentially useful as fluorogenic probes for detecting alkenes in vivo.
Bakthadoss, Manickam; Vinayagam, Varathan
2015-10-21
An efficient method towards the synthesis of quinoline fused tricyclic compounds involving an intramolecular 1,3-dipolar nitrile oxide cycloaddition reaction utilizing Baylis-Hillman derivatives in good yields has been described for the first time. A highly functionalized tricyclic framework was created by forming two rings and two adjacent stereocentres through the formation of two N-C bonds, one C-C bond and one O-C bond in a highly regio and diastereoselective manner.
Lian, Xiangjin; Guo, Songsong; Wang, Gang; Lin, Lili; Liu, Xiaohua; Feng, Xiaoming
2014-08-15
A highly enantioselective 1,3-dipolar cycloaddition of nitrile oxides with 3-arylidene-oxindoles was realized by a chiral N,N'-dioxide-nickel(II) complex catalyst under mild reaction conditions. A series of spiro-isoxazoline-oxindole derivatives were obtained in moderate yields (up to 65%) with good regioselectivities (up to 99:1), excellent enantioselectivities (up to 99% ee), and exclusive diastereoselectivity as well.
NASA Astrophysics Data System (ADS)
Varma, G.; Girard, O. M.; Prevost, V. H.; Grant, A. K.; Duhamel, G.; Alsop, D. C.
2015-11-01
Comparison of off-resonance saturation with single and dual frequency irradiation indicates a contribution of inhomogeneously broadened lines to magnetization transfer in tissues. This inhomogeneous magnetization transfer (ihMT) phenomenon can be exploited to produce images that highlight tissues containing myelin, in vivo. Here, a model for ihMT is described that includes dipolar order effects from magnetization associated with motion-restricted macromolecules. In this model, equal irradiation at positive and negative frequency offsets eliminates dipolar order and achieves greater saturation than irradiation at a single offset frequency using the same power. Fitting of mouse and human volunteer brain data at different irradiation powers and offset frequencies was performed to assess the relevance of the model and approximate tissue parameters. A key parameter in determining ihMT signal was found to be the relaxation time T1D associated with the dipolar order reservoir and the fraction f of the semi-solid, bound magnetization that possessed a nonzero T1D. Indeed, better fits of myelinated tissue were achieved when assuming f ≠ 1. From such fits, estimated T1Ds of mice in the white matter, (34 ± 14)ms, were much longer than in muscle, T1D = (1 ± 1)ms and the average f from white matter volunteer data was 2.2 times greater than that in grey matter. The combination of f and longer T1Ds was primarily responsible for the much higher ihMT in myelinated tissues, and provided explanation for the species variation. This dipolar order ihMT model should help guide future research, pulse sequence optimization, and clinical applications.
Ahmadivand, Arash; Gerislioglu, Burak; Sinha, Raju; Karabiyik, Mustafa; Pala, Nezih
2017-01-01
Capacitive coupling and direct shuttling of charges in nanoscale plasmonic components across a dielectric spacer and through a conductive junction lead to excitation of significantly different dipolar and charge transfer plasmon (CTP) resonances, respectively. Here, we demonstrate the excitation of dipolar and CTP resonant modes in metallic nanodimers bridged by phase-change material (PCM) sections, material and electrical characteristics of which can be controlled by external stimuli. Ultrafast switching (in the range of a few nanoseconds) between amorphous and crystalline phases of the PCM section (here Ge2Sb2Te5 (GST)) allows for designing a tunable plasmonic switch for optical communication applications with significant modulation depth (up to 88%). Judiciously selecting the geometrical parameters and taking advantage of the electrical properties of the amorphous phase of the GST section we adjusted the extinction peak of the dipolar mode at the telecommunication band (λ~1.55 μm), which is considered as the OFF state. Changing the GST phase to crystalline via optical heating allows for direct transfer of charges through the junction between nanodisks and formation of a distinct CTP peak at longer wavelengths (λ~1.85 μm) far from the telecommunication wavelength, which constitutes the ON state. PMID:28205643
Ahmadivand, Arash; Gerislioglu, Burak; Sinha, Raju; Karabiyik, Mustafa; Pala, Nezih
2017-02-16
Capacitive coupling and direct shuttling of charges in nanoscale plasmonic components across a dielectric spacer and through a conductive junction lead to excitation of significantly different dipolar and charge transfer plasmon (CTP) resonances, respectively. Here, we demonstrate the excitation of dipolar and CTP resonant modes in metallic nanodimers bridged by phase-change material (PCM) sections, material and electrical characteristics of which can be controlled by external stimuli. Ultrafast switching (in the range of a few nanoseconds) between amorphous and crystalline phases of the PCM section (here Ge2Sb2Te5 (GST)) allows for designing a tunable plasmonic switch for optical communication applications with significant modulation depth (up to 88%). Judiciously selecting the geometrical parameters and taking advantage of the electrical properties of the amorphous phase of the GST section we adjusted the extinction peak of the dipolar mode at the telecommunication band (λ~1.55 μm), which is considered as the OFF state. Changing the GST phase to crystalline via optical heating allows for direct transfer of charges through the junction between nanodisks and formation of a distinct CTP peak at longer wavelengths (λ~1.85 μm) far from the telecommunication wavelength, which constitutes the ON state.
Siadati, Seyyed Amir; Mahboobifar, Ali; Nasiri, Ramin
2014-01-01
1,3-dipolar cycloaddition procedure is one of the most widely practiced methods in order to synthesize heterocyclic compounds. Although, it seems very simple, but, there are numerous precursors of heterocyclic molecules who have more than one positions to react with a 1,3-dipole species. As a result, while using a precursor with more than one position for reaction, it is probable to synthesize several products with different structures. This paper studies all possible interactions of vinyl acetylene, which has two positions for reaction, with methyl azide. This reaction could lead to the emergence of any 1,3-dipolar cycloaddition products. Our ultimate goal is to help researchers to find out how precursors containing both carbon-carbon double, and the triple bonds interact with 1,3- dipolar species. The present study used the DFT calculations at B3LYP/6-311++G(3df,pd) level to check all probable interactions between vinyl acetylene and methyl azide, and determined Potential Energy Surface, and optimized all species.
NASA Astrophysics Data System (ADS)
Ahmadivand, Arash; Gerislioglu, Burak; Sinha, Raju; Karabiyik, Mustafa; Pala, Nezih
2017-02-01
Capacitive coupling and direct shuttling of charges in nanoscale plasmonic components across a dielectric spacer and through a conductive junction lead to excitation of significantly different dipolar and charge transfer plasmon (CTP) resonances, respectively. Here, we demonstrate the excitation of dipolar and CTP resonant modes in metallic nanodimers bridged by phase-change material (PCM) sections, material and electrical characteristics of which can be controlled by external stimuli. Ultrafast switching (in the range of a few nanoseconds) between amorphous and crystalline phases of the PCM section (here Ge2Sb2Te5 (GST)) allows for designing a tunable plasmonic switch for optical communication applications with significant modulation depth (up to 88%). Judiciously selecting the geometrical parameters and taking advantage of the electrical properties of the amorphous phase of the GST section we adjusted the extinction peak of the dipolar mode at the telecommunication band (λ~1.55 μm), which is considered as the OFF state. Changing the GST phase to crystalline via optical heating allows for direct transfer of charges through the junction between nanodisks and formation of a distinct CTP peak at longer wavelengths (λ~1.85 μm) far from the telecommunication wavelength, which constitutes the ON state.
NASA Astrophysics Data System (ADS)
Ochoa, Andrés; Mejía-López, J.; Velásquez, E. A.; Mazo-Zuluaga, J.
2017-03-01
In this study we report on the magnetic properties of finite-length Fe nanowire arrays. The samples are built from nanowires that exhibit different anisotropy directions. There are L h-long wires per side, which are separated from each other by a distance d. h and d vary in the ranges 0.7–40.0 nm and 2.0–20.0 nm, respectively. These features allow us to discuss the dependence of the magnetic properties on the direction of the anisotropy, and the length of the wires and the separation between them. The system’s Hamiltonian is composed of (i) the magnetocrystalline anisotropy energy, which depends on the spin–orbit coupling; (ii) the dipolar interactions between the atomic magnetic moments comprising the wires (which give place to the shape anisotropy); (iii) the Zeeman interaction with an external magnetic field; and (iv) the dipolar interactions between the individual wires. We present and discuss the interesting non-monotonic dependences of the coercivity and remanence on the related parameters. We also discuss the interplay between size and the effects of dipolar and magnetic anisotropy energies. Our results indicate that the magnetic configurations and anisotropy properties can be tailored by tuning the length of the wires, their separation distances and the size of the arrays, which might be of interest for experiments in the field of technical applications.