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Dipolar field

Philipp Honegger, Michael Schmollngruber, Othmar Steinhauser
This computational study deals with the collective structure and dynamics as well as their interaction seen from a dielectric viewpoint in zwitterionic reverse micelles for which a force field was designed de novo. For this end, a dualistic strategy is followed: the raw data are generated by extensive microscopic molecular dynamics (MD) simulations while the subsequent analysis has a focus on mesoscopic dielectric properties. The unusually low dielectric signals as well as the remarkable acceleration of collective dynamics is elucidated in great detail...
April 12, 2018: Physical Chemistry Chemical Physics: PCCP
Abdallah Daddi-Moussa-Ider, Maciej Lisicki, Christian Hoell, Hartmut Löwen
The hydrodynamic flow field generated by self-propelled active particles and swimming microorganisms is strongly altered by the presence of nearby boundaries in a viscous flow. Using a simple model three-linked sphere swimmer, we show that the swimming trajectories near a no-slip wall reveal various scenarios of motion depending on the initial orientation and the distance separating the swimmer from the wall. We find that the swimmer can either be trapped by the wall, completely escape, or perform an oscillatory gliding motion at a constant mean height above the wall...
April 7, 2018: Journal of Chemical Physics
Hanu Arava, Peter M Derlet, Jaianth Vijayakumar, Jizhai Cui, N S Bingham, Armin Kleibert, Laura J Heyderman
Nanomagnets are a promising low-power alternative to traditional computing. However, the successful implementation of nanomagnets in logic gates has been hindered so far by a lack of reliability. Here, we present a novel design with dipolar-coupled nanomagnets arranged on a square lattice to (i) support transfer of information and (ii) perform logic operations. We introduce a thermal protocol, using thermally active nanomagnets as a means to perform computation. Within this scheme, the nanomagnets are initialized by a global magnetic field and thermally relax on raising the temperature with a resistive heater...
April 5, 2018: Nanotechnology
M Q Liu, C Y Zhao, B X Wang
We have achieved efficient polarization manipulations based on dipolar interferences and lattice couplings in one-dimensional cylindrical metalattices. First, we employ the scattering asymmetry factor g to quantify the directional scattering ability and find the maximum |g|max =1/2 for a cylinder with effective excitations of electric and magnetic dipoles simultaneously. Further, the strong negative-g (gp = -0.38) for p-polarization and positive-g (gs = 0.68) for s-polarization are obtained within a narrow visible band using c-Si with experimental data...
March 19, 2018: Optics Express
Marina Casiraghi, Marjorie Damian, Ewen Lescop, Jean-Louis Baneres, Laurent J Catoire
Conformational dynamics of GPCRs are central to their function but are difficult to explore at the atomic scale. Solution-state NMR has provided the major contribution in that area during the past decade, despite non-optimized labeling schemes due to the use of insect cells, and to a lesser extent yeast, as the main expression hosts. Indeed, the most efficient isotope-labeling scheme ever to address energy landscape issues for large proteins or protein complexes relies on the use of 13CH3 probes immersed in a perdeuterated dipolar environment, which is essentially out of reach of eukaryotic expression systems...
April 2, 2018: Biochemistry
Michela F Picardi, Anatoly V Zayats, Francisco J Rodríguez-Fortuño
Unidirectional scattering from circularly polarized dipoles has been demonstrated in near-field optics, where the quantum spin-Hall effect of light translates into spin-momentum locking. By considering the whole electromagnetic field, instead of its spin component alone, near-field directionality can be achieved beyond spin-momentum locking. This unveils the existence of the Janus dipole, with side-dependent topologically protected coupling to waveguides, and reveals the near-field directionality of Huygens dipoles, generalizing Kerker's condition...
March 16, 2018: Physical Review Letters
Meng Gao, Minxuan Kuang, Lihong Li, Meijin Liu, Libin Wang, Yanlin Song
Magnetosensing is a ubiquitous ability for many organism species in nature. 1D assembly, especially that arranged in single-particle-resolution regulation, is able to sense the direction of magnetic field depending on the enhanced dipolar interaction in the linear orientation. Inspired by the magnetosome structure in magnetotactic bacteria, a 1D assembly array of single particle resolution with controlled length and well-behaved configuration is prepared via inkjet printing method assisted with magnetic guiding...
March 25, 2018: Small
Selim Sami, Pi A B Haase, Riccardo Alessandri, Ria Broer, Remco W A Havenith
The low efficiency of organic photovoltaic devices has often been attributed to the strong Coulombic interactions between the electron and hole, impeding the charge separation process. Recently, it has been argued that by increasing the dielectric constant of materials used in OPVs, this strong interaction could be screened. In this work, we report the application of periodic density functional theory together with the coupled perturbed Kohn-Sham method to calculate the electronic contribution to the dielectric constant for fullerene C60 derivatives, a ubiquitous class of molecules in the field of organic photovoltaics...
March 21, 2018: Journal of Physical Chemistry. A
B P Abolins, R E Zillich, K B Whaley
The quantum phase transitions of dipoles confined to the vertices of two-dimensional lattices of square and triangular geometry is studied using path integral ground state quantum Monte Carlo. We analyze the phase diagram as a function of the strength of both the dipolar interaction and a transverse electric field. The study reveals the existence of a class of orientational phases of quantum dipolar rotors whose properties are determined by the ratios between the strength of the anisotropic dipole-dipole interaction, the strength of the applied transverse field, and the rotational constant...
March 14, 2018: Journal of Chemical Physics
Seung-Kyun Lee, Seon-Ha Hwang, Ji-Seong Barg, Seok-Jin Yeo
PURPOSE: To demonstrate a computationally efficient and theoretically artifact-free method to calculate static field (B0 ) inhomogeneity in a volume of interest induced by an arbitrary voxelated susceptibility distribution. METHODS: Our method computes B0 by circular convolution between a zero-filled susceptibility matrix and a shifted, voxel-integrated dipolar field kernel on a grid of size NS +NT - 1 in each dimension, where NS and NT are the sizes of the susceptibility source and B0 target grids, respectively...
March 9, 2018: Magnetic Resonance in Medicine: Official Journal of the Society of Magnetic Resonance in Medicine
Matthias Roos, Tuo Wang, Alexander A Shcherbakov, Mei Hong
Internuclear distances measured using NMR provide crucial constraints of three-dimensional structures, but are often restricted to about 5 Å due to the weakness of nuclear-spin dipolar couplings. For studying macromolecular assemblies in biology and materials science, distance constraints beyond 1 nm will be extremely valuable. Here we present an extensive and quantitative analysis of the feasibility of 19F spin exchange NMR for precise and robust measurements of inter-atomic distances to 1.6 nm at a magnetic field of 14...
February 27, 2018: Journal of Physical Chemistry. B
A Piñeiro Orioli, A Signoles, H Wildhagen, G Günter, J Berges, S Whitlock, M Weidemüller
How do isolated quantum systems approach an equilibrium state? We experimentally and theoretically address this question for a prototypical spin system formed by ultracold atoms prepared in two Rydberg states with different orbital angular momenta. By coupling these states with a resonant microwave driving, we realize a dipolar XY spin-1/2 model in an external field. Starting from a spin-polarized state, we suddenly switch on the external field and monitor the subsequent many-body dynamics. Our key observation is density dependent relaxation of the total magnetization much faster than typical decoherence rates...
February 9, 2018: Physical Review Letters
Eron Cemal, Mechthild Enderle, Reinhard K Kremer, Björn Fåk, Eric Ressouche, Jon P Goff, Mariya V Gvozdikova, Mike E Zhitomirsky, Tim Ziman
The mineral linarite, PbCuSO_{4}(OH)_{2}, is a spin-1/2 chain with frustrating nearest-neighbor ferromagnetic and next-nearest-neighbor antiferromagnetic exchange interactions. Our inelastic neutron scattering experiments performed above the saturation field establish that the ratio between these exchanges is such that linarite is extremely close to the quantum critical point between spin-multipolar phases and the ferromagnetic state. We show that the predicted quantum multipolar phases are fragile and actually suppressed by a tiny orthorhombic exchange anisotropy and weak interchain interactions in favor of a dipolar fan phase...
February 9, 2018: Physical Review Letters
Raphaël J Durand, Sébastien Gauthier, Sylvain Achelle, Thomas Groizard, Samia Kahlal, Jean-Yves Saillard, Alberto Barsella, Nicolas Le Poul, Françoise Robin Le Guen
The present work describes the one-pot synthesis and electrochemical, photophysical and second-order nonlinear optical (NLO) properties of a series of dipolar π-delocalized Ru(ii) dialkynyl complexes. The eight new asymmetrical D-π-Ru-π-A push-pull chromophores incorporate pyranylidene ligands as pro-aromatic donor groups (D) and formaldehyde, indane-1,3-dione, pyrimidine or pyrimidinium as electron-attracting groups (A) separated by ruthenium bis-acetylide fragments and π-conjugated linkers. The second-order nonlinear optical (NLO) properties of all eight complexes were determined by the Electric-Field-Induced Second Harmonic generation (EFISH) technique (operating at 1907 nm), and were compared to those of their purely organic analogs...
February 21, 2018: Dalton Transactions: An International Journal of Inorganic Chemistry
Ivo Klik, James McHugh, Roy W Chantrell, Ching-Ray Chang
Rate (master) equations are ubiquitous in statistical physics, yet, to the best of our knowledge, a rate equation with memory has previously never been considered. We write down an integro-differential rate equation for the evolution of a thermally relaxing system with memory. For concreteness we adopt as a model a single-domain magnetic particle driven by a small ac field and derive the modified Debye formulas. For any memory time Θ the in-phase component of the resultant ac susceptibility is positive at small probing frequencies ω, but becomes negative at large ω...
February 19, 2018: Scientific Reports
G A Basheed, Komal Jain, Saurabh Pathak, R P Pant
We investigate the effect of dilution on dipolar interaction with linear and non-linear rheological properties of kerosene based magnetic fluid. The steady-state behavior demonstrate a shear thinning behavior and corroborated with a power law, (η = c <mml:math display="block"> <mml:mover accent="true"> <mml:mi>γ</mml:mi> <mml:mo>˙</mml:mo> </mml:mover></mml:math>n + η∞) exponent, n ≤ 1. The shear-induced-breakup (separation) of nanoparticles and the yielding behavior has been explained by Bingham model...
April 1, 2018: Journal of Nanoscience and Nanotechnology
Nathalie Vonrüti, Ulrich Aschauer
The perovskite oxynitride LaTiO_{2}N is a promising material for photocatalytic water splitting under visible light. One of the obstacles towards higher efficiencies of this and similar materials stems from charge-carrier recombination, which could be suppressed by the surface charges resulting from the dipolar field in polar materials. In this study, we investigate the spontaneous polarization in epitaxially strained LaTiO_{2}N thin films via density functional theory calculations. The effect of epitaxial strain on the anion order, resulting out-of-plane polarization, energy barriers for polarization reversal, and corresponding coercive fields are studied...
January 26, 2018: Physical Review Letters
Deyao Li, Hui Wang, Zhenhui Ma, Xin Liu, Ying Dong, Zhiqi Liu, Tianli Zhang, Chengbao Jiang
Anisotropic exchange-coupled nanocomposites provide us a salient candidate for the new generation of permanent magnets owing to their huge predicted maximum energy product. However, previous research basically focused on thin films or bulk materials and the impact of easy-axis alignment on the exchange coupling behavior is not clear. Herein, strongly coupled FePt/Co core/shell nanoparticles with single-phase-like hysteresis loops were synthesized by the seed mediated method. Then, these nanoparticles were successfully aligned by the external magnetic field and fixed in an acrylic binder, so that FePt/Co core/shell nanoparticle-based anisotropic nanocomposites were obtained...
February 12, 2018: Nanoscale
Tobias Schubeis, Tanguy Le Marchand, Loren B Andreas, Guido Pintacuda
Building on a decade of continuous advances of the community, the recent development of very fast (60 kHz and above) magic-angle spinning (MAS) probes has revolutionised the field of solid-state NMR. This new spinning regime reduces the 1H-1H dipolar couplings, so that direct detection of the larger magnetic moment available from 1H is now possible at high resolution, not only in deuterated molecules but also in fully-protonated substrates. Such capabilities allow rapid "fingerprinting" of samples with a ten-fold reduction of the required sample amounts with respect to conventional approaches, and permit extensive, robust and expeditious assignment of small-to-medium sized proteins (up to ca...
February 2018: Journal of Magnetic Resonance
Emmanuel O Awosanya, Alexander A Nevzorov
A membrane-bound form of Pf1 coat protein reconstituted in magnetically aligned DMPC/DHPC bicelles was used as a molecular probe to quantify for the viscosity of the lipid membrane interior by measuring the uniaxial rotational diffusion coefficient of the protein. Orientationally dependent 15N NMR relaxation times in the rotating frame, or T1ρ, were determined by fitting individually the decay of the resolved NMR peaks corresponding to the transmembrane helix of Pf1 coat protein as a function of the spin-lock time incorporated into the 2D SAMPI4 pulse sequence...
January 23, 2018: Biophysical Journal
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