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Dipolar field

L Sánchez-García, M O Ramírez, C Tserkezis, R Sole, J J Carvajal, M Aguiló, F Díaz, L E Bausá
Increasing Yb(3+) absorption efficiency is currently desired in a number of applications including bio-imaging, photovoltaics, near infrared driven photocatalysis or ultra-short pulsed solid-state lasers. In this work, silver nanoparticles, which are connected forming disordered networks, have been self-assembled on Yb(3+) doped RbTiOPO4 crystals to produce a remarkable enhancement of Yb(3+) absorption, and hence in the photoluminescence of this ion. The results are interpreted taking into account the near-field response of the plasmonic networks, which display strong amplification of the electric field at the maximum of Yb(3+) excitation at around 900 nm, together with the anisotropic character of the Yb(3+) transitions in RbTiOPO4...
August 9, 2017: Nanoscale
Charles D Schwieters, Guillermo A Bermejo, G Marius Clore
Xplor-NIH is a popular software package for biomolecular structure determination from nuclear magnetic resonance (NMR) and other data sources. Here, some of Xplor-NIH's most useful data-associated energy terms are reviewed, including newer alternative options for using residual dipolar coupling data in structure calculations. Further, we discuss new developments in the implementation of strict symmetry for the calculation of symmetric homo-oligomers, and in the representation of the system as an ensemble of structures to account for motional effects...
August 2, 2017: Protein Science: a Publication of the Protein Society
Thangarasu Sriraman, Barnali Chakrabarti, Andrea Trombettoni, Paulsamy Muruganandam
Calculation of the Shannon information entropy (S) and its connection with the order-disorder transition and with inter-particle interaction provide a challenging research area in the field of quantum information. Experimental progress with cold trapped atoms has corroborated this interest. In the present work, S is calculated for the Bose-Einstein condensate (BEC) with dominant dipolar interaction for different dipole strengths, trap aspect ratios, and number of particles (N). Trapped dipolar bosons in an anisotropic trap provide an example of a system where the effective interaction is strongly determined by the trap geometry...
July 28, 2017: Journal of Chemical Physics
Nurit Manukovsky, Akiva Feintuch, Ilya Kuprov, Daniella Goldfarb
Gd(3+)-based spin labels are useful as an alternative to nitroxides for intramolecular distance measurements at high fields in biological systems. However, double electron-electron resonance (DEER) measurements using model Gd(3+) complexes featured a low modulation depth and an unexpected broadening of the distance distribution for short Gd(3+)-Gd(3+) distances, when analysed using the software designed for S = 1/2 pairs. It appears that these effects result from the different spectroscopic characteristics of Gd(3+)-the high spin, the zero field splitting (ZFS), and the flip-flop terms in the dipolar Hamiltonian that are often ignored for spin-1/2 systems...
July 28, 2017: Journal of Chemical Physics
Jyoti P Mahalik, Bobby G Sumpter, Rajeev Kumar
We use a field theory approach to study the effects of permanent dipoles on interpenetration and free energy changes as a function of distance between two identical planar polymer brushes. Melts (i.e., solvent-free) and solvated brushes made up of polymers grafted on non-adsorbing substrates are studied. In particular, the weak coupling limit of the dipolar interactions is considered, which leads to concentration dependent pairwise interactions and the effects of orientational order are neglected. It is predicted that a gradual increase in the dipole moment of the monomers can lead to attractive interactions at intermediate separation distances...
August 1, 2017: Langmuir: the ACS Journal of Surfaces and Colloids
Lau M Andersen, Robert Oostenveld, Christoph Pfeiffer, Silvia Ruffieux, Veikko Jousmäki, Matti Hämäläinen, Justin F Schneiderman, Daniel Lundqvist
The development of new magnetic sensor technologies that promise sensitivities approaching that of conventional MEG technology while operating at far lower operating temperatures has catalysed the growing field of on-scalp MEG. The feasibility of on-scalp MEG has been demonstrated via benchmarking of new sensor technologies performing neuromagnetic recordings in close proximity to the head surface against state-of-the-art in-helmet MEG sensor technology. However, earlier work has provided little information about how these two approaches compare, or about the reliability of observed differences...
2017: PloS One
Daniela Lalli, Matthew N Idso, Loren B Andreas, Sunyia Hussain, Naomi Baxter, Songi Han, Bradley F Chmelka, Guido Pintacuda
The structures and properties of membrane proteins in lipid bilayers are expected to closely resemble those in native cell-membrane environments, although they have been difficult to elucidate. By performing solid-state NMR measurements at very fast (100 kHz) magic-angle spinning rates and at high (23.5 T) magnetic field, severe sensitivity and resolution challenges are overcome, enabling the atomic-level characterization of membrane proteins in lipid environments. This is demonstrated by extensive (1)H-based resonance assignments of the fully protonated heptahelical membrane protein proteorhodopsin, and the efficient identification of numerous (1)H-(1)H dipolar interactions, which provide distance constraints, inter-residue proximities, relative orientations of secondary structural elements, and protein-cofactor interactions in the hydrophobic transmembrane regions...
August 11, 2017: Journal of the American Chemical Society
Neelam Yadav, V P Panov, V Swaminathan, S P Sreenilayam, J K Vij, T S Perova, R Dhar, A Panov, D Rodriguez-Lojo, P J Stevenson
Infrared and dielectric spectroscopic techniques are used to investigate the characteristics of two chiral smectics, namely, 1,1,3,3,5,5,5-heptamethyltrisiloxane 1-[4^{'}-(undecyl-1-oxy)-4-biphenyl(S,S)-2-chloro-3-methylpentanoate] (MSi_{3}MR_{11}) and tricarbosilane-hexyloxy-benzoic acid (S)-4'-(1-methyl-hexyloxy)-3'-nitro-biphenyl-4-yl ester (W599). The orientational features and the field dependencies of the apparent tilt angle and the dichroic ratio for homogeneous planar-aligned samples were calculated from the absorbance profiles obtained at different temperatures especially in the smectic-A* phase of these liquid crystals...
June 2017: Physical Review. E
Héctor Sánchez-Esquivel, Karen Y Raygoza-Sánchez, Raúl Rangel-Rojo, Emanuele Gemo, Niccolò Michieli, Boris Kalinic, Jorge Alejandro Reyes-Esqueda, Tiziana Cesca, Giovanni Mattei
Ordered metallic nanoprism arrays have been proposed as novel and versatile systems for the observation of nonlinear effects such as nonlinear absorption. The study of the effect of the local field reinforcement on the fast optical third order nonlinear response around the Surface Plasmon Resonance is of great interest for many plasmonic applications. In this work, silver nanoprism arrays have been synthesized by the nanosphere lithography method. A low repetition rate tunable picosecond laser source was used to study the irradiance and wavelength dependence of the nonlinear absorption properties around the dipolar and quadrupolar resonances of the nanoarray with the use of the z-scan technique...
July 13, 2017: Scientific Reports
Alexander J Grutter, Kathryn L Krycka, Elena V Tartakovskaya, Julie A Borchers, K Sai Madhukar Reddy, Eduardo Ortega, Arturo Ponce, Bethanie J H Stadler
A comprehensive three-dimensional picture of magnetic ordering in high-density arrays of segmented FeGa/Cu nanowires is experimentally realized through the application of polarized small-angle neutron scattering. The competing energetics of dipolar interactions, shape anisotropy, and Zeeman energy in concert stabilize a highly tunable spin structure that depends heavily on the applied field and sample geometry. Consequently, we observe ferromagnetic and antiferromagnetic interactions both among wires and between segments within individual wires...
July 20, 2017: ACS Nano
Bidhan Hazra, Kamalika Das, Manabendra Chandra
The structure and morphology of nanomateials strongly influence their nonlinear optical properties. In this work, we report a systematic investigation of second order nonlinear optical responses and their structural dependencies in the case of a plasmonically hybrid nanostructure, hollow gold nanoprisms (HGNs). The first hyperpolarizabilities (β) of the HGNs have been measured using the two-photon Rayleigh scattering (TPRS) technique. The measured hyperpolarizability values are extremely large for the HGNs, larger than those for gold nanospheres or gold nanorods with similar size and surface area...
July 5, 2017: Physical Chemistry Chemical Physics: PCCP
Martin D Gelenter, Tuo Wang, Shu-Yu Liao, Hugh O'Neill, Mei Hong
Site-specific determination of molecular motion and water accessibility by indirect detection of (2)H NMR spectra has advantages over dipolar-coupling based techniques due to the large quadrupolar couplings and the ensuing high angular resolution. Recently, a Rotor Echo Short Pulse IRrAdiaTION mediated cross polarization ((RESPIRATION)CP) technique was developed, which allowed efficient transfer of (2)H magnetization to (13)C at moderate (2)H radiofrequency field strengths available on most commercial MAS probes...
July 3, 2017: Journal of Biomolecular NMR
Johannes Hellwagner, Kshama Sharma, Kong Ooi Tan, Johannes J Wittmann, Beat H Meier, P K Madhu, Matthias Ernst
Pulse imperfections like pulse transients and radio-frequency field maladjustment or inhomogeneity are the main sources of performance degradation and limited reproducibility in solid-state nuclear magnetic resonance experiments. We quantitatively analyze the influence of such imperfections on the performance of symmetry-based pulse sequences and describe how they can be compensated. Based on a triple-mode Floquet analysis, we develop a theoretical description of symmetry-based dipolar recoupling sequences, in particular, R264(11), calculating first- and second-order effective Hamiltonians using real pulse shapes...
June 28, 2017: Journal of Chemical Physics
Mukul G Jain, G Rajalakshmi, Asif Equbal, Kaustubh R Mote, Vipin Agarwal, P K Madhu
Rotational-Echo DOuble-Resonance (REDOR) is a versatile experiment for measuring internuclear distance between two heteronuclear spins in solid-state NMR. At slow to intermediate magic-angle spinning (MAS) frequencies, the measurement of distances between strongly coupled spins is challenging due to rapid dephasing of magnetisation. This problem can be remedied by employing the pulse-shifted version of REDOR known as Shifted-REDOR (S-REDOR) that scales down the recoupled dipolar coupling. In this study, we propose a new variant of the REDOR sequence where the positions of the π pulses are determined by a sine-squared function...
June 28, 2017: Journal of Chemical Physics
Zdeněk Janů, František Soukup
We show a continuous reading superconducting quantum interference detector magnetometer used to measure the magnetic moment of small samples of materials as a function of an applied magnetic field, temperature, and time. A sample is held stationary while the magnetic field and sample temperature may be varied continuously in an arbitrary way, determined by the user. The applied field range is ±25 mT and the temperature range is 4.2-150 K. The advantage of a stationary sample technique is that the sample is not exposed to variations in the magnetic field or temperature, which may set in when the sample is moving...
June 2017: Review of Scientific Instruments
Yi Li, Xavier de Milly, Flavio Abreu Araujo, Olivier Klein, Vincent Cros, Julie Grollier, Grégoire de Loubens
Phase coupling between auto-oscillators is central for achieving coherent responses such as synchronization. Here we present an experimental approach to probe it in the case of two dipolarly coupled spin-torque vortex nano-oscillators using an external microwave field. By phase locking one oscillator to the external source, we observe frequency pulling on the second oscillator. From coupled phase equations we show analytically that this frequency pulling results from concerted actions of oscillator-oscillator and source-oscillator couplings...
June 16, 2017: Physical Review Letters
A Orlova, E L Green, J M Law, D I Gorbunov, G Chanda, S Krämer, M Horvatić, R K Kremer, J Wosnitza, G L J A Rikken
We report a ^{51}V nuclear magnetic resonance investigation of the frustrated spin-1/2 chain compound LiCuVO_{4}, performed in pulsed magnetic fields and focused on high-field phases up to 56 T. For the crystal orientations H∥c and H∥b, we find a narrow field region just below the magnetic saturation where the local magnetization remains uniform and homogeneous, while its value is field dependent. This behavior is the first microscopic signature of the spin-nematic state, breaking spin-rotation symmetry without generating any transverse dipolar order, and is consistent with theoretical predictions for the LiCuVO_{4} compound...
June 16, 2017: Physical Review Letters
Li Zhang, Yi-Quan Zhang, Peng Zhang, Lang Zhao, Mei Guo, Jinkui Tang
As the simplest entity carrying intramolecular magnetic interactions, a dinuclear lanthanide complex serves as a model to investigate the effects of magnetic interactions on relaxation of magnetization, and importantly, it proves to be an efficient method to obtain robust single-molecule magnets via improving the communication between lanthanide centers. Here, three Dy2 complexes (1, 2, 3) with a similar structural motif, namely, [Dy2(HL)2(NO3)2(CH3CN)2]·2CH3CN (1), [Dy2(HL)2(NO3)2(DMF)2]·2H2O (2), and Dy2(HL)2(NO3)2(DMF)4 (3), were successfully assembled...
July 17, 2017: Inorganic Chemistry
Gauri M Mangalgiri, Phillip Manley, Wiebke Riedel, Martina Schmid
This work elaborates on the high scattering which dielectric nanorods exhibit and how it can be exploited to control light propagation across material interfaces. A detailed overview of how dielectric nanorods interact with light through a combination of dipolar scattering and leaky modes is performed via outward power flux calculations. We establish and account for design parameters that best result in light magnification owing to resonant behavior of nanorods. Impact of material parameters on scattering and their dispersion have been calculated to establish that low loss dielectric oxides like ZnO when nanostructured show excellent antenna like resonances which can be used to control light coupling and propagation...
June 27, 2017: Scientific Reports
I Dierking, M Heberle, M A Osipov, F Giesselmann
Dispersions of magnetic nanoparticles in a nematic liquid crystal were investigated as magnetic fields were applied in three different boundary condition geometries: (i) planar substrates and B ⊥ n, (ii) planar substrates and B ‖ n, and (iii) homeotropic substrates and B ⊥ n. Particle chaining is observed when a magnetic field is applied, with a periodicity perpendicular to the chains. Furthermore, linear chains are observed for the magnetic field applied perpendicular to the director, while zigzag chains are formed when the magnetic field direction is parallel to the director field...
June 22, 2017: Soft Matter
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