Victor Henner

Collective effects due to dipolar fields as the origin of the extremely random behavior in hyperpolarized NMR maser: a theoretical and numerical study.

Numerical simulations based on microscopic approach are used to explore the spin dynamics encountered in the recently reported hyperpolarized (129)Xe NMR maser [D. J. Y. Marion, G. Huber, P. Berthault, and H. Desvaux, ChemPhysChem 9, 1395-1401 (2008)] where series of amplitude modulated rf emissions are observed. The integration of the dynamic features of the electronic detection circuit in the present simulations, based on non-linear Maxwell-Bloch differential equations with dipole-dipole interactions, allows us to prove that the experimentally observed extremely random amplitude modulations crucially require the long-distance dipolar couplings between the nuclear spins with the feedback field acting as an amplifier. The massive dipolar couplings act, when the magnetization is largely tilted off the longitudinal axis, as an apparent transverse self-relaxation mechanism which destroys coherence. This, in particular, explains why the final magnetization after emissions can still be opposite to the magnetic field direction, i.e., being in an unstable state.

Collective Magnetic Moment Relaxation in an Assembly of Ferromagnetic Nanoparticles

The idea of establishing coherent relaxation in an assembly of magnetic moments by placing it in a passive resonator [1, 2] is applied to the case of single-domain ferromagnetic nanoparticles. The magnetodynamics of a particle is governed by the Landau-Lifshitz equation modified by adding the resonator feedback field. The particle uniaxial magnetic anisotropy and the interparticle dipole-dipole interactions are taken into account.

Superradiation from Molecular Nanomagnets

The goal of this work is to justify a possibility to obtain and observe coherent spin relaxation—the superradiation (SR) effect—in molecular nanomagnetic structures. We note that giant-spin molecules have the magnetic moments of the order of and possess substantial magnetic anisotropy. Moreover, to invoke SR, such a system should be polarized to a high extent. When put together, these factors rule out the conventional treatment used e.g. for optical SR, and invoke development of novel approaches.

Photoluminescence in Functionalized/Doped Graphene Quantum Dots: Role of SurfaceStates

Photoluminescence in Functionalized/Doped Graphene Quantum Dots: Role of Surface States It has been shown that functionalization/doping of Graphene Quantum Dots (GQDs) can lead to further tuning of their already existing band gap. We have successfully functionalized GQDs (synthesized by hydrothermal process) with oxygen, hydrogen, fluorine, and doped with nitrogen using capacitively coupled plasma of respective gas as evidenced by Raman and X-ray photo emission spectroscopy (XPS). Room temperature photoluminescence (PL) of each functionalized GQD shows distinctive features and can be explained as due to charge transfers between the functional groups/dopants and GQDs as well as presence of mid gap states as a result of functionalization and doping. An energy diagram model is proposed to elucidate the PL modulation resulting from functionalization and doping.

SPIN-WAVE APPROACH TO THE 2D PARAMAGNETIC UNDER THE MAGNETIC FIELD

We study the possibility of collective spin excitations in 2D paramagnetic crystal with the dipole-dipole interaction and without the exchange interaction. The crystal is under uniform constant magnetic field. All the magnetic moments are oriented along the magnetic field at the saturation. Using the Holstein–Primakoff transformation, we describe the properties of paramagnetic in terms of the spin waves at the low-temperature limit. We obtain the dispersion relations for spin waves at the square and hexagonal flat lattices. It is shown the wavelength of the collective excitations and their bandwidth are determined by the external magnetic field direction. The long-wave perturbations have the lowest energy when the magnetic field is orthogonal to the lattice plane, and the short-wave perturbations are the most preferable when the field is parallel to the lattice. We provide the direct numerical simulation of the group of interacting magnetic moments under the constant external field with different orientation to the lattice. The total transversal spin and dipole energy evolution in time and their Fourier-spectrum are considered. The numerical results match the analytical calculation in spin-wave approach. Received 22.08.2016; accepted 31 .0 8 .2016

Ordinary and partial differential equations

Ordinary Differential Equations, Boundary Value Problems, Fourier Series, and the Introduction to Integral Equations First-Order Differential Equations Second-Order Differential Equations Systems of Differential Equations Boundary Value Problems for Second-Order ODE and Sturm-Liouville Theory Qualitative Methods and Stability of ODE Solutions Method of Laplace Transforms for ODE Integral Equations Series Solutions of ODEs and Bessel and Legendre Equations Fourier Series Partial Differential Equations Introduction to PDE One-Dimensional Hyperbolic Equations Two-Dimensional Hyperbolic Equations One-Dimensional Parabolic Equations Two-Dimensional Parabolic Equations Elliptic Equations Appendix 1: Eigenvalues and Eigenfunctions of One-Dimensional Sturm-Liouville Boundary Value Problem for Different Types of Boundary Conditions Appendix 2: Auxiliary Functions, w(x,t), for Different Types of Boundary Conditions Appendix 3: Eigenfunctions of Sturm-Liouville Boundary Value Problem for the Laplace Equation in a Rectangular Domain for Different Types of Boundary Conditions Appendix 4: A Primer on the Matrix Eigenvalue Problems and the Solution of the Selected Examples in Sec. 5.2 Appendix 5: How to Use the Software Associated with the Book Bibliography

Enhanced Spin Relaxation in Nanocrystals of Different Geometries

Various coherent magneto-dynamical effects can lead to the phenomenon qualitatively similar to optical super-radiation (SR). To realize SR for spins, a sample should be placed in a passive resonance circuit that, in response to the magnetization motion, generates a feedback magnetic field common for all the spins of the system. The electromagnetic radiation emitted by an assembly of nano-entities (molecules, dots, grains) by way of the feedback effect establishes their coherence thus greatly reducing the duration and enhancing the intensity of the deexcitation pulse.

Wavelet analysis of data in particle physics: Vector mesons in e + e − annihilation

AbstractThe advantages that wavelet analysis (WA) provides for resolving the structures in experimental data are demonstrated. Due to good scaling properties of the wavelets, one can consider data with various resolutions, which allows the resonances to be separated from the background and from each other. The WA is much less sensitive to noise than any other analysis and allows the role of statistical errors to be substantially reduced. The WA is applied to the e+e− annihilation into hadron states with quantum numbers of ρ and ω mesons, and to p-wave ππ scattering. Distinguishing the resonance structures from an experimental noise and the background allows us to make more reliable conclusions about the ρ′ and ω′ states. The WA yields a useful set of starting conditions for analysis of ω′ states with the multiresonance Breit-Wigner method preserving unitarity in the case of overlapping resonances. We also apply the WA for the ratio

Study of nitrogen doping of graphene via in-situ transport measurements

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