Regulation of fields excited by permanent magnets

International Nuclear Information System (INIS)

Savchenko, I.S.

1989-01-01

Two methods of fast regulation of fields excited by permanent magnets in salient-pole electron-optical lenses are described: 1)the hybrid method realized using the additional electromagnet introduced to a magnetic chain sequentially its field being composed or substracted with magnetosolid exciter field; 2)the method with saturation of a part of a magnetic circuit, with saturation being achievable at the begining or in the end of a regulation cycle. In the second method it is proposed to direct orthogonally the main flux excited by permanent magnets and the flux in the saturated part of the magnetic circuit excited using an electromagnet. It is shown that the second method allows one to reduce the required ampere-coils by more than an order as compared to the first method at one and the same regulation range and other equal conditions. The frequency of field regulation in the experimental mock-up was 10 kHz. 3 refs.; 2 figs

Interfacial Phenomena of Magnetic Fluid with Permanent Magnet in a Longitudinally Excited Container

International Nuclear Information System (INIS)

Sudo, Seiichi; Wakuda, Hirofumi; Yano, Tetsuya

2008-01-01

This paper describes the magnetic fluid sloshing in a longitudinally excited container. Liquid responses of magnetic fluid with a permanent magnet in a circular cylindrical container subject to vertical vibration are investigated. Experiments are performed on a vibration- testing system which provided longitudinal excitation. A cylindrical container made with the acrylic plastic is used in the experiment. A permanent magnet is in the state of floating in a magnetic fluid. The disk-shaped and ring-shaped magnets are examined. The different interfacial phenomena from the usual longitudinal liquid sloshing are observed. It is found that the wave motion frequency of magnetic fluid with a disk-shaped magnet in the container subject to vertical vibration is exactly same that of the excitation. In the case of ring-shaped magnet, the first symmetrical mode of one-half subharmonic response is dominant at lower excitation frequencies. The magnetic fluid disintegration of the free surface was also observed by a high-speed video camera system

Interfacial Phenomena of Magnetic Fluid with Permanent Magnet in a Longitudinally Excited Container

Science.gov (United States)

Sudo, Seiichi; Wakuda, Hirofumi; Yano, Tetsuya

2008-02-01

This paper describes the magnetic fluid sloshing in a longitudinally excited container. Liquid responses of magnetic fluid with a permanent magnet in a circular cylindrical container subject to vertical vibration are investigated. Experiments are performed on a vibration- testing system which provided longitudinal excitation. A cylindrical container made with the acrylic plastic is used in the experiment. A permanent magnet is in the state of floating in a magnetic fluid. The disk-shaped and ring-shaped magnets are examined. The different interfacial phenomena from the usual longitudinal liquid sloshing are observed. It is found that the wave motion frequency of magnetic fluid with a disk-shaped magnet in the container subject to vertical vibration is exactly same that of the excitation. In the case of ring-shaped magnet, the first symmetrical mode of one-half subharmonic response is dominant at lower excitation frequencies. The magnetic fluid disintegration of the free surface was also observed by a high-speed video camera system.

Optimized RVB states of the 2-d antiferromagnet: ground state and excitation spectrum

Science.gov (United States)

Chen, Yong-Cong; Xiu, Kai

1993-10-01

The Gutzwiller projection of the Schwinger-boson mean-field solution of the 2-d spin- {1}/{2} antiferromagnet in a square lattice is shown to produce the optimized, parameter-free RVB ground state. We get -0.6688 J/site and 0.311 for the energy and the staggered magnetization. The spectrum of the excited states is found to be linear and gapless near k≅0. Our calculation suggests, upon breaking of the rotational symmetry, ɛ k≅2JZ r1-γ 2k with Zr≅1.23.

New mode of magnetic excitation in praseodymium

DEFF Research Database (Denmark)

Clausen, K.N.; McEwen, K.A.; Jensen, J.

1994-01-01

A novel propagating mode of magnetic excitation has been observed in Pr. It takes the form of low-energy satellites to the crystal-field excitations on both the hexagonal and cubic sites which are very broad at long wavelengths, rise in energy and rapidly narrow with increasing q, and disappear...... beyond the point at which the two excitations would cross. The broadening may be abruptly quenched by a magnetic field. The satellite excitations are believed to be associated with the dynamics of the conduction electrons....

Dual structure in the charge excitation spectrum of electron-doped cuprates

Science.gov (United States)

Bejas, Matías; Yamase, Hiroyuki; Greco, Andrés

2017-12-01

Motivated by the recent resonant x-ray scattering (RXS) and resonant inelastic x-ray scattering (RIXS) experiments for electron-doped cuprates, we study the charge excitation spectrum in a layered t -J model with the long-range Coulomb interaction. We show that the spectrum is not dominated by a specific type of charge excitations, but by different kinds of charge fluctuations, and is characterized by a dual structure in the energy space. Low-energy charge excitations correspond to various types of bond-charge fluctuations driven by the exchange term (J term), whereas high-energy charge excitations are due to usual on-site charge fluctuations and correspond to plasmon excitations above the particle-hole continuum. The interlayer coupling, which is frequently neglected in many theoretical studies, is particularly important to the high-energy charge excitations.

Elementary excitations in single-chain magnets

Science.gov (United States)

Lutz, Philipp; Aguilà, David; Mondal, Abhishake; Pinkowicz, Dawid; Marx, Raphael; Neugebauer, Petr; Fâk, Björn; Ollivier, Jacques; Clérac, Rodolphe; van Slageren, Joris

2017-09-01

Single-chain magnets (SCMs) are one-dimensional coordination polymers or spin chains that display slow relaxation of the magnetization. Typically their static magnetic properties are described by the Heisenberg model, while the description of their dynamic magnetic properties is based on an Ising-like model. The types of excitations predicted by these models (collective vs localized) are quite different. Therefore we probed the nature of the elementary excitations for two SCMs abbreviated Mn2Ni and Mn2Fe , as well as a mononuclear derivative of the Mn2Fe chain, by means of high-frequency electron paramagnetic resonance spectroscopy (HFEPR) and inelastic neutron scattering (INS). We find that the HFEPR spectra of the chains are clearly distinct from those of the monomer. The momentum transfer dependence of the INS intensity did not reveal significant dispersion, indicating an essentially localized nature of the excitations. At the lowest temperatures these are modified by the occurrence of short-range correlations.

Elementary spin excitations in ultrathin itinerant magnets

Energy Technology Data Exchange (ETDEWEB)

Zakeri, Khalil, E-mail: zakeri@mpi-halle.de

2014-12-10

Elementary spin excitations (magnons) play a fundamental role in condensed matter physics, since many phenomena e.g. magnetic ordering, electrical (as well as heat) transport properties, ultrafast magnetization processes, and most importantly electron/spin dynamics can only be understood when these quasi-particles are taken into consideration. In addition to their fundamental importance, magnons may also be used for information processing in modern spintronics. Here the concept of spin excitations in ultrathin itinerant magnets is discussed and reviewed. Starting with a historical introduction, different classes of magnons are introduced. Different theoretical treatments of spin excitations in solids are outlined. Interaction of spin-polarized electrons with a magnetic surface is discussed. It is shown that, based on the quantum mechanical conservation rules, a magnon can only be excited when a minority electron is injected into the system. While the magnon creation process is forbidden by majority electrons, the magnon annihilation process is allowed instead. These fundamental quantum mechanical selection rules, together with the strong interaction of electrons with matter, make the spin-polarized electron spectroscopies as appropriate tools to excite and probe the elementary spin excitations in low-dimensional magnets e.g ultrathin films and nanostructures. The focus is put on the experimental results obtained by spin-polarized electron energy loss spectroscopy and spin-polarized inelastic tunneling spectroscopy. The magnon dispersion relation, lifetime, group and phase velocity measured using these approaches in various ultrathin magnets are discussed in detail. The differences and similarities with respect to the bulk excitations are addressed. The role of the temperature, atomic structure, number of atomic layers, lattice strain, electronic complexes and hybridization at the interfaces are outlined. A possibility of simultaneous probing of magnons and phonons

Magnetic excitations in ferromagnetic semiconductors

International Nuclear Information System (INIS)

Furdyna, J.K.; Liu, X.; Zhou, Y.Y.

2009-01-01

Magnetic excitations in a series of GaMnAs ferromagnetic semiconductor films were studied by ferromagnetic resonance (FMR). Using the FMR approach, multi-mode spin wave resonance spectra have been observed, whose analysis provides information on magnetic anisotropy (including surface anisotropy), distribution of magnetization precession within the GaMnAs film, dynamic surface spin pinning (derived from surface anisotropy), and the value of exchange stiffness constant D. These studies illustrate a combination of magnetism and semiconductor physics that is unique to magnetic semiconductors

Magnetic excitations in CuO

International Nuclear Information System (INIS)

Ain, M.; Reichardt, W.; Hennion, B.; Pepy, G.; Wanklyn, B.M.

1989-01-01

The authors have studied the magnetic excitations of CuO both in the ordered and the paramagnetic phase. Their results demonstrate the dominance of the magnetic interaction along the 10-1 Cu-O zigzag chains. In this direction the slope of the acoustic branch is 550 neV Angstrom

Magnetic excitations in thulium metal

International Nuclear Information System (INIS)

Fernandez-Baca, J.A.; Nicklow, R.M.; Rhyne, J.J.

1989-01-01

We have performed inelastic neutron scattering measurements on a single crystal specimen of Tm at wavevectors rvec κ = (1,1, ζ) and (0,0,2 + ζ) (ζ = 0, hor-ellipsis, 1). Most of the measurements have been made at T = 5K, where Tm exhibits a seven layer ferrimagnetic-antiphase-domain structure (four moments up, parallel to the c-axis, followed by three moments down). At this temperature the excitation spectra consist of three peaks. The two lower energy excitations have been identified as originating from magneto-vibrational scattering from the TA phonon, while the higher energy excitation is magnetic and exhibits only a weak dispersion (between 8.3 and 9.6 meV). At T = 50K, a temperature at which the system exhibits a c-axis sinusoidally modulated structure, the magnetic mode shows significant softening and broadening. The magneto-vibrational scattering vanishes above the Neel temperature (T N = 58.5K) while the magnetic mode persists at least up to T = 70K. These results suggest that the Hamiltonian in this system is dominated by the crystal-field-anistropy energy, and that the exchange interaction is relatively weak. 9 refs., 2 figs

Localized magnetic excitations for a line of magnetic impurities in a transverse Ising thin film ferromagnet

International Nuclear Information System (INIS)

Leite, R.V.; Oliveira Filho, L.O. de; Milton Pereira, J.; Cottam, M.G.; Costa Filho, R.N.

2009-01-01

A Green's function method is used to obtain the spectrum of spin excitations associated with a linear array of magnetic impurities implanted in a ferromagnetic thin film. The equations of motion for the Green's functions of the anisotropic film are written in the framework of the Ising model in a transverse field. The frequencies of localized modes are calculated as a function of the interaction parameters for the exchange coupling between impurity-spin pairs, host-spin pairs, and impurity-host neighbors, as well as the effective field parameter at the impurity sites.

Brillouin Light Scattering from Magnetic Excitations in Superparamagnetic and Ferromagnetic Co-Al-O Granular Films

Science.gov (United States)

Yoshihara, Akira; Maeda, Toshiteru; Kawamura, Satoshi; Nakamura, Shintaro; Nojima, Tsutomu; Takeda, Yoshihiko; Ohnuma, Shigehiro

2018-04-01

A systematic study of Brillouin light scattering (BLS) from superparamagnetic (SPM) and ferromagnetic (FM) Co-Al-O granular films was performed under magnetic fields of up to 4.6 kOe in the standard backscattering geometry at room temperature. The SPM and FM boundary, defined as the Co composition at which the exchange field vanishes, was found to be located at xC(Co) = 59.3 ± 1.3 at. %. From FM films we observed a pair of bulk spin-wave peaks on both the positive- and negative-frequency sides and a surface localized Damon-Eshbach peak only on the positive-frequency side under the present scattering conditions. From SPM films, a pair of broader but propagative excitation peaks with asymmetric intensity were observed on both frequency sides in a spectrum. We performed a numerical analysis of the BLS spectrum by employing the theory developed by Camley and Mills (CM) while retaining dipole and exchange couplings for FM films and only dipole coupling for SPM films. The CM theory successfully reproduced the observed spectrum for both SPM and FM films. The SPM spectrum exhibits a singlet-doublet peak structure similarly to an FM SW spectrum. The SPM peak stems from the dipole-coupled larger-amplitude precession motion of the granule magnetic moment around the external-field-induced magnetization.

Magnetic Excitations and Magnetic Ordering in Praseodymium

DEFF Research Database (Denmark)

Houmann, Jens Christian Gylden; Chapellier, M.; Mackintosh, A. R.

1975-01-01

The dispersion relations for magnetic excitons propagating on the hexagonal sites of double-hcp Pr provide clear evidence for a pronounced anisotropy in the exchange. The energy of the excitations decreases rapidly as the temperature is lowered, but becomes almost constant below about 7 K......, in agreement with a random-phase-approximation calculation. No evidence of magnetic ordering has been observed above 0.4 K, although the exchange is close to the critical value necessary for an antiferromagnetic state....

Optical spectroscopy of orbital and magnetic excitations in vanadates and cuprates

International Nuclear Information System (INIS)

Benckiser, Eva Vera

2007-10-01

ascertained that the theoretically predicted two-spinon-plus-phonon contribution describes roughly 74-97% of the observed spectral weight. We suggest that the remaining weight has to be ascribed to multi-spinon excitations. To explain the small magnetic absorption features in σ b (ω), we sketch a new mechanism which gives rise to a dipole moment perpendicular to the chains when holes are virtually exchanged along the chain. In particular, we point out the possible relevance of this contribution to the optical conductivity of many quasi-1D quantum spin systems. Our data of La 8 Cu 7 O 19 are the first experimental result on the magnetic excitations of n-leg ladders (n>2) at high energies. Amongst others, we compared our data with the well-investigated spectrum of the two-leg ladder and found a surprising resemblance. Although a detailed understanding of the observed line shape of the 5-leg ladder is missing up to now, our data strongly suggest the existence of bound states of magnetic excitations also in this system. The comparison of different low-dimensional S =1/2 systems suggests that the magnetic excitations in the high-energy continua are similar and develop smoothly from 1D to 2D. (orig.)

Transcranial magnetic stimulation provides means to assess cortical plasticity and excitability in humans with fragile X syndrome and autism spectrum disorder

Directory of Open Access Journals (Sweden)

Lindsay M Oberman

2010-06-01

Full Text Available Fragile X Syndrome (FXS is the most common heritable cause of intellectual disability. In vitro electrophysiologic data from mouse models of FXS suggest that loss of Fragile X Mental Retardation Protein (FMRP affects intracortical excitability and synaptic plasticity. Specifically, the cortex appears hyperexcitable, and use-dependent long-term potentiation (LTP and long-term depression (LTD of synaptic strength are abnormal. Though animal models provide important information, FXS and other neurodevelopmental disorders are human diseases and as such translational research to evaluate cortical excitability and plasticity must be applied in the human. Transcranial magnetic stimulation (TMS paradigms have recently been developed to noninvasively investigate cortical excitability using paired-pulse stimulation, as well as LTP- and LTD-like synaptic plasticity in response to theta burst stimulation (TBS in vivo in the human. TBS applied on consecutive days can be used to measure metaplasticity (the ability of the synapse to undergo a second plastic change following a recent induction of plasticity. The current study investigated intracortical inhibition, plasticity and metaplasticity in full mutation females with FXS, participants with autism spectrum disorders (ASD, and neurotypical controls. Results suggest that intracortical inhibition is normal in participants with FXS, while plasticity and metaplasticity appear abnormal. ASD participants showed abnormalities in plasticity and metaplasticity, as well as heterogeneity in intracortical inhibition. Our findings highlight the utility of noninvasive neurophysiological measures to translate insights from animal models to humans with neurodevelopmental disorders, and thus provide direct confirmation of cortical dysfunction in patients with FXS and ASD.

Magnon Accumulation by Clocked Laser Excitation as Source of Long-Range Spin Waves in Transparent Magnetic Films

Directory of Open Access Journals (Sweden)

M. Jäckl

2017-04-01

Full Text Available Optical tools are promising for spin-wave generation because of the possibilities of ultrafast manipulation and local excitation. However, a single laser pulse can inject spin waves (SWs only with a broad frequency spectrum, resulting in short propagation distances and low wave amplitudes. Here, we excite a magnetic garnet film by a train of fs-laser pulses with a 1-GHz repetition rate so that the pulse separation is shorter than the decay time of magnetic modes, which allows us to achieve a collective impact on the magnetization and establish a quasistationary source of spin waves, namely, a coherent accumulation of magnons (“magnon cloud”. This approach has several appealing features: (i The magnon source is tunable, (ii the SW amplitude can be significantly enhanced, (iii the SW spectrum is quite narrow, providing long-distance propagation, (iv the periodic pumping results in an almost constant-in-time SW amplitude for the distances larger than 20  μm away from the source, and (v the SW emission shows pronounced directionality. These results expand the capabilities of ultrafast coherent optical control of magnetization and pave the way for applications in data processing, including the quantum regime. The quasistationary magnon accumulation might also be of interest for applications in magnon Bose-Einstein condensates.

Excited eigenmodes in magnetic vortex states of soft magnetic half-spheres and spherical caps

Energy Technology Data Exchange (ETDEWEB)

Yoo, Myoung-Woo; Lee, Jae-Hyeok; Kim, Sang-Koog, E-mail: sangkoog@snu.ac.kr [National Creative Research Initiative Center for Spin Dynamics and Spin-Wave Devices, Nanospinics Laboratory, Research Institute of Advanced Materials, Department of Materials Science and Engineering, Seoul National University, Seoul 151-744 (Korea, Republic of)

2014-12-14

We studied the magnetization dynamics of excitation modes in special geometrical confinements of soft magnetic half-spheres and spherical caps in magnetic vortex states using finite-element micromagnetic numerical calculations. We found additional fine features of the zeroth- and first-order gyrotropic modes and asymmetric m = +1 and m = −1 azimuthal spin-wave modes, which detailed information is unobtainable from two-dimensional mesh-cell based numerical calculations. Moreover, we examined the perpendicular bias field dependence of the excited eigenmodes, which data provide for an efficient means of control over the excited modes. Such numerical calculations offer additional details or new underlying physics on dynamic features in arbitrary-shape magnetic nano-elements such as half-spheres and spherical caps in magnetic vortex states.

Neutron scattering studies on magnetic excitations in complex ordered manganites

International Nuclear Information System (INIS)

Senff, D.

2007-09-01

This thesis deals with magnetic excitations in three different Manganese oxides, single-layered LaSrMnO 4 , charge- and orbital-ordered La 1/2 Sr 3/2 MnO 4 , and multiferroic TbMnO 3 , which are studied by means of inelastic neutron scattering. The properties of the first system, LaSrMnO 4 , are governed by the complex interplay of orbital, spin, and lattice degrees of freedom typical for the physics of manganites. The magnetic low-temperature behavior is quite unusual, and the comprehensive analysis of the spin-wave spectrum of LaSrMnO 4 suggests a heterogenous ground state with ferromagnetic orbital polarons embedded in an antiferromagnetic background. The doped system La 1/2 Sr 3/2 MnO 4 exhibits a stable charge- and orbital-ordered state, which today is discussed very controversially, as it is of great relevance for the colossal increase of electric conductivity at the metal-insulator transition in perovskite manganites. Analyzing the spin-wave dispersion of the ordered state, we find an excellent agreement with classical predictions by Goodenough and reject a recent alternative proposal. The different strength of the ferromagnetic and antiferromagnetic exchange in the CE-type ordering leads to the conclusion that the magnetic state has to be considered as a weak AFM coupling of stable FM elements. This thesis is further supported by the thermal evolution of the ordered state, revealing anisotropic correlations and the close competition of FM and AFM correlations above the Neel transition, as well as by the doping dependence of the charge- and orbital-ordered state, which is interpreted on the basis of a different response of the magnetic system with respect to additional electrons or holes. In the orthorhombic perovskite TbMnO 3 the electric polarization is closely coupled to the magnetic degrees of freedom via a complex, non-collinear magnetic ordering. Precisely characterizing the different magnon excitations allows to identify all relevant modes of the

Resonance of magnetization excited by voltage in magnetoelectric heterostructures

Science.gov (United States)

Yu, Guoliang; Zhang, Huaiwu; Li, Yuanxun; Li, Jie; Zhang, Dainan; Sun, Nian

2018-04-01

Manipulation of magnetization dynamics is critical for spin-based devices. Voltage driven magnetization resonance is promising for realizing low-power information processing systems. Here, we show through Finite Element Method (FEM) simulations that magnetization resonance in nanoscale magnetic elements can be generated by a radio frequency (rf) voltage via the converse magnetoelectric (ME) effect. The magnetization dynamics induced by voltage in a ME heterostructures is simulated by taking into account the magnetoelastic and piezoelectric coupling mechanisms among magnetization, strain and voltage. The frequency of the excited magnetization resonance is equal to the driving rf voltage frequency. The proposed voltage driven magnetization resonance excitation mechanism opens a way toward energy-efficient spin based device applications.

Magnetic-Field Induced Enhancement in the Fluorescence Yield Spectrum of Doubly Excited States in Helium

International Nuclear Information System (INIS)

Stroem, Magnus; Saathe, Conny; Agaaker, Marcus; Soederstroem, Johan; Rubensson, Jan-Erik; Stranges, Stefano; Richter, Robert; Alagia, Michele; Gorczyca, T. W.; Robicheaux, F.

2006-01-01

An influence of static magnetic fields on the fluorescence yield spectrum of He in the vicinity of the N=2 thresholds has been observed. The experimental results are in excellent agreement with predictions based on multichannel quantum defect theory, and it is demonstrated that the Rydberg electron l mixing due to the diamagnetic interaction is essential for the description of the observed fluorescence yield intensity enhancement

Spectrum of acetylene fluorescence excited by single XUV photons

International Nuclear Information System (INIS)

Schmieder, R.W.

1982-01-01

The spectrum of visible emission from photofragments of acetylene excited by single 16.85 eV photons has been recorded for the first time. The spectrum is dominated by the Swan and Deslandres-d'Azambuja bands of C 2 and the 431.5 nm band of CH. The yields of these emissions are of the order 10 -3 photons per absorbed incident photon. The experimental conditions suggest that the emission results from primary C* 2 and CH* photofragments

High energy magnetic excitations

International Nuclear Information System (INIS)

Endoh, Yasuo

1988-01-01

The report emphasizes that the current development in condensed matter physics opens a research field fit to inelastic neutron scattering experiments in the eV range which is easilly accessed by spallation neutron sources. Several important subjects adopted at thermal reactors are shown. It is desired to extend the implementation of the spectroscopic experiments for investigation of higher energy magnetic excitations. For La 2 CuO 4 , which is the mother crystal of the first high Tc materials found by Bednortz and Muller, it seems to be believed that the magnetism is well characterized by the two-dimensional Heisenberg antiferromagnetic Hamiltonian, and it is widely accepted that the magnetism is a most probable progenitor of high Tc superconductors. The unusual properties of spin correlations in this crystal have been studied extensively by standard neutron scattering techniques with steady neutrons at BNL. FeSi is not ordered magnetically but shows a very unique feature of temperature induced magnetism, which also has been studied extensively by using the thermal neutron scattering technique at BNL. In these experiments, polarized neutrons are indispensable to extract the clean magnetic components out of other components of non-magnetic scattering. (N.K.)

High Tc Superconducting Magnet Excited by a Semiconductor Thermoelectric Element

Science.gov (United States)

Kuriyama, T.; Ono, M.; Tabe, S.; Oguchi, A.; Okamura, T.

2006-04-01

A high Tc superconducting (HTS) magnet excited by a thermal electromotive force of a thermoelectric element is studied. This HTS magnet has the advantages of compactness, lightweight and continuous excitation in comparison with conventional HTS magnets, because this HTS magnet does not need a large external power source. In this system, a heat input into the cryogenic environment is necessary to excite the thermoelectric element for constant operation. This heat generation, however, causes a rise in temperature of an HTS coil and reduces the system performance. In this paper, a newly designed magnet system which adopted a two-stage GM cryocooler was investigated. It enabled us to control the temperature of a thermoelectric element and that of an HTS coil independently. The temperature of the HTS coil could be kept at 10-20 K at the second stage of the GM cryocooler, while the thermoelectric element could be excited at higher temperature in the range of 50-70 K at the first stage, where the performance of the thermoelectric element was higher. The experimental results on this HTS magnet are shown and the possibility of the thermoelectric element as a main power source of the HTS magnets is discussed.

Optical spectroscopy of orbital and magnetic excitations in vanadates and cuprates

Energy Technology Data Exchange (ETDEWEB)

Benckiser, Eva Vera

2007-10-15

function of temperature and Ca substitution. We have found J{sub c}=(227{+-}4) meV for SrCuO{sub 2} at low temperatures and no effect on J{sub c} upon Ca-substitution of 10%. Furthermore, we ascertained that the theoretically predicted two-spinon-plus-phonon contribution describes roughly 74-97% of the observed spectral weight. We suggest that the remaining weight has to be ascribed to multi-spinon excitations. To explain the small magnetic absorption features in {sigma}{sub b}({omega}), we sketch a new mechanism which gives rise to a dipole moment perpendicular to the chains when holes are virtually exchanged along the chain. In particular, we point out the possible relevance of this contribution to the optical conductivity of many quasi-1D quantum spin systems. Our data of La{sub 8}Cu{sub 7}O{sub 19} are the first experimental result on the magnetic excitations of n-leg ladders (n>2) at high energies. Amongst others, we compared our data with the well-investigated spectrum of the two-leg ladder and found a surprising resemblance. Although a detailed understanding of the observed line shape of the 5-leg ladder is missing up to now, our data strongly suggest the existence of bound states of magnetic excitations also in this system. The comparison of different low-dimensional S =1/2 systems suggests that the magnetic excitations in the high-energy continua are similar and develop smoothly from 1D to 2D. (orig.)

Neutron scattering studies on magnetic excitations in complex ordered manganites

Energy Technology Data Exchange (ETDEWEB)

Senff, D

2007-09-15

This thesis deals with magnetic excitations in three different Manganese oxides, single-layered LaSrMnO{sub 4}, charge- and orbital-ordered La{sub 1/2}Sr{sub 3/2}MnO{sub 4}, and multiferroic TbMnO{sub 3}, which are studied by means of inelastic neutron scattering. The properties of the first system, LaSrMnO{sub 4}, are governed by the complex interplay of orbital, spin, and lattice degrees of freedom typical for the physics of manganites. The magnetic low-temperature behavior is quite unusual, and the comprehensive analysis of the spin-wave spectrum of LaSrMnO{sub 4} suggests a heterogenous ground state with ferromagnetic orbital polarons embedded in an antiferromagnetic background. The doped system La{sub 1/2}Sr{sub 3/2}MnO{sub 4} exhibits a stable charge- and orbital-ordered state, which today is discussed very controversially, as it is of great relevance for the colossal increase of electric conductivity at the metal-insulator transition in perovskite manganites. Analyzing the spin-wave dispersion of the ordered state, we find an excellent agreement with classical predictions by Goodenough and reject a recent alternative proposal. The different strength of the ferromagnetic and antiferromagnetic exchange in the CE-type ordering leads to the conclusion that the magnetic state has to be considered as a weak AFM coupling of stable FM elements. This thesis is further supported by the thermal evolution of the ordered state, revealing anisotropic correlations and the close competition of FM and AFM correlations above the Neel transition, as well as by the doping dependence of the charge- and orbital-ordered state, which is interpreted on the basis of a different response of the magnetic system with respect to additional electrons or holes. In the orthorhombic perovskite TbMnO{sub 3} the electric polarization is closely coupled to the magnetic degrees of freedom via a complex, non-collinear magnetic ordering. Precisely characterizing the different magnon excitations

Rotational temperature measurement of NO gas using two-photon excitation spectrum

Science.gov (United States)

Ozaki, Tadao; Matsui, Yoshihiko; Ohsawa, Toshihiko

1981-04-01

The rotational temperature of nitric oxide gas has been measured by means of a single-beam two-photon excitation spectrum method using a pulsed continuously tunable dye laser. The nitric oxide gas was enclosed at about 40 Torr in a quartz cell which was put in an electric oven. The NO γ (0-0) band and R11+Q21 branches were used to obtain the two-photon excitation spectrum. The rotational temperatures were determined using the fact that molecules are distributed in the rotational levels according to the Boltzmann law. The temperature range was from room temperature to about 470 K. Observed temperatures were in good agreement with cell temperatures which were obtained by using a thermocouple.

Magnetic structure and excitation spectrum of the hyperhoneycomb Kitaev magnet β -Li2IrO3

Science.gov (United States)

Ducatman, Samuel; Rousochatzakis, Ioannis; Perkins, Natalia B.

2018-03-01

We present a theoretical study of the static and dynamical properties of the three-dimensional, hyperhoneycomb Kitaev magnet β -Li2IrO3 . We argue that the observed incommensurate order can be understood in terms of a long-wavelength twisting of a nearby commensurate period-3 state, with the same key qualitatively features. The period-3 state shows very different structure when either the Kitaev interaction K or the off-diagonal exchange anisotropy Γ is dominant. A comparison of the associated static spin structure factors with reported scattering experiments in zero and finite fields gives strong evidence that β -Li2IrO3 lies in the regime of dominant Kitaev coupling, and that the Heisenberg exchange J is much weaker than both K and Γ . Our predictions for the magnon excitation spectra, the dynamical spin structure factors, and their polarization dependence provide additional distinctive fingerprints that can be checked experimentally.

Magnetic fluctuations due to thermally excited Alfven waves

International Nuclear Information System (INIS)

Agim, Y.Z.; Prager, S.C.

1990-01-01

Magnetic fluctuations due to the thermally excited MHD waves are investigated using fluid and kinetic models to describe a stable, uniform, compressible plasma in the range above the drift wave frequency and below the ion cyclotron frequency. It is shown that the fluid model with resistivity yields spectral densities which are roughly Lorentzian, exhibit equipartition with no apparent cutoff in wavenumber space and a Bohm-type diffusion coefficient. Under certain conditions, the ensuing transport may be comparable to classical values. For a phenomenological cutoff imposed on the spectrum, the typical fluctuating-to-equilibrium magnetic field ratio is found to be of the order of 10 -10 . Physical mechanisms to obtain decay profiles of the spectra with increasing wavenumber due to dispersion and/or different forms of damping are investigated analytically in a cold fluid approximation and numerically, with a kinetic model. The mode dispersion due to the finite ion-gyrofrequency is identified as the leading effect determining the spectral profile shapes. It is found that the amplitude of fluctuations may be within a factor of the value suggested by the cold plasma model. The results from both models are presented and compared in low- and high-β regimes. 21 refs., 6 figs

Magnetic dipole excitations of the 163Dy nucleus

Science.gov (United States)

Zenginerler, Zemine; Tabar, Emre; Yakut, Hakan; Kuliev, Ali Akbar; Guliyev, Ekber

2014-03-01

In this study some properties of the magnetic dipole excitations of the deformed odd mass 163Dy nucleus were studied by using Quasiparticle-phonon nuclear model (QPNM). The several of the ground-state and low-lying magnetic dipole (M1) mode characteristics were calculated for deformed odd-mass nuclei using a separable Hamiltonian within the QPNM. The M1 excited states, reduced transition probabilities B(M1), the ground-state magnetic properties such as magnetic moment (μ), intrinsic magnetic moment (gK) , effective spin factor (gseff.) are the fundamental characteristics of the odd-mass nucleus and provide key information to understand nuclear structure. The theoretical results were compared with the available experimental data and other theoretical approaches. Calculations show that the spin-spin interaction in this isotopes leads to polarization effect influencing the magnetic moments. Furthermore we found a strong fragmentation of the M1 strength in 163Dy nucleus which was in qualitative agreement with the experimental data. Sakarya University, Project Number: 2012-50-02-007 and Z.Zenginerler acknowledge to TUBITAK-TURKEY 2013, fellowship No: 2219.

Excitation spectrum of ferromagnetic xxz-chains

International Nuclear Information System (INIS)

Schneider, T.; Stoll, E.

1983-01-01

In the history of xxz-Heisenberg spin chains, understanding of the dynamic form factors (DFF) is much less advanced. In this paper the DFF of ferromagnetic xxz chains as a tool to probe and interpret excitation spectrum is reviewed. The Isingheisenberg chain, and the Planar-Heisenberg chain (where HF approximations become exact) are studied. The results provide instructive connections between spin systems, interacting fermions and bosons. Various new aspects--thermally induced bound state effects in terms of central peaks in DFF for Isinglike xxz chains; the possibility to observe bound states in S /SUB zz/ (q,w) accessible by neutron scattering techniques, in the planar system--are found

Magnetostrictive-piezoelectric magnetic sensor with current excitation

International Nuclear Information System (INIS)

Prieto, J.L.; Aroca, C.; Lopez, E.; Sanchez, M.C.; Sanchez, P.

2000-01-01

A new working configuration for magnetostrictive-piezoelectric magnetic sensors is presented. In this configuration, the excitation is caused using an electrical current flowing through the ferromagnetic sample and the induced signal is sensed in the piezoelectric support as an electrical voltage. This new idea allows a magnetic field detection without any coil and opens a possibility for a future miniaturisation of the sensor

Local magnetic properties of multiferroic Nd0.5Gd0.5Fe3(BO3)4 in the excited states of Nd3+ ion

International Nuclear Information System (INIS)

Malakhovskii, A.V.; Gnatchenko, S.L.; Kachur, I.S.; Piryatinskaya, V.G.; Sukhachev, A.L.; Temerov, V.L.

2015-01-01

Polarized absorption spectra of single-crystal Nd 0.5 Gd 0.5 Fe 3 (BO 3 ) 4 were studied in the region of the transition 4 I 9/2 →( 4 G 5/2 + 2 G 7/2 ) in Nd 3+ ion as a function of temperature (2–34 K) and magnetic field (0–65 kOe). The spectra of natural circular dichroism were measured in the range of 5–40 K. It was found out that the local magnetic properties in the vicinity of the excited ion substantially depended on its state. In particular, a weak ferromagnetic moment appears in some excited states. It was found out that the selection rules for electron transitions in the magnetically ordered state substantially deviated from those in the paramagnetic state of the crystal. They are different for different transitions and they are very sensitive to the orientation of the sublattice magnetic moment relative to the light polarization. In the spectrum of the natural circular dichroism, the transition is revealed which is not observed in the absorption spectrum. - Highlights: • Temperature and field dependences of f-f transitions in Nd 0.5 Gd 0.5 Fe 3 (BO 3 ) 4 . • Natural circular dichroism in Nd 0.5 Gd 0.5 Fe 3 (BO 3 ) 4 below T N . • Weak ferromagnetic moment was identified in some excited 4f states. • Selection rules for f-f transitions substantially change below T N . • Intensities of f-f transitions strongly depend on magnetic moment orientation

Excitations in the field-induced quantum spin liquid state of α-RuCl3

Science.gov (United States)

Banerjee, Arnab; Lampen-Kelley, Paula; Knolle, Johannes; Balz, Christian; Aczel, Adam Anthony; Winn, Barry; Liu, Yaohua; Pajerowski, Daniel; Yan, Jiaqiang; Bridges, Craig A.; Savici, Andrei T.; Chakoumakos, Bryan C.; Lumsden, Mark D.; Tennant, David Alan; Moessner, Roderich; Mandrus, David G.; Nagler, Stephen E.

2018-03-01

The celebrated Kitaev quantum spin liquid (QSL) is the paradigmatic example of a topological magnet with emergent excitations in the form of Majorana Fermions and gauge fluxes. Upon breaking of time-reversal symmetry, for example in an external magnetic field, these fractionalized quasiparticles acquire non-Abelian exchange statistics, an important ingredient for topologically protected quantum computing. Consequently, there has been enormous interest in exploring possible material realizations of Kitaev physics and several candidate materials have been put forward, recently including α-RuCl3. In the absence of a magnetic field this material orders at a finite temperature and exhibits low-energy spin wave excitations. However, at moderate energies, the spectrum is unconventional and the response shows evidence for fractional excitations. Here we use time-of-flight inelastic neutron scattering to show that the application of a sufficiently large magnetic field in the honeycomb plane suppresses the magnetic order and the spin waves, leaving a gapped continuum spectrum of magnetic excitations. Our comparisons of the scattering to the available calculations for a Kitaev QSL show that they are consistent with the magnetic field induced QSL phase.

Field dependence of magnetic order and excitations in the Kitaev candidate alpha-RuCl3

Science.gov (United States)

Banerjee, Arnab; Kelley, Paula; Winn, Barry; Aczel, Adam; Lumsden, Mark; Mandrus, David; Nagler, Stephen

The search for new quantum states of matter has been one of the forefront endeavors of condensed matter physics. The two-dimensional Kitaev quantum spin liquid (QSL) is of special interest as an exactly solvable spin-liquid model exhibiting exotic fractionalized excitations. Recently, alpha-RuCl3 has been identified as a candidate system for exhibiting some aspects of Kitaev QSL physics. The spins in this material exhibit zig-zag order at low temperatures, and show both low energy spin wave excitation arising from the ordered state as well as a continuum excitation extending to higher energies that has been taken as evidence for QSL relate Majorana fermions. In this talk, we show that the application of an in-plane magnetic field suppresses the zig-zag order possibly resulting in a state devoid of long-range order. Field-dependent inelastic neutron scattering on single-crystal shows a remarkable effect on the excitation spectrum above the critical field. The work is supported by US-DOE, Office of Science, Basic Energy Sciences and User Facilities Divisions, and also the Gordon and Betty Moore Foundation EPiQS Grant GBFM4416.

First-principles calculation of monitoring spin states of small magnetic nanostructures with IR spectrum of CO

International Nuclear Information System (INIS)

Li, C; Lefkidis, G; Huebner, W

2010-01-01

A fully ab initio controlled ultrafast magnetooptical switching mechanism in small magnetic clusters is achieved through exploiting spin-orbit-coupling enabled Λ processes. The idea is that in the magnetic molecules a fast transition between two almost degenerate states with different spins can be triggered by a laser pulse, which leads to an electron excitation from one of the degenerate states to a highly spin-mixed state and a deexcitation to the state of opposite spin. In this paper a CO molecule is attached to one magnetic center of the clusters, which serves as an experimental marker to map the laser-induced spin manipulation to the IR spectrum of CO. The predicted spin-state-dependent CO frequencies can facilitate experimental monitoring of the processes. We show that spin flip in magnetic atoms can be achieved in structurally optimized magnetic clusters in a subpicosecond regime with linearly polarized light.

Excitation spectrum and staggering transformations in lattice quantum models.

Science.gov (United States)

Faria da Veiga, Paulo A; O'Carroll, Michael; Schor, Ricardo

2002-08-01

We consider the energy-momentum excitation spectrum of diverse lattice Hamiltonian operators: the generator of the Markov semigroup of Ginzburg-Landau models with Langevin stochastic dynamics, the Hamiltonian of a scalar quantum field theory, and the Hamiltonian associated with the transfer matrix of a classical ferromagnetic spin system at high temperature. The low-lying spectrum consists of a one-particle state and a two-particle band. The two-particle spectrum is determined using a lattice version of the Bethe-Salpeter equation. In addition to the two-particle band, depending on the lattice dimension and on the attractive or repulsive character of the interaction between the particles of the system, there is, respectively, a bound state below or above the two-particle band. We show how the existence or nonexistence of these bound states can be understood in terms of a nonrelativistic single-particle lattice Schrödinger Hamiltonian with a delta potential. A staggering transformation relates the spectra of the attractive and the repulsive cases.

Neutron scattering investigation of magnetic excitations at high energy transfers

International Nuclear Information System (INIS)

Loong, C.K.

1984-01-01

With the advance of pulsed spallation neutron sources, neutron scattering investigation of elementary excitations in magnetic materials can now be extended to energies up to several hundreds of MeV. We have measured, using chopper spectrometers and time-of-flight techniques, the magnetic response functions of a series of d and f transition metals and compounds over a wide range of energy and momentum transfer. In PrO 2 , UO 2 , BaPrO 3 and CeB 6 we observed crystal-field transitions between the magnetic ground state and the excited levels in the energy range from 40 to 260 MeV. In materials exhibiting spin-fluctuation or mixed-valent character such as Ce 74 Th 26 , on the other hand, no sharp crystal-field lines but a broadened quasielastic magnetic peak was observed. The line width of the quasielastic component is thought to be connected to the spin-fluctuation energy of the 4f electrons. The significance of the neutron scattering results in relation to the ground state level structure of the magnetic ions and the spin-dynamics of the f electrons is discussed. Recently, in a study of the spin-wave excitations in itinerant magnetic systems, we have extended the spin-wave measurements in ferromagnetic iron up to about 160 MeV. Neutron scattering data at high energy transfers are of particular interest because they provide direct comparison with recent theories of itinerant magnetism. 26 references, 7 figures

Spin wave spectrum of magnetic nanotubes

International Nuclear Information System (INIS)

Gonzalez, A.L.; Landeros, P.; Nunez, Alvaro S.

2010-01-01

We investigate the spin wave spectra associated to a vortex domain wall confined within a ferromagnetic nanotube. Basing our study upon a simple model for the energy functional we obtain the dispersion relation, the density of states and dissipation induced life-times of the spin wave excitations in presence of a magnetic domain wall. Our aim is to capture the basics spin wave physics behind the geometrical confinement of nobel magnetic textures.

Coupling between the Magnetic Excitations and the Phonons in Praseodymium

DEFF Research Database (Denmark)

Jensen, J.

1976-01-01

of an external magnetic field applied along an a and a b direction. The magnetic excitations are approximated by pseudo-boson excitations of the spin sub-space, J=4, MJ=0 and +or-1, and the presence of the ions on the cubic sites is neglected. The selection rules deduced agree with experimental observations....... The experimental result for the strength of the exciton-phonon interaction is used in an estimate of the effects of an applied field on the elastic constants of Pr at zero temperature....

Self excitation of second harmonic ion-acoustic waves in a weakly magnetized plasma

International Nuclear Information System (INIS)

Tsukabayashi, I.; Yagishita, T.; Nakamura, Y.

1994-01-01

Electrostatic ion-acoustic waves in a weakly magnetized plasma are investigated experimentally. It is observed that finite amplitudes ion acoustic waves excite a new second harmonic wave train behind the initial ion waves excite a new second harmonic wave train behind the initial ion waves in a parallel magnetic field. The excitation of higher harmonic waves can be explained by non-linearity of finite amplitude ion-acoustic waves. The newly excited second harmonics waves satisfy a dispersion relation of the ion-acoustic waves. (author). 3 refs, 5 figs

Research on magnetic excitation model of magnetic flux leakage for coal mine hoisting wire rope

Directory of Open Access Journals (Sweden)

Jie Tian

2015-11-01

Full Text Available This study presents the optimal design of a magnetic excitation model for developing a nondestructive sensor for coal mine hoist wire ropes. The model was established using axial-symmetry finite-element analysis and calculations. The influence of the excitation device parameters on the local magnetization effect of the wire rope was investigated in detail using the axial-symmetry finite-element model. The excitation model parameters of the sensor were optimally designed using a combination of finite-element analysis and an optimization method. The experiments were performed to measure the leakage flux and evaluate the performance of the optimally designed sensor. The results show that the sensor based on the newly designed excitation model can not only improve the signal-to-noise ratio for defect detection in a coal mine hoist wire rope by 11% compared to an existing sensor but also reliably detect small defects with a high detection speed (5 m/s along the length of the coal mine wire rope.

Dynamics of Solid Body in Magnetic Suspension under Periodic Excitation

Directory of Open Access Journals (Sweden)

A. M. Gouskov

2017-01-01

Full Text Available The article studies dynamics of ferromagnetic body in hybrid magnetic suspension (HMS. The body is supposed to have one degree of freedom and a nonlinear magnetic force dependence on the current and displacement. The magnetic force induced in the HMS is divided into a passive component and an active one. Specifying the law of current variation in the coil allows us to generate nonlinear oscillations under electromagnet action. To provide periodic excitation the appropriate law of the current variation in the electromagnet coil is proposed. The mathematical model includes external periodic step-excitation. The equation of motion is formed. The scales of similarity are highlighted in the system, and the equation of motion is reduced to dimensionless form.The motion dynamics is studied numerically. The relaxation method was used to determine the periodic motions at different values of dimensionless frequency of the electromagnet excitation as well as to estimate the influence of other dimensionless parameters on the system dynamics. The amplitude-frequency curve analysis allows us to come to conclusion that the nature of system nonlinearity is rigid. Adding the external periodic step-excitation leads to the qualitative change in the nature of movement. This points to the occurrence of bifurcation.

Magnetic excitation spectrum of the square lattice S=1/2 Heisenberg antiferromagnet K₂V₃O₈

DEFF Research Database (Denmark)

Lumsden, M.D.; Nagler, S.E.; Sales, B.C.

2006-01-01

V. However, upon approaching the zone boundary, the observed excitation spectrum deviates significantly from the expectation of linear spin wave theory resulting in split modes at the (pi/2,pi/2) zone boundary point. The effects of magnon-phonon interaction, orbital degrees of freedom, multimagnon scattering...

Theory of spin and lattice wave dynamics excited by focused laser pulses

Science.gov (United States)

Shen, Ka; Bauer, Gerrit E. W.

2018-06-01

We develop a theory of spin wave dynamics excited by ultrafast focused laser pulses in a magnetic film. We take into account both the volume and surface spin wave modes in the presence of applied, dipolar and magnetic anisotropy fields and include the dependence on laser spot exposure size and magnetic damping. We show that the sound waves generated by local heating by an ultrafast focused laser pulse can excite a wide spectrum of spin waves (on top of a dominant magnon–phonon contribution). Good agreement with recent experiments supports the validity of the model.

Observation of non-linear effects in a quasi-one-dimensional antiferromagnet: magnetic excitations in CsVCl sub 3

CERN Document Server

Inami, T; Tanaka, H

1997-01-01

The spin dynamics of the hexagonal ABX sub 3 -type quasi-one-dimensional antiferromagnet CsVCl sub 3 is investigated by means of an inelastic neutron scattering technique. In good qualitative agreement with a recent spin-wave calculation including higher-order terms, a large scattering cross-section arising from two-magnon excitations is observed at the one-dimensional antiferromagnetic zone centre. In addition, we measured spin-wave excitations between the chains precisely and revealed that the spin-wave dispersion curves are modified in energy and in intensity on account of the anticrossing between the one-magnon branches and two-magnon continuum. These results demonstrate that anharmonic terms are important in the spin dynamics of CsVCl sub 3 even at low temperatures. We also measured the temperature dependence of the magnetic excitations and found that far above the Neel temperature the two-magnon process gives a considerable contribution to the inelastic spectrum. (author)

Cerebro-Cerebellar Functional Connectivity is Associated with Cerebellar Excitation-Inhibition Balance in Autism Spectrum Disorder.

Science.gov (United States)

Hegarty, John P; Weber, Dylan J; Cirstea, Carmen M; Beversdorf, David Q

2018-05-23

Atypical functional connectivity (FC) and an imbalance of excitation-to-inhibition (E/I) have been previously reported in cerebro-cerebellar circuits in autism spectrum disorder (ASD). The current investigation used resting state fMRI and proton magnetic resonance spectroscopy ( 1 H-MRS) to examine the relationships between E/I (glutamate + glutamine/GABA) and FC of the dorsolateral prefrontal cortex and posterolateral cerebellar hemisphere from 14 adolescents/adults with ASD and 12 age/sex/IQ-matched controls. In this pilot sample, cerebro-cerebellar FC was positively associated with cerebellar E/I and listening comprehension abilities in individuals with ASD but not controls. Additionally, a subgroup of individuals with ASD and low FC (n = 5) exhibited reduced E/I and impaired listening comprehension. Thus, altered functional coherence of cerebro-cerebellar circuits in ASD may be related with a cerebellar E/I imbalance.

Laser excited fluorescence spectrum of Ho3+:SrF2 single crystal

International Nuclear Information System (INIS)

Lal, Bansi; Ramachandra Rao, D.

1980-01-01

The fluorescence spectrum of Ho 3+ : SrF 2 single crystal excited by the various lines of an Ar + laser, is reported. The three fluorescence groups recorded in the region 5300-7700 A, correspond to the transitions from ( 5 F 4 , 5 S 2 ) to 5 I 8 , 5 F 5 to 5 I 8 , 5 F 3 to 5 I 7 and ( 5 F 4 , 5 S 2 ) to 5 I 7 . Marked changes in the total integrated intensity of the various fluorescence groups with the change in the exciting wavelength are observed. (author)

Pulsed air-core deflector-magnet design parameters

International Nuclear Information System (INIS)

Jason, A.J.; Cooper, R.K.; Liebman, A.D.; Blind, B.; Koelle, A.R.

1983-01-01

The response of air-core magnets to pulsed excitation is dependent on the pulse frequency spectrum because of fields produced by induced currents in the magnet structure. We discuss this phenomenon quantitatively in terms of magnet performance optimization

Power system stabilization by superconducting magnetic energystorage connected to rotating exciter

OpenAIRE

Mitani, Yasunori; Tsuji, K

1993-01-01

The authors describe a combination of a rotating exciter and a superconducting magnetic energy storage (SMES) system for efficient power system stabilization. A SMES system connected to an exciter rotating with a turbine-rotor shaft is proposed. The exciter is installed exclusively to supply current for the SMES. Since electrical power output from the SMES is converted into a mechanical torque of the generator directly by the exciter, it is expected that power swings of the generator will be ...

Polarized fine structure in the excitation spectrum of a negatively charged quantum dot

OpenAIRE

Ware, M. E.; Stinaff, E. A.; Gammon, D.; Doty, M. F.; Bracker, A. S.; Gershoni, D.; Korenev, V. L.; Badescu, S. C.; Lyanda-Geller, Y.; Reinecke, T. L.

2005-01-01

We report polarized photoluminescence excitation spectroscopy of the negative trion in single charge tunable InAs/GaAs quantum dots. The spectrum exhibits a p-shell resonance with polarized fine structure arising from the direct excitation of the electron spin triplet states. The energy splitting arises from the axially symmetric electron-hole exchange interaction. The magnitude and sign of the polarization are understood from the spin character of the triplet states and a small amount of qua...

Uniform magnetic excitations in NiO nanoparticles

DEFF Research Database (Denmark)

Bahl, C.R.H.; Kuhn, L.T.; Lefmann, K.

2006-01-01

A sample of isolated disc shaped NiO nanoparticles was studied at the RITA-II triple axis spectrometer at SINQ (PSI) using the newly implemented multi-analyser blade imaging mode. The particles were 13 nm in diameter and had a thickness of about 2.5 nm. A non-dispersive spin excitation was observed...... at the antiferromagnetic ((1)/(2) (1)/(2) (1)/(2)) reflection at a scattering vector of kappa = 1.30 angstrom(-1), at an energy of 2 0.51 +/- 0.02 meV. This is shown to be due to uniform magnetic excitations in the nanoparticles. (c) 2006 Elsevier B.V. All rights reserved....

Temperature-dependent transformation of the magnetic excitation spectrum on approaching superconductivity in Fe(1+y-x)(Ni/Cu)(x)Te(0.5)Se(0.5).

Science.gov (United States)

Xu, Zhijun; Wen, Jinsheng; Zhao, Yang; Matsuda, Masaaki; Ku, Wei; Liu, Xuerong; Gu, Genda; Lee, D-H; Birgeneau, R J; Tranquada, J M; Xu, Guangyong

2012-11-30

Spin excitations are one of the top candidates for mediating electron pairing in unconventional superconductors. Their coupling to superconductivity is evident in a large number of systems, by the observation of an abrupt redistribution of magnetic spectral weight at the superconducting transition temperature, T(c), for energies comparable to the superconducting gap. Here we report inelastic neutron scattering measurements on Fe-based superconductors, Fe(1+y-x)(Ni/Cu)(x)Te(0.5)Se(0.5) that emphasize an additional signature. The overall shape of the low energy magnetic dispersion changes from two incommensurate vertical columns at T≫T(c) to a distinctly different U-shaped dispersion at low temperature. Importantly, this spectral reconstruction is apparent for temperatures up to ~3T(c). If the magnetic excitations are involved in the pairing mechanism, their surprising modification on the approach to T(c) demonstrates that strong interactions are involved.

Strong electric and magnetic dipole excitations in deformed nuclei

International Nuclear Information System (INIS)

Kneissl, U.

1993-01-01

Systematic nuclear resonance fluorescence (NRF) experiments have been performed at the bremsstrahlung facility of the Stutgart dynamitron to investigate the distribution of magnetic and electric dipole excitations in deformed nuclei

Soft mode and magnetic phase transition in PrNi

International Nuclear Information System (INIS)

Alekseev, P.A.; Lazukov, V.N.; Sadikov, I.P.; Klement'ev, E.S.; Allenspach, P.; Chumlyakov, Yu.I.

2002-01-01

The spectrum of the magnetic excitation of the PrNi intermetallic compound monocrystal is studied through the neutrons inelastic scattering. Essential softening of certain collective modes of the magnetic excitation near the temperature of the ferromagnetic ordering T c ∼ 20 K is identified. The above result is analyzed from the viewpoint of the model, describing the magnetic phase transition in the systems with the directed magnetic moment [ru

Magnetic excitations in intermediate valence semiconductors with singlet ground state

International Nuclear Information System (INIS)

Kikoin, K.A.; Mishchenko, A.S.

1994-01-01

The explanation of the origin inelastic peaks in magnetic neutron scattering spectra of the mixed-valent semiconductor SmB 6 is proposed. It is shown that the excitonic theory of intermediate valence state not only gives the value of the peak frequency but also explains the unusual angular dependence of intensity of inelastic magnetic scattering and describes the dispersion of magnetic excitations in good agreement with experiment

Inelastic Neutron Scattering Investigations of the Magnetic Excitations

DEFF Research Database (Denmark)

Feile, R; Kjems, Jørgen; Hauser, A.

1984-01-01

The magnetic excitations perpendicular to the antiferromagnetic chains in CsVX3 (X = Cl, Br, I) have been measured in the ordered state by inelastic neutron scattering. The dispersion relations and intensity distributions are those expected for ordinary spin waves in a triangular xy-model....

Hybrid excited claw pole generator with skewed and non-skewed permanent magnets

Science.gov (United States)

Wardach, Marcin

2017-12-01

This article contains simulation results of the Hybrid Excited Claw Pole Generator with skewed and non-skewed permanent magnets on rotor. The experimental machine has claw poles on two rotor sections, between which an excitation control coil is located. The novelty of this machine is existence of non-skewed permanent magnets on claws of one part of the rotor and skewed permanent magnets on the second one. The paper presents the construction of the machine and analysis of the influence of the PM skewing on the cogging torque and back-emf. Simulation studies enabled the determination of the cogging torque and the back-emf rms for both: the strengthening and the weakening of magnetic field. The influence of the magnets skewing on the cogging torque and the back-emf rms have also been analyzed.

Alfven wave excitation in a cavity with a transverse magnetic field

International Nuclear Information System (INIS)

Bures, M.

1982-12-01

A transversely magnetized cylindrical plasma model with an internal rod conductor is used to approximate the FIVA internal ring device of Spherator type with a purely poloidal magnetic field. It is shown that an excitation asymmetry along the plasma column, i.e. with a wave number k sub (z) does not equal 0, introduces a coupling between the magnetoacoustic and shear Alfven waves in the frequency range #betta#<<#betta# sub (ci). The introduction of an equilibrium mass motion along the plasma cylinder introduces a flow continuum. Simultaneously the Alfven resonance frequency becomes Doppler shifted. The experimental observations indicate that cavity modes do not build up in the FIVA device in the case of nonsymmetric excitation. If on the other hand the exciting structure becomes symmetric, i.e. with k sub (z) equals 0, the magnetoacoustic resonance become excited. The resulting Q values are rather low which indicates that the coupling to the shear wave through the Hall electric field cannot be neglected. (Author)

Armature reaction of permanent magnet-excited small dc motors with shell type magnets and possibilities of power increase

Energy Technology Data Exchange (ETDEWEB)

Gutt, H J; Tran, Q N

1983-07-01

Permanent magnet-excited small dc motors allow an increase of power up to 30% compared with present permanent excited motors. The calculation of immediate irreversible demagnetization of the air-gap situated shell type magnets is necessary for a good motor design. Numerical calculated field line plots show the critical zones of the irreversible demagnetization at high armature reaction and refer how to avoid the flux loss and to increase the motor power.

Magnetic Excitations in α-RuCl3

Science.gov (United States)

Nagler, Stephen; Banerjee, Arnab; Bridges, Craig; Yan, Jiaqiang; Mandrus, David; Stone, Matthew; Aczel, Adam; Li, Ling; Yiu, Yuen; Lumsden, Mark; Knolle, Johannes; Moessner, Roderich; Tennant, Alan

2015-03-01

The layered material α-RuCl3 is composed of stacks of weakly coupled honeycomb lattices of octahedrally coordinated Ru3+ ions. The Ru ion ground state has 5 d electrons in the low spin state, with spin-orbit coupling very strong compared to other terms in the single ion Hamiltonian. The material is therefore an excellent candidate for investigating possible Heisenberg-Kitaev physics. In addition, this compound is very amenable to investigation by neutron scattering to explore the magnetic ground state and excitations in detail. Here we discuss new time-of-flight inelastic neutron scattering data on α-RuCl3. A high energy excitation near 200 meV is identified as a transition from the single ion J=1/2 ground state to the J=3/2 excited state, yielding a direct measurement of the spin orbit coupling energy. Higher resolution measurements reveal two collective modes at much lower energy scales. The results are compared with the theoretical expectations for excitations in the Heisenberg - Kitaev model on a honeycomb lattice, and show that Kitaev interactions are important. Research at SNS supported by the DOE BES Scientific User Facilities Division.

Hybrid excited claw pole generator with skewed and non-skewed permanent magnets

Directory of Open Access Journals (Sweden)

Wardach Marcin

2017-12-01

Full Text Available This article contains simulation results of the Hybrid Excited Claw Pole Generator with skewed and non-skewed permanent magnets on rotor. The experimental machine has claw poles on two rotor sections, between which an excitation control coil is located. The novelty of this machine is existence of non-skewed permanent magnets on claws of one part of the rotor and skewed permanent magnets on the second one. The paper presents the construction of the machine and analysis of the influence of the PM skewing on the cogging torque and back-emf. Simulation studies enabled the determination of the cogging torque and the back-emf rms for both: the strengthening and the weakening of magnetic field. The influence of the magnets skewing on the cogging torque and the back-emf rms have also been analyzed.

Compositional trends and magnetic excitations in binary and ternary Fe–Pd–X magnetic shape memory alloys

International Nuclear Information System (INIS)

Gruner, Markus Ernst; Hamann, Sven; Brunken, Hayo; Ludwig, Alfred; Entel, Peter

2013-01-01

Highlights: ► We discuss compositional trends in Fe–Pd–Cu and Fe–Pd–Mn magnetic shape memory alloys. ► We combine density functional theory and combinatorial thin film experiments. ► Magnetic excitations contribute decisively to the structural transformation behavior. -- Abstract: High throughput thin film experiments and first-principles calculations are combined in order to get insight into the relation between finite temperature transformation behavior and structural ground state properties of ternary Fe–Pd–X alloys. In particular, we consider the binding surface, i.e., the energy of the disordered alloy calculated along the Bain path between bcc and fcc which we model by a 108 atom supercell. We compare stoichiometric Fe 75 Pd 25 with ternary systems, where 4.6% of the Fe atoms were substituted by Cu and Mn, respectively. The computational trends are related to combinatorial experiments on thin film libraries for the systems Fe–Pd–Mn and Fe–Pd–Cu which reveal a systematic evolution of the martensitic start temperature with composition within the relevant concentration range for magnetic shape memory (MSM) applications. Our calculations include atomic relaxations, which were shown to be relevant for a correct description of the structural properties. Furthermore, we find that magnetic excitations can substantially alter the binding surface. The comparison of experimental and theoretical trends indicates that, both, compositional changes and magnetic excitations contribute significantly to the structural stability which may thus be tailored by specifically adding antiferromagnetic components

A short model excitation of an asymmetric force free superconducting transmission line magnet

Energy Technology Data Exchange (ETDEWEB)

Wake, M.; Sato, H.; /KEK, Tsukuba; Carcagno, R.; Foster, W.; Hays, S.; Kashikhin, V.; Oleck, A.; Piekarz, H.; Rabehl, R,; /Fermilab

2005-09-01

A short model of asymmetric force free magnet with single beam aperture was tested at Fermilab together with the excitation test of VLHC transmission line magnet. The design concept of asymmetric force free superconducting magnet was verified by the test. The testing reached up to 104 kA current and no indication of force imbalance was observed. Since the model magnet length was only 10cm, A 0.75m model was constructed and tested at KEK with low current to ensure the validity of the design. The cool down and the excitation at KEK were also successful finding very small thermal contraction of the conductor and reasonable field homogeneity.

The millimeter-wave spectrum of highly vibrationally excited SiO

International Nuclear Information System (INIS)

Mollaaghababa, R.; Gottlieb, C.A.; Vrtilek, J.M.; Thaddeus, P.

1991-01-01

The millimeter-wave rotational spectra of SiO in high vibrational states (v = 0-40) in its electronic ground state were measured between 228 and 347 GHz in a laboratory discharge through SiH4 and CO. On ascending the vibrational ladder, populations decline precipitously for the first few levels, with a vibrational temperature of about 1000 K; at v of roughly 3, however, they markedly flatten out, and from there to v of roughly 40 the temperature is of the order of 10,000 K. With the Dunham coefficients determined here, the rotational spectrum of highly vibrationally excited SiO can now be calculated into the far-infrared to accuracies required for radioastronomy. Possible astronomical sources of highly vibrationally excited SiO are certain stellar atmospheres, ultracompact H II regions, very young supernova ejecta, and dense interstellar shocks. 16 refs

Magnetic resonance described in the excitation dependent rotating frame of reference.

Science.gov (United States)

Tahayori, Bahman; Johnston, Leigh A; Mareels, Iven M Y; Farrell, Peter M

2008-01-01

An excitation dependent rotating frame of reference to observe the magnetic resonance phenomenon is introduced in this paper that, to the best of our knowledge, has not been used previously in the nuclear magnetic resonance context. The mathematical framework for this new rotating frame of reference is presented based on time scaling the Bloch equation after transformation to the classical rotating frame of reference whose transverse plane is rotating at the Larmor frequency. To this end, the Bloch equation is rewritten in terms of a magnetisation vector observed from the excitation dependent rotating frame of reference. The resultant Bloch equation is referred to as the time scaled Bloch equation. In the excitation dependent rotating frame of reference whose coordinates are rotating at the instantaneous Rabi frequency the observed magnetisation vector is a much slower signal than the true magnetisation in the rotating frame of reference. As a result the ordinary differential equation solvers have the ability to solve the time scaled version of the Bloch equation with a larger step size resulting in a smaller number of samples for solving the equation to a desired level of accuracy. The simulation results for different types of excitation are presented in this paper. This method may be used in true Bloch simulators in order to reduce the simulation time or increase the accuracy of the numerical solution. Moreover, the time scaled Bloch equation may be employed to determine the optimal excitation pattern in magnetic resonance imaging as well as designing pulses with better slice selectivity which is an active area of research in this field.

Line shape of magnetic excitations in singlet-ground-state systems

International Nuclear Information System (INIS)

Bak, P.

1976-08-01

The excitation spectrum in a paramagnetic singlet doublet system is calculated using a diagrammatic expansion technique, and the theoretical predictions are compared with experiments on praseodymium. The theory gives an accurate description of the dramatic temperature dependence of the energies and lineshapes for the exciton modes

Use of a magnetic force exciter to vibrate a piezocomposite generating element in a small-scale windmill

International Nuclear Information System (INIS)

Luong, Hung Truyen; Goo, Nam Seo

2012-01-01

A piezocomposite generating element (PCGE) can be used to convert ambient vibrations into electrical energy that can be stored and used to power other devices. This paper introduces a design of a magnetic force exciter for a small-scale windmill that vibrates a PCGE to convert wind energy into electrical energy. A small-scale windmill was designed to be sensitive to low-speed wind in urban regions for the purpose of collecting wind energy. The magnetic force exciter consists of exciting magnets attached to the device’s input rotor and a secondary magnet fixed at the tip of the PCGE. The PCGE is fixed to a clamp that can be adjusted to slide on the windmill’s frame in order to change the gap between exciting and secondary magnets. Under an applied wind force, the input rotor rotates to create a magnetic force interaction that excites the PCGE. The deformation of the PCGE enables it to generate electric power. Experiments were performed with different numbers of exciting magnets and different gaps between the exciting and secondary magnets to determine the optimal configuration for generating the peak voltage and harvesting the maximum wind energy for the same range of wind speeds. In a battery-charging test, the charging time for a 40 mA h battery was approximately 3 h for natural wind in an urban region. The experimental results show that the prototype can harvest energy in urban regions with low wind speeds and convert the wasted wind energy into electricity for city use. (paper)

Polarized neutron determination of the magnetic excitations in YBa2Cu3O7

DEFF Research Database (Denmark)

Mook, H.A.; Yethiraj, M.; Aeppli, G.

1993-01-01

Polarization analysis has been used to identify the magnetic excitations in YBa2Cu3O7. The dominant feature in the spectra is a peak at the (pi,pi) reciprocal lattice position and centered at 41 meV. The behavior of the peak is shown to change dramatically at T(c), so that the magnetic excitations...

Mott transition: Low-energy excitations and superconductivity

International Nuclear Information System (INIS)

Ioffe, L.B.; Larkin, A.I.

1988-09-01

It is possible that metal-dielectric transition does not result in changes of magnetic or crystallographic symmetry. In this case a fermionic spectrum is not changed at the transition, but additional low-energy excitations appear which can be described as a gauge field that has the same symmetry as an electromagnetic one. In the case of a non half-filled band gapless scalar Bose excitations also appear. Due to the presence of additional gauge field the physical conductivity is determined by the lowest conductivity of the Fermi or Bose subsystems. (author). 11 refs

Electric excitations in liquid He4 and their role in neutron scattering spectrum

International Nuclear Information System (INIS)

Poluehktov, Yu.M.; Karnatsevich, L.V.

2001-01-01

Data of experiments on excitation spectrum in liquid He 4 by inelastic neutron scattering method are discussed. Exact solution of particle scattering in ideal Bose-gas is given. Influence of inter-particle interactions on the structure of many-particle Bose system is analysed qualitatively. 55 refs., 1 figs

Three types magnetic moment distribution of nonlinear excitations in a Heisenberg helimagnet

Energy Technology Data Exchange (ETDEWEB)

Qi, Jian-Wen [School of Physics, Northwest University, Xi' an 710069 (China); Shaanxi Key Laboratory for Theoretical Physics Frontiers, Xi' an 710069 (China); Li, Zai-Dong [Department of Applied Physics, Hebei University of Technology, Tianjin 300401 (China); Yang, Zhan-Ying, E-mail: zyyang@nwu.edu.cn [School of Physics, Northwest University, Xi' an 710069 (China); Shaanxi Key Laboratory for Theoretical Physics Frontiers, Xi' an 710069 (China); Yang, Wen-Li [Shaanxi Key Laboratory for Theoretical Physics Frontiers, Xi' an 710069 (China); Institute of Modern Physics, Northwest University, Xi' an 710069 (China)

2017-06-15

Highlights: • Three different types of soliton excitations under the spin-wave background are demonstrated in spin chain system. • The magnetic moment distributions corresponding to these solitons are characterized in detail. • The formation mechanisms of those excitations are explained by the magnon density distribution. - Abstract: We study the nonlinear spin dynamics of an anisotropic Heisenberg helimagnet in a fourth-order integrable nonlinear Schrödinger equation. We demonstrate that there are three types of nonlinear spin excitations on a spin-wave background in the Heisenberg helimagnet, notably including anti-dark soliton, W-shaped soliton, and multi-peak soliton. The magnetic moment distribution that corresponds to each of these are characterized in detail. Additionally, the formation mechanism is clarified by the magnon density distribution.

Exponential Frequency Spectrum in Magnetized Plasmas

International Nuclear Information System (INIS)

Pace, D. C.; Shi, M.; Maggs, J. E.; Morales, G. J.; Carter, T. A.

2008-01-01

Measurements of a magnetized plasma with a controlled electron temperature gradient show the development of a broadband spectrum of density and temperature fluctuations having an exponential frequency dependence at frequencies below the ion cyclotron frequency. The origin of the exponential frequency behavior is traced to temporal pulses of Lorentzian shape. Similar exponential frequency spectra are also found in limiter-edge plasma turbulence associated with blob transport. This finding suggests a universal feature of magnetized plasma turbulence leading to nondiffusive, cross-field transport, namely, the presence of Lorentzian shaped pulses

Micromagnetic simulation of energy consumption and excited eigenmodes in elliptical nanomagnetic switches

International Nuclear Information System (INIS)

Carlotti, G.; Madami, M.; Gubbiotti, G.; Tacchi, S.

2014-01-01

Sub-200 nm patterned magnetic dots are key elements for the design of magnetic switches, memory cells or elementary units of nanomagnetic logic circuits. In this paper, we analyse by micromagnetic simulations the magnetization reversal, the dissipated energy and the excited spin eigenmodes in bistable magnetic switches, consisting of elliptical nanodots with 100×60 nm lateral dimensions. Two different strategies for reversal are considered and the relative results compared: (i) the irreversible switching obtained by the application of an external field along the easy axis, in the direction opposite to the initial magnetization; (ii) the precessional switching accomplished by the application of a short magnetic field pulse, oriented perpendicular to the initial magnetization direction. The obtained results are discussed in terms of deviation from the macrospin behavior, energy dissipation and characteristics of the spectrum of spin eigenmodes excited during the magnetization reversal process

Magnetic Excitations in Cu2Fe2Ge4O13

International Nuclear Information System (INIS)

Masuda, Takatsugu; Zheludev, Andrey I.; Sales, Brian C.; Imai, S.; Uchinokura, K.

2005-01-01

Magnetic excitations in the cooperative ordered state in a weakly coupled Fe chains and Cu dimers compound Cu 2 Fe 2 Ge 4 O 13 is studied by thermal neutron scattering technique. We show that the low energy excitations up to 10 meV in wide q range are well described by spin wave theory of weakly coupled Fe chains. In higher energy range a narrow band excitation that can be associated with Cu dimers is observed at ℎω-24 meV. Both types of excitations can be understood by treating the weak coupling between Fe chains and Cu dimers at the level of Mean Field/Random Phase Approximation.

Tunable spin waves in diluted magnetic semiconductor nanoribbon

Science.gov (United States)

Lyu, Pin; Zhang, Jun-Yi

2018-01-01

The spin wave excitation spectrum in diluted magnetic semiconductor (DMS) nanoribbons was calculated by taking account of the quantum confinement effect of carriers and spin waves. By introducing the boundary condition for the spin waves, we derived the spin wave dispersion using the path-integral formulation and Green's function method. It was shown that the spin wave excitation spectrum is discrete due to the confinement effect and strongly dependent on the carrier density, the magnetic ion density, and the width of the nanoribbon. When the width of the nanoribbon is beyond the typical nanoscales, the size effect on the excitation energies of the spin waves disappears in our calculation, which is in qualitative agreement with no obvious size effect observed in the as-made nanodevices of (Ga,Mn)As in this size regime. Our results provide a potential way to control the spin waves in the DMS nanoribbon not only by the carrier density and the magnetic ion density but also by the nanostructure geometry.

Dissociative Excitation of Acetylene Induced by Electron Impact: Excitation-emission Cross-sections

Energy Technology Data Exchange (ETDEWEB)

Országh, Juraj; Danko, Marián; Čechvala, Peter; Matejčík, Štefan, E-mail: matejcik@fmph.uniba.sk [Department of Experimental Physics, Faculty of Mathematics, Physics and Informatics, Comenius University in Bratislava, Mlynská dolina F-2, 842 48 Bratislava (Slovakia)

2017-05-20

The optical emission spectrum of acetylene excited by monoenergetic electrons was studied in the range of 190–660 nm. The dissociative excitation and dissociative ionization associated with excitation of the ions initiated by electron impact were dominant processes contributing to the spectrum. The spectrum was dominated by the atomic lines (hydrogen Balmer series, carbon) and molecular bands (CH(A–X), CH(B–X), CH{sup +}(B–A), and C{sub 2}). Besides the discrete transitions, we have detected the continuum emission radiation of ethynyl radical C{sub 2}H(A–X). For most important lines and bands of the spectrum we have measured absolute excitation-emission cross sections and determined the energy thresholds of the particular dissociative channels.

The spectrum of massive excitations of 3d 3-state Potts model and universality

International Nuclear Information System (INIS)

Falcone, R.; Fiore, R.; Gravina, M.; Papa, A.

2007-01-01

We consider the mass spectrum of the 3d 3-state Potts model in the broken phase (a) near the second order Ising critical point in the temperature-magnetic field plane and (b) near the weakly first order transition point at zero magnetic field. In the case (a), we compare the mass spectrum with the prediction from universality of mass ratios in the 3d Ising class; in the case (b), we determine a mass ratio to be compared with the corresponding one in the spectrum of screening masses of the (3+1)d SU(3) pure gauge theory at finite temperature in the deconfined phase near the transition. The agreement in the comparison in the case (a) would represent a non-trivial test of validity of the conjecture of spectrum universality. A positive answer to the comparison in the case (b) would suggest the possibility to extend this conjecture to weakly first order phase transitions

Polarized Fine Structure in the Photoluminescence Excitation Spectrum of a Negatively Charged Quantum Dot

Science.gov (United States)

Ware, M. E.; Stinaff, E. A.; Gammon, D.; Doty, M. F.; Bracker, A. S.; Gershoni, D.; Korenev, V. L.; Bădescu, Ş. C.; Lyanda-Geller, Y.; Reinecke, T. L.

2005-10-01

We report polarized photoluminescence excitation spectroscopy of the negative trion in single charge-tunable InAs/GaAs quantum dots. The spectrum exhibits a p-shell resonance with polarized fine structure arising from the direct excitation of the electron spin triplet states. The energy splitting arises from the axially symmetric electron-hole exchange interaction. The magnitude and sign of the polarization are understood from the spin character of the triplet states and a small amount of quantum dot asymmetry, which mixes the wave functions through asymmetric e-e and e-h exchange interactions.

D0-D4 brane tachyon condensation to a BPS state and its excitation spectrum in noncommutative super Yang-Mills theory

International Nuclear Information System (INIS)

Wimmer, Robert

2005-01-01

We investigate the D0-D4-brane system for different B-field backgrounds including the small instanton singularity in noncommutative SYM theory. We discuss the excitation spectrum of the unstable state as well as for the BPS D0-D4 bound state. We compute the tachyon potential which reproduces the complete mass defect. The relevant degrees of freedom are the massless (4,4) strings. Both results are in contrast with existing string field theory calculations. The excitation spectrum of the small instanton is found to be equal to the excitation spectrum of the fluxon solution on R θ 2 x R which we trace back to T-duality. For the effective theory of the (0,0) string excitations we obtain a BFSS matrix model. The number of states in the instanton background changes significantly when the B-field becomes self-dual. This leads us to the proposal of the existence of a phase transition or cross over at self-dual B-field

Magnetic excitations and exchange interactions in the spin-gap system TlCuCl sub 3

CERN Document Server

Oosawa, A; Kato, T; Kakurai, K; Müller, M; Mikeska, H J

2002-01-01

The magnetic excitations from the gapped ground state in TlCuCl sub 3 have been investigated by means of inelastic neutron scattering experiments. The excitation data were collected along four different directions in the a sup * -c sup * plane. A well-defined single magnetic excitation mode was observed. The lowest excitation occurs at Q=(h,0,l) with integer h and odd l, as observed in KCuCl sub 3. The dispersion relations were analyzed by the cluster-series expansion up to the sixth order, so that the individual exchange interactions were evaluated. It was demonstrated that TlCuCl sub 3 is a strongly coupled spin-dimer system. (orig.)

Shaped excitation current for synchrotron magnets

International Nuclear Information System (INIS)

Foss, M.; Praeg, W.

1981-01-01

A 500-MeV synchrotron at Argonne National Laboratory (ANL) operates at 30 Hz with its beam spill locked to neutron choppers with a precision of +- 0.5 μs. The average beam will be increased by running the magnets at 45 Hz. Three 45-Hz circuits are discussed which differ greatly in overall cost and complexity. The first is a conventional 45-Hz sine wave circuit. The reduction in time for beam acceleration results in a costly increase in peak rf power. This problem is avoided in the other two circuits by making the field rise slowly and fall rapidly. The second circuit discussed is resonant at 45 Hz and 90 Hz. Exciting this circuit with a mixture of dc, 45 Hz, and 90 Hz can produce a magnetic field with the same maximum dB/dt as the present 30-Hz field. A third, and possibly least expensive, solution is a novel circuit which produces 30 Hz during acceleration and 90 Hz when the magnets are reset. The rf requirements are, of course, identical to present requirements during acceleration. Circuit details are given

Magnetic excitations of Nd in Nd{sub 2-x}Ce{sub x}CuO{sub 4} (x=0,0.09,0.13)

Energy Technology Data Exchange (ETDEWEB)

Henggeler, W.; Furrer, A. [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Chattopadyay, T.; Roessli, B. [Institut Max von Laue - Paul Langevin, 75 - Paris (France); Vorderwisch, P. [Hahn-Meitner-Institut Berlin GmbH (Germany); Thalmeier, P. [MPI Dresden (Germany)

1997-09-01

We have studied the wave vector dependence of the magnetic excitation spectrum of Nd in Nd{sub 2-x}Ce{sub x}CuO{sub 4} (x=0,0.09,0.13) by inelastic neutron scattering experiments on single crystals. The results are analyzed with the help of model calculations which are performed in the context of the mean field random-phase approximation. This enables us to obtain direct information on the coupling constants between the rare earth ions. (author) 1 fig., 2 refs.

A full-spectrum analysis of high-speed train interior noise under multi-physical-field coupling excitations

Science.gov (United States)

Zheng, Xu; Hao, Zhiyong; Wang, Xu; Mao, Jie

2016-06-01

High-speed-railway-train interior noise at low, medium, and high frequencies could be simulated by finite element analysis (FEA) or boundary element analysis (BEA), hybrid finite element analysis-statistical energy analysis (FEA-SEA) and statistical energy analysis (SEA), respectively. First, a new method named statistical acoustic energy flow (SAEF) is proposed, which can be applied to the full-spectrum HST interior noise simulation (including low, medium, and high frequencies) with only one model. In an SAEF model, the corresponding multi-physical-field coupling excitations are firstly fully considered and coupled to excite the interior noise. The interior noise attenuated by sound insulation panels of carriage is simulated through modeling the inflow acoustic energy from the exterior excitations into the interior acoustic cavities. Rigid multi-body dynamics, fast multi-pole BEA, and large-eddy simulation with indirect boundary element analysis are first employed to extract the multi-physical-field excitations, which include the wheel-rail interaction forces/secondary suspension forces, the wheel-rail rolling noise, and aerodynamic noise, respectively. All the peak values and their frequency bands of the simulated acoustic excitations are validated with those from the noise source identification test. Besides, the measured equipment noise inside equipment compartment is used as one of the excitation sources which contribute to the interior noise. Second, a full-trimmed FE carriage model is firstly constructed, and the simulated modal shapes and frequencies agree well with the measured ones, which has validated the global FE carriage model as well as the local FE models of the aluminum alloy-trim composite panel. Thus, the sound transmission loss model of any composite panel has indirectly been validated. Finally, the SAEF model of the carriage is constructed based on the accurate FE model and stimulated by the multi-physical-field excitations. The results show

Magnetic Excitations and Continuum of a Possibly Field-Induced Quantum Spin Liquid in α-RuCl_{3}.

Science.gov (United States)

Wang, Zhe; Reschke, S; Hüvonen, D; Do, S-H; Choi, K-Y; Gensch, M; Nagel, U; Rõõm, T; Loidl, A

2017-12-01

We report on terahertz spectroscopy of quantum spin dynamics in α-RuCl_{3}, a system proximate to the Kitaev honeycomb model, as a function of temperature and magnetic field. We follow the evolution of an extended magnetic continuum below the structural phase transition at T_{s2}=62  K. With the onset of a long-range magnetic order at T_{N}=6.5  K, spectral weight is transferred to a well-defined magnetic excitation at ℏω_{1}=2.48  meV, which is accompanied by a higher-energy band at ℏω_{2}=6.48  meV. Both excitations soften in a magnetic field, signaling a quantum phase transition close to B_{c}=7  T, where a broad continuum dominates the dynamical response. Above B_{c}, the long-range order is suppressed, and on top of the continuum, emergent magnetic excitations evolve. These excitations follow clear selection rules and exhibit distinct field dependencies, characterizing the dynamical properties of a possibly field-induced quantum spin liquid.

Repetitive transcranial magnetic stimulation for hallucination in schizophrenia spectrum disorders: A meta-analysis.

Science.gov (United States)

Zhang, Yingli; Liang, Wei; Yang, Shichang; Dai, Ping; Shen, Lijuan; Wang, Changhong

2013-10-05

This study assessed the efficacy and tolerability of repetitive transcranial magnetic stimulation for treatment of auditory hallucination of patients with schizophrenia spectrum disorders. Online literature retrieval was conducted using PubMed, ISI Web of Science, EMBASE, Medline and Cochrane Central Register of Controlled Trials databases from January 1985 to May 2012. Key words were "transcranial magnetic stimulation", "TMS", "repetitive transcranial magnetic stimulation", and "hallucination". Selected studies were randomized controlled trials assessing therapeutic efficacy of repetitive transcranial magnetic stimulation for hallucination in patients with schizophrenia spectrum disorders. Experimental intervention was low-frequency repetitive transcranial magnetic stimulation in left temporoparietal cortex for treatment of auditory hallucination in schizophrenia spectrum disorders. Control groups received sham stimulation. The primary outcome was total scores of Auditory Hallucinations Rating Scale, Auditory Hallucination Subscale of Psychotic Symptom Rating Scale, Positive and Negative Symptom Scale-Auditory Hallucination item, and Hallucination Change Scale. Secondary outcomes included response rate, global mental state, adverse effects and cognitive function. Seventeen studies addressing repetitive transcranial magnetic stimulation for treatment of schizophrenia spectrum disorders were screened, with controls receiving sham stimulation. All data were completely effective, involving 398 patients. Overall mean weighted effect size for repetitive transcranial magnetic stimulation versus sham stimulation was statistically significant (MD = -0.42, 95%CI: -0.64 to -0.20, P = 0.000 2). Patients receiving repetitive transcranial magnetic stimulation responded more frequently than sham stimulation (OR = 2.94, 95%CI: 1.39 to 6.24, P = 0.005). No significant differences were found between active repetitive transcranial magnetic stimulation and sham stimulation for

Thermal chiral vortical and magnetic waves: New excitation modes in chiral fluids

Energy Technology Data Exchange (ETDEWEB)

Kalaydzhyan, Tigran, E-mail: tigran@caltech.edu [Department of Physics, University of Illinois, 845 W Taylor Street, Chicago, IL 60607 (United States); Jet Propulsion Laboratory, 4800 Oak Grove Dr, M/S 298, Pasadena, CA 91109 (United States); Murchikova, Elena [TAPIR, California Institute of Technology, MC 350-17, Pasadena, CA 91125 (United States)

2017-06-15

In certain circumstances, chiral (parity-violating) medium can be described hydrodynamically as a chiral fluid with microscopic quantum anomalies. Possible examples of such systems include strongly coupled quark–gluon plasma, liquid helium {sup 3}He-A, neutron stars and the Early Universe. We study first-order hydrodynamics of a chiral fluid on a vortex background and in an external magnetic field. We show that there are two previously undiscovered modes describing heat waves propagating along the vortex and magnetic field. We call them the Thermal Chiral Vortical Wave and Thermal Chiral Magnetic Wave. We also identify known gapless excitations of density (chiral vortical and chiral magnetic waves) and transverse velocity (chiral Alfvén wave). We demonstrate that the velocity of the chiral vortical wave is zero, when the full hydrodynamic framework is applied, and hence the wave is absent and the excitation reduces to the charge diffusion mode. We also comment on the frame-dependent contributions to the obtained propagation velocities.

Thermal chiral vortical and magnetic waves: New excitation modes in chiral fluids

International Nuclear Information System (INIS)

Kalaydzhyan, Tigran; Murchikova, Elena

2017-01-01

In certain circumstances, chiral (parity-violating) medium can be described hydrodynamically as a chiral fluid with microscopic quantum anomalies. Possible examples of such systems include strongly coupled quark–gluon plasma, liquid helium "3He-A, neutron stars and the Early Universe. We study first-order hydrodynamics of a chiral fluid on a vortex background and in an external magnetic field. We show that there are two previously undiscovered modes describing heat waves propagating along the vortex and magnetic field. We call them the Thermal Chiral Vortical Wave and Thermal Chiral Magnetic Wave. We also identify known gapless excitations of density (chiral vortical and chiral magnetic waves) and transverse velocity (chiral Alfvén wave). We demonstrate that the velocity of the chiral vortical wave is zero, when the full hydrodynamic framework is applied, and hence the wave is absent and the excitation reduces to the charge diffusion mode. We also comment on the frame-dependent contributions to the obtained propagation velocities.

Thermal chiral vortical and magnetic waves: New excitation modes in chiral fluids

Directory of Open Access Journals (Sweden)

Tigran Kalaydzhyan

2017-06-01

Full Text Available In certain circumstances, chiral (parity-violating medium can be described hydrodynamically as a chiral fluid with microscopic quantum anomalies. Possible examples of such systems include strongly coupled quark–gluon plasma, liquid helium 3He-A, neutron stars and the Early Universe. We study first-order hydrodynamics of a chiral fluid on a vortex background and in an external magnetic field. We show that there are two previously undiscovered modes describing heat waves propagating along the vortex and magnetic field. We call them the Thermal Chiral Vortical Wave and Thermal Chiral Magnetic Wave. We also identify known gapless excitations of density (chiral vortical and chiral magnetic waves and transverse velocity (chiral Alfvén wave. We demonstrate that the velocity of the chiral vortical wave is zero, when the full hydrodynamic framework is applied, and hence the wave is absent and the excitation reduces to the charge diffusion mode. We also comment on the frame-dependent contributions to the obtained propagation velocities.

Imaging Magnetic Vortices Dynamics Using Lorentz Electron Microscopy with GHz Excitations

Science.gov (United States)

Zhu, Yimei

2015-03-01

Magnetic vortices in thin films are naturally formed spiral spin configurations with a core polarization pointing out of the film plane. They typically represent ground states with high structural and thermal stability as well as four different chirality-polarity combinations, offering great promise in the development of spin-based devices. For applications to spin oscillators, non-volatile memory and logic devices, the fundamental understanding and precise control of vortex excitations and dynamic switching behavior are essential. The compact dimensionality and fast spin dynamics set grand challenges for direct imaging technologies. Recently, we have developed a unique method to directly visualize the dynamic magnetic vortex motion using advanced Lorentz electron microscopy combined with GHz electronic excitations. It enables us to map the orbit of a magnetic vortex core in a permalloy square with modality. Our approach is complementary to X-ray magnetic circular dichroism and is of general interest to the magnetism community as it paves a way to study fundamental spin phenomena with unprecedented resolution and accuracy. Collaborations with S.D. Pollard, J.F. Pulecio, D.A. Arena and K.S. Buchanan are acknowledged. Work supported by DOE-BES, Material Sciences and Engineering Division, under Contract No. DE-AC02-98CH10886.

High-frequency domain wall excitations in magnetic garnet films with in-plane magnetization

International Nuclear Information System (INIS)

Synogach, V.T.; Doetsch, H.

1996-01-01

Magnetic garnet films of compositions (YBi) 3 Fe 5 O 12 and (LuBi) 3 Fe 5 O 12 are grown by liquid-phase epitaxy on [110]- and [100]-oriented substrates of gadolinium gallium garnet, respectively. All films have in-plane magnetization. 180 degree and 90 degree domain walls in these films are studied by microwave technique. In addition to the known low-frequency mode of wall translation new multiple resonant modes of both 90 degree and 180 degree domain walls with very small linewidth (4.2 MHz) are observed at frequencies near 1 GHz. Resonances are effectively excited by an rf magnetic field which is parallel or perpendicular to the wall plane. Resonance frequencies are shown to have nonlinear dispersion dependence on the mode number: they decrease with increasing in-plane magnetic field normal to the wall plane. copyright 1996 The American Physical Society

The effect of a neutrino magnetic moment on nuclear excitation processes

International Nuclear Information System (INIS)

Dodd, A.C.; Papageorgiu, E.; Ranfone, S.

1991-01-01

It is shown that the MeV-range neutrinos with a magnetic moment of ≅ 10 -11 Bohr magnetons would excite nuclei, like 12 C, with cross sections comparable to those obtained in the Standard Model. This implies the possibility of improving the present experimental bounds on the magnetic moment of any flavour of neutrinos by one order of magnitude. Such a magnetic moment would also enhance the coherent neutrino-nuclear scattering in low-temperature detectors, enabling them to set comparable limits. (author)

Effect of magnetic field on the impurity binding energy of the excited ...

Indian Academy of Sciences (India)

The effect of external magnetic field on the excited state energies in a spherical quantum dot was studied. The impurity energy and binding energy were calculated using the variational method within the effective mass approximation and finite barrier potential. The results showed that by increasing the magnetic field, the ...

Effect of magnetic field on the impurity binding energy of the excited ...

Indian Academy of Sciences (India)

Abstract. The effect of external magnetic field on the excited state energies in a spher- ical quantum dot was studied. The impurity energy and binding energy were calculated using the variational method within the effective mass approximation and finite barrier potential. The results showed that by increasing the magnetic ...

Multi-photon excited luminescence of magnetic FePt core-shell nanoparticles.

Science.gov (United States)

Seemann, K M; Kuhn, B

2014-07-01

We present magnetic FePt nanoparticles with a hydrophilic, inert, and biocompatible silico-tungsten oxide shell. The particles can be functionalized, optically detected, and optically manipulated. To show the functionalization the fluorescent dye NOPS was bound to the FePt core-shell nanoparticles with propyl-triethoxy-silane linkers and fluorescence of the labeled particles were observed in ethanol (EtOH). In aqueous dispersion the NOPS fluorescence is quenched making them invisible using 1-photon excitation. However, we observe bright luminescence of labeled and even unlabeled magnetic core-shell nanoparticles with multi-photon excitation. Luminescence can be detected in the near ultraviolet and the full visible spectral range by near infrared multi-photon excitation. For optical manipulation, we were able to drag clusters of particles, and maybe also single particles, by a focused laser beam that acts as optical tweezers by inducing an electric dipole in the insulated metal nanoparticles. In a first application, we show that the luminescence of the core-shell nanoparticles is bright enough for in vivo multi-photon imaging in the mouse neocortex down to cortical layer 5.

Magnetic excitations and amplitude fluctuations in insulating cuprates

Science.gov (United States)

Chelwani, N.; Baum, A.; Böhm, T.; Opel, M.; Venturini, F.; Tassini, L.; Erb, A.; Berger, H.; Forró, L.; Hackl, R.

2018-01-01

We present results from light scattering experiments on three insulating antiferromagnetic cuprates, YBa2Cu3O6.05 , Bi2Sr2YCu2O8 +δ , and La2CuO4 as a function of polarization and excitation energy using samples of the latest generation. From the raw data we derive symmetry-resolved spectra. The spectral shape in B1 g symmetry is found to be nearly universal and independent of excitation energy. The spectra agree quantitatively with predictions by field theory [Eur. Phys. J. B 88, 237 (2015), 10.1140/epjb/e2015-60438-1] facilitating the precise extraction of the Heisenberg coupling J . In addition, the asymmetric lineshape on the high-energy side is found to be related to amplitude fluctuations of the magnetization. In La2CuO4 alone, minor contributions from resonance effects may be identified. The spectra in the other symmetries are not universal. The variations may be traced back to weak resonance effects and extrinsic contributions. For all three compounds we find support for the existence of chiral excitations appearing as a continuum in A2 g symmetry having an onset slightly below 3 J . In La2CuO4 an additional isolated excitation appears on top of the A2 g continuum.

Modeling of Self-Excited Isolated Permanent Magnet Induction Generator Using Iterative Numerical Method

Directory of Open Access Journals (Sweden)

Mohamed Mostafa R.

2016-01-01

Full Text Available Self-Excited Permanent Magnet Induction Generator (PMIG is commonly used in wind energy generation systems. The difficulty of Self-Excited Permanent Magnet Induction Generator (SEPMIG modeling is the circuit parameters of the generator vary at each load conditions due to the a change in the frequency and stator voltage. The paper introduces a new modeling for SEPMIG using Gauss-sidle relaxation method. The SEPMIG characteristics using the proposed method are studied at different load conditions according to the wind speed variation, load impedance changes and different shunted capacitor values. The system modeling is investigated due to the magnetizing current variation, the efficiency variation, the power variation and power factor variation. The proposed modeling system satisfies high degree of simplicity and accuracy.

Magnetic excitations in (VO)HPO4· 1/2 H2O

International Nuclear Information System (INIS)

Garrett, A.W.; Nagler, S.E.; Tennant, D.A.

1997-01-01

The magnetic excitations of an antiferromagnetic spin dimer system, (VO)HPO 4 · 1/2 H 2 O, are examined using inelastic neutron scattering. A dispersionless mode is found, consistent with expectations for a dimer excitation. The intensity variation of the mode reveals a V 4+ - V 4+ dimer separation of 4.43 angstrom, almost 50% larger than the originally expected length

Dispersion Relations for Magnetic Excitons in NdAl2

DEFF Research Database (Denmark)

Houmann, Jens Christian Gylden; Bak, P.; Purwins, H. -G.

1974-01-01

The magnetic excitation spectrum in NdAl2 has been measured by means of inelastic neutron scattering at 5.3K for momentum transfer in the (110) direction. Several excitation branches are observed and discussed in terms of a hamiltonian including an isotropic Heisenberg exchange interaction...

Interplay between magnetism and superconductivity in iron based high temperature superconductors

International Nuclear Information System (INIS)

Price, Stephen

2013-01-01

In this thesis, magnetic properties of a series of different Fe-based superconducting materials have been studied by means of neutron scattering techniques. Magnetic correlations in underdoped Ba(Fe 0.95 Co 0.05 ) 2 As 2 have been investigated for three phases of the phase diagram. It was possible to detect the spin gap and spin resonance signal, two features of the particle hole excitation spectrum at Q=(0.5,0.5,0), characteristic for the superconducting phase. The spin wave excitations present in the ordered phase have been analyzed quantitatively in terms of a linear spin wave model, whereas a spin diffusion model was applied to the collective excitations of the paramagnetic phase. However, it was found that both models can be applied to excitations in all three phases. In optimally doped CaFe 0.88 Co 0.12 AsF, a spin resonance signal was detected as part of the spin excitation spectrum at Q=(0.5,0.5,0). The observation of the spin resonance signal supports the s ± symmetry of the superconducting gap function. In the undoped CaFeAsF compound three dimensional spin wave like excitations of the static Fe-SDW order have been observed at Q AFM =(0.5,0.5,0.5), for temperatures below T N . Above T N and for energies below 20 meV, the spin wave like excitations are replaced by short range two dimensional paramagnetic excitations, which persist up to 270 K. In superconducting FeSe 0.5 Te 0.5 polarized neutron scattering investigations revealed the magnetic nature of the spin resonance signal and the excitation spectrum at Q=(0.5,0.5,0) up to 30 meV. The whole excitation spectrum including the spin resonance signal consists of an isotropic distribution of spin excitations with magnetic moments fluctuating in the ab-plane and perpendicular to the ab-plane, χ ab ''(Q,ω)∼χ c ''(Q,ω). In Eu(Fe 1-x Co x ) 2 As 2 and EuFe 2 (As 1-x P x ) 2 the effect of impurity doping on the static order of the magnetic lattice of the Eu 2+ -moments has been studied by means of

Repetitive transcranial magnetic stimulation for hallucination in schizophrenia spectrum disorders A meta-analysis***

Institute of Scientific and Technical Information of China (English)

Yingli Zhang; Wei Liang; Shichang Yang; Ping Dai; Lijuan Shen; Changhong Wang

2013-01-01

OBJECTIVE: This study assessed the efficacy and tolerability of repetitive transcranial magnetic stimulation for treatment of auditory hal ucination of patients with schizophrenia spectrum disorders. DATA SOURCES: Online literature retrieval was conducted using PubMed, ISI Web of Science, EMBASE, Medline and Cochrane Central Register of Control ed Trials databases from January 1985 to May 2012. Key words were “transcranial magnetic stimulation”, “TMS”, “repetitive transcranial magnetic stimulation”, and “hal ucination”. STUDY SELECTION: Selected studies were randomized control ed trials assessing therapeutic ef-ficacy of repetitive transcranial magnetic stimulation for hal ucination in patients with schizophrenia spectrum disorders. Experimental intervention was low-frequency repetitive transcranial magnetic stimulation in left temporoparietal cortex for treatment of auditory hal ucination in schizophrenia spectrum disorders. Control groups received sham stimulation. MAIN OUTCOME MEASURES: The primary outcome was total scores of Auditory Hal ucinations Rating Scale, Auditory Hal ucination Subscale of Psychotic Symptom Rating Scale, Positive and Negative Symptom Scale-Auditory Hal ucination item, and Hal ucination Change Scale. Secondary outcomes included response rate, global mental state, adverse effects and cognitive function. RESULTS: Seventeen studies addressing repetitive transcranial magnetic stimulation for treatment of schizophrenia spectrum disorders were screened, with controls receiving sham stimulation. Al data were completely effective, involving 398 patients. Overal mean weighted effect size for repeti-tive transcranial magnetic stimulation versus sham stimulation was statistical y significant (MD =-0.42, 95%CI: -0.64 to -0.20, P = 0.000 2). Patients receiving repetitive transcranial magnetic stimulation responded more frequently than sham stimulation (OR = 2.94, 95%CI: 1.39 to 6.24, P =0.005). No significant differences were found

Magnetic excitations in modulated PrNi2Si2

International Nuclear Information System (INIS)

Blanco, J.A.; Nicklow, R.M.; Schmitt, D.

1994-01-01

The magnetic excitations in a single crystal of PrNi 2 Si 2 have been studied by inelastic neutron scattering. Dispersion curves have been followed through the centered tetragonal Brillouin zone. In the paramagnetic phase, at 39 K, the lowest energy magnetic branch exhibits an important dispersion ranging from 1.9 to 3.5 meV, the minimum energy occuring at the wave vector of the ordered phase; from the observed dispersion the inter-ionic isotropic bilinear exchange parameters are deduced. At 4.2 K, in the modulated phase, the same branch presents a dispersion slightly larger, but not significantly different

Ultrasensitive magnetometers based on rotational magnetic excitation

International Nuclear Information System (INIS)

Hristoforou, E.; Svec, P. Sr.

2014-01-01

Three new types of fluxgate magnetometers are presented in this paper, able to monitor the three components of the ambient field, all of them based on the principle of rotational excitation field. The first type is based on Yttrium- Iron Garnet (YIG) single crystal film, magnetized with rotational field on its plane, where the 2"n"d, 4"t"h and 6"t"h harmonics offer the three components of the ambient field with sensitivity better than 1 pT at 0.2 Hz, its size being 25 cm"3. The second type is based on permalloy film, where the rotational excitation field on its plane offers change of magnetoresistance with sensitivity better than 10 pT at 1 Hz, uncertainty of 1 ppm and size ∼ 8 cm"3. The third type, is based on amorphous film, where the rotation field mode offer sensitivity better than 100 pT at 1 Hz, uncertainty of 10 ppm and size ∼ 10 mm"3. (authors)

Study of resonant magnet exciting system for the 3 GeV proton synchrotron

Energy Technology Data Exchange (ETDEWEB)

Koseki, Shoichiro; Zhang, Fengqing; Watanabe, Yasuhiro; Tani, Norio [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment; Adachi, Toshikazu; Someya, Hirohiko [High Energy Accelerator Research Organization, Tsukuba, Ibaraki (Japan)

2001-07-01

Exciting system for magnets of the 3 GeV Proton synchrotron is under consideration. A resonant exciting system is studied, and two type of power supply are compared. One is a parallel supply that is used generally. Another is a modified series supply. Either of them uses IGBT sinusoidal converters. Capacity of the power converter of the series supply for bending magnets becomes 28.8 MVAp. This is lager more than twice compared with the parallel supply. In the other hand, the series supply has good control performance and flexibility. More study is necessary to decide finally. (author)

Formation of spectrum of accelerated particles and the hydromagnetic turbulence in the variable magnetic field

International Nuclear Information System (INIS)

Savane, Y. Sy; Diaby, I.; Faza Barry, M.; Lomonossov, V.

2002-11-01

We study the acceleration of charged particles by the variable magnetic field. The study is based on the determination of spectrum of accelerated particles and the spectrum of hydro magnetic turbulence. We plan the self-consistent system of equation and we also find out the solution of the system for the spectrum of particles and hydro magnetic turbulence with the conditions of effective acceleration in the cosmic space of solar system. (author)

Dissociative Excitation of Thymine by Electron Impact

Science.gov (United States)

McConkey, William; Tiessen, Collin; Hein, Jeffrey; Trocchi, Joshuah; Kedzierski, Wladek

2014-05-01

A crossed electron-gas beam system coupled to a VUV spectrometer has been used to investigate the dissociation of thymine (C5H6N2O2) into excited atomic fragments in the electron-impact energy range from threshold to 375 eV. A special stainless steel oven is used to vaporize the thymine and form it into a beam where it is intersected by a magnetically collimated electron beam, typical current 50 μA. The main features in the spectrum are the H Lyman series lines. The probability of extracting excited C or N atoms from the ring is shown to be very small. In addition to spectral data, excitation probability curves as a function of electron energy will be presented for the main emission features. Possible dissociation channels and excitation mechanisms in the parent molecule will be discussed. The authors thank NSERC (Canada) for financial support.

A Hybrid Excited Machine with Flux Barriers and Magnetic Bridges

Directory of Open Access Journals (Sweden)

Marcin Wardach

2018-03-01

Full Text Available In this paper, an U-shape flux barrier rotor concept for a hybrid excited synchronous machine with flux magnetic bridges fixed on the rotor is presented. Using 3D finite element analysis, the influence of axial flux bridges on the field-weakening and -strengthening characteristics, electromagnetic torque, no-load magnetic flux linkage, rotor iron losses and back electromotive force is shown. Three different rotor designs are analyzed. Furthermore, the field control characteristics depending on additional DC control coil currents are shown.

Excitation of propagating magnetization waves by microstrip antennas

Science.gov (United States)

Dmitriev, V. F.; Kalinikos, B. A.

1988-11-01

We discuss the self-consistent theory of excitation of dipole-exchange magnetization waves by microstrip antennas in a metal-dielectric-ferrite-dielectric-metal stratified structure, magnetized under an arbitrary angle to the surface. Spin-wave Green's functions are derived, describing the response of the spin-system to a spatially inhomogeneous varying magnetic field. The radiative resistance of microstrip antenna is calculated. In this case the distribution of surface current density in the antenna is found on the basis of the analytic solution of a singular integral equation. The nature of the effect of metallic screens and redistributed surface current densities in the antenna on the frequency dependence of the resistive radiation is investigated. Approximate relations are obtained, convenient for practical calculations of radiative resistance of microstrip antennas both in a free and in a screened ferromagnetic film. The theoretical calculations are verified by data of experiments carried out on monocrystalline films of iron-yttrium garnet.

The far-UV spectrum of the low-excitation planetary nebula HD 138403

OpenAIRE

Surdej, Jean; Heck, A.

1982-01-01

Two high-resolution far-UV spectra of the low-excitation planetary nebula HD 138403 are analyzed which were obtained with the IUE satellite over the wavelength range from 1170 to 2070 A. It is shown that the nebula's far-UV spectrum comprises a stellar continuum on which are superimposed a few emission lines, numerous interstellar absorption lines, and various types of P Cygni profiles. Evidence is examined for substantial mass loss from the central nucleus, with terminal velocities of the or...

Observation of Ion Acoustic Waves Excited by Drift Waves in a Weakly Magnetized Plasma

International Nuclear Information System (INIS)

Tsukabayashi, Isao; Sato, Sugiya; Nakamura, Yoshiharu

2003-01-01

Spontaneous fluctuations excited by drift waves are investigated experimentally in magnetic multi-pole plasma. The magnetic multi-pole has been widely used in DP devices and so on. It was observed that the high level of density fluctuations was generated by the drift instability near a magnetic multi-pole or a dipole magnet. The waves propagate to the middle plasma region forming the envelope train waves

Canard and mixed mode oscillations in an excitable glow discharge plasma in the presence of inhomogeneous magnetic field

Energy Technology Data Exchange (ETDEWEB)

Shaw, Pankaj Kumar, E-mail: pankaj.shaw@saha.ac.in; Sekar Iyengar, A. N., E-mail: ansekar.iyengar@saha.ac.in [Plasma Physics Division, Saha Institute of Nuclear Physics, 1/AF, Bidhannagar, Kolkata 700064 (India); Nurujjaman, Md., E-mail: jaman-nonlinear@yahoo.co.in [Department of Physics, National Institute of Technology Sikkim, Ravangla, Sikkim 737139 (India)

2015-12-15

We report on the experimental observation of canard orbit and mixed mode oscillations (MMOs) in an excitable glow discharge plasma induced by an external magnetic field perturbation using a bar magnet. At a small value of magnetic field, small amplitude quasiperiodic oscillations were excited, and with the increase in the magnetic field, large amplitude oscillations were excited. Analyzing the experimental results, it seems that the magnetic field could be playing the role of noise for such nonlinear phenomena. It is observed that the noise level increases with the increase in magnetic field strength. The experimental results have also been corroborated by a numerical simulation using a FitzHugh-Nagumo like macroscopic model derived from the basic plasma equations and phenomenology, where the noise has been included to represent the internal plasma noise. This macroscopic model shows MMO in the vicinity of the canard point when an external noise is added.

Rotating permanent magnet excitation for blood flow measurement.

Science.gov (United States)

Nair, Sarath S; Vinodkumar, V; Sreedevi, V; Nagesh, D S

2015-11-01

A compact, portable and improved blood flow measurement system for an extracorporeal circuit having a rotating permanent magnetic excitation scheme is described in this paper. The system consists of a set of permanent magnets rotating near blood or any conductive fluid to create high-intensity alternating magnetic field in it and inducing a sinusoidal varying voltage across the column of fluid. The induced voltage signal is acquired, conditioned and processed to determine its flow rate. Performance analysis shows that a sensitivity of more than 250 mV/lpm can be obtained, which is more than five times higher than conventional flow measurement systems. Choice of rotating permanent magnet instead of an electromagnetic core generates alternate magnetic field of smooth sinusoidal nature which in turn reduces switching and interference noises. These results in reduction in complex electronic circuitry required for processing the signal to a great extent and enable the flow measuring device to be much less costlier, portable and light weight. The signal remains steady even with changes in environmental conditions and has an accuracy of greater than 95%. This paper also describes the construction details of the prototype, the factors affecting sensitivity and detailed performance analysis at various operating conditions.

Spin-orbit excitations and electronic structure of the putative Kitaev magnet $\\alpha$-RuCl$_3$

OpenAIRE

Sandilands, Luke J.; Tian, Yao; Reijnders, Anjan A.; Kim, Heung-Sik; Plumb, Kemp W.; Kee, Hae-Young; Kim, Young-June; Burch, Kenneth S.

2015-01-01

Mott insulators with strong spin-orbit coupling have been proposed to host unconventional magnetic states, including the Kitaev quantum spin liquid. The 4$d$ system $\\alpha$-RuCl$_3$ has recently come into view as a candidate Kitaev system, with evidence for unusual spin excitations in magnetic scattering experiments. We apply a combination of optical spectroscopy and Raman scattering to study the electronic structure of this material. Our measurements reveal a series of orbital excitations i...

Nonlinear localized excitations in magnets with a weak exchange interaction as a soliton problem

International Nuclear Information System (INIS)

Gvozdikova, M.V.; Kovalev, A.S.

1998-01-01

The spin dynamics of soliton-like localized excitations in a discrete ferromagnet chain with an easy axis anisotropy and a weak exchange interaction is studied. The connection of these excitations with longwave magnetic solitons is discussed. The localized excitation frequency dependence on exchange interaction is found for a fixed number of spin deviation. It is shown that this dependence modifies essentially when the exchange interaction becomes comparable with an anisotropy value

Enhanced electric and magnetic response of a THz sub-wavelength fiber excited by a localized source

DEFF Research Database (Denmark)

Atakaramians, Shaghik; Stefani, Alessio; Shardivov, Ilya V.

2017-01-01

the magnetic response of the coupled system when excited with an electric dipole oriented along the circumference of the fiber. This result introduces a new platform for achieving enhanced magnetic response, which is the fundamental building block for metamaterial devices. Here we investigate experimentally......Recently we have shown that a nanofiber excited by a localized electric source can have enhanced electric and magnetic response depending of the relative orientation of the source and the fiber [1]. We have demonstrated that the dielectric nanofiber can suppress the electric response and enhance...

Investigation of wire motion in superconducting magnets

International Nuclear Information System (INIS)

Ogitsu, T.; Tsuchiya, K.; Devred, A.

1990-09-01

The large Lorentz forces occuring during the excitation of superconducting magnets can provoke sudden motions of wire, which eventually release enough energy to trigger a quench. These wire motions are accompanied by two electromagnetic effects: an induced emf along the moved wire, and a local change in flux caused by the minute dislocation of current. Both effects cause spikes in the coil voltage. Voltage data recorded during the excitation of a superconducting quadrupole magnet which early exhibit such events are here reported. Interpretations of the voltage spikes in terms of energy release are also presented, leading to insights on the spectrum of the disturbances which occur in real magnets. 15 refs

Development of Selective Excitation Methods in Nuclear Magnetic Resonance: Investigation of Hemoglobin Oxygenation in Erythrocytes Using Proton and Phosphorus -31 Nuclear Magnetic Resonance

Science.gov (United States)

Fetler, Bayard Keith

1993-01-01

Nuclear magnetic resonance (NMR) offers a potential method for making measurements of the percent oxygenation of hemoglobin (Hb) in living tissue non-invasively. As a demonstration of the feasibility of such measurements, we measured the percent oxygenation of Hb in red blood cells (erythrocytes) using resonances in the proton-NMR (^1H-NMR) spectrum which are characteristic of oxyhemoglobin (oxy-Hb) and deoxyhemoglobin (deoxy-Hb), and are due to the unique magnetic properties of these molecules. To perform these measurements, we developed a new NMR method of selectively exciting signals in a region of interest with uniform phase and amplitude, while suppressing the signal of the water resonance. With this method, we are able to make exact calculations distinguishing between uniform phase excitation produced at large flip-angles using the non-linear properties of the Bloch equations, and uniform phase excitation produced at small flip-angles using asymmetric pulse excitation functions. We measured the percent oxygenation of three characteristic ^1H-NMR resonances of Hb: two from deoxy-Hb, originating from the N_delta H protons of histidine residue F8, which occur at different frequencies for the alpha and beta chains of Hb; and one from oxy-Hb, originating from the gamma_2 -CH_3 protons of valine residue E11. We performed experiments both on fresh erythrocytes and on erythrocytes depleted of 2,3-diphosphoglycerate (2,3-DPG), and found that oxygen is more tightly bound to Hb in the former case. In both fresh and 2,3-DPG-depleted samples, we found that: (i) from the deoxy-Hb marker resonances, there is a small but significant difference in the oxygen saturation between the alpha and beta chains; (ii) the decrease in the areas of the deoxy-Hb marker resonances correlates well with the increase in the percent oxygenation of Hb as measured optically; (iii) the area of the oxy-Hb marker resonance may be up to ~15% less than the optically measured Hb saturation. We are

Theory of singlet-doublet excitations in praseodymium

International Nuclear Information System (INIS)

Bak, P.

1975-10-01

The magnetic excitation spectrum in a paramagnetic singlet-doublet system is calculated using a diagrammatic high density expansion technique. The lowest order diagrams, which correspond to the random phase approximation (RPA), give a detailed description of the wave vector and temperature dependence of the four exciton modes in praseodymium in terms of a Hamiltonian including isotropic Heisenberg exchange interactions and anisotropic, dipolar-like interactions. The leading contributions to the linewidths of the excitations are obtained by extending the 1/Z expansion of the generalized susceptibility propagators one order beyond the random phase approximation. This damping corresponds to spin wave scattering on single-site fluctuations. The theoretical spectral functions are in detailed agreement with experiment

Quantum renormalizations in anisotropic multisublattice magnets and the modification of magnetic susceptibility under irradiation

Science.gov (United States)

Val'kov, V. V.; Shustin, M. S.

2015-11-01

The dispersion equation of a strongly anisotropic one-dimensional magnet catena-[FeII(ClO4)2{FeIII(bpca)2}]ClO4 containing alternating high-spin (HS) ( S = 2) and low-spin (LS) ( S = 1/2) iron ions is obtained by the diagram technique for Hubbard operators. The analysis of this equation yields six branches in the excitation spectrum of this magnet. It is important that the crystal field for ions with spin S = 2 is described by the Hamiltonian of single-ion easy-plane anisotropy, whose orientation is changed by 90° when passing from one HS iron ion to another. The U( N) transformation technique in the atomic representation is applied to diagonalize a single-ion Hamiltonian with a large number of levels. It is shown that the modulation of the orientation of easy magnetization planes leads to a model of a ferrimagnet with easy-axis anisotropy and to the formation of energy spectrum with a large gap. For HS iron ions, a decrease in the mean value of the spin projection due to quantum fluctuations is calculated. The analysis of the specific features of the spectrum of elementary excitations allows one to establish a correspondence to a generalized Ising model for which the magnetic susceptibility is calculated in a wide range of temperatures by the transfer-matrix method. The introduction of a statistical ensemble that takes into account the presence of chains of different lengths and the presence of iron ions with different spins allows one to describe the experimentally observed modification of the magnetic susceptibility of the magnet under optical irradiation.

Elementary Theoretical Forms for the Spatial Power Spectrum of Earth's Crustal Magnetic Field

Science.gov (United States)

Voorhies, C.

1998-01-01

The magnetic field produced by magnetization in Earth's crust and lithosphere can be distinguished from the field produced by electric currents in Earth's core because the spatial magnetic power spectrum of the crustal field differs from that of the core field. Theoretical forms for the spectrum of the crustal field are derived by treating each magnetic domain in the crust as the point source of a dipole field. The geologic null-hypothesis that such moments are uncorrelated is used to obtain the magnetic spectrum expected from a randomly magnetized, or unstructured, spherical crust of negligible thickness. This simplest spectral form is modified to allow for uniform crustal thickness, ellipsoidality, and the polarization of domains by an periodically reversing, geocentric axial dipole field from Earth's core. Such spectra are intended to describe the background crustal field. Magnetic anomalies due to correlated magnetization within coherent geologic structures may well be superimposed upon this background; yet representing each such anomaly with a single point dipole may lead to similar spectral forms. Results from attempts to fit these forms to observational spectra, determined via spherical harmonic analysis of MAGSAT data, are summarized in terms of amplitude, source depth, and misfit. Each theoretical spectrum reduces to a source factor multiplied by the usual exponential function of spherical harmonic degree n due to geometric attenuation with attitude above the source layer. The source factors always vary with n and are approximately proportional to n(exp 3) for degrees 12 through 120. The theoretical spectra are therefore not directly proportional to an exponential function of spherical harmonic degree n. There is no radius at which these spectra are flat, level, or otherwise independent of n.

Interplay between magnetism and superconductivity in iron based high temperature superconductors

Energy Technology Data Exchange (ETDEWEB)

Price, Stephen

2013-07-01

In this thesis, magnetic properties of a series of different Fe-based superconducting materials have been studied by means of neutron scattering techniques. Magnetic correlations in underdoped Ba(Fe{sub 0.95}Co{sub 0.05}){sub 2}As{sub 2} have been investigated for three phases of the phase diagram. It was possible to detect the spin gap and spin resonance signal, two features of the particle hole excitation spectrum at Q=(0.5,0.5,0), characteristic for the superconducting phase. The spin wave excitations present in the ordered phase have been analyzed quantitatively in terms of a linear spin wave model, whereas a spin diffusion model was applied to the collective excitations of the paramagnetic phase. However, it was found that both models can be applied to excitations in all three phases. In optimally doped CaFe{sub 0.88}Co{sub 0.12}AsF, a spin resonance signal was detected as part of the spin excitation spectrum at Q=(0.5,0.5,0). The observation of the spin resonance signal supports the s{sub ±} symmetry of the superconducting gap function. In the undoped CaFeAsF compound three dimensional spin wave like excitations of the static Fe-SDW order have been observed at Q{sub AFM}=(0.5,0.5,0.5), for temperatures below T{sub N}. Above T{sub N} and for energies below 20 meV, the spin wave like excitations are replaced by short range two dimensional paramagnetic excitations, which persist up to 270 K. In superconducting FeSe{sub 0.5}Te{sub 0.5} polarized neutron scattering investigations revealed the magnetic nature of the spin resonance signal and the excitation spectrum at Q=(0.5,0.5,0) up to 30 meV. The whole excitation spectrum including the spin resonance signal consists of an isotropic distribution of spin excitations with magnetic moments fluctuating in the ab-plane and perpendicular to the ab-plane, χ{sub ab}''(Q,ω)∼χ{sub c}''(Q,ω). In Eu(Fe{sub 1-x}Co{sub x}){sub 2}As{sub 2} and EuFe{sub 2}(As{sub 1-x}P{sub x}){sub 2} the effect of

Electron impact excitation and ionization of laser-excited sodium atoms Na*(7d)

International Nuclear Information System (INIS)

Nienhaus, J.; Dorn, A.; Mehlhorn, W.; Zatsarinny, O.I.

1997-01-01

We have investigated the ejected-electron spectrum following impact excitation and ionization of laser-excited Na * (nl) atoms by 1.5 keV electrons. By means of two-laser excitation 3s → 3p 3/2 → 7d and subsequent cascading transitions about 8% (4%) of the target atoms were in excited states with n > 3 (7d). The experimental ejected-electron spectrum due to the decay of Auger and autoionization states of laser-excited atoms Na * (nl) with n = 4-7 has been fully interpreted by comprehensive calculations of the energies, cross sections and decay probabilities of the corresponding states. The various processes contributing to the ejected-electron spectrum are with decreasing magnitude: 2s ionization leading to 2s2p 6 nl Auger states, 2p → 3s excitation leading to 2p 5 3s( 1 P)nl autoionization states and 2s → 3l' excitation leading to 2s2p 6 3l'( 1 L)nl autoionization states. (Author)

Magnetic field effects on the quantum wire energy spectrum and Green's function

International Nuclear Information System (INIS)

Morgenstern Horing, Norman J.

2010-01-01

We analyze the energy spectrum and propagation of electrons in a quantum wire on a 2D host medium in a normal magnetic field, representing the wire by a 1D Dirac delta function potential which would support just a single subband state in the absence of the magnetic field. The associated Schroedinger Green's function for the quantum wire is derived in closed form in terms of known functions and the Landau quantized subband energy spectrum is examined.

Macroscopic theory of the relaxation of collective excitations in disordered and noncollinear magnets

International Nuclear Information System (INIS)

Bar'yakhtar, V.G.; Belykh, V.G.; Soboleva, T.K.

1989-01-01

In the framework of the general hydrodynamic approach a method is proposed for describing the relaxation of low-frequency magnetic excitations in disordered spin systems and many-sublattice magnets. Expressions are obtained in terms of Goldstone fields for the dissipation function both in the exchange approximation and when allowance is made for relativistic interactions

Automated design of DC-excited flux-switching in-wheel motor using magnetic equivalent circuits

NARCIS (Netherlands)

Tang, Y.; Paulides, J.J.H.; Lomonova, E.A.

2015-01-01

DC-excited flux-switching motors (DCEFSMs) are increasingly considered as candidate traction motors for electric vehicles due to their robust and magnet-free structure with relatively high torque density and extendable speed range. In this paper, an automated design tool based on nonlinear magnetic

Use of Advanced Magnetic Resonance Imaging Techniques in Neuromyelitis Optica Spectrum Disorder

DEFF Research Database (Denmark)

Kremer, S.; Renard, F.; Achard, S.

2015-01-01

Brain parenchymal lesions are frequently observed on conventional magnetic resonance imaging (MRI) scans of patients with neuromyelitis optica (NMO) spectrum disorder but the specific morphological and temporal patterns distinguishing them uneqtaivcally from lesions caused by other disorders have...... not been identified. This literature review summarizes the literature on advanced quantitative imaging measures reported for patients with NMO spectrum disorder, including proton MR spectroscopy, diffusion tensor imaging, magnetization transfer imaging, quantitative MR voltametry, and ultrahigh...... diffusion-weighted imaging and brain tissue volumetry indicate greater white matter than gray matter degradation. These findings could be confirmed by ultrahigh-field MRI. The use of nonconventional MR I techniques may further our understanding of the pathogenic processes hi NMO spectrum disorders and may...

Magnetic excitation spectra of strongly correlated quasi-one-dimensional systems: Heisenberg versus Hubbard-like behavior

Science.gov (United States)

Nocera, A.; Patel, N. D.; Fernandez-Baca, J.; Dagotto, E.; Alvarez, G.

2016-11-01

We study the effects of charge degrees of freedom on the spin excitation dynamics in quasi-one-dimensional magnetic materials. Using the density matrix renormalization group method, we calculate the dynamical spin structure factor of the Hubbard model at half electronic filling on a chain and on a ladder geometry, and compare the results with those obtained using the Heisenberg model, where charge degrees of freedom are considered frozen. For both chains and two-leg ladders, we find that the Hubbard model spectrum qualitatively resembles the Heisenberg spectrum—with low-energy peaks resembling spinonic excitations—already at intermediate on-site repulsion as small as U /t ˜2 -3 , although ratios of peak intensities at different momenta continue evolving with increasing U /t converging only slowly to the Heisenberg limit. We discuss the implications of these results for neutron scattering experiments and we propose criteria to establish the values of U /t of quasi-one-dimensional systems described by one-orbital Hubbard models from experimental information.

Raman Scattering as a Probe of the Magnetic State of BEDT-TTF Based Mott Insulators

Directory of Open Access Journals (Sweden)

Nora Hassan

2018-05-01

Full Text Available Quasi-two-dimensional Mott insulators based on BEDT-TTF molecules have recently demonstrated a variety of exotic states, which originate from electron–electron correlations and geometrical frustration of the lattice. Among those states are a triangular S = 1/2 spin liquid and quantum dipole liquid. In this article, we show the power of Raman scattering technique to characterize magnetic and electronic excitations of these states. Our results demonstrate a distinction between a spectrum of magnetic excitations in a simple Mott insulator with antiferromagnetic interactions, and a spectrum of an insulator with an additional on-site charge degree of freedom.

Quantum phase transition of a magnet in a spin bath

DEFF Research Database (Denmark)

Rønnow, H.M.; Parthasarathy, R.; Jensen, J.

2005-01-01

The excitation spectrum of a model magnetic system, LiHoF(4), was studied with the use of neutron spectroscopy as the system was tuned to its quantum critical point by an applied magnetic field. The electronic mode softening expected for a quantum phase transition was forestalled by hyperfine...

Fractional and hidden magnetic excitations in f-electron metal Yb2Pt2Pb

Science.gov (United States)

Zaliznyak, Igor

Quantum states with fractionalized excitations such as spinons in one-dimensional chains are commonly viewed as belonging to the domain of S=1/2 spin systems. However, recent experiments on the quantum antiferromagnet Yb2Pt2Pb, part of a large family of R2T2X (R=rare earth, T=transition metal, X=main group) materials spectacularly disqualify this opinion. The results show that spinons can also emerge in an f-electron system with strong spin-orbit coupling, where magnetism is mainly associated with large and anisotropic orbital moment. Here, the competition of several high-energy interactions Coulomb repulsion, spin-orbit coupling, crystal field, and the peculiar crystal structure, which combines low dimensionality and geometrical frustration, lead to the emergence, at low energy, of an effective spin-1/2, purely quantum Hamiltonian. Consequently, it produces unusual spin-liquid states and fractional excitations enabled by the inherently quantum mechanical nature of the moments. The emergent quantum spins bear the unique birthmark of their unusual origin in that they only lead to measurable longitudinal magnetic fluctuations, while the transverse excitations such as spin waves remain invisible to scattering experiments. Similarlyhidden would be transverse magnetic ordering, although it would have visible excitations. The rich magnetic phase diagram of Yb2Pt2Pb is suggestive of the existence of hidden-order phases, while the recent experiments indeed reveal the dark magnon, a hidden excitation in the saturated ferromagnetic (FM) phase of Yb2Pt2Pb. Unlike copper-based spin-1/2 chains, where the magnon in the FM state accounts for the full spectral weight of the zero-field spinon continuum, in the spin-orbital chains in Yb2Pt2Pb it is 100 times, or more weaker. It thus presents an example of dark magnon matter\\x9D, whose Hamiltonian is that of the effective spin-1/2 chain, but whose coupling to magnetic field, the physical probe at our disposal, is vanishingly small

Comparison of electric dipole and magnetic loop antennas for exciting whistler modes

International Nuclear Information System (INIS)

Stenzel, R. L.; Urrutia, J. M.

2016-01-01

The excitation of low frequency whistler modes from different antennas has been investigated experimentally in a large laboratory plasma. One antenna consists of a linear electric dipole oriented across the uniform ambient magnetic field B_0. The other antenna is an elongated loop with dipole moment parallel to B_0. Both antennas are driven by the same rf generator which produces a rf burst well below the electron cyclotron frequency. The antenna currents as well as the wave magnetic fields from each antenna are measured. Both the antenna currents and the wave fields of the loop antenna exceed that of the electric dipole by two orders of magnitude. The conclusion is that loop antennas are far superior to dipole antennas for exciting large amplitude whistler modes, a result important for active wave experiments in space plasmas.

Comparison of electric dipole and magnetic loop antennas for exciting whistler modes

Energy Technology Data Exchange (ETDEWEB)

Stenzel, R. L.; Urrutia, J. M. [Department of Physics and Astronomy, University of California, Los Angeles, California 90095-1547 (United States)

2016-08-15

The excitation of low frequency whistler modes from different antennas has been investigated experimentally in a large laboratory plasma. One antenna consists of a linear electric dipole oriented across the uniform ambient magnetic field B{sub 0}. The other antenna is an elongated loop with dipole moment parallel to B{sub 0}. Both antennas are driven by the same rf generator which produces a rf burst well below the electron cyclotron frequency. The antenna currents as well as the wave magnetic fields from each antenna are measured. Both the antenna currents and the wave fields of the loop antenna exceed that of the electric dipole by two orders of magnitude. The conclusion is that loop antennas are far superior to dipole antennas for exciting large amplitude whistler modes, a result important for active wave experiments in space plasmas.

On the spectrum emitted by excited particles ejected from the surface of a calcium target by a beam of Ar+ ions

International Nuclear Information System (INIS)

Kiyan, T.S.; Gritsyna, V.V.; Fogel, Ya.M.

1976-01-01

The spectrum of the luminous aureole near the calcium target radiated by excited particles ejected from its surface by a beam of Ar + (energy 30 keV, current density 200 μA/cm 2 ) was investigated. This spectrum contains lines of the singlet and triplet systems of the one-and-two-electron excited states of the calcium atom and some bands of CaO and O + 2 molecules. The width of a conductivity band of CaO was measured. Some information on oxidation processes on calcium in a residual gas and rarefied nitrogen atmosphere was obtained. (Auth.)

Modulation of motor cortex excitability by paired peripheral and transcranial magnetic stimulation.

Science.gov (United States)

Kumru, Hatice; Albu, Sergiu; Rothwell, John; Leon, Daniel; Flores, Cecilia; Opisso, Eloy; Tormos, Josep Maria; Valls-Sole, Josep

2017-10-01

Repetitive application of peripheral electrical stimuli paired with transcranial magnetic stimulation (rTMS) of M1 cortex at low frequency, known as paired associative stimulation (PAS), is an effective method to induce motor cortex plasticity in humans. Here we investigated the effects of repetitive peripheral magnetic stimulation (rPMS) combined with low frequency rTMS ('magnetic-PAS') on intracortical and corticospinal excitability and whether those changes were widespread or circumscribed to the cortical area controlling the stimulated muscle. Eleven healthy subjects underwent three 10min stimulation sessions: 10HzrPMS alone, applied in trains of 5 stimuli every 10s (60 trains) on the extensor carpi radialis (ECR) muscle; rTMS alone at an intensity 120% of ECR threshold, applied over motor cortex of ECR and at a frequency of 0.1Hz (60 stimuli) and magnetic PAS, i.e., paired rPMS and rTMS. We recorded motor evoked potentials (MEPs) from ECR and first dorsal interosseous (FDI) muscles. We measured resting motor threshold, motor evoked potentials (MEP) amplitude at 120% of RMT, short intracortical inhibition (SICI) at interstimulus interval (ISI) of 2ms and intracortical facilitation (ICF) at an ISI of 15ms before and immediately after each intervention. Magnetic-PAS , but not rTMS or rPMS applied separately, increased MEP amplitude and reduced short intracortical inhibition in ECR but not in FDI muscle. Magnetic-PAS can increase corticospinal excitability and reduce intracortical inhibition. The effects may be specific for the area of cortical representation of the stimulated muscle. Application of magnetic-PAS might be relevant for motor rehabilitation. Copyright © 2017 International Federation of Clinical Neurophysiology. All rights reserved.

Decrease of motor cortex excitability following exposure to a 20 Hz magnetic field as generated by a rotating permanent magnet.

Science.gov (United States)

Gallasch, Eugen; Rafolt, Dietmar; Postruznik, Magdalena; Fresnoza, Shane; Christova, Monica

2018-04-19

Rotation of a static magnet over the motor cortex (MC) generates a transcranial alternating magnetic field (tAMF), and a linked alternating electrical field. The aim of this transcranial magnetic stimulation (TMS) study is to investigate whether such fields are able to influence MC excitability, and whether there are parallels to tACS induced effects. Fourteen healthy volunteers received 20 Hz tAMF stimulation over the MC, over the vertex, and 20 Hz tACS over the MC, each with a duration of 15 min. TMS assessments were performed before and after the interventions. Changes in motor evoked potentials (MEP), short interval intra-cortical inhibition (SICI) and intra-cortical facilitation (ICF) were evaluated. The tACS and the tAMF stimulation over the MC affected cortical excitability in a different way. After tAMF stimulation MEP amplitudes and ICF decreased and the effect of SICI increased. After tACS MEP amplitudes increased and there were no effects on SICI and ICF. The recorded single and paired pulse MEPs indicate a general decrease of MC excitability following 15 min of tAMF stimulation. The effects demonstrate that devices based on rotating magnets are potentially suited to become a novel brain stimulation tool in clinical neurophysiology. Copyright © 2018 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. All rights reserved.

Study on excitation and fluorescence spectrums of Japanese citruses to construct machine vision systems for acquiring fluorescent images

Science.gov (United States)

Momin, Md. Abdul; Kondo, Naoshi; Kuramoto, Makoto; Ogawa, Yuichi; Shigi, Tomoo

2011-06-01

Research was conducted to acquire knowledge of the ultraviolet and visible spectrums from 300 -800 nm of some common varieties of Japanese citrus, to investigate the best wave-lengths for fluorescence excitation and the resulting fluorescence wave-lengths and to provide a scientific background for the best quality fluorescent imaging technique for detecting surface defects of citrus. A Hitachi U-4000 PC-based microprocessor controlled spectrophotometer was used to measure the absorption spectrum and a Hitachi F-4500 spectrophotometer was used for the fluorescence and excitation spectrums. We analyzed the spectrums and the selected varieties of citrus were categorized into four groups of known fluorescence level, namely strong, medium, weak and no fluorescence.The level of fluorescence of each variety was also examined by using machine vision system. We found that around 340-380 nm LEDs or UV lamps are appropriate as lighting devices for acquiring the best quality fluorescent image of the citrus varieties to examine their fluorescence intensity. Therefore an image acquisition device was constructed with three different lighting panels with UV LED at peak 365 nm, Blacklight blue lamps (BLB) peak at 350 nm and UV-B lamps at peak 306 nm. The results from fluorescent images also revealed that the findings of the measured spectrums worked properly and can be used for practical applications such as for detecting rotten, injured or damaged parts of a wide variety of citrus.

Magnetic fluctuations in UNi4B

DEFF Research Database (Denmark)

Mentink, S.A.M.; Mason, T.E.; Buyers, W.J.L.

1997-01-01

We investigate the magnetic fluctuation spectrum of the geometrically frustrated antiferromagnetic compound UNi4B, which partially orders below T-N = 20 K. An overdamped spin excitation is observed at the AF wave vector around 2.4 meV. Low-frequency, weakly Q-dependent inelastic scattering...

Interplay of spin-dependent delocalization and magnetic anisotropy in the ground and excited states of [Gd2@C78]- and [Gd2@C80]-

Science.gov (United States)

Mansikkamäki, Akseli; Popov, Alexey A.; Deng, Qingming; Iwahara, Naoya; Chibotaru, Liviu F.

2017-09-01

The magnetic properties and electronic structure of the ground and excited states of two recently characterized endohedral metallo-fullerenes, [Gd2@C78]- (1) and [Gd2@C80]- (2), have been studied by theoretical methods. The systems can be considered as [Gd2]5+ dimers encapsulated in a fullerene cage with the fifteen unpaired electrons ferromagnetically coupled into an S = 15/2 high-spin configuration in the ground state. The microscopic mechanisms governing the Gd-Gd interactions leading to the ferromagnetic ground state are examined by a combination of density functional and ab initio calculations and the full energy spectrum of the ground and lowest excited states is constructed by means of ab initio model Hamiltonians. The ground state is characterized by strong electron delocalization bordering on a σ type one-electron covalent bond and minor zero-field splitting (ZFS) that is successfully described as a second order spin-orbit coupling effect. We have shown that the observed ferromagnetic interaction originates from Hund's rule coupling and not from the conventional double exchange mechanism. The calculated ZFS parameters of 1 and 2 in their optimized geometries are in qualitative agreement with experimental EPR results. The higher excited states display less electron delocalization, but at the same time they possess unquenched first-order angular momentum. This leads to strong spin-orbit coupling and highly anisotropic energy spectrum. The analysis of the excited states presented here constitutes the first detailed study of the effects of spin-dependent delocalization in the presence of first order orbital angular momentum and the obtained results can be applied to other mixed valence lanthanide systems.

Spin–transfer torque oscillator in magnetic tunneling junction with short–wavelength magnon excitation

Directory of Open Access Journals (Sweden)

Shizhu Qiao

2018-05-01

Full Text Available Bloch–Bloembergen–Slonczewski (BBS equation is established by extending Bloch–Bloembergen equation, and it is used to study magnetization oscillation in the free magnetic layer of a magnetic tunneling junction. Since both short–wavelength magnon excitation and spin–transfer torque are taken into account in the BBS equation, it is distinguished from Landau–Lifshitz–Gilbert–Slonczewski equation. The macro–spin BBS model predicts that the transverse relaxation time in free magnetic layer should be long enough, as compared with the longitudinal relaxation time, to achieve stable magnetization oscillation for spin–transfer torque oscillator application. Moreover, field–like torque favors the tolerance of fast transverse relaxation, which makes magnetic tunneling junction a better choice than spin valve for the spin–transfer torque oscillator application.

Use of Advanced Magnetic Resonance Imaging Techniques in Neuromyelitis Optica Spectrum Disorder

Science.gov (United States)

Kremer, Stephane; Renard, Felix; Achard, Sophie; Lana-Peixoto, Marco A.; Palace, Jacqueline; Asgari, Nasrin; Klawiter, Eric C.; Tenembaum, Silvia N.; Banwell, Brenda; Greenberg, Benjamin M.; Bennett, Jeffrey L.; Levy, Michael; Villoslada, Pablo; Saiz, Albert; Fujihara, Kazuo; Chan, Koon Ho; Schippling, Sven; Paul, Friedemann; Kim, Ho Jin; de Seze, Jerome; Wuerfel, Jens T.

2016-01-01

Brain parenchymal lesions are frequently observed on conventional magnetic resonance imaging (MRI) scans of patients with neuromyelitis optica (NMO) spectrum disorder, but the specific morphological and temporal patterns distinguishing them unequivocally from lesions caused by other disorders have not been identified. This literature review summarizes the literature on advanced quantitative imaging measures reported for patients with NMO spectrum disorder, including proton MR spectroscopy, diffusion tensor imaging, magnetization transfer imaging, quantitative MR volumetry, and ultrahigh-field strength MRI. It was undertaken to consider the advanced MRI techniques used for patients with NMO by different specialists in the field. Although quantitative measures such as proton MR spectroscopy or magnetization transfer imaging have not reproducibly revealed diffuse brain injury, preliminary data from diffusion-weighted imaging and brain tissue volumetry indicate greater white matter than gray matter degradation. These findings could be confirmed by ultrahigh-field MRI. The use of nonconventional MRI techniques may further our understanding of the pathogenic processes in NMO spectrum disorders and may help us identify the distinct radiographic features corresponding to specific phenotypic manifestations of this disease. PMID:26010909

Analysis of axial compressive loaded beam under random support excitations

Science.gov (United States)

Xiao, Wensheng; Wang, Fengde; Liu, Jian

2017-12-01

An analytical procedure to investigate the response spectrum of a uniform Bernoulli-Euler beam with axial compressive load subjected to random support excitations is implemented based on the Mindlin-Goodman method and the mode superposition method in the frequency domain. The random response spectrum of the simply supported beam subjected to white noise excitation and to Pierson-Moskowitz spectrum excitation is investigated, and the characteristics of the response spectrum are further explored. Moreover, the effect of axial compressive load is studied and a method to determine the axial load is proposed. The research results show that the response spectrum mainly consists of the beam's additional displacement response spectrum when the excitation is white noise; however, the quasi-static displacement response spectrum is the main component when the excitation is the Pierson-Moskowitz spectrum. Under white noise excitation, the amplitude of the power spectral density function decreased as the axial compressive load increased, while the frequency band of the vibration response spectrum increased with the increase of axial compressive load.

Spin excitations in 3D molecular magnets probed by neutron scattering

CERN Document Server

Bordallo, H N; Chapon, L C; Manson, J L; Cook, J C; Lee, S H; Copley, J R D; Yildirim, T; Kern, S

2002-01-01

The emerging field of molecular magnetism constitutes a new branch of materials science that deals with the magnetic properties of molecules, or assemblies of molecules, that contain magnetic centers. The growing interest in understanding the origin of the magnetic ordering in these materials is to obtain novel multiproperty molecular magnetic materials with high transition temperatures. Molecules based on the dicyanamide ion [N ident to C-N-C ident to N], abbreviated (dca), such as M(dca) sub 2 [M=Mn, Ni], have shown interesting bulk properties that prompted our inelastic neutron scattering (INS) studies. While the Mn sup 2 sup + ion is isotropic because of its L=0 configuration, the isostructural Ni analog has S=1 and demonstrates marked single-ion anisotropy. Mn(dca) sub 2 is a canted antiferromagnet below 16 K, while Ni(dca) sub 2 is a ferromagnet below 21 K. INS has been used to investigate the magnetic excitations in Mn(dca) sub 2 and Ni(dca) sub 2. For Mn(dca) sub 2 , a Heisenberg model gives good corr...

Experimental results of high power dual frequency resonant magnet excitation at TRIUMF

International Nuclear Information System (INIS)

Reiniger, K.W.; Heritier, G.

1988-06-01

We present some results of duel frequency resonant magnet excitation at full power using the old NINA synchrotron dipoles. These tests will simulate a typical resonant cell as proposed for the accelerating rings of the TRIUMF KAON Factory. These test have two main purposes: to verify circuit parameters and component ratings for the dual frequency resonant power supply system; and to measure directly electrical losses in a transverse magnet field, such as eddy current losses in magnet conductors, vacuum tubes and core losses in laminations. These data will be required for the detailed design of the accelerator system components. (Author) (Ref., 9 figs., tab.)

Hofstadter spectrum in electric and magnetic fields

International Nuclear Information System (INIS)

Kunold, Alejandro; Torres, Manuel

2005-01-01

The problem of Bloch electrons in two dimensions subjected to magnetic and intense electric fields is investigated. Magnetic translations, electric evolution, and energy translation operators are used to specify the solutions of the Schroedinger equation. For rational values of the magnetic flux quanta per unit cell and commensurate orientations of the electric field relative to the original lattice, an extended superlattice can be defined and a complete set of mutually commuting space-time symmetry operators is obtained. Dynamics of the system is governed by a finite difference equation that exactly includes the effects of: an arbitrary periodic potential, an electric field orientated in a commensurable direction of the lattice, and coupling between Landau levels. A weak periodic potential broadens each Landau level in a series of minibands, separated by the corresponding minigaps. The addition of the electric field induces a series of avoided and exact crossing of the quasienergies, for sufficiently strong electric field the spectrum evolves into equally spaced discreet levels, in this 'magnetic Stark ladder' the energy separation is an integer multiple of hE/aB, with a the lattice parameter

Plane-wise sensitivity based inhomogeneous excitation fields for magnetorelaxometry imaging of magnetic nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Baumgarten, Daniel, E-mail: daniel.baumgarten@tu-ilmenau.de [Institute of Biomedical Engineering and Informatics, Technische Universität Ilmenau, 98693 Ilmenau (Germany); IJN-UTM Cardiovascular Engineering Centre, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor Bahru (Malaysia); Braune, Friedemann [Institute of Biomedical Engineering and Informatics, Technische Universität Ilmenau, 98693 Ilmenau (Germany); Supriyanto, Eko [IJN-UTM Cardiovascular Engineering Centre, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor Bahru (Malaysia); Haueisen, Jens [Institute of Biomedical Engineering and Informatics, Technische Universität Ilmenau, 98693 Ilmenau (Germany)

2015-04-15

Promising biomedical applications of magnetic nanoparticles share the need for a quantitative knowledge of their in vivo distribution. From multichannel magnetorelaxometry measurements with sequential activation of inhomogeneous excitation fields, the distribution can be quantitatively determined. In first studies, single excitation coils were consecutively activated. We aim at further advancing this imaging technology by suitable activation patterns involving multiple excitation coils. In this work, we propose the estimation of these patterns based on the spatial sensitivity in order to reduce the number of required measurements. The sensitivity of a voxel carrying magnetic nanoparticles is determined by its position relative to the sensors and the excitation field. Whereas the position is fixed within a given setup, the excitation is controlled by the currents in the coils. The currents required for a defined target sensitivity are estimated by solving an inverse problem. In our work, two target sensitivity paradigms are presented: (a) plane-wise activation, where only one plane with high sensitivities is sought and moved through the source space and (b) plane-wise non-activation, where all voxels except for one plane should receive high sensitivity. Our approach is investigated in simulation studies using a setup with a cubic region of interest and a planar sensor array. The imaging quality of both activation paradigms is evaluated. Our results demonstrate the principal applicability of this spatial sensitivity based approach for defining inhomogeneous activation patterns. The obtained patterns allow for a similar imaging quality using a lower number of activation sequences compared to the conventional single coil activation.

Plane-wise sensitivity based inhomogeneous excitation fields for magnetorelaxometry imaging of magnetic nanoparticles

International Nuclear Information System (INIS)

Baumgarten, Daniel; Braune, Friedemann; Supriyanto, Eko; Haueisen, Jens

2015-01-01

Promising biomedical applications of magnetic nanoparticles share the need for a quantitative knowledge of their in vivo distribution. From multichannel magnetorelaxometry measurements with sequential activation of inhomogeneous excitation fields, the distribution can be quantitatively determined. In first studies, single excitation coils were consecutively activated. We aim at further advancing this imaging technology by suitable activation patterns involving multiple excitation coils. In this work, we propose the estimation of these patterns based on the spatial sensitivity in order to reduce the number of required measurements. The sensitivity of a voxel carrying magnetic nanoparticles is determined by its position relative to the sensors and the excitation field. Whereas the position is fixed within a given setup, the excitation is controlled by the currents in the coils. The currents required for a defined target sensitivity are estimated by solving an inverse problem. In our work, two target sensitivity paradigms are presented: (a) plane-wise activation, where only one plane with high sensitivities is sought and moved through the source space and (b) plane-wise non-activation, where all voxels except for one plane should receive high sensitivity. Our approach is investigated in simulation studies using a setup with a cubic region of interest and a planar sensor array. The imaging quality of both activation paradigms is evaluated. Our results demonstrate the principal applicability of this spatial sensitivity based approach for defining inhomogeneous activation patterns. The obtained patterns allow for a similar imaging quality using a lower number of activation sequences compared to the conventional single coil activation

Topological honeycomb magnon Hall effect: A calculation of thermal Hall conductivity of magnetic spin excitations

Energy Technology Data Exchange (ETDEWEB)

Owerre, S. A., E-mail: solomon@aims.ac.za [African Institute for Mathematical Sciences, 6 Melrose Road, Muizenberg, Cape Town 7945, South Africa and Perimeter Institute for Theoretical Physics, 31 Caroline St. N., Waterloo, Ontario N2L 2Y5 (Canada)

2016-07-28

Quite recently, the magnon Hall effect of spin excitations has been observed experimentally on the kagome and pyrochlore lattices. The thermal Hall conductivity κ{sup xy} changes sign as a function of magnetic field or temperature on the kagome lattice, and κ{sup xy} changes sign upon reversing the sign of the magnetic field on the pyrochlore lattice. Motivated by these recent exciting experimental observations, we theoretically propose a simple realization of the magnon Hall effect in a two-band model on the honeycomb lattice. The magnon Hall effect of spin excitations arises in the usual way via the breaking of inversion symmetry of the lattice, however, by a next-nearest-neighbour Dzyaloshinsky-Moriya interaction. We find that κ{sup xy} has a fixed sign for all parameter regimes considered. These results are in contrast to the Lieb, kagome, and pyrochlore lattices. We further show that the low-temperature dependence on the magnon Hall conductivity follows a T{sup 2} law, as opposed to the kagome and pyrochlore lattices. These results suggest an experimental procedure to measure thermal Hall conductivity within a class of 2D honeycomb quantum magnets and ultracold atoms trapped in a honeycomb optical lattice.

Magnetic excitations in iron chalcogenide superconductors.

Science.gov (United States)

Kotegawa, Hisashi; Fujita, Masaki

2012-10-01

Nuclear magnetic resonance and neutron scattering experiments in iron chalcogenide superconductors are reviewed to make a survey of the magnetic excitations in FeSe, FeSe 1- x Te x and alkali-metal-doped A x Fe 2- y Se 2 ( A = K, Rb, Cs, etc). In FeSe, the intimate relationship between the spin fluctuations and superconductivity can be seen universally for the variations in the off-stoichiometry, the Co-substitution and applied pressure. The isovalent compound FeTe has a magnetic ordering with different wave vector from that of other Fe-based magnetic materials. The transition temperature T c of FeSe increases with Te substitution in FeSe 1- x Te x with small x , and decreases in the vicinity of the end member FeTe. The spin fluctuations are drastically modified by the Te substitution. In the vicinity of the end member FeTe, the low-energy part of the spin fluctuation is dominated by the wave vector of the ordered phase of FeTe; however, the reduction of T c shows that it does not support superconductivity. The presence of same wave vector as that of other Fe-based superconductors in FeSe 1- x Te x and the observation of the resonance mode demonstrate that FeSe 1- x Te x belongs to the same group as most of other Fe-based superconductors in the entire range of x , where superconductivity is mediated by the spin fluctuations whose wave vector is the same as the nesting vector between the hole pockets and the electron pockets. On the other hand, the spin fluctuations differ for alkali-metal-doped A x Fe 2- y Se 2 and FeSe or other Fe-based superconductors in their wave vector and strength in the low-energy part, most likely because of the different Fermi surfaces. The resonance mode with different wave vector suggests that A x Fe 2- y Se 2 has an exceptional superconducting symmetry among Fe-based superconductors.

Mixed quantum-classical molecular dynamics study of the hydroxyl stretch in methanol/carbon-tetrachloride mixtures II: excited state hydrogen bonding structure and dynamics, infrared emission spectrum, and excited state lifetime.

Science.gov (United States)

Kwac, Kijeong; Geva, Eitan

2012-03-08

We present a mixed quantum-classical molecular dynamics study of the hydrogen-bonding structure and dynamics of a vibrationally excited hydroxyl stretch in methanol/carbon-tetrachloride mixtures. The adiabatic Hamiltonian of the quantum-mechanical hydroxyl is diagonalized on-the-fly to obtain the ground and first-excited adiabatic energy levels and wave functions which depend parametrically on the instantaneous configuration of the classical degrees of freedom. The dynamics of the classical degrees of freedom are determined by Hellmann-Feynman forces obtained by taking the expectation value of the force with respect to the ground or excited vibrational wave functions. Polarizable force fields are used which were previously shown to reproduce the experimental infrared absorption spectrum rather well, for different isotopomers and over a wide composition range [Kwac, K.; Geva, E. J. Phys. Chem. B 2011, 115, 9184]. We show that the agreement of the absorption spectra with experiment can be further improved by accounting for the dependence of the dipole moment derivatives on the configuration of the classical degrees of freedom. We find that the propensity of a methanol molecule to form hydrogen bonds increases upon photoexcitation of its hydroxyl stretch, thereby leading to a sizable red-shift of the corresponding emission spectrum relative to the absorption spectrum. Treating the relaxation from the first excited to the ground state as a nonadiabatic process, and calculating its rate within the framework of Fermi's golden rule and the harmonic-Schofield quantum correction factor, we were able to predict a lifetime which is of the same order of magnitude as the experimental value. The experimental dependence of the lifetime on the transition frequency is also reproduced. Nonlinear mapping relations between the hydroxyl transition frequency and bond length in the excited state and the electric field along the hydroxyl bond axis are established. These mapping relations

Use of Transcranial Magnetic Stimulation in Autism Spectrum Disorders

Science.gov (United States)

Oberman, Lindsay M.; Rotenberg, Alexander; Pascual-Leone, Alvaro

2015-01-01

The clinical, social and financial burden of autism spectrum disorder (ASD) is staggering. We urgently need valid and reliable biomarkers for diagnosis and effective treatments targeting the often debilitating symptoms. Transcranial magnetic stimulation (TMS) is beginning to be used by a number of centers worldwide and may represent a novel…

Use of synchrotron and laser radiations for present and future photoionization studies in excited atoms and ions

International Nuclear Information System (INIS)

Wuilleumier, F.J.

1984-01-01

The status of experiments in photoionization of atoms in excited states is reviewed, with emphasis given to synchrotron and laser photon sources. A technique for exciting the photoionization spectrum of Na atoms using the flux emitted from the bending magnetic of a storage ring is discussed in detail. Some problems in interpreting photoionization spectrum of Ba in the excited state, due to the presence of higher orders are considered. A design approach for a positron storage ring to produce coherent radiation in the VUV is described. It is shown that combined use of a CW dye laser and the positron storage ring will allow new progress to be made in photoionization studies of excited atoms. Some of the experiments to be carried out using the positron storage ring include: measurements of collisional ionization in rare earth metal atoms of low atomic density; photoionization measurements at lower laser powers, leading to an extension of the CW tunability range; and photoionization studies of multiply charged positive ions. 21 references

Individual magnetization reversal of a square dot matrix by common current excitation

International Nuclear Information System (INIS)

Elyasi, Mehrdad; Bhatia, Charanjit S; Yang, Hyunsoo

2015-01-01

We have proposed a method for magnetization reversal of individual sites of a 2 by 2 matrix of perpendicularly magnetized dots by common current excitation. The spin-polarized current signal consists of a dc-biased ac part followed by a pure dc one. The amplitude of the dc and ac parts of the current, as well as the phase and duration of the ac current, determine the reversal sites through the magnetostatic interaction among the dots. We show that the individual selectivity in magnetization reversal occurs through two consecutive steps, dephasing of the matrix dyadic pairs dynamics followed by nonlinear dephasing of the individual elements. This method can be utilized to increase the storage density of magnetic random access memory by enabling common access for four or more bits. (paper)

Electronic excitation-induced structural, optical, and magnetic properties of Ni-doped HoFeO3 thin films

International Nuclear Information System (INIS)

Habib, Zubida; Ikram, Mohd; Mir, Sajad A.; Sultan, Khalid; Abida; Majid, Kowsar; Asokan, K.

2017-01-01

Present study investigates the electronic excitation-induced modifications in the structural, optical, and magnetic properties of Ni-doped HoFeO 3 thin films grown by pulsed laser deposition on LaAlO 3 substrates. Electronic excitations were induced by 200 MeV Ag 12+ ion beam. These thin films were then characterized using X-ray diffraction (XRD), atomic force microscopy (AFM), UV-Vis spectroscopy, and magnetic measurements. X-ray diffraction analysis confirms that the crystallite growth occurs in the preferred (111) orientation with orthorhombic structure. The XRD results also show that the crystallite size decreases with ion irradiation. AFM results after irradiation show significant changes in the surface roughness and morphology of these films. The optical parameters measured from absorption measurements reveal reduction in the band gap with Ni doping and enhancement of band gap after irradiation. The magnetization vs field measurement at 75 K shows enhancement in saturation magnetization after irradiation for HoFe 1-x Ni x O 3 (x = 0.1 and 0.3) films compared to HoFeO 3 film. Present study shows electronic excitation induces significant changes in the physical properties of these films. (orig.)

Direct observation of spin-quadrupolar excitations in Sr2CoGe2O7 by high-field electron spin resonance

Science.gov (United States)

Akaki, Mitsuru; Yoshizawa, Daichi; Okutani, Akira; Kida, Takanori; Romhányi, Judit; Penc, Karlo; Hagiwara, Masayuki

2017-12-01

Exotic spin-multipolar ordering in spin transition metal insulators has so far eluded unambiguous experimental observation. A less studied, but perhaps more feasible fingerprint of multipole character emerges in the excitation spectrum in the form of quadrupolar transitions. Such multipolar excitations are desirable as they can be manipulated with the use of light or electric field and can be captured by means of conventional experimental techniques. Here we study single crystals of multiferroic Sr2CoGe2O7 and observe a two-magnon spin excitation appearing above the saturation magnetic field in electron spin resonance (ESR) spectra. Our analysis of the selection rules reveals that this spin excitation mode does not couple to the magnetic component of the light, but it is excited by the electric field only, in full agreement with the theoretical calculations. Due to the nearly isotropic nature of Sr2CoGe2O7 , we identify this excitation as a purely spin-quadrupolar two-magnon mode.

Magnetic field effects on electrical parameters of rf excited CO{sub 2} lasers

Energy Technology Data Exchange (ETDEWEB)

Tavassoli, S.H. [Laser Research Institute and Physics Department of Shahid Beheshti University, Evin, Tehran (Iran, Islamic Republic of)]. E-mail: h-tavassoli@cc.sbu.ac.ir; Latifi, H. [Laser Research Institute and Physics Department of Shahid Beheshti University, Evin, Tehran (Iran, Islamic Republic of)

2005-02-14

In the present Letter a rf excited CO{sub 2} laser embedded in an external, constant, and homogeneous magnetic field is considered. The magnetic field effects on some discharge parameters such as V-I characteristics, impedance of sheaths and positive column of plasma, intensity of visible emission from plasma and thickness of positive column are investigated. There is an increase in thickness of positive column and output power in presence of magnetic field. Magnetic field leads to an increase in the discharge voltage and impedance for lower current densities and a decrease for higher ones. There is a current density in which the magnetic field has no effects on discharge voltage and impedance. There are two peaks on intensity of visible emission from the discharge which at higher magnetic field are pushed out toward the electrodes.

Ion-Flow-Induced Excitation of Electrostatic Cyclotron Mode in Magnetized Dusty Plasma

Science.gov (United States)

Bezbaruah, P.; Das, N.

2018-05-01

The stability of electrostatic cyclotron mode is investigated in a flowing magnetized dusty plasma in the presence of strong ion-neutral collisions. In the high magnetic field limit, when the dust magnetization becomes important, it is expected that the collective behavior of magnetized dust grains suspended in the near-sheath region substantially influences the dispersion properties of electrostatic modes. The growth/damping of the collective excitation is significantly controlled by such parameters as the ion-neutral collision frequency, Mach number, and magnetic field strength. In our case, the explicit dependence of the Mach number on the magnetic field and collision frequency has been taken into account and possible implications on the stability of the mode is analyzed. Streaming instability of cyclotron modes may be important to understand issues related to the interaction mechanism between dust grains and other associated phenomena like Coulomb crystallization, phase behavior, transport properties, etc., in the relatively strong magnetic field limit, which is currently accessible in the DPD (Kiel University) and MDPX (PSL, Auburn University) experiments.

Theory of propagation of spectrum and correlations of radiation in optically dense gas in the case of the closed excitation contour

International Nuclear Information System (INIS)

Barantsev, K.A.; Litvinov, A.N.; Popov, E.N.

2017-01-01

This work is devoted to generalization of the semi-classical theory of interaction of broadband laser radiation with the atomic gas at the room temperature in the cell in the case of the closed excitation contour. The atomic density matrix equations and spectrum and correlations transport equations have been derived for excitation by fluctuating field with Gaussian statistics. It is shown that the spatial oscillations of radiation intensity and atomic density matrix can be excited. It was found that such medium can serve as a filter of incoherent part of the radiation.

Analysis and optimization of hybrid excitation permanent magnet synchronous generator for stand-alone power system

Science.gov (United States)

Wang, Huijun; Qu, Zheng; Tang, Shaofei; Pang, Mingqi; Zhang, Mingju

2017-08-01

In this paper, electromagnetic design and permanent magnet shape optimization for permanent magnet synchronous generator with hybrid excitation are investigated. Based on generator structure and principle, design outline is presented for obtaining high efficiency and low voltage fluctuation. In order to realize rapid design, equivalent magnetic circuits for permanent magnet and iron poles are developed. At the same time, finite element analysis is employed. Furthermore, by means of design of experiment (DOE) method, permanent magnet is optimized to reduce voltage waveform distortion. Finally, the validity of proposed design methods is validated by the analytical and experimental results.

Coulomb excitation

International Nuclear Information System (INIS)

McGowan, F.K.; Stelson, P.H.

1974-01-01

The theory of Coulomb excitation and a brief review of pertinent treatments of the Coulomb excitation process that are useful for the analysis of experiments are given. Examples demonstrating the scope of nuclear structure information obtainable from gamma spectroscopy are presented. Direct Elambda excitation of 232 Th is discussed in terms of the one phonon octupole vibrational spectrum. B(MI) reduced transition probabilities resulting from Coulomb excitation of odd-A deformed nuclei with heavy ions are presented as a test of the rotational model. The use of gamma ray coincidence and particle-gamma coincidence as tools for investigating Coulomb excitation is discussed. (U.S.)

46 CFR 111.12-3 - Excitation.

Science.gov (United States)

2010-10-01

... 46 CFR 110.10-1). In particular, no static exciter may be used for excitation of an emergency generator unless it is provided with a permanent magnet or a residual-magnetism-type exciter that has the...

The essential spectrum of Schroedinger operators with asymptotically constant magnetic fields on the Poincare upper-half plane

International Nuclear Information System (INIS)

Inahama, Yuzuru; Shirai, Shin-ichi

2003-01-01

We study the essential spectrum of the magnetic Schroedinger operators on the Poincare upper-half plane and establish a hyperbolic analog of Iwatsuka's result [J. Math. Kyoto Univ. 23(3), 475-480 (1983)] on the stability of the essential spectrum under perturbations from constant magnetic fields

Electric magnetic duality in string theory

International Nuclear Information System (INIS)

Sen, A.

1992-07-01

The electric-magnetic duality transformation in four dimensional heterotic string theory discussed by Shapere, Trivedi and Wilczek is shown to be an exact symmetry of the equations of motion of low energy effective field theory even after including the scalar and the vector fields, arising due to compactification, in the effective field theory. Using this duality transformation we construct rotating black hole solutions in the effective field theory carrying both electric and magnetic charges. The spectrum of extremal magnetically charged black holes turn out to be similar to that of electrically charged elementary string excitations lying on the leading Regge trajectory. We also discuss the possibility that the duality symmetry is an exact symmetry of the full string theory under which electrically charged elementary string excitations get exchanged with magnetically charged soliton like solutions. This proposal might be made concrete following the suggestion of Dabholkar et. al. that fundamental strings may be regarded as soliton like classical solutions in the effective field theory. (author). 20 refs

Effect of external magnetic field on the Kβ/Kα X-ray intensity ratios of TixNi1-x alloys excited by 59.54 and 22.69keV photons.

Science.gov (United States)

Perişanoğlu, Ufuk; Alım, Bünyamin; Uğurlu, Mine; Demir, Lütfü

2016-09-01

The effects of external magnetic field and exciting photon energies on the Kβ/Kα X-ray intensity ratios of various alloy compositions of Ti-Ni transition metal alloys have been investigated in this work using X-ray fluorescence spectroscopy. The spectrum of characteristic K-X-ray photons from pure Ti, pure Ni and TixNi1-x (x=0.30; 0.40; 0.50; 0.60; 0.70) alloys were detected with a high resolution Si (Li) solid-state detector. Firstly, Kβ/Kα X-ray intensity ratios of pure Ti, pure Ni and TixNi1-x alloys were measured following excitation by 59.54keV γ-rays from a 200mCi (241)Am radioactive point source without any magnetic field and under 0.5 and 1T external magnetic fields, separately. Later, the same measurements were repeated under the same experimental conditions for 22.69keV X-rays from a 370 MBq(1)(0)(9)Cd radioactive point source. The results obtained for Kβ/Kα X-ray intensity ratios of pure Ti, pure Ni, Ti and Ni in various Ti-Ni alloys were evaluated in terms of both external magnetic field effect and exciting photon energy effect. When the results obtained for both exciting photon energies are evaluated in terms of changing of Kβ/Kα X-ray intensity ratios depending on the alloy composition, the tendency of these changes are observed to be similar. Also, Kβ/Kα X-ray intensity ratios for all samples examined have changed with increasing external magnetic field. Therefore, the results obtained have shown that Kβ/Kα X-ray intensity ratios of Ti and Ni in TixNi1-x alloys are connected with the external magnetic field. The present study makes it possible to perform reliable interpretation of experimental Kβ/Kα X-ray intensity ratios for Ti, Ni and TixNi1-x alloys and can also provide quantitative information about the changes of the Kβ/Kα X-ray intensity ratios of these metals with alloy composition. Copyright © 2016 Elsevier Ltd. All rights reserved.

Core losses of a permanent magnet synchronous motor with an amorphous stator core under inverter and sinusoidal excitations

Science.gov (United States)

Yao, Atsushi; Sugimoto, Takaya; Odawara, Shunya; Fujisaki, Keisuke

2018-05-01

We report core loss properties of permanent magnet synchronous motors (PMSM) with amorphous magnetic materials (AMM) core under inverter and sinusoidal excitations. To discuss the core loss properties of AMM core, a comparison with non-oriented (NO) core is also performed. In addition, based on both experiments and numerical simulations, we estimate higher (time and space) harmonic components of the core losses under inverter and sinusoidal excitations. The core losses of PMSM are reduced by about 59% using AMM stator core instead of NO core under sinusoidal excitation. We show that the average decrease obtained by using AMM instead of NO in the stator core is about 94% in time harmonic components.

Core losses of a permanent magnet synchronous motor with an amorphous stator core under inverter and sinusoidal excitations

Directory of Open Access Journals (Sweden)

Atsushi Yao

2018-05-01

Full Text Available We report core loss properties of permanent magnet synchronous motors (PMSM with amorphous magnetic materials (AMM core under inverter and sinusoidal excitations. To discuss the core loss properties of AMM core, a comparison with non-oriented (NO core is also performed. In addition, based on both experiments and numerical simulations, we estimate higher (time and space harmonic components of the core losses under inverter and sinusoidal excitations. The core losses of PMSM are reduced by about 59% using AMM stator core instead of NO core under sinusoidal excitation. We show that the average decrease obtained by using AMM instead of NO in the stator core is about 94% in time harmonic components.

Magnetic-sublevel cross sections for excitation of the n 1P levels of helium by electron impact

International Nuclear Information System (INIS)

Csanak, G.; Cartwright, D.C.; Trajmar, S.

1992-01-01

First-order many-body theory has been used to calculate collision-frame magnetic-sublevel differential cross sections for electron-impact excitation of the n 1 P (n=2,3,4,5,6) levels of helium for electrons with incident energy in the 25--500-eV range. By combining results from electron-impact differential-cross-section measurements and electron-photon coincidence measurements, experimental magnetic-sublevel cross sections have also been derived for the excitation of the 2 1 P and 3 1 P levels. The theory predicts a pronounced minimum for the M=0 magnetic-sublevel differential cross section for incident electron energies around 30 eV. Our theoretical results are compared to the experimental data and some other theoretical results

Wake-Field Wave Resonant Excitation in Magnetized Plasmas by Electromagnetic Pulse

International Nuclear Information System (INIS)

Milant'ev, V.P.; Turikov, V.A.

2006-01-01

In this paper the space charge wave excitation process at electromagnetic pulse propagation along external magnetic field in vicinity of electron cyclotron resonance. In hydrodynamic approach it is obtained an equation for plasma density under ponderomotive force action. With help of this equation we investigated a wake-field wave amplitude dependence from resonance detuning. The numerical simulation using a PIC method electromagnetic pulse propagation process in the resonant conditions was done

Electronic excitation-induced structural, optical, and magnetic properties of Ni-doped HoFeO{sub 3} thin films

Energy Technology Data Exchange (ETDEWEB)

Habib, Zubida [National Institute of Technology, Department of Chemistry, Srinagar (India); National Institute of Technology, Department of Physics, Srinagar (India); Ikram, Mohd; Mir, Sajad A. [National Institute of Technology, Department of Physics, Srinagar (India); Sultan, Khalid [Central University of Kashmir, Department of Physics, Srinagar (India); Abida [Govt Degree College for Women, Department of Physics, Anantnag, Kashmir (India); Majid, Kowsar [National Institute of Technology, Department of Chemistry, Srinagar (India); Asokan, K. [Inter University Accelerator Centre, New Delhi (India)

2017-06-15

Present study investigates the electronic excitation-induced modifications in the structural, optical, and magnetic properties of Ni-doped HoFeO{sub 3} thin films grown by pulsed laser deposition on LaAlO{sub 3} substrates. Electronic excitations were induced by 200 MeV Ag{sup 12+} ion beam. These thin films were then characterized using X-ray diffraction (XRD), atomic force microscopy (AFM), UV-Vis spectroscopy, and magnetic measurements. X-ray diffraction analysis confirms that the crystallite growth occurs in the preferred (111) orientation with orthorhombic structure. The XRD results also show that the crystallite size decreases with ion irradiation. AFM results after irradiation show significant changes in the surface roughness and morphology of these films. The optical parameters measured from absorption measurements reveal reduction in the band gap with Ni doping and enhancement of band gap after irradiation. The magnetization vs field measurement at 75 K shows enhancement in saturation magnetization after irradiation for HoFe{sub 1-x}Ni{sub x}O{sub 3} (x = 0.1 and 0.3) films compared to HoFeO{sub 3} film. Present study shows electronic excitation induces significant changes in the physical properties of these films. (orig.)

Extremely long-lived magnetic excitations in supported Fe chains

Science.gov (United States)

Gauyacq, J. P.; Lorente, N.

2016-07-01

We report on a theoretical study of the lifetime of the first excited state of spin chains made of an odd number of Fe atoms on C u2N /Cu (100 ) . Yan, Choi, Burgess, Rolf-Pissarczyk, and Loth [Nat. Nanotech. 10, 40 (2015), 10.1038/nnano.2014.281] recently observed very long lifetimes in the case of F e3 chains. We consider the decay of the first excited state induced by electron-hole pair creation in the substrate. For a finite magnetic field, the two lowest-lying states in the chain have a quasi-Néel state structure. Decay from one state to the other strongly depends on the degree of entanglement of the local spins in the chain. The weak entanglement in the chain accounts for the long lifetimes that increase exponentially with chain length. Despite their apparently very different properties, the behavior of odd and even chains is governed by the same kind of phenomena, in particular entanglement effects. The present results account quite well for the lifetimes recently measured by Yan et al. on F e3 .

Gravitational Resonance Spectroscopy with an Oscillating Magnetic Field Gradient in the GRANIT Flow through Arrangement

International Nuclear Information System (INIS)

Rebreyend, D.; Pignol, G.; Baeßler, S.; Nesvizhevsky, V. V.; Protasov, K.; Voronin, A.

2014-01-01

Gravitational resonance spectroscopy consists in measuring the energy spectrum of bouncing ultracold neutrons above a mirror by inducing resonant transitions between different discrete quantum levels. We discuss how to induce the resonances with a flow through arrangement in the GRANIT spectrometer, excited by an oscillating magnetic field gradient. The spectroscopy could be realized in two distinct modes (so called DC and AC) using the same device to produce the magnetic excitation. We present calculations demonstrating the feasibility of the newly proposed AC mode

Spectrum of a linear antenna in a cold magnetized plasma

International Nuclear Information System (INIS)

Eldridge, O.; Kritz, A.H.

1975-04-01

The fields radiated by a linear antenna in a cold magnetized plasma are calculated. The principal results are expressed in the input impedance and power spectrum of the near field, expressed as a function of the wavenumber or index of refraction parallel to the field. For frequencies below the electron plasma frequency and above the lower hybrid frequency the spectrum shows a broad maximum for short parallel wavelengths. The parallel index of refraction at this maximum is approximately the ratio of free space wavelength to antenna length. A spectrum of this sort is required by the accessibility conditions for heating at the lower hybrid resonance from a wave launched in a region of lower density. The impedance of a short antenna in this region is capacitive and a few hundred ohms in magnitude. (U.S.)

Self running actuators moving in the same direction as the exciting magnetic field

International Nuclear Information System (INIS)

Enokizono, M.; Todaka, T.; Goto, K.

1998-01-01

This paper presents two kinds of drive units whose rotation axes are parallel to the exciting outer magnetic field. One is a hard-material-type that uses permanent magnets and silicon steel sheets to obtain the radial components of the field strength, and the other is a soft-material-type that uses the vibration of an amorphous ribbon to induce a rotational force. These drive units were developed to improve the freedom of movement of sensing devices. By combining the developed units with conventional ones, it will be possible to control the movement of devices freely by means of the outer magnetic field. In this paper, the basic characteristics of the drive units and their applicability are discussed. (author)

Evolution of the low-energy excitation spectrum from the pure Hubbard ladder to the SO(5) ladder: A numerical study

International Nuclear Information System (INIS)

Duffy, D.; Haas, S.; Kim, E.

1998-01-01

The Hubbard Hamiltonian on a two-leg ladder is studied numerically using quantum Monte Carlo and exact diagonalization techniques. A rung interaction, V, is turned on such that the resulting model has an exact SO(5) symmetry when V=-U. The evolution of the low-energy excitation spectrum is presented from the pure Hubbard ladder to the SO(5) ladder. It is shown that the low-energy excitations in the pure Hubbard ladder have an approximate SO(5) symmetry. copyright 1998 The American Physical Society

Resonant spin wave excitations in a magnonic crystal cavity

Science.gov (United States)

Kumar, N.; Prabhakar, A.

2018-03-01

Spin polarized electric current, injected into permalloy (Py) through a nano contact, exerts a torque on the magnetization. The spin waves (SWs) thus excited propagate radially outward. We propose an antidot magnonic crystal (MC) with a three-hole defect (L3) around the nano contact, designed so that the frequency of the excited SWs, lies in the band gap of the MC. L3 thus acts as a resonant SW cavity. The energy in this magnonic crystal cavity can be tapped by an adjacent MC waveguide (MCW). An analysis of the simulated micromagnetic power spectrum, at the output port of the MCW reveals stable SW oscillations. The quality factor of the device, calculated using the decay method, was estimated as Q > 105 for an injected spin current density of 7 ×1012 A/m2.

Study of Landau spectrum for a two-dimensional random magnetic field

International Nuclear Information System (INIS)

Furtlehner, C.

1997-01-01

This thesis deals with the two-dimensional problem of a charged particle coupled to a random magnetic field. Various situations are considered, according to the relative importance of the mean value of field and random component. The last one is conceived as a distribution of magnetic impurities (punctual vortex), having various statistical properties (local or non-local correlations, Poisson distribution, etc). The study of this system has led to two distinct situations: - the case of the charged particle feeling the influence of mean field that manifests its presence in the spectrum of broadened Landau levels; - the disordered situation in which the spectrum can be distinguished from the free one only by a low energy Lifshits behaviour. Additional properties are occurring in the limit of 'strong' mean field, namely a non-conventional low energy behaviour (in contrast to Lifshits behaviour) which was interpreted in terms of localized states. (author)

Melanin fluorescence spectra by step-wise three photon excitation

Science.gov (United States)

Lai, Zhenhua; Kerimo, Josef; DiMarzio, Charles A.

2012-03-01

Melanin is the characteristic chromophore of human skin with various potential biological functions. Kerimo discovered enhanced melanin fluorescence by stepwise three-photon excitation in 2011. In this article, step-wise three-photon excited fluorescence (STPEF) spectrum between 450 nm -700 nm of melanin is reported. The melanin STPEF spectrum exhibited an exponential increase with wavelength. However, there was a probability of about 33% that another kind of step-wise multi-photon excited fluorescence (SMPEF) that peaks at 525 nm, shown by previous research, could also be generated using the same process. Using an excitation source at 920 nm as opposed to 830 nm increased the potential for generating SMPEF peaks at 525 nm. The SMPEF spectrum peaks at 525 nm photo-bleached faster than STPEF spectrum.

Spin-orbit excitations and electronic structure of the putative Kitaev magnet α -RuCl3

Science.gov (United States)

Sandilands, Luke J.; Tian, Yao; Reijnders, Anjan A.; Kim, Heung-Sik; Plumb, K. W.; Kim, Young-June; Kee, Hae-Young; Burch, Kenneth S.

2016-02-01

Mott insulators with strong spin-orbit coupling have been proposed to host unconventional magnetic states, including the Kitaev quantum spin liquid. The 4 d system α -RuCl3 has recently come into view as a candidate Kitaev system, with evidence for unusual spin excitations in magnetic scattering experiments. We apply a combination of optical spectroscopy and Raman scattering to study the electronic structure of this material. Our measurements reveal a series of orbital excitations involving localized total angular momentum states of the Ru ion, implying that strong spin-orbit coupling and electron-electron interactions coexist in this material. Analysis of these features allows us to estimate the spin-orbit coupling strength, as well as other parameters describing the local electronic structure, revealing a well-defined hierarchy of energy scales within the Ru d states. By comparing our experimental results with density functional theory calculations, we also clarify the overall features of the optical response. Our results demonstrate that α -RuCl3 is an ideal material system to study spin-orbit coupled magnetism on the honeycomb lattice.

A simplified multisupport response spectrum method

Science.gov (United States)

Ye, Jihong; Zhang, Zhiqiang; Liu, Xianming

2012-03-01

A simplified multisupport response spectrum method is presented. The structural response is a sum of two components of a structure with a first natural period less than 2 s. The first component is the pseudostatic response caused by the inconsistent motions of the structural supports, and the second is the structural dynamic response to ground motion accelerations. This method is formally consistent with the classical response spectrum method, and the effects of multisupport excitation are considered for any modal response spectrum or modal superposition. If the seismic inputs at each support are the same, the support displacements caused by the pseudostatic response become rigid body displacements. The response spectrum in the case of multisupport excitations then reduces to that for uniform excitations. In other words, this multisupport response spectrum method is a modification and extension of the existing response spectrum method under uniform excitation. Moreover, most of the coherency coefficients in this formulation are simplified by approximating the ground motion excitation as white noise. The results indicate that this simplification can reduce the calculation time while maintaining accuracy. Furthermore, the internal forces obtained by the multisupport response spectrum method are compared with those produced by the traditional response spectrum method in two case studies of existing long-span structures. Because the effects of inconsistent support displacements are not considered in the traditional response spectrum method, the values of internal forces near the supports are underestimated. These regions are important potential failure points and deserve special attention in the seismic design of reticulated structures.

Getting super-excited with modified dispersion relations

Energy Technology Data Exchange (ETDEWEB)

Ashoorioon, Amjad; Casadio, Roberto [INFN—Sezione di Bologna, viale B. Pichat 6/2, I-40127 Bologna (Italy); Geshnizjani, Ghazal; Kim, Hyung J., E-mail: amjad.ashoorioon@bo.infn.it, E-mail: roberto.casadio@bo.infn.it, E-mail: ggeshniz@uwaterloo.ca, E-mail: h268kim@uwaterloo.ca [Department of Applied Mathematics, University of Waterloo Waterloo, Ontario, N2L 3G1 (Canada)

2017-09-01

We demonstrate that in some regions of parameter space, modified dispersion relations can lead to highly populated excited states, which we dub as 'super-excited' states. In order to prepare such super-excited states, we invoke dispersion relations that have negative slope in an interim sub-horizon phase at high momenta. This behaviour of quantum fluctuations can lead to large corrections relative to the Bunch-Davies power spectrum, which mimics highly excited initial conditions. We identify the Bogolyubov coefficients that can yield these power spectra. In the course of this computation, we also point out the shortcomings of the gluing method for evaluating the power spectrum and the Bogolyubov coefficients. As we discuss, there are other regions of parameter space, where the power spectrum does not get modified. Therefore, modified dispersion relations can also lead to so-called 'calm excited states'. We conclude by commenting on the possibility of obtaining these modified dispersion relations within the Effective Field Theory of Inflation.

Magnetic sublevel population in 1s-2p excitation of helium by fast electrons and protons

Energy Technology Data Exchange (ETDEWEB)

Godunov, A.L.; McGuire, J.H. [Department of Physics, Tulane University, New Orleans, LA (United States); Merabet, H.; Bruch, R.; Hanni, J. [Department of Physics, University of Nevada Reno, Reno, NV (United States); Schipakov, V.S. [Troitsk Institute for Innovation and Fusion Research, Troitsk, (Russian Federation)

2001-07-14

We report experimental and theoretical results for the magnetic sublevel population of the helium atom in collisions with fast (v{sub i}=3-9 au) electrons and protons. Cross sections for excitation of magnetic sublevels with M=0 and {+-}1 have been obtained using polarization measurements of emitted radiation in combination with differential cross sections. Calculations have been carried out using the expansion of the transition amplitude in the Born series over the projectile-target interaction through the second order. Results of calculations are in agreement with experimental data. We find that the particle-antiparticle Z{sup {+-}} difference exceeds the statistical error of measurement up to collision velocities v{sub i}{approx}6 au for excitation of sublevels with M=0. (author)

Variability of the Magnetic Field Power Spectrum in the Solar Wind at Electron Scales

Science.gov (United States)

Roberts, Owen Wyn; Alexandrova, O.; Kajdič, P.; Turc, L.; Perrone, D.; Escoubet, C. P.; Walsh, A.

2017-12-01

At electron scales, the power spectrum of solar-wind magnetic fluctuations can be highly variable and the dissipation mechanisms of the magnetic energy into the various particle species is under debate. In this paper, we investigate data from the Cluster mission’s STAFF Search Coil magnetometer when the level of turbulence is sufficiently high that the morphology of the power spectrum at electron scales can be investigated. The Cluster spacecraft sample a disturbed interval of plasma where two streams of solar wind interact. Meanwhile, several discontinuities (coherent structures) are seen in the large-scale magnetic field, while at small scales several intermittent bursts of wave activity (whistler waves) are present. Several different morphologies of the power spectrum can be identified: (1) two power laws separated by a break, (2) an exponential cutoff near the Taylor shifted electron scales, and (3) strong spectral knees at the Taylor shifted electron scales. These different morphologies are investigated by using wavelet coherence, showing that, in this interval, a clear break and strong spectral knees are features that are associated with sporadic quasi parallel propagating whistler waves, even for short times. On the other hand, when no signatures of whistler waves at ∼ 0.1{--}0.2{f}{ce} are present, a clear break is difficult to find and the spectrum is often more characteristic of a power law with an exponential cutoff.

Effect of metallurgical factors on the magnetic properties of non-oriented electrical steels under PWM excitation

International Nuclear Information System (INIS)

Tanaka, T.; Yashiki, H.; Takada, S.; Sasaki, T.

1994-01-01

Magnetic properties of non-oriented electrical steel sheets under PWM voltage excitation as well as those under sinusoidal excitation have been investigated from a metallurgical point of view. The core loss under PWM excitation is slightly larger than that under sinusoidal excitation. The induction dependence of the core loss difference between the two excitation conditions changes by changing Si content and grain size. The higher the induction, the larger the core loss difference of 0.2% Si steel with small grains. In the case of higher Si steels and 0.2% Si steel with large grain sizes, however, the core loss difference at inductions over 1.3 T decreases with increasing induction. At low induction levels the core loss difference has little relationship to the grain size. On the other hand, at high induction levels this difference decreases with increasing grain size. ((orig.))

Collisional-radiative model for the visible spectrum of W{sup 26+} ions

Energy Technology Data Exchange (ETDEWEB)

Ding, Xiaobin, E-mail: dingxb@nwnu.edu.cn [Key Laboratory of Atomic and Molecular Physics and Functional Materials of Gansu Province, College of Physics and Electronic Engineering, Northwest Normal University, Lanzhou 730070 (China); Liu, Jiaxin [Key Laboratory of Atomic and Molecular Physics and Functional Materials of Gansu Province, College of Physics and Electronic Engineering, Northwest Normal University, Lanzhou 730070 (China); Koike, Fumihiro [Department of Physics, Sophia University, Tokyo, 102-8554 (Japan); Murakami, Izumi; Kato, Daiji; Sakaue, Hiroyuki A. [National Institute for Fusion Science, Toki, Gifu 509-5292 (Japan); Nakamura, Nobuyuki [Institute for Laser Science, The University of Electro-Communications, Chofu, Tokyo 182-8585 (Japan); Dong, Chenzhong [Key Laboratory of Atomic and Molecular Physics and Functional Materials of Gansu Province, College of Physics and Electronic Engineering, Northwest Normal University, Lanzhou 730070 (China)

2016-02-22

Plasma diagnostics in magnetic confinement fusion plasmas by using visible spectrum strongly depends on the knowledge of fundamental atomic properties. A detailed collisional-radiative model of W{sup 26+} ions has been constructed by considering radiative and electron excitation processes, in which the necessary atomic data had been calculated by relativistic configuration interaction method with the implementation of Flexible Atomic Code. The visible spectrum observed at an electron beam ion trap (EBIT) in Shanghai in the range of 332 nm to 392 nm was reproduced by present calculations. Some transition pairs of which the intensity ratio is sensitive to the electron density were selected as potential candidates of plasma diagnostics. Their electron density dependence is theoretically evaluated for the cases of EBIT plasmas and magnetic confinement fusion plasmas.

Fatigue Damage Spectrum calculation in a Mission Synthesis procedure for Sine-on-Random excitations

International Nuclear Information System (INIS)

Angeli, Andrea; Troncossi, Marco; Cornelis, Bram

2016-01-01

In many real-life environments, certain mechanical and electronic components may be subjected to Sine-on-Random vibrations, i.e. excitations composed of random vibrations superimposed on deterministic (sinusoidal) contributions, in particular sine tones due to some rotating parts of the system (e.g. helicopters, engine-mounted components,...). These components must be designed to withstand the fatigue damage induced by the “composed” vibration environment, and qualification tests are advisable for the most critical ones. In the case of an accelerated qualification test, a proper test tailoring which starts from the real environment (measured vibration signals) and which preserves not only the accumulated fatigue damage but also the “nature” of the excitation (i.e. sinusoidal components plus random process) is important to obtain reliable results. In this paper, the classic time domain approach is taken as a reference for the comparison of different methods for the Fatigue Damage Spectrum (FDS) calculation in case of Sine-on-Random vibration environments. Then, a methodology to compute a Sine-on-Random specification based on a mission FDS is proposed. (paper)

General expression for spectrum of magnetic anomaly due to long tabular body and its characteristics

Digital Repository Service at National Institute of Oceanography (India)

Mishra, D.C.; Murthy, K.S.R.; Rao, T.C.S.

A general expression for spectrum of magnetic anomalies-vertical, horizontal and total intensity - due to a long tabular body is derived which is used to estimate the body parameters. The analysis is extended to a marine magnetic anomaly recorded...

Modeling the collective excitations in a full Heusler Co2 FeAl0.5 Si0.5 (CFAS) spin valve magnetic nanopillar in the electromagnetic field

International Nuclear Information System (INIS)

David, Cherine; Arumugam, Brinda; Rajamani, Amuda; Natarajan, Kanimozhi

2014-01-01

This paper describes the physics of collective excitations that are caused by spin-transfer torques in CFAS magnetic multilayer. When the magnetizations of the pinned and free layers are not collinear with each other, the spin-polarized currents transfer angular momentum to the magnetizations near the interfaces, giving rise to spin-transfer torques. The currents in magnetic multilayer are spin polarised and can carry enough angular momentum. When an electron spin carried by the current interacts with a magnetic layer, the exchange interaction leads to torque between the spin and the magnetization vector of the free layer. This is Spin Transfer Torque (STT) and it excites the magnetization when it is large enough. The Spin Transfer Torque induced collective excitations for the CFAS spin valve pillar have been extensively studied in this paper. - Highlights: • We have modeled LLGS equation for CFAS multilayer array. • The dynamics of collective excitation induced by STT is investigated. • The interactions exhibit solitonic behaviour at both limiting modes of polarization. • The spin components of the solitons are graphically represented

Use of advanced magnetic resonance imaging techniques in neuromyelitis optica spectrum disorder

NARCIS (Netherlands)

S. Kremer (Stephane); F. Renard (Felix); S. Achard (Sophie); M.A. Lana-Peixoto (Marco A.); J. Palace (Jacqueline); N. Asgari (Nasrin); E.C. Klawiter (Eric C.); S. Tenembaum (Silvia); B. Banwell (Brenda); B.M. Greenberg (Benjamin M.); J.L. Bennett (Jeffrey); M. Levy (Michael); P. Villoslada (Pablo); A. Saiz (Albert Abe); K. Fujihara (Kazuo); K.H. Chan (Koon Ho); S. Schippling (Sven); F. Paul (Friedemann); H.J. Kim (Ho Jin); J. De Seze (Jerome); J.T. Wuerfel (Jens T.); P. Cabre (Philippe); R. Marignier (Romain); T. Tedder (Thomas); E.D. van Pelt - Gravesteijn (Daniëlle); S. Broadley (Simon); T. Chitnis (Tanuja); D. Wingerchuk (Dean); L. Pandit (Lekha); M.I. Leite (M. Isabel); M. Apiwattanakul (Metha); I. Kleiter (Ingo); N. Prayoonwiwat (Naraporn); M. Han (May); K. Hellwig (Kerstin); K. Van Herle (Katja); G. John (Gareth); D.C. Hooper (D. Craig); I. Nakashima (Ichiro); D. Sato (Douglas); M.R. Yeaman (Michael R.); E. Waubant (Emmanuelle); S. Zamvil (Scott); O. Stüve (Olaf); O. Aktas (Orhan); T.J. Smith (Terry J.); A. Jacob (Anu); K. O'Connor (Kevin)

2015-01-01

textabstractBrain parenchymal lesions are frequently observed on conventional magnetic resonance imaging (MRI) scans of patients with neuromyelitis optica (NMO) spectrum disorder, but the specific morphological and temporal patterns distinguishing them unequivocally from lesions caused by other

Excitation of plasma waves by unstable photoelectron and thermal electron populations on closed magnetic field lines in the Martian ionosphere

Directory of Open Access Journals (Sweden)

N. Borisov

2005-06-01

Full Text Available It is argued that anisotropic electron pitch angle distributions in the closed magnetic field regions of the Martian ionosphere gives rise to excitation of plasma instabilities. We discuss two types of instabilities that are excited by two different populations of electrons. First, the generation of Langmuir waves by photoelectrons with energies of the order of 10eV is investigated. It is predicted that the measured anisotropy of their pitch angle distribution at the heights z≈400km causes excitation of waves with frequencies f~30kHz and wavelengths λ~30m. Near the terminators the instability of the electrostatic waves with frequencies of the order of or less than the electron gyrofrequency exited by thermal electrons is predicted. The typical frequencies of these waves depend on the local magnitude of the magnetic field and can achieve values f~3-5kHz above strong crustal magnetic fields.

Ultra-small v-shaped gold split ring resonators for biosensing using fundamental magnetic resonance in the visible spectrum

Science.gov (United States)

Mauluidy Soehartono, Alana; Mueller, Aaron David; Tobing, Landobasa Yosef Mario; Chan, Kok Ken; Zhang, Dao Hua; Yong, Ken-Tye

2017-10-01

Strong light localization within metal nanostructures occurs by collective oscillations of plasmons in the form of electric and magnetic resonances. This so-called localized surface plasmon resonance (LSPR) has gained much interest in the development of low-cost sensing platforms in the visible spectrum. However, demonstrations of LSPR-based sensing are mostly limited to electric resonances due to the technological limitations for achieving magnetic resonances in the visible spectrum. In this work, we report the first demonstration of LSPR sensing based on fundamental magnetic resonance in the visible spectrum using ultrasmall gold v-shaped split ring resonators. Specifically, we show the ability for detecting adsorption of bovine serum albumin and cytochrome c biomolecules at monolayer levels, and the selective binding of protein A/G to immunoglobulin G.

Searching for Cross-Diagnostic Convergence: Neural Mechanisms Governing Excitation and Inhibition Balance in Schizophrenia and Autism Spectrum Disorders.

Science.gov (United States)

Foss-Feig, Jennifer H; Adkinson, Brendan D; Ji, Jie Lisa; Yang, Genevieve; Srihari, Vinod H; McPartland, James C; Krystal, John H; Murray, John D; Anticevic, Alan

2017-05-15

Recent theoretical accounts have proposed excitation and inhibition (E/I) imbalance as a possible mechanistic, network-level hypothesis underlying neural and behavioral dysfunction across neurodevelopmental disorders, particularly autism spectrum disorder (ASD) and schizophrenia (SCZ). These two disorders share some overlap in their clinical presentation as well as convergence in their underlying genes and neurobiology. However, there are also clear points of dissociation in terms of phenotypes and putatively affected neural circuitry. We highlight emerging work from the clinical neuroscience literature examining neural correlates of E/I imbalance across children and adults with ASD and adults with both chronic and early-course SCZ. We discuss findings from diverse neuroimaging studies across distinct modalities, conducted with electroencephalography, magnetoencephalography, proton magnetic resonance spectroscopy, and functional magnetic resonance imaging, including effects observed both during task and at rest. Throughout this review, we discuss points of convergence and divergence in the ASD and SCZ literature, with a focus on disruptions in neural E/I balance. We also consider these findings in relation to predictions generated by theoretical neuroscience, particularly computational models predicting E/I imbalance across disorders. Finally, we discuss how human noninvasive neuroimaging can benefit from pharmacological challenge studies to reveal mechanisms in ASD and SCZ. Collectively, we attempt to shed light on shared and divergent neuroimaging effects across disorders with the goal of informing future research examining the mechanisms underlying the E/I imbalance hypothesis across neurodevelopmental disorders. We posit that such translational efforts are vital to facilitate development of neurobiologically informed treatment strategies across neuropsychiatric conditions. Copyright © 2017 Society of Biological Psychiatry. Published by Elsevier Inc. All rights

Magnetic polarons in a nonequilibrium polariton condensate

Science.gov (United States)

Mietki, Paweł; Matuszewski, Michał

2017-09-01

We consider a condensate of exciton polaritons in a diluted magnetic semiconductor microcavity. Such a system may exhibit magnetic self-trapping in the case of sufficiently strong coupling between polaritons and magnetic ions embedded in the semiconductor. We investigate the effect of the nonequilibrium nature of exciton polaritons on the physics of the resulting self-trapped magnetic polarons. We find that multiple polarons can exist at the same time, and we derive a critical condition for self-trapping that is different from the one predicted previously in the equilibrium case. Using the Bogoliubov-de Gennes approximation, we calculate the excitation spectrum and provide a physical explanation in terms of the effective magnetic attraction between polaritons, mediated by the ion subsystem.

Contributions to the study of elementary excitations in crystal lattice of real solids

International Nuclear Information System (INIS)

Vamanu, V.D.

1978-01-01

Two methods for the determination of magnon and phonon elementary excitation spectrum in crystal lattices of certain real solid models have been proposed, tracing down their efficiency in interpreting and predicting certain macroscopic characteristics and behaviour of the materials from the technological point of view, such as saturation magnetization, stability of magnetic phases, spin wave resonance spectra, specific heat, radiation emission and absorbtion etc. The models selected for the real solid are created by supplying the ideal solid model - i.e.a. boundless, periodic solid crystal - with limits, shape and inner defects. Therefore, the paper investigates two typical varieties: the thin monocrystal layer and the crystal itself characterized by impurities. (author)

Analysis and optimization of hybrid excitation permanent magnet synchronous generator for stand-alone power system

Energy Technology Data Exchange (ETDEWEB)

Wang, Huijun, E-mail: huijun024@gmail.com [School of Instrumentation Science and Opto-electronics Engineering, Beihang University (China); Qu, Zheng; Tang, Shaofei; Pang, Mingqi [School of Instrumentation Science and Opto-electronics Engineering, Beihang University (China); Zhang, Mingju [Shanghai Aerospace Control Technology Institute, Shanghai (China)

2017-08-15

Highlights: • One novel permanent magnet generator structure has been proposed to reduce voltage regulation ratio. • Finite element method and equivalent circuit methods are both employed to realize rapid generator design. • Design of experiment (DOE) method is used to optimize permanent magnet shape for reduce voltage waveform distortion. • The obtained analysis and experiment results verify the proposed design methods. - Abstract: In this paper, electromagnetic design and permanent magnet shape optimization for permanent magnet synchronous generator with hybrid excitation are investigated. Based on generator structure and principle, design outline is presented for obtaining high efficiency and low voltage fluctuation. In order to realize rapid design, equivalent magnetic circuits for permanent magnet and iron poles are developed. At the same time, finite element analysis is employed. Furthermore, by means of design of experiment (DOE) method, permanent magnet is optimized to reduce voltage waveform distortion. Finally, the validity of proposed design methods is validated by the analytical and experimental results.

Analysis and optimization of hybrid excitation permanent magnet synchronous generator for stand-alone power system

International Nuclear Information System (INIS)

Wang, Huijun; Qu, Zheng; Tang, Shaofei; Pang, Mingqi; Zhang, Mingju

2017-01-01

Highlights: • One novel permanent magnet generator structure has been proposed to reduce voltage regulation ratio. • Finite element method and equivalent circuit methods are both employed to realize rapid generator design. • Design of experiment (DOE) method is used to optimize permanent magnet shape for reduce voltage waveform distortion. • The obtained analysis and experiment results verify the proposed design methods. - Abstract: In this paper, electromagnetic design and permanent magnet shape optimization for permanent magnet synchronous generator with hybrid excitation are investigated. Based on generator structure and principle, design outline is presented for obtaining high efficiency and low voltage fluctuation. In order to realize rapid design, equivalent magnetic circuits for permanent magnet and iron poles are developed. At the same time, finite element analysis is employed. Furthermore, by means of design of experiment (DOE) method, permanent magnet is optimized to reduce voltage waveform distortion. Finally, the validity of proposed design methods is validated by the analytical and experimental results.

Magnetism in layered Ruthenates

Energy Technology Data Exchange (ETDEWEB)

Steffens, Paul C.

2008-07-01

In this thesis, the magnetism of the layered Ruthenates has been studied by means of different neutron scattering techniques. Magnetic correlations in the single-layer Ruthenates of the series Ca{sub 2-x}Sr{sub x}RuO{sub 4} have been investigated as function of Sr-concentration (x=0.2 and 0.62), temperature and magnetic field. These inelastic neutron scattering studies demonstrate the coexistence of ferromagnetic paramagnon scattering with antiferromagnetic fluctuations at incommensurate wave vectors. The temperature dependence of the amplitudes and energies of both types of excitations indicate the proximity to magnetic instabilities; their competition seems to determine the complex behavior of these materials. In Ca{sub 1.8}Sr{sub 0.2}RuO{sub 4}, which shows a metamagnetic transition, the ferromagnetic fluctuations are strongly suppressed at low temperature, but appear at higher temperature or application of a magnetic field. In the high-field phase of Ca{sub 1.8}Sr{sub 0.2}RuO{sub 4} above the metamagnetic transition, a ferromagnetic magnon dominates the excitation spectrum. Polarized neutron scattering revealed the existence of a very broad signal around the zone centre, in addition to the well-known incommensurate excitations at Q=(0.3,0.3,0) in the unconventional superconductor Sr{sub 2}RuO{sub 4}. With this additional contribution, it is possible to set up a general model for the Q-dependent magnetic susceptibility, which is well consistent with the results of other measurement methods that do not resolve the Q-dependence. Upon doping with Ti, the incommensurate fluctuations are enhanced, in particular near the critical concentration for the onset of magnetic order, but no divergence down to very low temperature is observed. In the bilayer Ti-doped Ca{sub 3}Ru{sub 2}O{sub 7}, the existence of magnetic order with a propagation vector of about ((1)/(4),(1)/(4),0) has been discovered and characterized in detail. Above and below T{sub N}, excitations at this

Magnetism in layered Ruthenates

International Nuclear Information System (INIS)

Steffens, Paul C.

2008-01-01

In this thesis, the magnetism of the layered Ruthenates has been studied by means of different neutron scattering techniques. Magnetic correlations in the single-layer Ruthenates of the series Ca 2-x Sr x RuO 4 have been investigated as function of Sr-concentration (x=0.2 and 0.62), temperature and magnetic field. These inelastic neutron scattering studies demonstrate the coexistence of ferromagnetic paramagnon scattering with antiferromagnetic fluctuations at incommensurate wave vectors. The temperature dependence of the amplitudes and energies of both types of excitations indicate the proximity to magnetic instabilities; their competition seems to determine the complex behavior of these materials. In Ca 1.8 Sr 0.2 RuO 4 , which shows a metamagnetic transition, the ferromagnetic fluctuations are strongly suppressed at low temperature, but appear at higher temperature or application of a magnetic field. In the high-field phase of Ca 1.8 Sr 0.2 RuO 4 above the metamagnetic transition, a ferromagnetic magnon dominates the excitation spectrum. Polarized neutron scattering revealed the existence of a very broad signal around the zone centre, in addition to the well-known incommensurate excitations at Q=(0.3,0.3,0) in the unconventional superconductor Sr 2 RuO 4 . With this additional contribution, it is possible to set up a general model for the Q-dependent magnetic susceptibility, which is well consistent with the results of other measurement methods that do not resolve the Q-dependence. Upon doping with Ti, the incommensurate fluctuations are enhanced, in particular near the critical concentration for the onset of magnetic order, but no divergence down to very low temperature is observed. In the bilayer Ti-doped Ca 3 Ru 2 O 7 , the existence of magnetic order with a propagation vector of about ((1)/(4),(1)/(4),0) has been discovered and characterized in detail. Above and below T N , excitations at this wave vector and another one, related to Sr 3 Ru 2 O 7 , have been

Magnetic resonance imaging is often misleading when used as an adjunct to ultrasound in the management of placenta accreta spectrum disorders.

Science.gov (United States)

Einerson, Brett D; Rodriguez, Christina E; Kennedy, Anne M; Woodward, Paula J; Donnelly, Meghan A; Silver, Robert M

2018-06-01

Magnetic resonance imaging is reported to have good sensitivity and specificity in the diagnosis of placenta accreta spectrum disorders, and is often used as an adjunct to ultrasound. But the additional utility of obtaining magnetic resonance imaging to assist in the clinical management of patients with placenta accreta spectrum disorders, above and beyond the information provided by ultrasound, is unknown. We aimed to determine whether magnetic resonance imaging provides data that may inform clinical management by changing the sonographic diagnosis of placenta accreta spectrum disorders. In all, 78 patients with sonographic evidence or clinical suspicion of placenta accreta spectrum underwent magnetic resonance imaging of the abdomen and pelvis in orthogonal planes through the uterus utilizing T1- and T2-weighted imaging sequences at the University of Utah and the University of Colorado from 1997 through 2017. The magnetic resonance imaging was interpreted by radiologists with expertise in diagnosis of placenta accreta spectrum who had knowledge of the sonographic interpretation and clinical risk factors for placenta accreta spectrum disorders. The primary outcome was a change in diagnosis from sonographic interpretation that could alter clinical management, which was defined a priori. Diagnostic accuracy was verified by surgical and histopathologic diagnosis at the time of delivery. A change in diagnosis that could potentially alter clinical management occurred in 28 (36%) cases. Magnetic resonance imaging correctly changed the diagnosis in 15 (19%), and correctly confirmed the diagnosis in 34 (44%), but resulted in an incorrect change in diagnosis in 13 (17%), and an incorrect confirmation of ultrasound diagnosis in 15 (21%). Magnetic resonance imaging was not more likely to change a diagnosis in the 24 cases of posterior and lateral placental location compared to anterior location (33% vs 37%, P = .84). Magnetic resonance imaging resulted in overdiagnosis in

High energy excitations in itinerant ferromagnets

International Nuclear Information System (INIS)

Prange, R.E.

1984-01-01

Itinerant magnets, those whose electrons move throughout the crystal, are described by band theory. Single particle excitations offer confirmation of band theory, but their description requires important corrections. The energetics of magnetism in iron and nickel is also described in band theory but requires complex bands. Magnetism above the critical temperature and the location of the critical temperature offer discriminants between the two major models of magnetism at high temperature and can be addressed by high energy excitations

Quasiparticle Excitations with Berry Curvature in Insulating Magnets and Weyl Semimetals

Science.gov (United States)

Hirschberger, Maximilian Anton

The concept of the geometric Berry phase of the quantum mechanical wave function has led to a better theoretical understanding of natural phenomena in all fields of fundamental physics research. In condensed matter physics, the impact of this theoretical discovery has been particularly profound: The quantum Hall effect, the anomalous Hall effect, the quantum spin Hall effect, magnetic skyrmions, topological insulators, and topological semimetals are but a few subfields that have witnessed rapid developments over the three decades since Michael Berry's landmark paper. In this thesis, I will present and discuss the results of three experiments where Berry's phase leads to qualitatively new transport behavior of electrons or magnetic spin excitations in solids. We introduce the theoretical framework that leads to the prediction of a thermal Hall effect of magnons in Cu(1,3-bdc), a simple two-dimensional layered ferromagnet on a Kagome net of spin S = 1/2 copper atoms. Combining our experimental results measured down to very low temperatures T = 0.3 K with published data from inelastic neutron scattering, we report a quantitative comparison with the theory. This confirms the expected net Berry curvature of the magnon band dispersion in this material. Secondly, we have studied the thermal Hall effect in the frustrated pyrochlore magnet Tb2Ti2O7, where the thermal Hall effect is large in the absence of long-range magnetic order. We establish the magnetic nature of the thermal Hall effect in Tb2Ti2O7, introducing this material as the first example of a paramagnet with non-trivial low-lying spin excitations. Comparing our results to other materials with zero thermal Hall effect such as the classical spin ice Dy2Ti 2O7 and the non-magnetic analogue Y2Ti2O 7, we carefully discuss the experimental limitations of our setup and rule out spurious background signals. The third and final chapter of this thesis is dedicated to electrical transport and thermopower experiments on the

Characteristics of the self-excited ionization waves in a magnetized positive column

International Nuclear Information System (INIS)

Maruyama, Takeo; Yamamura, Yasuhiro; Takano, Saburo; Miura, Kosuke; Imazu, Shingo.

1979-01-01

In the past, metastable atoms were not considered in the investigations of ionization waves generated in a positive column weakly ionized. However, metastable atoms seem to be important for the generation of ionization waves, and there are many unknown factors. In this paper, the fundamental equations and dispersion relation are explained under the assumption of axi-symmetrical positive column plasma placed in a uniform magnetic field, and the direct ionization frequency and excitation frequency, cumulative ionization coefficient, electron density and metastable atom density, the energy loss factor for electrons, the dependence of plasma quantities on magnetic field and dispersion characteristics are calculated. Experiments have been conducted using Ne gas in a discharge tube of 80 cm long and 1 cm radius with heated oxide cathode. Magnetic field was obtained with a solenoid coil of 75 cm long, 9 cm I.D. and 27 cm O.D. The axially uniform magnetic field was in the range of 35 to 40 cm. As the results, the following points have become clear. (1) The number of waves, angular frequency and phase velocity of ionization waves decrease with the increase of magnetic field. (2) By the consideration of the presence of metastable atoms, the theoretical values were improved pretty well and agreed with the experimental values qualitatively and quantitatively. (3) Longitudinal magnetic field has the effect of suppressing the growth of ionization waves because of the reduction of time and spatial growth rates with the increase of magnetic field. (Wakatsuki, Y.)

Measurements of the power spectrum and dispersion relation of self-excited dust acoustic waves

Science.gov (United States)

Nosenko, V.; Zhdanov, S. K.; Kim, S.-H.; Heinrich, J.; Merlino, R. L.; Morfill, G. E.

2009-12-01

The spectrum of spontaneously excited dust acoustic waves was measured. The waves were observed with high temporal resolution using a fast video camera operating at 1000 frames per second. The experimental system was a suspension of micron-size kaolin particles in the anode region of a dc discharge in argon. Wave activity was found at frequencies as high as 450 Hz. At high wave numbers, the wave dispersion relation was acoustic-like (frequency proportional to wave number). At low wave numbers, the wave frequency did not tend to zero, but reached a cutoff frequency instead. The cutoff value declined with distance from the anode. We ascribe the observed cutoff to the particle confinement in this region.

Excitation processes in organic systems under irradiation with vacuum ultraviolet radiation

International Nuclear Information System (INIS)

Shefer, Y.

1983-08-01

The subject of this work is the fluorescence of organic systems in the excitation range where phenomena of photon multiplication begin. It was hoped to reach the excitation energy above which the distribution of the various phenomena was constant and as a result, a linear function between the variation of the fluorescence intensity with variations of the excitation, would be obtained. The experimental set-up consisted mainly of suitable light sources, monochromators and detectors. The gated measuring system consisted of an oscilloscope, integrator and recorder. The material predominantly used in the experiments was anthracene whose absorption spectrum was investigated and calculated. The absorption spectra of various polycrystalline layers were also calculated. The absorption spectrum of a randomly ordered polycrystalline layer was compared with that of a hexane solution and a good correlation between the two spectra was obtained. For the study of the relationship between the excitation spectrum of anthracene and the order of crystal, the excitation spectrum of single crystals of anthracene was measured from 4 eV to 107 eV. For the excitation region from 10 eV to 23 eV the efficiency of exciting a singlet level by a photoelectron was calculated as a function of the kinetic energy of the photoelectron, assuming the efficiency of the recombination to be constant. The excitation spectra of single crystals of p-terphenyl, pyrene and phenanthrene were also examined. In all four crystals the excitation spectrum rises monotonically with an increase in the energy of the exciting photon. (author)

Excited State s-cis Rotamers Produced by Extreme Red Edge Excitation of all-trans-1,4-Diphenyl-1,3-butadiene

DEFF Research Database (Denmark)

Wallace-Williams, Stacie E.; Møller, Søren; Goldbeck, Robert A.

1993-01-01

with the wavelength independence observed for the excited singlet-state absorption and fluorescence emission spectra of 1,5-diphenyl-2,3,4,6,7,8- hexahydronaphthalene and for the fluorescence emission spectra of 1,4diphenyl-1,3-cyclopentadiene, s-trans and s-cis structural analogs of DPB, respectively. The spectral...... changes in DPB can be explained in terms of an excitation wavelength-dependent production of s-cis and s-trans rotamer populations in the excited state. The DPB fluorescence emission spectrum was resolved into s-cis and s-trans components. The vibronic structure of the s-cis fluorescence spectrum...... is similar to that of s-trans, but the band origin is red-shifted and there is a slightly larger amplitude on the red edge. The excited-state absorption spectrum of s-cis DPB appears to be red-shifted relative to that of s-trans DPB as well....

Resonantly enhanced production of excited fragments of gaseous molecules following core-level excitation

International Nuclear Information System (INIS)

Chen, J.M.; Lu, K.T.; Lee, J.M.; Ho, S.C.; Chang, H.W.; Lee, Y.Y.

2005-01-01

State-selective dissociation dynamics for the excited fragments of gaseous Si(CH 3 ) 2 Cl 2 following Cl 2p and Si 2p core-level excitations have been investigated by resonant photoemission spectroscopy and dispersed UV/optical fluorescence spectroscopy. The main features in the gaseous Si(CH 3 ) 2 Cl 2 fluorescence spectrum are identified as the emission from excited Si*, Si + *, CH* and H*. The core-to-Rydberg excitations at both Si 2p and Cl 2p edges lead to a noteworthy production of not only the excited atomic fragments, neutral and ionic (Si*, Si + *) but also the excited diatomic fragments (CH*). In particular, the excited neutral atomic fragments Si* are significantly reinforced. The experimental results provide deeper insight into the state-selective dissociation dynamics for the excited fragments of molecules via core-level excitation

Emission spectroscopic studies on dynamics of molecular excitation and dissociation by controlled electron impact

International Nuclear Information System (INIS)

Ogawa, Teiichiro

1986-01-01

Emission spectrum by controlled electron impact has been a successful technique for the investigation of molecular dynamics. (1) Molecular excitation. Aromatic molecules give an optical emission similar to fluorescence. However, as is shown by the vibrational structure and the electron energy dependence of benzene emission, its excitation process is not necessarily optical. Some aliphatic molecules also exhibit an emission band at the ultraviolet region. (2) Molecular dissociation. Analysis of the Doppler profile, the threshold energy, the excitation function and the isotope effect of the atomic emission produced in electron-molecule collisions has clarified the dynamics of the molecular dissociation. Especially the Doppler profile has given the translational energy distribution of the fragment atom, which is very useful to disclose the potential energy curve. Its angular dependence has recently found to allow determination of the symmetry of the intermediate excited state and the magnetic sublevel distribution of the fragment atom. These finding has revealed detailed state-to-state dynamics of the molecular dissociation. (author)

Electrostatic lower hybrid waves excited by electromagnetic whistler mode waves scattering from planar magnetic-field-aligned plasma density irregularities

International Nuclear Information System (INIS)

Bell, T.F.; Ngo, H.D.

1990-01-01

Recent satellite observations demonstrate that high amplitude, short wavelength (5 m ≤ λ ≤ 100 m) electrostatic waves are commonly excited by electromagnetic whistler mode waves propagating in regions of the magnetosphere and topside ionosphere where small-scale magnetic-field-aligned plasma density irregularities are thought to exist. A new theoretical model of this phenomenon is presented, based upon passive linear scattering in a cold magnetoplasma. In this model the electrostatic waves are excited by linear mode coupling as the incident electromagnetic whistler mode waves scatter from the magnetic-field-aligned plasma density irregularities. The excited short wavelength waves are quasi-electrostatic whistler mode waves, a type of lower hybrid wave, whose wave normal lies near the whistler mode resonance cone where the wave refractive index becomes very large. The amplitude of the excited electrostatic lower hybrid waves is calculated for a wide range of values of input electromagnetic wave frequency, wave normal direction, electron plasma frequency, gyrofrequency, ion composition, and irregularity scale and density enhancement. Results indicate that high amplitude lower hybrid waves can be excited over a wide range of parameters for irregularity density enhancements as low as 5% whenever the scale of the irregularity is of the same order as the lower hybrid wavelength

Energy spectrum of two-dimensional tight-binding electrons in a spatially varying magnetic field

International Nuclear Information System (INIS)

Oh, G.Y.; Lee, M.H.

1996-01-01

The electronic energy spectrum of a two-dimensional lattice in a spatially varying magnetic field is studied within the framework of the tight-binding model by using the scheme of the transfer matrix. It is found that, in comparison with the case of a uniform magnetic field, the energy spectrum exhibits more complicated behavior; band broadening (or gap closing) and band splitting (or gap opening) occur depending on characteristic parameters of the lattice. The origin of these phenomena lies in the existence of direct touching and indirect overlapping between neighboring subbands. Dependence of direct touching and indirect overlapping, and thus the electronic band structure together with the density of states, on characteristic parameters of the lattice is elucidated in detail. copyright 1996 The American Physical Society

Theory of singlet-ground-state magnetism. Application to field-induced transitions in CsFeCl3 and CsFeBr3

DEFF Research Database (Denmark)

Lindgård, P.-A.; Schmid, B.

1993-01-01

In the singlet ground-state systems CsFeCl3 and CsFeBr3 a large single-ion anisotropy causes a singlet ground state and a doubly degenerate doublet as the first excited states of the Fe2+ ion. In addition the magneteic interaction is anisotropic being much larger along the z axis than perpendicular...... to it. Therefore, these quasi-one-dimensional magnetic model systems are ideal to demonstrate unique correlation effects. Within the framework of the correlation theory we derive the expressions for the excitation spectrum. When a magnetic field is applied parallel to the z axis both substances have...

Nuclear structure studies by means of magnetic moments of excited states

International Nuclear Information System (INIS)

Kaeubler, L.; Prade, H.; Schneider, L.; Brinckmann, H.F.; Stary, F.

1981-09-01

Experimental arrangements installed at the cyclotron U-120 and the tandem accelerator EGP-10 for the in-beam measurement of magnetic moments of excited nuclear states are discribed. The Perturbed-Angular-Distribution-method (PAD) has been used. A new evaluation method has been developed for the unique determination of the Larmor frequency from spin-procession spectra R(t) with less than half of an oscillation period between consecutive particle pulses. Magnetic moments in transitional nuclei or in nuclei near closed shells ( 103 Pd, 105 Ag, 117 Sb, 117 Te, 121 Te, 121 I, 143 Pm and 207 Bi) were measured. The results are discussed with the aim to get information about the nuclear structure of the corresponding isomeric states in connection with complex spectroscopic investigations. Therefore, the experimental values are compared to the results of model calculations (core-polarization, core-particle-coupling, Nilsson, particle-rotation-coupling or shell-model) or to the estimates on the basis of the additivity of effective magnetic moments. Single-particle aspects are discussed in connection with the magnetic moments of hsub(11/2)-, dsub(5/2)- and gsub(7/2)-neutron (ν) and proton (π) states in the nuclei 103 Pd, 117 Te, 121 Te and 143 Pm, respectively. The configurations of (π) 3 and (π)(ν) 2 -three-particle states in 105 Ag, 117 Sb, 121 I and 207 Bi could be determined using the additivity rule. The experimental magnetic moments of states in 143 Pm agree very well with the results of shell-model calculations, which have firstly been carried out also for negative-parity states in this mass region. Considering magnetic moments in 117 Te and 121 Te we could demonstrate the influence of different nuclear deformations on the magnetic moments in transitional nuclei. (author)

Properties of magnetic nano-particles

DEFF Research Database (Denmark)

Lindgård, Per-Anker

1997-01-01

The intrinsic thermodynamic magnetic properties of clusters are discussed using spin wave theory for a Heisenberg model, with a fixed magnitude of the spins S-i = S and site independent nearest neighbor exchange interaction. The consequences of the more realistic Hubbard model is considered...... in which we allow for a magnetization profile at T = 0 and a structural relaxation, which in turn will give rise to a site dependent exchange interaction. Et is concluded that correlation effects among the electrons play a very important role in small clusters, albeit not modifying the thermodynamic...... properties drastically. The finite cluster size gives foremost rise to a discrete excitation spectrum with a large energy gap to the ground state. The relaxation of the magnetization during the reversal of the external magnetic field is discussed. A first step towards a quantitative understanding...

Excitation of upper-hybrid waves by a thermal parametric instability

International Nuclear Information System (INIS)

Lee, M.C.; Kuo, S.P.

1983-01-01

A purely growing instability characterized by a four-wave interaction is analysed in a uniform, magnetized plasma. Up-shifted and down-shifted upper-hybrid waves and a non-oscillatory mode can be excited by a pump wave of ordinary rather than extraordinary polarization in the case of ionospheric heating. The differential Ohmic heating force dominates over the ponderomotive force as the wave-wave coupling mechanism. The beating current at zero frequency produces a significant stabilizing effect on the excitation of short-scale modes by counterbalancing the destabilizing effect of the differential Ohmic heating. The effect of ionospheric inhomogeneity is estimated, showing a tendency to raise the thresholds of the instability. When applied to ionospheric heating experiments, the present theory can explain the excitation of field-aligned plasma lines and ionospheric irregularities with a continuous spectrum ranging from metre-scale to hundreds of metre-scale. Further, the proposed mechanism may become a competitive process to the parametric decay instability and be responsible for the overshoot phenomena of the plasma line enhancement at Arecibo. (author)

Excitation gap of fractal quantum hall states in graphene

International Nuclear Information System (INIS)

Luo, Wenchen; Chakraborty, Tapash

2016-01-01

In the presence of a magnetic field and an external periodic potential the Landau level spectrum of a two-dimensional electron gas exhibits a fractal pattern in the energy spectrum which is described as the Hofstadter’s butterfly. In this work, we develop a Hartree–Fock theory to deal with the electron-electron interaction in the Hofstadter’s butterfly state in a finite-size graphene with periodic boundary conditions, where we include both spin and valley degrees of freedom. We then treat the butterfly state as an electron crystal so that we could obtain the order parameters of the crystal in the momentum space and also in an infinite sample. A phase transition between the liquid phase and the fractal crystal phase can be observed. The excitation gaps obtained in the infinite sample is comparable to those in the finite-size study, and agree with a recent experimental observation. (paper)

The effect of magnetic field and donor impurity on electron spectrum in spherical core-shell quantum dot

Science.gov (United States)

Holovatsky, V. A.; Voitsekhivska, O. M.; Yakhnevych, M. Ya

2018-04-01

The effect of homogeneous magnetic field and location of donor impurity on the electron energy spectrum and distribution of its probability density in spherical core-shell quantum dot is investigated. In the framework of the effective mass approximation and rectangular infinitely deep potential well, the solutions of the Schrodinger equation are found using the matrix method. The wave functions are expanded over the complete set of exact functions obtained without the magnetic field and impurity. It is shown that when the induction of magnetic field increases, the ground state of electron in the nanostructure without impurity or on-center impurity is successively formed by the states with m = 0, -1, -2, … (Aharonov-Bohm effect). When donor impurity is located in the shell of the nanostructure the Aharonov-Bohm effect vanishes. The dependences of electron energy spectrum and its wave functions on the location of impurity, placed along the direction of magnetic field or perpendicularly to it, are studied. It is shown, that in the first case, the quantum states are characterized by the certain value of magnetic quantum number m and the expansion contains the wave functions of the states with it only. In the second case, the cylindrical symmetry of the problem is broken and the new quantum states are formed from the states with different values of all three quantum numbers n, l, m and electron energy spectrum weakly depends on the magnetic field induction.

Magnetic antenna excitation of whistler modes. IV. Receiving antennas and reciprocity

Energy Technology Data Exchange (ETDEWEB)

Stenzel, R. L., E-mail: stenzel@physics.ucla.edu; Urrutia, J. M. [Department of Physics and Astronomy, University of California, Los Angeles, California 90095-1547 (United States)

2015-07-15

Antenna radiation patterns are an important property of antennas. Reciprocity holds in free space and the radiation patterns for exciting and receiving antennas are the same. In anisotropic plasmas, radiation patterns are complicated by the fact that group and phase velocities differ and certain wave properties like helicity depend on the direction of wave propagation with respect to the background magnetic field B{sub 0}. Interference and wave focusing effects are different than in free space. Reciprocity does not necessarily hold in a magnetized plasma. The present work considers the properties of various magnetic antennas used for receiving whistler modes. It is based on experimental data from exciting low frequency whistler modes in a large uniform laboratory plasma. By superposition of linear waves from different antennas, the radiation patterns of antenna arrays are derived. Plane waves are generated and used to determine receiving radiation patterns of different receiving antennas. Antenna arrays have radiation patterns with narrow lobes, whose angular position can be varied by physical rotation or electronic phase shifting. Reciprocity applies to broadside antenna arrays but not to end fire arrays which can have asymmetric lobes with respect to B{sub 0}. The effect of a relative motion between an antenna and the plasma has been modeled by the propagation of a short wave packet moving along a linear antenna array. An antenna moving across B{sub 0} has a radiation pattern characterized by an oscillatory “whistler wing.” A receiving antenna in motion can detect any plane wave within the group velocity resonance cone. The radiation pattern also depends on loop size relative to the wavelength. Motional effects prevent reciprocity. The concept of the radiation pattern loses its significance for wave packets since the received signal does not only depend on the antenna but also on the properties of the wave packet. The present results are of fundamental

Magnetic antenna excitation of whistler modes. IV. Receiving antennas and reciprocity

International Nuclear Information System (INIS)

Stenzel, R. L.; Urrutia, J. M.

2015-01-01

Antenna radiation patterns are an important property of antennas. Reciprocity holds in free space and the radiation patterns for exciting and receiving antennas are the same. In anisotropic plasmas, radiation patterns are complicated by the fact that group and phase velocities differ and certain wave properties like helicity depend on the direction of wave propagation with respect to the background magnetic field B 0 . Interference and wave focusing effects are different than in free space. Reciprocity does not necessarily hold in a magnetized plasma. The present work considers the properties of various magnetic antennas used for receiving whistler modes. It is based on experimental data from exciting low frequency whistler modes in a large uniform laboratory plasma. By superposition of linear waves from different antennas, the radiation patterns of antenna arrays are derived. Plane waves are generated and used to determine receiving radiation patterns of different receiving antennas. Antenna arrays have radiation patterns with narrow lobes, whose angular position can be varied by physical rotation or electronic phase shifting. Reciprocity applies to broadside antenna arrays but not to end fire arrays which can have asymmetric lobes with respect to B 0 . The effect of a relative motion between an antenna and the plasma has been modeled by the propagation of a short wave packet moving along a linear antenna array. An antenna moving across B 0 has a radiation pattern characterized by an oscillatory “whistler wing.” A receiving antenna in motion can detect any plane wave within the group velocity resonance cone. The radiation pattern also depends on loop size relative to the wavelength. Motional effects prevent reciprocity. The concept of the radiation pattern loses its significance for wave packets since the received signal does not only depend on the antenna but also on the properties of the wave packet. The present results are of fundamental interest and of

Magnetic field effects on exciplex-forming systems: the effect on the locally excited fluorophore and its dependence on free energy.

Science.gov (United States)

Kattnig, Daniel R; Rosspeintner, Arnulf; Grampp, Günter

2011-02-28

This study addresses magnetic field effects in exciplex forming donor-acceptor systems. For moderately exergonic systems, the exciplex and the locally excited fluorophore emission are found to be magneto-sensitive. A previously introduced model attributing this finding to excited state reversibility is confirmed. Systems characterised by a free energy of charge separation up to approximately -0.35 eV are found to exhibit a magnetic field effect on the fluorophore. A simple three-state model of the exciplex is introduced, which uses the reaction distance and the asymmetric electron transfer reaction coordinate as pertinent variables. Comparing the experimental emission band shapes with those predicted by the model, a semi-quantitative picture of the formation of the magnetic field effect is developed based on energy hypersurfaces. The model can also be applied to estimate the indirect contribution of the exchange interaction, even if the perturbative approach fails. The energetic parameters that are essential for the formation of large magnetic field effects on the exciplex are discussed.

Study of magnetic excitations in the high critical temperature La2-xSrxCuO4 superconductor with neutrons inelastic scattering

International Nuclear Information System (INIS)

Petit, S.

1997-01-01

In this work, we question the relevance of spin correlations in the problem of high-T c superconductivity. To characterize these correlations, we present a detailed inelastic neutron scattering study of the magnetic excitations spectrum, in the high T c La 2-x Sr x CuO 4 copper oxide superconductor, as a function of temperature and strontium content x. Our study demonstrates the existence of two distinct types of fluctuations. The first type corresponds to two-dimensional isotropic fluctuations peaked at incommensurate points around the antiferromagnetic wavevector. These fluctuations show a gap below T c . The second type of fluctuations corresponds to two-dimensional very low energy, typically 1 MeV, antiferromagnetic correlations. They arise at low temperatures, for T ≤T f ∼ 10 K ≤T c . Different scenarios are discussed, namely particle-hole excitation arising because of nesting properties of the Fermi surface, stripes, and localized carriers in the CuO 2 plane because of the La/Sr substitution disorder. Next, aiming to study the interrelation between magnetism and superconductivity, we present a theoretical perturbative treatment of the t-t'-J model. This model is believed to describe the physics of the CuO 2 plane. The considered quasiparticles describe the motion of a doped hole, followed by localized spins on the copper sites. For a given doping x, two phases can exist, containing either x or 1 + x of these quasiparticles. We show at in the second phase, the exchange interaction between localized spins, combined to the intrinsic anharmonicity of these quasiparticles leads to an attractive interaction between them. We study the stability and the symmetry of a superconducting phase based on this mechanism. (author)

Analysis of the power flow in nonlinear oscillators driven by random excitation using the first Wiener kernel

Science.gov (United States)

Hawes, D. H.; Langley, R. S.

2018-01-01

Random excitation of mechanical systems occurs in a wide variety of structures and, in some applications, calculation of the power dissipated by such a system will be of interest. In this paper, using the Wiener series, a general methodology is developed for calculating the power dissipated by a general nonlinear multi-degree-of freedom oscillatory system excited by random Gaussian base motion of any spectrum. The Wiener series method is most commonly applied to systems with white noise inputs, but can be extended to encompass a general non-white input. From the extended series a simple expression for the power dissipated can be derived in terms of the first term, or kernel, of the series and the spectrum of the input. Calculation of the first kernel can be performed either via numerical simulations or from experimental data and a useful property of the kernel, namely that the integral over its frequency domain representation is proportional to the oscillating mass, is derived. The resulting equations offer a simple conceptual analysis of the power flow in nonlinear randomly excited systems and hence assist the design of any system where power dissipation is a consideration. The results are validated both numerically and experimentally using a base-excited cantilever beam with a nonlinear restoring force produced by magnets.

Magnetotransport properties in the magnetic phase of BaFe2 -xTxAs2 (T =Co ,Ni ) : A magnetic excitations approach

Science.gov (United States)

Peña, J. P.; Piva, M. M.; Rosa, P. F. S.; Pagliuso, P. G.; Adriano, C.; Grant, T.; Fisk, Z.; Baggio-Saitovitch, E.; Pureur, P.

2018-03-01

Because of their complex Fermi surfaces, the identification of the physical phenomena contributing to electronic scattering in the Fe-based superconductors is a difficult task. Here, we report on the electrical resistivity, magnetoresistance, and Hall effect in two series of BaFe2 -xTxAs2 (T =Co ,Ni ) crystals with different values of x . The T contents were chosen so that the majority of the investigated samples present an intermediate magnetically ordered state and a superconducting ground state. We interpret the obtained results in terms of scattering of charge carriers by magnetic excitations instead of describing them as resulting uniquely from effects related to multiple-band conduction. Our samples are single crystals from the structural point of view and their overall magnetotransport properties are dominated by a single magnetic state.

Impact of ultrafast demagnetization process on magnetization reversal in L10 FePt revealed using double laser pulse excitation

Science.gov (United States)

Shi, J. Y.; Tang, M.; Zhang, Z.; Ma, L.; Sun, L.; Zhou, C.; Hu, X. F.; Zheng, Z.; Shen, L. Q.; Zhou, S. M.; Wu, Y. Z.; Chen, L. Y.; Zhao, H. B.

2018-02-01

Ultrafast laser induced magnetization reversal in L10 FePt films with high perpendicular magnetic anisotropy was investigated using single- and double-pulse excitations. Single-pulse excitation beyond 10 mJ cm-2 caused magnetization (M) reversal at the applied fields much smaller than the static coercivity of the films. For double-pulse excitation, both coercivity reduction and reversal percentage showed a rapid and large decrease with the increasing time interval (Δt) of the two pulses in the range of 0-2 ps. In this Δt range, the maximum demagnetization (ΔMp) was also strongly attenuated, whereas the integrated demagnetization signals over more than 10 ps, corresponding to the average lattice heat effect, showed little change. These results indicate that laser induced M reversal in FePt films critically relies on ΔMp. Because ΔMp is determined by spin temperature, which is higher than lattice temperature, utilizing an ultrafast laser instead of a continuous-wave laser in laser-assisted M reversal may reduce the overall deposited energy and increase the speed of recording. The effective control of M reversal by slightly tuning the time delay of two laser pulses may also be useful for ultrafast spin manipulation.

Balance of excitation and inhibition determines 1/f power spectrum in neuronal networks.

Science.gov (United States)

Lombardi, F; Herrmann, H J; de Arcangelis, L

2017-04-01

The 1/f-like decay observed in the power spectrum of electro-physiological signals, along with scale-free statistics of the so-called neuronal avalanches, constitutes evidence of criticality in neuronal systems. Recent in vitro studies have shown that avalanche dynamics at criticality corresponds to some specific balance of excitation and inhibition, thus suggesting that this is a basic feature of the critical state of neuronal networks. In particular, a lack of inhibition significantly alters the temporal structure of the spontaneous avalanche activity and leads to an anomalous abundance of large avalanches. Here, we study the relationship between network inhibition and the scaling exponent β of the power spectral density (PSD) of avalanche activity in a neuronal network model inspired in Self-Organized Criticality. We find that this scaling exponent depends on the percentage of inhibitory synapses and tends to the value β = 1 for a percentage of about 30%. More specifically, β is close to 2, namely, Brownian noise, for purely excitatory networks and decreases towards values in the interval [1, 1.4] as the percentage of inhibitory synapses ranges between 20% and 30%, in agreement with experimental findings. These results indicate that the level of inhibition affects the frequency spectrum of resting brain activity and suggest the analysis of the PSD scaling behavior as a possible tool to study pathological conditions.

Nano-polarization-converter based on magnetic plasmon resonance excitation in an L-shaped slot antenna.

Science.gov (United States)

Yang, Jing; Zhang, Jiasen

2013-04-08

We propose a nano-polarization-converter made of a resonant L-shaped slot antenna in a gold film and study its optical properties using the finite-difference time-domain method. Phase retardation between the fast and slow axes of the nano-polarization-converter originates from the simultaneous excitation of both single-surface first-order magnetic plasmon resonance mode and second-order magnetic plasmon resonance mode at the working wavelength. By adjusting the size of the slot antenna, which is still much smaller than the wavelength, the working wavelength can be tuned within a large wavelength range.

Observed periodicities and the spectrum of field variations in Holocene magnetic records

DEFF Research Database (Denmark)

Panovska, S.; Finlay, Chris; Hirt, A.M.

2013-01-01

, globally observed, periods. Rather we find a continuous broadband spectrum, with a slope corresponding to a power law with exponent of -2.3 ± 0.6 for the period range between 300 and 4000 yr. This is consistent with the hypothesis that chaotic convection in the outer core drives the majority of secular......In order to understand mechanisms that maintain and drive the evolution of the Earth's magnetic field, a characterization of its behavior on time scales of centuries to millennia is required. We have conducted a search for periodicities in Holocene sediment magnetic records, by applying three...

Statistical mechanics of magnetic excitations from spin waves to stripes and checkerboards

CERN Document Server

Rastelli, Enrico

2013-01-01

The aim of this advanced textbook is to provide the reader with a comprehensive explanation of the ground state configurations, the spin wave excitations and the equilibrium properties of spin lattices described by the Ising-Heisenberg Hamiltonians in the presence of short (exchange) and long range (dipole) interactions.The arguments are presented in such detail so as to enable advanced undergraduate and graduate students to cross the threshold of active research in magnetism by using both analytic calculations and Monte Carlo simulations.Recent results about unorthodox spin configurations suc

Investigation of the effect of Zn impurities and magnetic field on the spin dynamics in underdoped YBa2(Cu1-yZny)3Ox

International Nuclear Information System (INIS)

Suchaneck, Anton

2009-01-01

This work employs neutron scattering to examine the changes in the spin excitation spectrum of the underdoped high-temperature superconductor YBa 2 Cu 3 O x which is doped with zinc or subject to a strong magnetic field. Doping levels of x=6.6 and x=6.45 are used with an optional zinc substitution of 2% zinc per copper atom. A detwinning procedure is an important factor in order to reorient all twinning domains of the orthorhombic crystal cell in the same direction. Numerous single crystals were oriented and assembled to create a sample of total mass 2 g neccessary for neutron scattering experiments. The experiments were performed on triple axis neutron scattering spectrometers to measure spin excitations around the antiferromagnetic wave vector at energies up to 50 meV. Zinc substitution and magnetic field influence the spin excitations, which in the pure compound feature the resonance mode, a spin gap and an hour-glass dispersion. Upon zinc substitution the spectrum of YBa 2 (Cu 0.98 Zn 0.02 ) 3 O 6.6 is quantitatively unchanged around the resonance energy, however its marked temperature onset disappears. At lower energies new induced quasi-static excitations emerge. Similar finding have been observed in other cuprate compounds. The induced excitation exhibit a strong anisotropy in the copper planes. All these results are compared to other experimental techniques which provide comparable experimental evidence. Another compounds examined in this work is the more strongly oxygen underdoped YBa 2 (Cu 0.98 Zn 0.02 ) 3 O 6.45 . The common bilayer related signal remains unchanged with zinc substitution, however a new inter-plane correlated signal is induced indicating ordering between copper planes. A comparison with other experimental techniques indicated that the superconducting critical temperature is the sole determining factor of the qualitative spin excitation spectrum, no matter what factor are responsible for it. Additional examinations have been devoted to the

Fluorescent excitation of interstellar H2

NARCIS (Netherlands)

Black, J.H.; Dishoeck, van E.F.

1987-01-01

The infrared emission spectrum of H2 excited by ultraviolet absorption, followed by fluorescence, was investigated using comprehensive models of interstellar clouds for computing the spectrum and to assess the effects on the intensity to various cloud properties, such as density, size, temperature,

Collective excitations in itinerant spiral magnets

International Nuclear Information System (INIS)

Kampf, A.P.

1996-01-01

We investigate the coupled charge and spin collective excitations in the spiral phases of the two-dimensional Hubbard model using a generalized random-phase approximation. Already for small doping the spin-wave excitations are strongly renormalized due to low-energy particle-hole excitations. Besides the three Goldstone modes of the spiral state the dynamical susceptibility reveals an extra zero mode for low doping and strong coupling values signaling an intrinsic instability of the homogeneous spiral state. In addition, near-zero modes are found in the vicinity of the spiral pitch wave number for out-of-plane spin fluctuations. Their origin is found to be the near degeneracy with staggered noncoplanar spiral states which, however, are not the lowest energy Hartree-Fock solutions among the homogeneous spiral states. copyright 1996 The American Physical Society

Magnetic Excitations in Weakly Coupled Spin Dimers and Chains Material Cu2Fe2Ge4O13

International Nuclear Information System (INIS)

Masuda, Takatsugu; Zheludev, Andrey I.; Sales, Brian C.; Imai, S.; Uchinokura, K.; Park, S.

2005-01-01

Magnetic excitations in a weakly coupled spin dimers and chains compound Cu 2 Fe 2 Ge 4 O 13 are measured by inelastic neutron scattering. Both structure factors and dipsersion of low-energy excitations up to 10 meV energy transfer are well described by a semiclassical spin wave theory involving interacting Fe 3+ (S=5/2) chains. Additional dispersionsless excitations are observed at higher energies, at ℎω=24 meV, and associated with singlet-triplet transitions within Cu 2+ dimers. Both types of excitations can be understood by treating weak interactions between the Cu 2+ and Fe 3+ subsystems at the level of the mean-field random phase approximation. However, this simple model fails to account for the measured temperature dependence of the 24 meV mode.

Statistical moments of the angular spectrum of normal waves in a turbulent collisional magnetized plasma

International Nuclear Information System (INIS)

Aistov, A.V.; Gavrilenko, V.G.

1996-01-01

The normal incidence of a small-amplitude electromagnetic wave upon a semi-infinite turbulent collisional plasm with an oblique external magnetic field is considered. Within a small-angle-scattering approximation of the radiative transport theory, a system of differential equations is derived for statistical moments of the angular power spectrum of radiation. The dependences of the spectrum centroid, dispersion, and asymmetry on the depth of penetration are studied numerically. The nonmonotonic behavior of the dispersion is revealed, and an increase in the spectrum width with absorption anisotropy is found within some depth interval. It is shown that, at large depths, the direction of the displacement of the spectrum centroid, does not always coincide with the direction of minimum absorption

Fine structure of the magnetic spectrum of. cap alpha. -rays of ionium

Energy Technology Data Exchange (ETDEWEB)

Rosenblum, S; Valadares, M; Vial, J

1948-11-22

Using as source of Io--Th an electrolytic deposit on Pt made in 1945 (27% Io), the authors studied the magnetic spectrum of the ..cap alpha..-radiation of Io from long-exposure photographs (4 to 21 days) submitted to a microscopic counting. From a simultaneously obtained ..cap alpha..-spectrum of ThC a ratio was obtained which permitted the assigning of a value of 4682 +- 10 keV to the energy of the most rapid group of Io. This group is separated from another, of a similar order of intensity, by 69 keV. A still slower group seems to exist at 170 keV from the first one (cf Ward, Proc Cambridge Phil Soc 35 322(1939)). There are indications that the groups are of a complex nature, which points to the possible existence either of a soft gamma spectrum or of a complicated beta spectrum. The presence of Ra accumulated since 1945 is visible on the spectra obtained; in a few years it will be possible to determine directly, by the method used, the half life of Ra.

Transverse magnetic field impact on waveguide modes of photonic crystals.

Science.gov (United States)

Sylgacheva, Daria; Khokhlov, Nikolai; Kalish, Andrey; Dagesyan, Sarkis; Prokopov, Anatoly; Shaposhnikov, Alexandr; Berzhansky, Vladimir; Nur-E-Alam, Mohammad; Vasiliev, Mikhail; Alameh, Kamal; Belotelov, Vladimir

2016-08-15

This Letter presents a theoretical and experimental study of waveguide modes of one-dimensional magneto-photonic crystals magnetized in the in-plane direction. It is shown that the propagation constants of the TM waveguide modes are sensitive to the transverse magnetization and the spectrum of the transverse magneto-optical Kerr effect has resonant features at mode excitation frequencies. Two types of structures are considered: a non-magnetic photonic crystal with an additional magnetic layer on top and a magneto-photonic crystal with a magnetic layer within each period. We found that the magneto-optical non-reciprocity effect is greater in the first case: it has a magnitude of δ∼10-4, while the second structure type demonstrates δ∼10-5 only, due to the higher asymmetry of the claddings of the magnetic layer. Experimental observations show resonant features in the optical and magneto-optical Kerr effect spectra. The measured dispersion properties are in good agreement with the theoretical predictions. An amplitude of light intensity modulation of up to 2.5% was observed for waveguide mode excitation within the magnetic top layer of the non-magnetic photonic crystal structure. The presented theoretical approach may be utilized for the design of magneto-optical sensors and modulators requiring pre-determined spectral features.

Longitudinal Spin Excitations and Magnetic Anisotropy in Antiferromagnetically Ordered BaFe_{2}As_{2}

Directory of Open Access Journals (Sweden)

Chong Wang

2013-12-01

Full Text Available We report on a spin-polarized inelastic neutron-scattering study of spin waves in the antiferromagnetically ordered state of BaFe_{2}As_{2}. Three distinct excitation components are identified, with spins fluctuating along the c axis, perpendicular to the ordering direction in the ab plane and parallel to the ordering direction. While the first two “transverse” components can be described by a linear spin-wave theory with magnetic anisotropy and interlayer coupling, the third “longitudinal” component is generically incompatible with the local-moment picture. It points toward a contribution of itinerant electrons to the magnetism that is already in the parent compound of this family of Fe-based superconductors.

A high excitation magnetic quadrupole lens quadruplet incorporating a single octupole lens for a low spherical aberration probe forming lens system

Science.gov (United States)

Dou, Yanxin; Jamieson, David N.; Liu, Jianli; Li, Liyi

2018-03-01

This paper describes the design of a new probe forming lens system consisting of a high excitation magnetic quadrupole lens quadruplet that incorporates a single magnetic octupole lens. This system achieves both a high demagnification and a low spherical aberration compared to conventional high excitation systems and is intended for deployment for the Harbin 300 MeV proton microprobe for applications in space science and ion beam therapy. This relative simplicity of the ion optical design to include a single octupole lens minimizes the risks associated with the constructional and operational precision usually needed for the probe forming lens system and this system could also be deployed in microprobe systems that operate with less magnetically rigid ions. The design of the new system is validated with reference to two independent ion optical computer codes.

Optimum design and research on novel vehicle hybrid excitation synchronous generator

Directory of Open Access Journals (Sweden)

Liu Zhong-Shu

2017-01-01

Full Text Available Hybrid excitation is an organic combination of permanent magnet excitation and electric excitation. Hybrid excitation synchronous generator (HESG both has the advantages of light quality, less losses and high efficiency like permanent magnet generator and the advantages of good magnetic field adjusting performance like electric excitation generator, so it is very suitable for the vehicle application. This paper presented a novel vehicle HESG which has skew stator core, permanent magnet rotor and both armature winding and field winding in the stator. Using ANSYS software, simulating the electric excitation field and the magnetic field, and finally the main parameters of HESG were designed. The simulation and the test results both show that the novel vehicle PMSG has the advantages of small cogging torque, high efficiency, small harmonic component output voltage and low waveform aberration, so as to meet the design requirements fully.

[Effect of different excitation monitoring wavelengths on emission spectrum of red long afterglow phosphor Sr3Al2O6 : Eu2+, Dy3+].

Science.gov (United States)

Cui, Cai-e; Li, Jian; Huang, Ping; Liang, Li-ping; Wu, Yin-lan

2012-01-01

The Eu2+ and Dy3+ ion co-doped Sr3Al2O6 phosphor powders with long afterglow were prepared with high temperature solid-state reaction. The phase and the spectra properties of the material were characterized by X-ray diffraction (XRD) and fluorescence spectrophotometer. It was found that the sample is composed of pure Sr3Al2O6 phase. Furthermore, the emission peak of 537 nm under 360 nm excitation and that of 590 nm excited by 468 nm-light were obtained, respectively, and it is more interesting that the emission peaks were at 537 and 590 nm under 394 nm excitation. The effects of different excitation wavelengths on the emission spectrum were explained reasonably by the effect of nephelauxetic effect and crystal field. It revealed that the two types of luminescence with different color were caused by the differences of the center of gravity of the 5d excited state energy level and the split range of 5d energy level.

Weak turbulence and broad-spectrum excitation in a nonmagnetized electron beam via second-harmonic generation

International Nuclear Information System (INIS)

Bogdanov, A.T.

1990-01-01

The nonlinear evolution of an initially monoenergetic [ν-bar(t = 0) = (0,0,u)] electron beam propagating in a nonmagnetized dielectric medium of permittivity ε > 1, with initial velocity u ≥ c/√ε (where c is the vacuum speed of light) is investigated. The specific instability of the beam under such conditions is the cause of the generation of a broad spectrum of transverse electromagnetic waves coupled to the simultaneous excitation of the second harmonic of the beam's oscillations, both at the expense of the beam's initial kinetic energy. The system of self-consistent nonlinear equations, describing the particle-field dynamics, is treated in the spirit of the weak-turbulence approach. The integrals of the resulting nonlinear system of equations for the amplitudes of the fields of the electron density are used to evaluate the spectral distribution of the amplitudes in the saturation phase, and hence the efficiency of the transformation of the beam's energy into electromagnetic radiation as a function of the width of the spectrum of the initially present electromagnetic fluctuations. A substantial increase in this efficiency is observed in comparison with the single-mode case. (author)

Extended quantum critical phase in a magnetized spin-1/2 antiferromagnetic chain

DEFF Research Database (Denmark)

Stone, M.B.; Reich, D.H.; Broholm, C.

2003-01-01

Measurements are reported of the magnetic field dependence of excitations in the quantum critical state of the spin S=1/2 linear chain Heisenberg antiferromagnet copper pyrazine dinitrate (CuPzN). The complete spectrum was measured at k(B)T/Jless than or equal to0.025 for H=0 and H=8.7 T, where...

New formalism for determining excitation spectra of many-body systems

International Nuclear Information System (INIS)

Saito, S.; Zhang, S.B.; Louie, S.G.; Cohen, M.L.

1990-01-01

We present a new general formalism for determining the excitation spectrum of interacting many-body systems. The basic assumption is that the number of the excitations is equal to the number of sites. Within this approximation, it is shown that the density-density response functions with two different pure-imaginary energies determine the excitation spectrum. The method is applied to the valence electrons of sodium clusters of differing sizes in the time-dependent local-density approximation (TDLDA). A jellium-sphere background model is used for the ion cores. The excitation spectra obtained in this way represent well the excitation spectra given by the full TDLDA calculation along the real energy axis. Important collective modes are reproduced very well

Spin wave relaxation and magnetic properties in [M/Cu] super-lattices; M=Fe, Co and Ni

International Nuclear Information System (INIS)

Fahmi, A.; Qachaou, A.

2009-01-01

In this work, we study the elementary excitations and magnetic properties of the [M/Cu] super-lattices with: M=Fe, Co and Ni, represented by a Heisenberg ferromagnetic system with N atomic planes. The nearest neighbour (NN), next nearest neighbour (NNN) exchange, dipolar interactions and surface anisotropy effects are taken into account and the Hamiltonian is studied in the framework of the linear spin wave theory. In the presence of the exchange alone, the excitation spectrum E(k) and the magnetization z >/S analytical expressions are obtained using the Green's function formalism. The obtained relaxation time of the magnon populations is nearly the same in the Fe and Co-based super-lattices, while these magnetic excitations would last much longer in the Ni-based super lattice. A numerical study of the surface anisotropy and long-ranged dipolar interaction combined effects are also reported. The exchange integral values deduced from a comparison with experience for the three super-lattices are coherent.

Theoretical research relating to excitation spectrum of furan. Application of integral direct coupled cluster linear response (direct CCLR) method; Furan no reiki supekutoru ni kansuru ronriteki kenkyu. Integral-direct Coupled Cluster Linear Response (direct CCLR) ho no tekiyo

Energy Technology Data Exchange (ETDEWEB)

Shigemitsu, Yasuhiro. [Nagasaki Industrial Technology Center, Nagasaki (Japan)

1999-07-01

heoretical researches relating to excitation spectrum of furan have been carried out for many years, and they reveal the problems that should be solved in order to predict highly reliable excitation energy. In general, it is difficult to uniformly obtain highly reliable calculation results for all excitation states since different excitation states show different electronic correlative effects. Means for obtaining the electron states in ground state and excited state and calculating the energy difference thereof is the mainstream of the theoretical calculation of the excitation energy. CASSCF/CASPT 2 developed by Roos et al. is a typical method excellent in quantitative description. Recently, the comparison between direct CCLR and CASSCF/CASPT 2 as examples for calculating the excitation spectrum of furan was carried out by using the same ground function. For Rydberg excitation, CC3, CAS, CASPT 2 show good agreement with each other. (NEDO)

Magnetically levitated autoparametric broadband vibration energy harvesting

International Nuclear Information System (INIS)

Kurmann, L.; Jia, Y.; Manoli, Y.; Woias, P.

2016-01-01

Some of the lingering challenges within the current paradigm of vibration energy harvesting (VEH) involve narrow operational frequency range and the inevitable non-resonant response from broadband noise excitations. Such VEHs are only suitable for limited applications with fixed sinusoidal vibration, and fail to capture a large spectrum of the real world vibration. Various arraying designs, frequency tuning schemes and nonlinear vibratory approaches have only yielded modest enhancements. To fundamentally address this, the paper proposes and explores the potentials in using highly nonlinear magnetic spring force to activate an autoparametric oscillator, in order to realize an inherently broadband resonant system. Analytical and numerical modelling illustrate that high spring nonlinearity derived from magnetic levitation helps to promote the 2:1 internal frequency matching required to activate parametric resonance. At the right internal parameters, the resulting system can intrinsically exhibit semi-resonant response regardless of the bandwidth of the input vibration, including broadband white noise excitation. (paper)

Harmonic excitations in quasicrystals

International Nuclear Information System (INIS)

Luck, J.M.

1986-03-01

The harmonic excitations (phonons) of quasicrystals are studied in a simple one-dimensional model. The spectrum is a Cantor set, which exhibits selfsimilarity properties. The eigenstates are generically ''critical'', i.e. neither extended nor localized

Topics in magnetism: magnetic excitations in insulators

International Nuclear Information System (INIS)

Rezende, S.M.

1975-01-01

The concept of spin waves is introduced and green's functions formalism is used in connection with thermodynamic properties of ferromagnets. Simple features of magnons in ferromagnetic insulators are discussed and also of those with dipolar and anisotropic contributions in the hamiltonian. Magnons in more complex systems, e.g. antiferromagnetic crystals, are dealt with. Finally, excitation and detection of magnons are also discussed [pt

Broadband excitation by chirped pulses: application to single electron spins in diamond

International Nuclear Information System (INIS)

Niemeyer, I; Shim, J H; Zhang, J; Suter, D; Taniguchi, T; Teraji, T; Abe, H; Onoda, S; Yamamoto, T; Ohshima, T; Isoya, J; Jelezko, F

2013-01-01

Pulsed excitation of broad spectra requires very high field strengths if monochromatic pulses are used. If the corresponding high power is not available or not desirable, the pulses can be replaced by suitable low-power pulses that distribute the power over a wider bandwidth. As a simple case, we use microwave pulses with a linear frequency chirp. We use these pulses to excite spectra of single nitrogen–vacancy centres in a Ramsey experiment. Compared to the conventional Ramsey experiment, our approach increases the bandwidth by at least an order of magnitude. Compared to the conventional continuous wave-ODMR experiment, the chirped Ramsey experiment does not suffer from power broadening and increases the resolution by at least an order of magnitude. As an additional benefit, the chirped Ramsey spectrum contains not only ‘allowed’ single quantum transitions, but also ‘forbidden’ zero- and double quantum transitions, which can be distinguished from the single quantum transitions by phase-shifting the readout pulse with respect to the excitation pulse or by variation of the external magnetic field strength. (paper)

A Novel Dual-Permanent-Magnet-Excited Machine with Flux Strengthening Effect for Low-Speed Large-Torque Applications

Directory of Open Access Journals (Sweden)

Yujun Shi

2018-01-01

Full Text Available This paper proposes a novel dual-permanent-magnet-excited (DPME machine. It employs two sets of permanent magnets (PMs. One is on the rotor, the other is on the stator with PM arrays. When compared with the existing DPME machines, not all of the PMs are located in the slots formed by the iron teeth. Specifically, the radially magnetized PMs in the arrays are located under the short iron teeth, while the tangentially magnetized PMs are located in the slots formed by the long stator iron teeth and the radially magnetized PMs. Each long stator iron tooth is sandwiched by two tangentially magnetized PMs with opposite directions, thus resulting in the flux strengthening effect. The simulation analysis indicates that the proposed machine can offer large back EMF with low THD and large torque density with low torque ripple when compared with Machine I from a literature. Meanwhile, by comparison, the proposed machine has great potential in improving the power factor and efficiency.

Magnon spectrum of the helimagnetic insulator Cu2OSeO3.

Science.gov (United States)

Portnichenko, P Y; Romhányi, J; Onykiienko, Y A; Henschel, A; Schmidt, M; Cameron, A S; Surmach, M A; Lim, J A; Park, J T; Schneidewind, A; Abernathy, D L; Rosner, H; van den Brink, Jeroen; Inosov, D S

2016-02-25

Complex low-temperature-ordered states in chiral magnets are typically governed by a competition between multiple magnetic interactions. The chiral-lattice multiferroic Cu2OSeO3 became the first insulating helimagnetic material in which a long-range order of topologically stable spin vortices known as skyrmions was established. Here we employ state-of-the-art inelastic neutron scattering to comprehend the full three-dimensional spin-excitation spectrum of Cu2OSeO3 over a broad range of energies. Distinct types of high- and low-energy dispersive magnon modes separated by an extensive energy gap are observed in excellent agreement with the previously suggested microscopic theory based on a model of entangled Cu4 tetrahedra. The comparison of our neutron spectroscopy data with model spin-dynamical calculations based on these theoretical proposals enables an accurate quantitative verification of the fundamental magnetic interactions in Cu2OSeO3 that are essential for understanding its abundant low-temperature magnetically ordered phases.

Excitation mechanisms of 2s1/2-2p3/2 and 2p1/2-2p3/2 transitions in U82+ through U89+

International Nuclear Information System (INIS)

Decaux, V.; Beiersdorfer, P.; Osterheld, A.

1994-01-01

A model based on detailed calculations of the electron-impact excitation of n = 2 electrons in the Li- to Ne-like uranium ions was developed to interpret and explain measurements on EBIT (Electron Beam Ion Trap). While only considering the direct excitation process provided a good model for the electric dipole (El) transitions, it was necessary for the magnetic dipole (Ml) spectrum to include various additional excitation processes in the model. In particular, the model was expanded to include electron-impact excitation of n = 3 levels followed by radiative cascades. Moreover, excitation by the ionization of 2s 1/2 , 2p 1/2 , and 2p 3/2 electrons and by radiative capture of beam electrons into excited levels was added. The new model demonstrates that the dipole-forbidden lines are almost exclusively produced by indirect excitation processes

Sensory tricks and brain excitability in cervical dystonia: a transcranial magnetic stimulation study.

Science.gov (United States)

Amadio, Stefano; Houdayer, Elise; Bianchi, Francesca; Tesfaghebriel Tekle, Habtom; Urban, Ivan Pietro; Butera, Calogera; Guerriero, Roberta; Cursi, Marco; Leocani, Letizia; Comi, Giancarlo; Del Carro, Ubaldo

2014-08-01

Sensory tricks such as touching the face with fingertips often improve cervical dystonia [CD]. This study is to determine whether sensory tricks modulate motor cortex excitability, assessed by paired-pulse transcranial magnetic stimulation [p-pTMS]. Eight patients with rotational CD underwent p-pTMS, at rest and when the sensory trick was applied. To test intracortical inhibition [ICI] and facilitation [ICF], the amplitude ratio between conditioned and unconditioned cortical motor evoked potentials was measured at several interstimulus intervals (ISI 1, 3, 15, and 20 ms) and compared with controls mimicking patients' sensory tricks. At rest, a significant ICF enhancement was found at ISIs 15 through 20 in patients compared with controls, whereas no significant ICI changes were observed. Sensory tricks significantly reduced the abnormal ICF in patients and did not induce any change in controls. In our CD patients, sensory tricks seem to improve dystonia through an inhibitory effect on motor cortex excitability. © 2014 International Parkinson and Movement Disorder Society.

Characterization of weakly excited final states by shakedown spectroscopy of laser-excited potassium

International Nuclear Information System (INIS)

Schulz, J.; Heinaesmaeki, S.; Aksela, S.; Aksela, H.; Sankari, R.; Rander, T.; Lindblad, A.; Bergersen, H.; Oehrwall, G.; Svensson, S.; Kukk, E.

2006-01-01

3p shakedown spectra of laser excited potassium atoms as well as direct 3p photoemission of ground state potassium have been studied. These two excitation schemes lead to the same final states and thereby provide a good basis for a detailed study of the 3p 5 (4s3d) 1 configurations of singly ionized potassium and the photoemission processes leading to these configurations. The comparison of direct photoemission from the ground state and conjugate shakedown spectra from 4p 1/2 laser excited potassium made it possible to experimentally determine the character of final states that are only weakly excited in the direct photoemission but have a much higher relative intensity in the shakedown spectrum. Based on considerations of angular momentum and parity conservation the excitation scheme of the final states can be understood

Seismic response analysis of structural system subjected to multiple support excitation

International Nuclear Information System (INIS)

Wu, R.W.; Hussain, F.A.; Liu, L.K.

1978-01-01

In the seismic analysis of a multiply supported structural system subjected to nonuniform excitations at each support point, the single response spectrum, the time history, and the multiple response spectrum are the three commonly employed methods. In the present paper the three methods are developed, evaluated, and the limitations and advantages of each method assessed. A numerical example has been carried out for a typical piping system. Considerably smaller responses have been predicted by the time history method than that by the single response spectrum method. This is mainly due to the fact that the phase and amplitude relations between the support excitations are faithfully retained in the time history method. The multiple response spectrum prediction has been observed to compare favourably with the time history method prediction. Based on the present evaluation, the multiple response spectrum method is the most efficient method for seismic response analysis of structural systems subjected to multiple support excitation. (Auth.)

Comparison of multiple support excitation solution techniques for piping systems

International Nuclear Information System (INIS)

Sterkel, H.P.; Leimbach, K.R.

1980-01-01

Design and analysis of nuclear power plant piping systems exposed to a variety of dynamic loads often require multiple support excitation analysis by modal or direct time integration methods. Both methods have recently been implemented in the computer program KWUROHR for static and dynamic analysis of piping systems, following the previous implementation of the multiple support excitation response spectrum method (see papers K 6/15 and K 6/15a of the SMiRT-4 Conference). The results of multiple support excitation response spectrum analyses can be examined by carrying out the equivalent time history analyses which do not distort the time phase relationship between the excitations at different support points. A frequent point of discussion is multiple versus single support excitation. A single support excitation analysis is computationally straightforward and tends to be on the conservative side, as the numerical results show. A multiple support excitation analysis, however, does not incur much more additional computer cost than the expenditure for an initial static solution involving three times the number, L, of excitation levels, i.e. 3L static load cases. The results are more realistic than those from a single support excitation analysis. A number of typical nuclear plant piping systems have been analyzed using single and multiple support excitation algorithms for: (1) the response spectrum method, (2) the modal time history method via the Wilson, Newmark and Goldberg integration operators and (3) the direct time history method via the Wilson integration operator. Characteristic results are presented to compare the computational quality of all three methods. (orig.)

Ordering and thermal excitations in dipolar coupled single domain magnet arrays (Presentation Recording)

Science.gov (United States)

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.

A Preliminary Transcranial Magnetic Stimulation Study of Cortical Inhibition and Excitability in High-Functioning Autism and Asperger Disorder

Science.gov (United States)

Enticott, Peter G.; Rinehart, Nicole J.; Tonge, Bruce J.; Bradshaw, John L.; Fitzgerald, Paul B.

2010-01-01

Aim: Controversy surrounds the distinction between high-functioning autism (HFA) and Asperger disorder, but motor abnormalities are associated features of both conditions. This study examined motor cortical inhibition and excitability in HFA and Asperger disorder using transcranial magnetic stimulation (TMS). Method: Participants were diagnosed by…

Landau Quasi-energy Spectrum Destruction for an Electron in Both a Static Magnetic Field and a Resonant Electromagnetic Wave

International Nuclear Information System (INIS)

Skoblin, A.A.

1994-01-01

Free nonrelativistic electrons in both a static magnetic field and an electromagnetic wave are considered. A plane-polarized wave propagates along a magnetic field, its frequency is close to the electron rotation frequency in a magnetic field. Electron spin is taken into account. An electron quasi energy spectrum and steady states (quasi energy states) are constructed. 6 refs

Production of large number of water-cooled excitation coils with improved techniques for multipole magnets of INDUS -2

International Nuclear Information System (INIS)

Karmarkar, M.G.; Sreeramulu, K.; Kulshreshta, P.K.

2003-01-01

Accelerator multipole magnets are characterized by high field gradients powered with relatively high current excitation coils. Due to space limitations in the magnet core/poles, compact coil geometry is also necessary. The coils are made of several insulated turns using hollow copper conductor. High current densities in these require cooling with low conductivity water. Additionally during operation, these are subjected to thermal fatigue stresses. A large number of coils ( Qty: 650 nos.) having different geometries were required for all multipole magnets like quadrupole (QP), sextupole (SP). Improved techniques for winding, insulation and epoxy consolidation were developed in-house at M D Lab and all coils have been successfully made. Improved technology, production techniques adopted for magnet coils and their inspection are briefly discussed in this paper. (author)

Anisotropic Weyl fermions from the quasiparticle excitation spectrum of a 3D Fulde-Ferrell superfluid.

Science.gov (United States)

Xu, Yong; Chu, Rui-Lin; Zhang, Chuanwei

2014-04-04

Weyl fermions, first proposed for describing massless chiral Dirac fermions in particle physics, have not been observed yet in experiments. Recently, much effort has been devoted to explore Weyl fermions around band touching points of single-particle energy dispersions in certain solid state materials (named Weyl semimetals), similar as graphene for Dirac fermions. Here we show that such Weyl semimetals also exist in the quasiparticle excitation spectrum of a three-dimensional spin-orbit-coupled Fulde-Ferrell superfluid. By varying Zeeman fields, the properties of Weyl fermions, such as their creation and annihilation, number and position, as well as anisotropic linear dispersions around band touching points, can be tuned. We study the manifestation of anisotropic Weyl fermions in sound speeds of Fulde-Ferrell fermionic superfluids, which are detectable in experiments.

Characterizing the Motion of Solar Magnetic Bright Points at High Resolution

Science.gov (United States)

Van Kooten, Samuel J.; Cranmer, Steven R.

2017-11-01

Magnetic bright points in the solar photosphere, visible in both continuum and G-band images, indicate footpoints of kilogauss magnetic flux tubes extending to the corona. The power spectrum of bright-point motion is thus also the power spectrum of Alfvén wave excitation, transporting energy up flux tubes into the corona. This spectrum is a key input in coronal and heliospheric models. We produce a power spectrum of bright-point motion using radiative magnetohydrodynamic simulations, exploiting spatial resolution higher than can be obtained in present-day observations, while using automated tracking to produce large data quantities. We find slightly higher amounts of power at all frequencies compared to observation-based spectra, while confirming the spectrum shape of recent observations. This also provides a prediction for observations of bright points with DKIST, which will achieve similar resolution and high sensitivity. We also find a granule size distribution in support of an observed two-population distribution, and we present results from tracking passive tracers, which show a similar power spectrum to that of bright points. Finally, we introduce a simplified, laminar model of granulation, with which we explore the roles of turbulence and of the properties of the granulation pattern in determining bright-point motion.

Switchable directional excitation surface plasmon polaritons with dielectric nanoantennas

DEFF Research Database (Denmark)

Sinev, I.; Komissarenko, F.; Bogdanov, A.

We demonstrate directional launching of surface plasmon polaritons on thin goldfilm with a single silicon nanosphere. The directivity pattern of the excited surface waves exhibits rapid switching from forward to backward excitation, which is driven by the mutual interference of magnetic and elect......We demonstrate directional launching of surface plasmon polaritons on thin goldfilm with a single silicon nanosphere. The directivity pattern of the excited surface waves exhibits rapid switching from forward to backward excitation, which is driven by the mutual interference of magnetic...

Hydrogen atoms in the presence of a homogeneous magnetic field

International Nuclear Information System (INIS)

Brandi, H.S.; Koiller, B.

1978-01-01

A variational scheme to obtain the spectrum of the hydrogen atom in the presence of an external homogeneous magnetic field is proposed. Two different sets of basis function to diagonalize the Hamiltonian describing the system are used, namely the eigenfunctions of the free hydrogen atom and of the three-dimensional harmonic oscillator; both having their radial coordinates properly scaled by a variational parammeter. Because of its characteristics, the present approach is suitable to describe the ground state as well as an infinite number of excited states also for a wide range of magnetic field strengths [pt

Single excitation-emission fluorescence spectrum (EEF) for determination of cetane improver in diesel fuel.

Science.gov (United States)

Insausti, Matías; Fernández Band, Beatriz S

2015-04-05

A highly sensitive spectrofluorimetric method has been developed for the determination of 2-ethylhexyl nitrate in diesel fuel. Usually, this compound is used as an additive in order to improve cetane number. The analytical method consists in building the chemometric model as a first step. Then, it is possible to quantify the analyte with only recording a single excitation-emission fluorescence spectrum (EEF), whose data are introduced in the chemometric model above mentioned. Another important characteristic of this method is that the fuel sample was used without any pre-treatment for EEF. This work provides an interest improvement to fluorescence techniques using the rapid and easily applicable EEF approach to analyze such complex matrices. Exploding EEF was the key to a successful determination, obtaining a detection limit of 0.00434% (v/v) and a limit of quantification of 0.01446% (v/v). Copyright © 2015 Elsevier B.V. All rights reserved.

A general electromagnetic excitation model for electrical machines considering the magnetic saturation and rub impact

Science.gov (United States)

Xu, Xueping; Han, Qinkai; Chu, Fulei

2018-03-01

The electromagnetic vibration of electrical machines with an eccentric rotor has been extensively investigated. However, magnetic saturation was often neglected. Moreover, the rub impact between the rotor and stator is inevitable when the amplitude of the rotor vibration exceeds the air-gap. This paper aims to propose a general electromagnetic excitation model for electrical machines. First, a general model which takes the magnetic saturation and rub impact into consideration is proposed and validated by the finite element method and reference. The dynamic equations of a Jeffcott rotor system with electromagnetic excitation and mass imbalance are presented. Then, the effects of pole-pair number and rubbing parameters on vibration amplitude are studied and approaches restraining the amplitude are put forward. Finally, the influences of mass eccentricity, resultant magnetomotive force (MMF), stiffness coefficient, damping coefficient, contact stiffness and friction coefficient on the stability of the rotor system are investigated through the Floquet theory, respectively. The amplitude jumping phenomenon is observed in a synchronous generator for different pole-pair numbers. The changes of design parameters can alter the stability states of the rotor system and the range of parameter values forms the zone of stability, which lays helpful suggestions for the design and application of the electrical machines.

Production of excited double hypernuclei via Fermi breakup of excited strange systems

International Nuclear Information System (INIS)

Sanchez Lorente, Alicia; Botvina, Alexander S.; Pochodzalla, Josef

2011-01-01

Precise spectroscopy of multi-strange hypernuclei provides a unique chance to explore the hyperon-hyperon interaction. In the present work we explore the production of excited states in double hypernuclei following the micro-canonical break-up of an initially excited double hypernucleus which is created by the absorption and conversion of a stopped Ξ - hyperon. Rather independent on the spectrum of possible excited states in the produced double hypernuclei the formation of excited states dominates in our model. For different initial target nuclei which absorb the Ξ - , different double hypernuclei nuclei dominate. Thus the ability to assign the various observable γ-transitions in a unique way to a specific double hypernuclei by exploring various light targets as proposed by the PANDA Collaboration seems possible. We also confront our predictions with the correlated pion spectra measured by the E906 Collaboration.

Interacting Electrons and Holes in Quasi-2D Quantum Dots in Strong Magnetic Fields

Science.gov (United States)

Hawrylak, P.; Sheng, W.; Cheng, S.-J.

2004-09-01

Theory of optical properties of interacting electrons and holes in quasi-2D quantum dots in strong magnetic fields is discussed. In two dimensions and the lowest Landau level, hidden symmetries control the interaction of the interacting system with light. By confining electrons and holes into quantum dots hidden symmetries can be removed and the excitation spectrum of electrons and excitons can be observed. We discuss a theory electronic and of excitonic quantum Hall droplets at a filling factorν=2. For an excitonic quantum Hall droplet the characteristic emission spectra are predicted to be related to the total spin of electron and hole configurations. For the electronic droplet the excitation spectrum of the droplet can be mapped out by measuring the emission for increasing number of electrons.

Interacting electrons and holes in quasi-2D quantum dots in strong magnetic fields

International Nuclear Information System (INIS)

Hawrylak, P.; Sheng, W.; Cheng, S.-J.

2004-01-01

Theory of optical properties of interacting electrons and holes in quasi-2D quantum dots in strong magnetic fields is discussed. In two dimensions and the lowest Landau level, hidden symmetries control the interaction of the interacting system with light. By confining electrons and holes into quantum dots hidden symmetries can be removed and the excitation spectrum of electrons and excitons can be observed. We discuss a theory electronic and excitonic quantum Hall droplets at a filling factor υ = 2. For an excitonic quantum Hall droplet the characteristic emission spectra are predicted to be related to the total spin of electron and hole configurations. For the electronic droplet the excitation spectrum of the droplet can be mapped out by measuring the emission for increasing number of electrons. (author)

Magnetic vortex excitation as spin torque oscillator and its unusual trajectories

Science.gov (United States)

Natarajan, Kanimozhi; Muthuraj, Ponsudana; Rajamani, Amuda; Arumugam, Brinda

2018-05-01

We report an interesting observation of unusual trajectories of vortex core oscillations in a spin valve pillar. Micromagnetic simulation in the composite free layer spin valve nano-pillar shows magnetic vortex excitation under critical current density. When current density is slightly increased and wave vector is properly tuned, for the first time we observe a star like and square gyration. Surprisingly this star like and square gyration also leads to steady, coherent and sustained oscillations. Moreover, the frequency of gyration is also very high for this unusual trajectories. The power spectral analysis reveals that there is a marked increase in output power and frequency with less distortions. Our investigation explores the possibility of these unusual trajectories to exhibit spin torque oscillations.

Highly excited atoms

International Nuclear Information System (INIS)

Kleppner, D.; Littman, M.G.; Zimmerman, M.L.

1981-01-01

Highly excited atoms are often called Rydberg atoms. These atoms have a wealth of exotic properties which are discussed. Of special interest, are the effects of electric and magnetic fields on Rydberg atoms. Ordinary atoms are scarcely affected by an applied electric or magnetic field; Rydberg atoms can be strongly distorted and even pulled apart by a relatively weak electric field, and they can be squeezed into unexpected shapes by a magnetic field. Studies of the structure of Rydberg atoms in electric and magnetic fields have revealed dramatic atomic phenomena that had not been observed before

Quenching long range magnetic excitations in oxygen sub-lattice reconstructed thin films of (SrCuO{sub 2}){sub n}/(SrTiO{sub 2}){sub 2} superlattices

Energy Technology Data Exchange (ETDEWEB)

Dantz, Marcus; Pelliciari, Jonathan; Huang, Yaobo; Bisogni, Valentina; Olalde-Velasco, Paul; Strocov, Vladimir; Schmitt, Thorsten [Paul Scherrer Institut, Villigen PSI (Switzerland); Samal, Debakanta; Koster, Gertjan [MESA+ Institute for Nanotechnology, University of Twente (Netherlands)

2015-07-01

Multi-layered thin cuprate films allow inducing subtle structural changes with which local crystal field and long range magnetic excitations can be finely tuned. In (SrCuO{sub 2}){sub n}/(SrTiO{sub 2}){sub 2} cuprate superlattices, in particular, a structural transformation from a bulk infinite planar to a sheet-like local domain environment has recently been predicted and subsequently observed. Here we present results on the influence of this subtle structural reconstruction on the collective magnetic excitations using high-resolution resonant inelastic x-ray scattering (RIXS) at the Cu L{sub 3} edge. While bulk like infinite layer films exhibit magnon excitations throughout the whole Brillouin zone, decreasing the thickness of the cuprate layers leads to quenching of the magnons starting from the Gamma point successively to the zone boundary, allowing us to study the coherence length of the collective long range magnetic excitations in these cuprate superlattices.

New even parity energy levels of Pr I found by excitation of transitions in the region 560 - 695 nm

Energy Technology Data Exchange (ETDEWEB)

Syed, Tanweer Iqbal; Khan, Shamim; Imran, Siddiqui; Zaheer, Uddin; Windholz, Laurentius [Inst. f. Experimentalphysik, Techn. Univ. Graz, Petersgasse 16, A-8010 Graz (Austria)

2011-07-01

The knowledge of electronic levels is essentially needed for a description of the interactions between the electrons of an atom and for the classification of an atomic spectrum. We have studied the hyperfine structure of Praseodymium spectral lines in the region from 560 to 695 nm. The hyperfine structure of a large number of unclassified Pr I-lines have been investigated by using the method of laser induced fluorescence in a hollow cathode discharge. During this investigation, we have discovered twelve energy levels with even parity, which were previously unknown. The excitation source was a ring dye laser operated with R6G, Kiton red, or DCM. J-quantum numbers and magnetic dipole interaction constants A for upper and lower levels have been determined from the recorded hyperfine structures. The energies of new levels have been determined by using these constants, excitation and fluorescence wavelengths. Promising excitation wavelengths have been taken from Fourier transform spectra. The new levels were confirmed by at least one second laser excitation.

Pulsed magnetization transfer contrast MRI by a sequence with water selective excitation

Energy Technology Data Exchange (ETDEWEB)

Schick, F. [Univ. of Tuebingen (Germany)

1996-01-01

A water selective SE imaging sequence was developed providing suitable properties for the assessment of magnetization transfer (MT) effects in tissues with considerable amounts of fat. The sequence with water selective excitation and slice selective refocusing combines the following features: The RIF exposure on the macromolecular protons is relatively low for single slice imaging without MT prepulses, since no additional pulses for fat saturation are necessary. Water selection by frequency selective excitation diminishes faults in the subtraction of images recorded with and without MT prepulses (which might arise from movements). High differences in the signal amplitudes from hyaline cartilage and muscle tissue were obtained comparing images recorded with irradiation of the series of prepulses for MT and those lacking MT prepulses. Utilizations of the described water selective approach for the assessment of MT effects in lesions of cartilage and bone are demonstrated. MT saturation was also examined in muscles with fatty degeneration of patients suffering from progressive muscular dystrophy. The described technique allows determination of MT effects with good precision in a single slice, especially in regions with dominating fat signals. 22 refs., 5 figs.

MODELING OF EQUIVALENT STIFFNESS OF A MAGNETIC SPRING OF VIBRATION EXCITER BASED ON COAXIAL-LINEAR MOTOR

Directory of Open Access Journals (Sweden)

G.M. Golenkov

2015-12-01

Full Text Available Purpose. The research of the influence of value and direction of current on the equivalent spring magnetic force based on coaxial-linear motor (CLM – MS. Methodology. We carried out investigation of the equivalent harshness of magnetic spring with determination of electromechanical propulsion performance characteristics by the methods of computer modeling and experimental research of physical model of CLM – MS. The modeling of magnetic spring of CLM – MS is carried out by the finite-element method. The challenge is met as an axisymmetric challenge in cylindrical co-ordinates in magnetostatic approach. The experimental investigattion of the propulsion performance characteristics of magnetic spring is carried out on the test bench. Results. After the computer modeling and the experimental investigation of the electromechanical propulsion performance characteristics of magnetic spring the expressions of equivalent stiffness coefficient depending on the current in winding are obtained. The results of computer modeling are confirmed experimentally. Originality. The determination of equivalent stiffness coefficient of magnetic spring of vibration exciter based on coaxial-linear motor. Practical value. The obtained determination of equivalent stiffness coefficient of magnetic spring may be used in process of designing of vibration machines with devices for change of natural oscillation frequency.

Pseudo-Goldstone Magnons in the Frustrated S=3/2 Heisenberg Helimagnet ZnCr_{2}Se_{4} with a Pyrochlore Magnetic Sublattice

Directory of Open Access Journals (Sweden)

Y. V. Tymoshenko

2017-11-01

Full Text Available Low-energy spin excitations in any long-range ordered magnetic system in the absence of magnetocrystalline anisotropy are gapless Goldstone modes emanating from the ordering wave vectors. In helimagnets, these modes hybridize into the so-called helimagnon excitations. Here we employ neutron spectroscopy supported by theoretical calculations to investigate the magnetic excitation spectrum of the isotropic Heisenberg helimagnet ZnCr_{2}Se_{4} with a cubic spinel structure, in which spin-3/2 magnetic Cr^{3+} ions are arranged in a geometrically frustrated pyrochlore sublattice. Apart from the conventional Goldstone mode emanating from the (0 0 q_{h} ordering vector, low-energy magnetic excitations in the single-domain proper-screw spiral phase show soft helimagnon modes with a small energy gap of ∼0.17  meV, emerging from two orthogonal wave vectors (q_{h} 0 0 and (0 q_{h} 0 where no magnetic Bragg peaks are present. We term them pseudo-Goldstone magnons, as they appear gapless within linear spin-wave theory and only acquire a finite gap due to higher-order quantum-fluctuation corrections. Our results are likely universal for a broad class of symmetric helimagnets, opening up a new way of studying weak magnon-magnon interactions with accessible spectroscopic methods.

Analytical calculation of spin tunneling effect in single molecule magnet Fe8 with considering quadrupole excitation

Directory of Open Access Journals (Sweden)

Y Yousefi

2018-02-01

Full Text Available Spin tunneling effect in Single Molecule Magnet Fe8 is studied by instanton calculation technique using SU(3 generalized spin coherent state in real parameter as a trial function. For this SMM, tunnel splitting arises due to the presence of a Berry like phase in action, which causes interference between tunneling trajectories (instantons. For this SMM, it is established that the use of quadrupole excitation (g dependence changes not only the location of the quenching points, but also the number of these points. Also, these quenching points are the steps in hysteresis loops of this SMM. If dipole and quadrupole excitations in classical energy considered, the number of these steps equals to the number that obtained from experimental data.

Spin-orbit excitation energies, anisotropic exchange, and magnetic phases of honeycomb RuCl3

OpenAIRE

Yadav, Ravi; Bogdanov, Nikolay A.; Katukuri, Vamshi M.; Nishimoto, Satoshi; Brink, Jeroen van den; Hozoi, Liviu

2016-01-01

Large anisotropic exchange in 5d and 4d oxides and halides open the door to new types of magnetic ground states and excitations, inconceivable a decade ago. A prominent case is the Kitaev spin liquid, host of remarkable properties such as protection of quantum information and the emergence of Majorana fermions. Here we discuss the promise for spin-liquid behavior in the 4d 5 honeycomb halide ?-RuCl3. From advanced electronic-structure calculations, we find that the Kitaev interaction is ferro...

Transition rate diagrams - A new approach to the study of selective excitation processes: The spectrum of manganese in a Grimm-type glow discharge

Science.gov (United States)

Weiss, Zdeněk; Steers, Edward B. M.; Pickering, Juliet C.; Mushtaq, Sohail

2014-02-01

The emission spectra of manganese observed using a Grimm-type glow discharge in pure argon, argon with 0.3% v/v hydrogen and pure neon were studied in order to identify major excitation and ionization processes of manganese in the plasma. A new procedure is proposed, in which each observed emission line is associated with the corresponding transition between different states of the Mn atom or Mn ion, and, by considering all the observed transitions from and into a specific state, a measure of the total rate is determined at which this state is radiatively populated and depopulated. These resulting population/depopulation rates are then plotted as function of level energy. Such plots, called here “transition rate diagrams”, show the role of individual states in the formation of the observed spectrum and can be used to identify possible selective excitation processes. Also, cascade excitation by radiative decay of higher excited states can be conveniently evaluated in this way. A detailed description of the observed Mn I and Mn II spectra is given for Ar, Ar-H2 and Ne plasmas and relevant excitation/ionization mechanisms are discussed. Matrix effects in analysis of manganese by glow discharge spectroscopy are discussed. A list of important Mn I and Mn II lines excited in the glow discharge plasma is given.

Energy spectrum of tearing mode turbulence in sheared background field

Science.gov (United States)

Hu, Di; Bhattacharjee, Amitava; Huang, Yi-Min

2018-06-01

The energy spectrum of tearing mode turbulence in a sheared background magnetic field is studied in this work. We consider the scenario where the nonlinear interaction of overlapping large-scale modes excites a broad spectrum of small-scale modes, generating tearing mode turbulence. The spectrum of such turbulence is of interest since it is relevant to the small-scale back-reaction on the large-scale field. The turbulence we discuss here differs from traditional MHD turbulence mainly in two aspects. One is the existence of many linearly stable small-scale modes which cause an effective damping during the energy cascade. The other is the scale-independent anisotropy induced by the large-scale modes tilting the sheared background field, as opposed to the scale-dependent anisotropy frequently encountered in traditional critically balanced turbulence theories. Due to these two differences, the energy spectrum deviates from a simple power law and takes the form of a power law multiplied by an exponential falloff. Numerical simulations are carried out using visco-resistive MHD equations to verify our theoretical predictions, and a reasonable agreement is found between the numerical results and our model.

Ion-Beam-Excited Electrostatic Ion Cyclotron Waves

DEFF Research Database (Denmark)

Michelsen, Poul; Pécseli, Hans; Juul Rasmussen, Jens

1976-01-01

Self-excited electrostatic ion cyclotron waves were observed in an ion-beam-plasma system produced in a DP-operated Q-machine. The frequency of the waves showed the theoretically predicted variation with the magnetic field.......Self-excited electrostatic ion cyclotron waves were observed in an ion-beam-plasma system produced in a DP-operated Q-machine. The frequency of the waves showed the theoretically predicted variation with the magnetic field....

Magnetic excitations of single-crystal PrBa₂Cu₃O_6.2

DEFF Research Database (Denmark)

Lister, S.J.S.; Boothroyd, A.T.; Andersen, N.H.

2000-01-01

Measurements of the low-energy magnetic excitations in single-crystal PrBa2Cu3O6.2, and in YBa2Cu3O6.2 for comparison, have been performed using inelastic neutron scattering. An excitation with weak dispersion is seen, which is compared to a spin-wave model based on the lowest lying crystal field...

Pulsed rf excited spectrometer having improved pulse width control

International Nuclear Information System (INIS)

1977-01-01

RF excitation for a spectrometer is obtained by pulse width modulating an RF carrier to produce the desired broadband RF exciting spectrum. The RF excitation includes a train of composite RF pulses, each composite pulse having a primary pulse portion of a first RF phase and a second pulse portion of a second RF phase opposite that of the first. In this manner, the finite rise and fall times of the primary pulse portion are compensated for by the corresponding rise and fall times of the secondary pulse portion. The primary pulse portion is lengthened by an amount equal to the secondary pulse portion so that the secondary pulse portion cancels the added primary pulse portion. In a spectrometer, the compensating second pulse component removes certain undesired side bands of the RF excitation caused by the finite rise and fall times of the applied RF pulses. The compensating second pulse component removes certain undesired side bands associated with each of the resonant lines of the excited resonance spectrum of the sample under analysis, particularly for wide band RF excitation

Magnetic excitations of layered cuprates studied by RIXS at Cu L{sub 3} edge

Energy Technology Data Exchange (ETDEWEB)

Ghiringhelli, G., E-mail: giacomo.ghiringhelli@fisi.polimi.it [CNR/SPIN, CNISM and Dipartimento di Fisica, Politecnico di Milano, piazza Leonardo da Vinci 32, 20133 Milano (Italy); Braicovich, L. [CNR/SPIN, CNISM and Dipartimento di Fisica, Politecnico di Milano, piazza Leonardo da Vinci 32, 20133 Milano (Italy)

2013-06-15

Highlights: ► We have developed very high resolution RIXS instrumentation. ► Cu L{sub 3} RIXS is ideal for studying magnetic excitations in layered cuprates. ► RIXS has been used to map magnon and paramagnon dispersion in HTcS. ► We have developed the first partial polarization analyzer for RIXS in the soft X-rays. -- Abstract: The inelastic scattering of X-rays is becoming a powerful alternative to better established techniques, based on neutrons or low energy photons, for the study of low- and medium-energy excitations in solids. When performed in the soft range the resonant inelastic X-ray scattering (RIXS) is ideal for strongly correlated electron systems based on 3d transition metals. The remarkable evolution of Cu L{sub 3} RIXS has been boosted by the steady improvement of experimental energy resolution, and by the fortunate fact that cuprates give intense and richly featured spectra. Over the last 8 years several key results were obtained using the AXES (ESRF) and the SAXES (SLS) spectrometers. This initial success is now supporting several new projects for soft X-ray RIXS worldwide. We briefly present here the case of spin excitation dispersion in insulating and superconducting cuprates and the first RIXS spectra with partial polarization analysis of the scattered photons.

Contribution to the design and the control of synchronous double excitation machines: hybrid vehicle application; Contribution a la conception et a la commande des machines synchrones a double excitation: application au vehicule hybride

Energy Technology Data Exchange (ETDEWEB)

Amara, Y

2001-12-01

Double excitation machines are synchronous machines where two excitation circuits coexist: one with permanent magnets and the other with windings. This study shows that double excitation allows to combine the advantages of synchronous machines with winded inductor with those of permanent magnet machines. This concept allows a better dimensioning of the converter-machine set and a better energy management. In order to allow the operation of permanent magnet machines over a wide range of speeds, it is necessary to have a magnetic reaction of the induced circuit of the same order than the excitation flux. On the other hand, the power factor is weaker and the power supply converter is over-dimensioned. The double excitation allows the permanent magnet machines to work over a large speed range with a better power factor, even when the magnetic reaction of the induced circuit is relatively weak with respect to the excitation flux. (J.S.)

Magnetic excitations in low-dimensional spin systems: neutron scattering study on AV2O5

International Nuclear Information System (INIS)

Nakajima, Kenji

1997-01-01

Recent experiments on vanadium oxide bronzes AV 2 O 5 (A=Na, Mg, Li) are reviewed. Experiments are carried out combining two triple-axis spectrometers installed at a thermal beam port and a cold neutron guide at JRR-3M. Spin-wave excitations in single crystals NaV 2 O 5 in the spin-Peierls state shows a steep intra-chain dispersion, which is consistent with estimated exchange interaction from magnetization measurement, and a weak inter-chain dispersion. In the low energy excitation measurement on powder sample of MgV 2 O 5 , we have observed energy gap of 2 meV, which indicates that this material is a ladder system with strong 1D character. Preliminary result on LiV 2 O 5 , which is expected to be a simple 1D antiferromagnet or a zig-zag chain, is also mentioned

THE EXCITED LOADS OF ATTRACTION IN A SYMMETRICAL INDUCTOR SYSTEM FOR THE MAGNETIC PULSE REMOVING OF THE BODY CAR

Directory of Open Access Journals (Sweden)

A. V. Gnatov

2015-04-01

Full Text Available Recently, repair and recovery of vehicle body operations become more and more popular. A special place here is taken by equipment that provides performance of given repair operations. The most interesting are methods for recovery of car body panels that allow the straightening without disassembling of car body panels and damaging of existing protective coating. Now, there are several technologies for repair and recovery of car body panels without their disassembly and dismantling. The most perspective is magnetic-pulse technology of external noncontact straightening. Results. The calculation of excited loads attractions in a symmetrical inductor system in the universal tool of magnetic-pulse straightening is provided. According to the obtained analytical dependence of the numerical evaluation of volumetric construction diagrams, phase and amplitude of the radial dependence of the spatial distribution of the excited efforts of attraction is obtained. The influence of the magnetic properties of the blank screen and manifested in the appearance of powerful magnetic attraction forces is determined. Originality. A new trend of research of magnetic-pulse working of thin-walled metals has been formulated and received further development, which allows to create not only new equipment, but principally new technological processes of external non-contact repair and recovery of vehicle body panels. Scientific basis of electrodynamic and magnetic attraction of thin-walled sheet metals with using the energy of high-power pulsed fields was created for the first time and proved theoretically and experimentally. Scientific and technical solutions in design of effective tools based on single-turn inductor systems of cylindrical geometry for straightening and recovery of car body panels were formulated and proved theoretically, as well as experimentally. Practical value. Using the results of the calculations we can create effective tools for an external magnetic

Standard Wiggler magnets

International Nuclear Information System (INIS)

Winick, H.; Helm, R.H.

1977-09-01

Interest in Wiggler magnets (a close sequence of transverse fields with alternating polarity) to extend and enhance the spectrum of synchrotron radiation from electron storage rings has increased significantly during the past few years. Standard wigglers, i.e., wigglers in which interference effects on the spectrum of synchrotron radiation are not important, are considered. In standard wigglers the spectrum of synchrotron radiation has the same general shape as the spectrum from ring bending magnets. However, the critical energy of the wiggler spectrum may be different. The critical energy of the wiggler spectrum is given by epsilon/sub CW/ = epsilon/sub CB/(B/sub W//B/sub B/) where epsilon/sub CB/ is the critical energy from the bending magnets and B/sub W/ and B/sub B/ are the magnetic field strengths of the wiggler magnet and bending magnets respectively. Since most electron storage rings operate with relatively low bending magnet fields (B/sub B/ less than or equal to 12 kG), even a modest wiggler magnet field (less than or equal to 18 kG) can significantly increase the critical energy. Such magnets are planned for ADONE and SPEAR. Higher field (30 to 50 kG) superconducting magnets are planned at Brookhaven, Daresbury, and Novosibirsk to produce even larger increase in the critical energy. For some standard wigglers a further enhancement of the spectrum is produced due tothe superposition of the radiation from the individual poles. Wiggler designs are discussed as well as the effect of wigglers on the synchrotron radiation spectrum and on the operation of storage rings

TORSIONAL OSCILLATIONS OF A MAGNETAR WITH A TANGLED MAGNETIC FIELD

Energy Technology Data Exchange (ETDEWEB)

Link, Bennett; Van Eysden, C. Anthony, E-mail: link@montana.edu, E-mail: anthonyvaneysden@montana.edu [Department of Physics, Montana State University, Bozeman, MT 59717 (United States)

2016-05-20

Motivated by stability considerations and observational evidence, we argue that magnetars possess highly tangled internal magnetic fields. We propose that the quasi-periodic oscillations (QPOs) seen to accompany giant flares can be explained as torsional modes supported by a tangled magnetic field, and we present a simple model that supports this hypothesis for SGR 1900+14. Taking the strength of the tangle as a free parameter, we find that the magnetic energy in the tangle must dominate that in the dipolar component by a factor of ∼14 to accommodate the observed 28 Hz QPO. Our simple model provides useful scaling relations for how the QPO spectrum depends on the bulk properties of the neutron star and the tangle strength. The energy density in the tangled field inferred for SGR 1900+14 renders the crust nearly dynamically irrelevant, a significant simplification for study of the QPO problem. The predicted spectrum is about three times denser than observed, which could be explained by preferential mode excitation or beamed emission. We emphasize that field tangling is needed to stabilize the magnetic field, so should not be ignored in treatment of the QPO problem.

Non-Linear Excitation of Ion Acoustic Waves

DEFF Research Database (Denmark)

Michelsen, Poul; Hirsfield, J. L.

1974-01-01

The excitation of ion acoustic waves by nonlinear coupling of two transverse magnetic waves generated in a microwave cavity was investigated. Measurements of the wave amplitude showed good agreement with calculations based on the Vlasov equation.......The excitation of ion acoustic waves by nonlinear coupling of two transverse magnetic waves generated in a microwave cavity was investigated. Measurements of the wave amplitude showed good agreement with calculations based on the Vlasov equation....

Equivalent non-Gaussian excitation method for response moment calculation of systems under non-Gaussian random excitation

International Nuclear Information System (INIS)

Tsuchida, Takahiro; Kimura, Koji

2015-01-01

Equivalent non-Gaussian excitation method is proposed to obtain the moments up to the fourth order of the response of systems under non-Gaussian random excitation. The excitation is prescribed by the probability density and power spectrum. Moment equations for the response can be derived from the stochastic differential equations for the excitation and the system. However, the moment equations are not closed due to the nonlinearity of the diffusion coefficient in the equation for the excitation. In the proposed method, the diffusion coefficient is replaced with the equivalent diffusion coefficient approximately to obtain a closed set of the moment equations. The square of the equivalent diffusion coefficient is expressed by the second-order polynomial. In order to demonstrate the validity of the method, a linear system to non-Gaussian excitation with generalized Gaussian distribution is analyzed. The results show the method is applicable to non-Gaussian excitation with the widely different kurtosis and bandwidth. (author)

Coupled hydromagnetic wave excitation and ion acceleration upstream of the earth's bow shock

International Nuclear Information System (INIS)

Lee, M.A.

1982-01-01

A self-consistent theory is presented for the excitation of hydromagnetic waves and the acceleration of diffuse ions upstream of the earth's bow shock in the quasi-equilibrium that results when the solar wind velocity and the interplanetary magnetic field are nearly parallel. For the waves the quasi-equilibrium results from a balance between excitation by the ions, which stream relative to the solar wind plasma, and convective loss to the magnetosheath. For the diffuse ions the quasi-equilibrium results from a balance between injection at the shock front, confinement to the foreshock by pitch angle scattering on the waves, acceleration by compression at the shock front, loss to the magnetosheath, loss due to escape upstream of the foreshock, and loss via diffusion perpendicular to the average magnetic field onto field lines that do not connect to the shock front. Diffusion equations describing the ion transport and wave kinetic equations describing the hydromagnetic wave transport are solved self-consistently to yield analytical expressions for the differential wave intensity spectrum as a function of frequency and distance from the bow shock z and for the ion omnidirectional distribution functions and anisotropies as functions of energy and z, In quantitative agreement with observations, the theory predicts (1) exponential spectra at the bow shock in energy per charge, (2) a decrease in intensity and hardening of the ion spectra with increasing z, (3) a 30-keV proton anisotropy parallel to z increasing from -0.28 at the bow shock to +0.51 as z→infinity (4) a linearly polarized wave intensity spectrum with a minimum at approx.6 x 10 -3 Hz and a maximum at approx.2--3 x 10 -2 Hz, (5) a decrease in the wave intensity spectrum with increasing z, (6) a total energy density in protons with energies >15 keV about eight times that in the hydromagnetic waves

Variable flip angle excitation for reduced acquisition time magnetic resonance imaging

International Nuclear Information System (INIS)

Mills, T.C.; Ortendahl, D.A.; Hylton, N.M.; Carlson, J.W.; Crooks, L.E.; Kaufman, L.

1987-01-01

This paper describes an MRI technique which can be used to acquire images at short TR values while maintaining the sensitivity to disease found in longer TR images. For spin echo imaging there are three acquisition parameters that can be set in the imaging protocol; TR, the repetition interval; TE, the time of echo and Θ, the excitation flip angle. Standard imaging techniques set Θ to 90 degrees regardless of the TR value. With Θ fixed, imaging systems have been optimized by varying the value for TE and TR with the results in general indicating the need for long TR values. However, if the flip angle is included as a variable acquisition parameter the optimal operating point can be changed. The solution to the Bloch equation shows a functional relationship between the flip angle and the ratio TR/T1. This functionality was first observed by Ernst and Anderson as a method to increase the signal generated in fourier transform magnetic resonance spectroscopy. When TR/T1<1 the optimum flip angle for producing maximum magnetization in the transverse plane is less then 90 degrees. Therefore, by reducing both TR and flip angle it is possible to maintain signal intensity while reducing the time of data acquisition

Calibrated Noncontact Exciters for Optical Modal Analysis

Directory of Open Access Journals (Sweden)

Henrik O. Saldner

1996-01-01

Full Text Available Two types of exciters were investigated experimentally One of the exciters uses a small permanent magnet fastened on the object. The force is introduced by the change in the electromagnetic field from a coil via an air gap. The second exciter is an eddy-current electromagnet one. The amplitude of the forces from these exciters are calibrated by using dynamic reciprocity in conjunction with electronic holography. These forces strongly depend upon the distance between the exciter and the object.

Excitation spectrum of correlated Dirac fermions

Science.gov (United States)

Jalali, Z.; Jafari, S. A.

2015-04-01

Motivated by the puzzling optical conductivity measurements in graphene, we speculate on the possible role of strong electronic correlations on the two-dimensional Dirac fermions. In this work we employ the slave-particle method to study the excitations of the Hubbard model on honeycomb lattice, away from half-filling. Since the ratio U/t ≈ 3.3 in graphene is not infinite, double occupancy is not entirely prohibited and hence a finite density of doublonscan be generated. We therefore extend the Ioff-Larkin composition rule to include a finite density of doublons. We then investigate the role played by each of these auxiliary particles in the optical absorption of strongly correlated Dirac fermions.

Effects of the competition between the exchange and dipolar interactions in the spin-wave spectrum of two-dimensional circularly magnetized nanodots

International Nuclear Information System (INIS)

Mamica, S; Krawczyk, M; Lévy, J-C S

2014-01-01

We use a microscopic theory taking into account the dipolar and nearest-neighbour exchange interactions for exploring spin-wave excitations in two-dimensional magnetic dots in the vortex state. Normal modes of different profiles are observed: azimuthal and radial modes, as well as fundamental (quasiuniform) and highly localized modes. We examine the dependence of the frequencies and profiles of these modes on the dipolar-to-exchange interaction ratio and the size of the dot. Special attention is paid to some particular modes, including the lowest mode in the spectrum and the evolution of its profile, and the fundamental mode, the frequency of which proves almost independent of the dipolar-to-exchange interaction ratio. We also provide a selective overview of the experimental, analytical and numerical results from the literature, where different profiles of the lowest mode are reported. We attribute this diversity to the competition between the dipolar and exchange interactions. Finally, we study the hybridization of the modes, show the multi-mode hybridization and explain the selection rules. (paper)

Singlet Ground State Magnetism: III Magnetic Excitons in Antiferromagnetic TbP

DEFF Research Database (Denmark)

Knorr, K.; Loidl, A.; Kjems, Jørgen

1981-01-01

The dispersion of the lowest magnetic excitations of the singlet ground state system TbP has been studied in the antiferromagnetic phase by inelastic neutron scattering. The magnetic exchange interaction and the magnetic and the rhombohedral molecular fields have been determined.......The dispersion of the lowest magnetic excitations of the singlet ground state system TbP has been studied in the antiferromagnetic phase by inelastic neutron scattering. The magnetic exchange interaction and the magnetic and the rhombohedral molecular fields have been determined....

On setting magnets in the PEP beam-transport line

International Nuclear Information System (INIS)

Peterson, J.M.

1979-01-01

This paper discusses magnets in the PEP beam-transport line. Topics discussed are: conditioning, direction of excitation, rate of excitation; determination of the excitation current for the principal bend magnets; steering mechanisms; bump magnets; and determination of excitation currents of the quadrupole magnets

Luminescence from ZnSe excited by picosecond mid-infrared FEL pulses

International Nuclear Information System (INIS)

Mitsuyu, T.; Suzuki, T.; Tomimasu, T.

1998-01-01

We have observed blue band-edge emission from a ZnSe crystal under irradiation of mid-infrared picosecond free electron laser (FEL) pulses. The emission characteristics including spectrum, excitation power dependence, excitation wavelength dependence, and decay time have been investigated. The experimental results have indicated that it is difficult to understand the excitation process by multiphoton excitation, thermal excitation, or excitation through mid-gap levels. (Copyright (c) 1998 Elsevier Science B.V., Amsterdam. All rights reserved.)

High Magnetic Field Vortex Microscopy by NMR

Science.gov (United States)

Mitrović, V. F.; Sigmund, E. E.; Bachman, H. N.; Halperin, W. P.; Reyes, A. P.; Kuhns, P.; Moulton, W. G.

2001-03-01

At low temperatures the ^17O NMR spectrum of HTS exhibits a characteristic vortex lattice line shape. Measurements of spin-lattice relaxation rate, T_1-1, across the vortex spectrum represent a probe of low-energy quasiparticle excitations as a function of distance from the vortex core. We report ^17O(2,3) T_1-1 measurements of YBa_2Cu_3O7 at low temperatures in magnetic fields up to 37 T. We find that the rate increases on approaching the vortex core. In the vortex core region at 37 T we observe an additional increase in the relaxation rate. The temperature dependence of the rate will also be discussed. Work at Northwestern University is supported by the NSF (DMR 91-20000) through the Science and Technology Center for Superconductivity.

Excitation of solar and stellar oscillations

International Nuclear Information System (INIS)

Baudin, Frederic

2009-01-01

In this report for an Accreditation to Supervise Research (HDR), and after an introduction which outlines the potential of helio-seismology, the author addresses the problem of excitation and amplitude of stellar oscillations with respect to their most important aspects, i.e. the theoretical framework of the present understanding of excitation mechanisms, and instrumental influences on measurements which are used to assess excitation rates, the difficulty to perform these measurements, and their analysis in some various cases. Thus, the author addresses excitation mechanisms of stellar oscillation (stochastic excitation, opacity- related excitation, and other excitation mechanisms), the excitation of solar modes (observation and theoretical predictions, influence of magnetic phenomena, solar g modes), and the excitation of modes in other stars (solar-type pulsators, red giants, and not so conventional pulsators such as HD180642 and Be stars like HD49330)

High-transmission excited-state Faraday anomalous dispersion optical filter edge filter based on a Halbach cylinder magnetic-field configuration.

Science.gov (United States)

Rudolf, Andreas; Walther, Thomas

2012-11-01

We report on the realization of an excited-state Faraday anomalous dispersion optical filter (ESFADOF) edge filter based on the 5P(3/2)→8D(5/2) transition in rubidium. A maximum transmission of 81% has been achieved. This high transmission is only possible by utilizing a special configuration of magnetic fields taken from accelerator physics to provide a strong homogeneous magnetic field of approximately 6000 G across the vapor cell. The two resulting steep transmission edges are separated by more than 13 GHz, enabling its application in remote sensing.

Triple focussing electron spectrum selector (TESS-II) with a pair of sector magnets

International Nuclear Information System (INIS)

Nagai, Y.; Ejiri, H.; Shibata, T.; Okada, K.; Nakayama, S.; Suzuki, H.; Ohsumi, H.; Adachi, Y.; Osaka Univ., Toyonaka; Sakai, H.

1982-01-01

An achromatic geminate nuclear electron selector (AGNES) has been constructed for in-beam electron spectroscopy. It is essentially a pair of triple-focussing electron spectrum selectors (TESS). It consists of a pair of sector magnets with a field index n = 0. Conversion electrons emitted at 90 0 and 180 0 with respect to the beam axis are transported achromatically through the pair of sector magnets to two focussing points. Electrons are triply focussed in radial, vertical and momentum axes, and their energies are analyzed by cooled Si(Li) detectors. It has a large solid angle of 50 msr x 2 and a large momentum range of 57%. It is quite useful not only for measuring conversion coefficients and electron anisotropy but also for nuclear electron pairs. (orig.)

Investigation of the effect of Zn impurities and magnetic field on the spin dynamics in underdoped YBa{sub 2}(Cu{sub 1-y}Zn{sub y}){sub 3}O{sub x}

Energy Technology Data Exchange (ETDEWEB)

Suchaneck, Anton

2009-04-20

This work employs neutron scattering to examine the changes in the spin excitation spectrum of the underdoped high-temperature superconductor YBa{sub 2}Cu{sub 3}O{sub x} which is doped with zinc or subject to a strong magnetic field. Doping levels of x=6.6 and x=6.45 are used with an optional zinc substitution of 2% zinc per copper atom. A detwinning procedure is an important factor in order to reorient all twinning domains of the orthorhombic crystal cell in the same direction. Numerous single crystals were oriented and assembled to create a sample of total mass 2 g neccessary for neutron scattering experiments. The experiments were performed on triple axis neutron scattering spectrometers to measure spin excitations around the antiferromagnetic wave vector at energies up to 50 meV. Zinc substitution and magnetic field influence the spin excitations, which in the pure compound feature the resonance mode, a spin gap and an hour-glass dispersion. Upon zinc substitution the spectrum of YBa{sub 2}(Cu{sub 0.98}Zn{sub 0.02}){sub 3}O{sub 6.6} is quantitatively unchanged around the resonance energy, however its marked temperature onset disappears. At lower energies new induced quasi-static excitations emerge. Similar finding have been observed in other cuprate compounds. The induced excitation exhibit a strong anisotropy in the copper planes. All these results are compared to other experimental techniques which provide comparable experimental evidence. Another compounds examined in this work is the more strongly oxygen underdoped YBa{sub 2}(Cu{sub 0.98}Zn{sub 0.02}){sub 3}O{sub 6.45}. The common bilayer related signal remains unchanged with zinc substitution, however a new inter-plane correlated signal is induced indicating ordering between copper planes. A comparison with other experimental techniques indicated that the superconducting critical temperature is the sole determining factor of the qualitative spin excitation spectrum, no matter what factor are responsible

Proton magnetic resonance spectroscopy in children with fetal alcohol spectrum disorders

Energy Technology Data Exchange (ETDEWEB)

Goncalves, Rita de Cassia Ferreira; Vasconcelos, Marcio Moacyr; Faleiros, Leticia Oliveira; Brito, Adriana Rocha; Werner Junior, Jairo; Herdy, Gesmar Volga Haddad [Universidade Federal Fluminense (UFF), Niteroi, RJ (Brazil). Faculdade de Medicina], e-mail: rcgonc@hotmail.com; Cruz Junior, Luiz Celso Hygino da; Domingues, Romeu Cortes [Multi-Imagem, Rio de Janeiro, RJ (Brazil)

2009-06-15

To analyze the metabolic constitution of brain areas through proton magnetic resonance spectroscopy in children affected with fetal alcohol spectrum disorder compared with normal children. Method: The sample of this case-control study included eight boys with epidemiologic history of in utero exposure to alcohol (median age 13.6{+-}3.8 years) who were diagnosed with fetal alcohol spectrum disorder, and eight controls (median age 12.1{+-}3,4 years). An 8 cm{sup 3} single voxel approach was used, with echo time 30 ms, repetition time 1500 ms, and 128 acquisitions in a 1.5T scanner, and four brain areas were analyzed: anterior cingulate, left frontal lobe, left striatum, and left cerebellar hemisphere. Peaks and ratios of metabolites N-acetylaspartate, choline, creatine, and myo-inositol were measured. Results: Children with fetal alcohol spectrum disorder showed a decrease in choline/creatine ratio (p=0.020) in left striatum and an increase in myo-inositol/creatine ratio (p=0.048) in left cerebellum compared with controls. There was no statistically significant difference in all peaks and ratios from the anterior cingulate and frontal lobe between the two groups. Conclusion: This study found evidence that the left striatum and left cerebellum are affected by intrauterine exposure to alcohol. Additional studies with larger samples are necessary to expand our knowledge of the effects of fetal exposure to alcohol. (author)

Proton magnetic resonance spectroscopy in children with fetal alcohol spectrum disorders

International Nuclear Information System (INIS)

Goncalves, Rita de Cassia Ferreira; Vasconcelos, Marcio Moacyr; Faleiros, Leticia Oliveira; Brito, Adriana Rocha; Werner Junior, Jairo; Herdy, Gesmar Volga Haddad

2009-01-01

To analyze the metabolic constitution of brain areas through proton magnetic resonance spectroscopy in children affected with fetal alcohol spectrum disorder compared with normal children. Method: The sample of this case-control study included eight boys with epidemiologic history of in utero exposure to alcohol (median age 13.6±3.8 years) who were diagnosed with fetal alcohol spectrum disorder, and eight controls (median age 12.1±3,4 years). An 8 cm 3 single voxel approach was used, with echo time 30 ms, repetition time 1500 ms, and 128 acquisitions in a 1.5T scanner, and four brain areas were analyzed: anterior cingulate, left frontal lobe, left striatum, and left cerebellar hemisphere. Peaks and ratios of metabolites N-acetylaspartate, choline, creatine, and myo-inositol were measured. Results: Children with fetal alcohol spectrum disorder showed a decrease in choline/creatine ratio (p=0.020) in left striatum and an increase in myo-inositol/creatine ratio (p=0.048) in left cerebellum compared with controls. There was no statistically significant difference in all peaks and ratios from the anterior cingulate and frontal lobe between the two groups. Conclusion: This study found evidence that the left striatum and left cerebellum are affected by intrauterine exposure to alcohol. Additional studies with larger samples are necessary to expand our knowledge of the effects of fetal exposure to alcohol. (author)

Reduction effect of neutral density on the excitation of turbulent drift waves in a linear magnetized plasma with flow

International Nuclear Information System (INIS)

Saitou, Y.; Yonesu, A.; Shinohara, S.; Ignatenko, M. V.; Kasuya, N.; Kawaguchi, M.; Terasaka, K.; Nishijima, T.; Nagashima, Y.; Kawai, Y.; Yagi, M.; Itoh, S.-I.; Azumi, M.; Itoh, K.

2007-01-01

The importance of reducing the neutral density to reach strong drift wave turbulence is clarified from the results of the extended magnetohydrodynamics and Monte Carlo simulations in a linear magnetized plasma. An upper bound of the neutral density relating to the ion-neutral collision frequency for the excitation of drift wave instability is shown, and the necessary flow velocity to excite this instability is also estimated from the neutral distributions. Measurements of the Mach number and the electron density distributions using Mach probe in the large mirror device (LMD) of Kyushu University [S. Shinohara et al., Plasma Phys. Control. Fusion 37, 1015 (1995)] are reported as well. The obtained results show a controllability of the neutral density and provide the basis for neutral density reduction and a possibility to excite strong drift wave turbulence in the LMD

Infrared emission from a polycyclic aromatic hydrocarbon (PAH) excited by ultraviolet laser

International Nuclear Information System (INIS)

Cherchneff, I.; Barker, J.R.

1989-01-01

The infrared fluorescence spectrum from the C-H stretch modes of vibrationally excited azulene (C10H8), a PAH was measured in the laboratory. PAHs are candidates as carriers of the unidentified infrared emission bands that are observed in many astronomical objects associated with dust and ultraviolet light. In the present experiment, gas phase azulene was excited with light from a 308 nm pulsed laser, and the infrared emission spectrum was time-resolved and wavelength-resolved. Moreover, the infrared absorption spectrum of gas phase azulene was obtained using an FTIR spectrometer. The laboratory emission spectrum resembles observed infrared emission spectra from the interstellar medium, providing support for the hypothesis that PAHs are the responsible carriers. The azulene C-H stretch emission spectrum is more asymmetric than the absorption spectrum, probably due to anharmonicity of levels higher than nu = 1. 36 refs

Structural Magnetic Resonance Imaging Data Do Not Help Support DSM-5 Autism Spectrum Disorder Category

Science.gov (United States)

Pina-Camacho, Laura; Villero, Sonia; Boada, Leticia; Fraguas, David; Janssen, Joost; Mayoral, Maria; Llorente, Cloe; Arango, Celso; Parellada, Mara

2013-01-01

This systematic review aims to determine whether or not structural magnetic resonance imaging (sMRI) data support the DSM-5 proposal of an autism spectrum disorder (ASD) diagnostic category, and whether or not classical DSM-IV autistic disorder (AD) and Asperger syndrome (AS) categories should be subsumed into it. The most replicated sMRI findings…

A 3-Axis Miniature Magnetic Sensor Based on a Planar Fluxgate Magnetometer with an Orthogonal Fluxguide.

Science.gov (United States)

Lu, Chih-Cheng; Huang, Jeff

2015-06-19

A new class of tri-axial miniature magnetometer consisting of a planar fluxgate structure with an orthogonal ferromagnetic fluxguide centrally situated over the magnetic cores is presented. The magnetic sensor possesses a cruciform ferromagnetic core placed diagonally upon the square excitation coil under which two pairs of pick-up coils for in-plane field detection are allocated. Effective principles and analysis of the magnetometer for 3-D field vectors are described and verified by numerically electromagnetic simulation for the excitation and magnetization of the ferromagnetic cores. The sensor is operated by applying the second-harmonic detection technique that can verify V-B relationship and device responsivity. Experimental characterization of the miniature fluxgate device demonstrates satisfactory spatial magnetic field detection results in terms of responsivity and noise spectrum. As a result, at an excitation frequency of 50 kHz, a maximum in-plane responsivity of 122.4 V/T appears and a maximum out-of-plane responsivity of 11.6 V/T is obtained as well. The minimum field noise spectra are found to be 0.11 nT/√Hz and 6.29 nT/√Hz, respectively, in X- and Z-axis at 1 Hz under the same excitation frequency. Compared with the previous tri-axis fluxgate devices, this planar magnetic sensor with an orthogonal fluxguide provides beneficial enhancement in both sensory functionality and manufacturing simplicity. More importantly, this novel device concept is considered highly suitable for the extension to a silicon sensor made by the current CMOS-MEMS technologies, thus emphasizing its emerging applications of field detection in portable industrial electronics.

Functional magnetic resonance imaging of autism spectrum disorders

Science.gov (United States)

Dichter, Gabriel S.

2012-01-01

This review presents an overview of functional magnetic resonance imaging findings in autism spectrum disorders (ASDs), Although there is considerable heterogeneity with respect to results across studies, common themes have emerged, including: (i) hypoactivation in nodes of the “social brain” during social processing tasks, including regions within the prefrontal cortex, the posterior superior temporal sulcus, the amygdala, and the fusiform gyrus; (ii) aberrant frontostriatal activation during cognitive control tasks relevant to restricted and repetitive behaviors and interests, including regions within the dorsal prefrontal cortex and the basal ganglia; (iii) differential lateralization and activation of language processing and production regions during communication tasks; (iv) anomalous mesolimbic responses to social and nonsocial rewards; (v) task-based long-range functional hypoconnectivity and short-range hyper-connectivity; and (vi) decreased anterior-posterior functional connectivity during resting states. These findings provide mechanistic accounts of ASD pathophysiology and suggest directions for future research aimed at elucidating etiologic models and developing rationally derived and targeted treatments. PMID:23226956

Spin Chirality of Cu3 and V3 Nanomagnets. 1. Rotation Behavior of Vector Chirality, Scalar Chirality, and Magnetization in the Rotating Magnetic Field, Magnetochiral Correlations.

Science.gov (United States)

Belinsky, Moisey I

2016-05-02

The rotation behavior of the vector chirality κ, scalar chirality χ, and magnetization M in the rotating magnetic field H1 is considered for the V3 and Cu3 nanomagnets, in which the Dzialoshinsky-Moriya coupling is active. The polar rotation of the field H1 of the given strength H1 results in the energy spectrum characterized by different vector and scalar chiralities in the ground and excited states. The magnetochiral correlations between the vector and scalar chiralities, energy, and magnetization in the rotating field were considered. Under the uniform polar rotation of the field H1, the ground-state chirality vector κI performs sawtooth oscillations and the magnetization vector MI performs the sawtooth oscillating rotation that is accompanied by the correlated transformation of the scalar chirality χI. This demonstrates the magnetochiral effect of the joint rotation behavior and simultaneous frustrations of the spin chiralities and magnetization in the rotating field, which are governed by the correlation between the chiralities and magnetization.

Transition rate diagrams — A new approach to the study of selective excitation processes: The spectrum of manganese in a Grimm-type glow discharge

International Nuclear Information System (INIS)

Weiss, Zdeněk; Steers, Edward B.M.; Pickering, Juliet C.; Mushtaq, Sohail

2014-01-01

The emission spectra of manganese observed using a Grimm-type glow discharge in pure argon, argon with 0.3% v/v hydrogen and pure neon were studied in order to identify major excitation and ionization processes of manganese in the plasma. A new procedure is proposed, in which each observed emission line is associated with the corresponding transition between different states of the Mn atom or Mn ion, and, by considering all the observed transitions from and into a specific state, a measure of the total rate is determined at which this state is radiatively populated and depopulated. These resulting population/depopulation rates are then plotted as function of level energy. Such plots, called here “transition rate diagrams”, show the role of individual states in the formation of the observed spectrum and can be used to identify possible selective excitation processes. Also, cascade excitation by radiative decay of higher excited states can be conveniently evaluated in this way. A detailed description of the observed Mn I and Mn II spectra is given for Ar, Ar–H 2 and Ne plasmas and relevant excitation/ionization mechanisms are discussed. Matrix effects in analysis of manganese by glow discharge spectroscopy are discussed. A list of important Mn I and Mn II lines excited in the glow discharge plasma is given. - Highlights: • We measured GD-OES spectra of Mn in Ar, Ar(H) and Ne discharges. • We determined transition rate diagrams of Mn I and Mn II in these discharges. • Using those diagrams, we identified major excitation processes involved

Anisotropy of exciton spectrum and spin-orbit interactions in quantum wells in tilted magnetic field

International Nuclear Information System (INIS)

Olendski, Oleg; Shahbazyan, Tigran V

2006-01-01

We study theoretically excitonic energy spectrum and optical absorption in narrowgap semiconductor quantum wells in strong magnetic field. We show that, in the presence of an in-plane field component, the absorption coefficient exhibit a double-peak structure due to hybridization of bright and dark excitons. If both Rashba and Dresselhaus spin-orbit terms are present, the spectrum is anisotropic in in-plane field orientation with respect to [100] axis. In particular, the magnitude of the splitting can be tuned in a wide interval by varying the azimuthal angle of the in-plane field. The absorption spectrrum anisotropy would allow simultaneous measurement Dresselhaus and Rashba spin-orbit coefficients

Complex-Spectrum Magnetic Environment enhances and/or modifies Bioeffects of Hypokinetic Stress Condition: an Animal Study

Science.gov (United States)

Temuriantz, N. A.; Martinyuk, V. S.; Ptitsyna, N. G.; Villoresi, G.; Iucci, N.; Tyasto, M. I.; Dorman, L. I.

During last decades it was shown by many authors that ultra-low and extremely low frequency electric and magnetic fields ULF 0-10 Hz ELF 10-1000 Hz may produce biological effects and consequently may be a possible source for health problems Spaceflight electric and magnetic environments are characterized by complex combination of static and time-varying components in ULF-ELF range and by high variability The objective of this study was to investigate the possible influence of such magnetic fields on rats to understand the pathway regarding functional state of cardiovascular system Magnetic field MF pattern with variable complex spectra in 0-150 Hz frequency range was simulated using 3-axial Helmholtz coils and special computer-based equipment The effect of the real world MF exposure on rats was also tested in combination with hypokinetic stress condition which is typical for spaceflights It was revealed that variable complex-spectrum MF acts as a weak or moderate stress-like factor which amplifies and or modifies the functional shifts caused by other stress-factors The value and direction of the functional shifts caused by MF exposure significantly depend on gender individual-typological constitutional features and also on the physiological state norm stress of organism Our results support the idea that variable complex-spectrum MF action involves sympathetic activation overload in cholesterol transport in blood and also secretor activation of tissue basophyls mast cells that can influence the regional haemodynamics These

Autism Spectrum Disorders and Schizophrenia Spectrum Disorders: Excitation/Inhibition Imbalance and Developmental Trajectories

Directory of Open Access Journals (Sweden)

Roberto Canitano

2017-05-01

Full Text Available Autism spectrum disorders (ASD and schizophrenia spectrum disorders (SSD share clinical and genetic components that have long been recognized. The two disorders co-occur more frequently than would be predicted by their respective prevalence, suggesting that a complex, multifactor association is involved. However, DSM-5 maintains the distinction between ASD, with core social and communication impairments, and SSD, including schizophrenia (SCZ, with hallucinations, delusions, and thought disorder as essential features. ASD and SSD have common biological underpinnings that may emerge early in development and unfold over time. One of the hypotheses supporting the similarities in the social and cognitive disturbances of ASD and SSD relates to abnormalities in the ratio of excitatory to inhibitory cortical activity (E/I imbalance. E/I imbalance in neurodevelopmental disorders could be the consequence of abnormalities in genes coding for glutamatergic and GABAergic receptors or synaptic proteins followed by system derangements. SSD and ASD have been characterized as polygenic disorders in which to the onset and progression of disease is triggered by interactions among multiple genes. Mammalian target of rapamycin signaling is under intense investigation as a convergent altered pathway in the two spectrum disorders. Current understanding of shared and divergent patterns between ASD and SSD from molecular to clinical aspects is still incomplete and may be implemented by the research domain criteria approach.

Cross sections for the vibrational excitation of the H2 X 1Σ+g(v) levels generated by electron collisional excitation of the higher singlet states

International Nuclear Information System (INIS)

Hiskes, J.R.

1991-01-01

The excitation cross sections, σ(v,v double-prime), for an H 2 molecule initially in any one of the 15 vibrational levels, v belonging to the ground electronic state and excited to a final vibrational level, v double-prime are evaluated for direct excitations via all members of the excited electronic singlet spectrum. Account is taken of predissociation, autoionization, and radiative decay of the excited electronic spectrum that leads to a final population distribution for the ground electronic state, X 1 Σ + g (v double-prime). For v=0, account is taken explicitly of transitions via the B, C, B', and D electronic states in evaluating the cross sections. The additional contribution of excitations via all Rydberg states lying above the D state enhances these cross sections by approximately 10%. For v>0, cross sections are evaluated taking explicit account of transitions through the B and C states; higher singlet excitations enhance these values by 25%. The choice of the reference total cross sections remains a subjective one, causing the values calculated here to have a possible uncertainty of +20% -30% . For excitations occurring within a hydrogen discharge, collisional excitation-ionization events among the intermediate singlet states will effectively quench the v, v double-prime excitation process for discharge densities in excess of the range 10 15 --10 16 electrons/cm -3

Didactic Considerations on Magnetic Circuits Excited by Permanent Magnets

Science.gov (United States)

Barmada, S.; Rizzo, R.; Sani, L.

2009-01-01

In this paper, the authors focus their attention on the way magnetic circuits and permanent magnets are usually treated in most textbooks and electrical engineering courses. This paper demonstrates how this important topic is too often presented simplistically. This simplistic treatment does not allow the students to develop a complete…

Lowest excited-state impurity binding energy in InGaN/GaN parabolic QWW: magnetic field effect

International Nuclear Information System (INIS)

Haddou El Ghazi; Anouar Jorio; Izeddine Zorkani

2013-01-01

In this paper, we have investigated the magnetic field effect on the lowest excited-state binding energy of hydrogenic shallow-donor impurity in wurtzite (In,Ga)N/GaN parabolic transversal-section quantum-well wire (PQWW) using the finite-difference method within the quasi-one-dimensional effective potential model. The calculations are performed within the framework of the effective mass approximation. A cylindrical QWW effective radius is taken into account to describe the lateral confinement strength. The numerical results show that: (i) the probability density is the largest on a circularity whose radius is the effective radius and (ii) the lowest excited-state binding energy is the largest when an impurity is located on this circularity while it starts to decrease as the impurity is away from the circularity. (author)

Excited-state dynamics of acetylene excited to individual rotational level of the V04K01 subband

Science.gov (United States)

Makarov, Vladimir I.; Kochubei, Sergei A.; Khmelinskii, Igor V.

2006-01-01

Dynamics of the IR emission induced by excitation of the acetylene molecule using the (32Ka0,1,2,ÃAu1←41la1,X˜Σg+1) transition was investigated. The observed IR emission was assigned to transitions between the ground-state vibrational levels. Acetylene fluorescence quenching induced by external electric and magnetic fields acting upon the system prepared using the (34Ka1,ÃAu1←00la0,X˜Σg+1) excitation was also studied. External electric field creates an additional radiationless pathway to the ground-state levels, coupling levels of the ÃAu1 excited state to the quasiresonant levels of the X˜Σg+1 ground state. The level density of the ground state in the vicinity of the excited state is very high, thus the electric-field-induced transition is irreversible, with the rate constant described by the Fermi rule. Magnetic field alters the decay profile without changing the fluorescence quantum yield in collisionless conditions. IR emission from the CCH transient was detected, and was also affected by the external electric and magnetic fields. Acetylene predissociation was demonstrated to proceed by the direct S1→S0 mechanism. The results were explained using the previously developed theoretical approach, yielding values of the relevant model parameters.

Absorption spectrum of neutral phosphorus (P I) in the range 7700-8256 A

International Nuclear Information System (INIS)

Deng Lunhua; Li Chuanliang; Zhang Junli; Yang Xiaohua; Chen Yangqin

2010-01-01

The absorption spectrum of neutral phosphorus was recorded in the range 7700-8256 A using optical heterodyne magnetic rotation concentration modulation spectroscopy with a tunable Ti:sapphire laser as the light source. Phosphorus atoms were excited by discharging the mixed gases of phosphorus vapor and neon gas. The phosphorus vapor was prepared by heating white phosphorus chips placed on a cylindrical copper electrode during discharge. In total, 234 lines of P I were observed, of which 127 were assigned. The transition frequencies were obtained with an uncertainty of 0.007 cm -1 . Empirical line intensities were provided covering four orders of magnitude.

Absorption spectrum of neutral phosphorus (P I) in the range 7700-8256 Å

Science.gov (United States)

Deng, Lunhua; Li, Chuanliang; Zhang, Junli; Yang, Xiaohua; Chen, Yangqin

2010-12-01

The absorption spectrum of neutral phosphorus was recorded in the range 7700-8256 Å using optical heterodyne magnetic rotation concentration modulation spectroscopy with a tunable Ti:sapphire laser as the light source. Phosphorus atoms were excited by discharging the mixed gases of phosphorus vapor and neon gas. The phosphorus vapor was prepared by heating white phosphorus chips placed on a cylindrical copper electrode during discharge. In total, 234 lines of P I were observed, of which 127 were assigned. The transition frequencies were obtained with an uncertainty of 0.007 cm-1. Empirical line intensities were provided covering four orders of magnitude.

Analytic treatment of the excited instability spectra of the magnetically charged SU(2) Reissner-Nordström black holes

Energy Technology Data Exchange (ETDEWEB)

Hod, Shahar [The Ruppin Academic Center, Emeq Hefer 40250 (Israel); The Hadassah Academic College, Jerusalem 91010 (Israel)

2017-03-14

The magnetically charged SU(2) Reissner-Nordström black-hole solutions of the coupled nonlinear Einstein-Yang-Mills field equations are known to be characterized by infinite spectra of unstable (imaginary) resonances {ω_n(r_+,r_−)}{sub n=0}{sup n=∞} (here r{sub ±} are the black-hole horizon radii). Based on direct numerical computations of the black-hole instability spectra, it has recently been observed that the excited instability eigenvalues of the magnetically charged black holes exhibit a simple universal behavior. In particular, it was shown that the numerically computed instability eigenvalues of the magnetically charged black holes are characterized by the small frequency universal relation ω{sub n}(r{sub +}−r{sub −})=λ{sub n}, where {λ_n} are dimensionless constants which are independent of the black-hole parameters. In the present paper we study analytically the instability spectra of the magnetically charged SU(2) Reissner-Nordström black holes. In particular, we provide a rigorous analytical proof for the numerically-suggested universal behavior ω{sub n}(r{sub +}−r{sub −})=λ{sub n} in the small frequency ω{sub n}r{sub +}≪(r{sub +}−r{sub −})/r{sub +} regime. Interestingly, it is shown that the excited black-hole resonances are characterized by the simple universal relation ω{sub n+1}/ω{sub n}=e{sup −2π/√3}. Finally, we confirm our analytical results for the black-hole instability spectra with numerical computations.

Three-dimensional simulations of magnetic reconnection in slab geometry

International Nuclear Information System (INIS)

Onofri, M.; Primavera, L.; Malara, F.; Veltri, P.

2004-01-01

Magnetic reconnection in an incompressible plasma in three-dimensional slab geometry has been studied through magnetohydrodynamics numerical simulations. Particular attention has been paid to the case in which several unstable modes that correspond to resonant surfaces in different positions of the simulation domain, are excited at the beginning of the simulation. The dynamical evolution of such a system leads to a behavior different than what is expected from the linear theory. In particular the effects of the equilibrium field dissipation and the fact that several resonant surfaces are initially excited both concur in modifying the initial growth rates of the instability. In the nonlinear phase two basic phenomena are observed: first, the rapid transfer of energy to large wave numbers, corresponding to a direct cascade of the energy in the spectrum, which approaches, with increasing time, a power law; second, an energy transfer towards smaller wave numbers, which corresponds in the physical space to a coalescence of magnetic islands. Finally, the spectra in the periodic directions exhibit a strongly anisotropic behavior

A benchmark study of electronic excitation energies, transition moments, and excited-state energy gradients on the nicotine molecule

Energy Technology Data Exchange (ETDEWEB)

Egidi, Franco, E-mail: franco.egidi@sns.it; Segado, Mireia; Barone, Vincenzo, E-mail: vincenzo.barone@sns.it [Scuola Normale Superiore, Piazza dei Cavalieri, 7 I-56126 Pisa (Italy); Koch, Henrik [Department of Chemistry, Norwegian University of Science and Technology, 7491 Trondheim (Norway); Cappelli, Chiara [Dipartimento di Chimica e Chimica Industriale, Università di Pisa, via G. Moruzzi, 3 I-56124 Pisa (Italy)

2014-12-14

In this work, we report a comparative study of computed excitation energies, oscillator strengths, and excited-state energy gradients of (S)-nicotine, chosen as a test case, using multireference methods, coupled cluster singles and doubles, and methods based on time-dependent density functional theory. This system was chosen because its apparent simplicity hides a complex electronic structure, as several different types of valence excitations are possible, including n-π{sup *}, π-π{sup *}, and charge-transfer states, and in order to simulate its spectrum it is necessary to describe all of them consistently well by the chosen method.

Analytical calculation of spin tunneling effect in single molecule magnet Fe8 with considering quadrupole excitation

OpenAIRE

Y Yousefi; H Fakhari; K Muminov; M R Benam

2018-01-01

Spin tunneling effect in Single Molecule Magnet Fe8 is studied by instanton calculation technique using SU(3) generalized spin coherent state in real parameter as a trial function. For this SMM, tunnel splitting arises due to the presence of a Berry like phase in action, which causes interference between tunneling trajectories (instantons). For this SMM, it is established that the use of quadrupole excitation (g dependence) changes not only the location of the quenching points, but also the n...

Perturbed soliton excitations of Rao-dust Alfvén waves in magnetized dusty plasmas

Energy Technology Data Exchange (ETDEWEB)

Kavitha, L., E-mail: louiskavitha@yahoo.co.in [Department of Physics, School of Basic and Applied Sciences, Central University of Tamil Nadu, Thiruvarur 610 101 (India); The Abdus Salam International Centre for Theoretical Physics, Trieste (Italy); Lavanya, C.; Senthil Kumar, V. [Department of Physics, Periyar University, Salem, Tamil Nadu 636 011 (India); Gopi, D. [Department of Chemistry, Periyar University, Salem 636 011 (India); Center for Nanoscience and Nanotechnology, Periyar University, Salem, Tamil Nadu 636 011 (India); Pasqua, A. [Department of Physics, University of Trieste, Trieste (Italy)

2016-04-15

We investigate the propagation dynamics of the perturbed soliton excitations in a three component fully ionized dusty magnetoplasma consisting of electrons, ions, and heavy charged dust particulates. We derive the governing equation of motion for the two dimensional Rao-dust magnetohydrodynamic (R-D-MHD) wave by employing the inertialess electron equation of motion, inertial ion equation of motion, the continuity equations in a plasma with immobile charged dust grains, together with the Maxwell's equations, by assuming quasi neutrality and neglecting the displacement current in Ampere's law. Furthermore, we assume the massive dust particles are practically immobile since we are interested in timescales much shorter than the dusty plasma period, thereby neglecting any damping of the modes due to the grain charge fluctuations. We invoke the reductive perturbation method to represent the governing dynamics by a perturbed cubic nonlinear Schrödinger (pCNLS) equation. We solve the pCNLS, along the lines of Kodama-Ablowitz multiple scale nonlinear perturbation technique and explored the R-D-MHD waves as solitary wave excitations in a magnetized dusty plasma. Since Alfvén waves play an important role in energy transport in driving field-aligned currents, particle acceleration and heating, solar flares, and the solar wind, this representation of R-D-MHD waves as soliton excitations may have extensive applications to study the lower part of the earth's ionosphere.

Electric motors and drives. Pt. 37. Permanent-magnet-excited synchronous motors. Pt. 3; Elektrische Maschinen und Antriebe. T. 37. Die permanentmagneterregte Synchronmaschine. T. 3

Energy Technology Data Exchange (ETDEWEB)

Baral, Andreas [FHWT - Private Fachhochschule fuer Wirtschaft und Technik, Oldenburg (Germany). Elektrische Maschinen und Antriebstechnik

2011-01-15

The contribution explains the principle of permanent-magnet-excited synchronous motors. They are used as positioning drives in many automation applications, usually in combination with a servo-controller.

Evolution of Excited Convective Cells in Plasmas

DEFF Research Database (Denmark)

Pécseli, Hans; Juul Rasmussen, Jens; Sugai, H.

1984-01-01

Convective cells are excited externally in a fully ionized magnetized plasma and their space-time evolution is investigated by two-dimensional potential measurements. A positive cell is excited externally by control of the end losses in the 'scrape off' layer of a plasma column produced by surface...

Localized spin-wave modes in a triangular magnetic element studied by micro-focused Brillouin light scattering

Energy Technology Data Exchange (ETDEWEB)

Hwang, S.; Kwon, J.-H. [School of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju 61005 (Korea, Republic of); Grünberg, P. [Grünberg Center for Magnetic Nanomaterials, Gwangju Institute of Science and Technology (GIST), Gwangju 61005 (Korea, Republic of); Cho, B.K., E-mail: chobk@gist.ac.kr [School of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju 61005 (Korea, Republic of)

2017-09-01

Highlights: • Direct evidence of localized mode in a triangular nano-magnet using μ-BLS. • Localized regions are identified by the internal field distribution. • The spatially resolved measurement was performed to obtain 2-D intensity map. • Spin modes in same positions can be distinguish comparing with simulated spectrum. • Localized modes were identified by comparing with the simulated spatial profiles. - Abstract: Localized spin-wave modes, which were thermally excited at a specific position in a triangular magnetic element, were investigated using micro-focused Brillouin light scattering in two saturated states, the buckle and Y-states, with an applied magnetic field of 0.24 T parallel and perpendicular to the basal edge, respectively. The measured frequency spectrum at a specific beam spot position, rather than an integrated spectrum, was analyzed by comparing it with the simulation data at a precisely selected position within the beam spot area. The analyzed results were used to plot a two-dimensional intensity map and simulation spatial profile to verify the validity of the analysis. From the analysis process, two localized spin-wave modes in a triangular magnetic element were successfully identified near the apex region in the buckle state and near the basal edge region in the Y-state.

A novel excitation assistance switched reluctance wind power generator

DEFF Research Database (Denmark)

Liu, Xiao; Park, Kiwoo; Chen, Zhe

2014-01-01

The high inductance of a general switched reluctance generator (SRG) may prevent the excitation of the magnetic field from being quickly established enough, which may further limit the output power of the SRG. A novel excitation assistance SRG (EASRG) for wind power generation is proposed...... in this paper to solve the above problem. C-shape stator cores are employed in a modular design concept for quick maintenance or replacement, and a ring-shape excitation assistant coil is sandwiched in the space between the modular stator cores. The magnetization and torque characteristics are simulated by 3-D...

Magnetic diffusion effects on the ultra-high energy cosmic ray spectrum and composition

Energy Technology Data Exchange (ETDEWEB)

Mollerach, Silvia; Roulet, Esteban, E-mail: mollerach@cab.cnea.gov.ar, E-mail: roulet@cab.cnea.gov.ar [CONICET, Centro Atómico Bariloche, Av. Bustillo 9500 (8400) (Argentina)

2013-10-01

We discuss the effects of diffusion of high energy cosmic rays in turbulent extra-galactic magnetic fields. We find an approximate expression for the low energy suppression of the spectrum of the different mass components (with charge Z) in the case in which this suppression happens at energies below ∼ Z EeV, so that energy losses are dominated by the adiabatic ones. The low energy suppression appears when cosmic rays from the closest sources take a time comparable to the age of the Universe to reach the Earth. This occurs for energies E < Z EeV (B/nG)√(l{sub c}/Mpc)(d{sub s}/70Mpc) in terms of the magnetic field RMS strength B, its coherence length l{sub c} and the typical separation between sources d{sub s}. We apply this to scenarios in which the sources produce a mixed composition and have a relatively low maximum rigidity (E{sub max} ∼ (2–10)Z EeV), finding that diffusion has a significant effect on the resulting spectrum, the average mass and on its spread, in particular reducing this last one. For reasonable values of B and l{sub c} these effects can help to reproduce the composition trends observed by the Auger Collaboration for source spectra compatible with Fermi acceleration.

A large electrically excited synchronous generator

DEFF Research Database (Denmark)

2014-01-01

This invention relates to a large electrically excited synchronous generator (100), comprising a stator (101), and a rotor or rotor coreback (102) comprising an excitation coil (103) generating a magnetic field during use, wherein the rotor or rotor coreback (102) further comprises a plurality...... adjacent neighbouring poles. In this way, a large electrically excited synchronous generator (EESG) is provided that readily enables a relatively large number of poles, compared to a traditional EESG, since the excitation coil in this design provides MMF for all the poles, whereas in a traditional EESG...... each pole needs its own excitation coil, which limits the number of poles as each coil will take up too much space between the poles....

Dynamic micromagnetic simulation of the magnetic spectrum of permalloy nanodot array with vortex state

Energy Technology Data Exchange (ETDEWEB)

Peng, Y. [College of Physics and Electronic Engineering, Sichuan Normal University, Chengdu 610066 (China); College of Materials Science and Engineering, Beijing University of Technology, Beijing 100124 (China); Zhao, G.P., E-mail: zhaogp@uestc.edu.cn [College of Physics and Electronic Engineering, Sichuan Normal University, Chengdu 610066 (China); Morvan, F.J.; Wu, S.Q. [College of Physics and Electronic Engineering, Sichuan Normal University, Chengdu 610066 (China); Yue, M. [College of Materials Science and Engineering, Beijing University of Technology, Beijing 100124 (China)

2017-01-15

Due to its potential applications in high-density magnetic storage and spin electronic devices, the ferromagnetic resonance absorption phenomenon has recently drawn much attention. By studying the influence of different materials with various shapes on this phenomenon, the new understandings gained could lead to other applications in the future. In this paper, dynamic magnetic susceptibilities of the vortex state in permalloy nanodot arrays have been investigated using a three-dimensional object oriented micromagnetic framework (OOMMF) code with a two-dimensional periodic boundary condition (2D-PBC) extension and compared with those of a single dot carefully. The resonance mode is excited in the vortex state of nanodot arrays by the microwave magnetic field perpendicular to the dot plane. In this case only radially symmetric spin wave modes can be excited. The influence of the geometric parameters on the resonance frequency has been studied systemically, including the dot radius, the number of repeating elements, and the dot distance. One can see that the resonance peak of the dot array is higher than that of a single dot because of the induced stronger magnetostatic coupling. A critical dot distance exists at which the dot array may be treated as a single dot. There is only one resonance peak for both the dot array and the single dot, as the radius changes. - Highlights: • Resonance peak of the dot array is higher than that of a single dot because of the induced stronger magnetostatic coupling. • A critical dot distance exists at which the dot array may be treated as a single dot. • There is only one resonance peak for both the dot array and the single dot, as the radius changes.

Dynamic micromagnetic simulation of the magnetic spectrum of permalloy nanodot array with vortex state

International Nuclear Information System (INIS)

Peng, Y.; Zhao, G.P.; Morvan, F.J.; Wu, S.Q.; Yue, M.

2017-01-01

Due to its potential applications in high-density magnetic storage and spin electronic devices, the ferromagnetic resonance absorption phenomenon has recently drawn much attention. By studying the influence of different materials with various shapes on this phenomenon, the new understandings gained could lead to other applications in the future. In this paper, dynamic magnetic susceptibilities of the vortex state in permalloy nanodot arrays have been investigated using a three-dimensional object oriented micromagnetic framework (OOMMF) code with a two-dimensional periodic boundary condition (2D-PBC) extension and compared with those of a single dot carefully. The resonance mode is excited in the vortex state of nanodot arrays by the microwave magnetic field perpendicular to the dot plane. In this case only radially symmetric spin wave modes can be excited. The influence of the geometric parameters on the resonance frequency has been studied systemically, including the dot radius, the number of repeating elements, and the dot distance. One can see that the resonance peak of the dot array is higher than that of a single dot because of the induced stronger magnetostatic coupling. A critical dot distance exists at which the dot array may be treated as a single dot. There is only one resonance peak for both the dot array and the single dot, as the radius changes. - Highlights: • Resonance peak of the dot array is higher than that of a single dot because of the induced stronger magnetostatic coupling. • A critical dot distance exists at which the dot array may be treated as a single dot. • There is only one resonance peak for both the dot array and the single dot, as the radius changes.

Probing the mid-infrared spectrum of YBa2Cu3O6.0 with high magnetic fields and Zink doping

NARCIS (Netherlands)

Gruninger, M; vanderMarel, D; vanBentum, PJM; Erb, A; Wolf, T; Kopp, T

1996-01-01

The mid-infrared phonon and spin-wave spectrum of antiferromagnetic YBa2Cu3O6.0 was investigated by infrared transmission measurements (k(-->) parallel to c-axis) at T=4K. Peaks at 178 meV, 346 meV and 470 meV were previously interpreted as excitations of single magnons of the optical branch and of

Non-linear radial spinwave modes in thin magnetic disks

International Nuclear Information System (INIS)

Helsen, M.; De Clercq, J.; Vansteenkiste, A.; Van Waeyenberge, B.; Gangwar, A.; Back, C. H.; Weigand, M.

2015-01-01

We present an experimental investigation of radial spin-wave modes in magnetic nano-disks with a vortex ground state. The spin-wave amplitude was measured using a frequency-resolved magneto-optical spectrum analyzer, allowing for high-resolution resonance curves to be recorded. It was found that with increasing excitation amplitude up to about 10 mT, the lowest-order mode behaves strongly non-linearly as the mode frequency redshifts and the resonance peak strongly deforms. This behavior was quantitatively reproduced by micromagnetic simulations. Micromagnetic simulations showed that at higher excitation amplitudes, the spinwaves are transformed into a soliton by self-focusing, and collapse onto the vortex core, dispersing the energy in short-wavelength spinwaves. Additionally, this process can lead to switching of the vortex polarization through the injection of a Bloch point

Exploring the vibrational fingerprint of the electronic excitation energy via molecular dynamics

International Nuclear Information System (INIS)

Deyne, Andy Van Yperen-De; Pauwels, Ewald; Ghysels, An; Waroquier, Michel; Van Speybroeck, Veronique; Hemelsoet, Karen; De Meyer, Thierry; De Clerck, Karen

2014-01-01

A Fourier-based method is presented to relate changes of the molecular structure during a molecular dynamics simulation with fluctuations in the electronic excitation energy. The method implies sampling of the ground state potential energy surface. Subsequently, the power spectrum of the velocities is compared with the power spectrum of the excitation energy computed using time-dependent density functional theory. Peaks in both spectra are compared, and motions exhibiting a linear or quadratic behavior can be distinguished. The quadratically active motions are mainly responsible for the changes in the excitation energy and hence cause shifts between the dynamic and static values of the spectral property. Moreover, information about the potential energy surface of various excited states can be obtained. The procedure is illustrated with three case studies. The first electronic excitation is explored in detail and dominant vibrational motions responsible for changes in the excitation energy are identified for ethylene, biphenyl, and hexamethylbenzene. The proposed method is also extended to other low-energy excitations. Finally, the vibrational fingerprint of the excitation energy of a more complex molecule, in particular the azo dye ethyl orange in a water environment, is analyzed

Excitation of Molecular Hydrogen in the Orion Bar Photodissociation Region from a Deep Near-infrared IGRINS Spectrum

Science.gov (United States)

Kaplan, Kyle F.; Dinerstein, Harriet L.; Oh, Heeyoung; Mace, Gregory N.; Kim, Hwihyun; Sokal, Kimberly R.; Pavel, Michael D.; Lee, Sungho; Pak, Soojong; Park, Chan; Sok Oh, Jae; Jaffe, Daniel T.

2017-04-01

We present a deep near-infrared spectrum of the Orion Bar Photodissociation Region (PDR) taken with the Immersion Grating INfrared Spectrometer (IGRINS) on the 2.7 m telescope at the McDonald Observatory. IGRINS has high spectral resolution (R˜ {{45,000}}) and instantaneous broad wavelength coverage (1.45-2.45 μm), enabling us to detect 87 emission lines from rovibrationally excited molecular hydrogen (H2) that arise from transitions out of 69 upper rovibration levels of the electronic ground state. These levels cover a large range of rotational and vibrational quantum numbers and excitation energies, making them excellent probes of the excitation mechanisms of H2 and physical conditions within the PDR. The Orion Bar PDR is thought to consist of cooler high density clumps or filaments (T=50{--}250 K, {n}H={10}5{--}{10}7 cm-3) embedded in a warmer lower density medium (T=250{--}1000 K, {n}H={10}4{--}{10}5 cm-3). We fit a grid of constant temperature and density Cloudy models, which recreate the observed H2 level populations well, to constrain the temperature to a range of 600-650 K and the density to {n}H=2.5× {10}3{--}{10}4 cm-3. The best-fit model gives T = 625 K and {n}H=5× {10}3 cm-3. This well-constrained warm temperature is consistent with kinetic temperatures found by other studies for the Orion Bar’s lower density medium. However, the range of densities well fit by the model grid is marginally lower than those reported by other studies. We could be observing lower density gas than the surrounding medium, or perhaps a density-sensitive parameter in our models is not properly estimated.

Dependence of spectrum on period and twist effect of the pulsars magnetic field

International Nuclear Information System (INIS)

Shitov, Yu.P.

1983-01-01

The analysis of flux depsities at 102, 408 and 2700 MHz shows that the mean spectral radio luminosity of pUlsars anti Lsub(ν) depends on their period P. The radio luminosity on the average, decreases with the increasing period at all three freqUercies. The character and power of the period dependence anti Lsub(ν)(P) are different at different freqUencies caUsing the corresponding period dependence of the mean radio spectrUm and, particularly, of the spectral index anti αsub(1-4)(102-408 MHz), anti αsub(1-4)(P) varies as Psup(1.7) for P 408 (P) varies as Psup(-1.3) in the period interval 0.3 408 and the period derivatives P, between αsub(1-4) and P. In this connection, the arthor draws the conclusion that period dependences of the spectral radio luminosity and of the spectrum of pulsars are caused by geometrical factors. Quantitative estimates show that the twist effect of magnetic field lines caused by the reaction of magnetic-dipole radiation may be such a geometrical factor, which increases the field line curvatUre (as compared to the dipole field). The twist curvature rhosub(rot)sup(-1) varies as PsUp(-3)xrsup(2) (r is the radial distance from a star) causes the observed period dependence anti Lsub(ν)(P) owing to the curvature emission mechanism. The twist effect of the magnetic field gives the possibility to estimate height levels r of the radio emission regions in a pulsar from the observed function anti Lsub(π)(P). At 408 MHz for an ''average statistic'' pulsar with P> or approximately 0.3 s the level r 408 =1x10 9 cm

NUMERICAL SIMULATION OF EXCITATION AND PROPAGATION OF HELIOSEISMIC MHD WAVES: EFFECTS OF INCLINED MAGNETIC FIELD

International Nuclear Information System (INIS)

Parchevsky, K. V.; Kosovichev, A. G.

2009-01-01

Investigation of propagation, conversion, and scattering of MHD waves in the Sun is very important for understanding the mechanisms of observed oscillations and waves in sunspots and active regions. We have developed a three-dimensional linear MHD numerical model to investigate the influence of the magnetic field on excitation and properties of the MHD waves. The results show that surface gravity waves (f-modes) are affected by the background magnetic field more than acoustic-type waves (p-modes). Comparison of our simulations with the time-distance helioseismology results from Solar and Heliospheric Observatory/MDI shows that the amplitude of travel time variations with azimuth around sunspots caused by the inclined magnetic field does not exceed 25% of the observed amplitude even for strong fields of 1400-1900 G. This can be an indication that other effects (e.g., background flows and nonuniform distribution of the magnetic field) can contribute to the observed azimuthal travel time variations. The azimuthal travel time variations caused by the wave interaction with the magnetic field are similar for simulated and observed travel times for strong fields of 1400-1900 G if Doppler velocities are taken at the height of 300 km above the photosphere where the plasma parameter β << 1. For the photospheric level the travel times are systematically smaller by approximately 0.12 minutes than for the height of 300 km above the photosphere for all studied ranges of the magnetic field strength and inclination angles. Numerical MHD wave modeling and new data from the HMI instrument of the Solar Dynamics Observatory will substantially advance our knowledge of the wave interaction with strong magnetic fields on the Sun and improve the local helioseismology diagnostics.

A scalable piezoelectric impulse-excited energy harvester for human body excitation

International Nuclear Information System (INIS)

Pillatsch, P; Yeatman, E M; Holmes, A S

2012-01-01

Harvesting energy from low-frequency and non-harmonic excitations typical of human motion presents specific challenges. While resonant devices do have an advantage in environments where the excitation frequency is constant, and while they can make use of the entire proof mass travel range in the case of excitation amplitudes that are smaller than the internal displacement limit, they are not suitable for body applications since the frequencies are random and the amplitudes tend to be larger than the device size. In this paper a piezoelectric, impulse-excited approach is presented. A cylindrical proof mass actuates an array of piezoelectric bi-morph beams through magnetic attraction. After the initial excitation these transducers are left to vibrate at their natural frequency. This increases the operational frequency range as well as the electromechanical coupling. The principle of impulse excitation is discussed and a centimetre-scale functional model is introduced as a proof of concept. The obtained data show the influence of varying the frequency, acceleration and proof mass. Finally, a commercially available integrated circuit for voltage regulation is tested. At a frequency of 2 Hz and an acceleration of 2.7 m s −2 a maximal power output of 2.1 mW was achieved. (paper)

Renormalization of Magnetic Excitations in Praseodymium

DEFF Research Database (Denmark)

Lindgård, Per-Anker

1975-01-01

The magnetic exciton renormalization and soft-mode behaviour as the temperature approaches zero of the singlet-doublet magnet (dhcp)pr are accounted for by a selfconsistent rpa theory with no adjustable parameters. The crystal-field splitting between the ground state and the doublet is d=3.74 mev...

Inelastic electron and light scattering from the elementary electronic excitations in quantum wells: Zero magnetic field

Directory of Open Access Journals (Sweden)

Manvir S. Kushwaha

2012-09-01

Full Text Available The most fundamental approach to an understanding of electronic, optical, and transport phenomena which the condensed matter physics (of conventional as well as nonconventional systems offers is generally founded on two experiments: the inelastic electron scattering and the inelastic light scattering. This work embarks on providing a systematic framework for the theory of inelastic electron scattering and of inelastic light scattering from the electronic excitations in GaAs/Ga1−xAlxAs quantum wells. To this end, we start with the Kubo's correlation function to derive the generalized nonlocal, dynamic dielectric function, and the inverse dielectric function within the framework of Bohm-Pines’ random-phase approximation. This is followed by a thorough development of the theory of inelastic electron scattering and of inelastic light scattering. The methodological part is then subjected to the analytical diagnoses which allow us to sense the subtlety of the analytical results and the importance of their applications. The general analytical results, which know no bounds regarding, e.g., the subband occupancy, are then specified so as to make them applicable to practicality. After trying and testing the eigenfunctions, we compute the density of states, the Fermi energy, the full excitation spectrum made up of intrasubband and intersubband – single-particle and collective (plasmon – excitations, the loss functions for all the principal geometries envisioned for the inelastic electron scattering, and the Raman intensity, which provides a measure of the real transitions induced by the (laser probe, for the inelastic light scattering. It is found that the dominant contribution to both the loss peaks and the Raman peaks comes from the collective (plasmon excitations. As to the single-particle peaks, the analysis indicates a long-lasting lack of quantitative comparison between theory and experiments. It is inferred that the inelastic electron

Large degeneracy of excited hadrons and quark models

International Nuclear Information System (INIS)

Bicudo, P.

2007-01-01

The pattern of a large approximate degeneracy of the excited hadron spectra (larger than the chiral restoration degeneracy) is present in the recent experimental report of Bugg. Here we try to model this degeneracy with state of the art quark models. We review how the Coulomb Gauge chiral invariant and confining Bethe-Salpeter equation simplifies in the case of very excited quark-antiquark mesons, including angular or radial excitations, to a Salpeter equation with an ultrarelativistic kinetic energy with the spin-independent part of the potential. The resulting meson spectrum is solved, and the excited chiral restoration is recovered, for all mesons with J>0. Applying the ultrarelativistic simplification to a linear equal-time potential, linear Regge trajectories are obtained, for both angular and radial excitations. The spectrum is also compared with the semiclassical Bohr-Sommerfeld quantization relation. However, the excited angular and radial spectra do not coincide exactly. We then search, with the classical Bertrand theorem, for central potentials producing always classical closed orbits with the ultrarelativistic kinetic energy. We find that no such potential exists, and this implies that no exact larger degeneracy can be obtained in our equal-time framework, with a single principal quantum number comparable to the nonrelativistic Coulomb or harmonic oscillator potentials. Nevertheless we find it plausible that the large experimental approximate degeneracy will be modeled in the future by quark models beyond the present state of the art

Quadrupole collective excitations in rapidly rotating nuclej

International Nuclear Information System (INIS)

Mikhajlov, I.N.

1983-01-01

The spectrum of collective quadrupole excitations in nuclei is investigated. The average nucleus field has the axial symmetry and rotation occurs relatively to this axis. Dependences of the spectrum of quadrupole oscillations on rotation rate for classic liquid drop (CLD) and for a drop of fermi-liquid (DFL) with fissionability parameter X=0.62 ( 154 Er) are presented. The dependence of probabilities of E2-transitions between single-phonon and phonon-free states on rotation rate for CLD and DFL with fussionability parameter X=0.62 ( 154 Er) is also presented. It is shown that for CLD collective E2-transition of states of yrast-consequence is absolutely forbidden. For DFL transitions are possible that lead to decay of phonon-free state with the excitation of phonons of γ-modes and decrease of angular momentum

A 3-Axis Miniature Magnetic Sensor Based on a Planar Fluxgate Magnetometer with an Orthogonal Fluxguide

Directory of Open Access Journals (Sweden)

Chih-Cheng Lu

2015-06-01

Full Text Available A new class of tri-axial miniature magnetometer consisting of a planar fluxgate structure with an orthogonal ferromagnetic fluxguide centrally situated over the magnetic cores is presented. The magnetic sensor possesses a cruciform ferromagnetic core placed diagonally upon the square excitation coil under which two pairs of pick-up coils for in-plane field detection are allocated. Effective principles and analysis of the magnetometer for 3-D field vectors are described and verified by numerically electromagnetic simulation for the excitation and magnetization of the ferromagnetic cores. The sensor is operated by applying the second-harmonic detection technique that can verify V-B relationship and device responsivity. Experimental characterization of the miniature fluxgate device demonstrates satisfactory spatial magnetic field detection results in terms of responsivity and noise spectrum. As a result, at an excitation frequency of 50 kHz, a maximum in-plane responsivity of 122.4 V/T appears and a maximum out-of-plane responsivity of 11.6 V/T is obtained as well. The minimum field noise spectra are found to be 0.11 nT/√Hz and 6.29 nT/√Hz, respectively, in X- and Z-axis at 1 Hz under the same excitation frequency. Compared with the previous tri-axis fluxgate devices, this planar magnetic sensor with an orthogonal fluxguide provides beneficial enhancement in both sensory functionality and manufacturing simplicity. More importantly, this novel device concept is considered highly suitable for the extension to a silicon sensor made by the current CMOS-MEMS technologies, thus emphasizing its emerging applications of field detection in portable industrial electronics.

Exponential frequency spectrum and Lorentzian pulses in magnetized plasmas

International Nuclear Information System (INIS)

Pace, D. C.; Shi, M.; Maggs, J. E.; Morales, G. J.; Carter, T. A.

2008-01-01

Two different experiments involving pressure gradients across the confinement magnetic field in a large plasma column are found to exhibit a broadband turbulence that displays an exponential frequency spectrum for frequencies below the ion cyclotron frequency. The exponential feature has been traced to the presence of solitary pulses having a Lorentzian temporal signature. These pulses arise from nonlinear interactions of drift-Alfven waves driven by the pressure gradients. In both experiments the width of the pulses is narrowly distributed resulting in exponential spectra with a single characteristic time scale. The temporal width of the pulses is measured to be a fraction of a period of the drift-Alfven waves. The experiments are performed in the Large Plasma Device (LAPD-U) [W. Gekelman et al., Rev. Sci. Instrum. 62, 2875 (1991)] operated by the Basic Plasma Science Facility at the University of California, Los Angeles. One experiment involves a controlled, pure electron temperature gradient associated with a microscopic (6 mm gradient length) hot electron temperature filament created by the injection a small electron beam embedded in the center of a large, cold magnetized plasma. The other experiment is a macroscopic (3.5 cm gradient length) limiter-edge experiment in which a density gradient is established by inserting a metallic plate at the edge of the nominal plasma column of the LAPD-U. The temperature filament experiment permits a detailed study of the transition from coherent to turbulent behavior and the concomitant change from classical to anomalous transport. In the limiter experiment the turbulence sampled is always fully developed. The similarity of the results in the two experiments strongly suggests a universal feature of pressure-gradient driven turbulence in magnetized plasmas that results in nondiffusive cross-field transport. This may explain previous observations in helical confinement devices, research tokamaks, and arc plasmas.

Proximate Kitaev quantum spin liquid behaviour in a honeycomb magnet.

Science.gov (United States)

Banerjee, A; Bridges, C A; Yan, J-Q; Aczel, A A; Li, L; Stone, M B; Granroth, G E; Lumsden, M D; Yiu, Y; Knolle, J; Bhattacharjee, S; Kovrizhin, D L; Moessner, R; Tennant, D A; Mandrus, D G; Nagler, S E

2016-07-01

Quantum spin liquids (QSLs) are topological states of matter exhibiting remarkable properties such as the capacity to protect quantum information from decoherence. Whereas their featureless ground states have precluded their straightforward experimental identification, excited states are more revealing and particularly interesting owing to the emergence of fundamentally new excitations such as Majorana fermions. Ideal probes of these excitations are inelastic neutron scattering experiments. These we report here for a ruthenium-based material, α-RuCl3, continuing a major search (so far concentrated on iridium materials) for realizations of the celebrated Kitaev honeycomb topological QSL. Our measurements confirm the requisite strong spin-orbit coupling and low-temperature magnetic order matching predictions proximate to the QSL. We find stacking faults, inherent to the highly two-dimensional nature of the material, resolve an outstanding puzzle. Crucially, dynamical response measurements above interlayer energy scales are naturally accounted for in terms of deconfinement physics expected for QSLs. Comparing these with recent dynamical calculations involving gauge flux excitations and Majorana fermions of the pure Kitaev model, we propose the excitation spectrum of α-RuCl3 as a prime candidate for fractionalized Kitaev physics.

Heisenberg spin-one chain in staggered magnetic field: A density matrix renormalization group study

International Nuclear Information System (INIS)

Jizhong Lou; Xi Dai; Shaojin Qin; Zhaobin Su; Lu Yu

1999-04-01

Using the density matrix renormalization group technique, we calculate numerically the low energy excitation spectrum and magnetization curve of the spin-1 antiferromagnetic chain in a staggered magnetic field, which is expected to describe the physics of R 2 BaNiO 5 (R ≠ Y) family below the Neel temperature of the magnetic rare-earth (R) sublattice. These results are valid in the entire range of the staggered field, and agree with those given by the non-linear σ model study for small fields, but differ from the latter for large fields. They are consistent with the available experimental data. The correlation functions for this model are also calculated. The transverse correlations display the anticipated exponential decay with shorter correlation length, while the longitudinal correlations show explicitly the induced staggered magnetization. (author)

Excitation of simple atoms by slow magnetic monopoles

International Nuclear Information System (INIS)

Kroll, N.M.; Parke, S.J.; Ganapathi, V.; Drell, S.D.

1984-01-01

We present a theory of excitation of simple atoms by slow moving massive monopoles. Previously presented results for a monopole of Dirac strength on hydrogen and helium are reviewed. The hydrogen theory is extended to include arbitrary integral multiples of the Dirac pole strength. The excitation of helium by double strength poles and by dyons is also discussed. It is concluded that a helium proportional counter is a reliable and effective detector for monopoles of arbitrary strength, and for negatively charged dyons

Excited meson spectroscopy with two chirally improved quarks

Science.gov (United States)

Engel, G.; Lang, C. B.; Mohler, D.; Limmer, M.; Schäfer, A.

The excited isovector meson spectrum is explored using two chirally improved dynamical quarks. Seven ensembles, with pion masses down to \\approx 250 MeV are discussed and used for extrapolations to the physical point. Strange mesons are investigated using partially quenched s-quarks. Using the variational method, we extract excited states in several channels and most of the results are in good agreement with experiment.

Excitation of autoionizing states of helium by 100 keV proton impact: II. Excitation cross sections and mechanisms of excitation

Energy Technology Data Exchange (ETDEWEB)

Godunov, A.L. [Department of Physics, Tulane University, New Orleans, LA 70118-5698 (United States); Ivanov, P.B.; Schipakov, V.A. [Troitsk Institute of Innovation and Fusion Research Troitsk, Moscow region, 142092 (Russian Federation); Moretto-Capelle, P.; Bordenave-Montesquieu, D.; Bordenave-Montesquieu, A. [Laboratoire Collisions, Agregats, Reactivite, IRSAMC, UMR 5589, CNRS-Universite Paul Sabatier, 31062 Toulouse Cedex (France)

2000-03-14

Mechanisms of two-electron excitation of the (2s{sup 2}){sup 1} S, (2p{sup 2} ){sup 1} D and (2s2p){sup 1} P autoionizing states of helium are studied both experimentally and theoretically. It is shown that an explicit introduction of a kinematic factor, with a process-specific phase leads to a productive parametrization of experimental cross sections of ionization, allowing one to extract cross sections of excitation of autoionizing states. Using a new fitting procedure together with the proposed parametrization made it possible to obtain the excitation cross sections and magnetic sublevel population from electron spectra as well as, for the first time, to resolve the contribution of resonance and interference components to resonance profiles. Interference with direct ionization is shown to contribute significantly into resonance formation even for backward ejection angles. We demonstrate theoretically that the excitation cross sections thus extracted from experimental electron spectra hold information about the interaction of autoionizing states with an adjacent continuum. (author)

Phonon excitations in multicomponent amorphous solids

International Nuclear Information System (INIS)

Vakarchuk, I.A.; Migal', V.M.; Tkachuk, V.M.

1988-01-01

The method of two-time temperature-dependent Green's functions is used to investigate phonon excitations in multicomponent amorphous solids. The equation obtained for the energy spectrum of the phonon excitations takes into account the damping associated with scattering of phonons by structure fluctuations. The quasicrystal approximation is considered, and as an example explicit expressions are obtained for the case of a two-component amorphous solid for the frequencies of the acoustical and optical modes and for the longitudinal and transverse velocities of sound. The damping is investigated

A theory of the Earth's magnetic field and of sunspots, based on a self-excited dynamo incorporating the Hall effect

Directory of Open Access Journals (Sweden)

A. de Paor

2001-01-01

Full Text Available A new viewpoint on the generation and maintenance of the Earth's magnetic field is put forward, which integrates self-exciting dynamo theory with the possibility of energy coupling along orthogonal axes provided by the Hall effect. A nonlinear third-order system is derived, with a fourth equation serving as an observer of unspecified geophysical processes which could result in field reversal. Lyapunov analysis proves that chaos is not intrinsic to this system. Relative constancy of one of the variables produces pseudo equilibrium in a second order subsystem and allows for self-excitation of the geomagnetic field. Electromagnetic analysis yields expressions for key parameters. Models for secular variations recorded at London, Palermo and at the Cape of Good Hope over the past four hundred years are offered. Offset of the Earth's magnetic axis from the geographic axis is central to time-varying declination, but its causes have not yet been established. Applicability of the model to the explanation of sunspot activity is outlined. A corroborating experiment published by Peter Barlow in 1831 is appended.

Effect of magnet/slot combination on triple-frequency magnetic force and vibration of permanent magnet motors

Science.gov (United States)

Huo, Mina; Wang, Shiyu; Xiu, Jie; Cao, Shuqian

2013-10-01

The relationship between magnet/slot combination and magnetic forces including unbalanced magnetic force (UMF) and cogging torque (CT) of permanent magnet (PM) motors is investigated by using superposition principle and mechanical and magnetic symmetries. The results show that magnetic force can be produced by all magnets passing a single slot, by all slots passing a single magnet, or by eccentricity, which respectively correspond to three frequency components. The results further show that net force/torque can be classified into three typical cases: UMF is suppressed and CT is excited, UMF excited and CT suppressed, and UMF and CT both suppressed, and consequently possible vibrations include three unique groups: rotational modes, translational modes, and balanced modes. The conclusion that combinations with the greatest common divisor (GCD) greater than unity can avoid UMF is mathematically verified, and at the same time lower CT harmonics are preliminarily addressed by the typical excitations. The above findings can create simple guidelines for the suppression of certain UMF and/or CT by using suitable combinations, which in turn can present approach to yield a more desirable response in high performance applications. The superposition effect and predicted relationship are verified by the transient magnetic Finite Element method. Since this work is motivated by symmetries, comparisons are made in order to give further insight into the inner force and vibration behaviors of general rotary power-transmission systems.

Response moments of dynamic systems under non-Gaussian random excitation by the equivalent non-Gaussian excitation method

International Nuclear Information System (INIS)

Tsuchida, Takahiro; Kimura, Koji

2016-01-01

Equivalent non-Gaussian excitation method is proposed to obtain the response moments up to the 4th order of dynamic systems under non-Gaussian random excitation. The non-Gaussian excitation is prescribed by the probability density and the power spectrum, and is described by an Ito stochastic differential equation. Generally, moment equations for the response, which are derived from the governing equations for the excitation and the system, are not closed due to the nonlinearity of the diffusion coefficient in the equation for the excitation even though the system is linear. In the equivalent non-Gaussian excitation method, the diffusion coefficient is replaced with the equivalent diffusion coefficient approximately to obtain a closed set of the moment equations. The square of the equivalent diffusion coefficient is expressed by a quadratic polynomial. In numerical examples, a linear system subjected to nonGaussian excitations with bimodal and Rayleigh distributions is analyzed by using the present method. The results show that the method yields the variance, skewness and kurtosis of the response with high accuracy for non-Gaussian excitation with the widely different probability densities and bandwidth. The statistical moments of the equivalent non-Gaussian excitation are also investigated to describe the feature of the method. (paper)

Excitations in a Two-Dimensional Random Antiferromagnet

DEFF Research Database (Denmark)

Birgeneau, R. J.; Walker, L. R.; Guggenheim, H. J.

1975-01-01

Inelastic neutron scattering studies of the magnetic excitations in the planar Heisenberg random antiferromagnet Rb2Mn0.5Ni0.5F4 at 7K are reported. Two well-defined bands of excitations are observed. A simple mean crystal model is found to predict accurately the measured dispersion relations using...

Creation of skyrmion through resonance excitation

Energy Technology Data Exchange (ETDEWEB)

Li, Zhi-xiong; Chen, Yi-fu; Zhou, Zhen-wei; Nie, Yao-zhuang; Xia, Qing-lin; Wang, Dao-wei; Guo, Guang-hua, E-mail: guogh@mail.csu.edu.cn

2017-07-01

Highlights: • Intrinsic oscillation modes of skyrmion are studied by using micromagnetic simulation. • Creation of skyrmion through resonant excitation is proposed. • The number of generated skyrmions can be effectively controlled by manipulating the driving field. • Skyrmion lattice in extended film is generated via resonant excitation. - Abstract: Controllable creation of magnetic skyrmions in nanostructures is a prerequisite for the application of skyrmions in spintronics. Here, we propose a new method for the creation of skyrmions. We show by using micromagnetic simulations that the skyrmions can be nucleated by resonantly exciting one of the skyrmion intrinsic oscillation modes. We first studied the dynamics of skyrmion in a ferromagnetic nanodisk with perpendicular anisotropy. One breathing mode and two non-degenerate gyrotropic modes are identified. Then we applied a circular-polarized microwave field to excite the uniformly magnetized nanodisk. When the frequency of the driving field is equal to the eigenfrequency of the skyrmion gyrotropic mode, stable skyrmions can be created from the initial uniform state. The number of skyrmions can be effectively controlled by appropriately choosing the duration of the driving field or tuning the field amplitude.

Lattice anomalies and magnetic excitations of the spin web compound Cu3TeO6

International Nuclear Information System (INIS)

Choi, K Y; Lemmens, P; Choi, E S; Berger, H

2008-01-01

We report on the magnetic susceptibility and Raman scattering measurements of the S = 1/2 three-dimensional (3D) spin web compound Cu 3 TeO 6 . The magnetic susceptibility shows an antiferromagnetic ordering at T N ∼61 K and a deviation from the Curie-Weiss law around 150 K. Raman spectra show the emergence of a new mode at 132 cm -1 for temperatures below T*∼50 K (∼0.8 T N ). At the same temperature, phonon anomalies in intensity and frequency show up. This gives evidence of pronounced magneto-elastic effects. In addition, we observe a two-magnon Raman spectrum around 214 cm -1 . Compared to typical 3D spin systems, its robust temperature dependence suggests that a frustrated spin topology with a reduced spin coordination number also enhances spin-phonon couplings.

Azimuthal spin-wave excitations in magnetic nanodots over the soliton background: Vortex, Bloch, and Néel-like skyrmions

Science.gov (United States)

Mruczkiewicz, M.; Gruszecki, P.; Krawczyk, M.; Guslienko, K. Y.

2018-02-01

We study azimuthal spin-wave (SW) excitations in a circular ferromagnetic nanodot in different inhomogeneous, topologically nontrivial magnetization states, specifically, vortex, Bloch-type skyrmion, and Néel-type skyrmion states. A continuous transition between these states is realized by gradually changing the out-of-plane magnetic anisotropy and the Dzyaloshinskii-Moriya exchange interaction (DMI), and the corresponding SW spectra are calculated for each state. We observe the lifting of degeneracy of SW mode frequencies and a change in the systematics of frequency levels. The latter effect is induced by the geometric Berry phase, which occurs in SWs localized at the edge of the dot in the vortex state, and vanishes in the skyrmion states. Furthermore, channeling of edge-localized azimuthal SWs and a related large frequency splitting are observed in the skyrmion states. This is attributed to DMI-induced nonreciprocity, while the coupling of the breathing and gyrotropic modes is related to the skyrmion motion. Finally, we demonstrate efficient coupling of the dynamic magnetization to a uniform magnetic field in nanodots of noncircular symmetry in the skyrmion states.

Magnetic resonance imaging apparatus

International Nuclear Information System (INIS)

Ehnholm, G.J.

1991-01-01

This patent describes an electron spin resonance enhanced magnetic resonance (MR) imaging (ESREMRI) apparatus able to generate a primary magnetic field during periods of nuclear spin transition excitation and magnetic resonance signal detection. This allows the generation of ESREMRI images of a subject. A primary magnetic field of a second and higher value generated during periods of nuclear spin transition excitation and magnetic resonance signal detection can be used to generate conventional MR images of a subject. The ESREMRI and native MR images so generated may be combined, (or superimposed). (author)

Abnormal Cortical Plasticity in Youth with Autism Spectrum Disorder: A Transcranial Magnetic Stimulation Case-Control Pilot Study.

Science.gov (United States)

Pedapati, Ernest V; Gilbert, Donald L; Erickson, Craig A; Horn, Paul S; Shaffer, Rebecca C; Wink, Logan K; Laue, Cameron S; Wu, Steve W

2016-09-01

This case-control study investigated the use of a low-intensity repetitive transcranial magnetic stimulation (rTMS) protocol to measure motor cortex (M1) plasticity in youth with autism spectrum disorder (ASD) compared with typically developing children (TDC). We hypothesized that impairments in long-term potentiation-like properties represent a neurophysiological biomarker of abnormal cortical function in ASD. We studied youth with ASD aged 11-18 years and matched controls (TDC). Intermittent theta burst stimulation (iTBS) was delivered to the dominant M1 at an intensity of 70% of resting motor threshold. Suprathreshold single-pulse TMS was performed to compare amplitudes of motor-evoked potentials (MEP) measured from surface electromyography electrodes on a target muscle before (20 pulses) and after (10 pulses/time point) iTBS at predefined timepoints (up to 30 minutes) to measure any potentiation effects. A linear mixed model was used to examine group differences in MEP amplitudes over time following iTBS. Nine youth with ASD (mean age 15.6; 7 males; 6 right-hand dominant) and 9 TDC (mean age 14.5; 5 males; 9 right-hand dominant) participated. All subjects tolerated the procedure well. Both groups had a mean increase in excitability after iTBS for 30 minutes; however, the time course of excitability changes differed (F9,144 = 2.05; p = 0.038). Post-hoc testing identified a significant decrease in amplitude of the ASD group at 20 minutes following iTBS compared with the TDC after correcting for multiple comparisons. In this study, we demonstrate early evidence for a potential physiological biomarker of cortical plasticity in youth with ASD using a rapid low-intensity rTMS protocol with a discriminate measure at 20 minutes following stimulation. The procedure was well tolerated by all 18 participants. Future work will include modification of the protocol to improve the ability to distinguish subtypes of ASD based on behavioral and cognitive testing.

Abnormal Cortical Plasticity in Youth with Autism Spectrum Disorder: A Transcranial Magnetic Stimulation Case–Control Pilot Study

Science.gov (United States)

Gilbert, Donald L.; Erickson, Craig A.; Horn, Paul S.; Shaffer, Rebecca C.; Wink, Logan K.; Laue, Cameron S.; Wu, Steve W.

2016-01-01

Abstract Objective: This case–control study investigated the use of a low-intensity repetitive transcranial magnetic stimulation (rTMS) protocol to measure motor cortex (M1) plasticity in youth with autism spectrum disorder (ASD) compared with typically developing children (TDC). We hypothesized that impairments in long-term potentiation-like properties represent a neurophysiological biomarker of abnormal cortical function in ASD. Methods: We studied youth with ASD aged 11–18 years and matched controls (TDC). Intermittent theta burst stimulation (iTBS) was delivered to the dominant M1 at an intensity of 70% of resting motor threshold. Suprathreshold single-pulse TMS was performed to compare amplitudes of motor-evoked potentials (MEP) measured from surface electromyography electrodes on a target muscle before (20 pulses) and after (10 pulses/time point) iTBS at predefined timepoints (up to 30 minutes) to measure any potentiation effects. A linear mixed model was used to examine group differences in MEP amplitudes over time following iTBS. Results: Nine youth with ASD (mean age 15.6; 7 males; 6 right-hand dominant) and 9 TDC (mean age 14.5; 5 males; 9 right-hand dominant) participated. All subjects tolerated the procedure well. Both groups had a mean increase in excitability after iTBS for 30 minutes; however, the time course of excitability changes differed (F9,144 = 2.05; p = 0.038). Post-hoc testing identified a significant decrease in amplitude of the ASD group at 20 minutes following iTBS compared with the TDC after correcting for multiple comparisons. Conclusion: In this study, we demonstrate early evidence for a potential physiological biomarker of cortical plasticity in youth with ASD using a rapid low-intensity rTMS protocol with a discriminate measure at 20 minutes following stimulation. The procedure was well tolerated by all 18 participants. Future work will include modification of the protocol to improve the ability to distinguish subtypes of

Raman spectrum of predissociating H/sub 2/S

International Nuclear Information System (INIS)

Kleinermanns, K.; Suntz, R.; Schneider, R.

1986-01-01

Emission spectroscopy of photodissociating molecules provides interesting insights into the short-time dynamics of bond raptures. The authors report here a resolved H/sub 2/S photoemission spectrum after excitation at 193 nm, although its electronic spectrum in this wavelength region is diffuse. The electronic spectrum of H/sub 2/S between 250 and 170 nm is nearly continuous probably due to predissociation

Fractional excitations in the square-lattice quantum antiferromagnet

DEFF Research Database (Denmark)

Piazza, B. Dalla; Mourigal, M.; Christensen, Niels Bech

2015-01-01

-projected trial wavefunctions. The excitation continuum is accounted for by the existence of spatially extended pairs of fractional S=1/2 quasiparticles, 2D analogues of 1D spinons. Away from the anomalous wavevector, these fractional excitations are bound and form conventional magnons. Our results establish...... the existence of fractional quasiparticles in the high-energy spectrum of a quasi-two-dimensional antiferromagnet, even in the absence of frustration....

Superconducting, magnetic, and charge correlations in the doped two-chain Hubbard model

International Nuclear Information System (INIS)

Asai, Y.

1995-01-01

We have studied the superconducting, magnetic, and charge correlation functions and the spin excitation spectrum in the doped two-chain Hubbard model by projector Monte Carlo and Lanczos diagonalization methods. The exponent of the interchain singlet superconducting correlation function, γ, is found to be close to 2.0 as long as two distinct noninteracting bands cross the Fermi level. Magnetic and charge correlation functions decay more rapidly than or as fast as the interchain singlet superconducting correlation function along the chains. The superconducting correlation in the doped two-chain Hubbard model is the most long-range correlation studied here. Implications of the results for the possible universality class of the doped two-chain Hubbard model are discussed

Two-step excitation structure changes of luminescence centers and strong tunable blue emission on surface of silica nanospheres

Energy Technology Data Exchange (ETDEWEB)

Yang, Lei, E-mail: nanoyang@qq.com; Jiang, Zhongcheng; Dong, Jiazhang; Zhang, Liuqian [Hunan University, College of Materials Science and Engineering (China); Pan, Anlian, E-mail: anlian.pan@gmail.com; Zhuang, Xiujuan [Hunan University, Key Laboratory for Micro-Nano Physics and Technology of Hunan Province (China)

2015-10-15

We report a scheme for investigating two-step stimulated structure change of luminescence centers. Amorphous silica nanospheres with uniform diameter of 9–15 nm have been synthesized by Stöber method. Strong hydroxyl-related infrared-absorption band is observed in infrared spectrum. The surface hydroxyl groups exert great influence on the luminescent behavior of silica. They provide stable and intermediate energy states to accommodate excitation electrons. The existence of these surface states reduces the energy barrier of photochemical reactions, creating conditions for two-step excitation process. By carefully examining excitation and emission process, the nearest excitation band is absent in both optical absorption spectrum and excitation spectrum. This later generated state confirms the generation of new luminescence centers as well as the existence of photochemical reactions. Stimulated by different energies, two-step excitation process impels different photochemical reactions, prompting generation of different lattice defects on surface area of silica. Thereby, tunable luminescence is achieved. After thermal treatment, strong gap excitation band appears with the disappearance of strong surface excitation band. Strong blue luminescence also disappears. The research is significance to precise introducing structural defects and controlling position of luminescence peaks.

Magnetic excitation and local magnetic susceptibility of the excitonic insulator Ta2NiSe5 investigated by 77Se NMR

Science.gov (United States)

Li, Shang; Kawai, Shunsuke; Kobayashi, Yoshiaki; Itoh, Masayuki

2018-04-01

77Se NMR measurements were made on polycrystalline and single-crystalline samples to elucidate local magnetic susceptibility and magnetic excitation of Ta2NiSe5 , which is proposed to undergo an exciton condensation accompanied by a structural transition at Tc=328 K . We determine the 77Se Knight shift tensors for the three Se sites and analyze their anisotropy based on the site symmetry. The temperature dependence of the Knight shift is discussed on the basis of spin and orbital susceptibilities calculated for two-chain and two-dimensional three-band models. The large fraction of the Se 4 p orbital polarization due to the mixing between Ni 3 d and Se 4 p orbitals is estimated from the analysis of the transferred hyperfine coupling constant. Also the nuclear spin-lattice relaxation rate 1 /T1 is found not to show a coherent peak just below Tc and to obey the thermally activated temperature dependence with a spin gap energy of 1770 ±40 K . This behavior of 1 /T1 monitors the exciton condensation as proposed by the theoretical study of 1 /T1 based on the three-chain Hubbard model for the excitonic insulator.

Multispectral code excited linear prediction coding and its application in magnetic resonance images.

Science.gov (United States)

Hu, J H; Wang, Y; Cahill, P T

1997-01-01

This paper reports a multispectral code excited linear prediction (MCELP) method for the compression of multispectral images. Different linear prediction models and adaptation schemes have been compared. The method that uses a forward adaptive autoregressive (AR) model has been proven to achieve a good compromise between performance, complexity, and robustness. This approach is referred to as the MFCELP method. Given a set of multispectral images, the linear predictive coefficients are updated over nonoverlapping three-dimensional (3-D) macroblocks. Each macroblock is further divided into several 3-D micro-blocks, and the best excitation signal for each microblock is determined through an analysis-by-synthesis procedure. The MFCELP method has been applied to multispectral magnetic resonance (MR) images. To satisfy the high quality requirement for medical images, the error between the original image set and the synthesized one is further specified using a vector quantizer. This method has been applied to images from 26 clinical MR neuro studies (20 slices/study, three spectral bands/slice, 256x256 pixels/band, 12 b/pixel). The MFCELP method provides a significant visual improvement over the discrete cosine transform (DCT) based Joint Photographers Expert Group (JPEG) method, the wavelet transform based embedded zero-tree wavelet (EZW) coding method, and the vector tree (VT) coding method, as well as the multispectral segmented autoregressive moving average (MSARMA) method we developed previously.

First Calorimetric Measurement of OI-line in the Electron Capture Spectrum of $^{163}$Ho

CERN Document Server

Ranitzsch, P. C. -O.; Wegner, M.; Kempf, S.; Fleischmann, A.; Enss, C.; Gastaldo, L.; Herlert, A.; Johnston, K.

2014-01-01

The isotope $^{163}$Ho undergoes an electron capture process with a recommended value for the energy available to the decay, $Q_{\\rm EC}$, of about 2.5 keV. According to the present knowledge, this is the lowest $Q_{\\rm EC}$ value for electron capture processes. Because of that, $^{163}$Ho is the best candidate to perform experiments to investigate the value of the electron neutrino mass based on the analysis of the calorimetrically measured spectrum. We present for the first time the calorimetric measurement of the atomic de-excitation of the $^{163}$Dy daughter atom upon the capture of an electron from the 5s shell in $^{163}$Ho, OI-line. The measured peak energy is 48 eV. This measurement was performed using low temperature metallic magnetic calorimeters with the $^{163}$Ho ion implanted in the absorber. We demonstrate that the calorimetric spectrum of $^{163}$Ho can be measured with high precision and that the parameters describing the spectrum can be learned from the analysis of the data. Finally, we dis...

[A magnetic therapy apparatus with an adaptable electromagnetic spectrum for the treatment of prostatitis and gynecopathies].

Science.gov (United States)

Kuz'min, A A; Meshkovskiĭ, D V; Filist, S A

2008-01-01

Problems of engineering and algorithm development of magnetic therapy apparatuses with pseudo-random radiation spectrum within the audio range for treatment of prostatitis and gynecopathies are considered. A typical design based on a PIC 16F microcontroller is suggested. It includes a keyboard, LCD indicator, audio amplifier, inducer, and software units. The problem of pseudo-random signal generation within the audio range is considered. A series of rectangular pulses is generated on a random-length interval on the basis of a three-component random vector. This series provides the required spectral characteristics of the therapeutic magnetic field and their adaptation to the therapeutic conditions and individual features of the patient.

New excitation equipment for 220 MW generators in Kozloduy NPP

International Nuclear Information System (INIS)

Tomerlin, D.

2001-01-01

Rehabilitation on the excitation equipment for Generator 5, Reactor Unit 3, in Kozloduy NPP was completed in November 2000. ABB's Static Excitation System based on UNITROL 5000 technology has been chosen by the Bulgarian National Utility and Kozloduy NPP to substitute the original Russian excitation system equipment with electro-magnetic voltage regulators. The substitution is in a rehabilitation package of four excitation system equipment for Generator 5 and 6 of Reactor Unit 3 and Generator 7 and 8 of Reactor Unit 4 after a short overview of the original excitation system this paper describes the new Static Excitation System UNITROL 5000 including configuration with block diagram, its main features and merits such as modes of operation, limiter, special control functions and diagnostic facilities. Furthermore, new facilities, which are implemented in UNITROL 5000, such as dynamic current distribution among the thyristors working in parallel as well as the start-up from the residual magnetism are mentioned. Special functions including a so-called free-running mode of operation and automatic change over sequence from new excitation system to the stand-by excitation system, which is DC exciter machine, are described. Some records of the transient responses performed during the commissioning and a photograph of a manufactured system are provided. (author)

Kicker magnet design

International Nuclear Information System (INIS)

Li, Z.; Thiessen, H.A.

1989-01-01

In this paper, the kicker magnet is studied by use of the program POISSON. For using the dc-code POISSON in the ac problem of the kicker magnet, an approximation of the ac effects is made, this simplifying the ac problem into a dc problem. The study of the magnet is taken in two steps: assuming the γ of the ferrite material is fixed in the calculation to get a preliminary design of the magnet; using the real B /minus/ H curve of the CMD5005 ferrite material in the calculation to get the final design of the magnet. The stored energy, the excitation curve and the excitation efficiency of the kicker magnet are also discussed. 10 figs., 7 tabs

Variational-integral perturbation corrections of some lower excited states for hydrogen atoms in magnetic fields

International Nuclear Information System (INIS)

Yuan Lin; Zhou Ben-Hu; Zhao Yun-Hui; Xu Jun; Hai Wen-Hua

2012-01-01

A variational-integral perturbation method (VIPM) is established by combining the variational perturbation with the integral perturbation. The first-order corrected wave functions are constructed, and the second-order energy corrections for the ground state and several lower excited states are calculated by applying the VIPM to the hydrogen atom in a strong uniform magnetic field. Our calculations demonstrated that the energy calculated by the VIPM only shows a negative value, which indicates that the VIPM method is more accurate than the other methods. Our study indicated that the VIPM can not only increase the accuracy of the results but also keep the convergence of the wave functions

Seismic analysis of piping systems subjected to multiple support excitations

International Nuclear Information System (INIS)

Sundararajan, C.; Vaish, A.K.; Slagis, G.C.

1981-01-01

The paper presents the results of a comparative study between the multiple response spectrum method and the time-history method for the seismic analysis of nuclear piping systems subjected to different excitation at different supports or support groups. First, the necessary equations for the above analysis procedures are derived. Then, three actual nuclear piping systems subjected to single and multiple excitations are analyzed by the different methods, and extensive comparisons of the results (stresses) are made. Based on the results, it is concluded that the multiple response spectrum analysis gives acceptable results as compared to the ''exact'', but much more costly, time-history analysis. 6 refs

Magnetic resonance study of bulk and thin film EuTiO3

International Nuclear Information System (INIS)

Laguta, V V; Kamba, S; Maryško, M; Andrzejewski, B; Kachlík, M; Maca, K; Lee, J H; Schlom, D G

2017-01-01

Magnetic resonance spectra of EuTiO 3 in both bulk and thin film form were taken at temperatures from 3–350 K and microwave frequencies from 9.2–9.8 and 34 GHz. In the paramagnetic phase, magnetic resonance spectra are determined by magnetic dipole and exchange interactions between Eu 2+ spins. In the film, a large contribution arises from the demagnetization field. From detailed analysis of the linewidth and its temperature dependence, the parameters of spin–spin interactions were determined: the exchange frequency is 10.5 GHz and the estimated critical exponent of the spin correlation length is  ≈0.4. In the bulk samples, the spectra exhibited a distinct minimum in the linewidth at the Néel temperature, T N   ≈  5.5 K, while the resonance field practically does not change even on cooling below T N . This is indicative of a small magnetic anisotropy ∼320 G in the antiferromagnetic phase. In the film, the magnetic resonance spectrum is split below T N into several components due to excitation of the magnetostatic modes, corresponding to a non-uniform precession of magnetization. Moreover, the film was observed to degrade over two years. This was manifested by an increase of defects and a change in the domain structure. The saturated magnetization in the film, estimated from the magnetic resonance spectrum, was about 900 emu cm −3 or 5.5 µ B /unit cell at T   =  3.5 K. (paper)

Bottomonium spectrum revisited

CERN Document Server

Segovia, Jorge; Entem, David R.; Fernández, Francisco

2016-01-01

We revisit the bottomonium spectrum motivated by the recently exciting experimental progress in the observation of new bottomonium states, both conventional and unconventional. Our framework is a nonrelativistic constituent quark model which has been applied to a wide range of hadronic observables from the light to the heavy quark sector and thus the model parameters are completely constrained. Beyond the spectrum, we provide a large number of electromagnetic, strong and hadronic decays in order to discuss the quark content of the bottomonium states and give more insights about the better way to determine their properties experimentally.

Interaction between pancreatic β cell and electromagnetic fields: A systematic study toward finding the natural frequency spectrum of β cell system.

Science.gov (United States)

Farashi, Sajjad

2017-01-01

Interaction between biological systems and environmental electric or magnetic fields has gained attention during the past few decades. Although there are a lot of studies that have been conducted for investigating such interaction, the reported results are considerably inconsistent. Besides the complexity of biological systems, the important reason for such inconsistent results may arise due to different excitation protocols that have been applied in different experiments. In order to investigate carefully the way that external electric or magnetic fields interact with a biological system, the parameters of excitation, such as intensity or frequency, should be selected purposefully due to the influence of these parameters on the system response. In this study, pancreatic β cell, the main player of blood glucose regulating system, is considered and the study is focused on finding the natural frequency spectrum of the system using modeling approach. Natural frequencies of a system are important characteristics of the system when external excitation is applied. The result of this study can help researchers to select proper frequency parameter for electrical excitation of β cell system. The results show that there are two distinct frequency ranges for natural frequency of β cell system, which consist of extremely low (or near zero) and 100-750 kHz frequency ranges. There are experimental works on β cell exposure to electromagnetic fields that support such finding.

Device for frequency modulation of a laser output spectrum

Science.gov (United States)

Beene, J.R.; Bemis, C.E. Jr.

1984-07-17

A device is provided for fast frequency modulating the output spectrum of multimode lasers and single frequency lasers that are not actively stabilized. A piezoelectric transducer attached to a laser cavity mirror is driven in an unconventional manner to excite resonance vibration of the tranducer to rapidly, cyclicly change the laser cavity length. The result is a cyclic sweeping of the output wavelength sufficient to fill the gaps in the laser output frequency spectrum. When a laser is used to excite atoms or molecules, complete absorption line coverage is made possible.

Energy spectrum and density of states for a graphene quantum dot in a magnetic field

International Nuclear Information System (INIS)

Morgenstern Horing, Norman J; Liu, S Y

2010-01-01

In this paper, we determine the spectrum and density of states of a graphene quantum dot in a normal quantizing magnetic field. To accomplish this, we employ the retarded Green function for a magnetized, infinite-sheet graphene layer to describe the dynamics of a tightly confined graphene quantum dot subject to Landau quantization. Considering a δ (2) (r) potential well that supports just one subband state in the well in the absence of a magnetic field, the effect of Landau quantization is to 'splinter' this single energy level into a proliferation of many Landau-quantized states within the well. Treating the graphene sheet and dot as a closed system subject to a fully Hermitian Hamiltonian (including boundary conditions), there is no indication of decay of the Landau-quantized graphene dot states into the quantized states of the host graphene sheet for 'tight' confinement by the δ (2) (r) potential well, notwithstanding extension of the dot Green function (and eigenfunctions) outside the δ (2) (r) potential well.

Correlation between the number of quantum-statistical modes of the exciting field and the number of lines in the resonance fluorescence spectrum

International Nuclear Information System (INIS)

Kryzhanovskii, Boris V; Sokolov, G B

2000-01-01

The quasi-energy wave functions of a two-level atom in an electromagnetic field, the state of which represents a superposition of coherent states, were found. The fluorescence spectrum of an atom excited by such a field was investigated. It was shown that a spectral fluorescence mode corresponds to each mode of the quantum-statistical distribution of the field incident on the atom. This means that the number of statistical modes of the incident field may be recorded as the number of data bits of the information carried by the light pulse. (laser applications and other topics in quantum electronics)

Magnetic loss and B(H) behaviour of non-oriented electrical sheets under a trapezoidal exciting field

Science.gov (United States)

Kedous-Lebouc, A.; Errard, S.; Cornut, B.; Brissonneau, P.

1994-05-01

The excess loss and hysteresis response of electrical steel are measured and discussed in the case of trapezoidal field excitation similar to the current provided by a current commutation supply of a self-synchronous rotating machine. Three industrial non-oriented SiFe samples of different magnetic grades and thicknesses are tested using an automatic Epstein frame equipment. The losses and the unusual observed B( H) loops are analysed in terms of the rate of change of the field, the diffusion of the induction inside the sheet and by the calculation of the theoretical hysteresis cycles due to the eddy currents.

Magnetic ordering and spin excitations in Mn(dca) sub 2 (pyz) [dca=N(CN) sub 2 sup - , pyz=pyrazine

CERN Document Server

Manson, J L; Argyriou, D N; Bordallo, H N; Lynn, J W; Huang, Q; Feyerherm, R; Loose, A

2002-01-01

We have studied the T- and H-dependent magnetism in Mn(dca) sub 2 (pyz) [dca=N(CN) sub 2 sup - , pyz=pyrazine] using neutron-scattering methods. The crystal structure can be viewed as a molecular analog of ReO sub 3 , where 1D Mn-pyz-Mn chains connect 2D Mn(dca) sub 2 square sheets to form a 3D network. In zero field, the Mn sup 2 sup + moments order antiferromagnetically below 2.53(2) K along the ac diagonal with a magnitude of 4.15(6) mu B at 1.35 K. The field-dependent response of the [111] magnetic reflection is consistent with spin-flop and induced ferromagnetic phase transitions as previously observed in magnetization measurements. Diffuse-scattering studies indicated no evidence for low-dimensional spin correlations. Using quasielastic neutron scattering, a low-energy spin-wave excitation was observed at propor to 0.23 meV, which is propor to 1/6 the momentum transfer observed in Mn(dca) sub 2 owing to a reduced number of magnetic nearest neighbors. (orig.)

Spin texture and magnetoroton excitations at nu=1/3.

Science.gov (United States)

Groshaus, Javier G; Dujovne, Irene; Gallais, Yann; Hirjibehedin, Cyrus F; Pinczuk, Aron; Tan, Yan-Wen; Stormer, Horst; Dennis, Brian S; Pfeiffer, Loren N; West, Ken W

2008-02-01

Neutral spin texture (ST) excitations at nu=1/3 are directly observed for the first time by resonant inelastic light scattering. They are determined to involve two simultaneous spin flips. At low magnetic fields, the ST energy is below that of the magnetoroton minimum. With increasing in-plane magnetic field these mode energies cross at a critical ratio of the Zeeman and Coulomb energies of eta(c)=0.020+/-0.001. Surprisingly, the intensity of the ST mode grows with temperature in the range in which the magnetoroton modes collapse. The temperature dependence is interpreted in terms of a competition between coexisting phases supporting different excitations. We consider the role of the ST excitations in activated transport at nu=1/3.

Numerical study of induced current perturbations in the vicinity of excitable cells exposed to extremely low frequency magnetic fields

International Nuclear Information System (INIS)

Hassan, Noha; Chatterjee, Indira; Publicover, Nelson G; Craviso, Gale L

2003-01-01

Realistic three-dimensional cell morphologies were modelled to determine the current density induced in excitable cell culture preparations exposed to 60 Hz magnetic fields and to identify important factors that can influence the responses of cells to these fields. Cell morphologies representing single spherical adrenal chromaffin cells, single elongated smooth muscle cells and chromaffin cell aggregates in a Petri dish containing culture medium were modelled using the finite element method. The computations for a spherical cell revealed alterations in the magnitude and spatial distribution of the induced current density in the immediate vicinity of the cell. Maxima occurred at the equatorial sides and minima at the poles. Proximity of cells to each other as well as cell aggregate shape, size and orientation with respect to the induced current influenced the magnitude and spatial distribution of the induced current density. For an elongated cell, effects on the induced current density were highly dependent on cell orientation with respect to the direction of the induced current. These results provide novel insights into the perturbations in induced current that occur in excitable cell culture preparations and lay a foundation for understanding the mechanisms of interaction with extremely low frequency magnetic fields at the tissue level

Self-consistent hole motion and spin excitations in a quantum antiferromagnet

International Nuclear Information System (INIS)

Su, Z.B.; Yu, L.; Li, Y.M.; Lai, W.Y.

1989-12-01

A new quantum Bogoliubov-de Gennes (BdeG) formalism is developed to study the self-consistent motion of holes and spin excitations in a quantum antiferromagnet within the generalized t-J model. On the one hand, the effects of local distortion of spin configurations and the renormalization of the hole motion due to virtual excitations of the distorted spin background are treated on an equal footing to obtain the hole wave function and its spectrum, as well as the effective mass for a propagating hole. On the other hand, the change of the spin excitation spectrum and the spin correlations due to the presence of dynamical holes are studied within the same adiabatic approximation. The stability of the hole states with respect to such changes justifies the self-consistency of the proposed formalism. (author). 25 refs, 6 figs, 1 tab

Design and development of a parametrically excited nonlinear energy harvester

International Nuclear Information System (INIS)

Yildirim, Tanju; Ghayesh, Mergen H.; Li, Weihua; Alici, Gursel

2016-01-01

Highlights: • A parametrically broadband energy harvester was fabricated. • Strong softening-type nonlinear behaviour was observed. • Experiments were conducted showing the large bandwidth of the device. - Abstract: An energy harvester has been designed, fabricated and tested based on the nonlinear dynamical response of a parametrically excited clamped-clamped beam with a central point-mass; magnets have been used as the central point-mass which pass through a coil when parametrically excited. Experiments have been conducted for the energy harvester when the system is excited (i) harmonically near the primary resonance; (ii) harmonically near the principal parametric resonance; (iii) by means of a non-smooth periodic excitation. An electrodynamic shaker was used to parametrically excite the system and the corresponding displacement of the magnet and output voltages of the coil were measured. It has been shown that the system displays linear behaviour at the primary resonance; however, at the principal parametric resonance, the motion characteristic of the magnet substantially changed displaying a strong softening-type nonlinearity. Theoretical simulations have also been conducted in order to verify the experimental results; the comparison between theory and experiment were within very good agreement of each other. The energy harvester developed in this paper is capable of harvesting energy close to the primary resonance as well as the principal parametric resonance; the frequency-band has been broadened significantly mainly due to the nonlinear effects as well as the parametric excitation.

A simple method for automatic measurement of excitation functions

International Nuclear Information System (INIS)

Ogawa, M.; Adachi, M.; Arai, E.

1975-01-01

An apparatus has been constructed to perform the sequence control of a beam-analysing magnet for automatic excitation function measurements. This device is also applied to the feedback control of the magnet to lock the beam energy. (Auth.)

Triplet State Resonance Raman Spectrum of all-trans-diphenylbutadiene

DEFF Research Database (Denmark)

Wilbrandt, Robert Walter; Grossman, W.E.L.; Killough, P.M

1984-01-01

The resonance Raman spectrum of all-trans-diphenylbutadiene (DPB) in its ground state and the resonance Raman spectrum (RRS) of DPB in its short-lived electronically excited triplet state are reported. Transient spectra were obtained by a pump-probe technique using two pulsed lasers...

Comprehensive cluster-theory analysis of the magnetic structures and excitations in CoCl2·2H2O

DEFF Research Database (Denmark)

Jensen, Jens; Larsen, Jacob; Hansen, Ursula B.

2018-01-01

The magnetic properties of CoCl2·2H2O are analyzed in the mean-field/random-phase approximation using a basis of clusters with four spins along the c-axis chains of Co ions. The model gives a unifying account of the bulk properties, the spin waves, and the higher-order cluster-spin excitations...... at a transverse field of 160 kOe and is found to agree closely with their observations....

Excitations and phase transitions in random anti-ferromagnets

International Nuclear Information System (INIS)

Cowley, R.A.; Birgeneau, R.J.; Shirane, G.

1979-01-01

Neutron scattering techniques can be used to study the magnetic excitations and phase transitions in the randomly mixed transition metal fluorides. The results for the excitations of samples with two different types of magnetic ions show two bands of excitations; each associated with excitations propagating largely on one type of ion. In the diluted salts the spectra show a complex line shape and greater widths. These results are in good accord with computer simulations showing that linear spin wave theory can be used, but have not been described satisfactorily using the coherent potential approximation. The phase transitions in these materials are always smeared, but it is difficult to ascertain if this smearing is due to macroscopic fluctuations in the concentration or of an intrinsic origin. Studies of these systems close to the percolation point have shown that the thermal disorder is associated with the one-dimensional weak links of the large clusters. Currently theory and experiment are in accord for the two-dimensional Ising system but features are still not understood in Heisenberg systems in both two and three dimensions

Recent experiments involving highly excited atoms

International Nuclear Information System (INIS)

Latimer, C.J.

1979-01-01

Very large and fragile atoms may be produced by exciting normal atoms with light or by collisions with other atomic particles. Atoms as large as 10 -6 m are now routinely produced in the laboratory and their properties studied. In this review some of the simpler experimental methods available for the production and detection of such atoms are described including tunable dye laser-excitation and field ionization. A few recent experiments which illustrate the collision properties and the effects of electric and and magnetic fields are also described. The relevance of highly excited atoms in other areas of research including radioastronomy and isotope separation are discussed. (author)

Band excitation method applicable to scanning probe microscopy

Science.gov (United States)

Jesse, Stephen [Knoxville, TN; Kalinin, Sergei V [Knoxville, TN

2010-08-17

Methods and apparatus are described for scanning probe microscopy. A method includes generating a band excitation (BE) signal having finite and predefined amplitude and phase spectrum in at least a first predefined frequency band; exciting a probe using the band excitation signal; obtaining data by measuring a response of the probe in at least a second predefined frequency band; and extracting at least one relevant dynamic parameter of the response of the probe in a predefined range including analyzing the obtained data. The BE signal can be synthesized prior to imaging (static band excitation), or adjusted at each pixel or spectroscopy step to accommodate changes in sample properties (adaptive band excitation). An apparatus includes a band excitation signal generator; a probe coupled to the band excitation signal generator; a detector coupled to the probe; and a relevant dynamic parameter extractor component coupled to the detector, the relevant dynamic parameter extractor including a processor that performs a mathematical transform selected from the group consisting of an integral transform and a discrete transform.

Three dimensional nuclear magnetic resonance spectroscopic imaging of sodium ions using stochastic excitation and oscillating gradients

International Nuclear Information System (INIS)

Frederick, B.deB.

1994-12-01

Nuclear magnetic resonance (NMR) spectroscopic imaging of 23 Na holds promise as a non-invasive method of mapping Na + distributions, and for differentiating pools of Na + ions in biological tissues. However, due to NMR relaxation properties of 23 Na in vivo, a large fraction of Na + is not visible with conventional NMR imaging methods. An alternate imaging method, based on stochastic excitation and oscillating gradients, has been developed which is well adapted to measuring nuclei with short T 2 . Contemporary NMR imaging techniques have dead times of up to several hundred microseconds between excitation and sampling, comparable to the shortest in vivo 23 Na T 2 values, causing significant signal loss. An imaging strategy based on stochastic excitation has been developed which greatly reduces experiment dead time by reducing peak radiofrequency (RF) excitation power and using a novel RF circuit to speed probe recovery. Continuously oscillating gradients are used to eliminate transient eddy currents. Stochastic 1 H and 23 Na spectroscopic imaging experiments have been performed on a small animal system with dead times as low as 25μs, permitting spectroscopic imaging with 100% visibility in vivo. As an additional benefit, the encoding time for a 32x32x32 spectroscopic image is under 30 seconds. The development and analysis of stochastic NMR imaging has been hampered by limitations of the existing phase demodulation reconstruction technique. Three dimensional imaging was impractical due to reconstruction time, and design and analysis of proposed experiments was limited by the mathematical intractability of the reconstruction method. A new reconstruction method for stochastic NMR based on Fourier interpolation has been formulated combining the advantage of a several hundredfold reduction in reconstruction time with a straightforward mathematical form

Gutzwiller approach for elementary excitations in S = 1 antiferromagnetic chains

International Nuclear Information System (INIS)

Liu, Zheng-Xin; Zhou, Yi; Ng, Tai-Kai

2014-01-01

In a previous paper (Liu et al 2012 Phys. Rev. B 85 195144), a variational Monte Carlo method (based on Gutzwiller projected states) was generalized to S = 1 systems. This method provided very good trial ground states for the gapped phases of an S = 1 bilinear-biquadratic (BLBQ) Heisenberg chain. In this paper, we extend the approach to study the low-lying elementary excitations in S = 1 chains. We calculate the one-magnon and two-magnon excitation spectra of the BLBQ Heisenberg chain and the results agree very well with recent data in the literature. In our approach, the difference of the excitation spectrum between the Haldane phase and the dimer phase (such as the even/odd size effect) can be understood from their different topologies of the corresponding mean field theory. We especially study the Takhtajan–Babujian critical point. Despite the fact that the ‘elementary excitations’ are spin-1 magnons, which are different from the spin-1/2 spinons in Bethe solution, we show that the excitation spectrum, critical exponent (η=0.74) and central charge (c = 1.45) calculated from our theory agree well with the Bethe ansatz solution and conformal field theory predictions. (paper)

Identification of the low-energy excitations in a quantum critical system

Directory of Open Access Journals (Sweden)

Tom Heitmann

2017-05-01

Full Text Available We have identified low-energy magnetic excitations in a doped quantum critical system by means of polarized neutron scattering experiments. The presence of these excitations could explain why Ce(Fe0.76Ru0.242Ge2 displays dynamical scaling in the absence of local critical behavior or long-range spin-density wave criticality. The low-energy excitations are associated with the reorientations of the superspins of fully ordered, isolated magnetic clusters that form spontaneously upon lowering the temperature. The system houses both frozen clusters and dynamic clusters, as predicted by Hoyos and Vojta [Phys. Rev. B 74, 140401(R (2006].

Advances in magnetic resonance 6

CERN Document Server

Waugh, John S

2013-01-01

Advances in Magnetic Resonance, Volume 6 focuses on the theoretical and practical aspects of applying magnetic resonance methods to various problems in physical chemistry, emphasizing the different aspects of the exegesis of these problems. This book discusses the gas phase magnetic resonance of electronically excited molecules; techniques for observing excited electronic states; NMR studies in liquids at high pressure; and effect of pressure on self-diffusion in liquids. The nuclear magnetic resonance investigations of organic free radicals; measurement of proton coupling constants by NMR; an

Passive Spectroscopic Diagnostics for Magnetically-confined Fusion Plasmas

International Nuclear Information System (INIS)

Stratton, B.C.; Bitter, M.; Hill, K.W.; Hillis, D.L.; Hogan, J.T.

2007-01-01

Spectroscopy of radiation emitted by impurities and hydrogen isotopes plays an important role in the study of magnetically-confined fusion plasmas, both in determining the effects of impurities on plasma behavior and in measurements of plasma parameters such as electron and ion temperatures and densities, particle transport, and particle influx rates. This paper reviews spectroscopic diagnostics of plasma radiation that are excited by collisional processes in the plasma, which are termed 'passive' spectroscopic diagnostics to distinguish them from 'active' spectroscopic diagnostics involving injected particle and laser beams. A brief overview of the ionization balance in hot plasmas and the relevant line and continuum radiation excitation mechanisms is given. Instrumentation in the soft X-ray, vacuum ultraviolet, ultraviolet, visible, and near-infrared regions of the spectrum is described and examples of measurements are given. Paths for further development of these measurements and issues for their implementation in a burning plasma environment are discussed.

Passive Spectroscopic Diagnostics for Magnetically-confined Fusion Plasmas

Energy Technology Data Exchange (ETDEWEB)

Stratton, B. C.; Biter, M.; Hill, K. W.; Hillis, D. L.; Hogan, J. T.

2007-07-18

Spectroscopy of radiation emitted by impurities and hydrogen isotopes plays an important role in the study of magnetically-confined fusion plasmas, both in determining the effects of impurities on plasma behavior and in measurements of plasma parameters such as electron and ion temperatures and densities, particle transport, and particle influx rates. This paper reviews spectroscopic diagnostics of plasma radiation that are excited by collisional processes in the plasma, which are termed 'passive' spectroscopic diagnostics to distinguish them from 'active' spectroscopic diagnostics involving injected particle and laser beams. A brief overview of the ionization balance in hot plasmas and the relevant line and continuum radiation excitation mechanisms is given. Instrumentation in the soft X-ray, vacuum ultraviolet, ultraviolet, visible, and near-infrared regions of the spectrum is described and examples of measurements are given. Paths for further development of these measurements and issues for their implementation in a burning plasma environment are discussed.

Crystal field excitations of YbMn{sub 2}Si{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Mole, R.A. [Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW 2234 (Australia); School of Physical, Environmental and Mathematical Sciences, The University of New South Wales at the Australian Defence Force Academy, Canberra, ACT 2600 (Australia); Hofmann, M. [School of Physical, Environmental and Mathematical Sciences, The University of New South Wales at the Australian Defence Force Academy, Canberra, ACT 2600 (Australia); Forschungsneutronenquelle Heinz Maier-Leibnitz (FRM II), Technische Universität München, 85747 Garching (Germany); Adroja, D.T. [ISIS Facility, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Didcot, OX11 OQX (United Kingdom); Moze, O. [Dipartimento di Fisica, Università degli Studi di Modena e Reggio Emilia, Modena (Italy); Campbell, S.J., E-mail: stewart.campbell@adfa.edu.au [School of Physical, Environmental and Mathematical Sciences, The University of New South Wales at the Australian Defence Force Academy, Canberra, ACT 2600 (Australia)

2013-12-15

The crystal field excitations of the rare earth intermetallic compound YbMn{sub 2}Si{sub 2} have been measured by inelastic neutron scattering over the temperature range 2.5–50 K. The YbMn{sub 2}Si{sub 2} spectra exhibit three low energy excitations (∼3–7 meV) in the antiferromagnetic AFil region above the magnetic phase transition at T{sub N2} = 30(5) K. The crystal field parameters have been determined for YbMn{sub 2}Si{sub 2} in the antiferromagnetic AFil region. A further two inelastic excitations (∼9 meV, 17 meV) are observed below T{sub N2}=30(5) K, the temperature at which the high temperature antiferromagnetic structure is reported to exhibit doubling of the magnetic cell. Energy level diagrams have been determined for Yb{sup 3+} ions in the different sites above (single site) and below the magnetic transition temperature (two sites). The excitation energies for both sites are shown to be temperature independent with the temperature dependences of the transition intensities for the two sites described well by a simple Boltzmann model. The spectra below T{sub N2} cannot be described fully in terms of molecular field models based on either a single Yb{sup 3+} site or two Yb{sup 3+} sites. This indicates that the magnetic behaviour of YbMn{sub 2}Si{sub 2} is more complicated than previously considered. The inability to account fully for excitations below the magnetic phase transition may be due to an, as yet, unresolved structural transition associated with the magnetic transition. - Highlights: • The inelastic neutron scattering from YbMn{sub 2}Si{sub 2} has been investigated over the temperature range 2.5–50 K. • The crystal field splitting has been monitored through the magnetic transition at 30(5) K. • We have determined the crystal field parameters for the antiferromagnetic AFil region. • The transition intensities are described well by Boltzmann occupancy models. • The spectra below the magnetic transition have been analysed by

Excited state mass spectra of doubly heavy baryons Ω{sub cc}, Ω{sub bb} and Ω{sub bc}

Energy Technology Data Exchange (ETDEWEB)

Shah, Zalak; Rai, Ajay Kumar [Sardar Vallabhbhai National Institute of Technology, Department of Applied Physics, Surat, Gujarat (India); Thakkar, Kaushal [GIDC Degree Engineering college, Department of Applied Sciences and Humanities, Abrama, Navsari (India)

2016-10-15

We discuss the mass spectrum of Ω baryon with two heavy quarks and one light quark (ccs, bbs, and bcs). The main goal of the paper is to calculate the ground state masses and after that, the positive and negative parity excited states masses are also obtained within a hypercentral constituent quark model, using Coulomb plus linear potential framework. We also added a first order correction to the potential. The mass spectra up to 5S for radial excited states and 1P-5P, 1D-4D, and 1F-2F states for orbital excited states are computed for Ω{sub cc}, Ω{sub bb} and Ω{sub bc} baryons. Our obtained results are compared with other theoretical predictions, which could be a useful complementary tool for the interpretation of experimentally unknown heavy baryon spectra. The Regge trajectory is constructed in both the (n{sub r}, M{sup 2}) and the (J, M{sup 2}) planes for Ω{sub cc}, Ω{sub bb} and Ω{sub bc} baryons and their slopes and intercepts are also determined. Magnetic moments of doubly heavy Ω{sup '}s are also calculated. (orig.) 8.

Proton Magnetic Resonance Spectroscopy and MRI Reveal No Evidence for Brain Mitochondrial Dysfunction in Children with Autism Spectrum Disorder

Science.gov (United States)

Corrigan, Neva M.; Shaw, Dennis. W. W.; Richards, Todd L.; Estes, Annette M.; Friedman, Seth D.; Petropoulos, Helen; Artru, Alan A.; Dager, Stephen R.

2012-01-01

Brain mitochondrial dysfunction has been proposed as an etiologic factor in autism spectrum disorder (ASD). Proton magnetic resonance spectroscopic imaging ([superscript 1]HMRS) and MRI were used to assess for evidence of brain mitochondrial dysfunction in longitudinal samples of children with ASD or developmental delay (DD), and cross-sectionally…

Evolution of spin excitations in a gapped antiferromagnet from the quantum to the high-temperature limit

DEFF Research Database (Denmark)

Kenzelmann, M.; Cowley, R.A.; Buyers, W.J.L.

2002-01-01

We have mapped from the quantum to the classical limit the spin excitation spectrum of the antiferromagnetic spin-1 Heisenberg chain system CsNiCl3 in its paramagnetic phase from T=5 to 200 K. Neutron scattering shows that the excitations are resonant and dispersive up to at least T=70 Ksimilar...... is in agreement with quantum Monte Carlo calculations for the spin-1 chain. xi is also consistent with the single mode approximation, suggesting that the excitations are short-lived single particle excitations. Below T=12 K where three-dimensional spin correlations are important, xi is shorter than predicted...... and the experiment is not consistent with the random phase approximation for coupled quantum chains. At T=200 K, the structure factor and second energy moment of the excitation spectrum are in excellent agreement with the high-temperature series expansion....

Contribution to the study of magnetic diffusion of neutrons; Contribution a l'etude de la diffusion magnetique des neutrons

Energy Technology Data Exchange (ETDEWEB)

Gennes, P.G. de [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

1959-07-01

Certain statistical aspects of a large collection of electronic spins coupled by exchange forces are examined. The treatment is limited to substances where the orbital magnetic moment can be considered fixed, and where the effect of thermal agitation of the ions can be neglected. A system of this kind can be followed experimentally by elastic and inelastic diffusion of neutrons. At high temperatures, inelastic diffusion allows the microscopic aspect, reversible, and the macroscopic aspect, irreversible, to be studied simultaneously and these 2 fields to be linked. At temperatures around the Curie point, the average phenomenon is the appearance of a critical opalescence. At low temperatures, collective spin excitations can be observed. In the neighborhood of the Curie point, the spin coefficient {lambda}, which governs the relaxation of fluctuations of magnetization, is calculated. An intrinsic factor is discussed in {lambda}, bound to the microscopic frequency of the spin exchanges, and to a factor due to the damping of the diffusion by the magnetic field. At the transition point, {lambda} is cancelled. The spectrum of the spin excitations in metals is discussed. (author)

Concerning the electromagnetic radiation spectrum of a hot plasma with Langmuir turbulence in a magnetic field

International Nuclear Information System (INIS)

Tirsky, V.V.; Ledenev, V.G.; Tomozov, V.M.

2001-01-01

We consider the process of generation of electromagnetic waves as a consequence of the merging of two Langmuir plasmons. The case of a hot plasma in a magnetic field is investigated. It is shown that under such conditions the frequency of Langmuir plasmons can vary over the range from 0.8 to 1.1 of the Langmuir frequency of electrons. The spectrum and polarization of electromagnetic radiation are analyzed. It is shown that allowance for the thermal motion of plasma particles under the conditions involved permits electromagnetic waves in the range from 1.6 to 2.2 of the Langmuir frequency of electrons to be generated. The degree of circular polarization of the radiation can reach 50% even in the case of an isotropic spectrum of Langmuir turbulence. (orig.)

Solar spectrum from 1173 to 1324 A

International Nuclear Information System (INIS)

Chipman, E.; Bruner, E.C. Jr.

1975-01-01

We present some of the results of a rocket flight which obtained a high-resolution stigmatic spectrum of the Sun in the region 1173--1324 A. A list of 179 lines observed in this region is presented, with intensities, widths, and approximate excitation classes for each line. A reproduction and finding chart of the spectrum is included, along with discussion of some individual lines of special interest

Increase in cortical pyramidal cell excitability accompanies depression-like behavior in mice: a transcranial magnetic stimulation study.

Science.gov (United States)

Sun, Peng; Wang, Furong; Wang, Li; Zhang, Yu; Yamamoto, Ryo; Sugai, Tokio; Zhang, Qing; Wang, Zhengda; Kato, Nobuo

2011-11-09

Clinical evidence suggests that cortical excitability is increased in depressives. We investigated its cellular basis in a mouse model of depression. In a modified version of forced swimming (FS), mice were initially forced to swim for 5 consecutive days and then were treated daily with repetitive transcranial magnetic stimulation (rTMS) or sham treatment for the following 4 weeks without swimming. On day 2 through day 5, the mice manifested depression-like behaviors. The next and last FS was performed 4 weeks later, which revealed a 4 week maintenance of depression-like behavior in the sham mice. In slices from the sham controls, excitability in cingulate cortex pyramidal cells was elevated in terms of membrane potential and frequencies of spikes evoked by current injection. Depolarized resting potential was shown to depend on suppression of large conductance calcium-activated potassium (BK) channels. This BK channel suppression was confirmed by measuring spike width, which depends on BK channels. Chronic rTMS treatment during the 4 week period significantly reduced the depression-like behavior. In slices obtained from the rTMS mice, normal excitability and BK channel activity were recovered. Expression of a scaffold protein Homer1a was reduced by the FS and reversed by rTMS in the cingulate cortex. Similar recovery in the same behavioral, electrophysiological, and biochemical features was observed after chronic imipramine treatment. The present study demonstrated that manifestation and disappearance of depression-like behavior are in parallel with increase and decrease in cortical neuronal excitability in mice and suggested that regulation of BK channels by Homer1a is involved in this parallelism.

Synthesis of ultrawideband radiation of combined antenna arrays excited by nanosecond bipolar voltage pulses

International Nuclear Information System (INIS)

Koshelev, V I; Plisko, V V; Sevostyanov, E A

2017-01-01

To broaden the spectrum of high-power ultrawideband radiation, it is suggested to synthesize an electromagnetic pulse summing the pulses of different length in free space. On the example of model pulses corresponding to radiation of combined antennas excited by bipolar voltage pulses of the length of 2 and 3 ns, the possibility of twofold broadening of the radiation spectrum was demonstrated. Radiation pulses with the spectrum width exceeding three octaves were obtained. Pattern formation by the arrays of different geometry excited by the pulses having different time shifts was considered. Optimum array structure with the pattern maximum in the main direction was demonstrated on the example of a 2×2 array. (paper)

Mirror neuron activity associated with social impairments but not age in autism spectrum disorder.

Science.gov (United States)

Enticott, Peter G; Kennedy, Hayley A; Rinehart, Nicole J; Tonge, Bruce J; Bradshaw, John L; Taffe, John R; Daskalakis, Zafiris J; Fitzgerald, Paul B

2012-03-01

The neurobiology of autism spectrum disorder (ASD) is not particularly well understood, and biomedical treatment approaches are therefore extremely limited. A prominent explanatory model suggests that social-relating symptoms may arise from dysfunction within the mirror neuron system, while a recent neuroimaging study suggests that these impairments in ASD might reduce with age. Participants with autism spectrum disorder (i.e., DSM-IV autistic disorder or Asperger's disorder) (n = 34) and matched control subjects (n = 36) completed a transcranial magnetic stimulation study in which corticospinal excitability was assessed during the observation of hand gestures. Regression analyses revealed that the ASD group presented with significantly reduced corticospinal excitability during the observation of a transitive hand gesture (relative to observation of a static hand) (p mirror neuron system activity within ventral premotor cortex/inferior frontal gyrus. Among the ASD group, there was also a negative association between putative mirror neuron activity and self-reported social-relating impairments, but there was no indication that mirror neuron impairments in ASD decrease with age. These data provide general support for the mirror neuron hypothesis of autism; researchers now must clarify the precise functional significance of mirror neurons to truly understand their role in the neuropathophysiology of ASD and to determine whether they should be used as targets for the treatment of ASD.

Resonance double magnetic bremsstrahlung in a strong magnetic field

International Nuclear Information System (INIS)

Fomin, P.I.; Kholodov, R.I.

2003-01-01

The possibility of resonance double magnetic bremsstrahlung in the approximation of weakly excited electron states in a strong external magnetic field is analyzed. The differential probability of this process in the Breit-Wigner form is obtained. The probability of double magnetic bremsstrahlung (second-order process of perturbation theory) is compared with the probability of magnetic bremsstrahlung (first-order process of perturbation theory)

Glass-like, low-energy excitations in neutron-irradiated quartz

International Nuclear Information System (INIS)

Gardner, J.W.

1980-01-01

The specific heat and thermal conductivity of neutron-irradiated crystalline quartz have been measured for temperatures approx. = 0.1 to 5 K. Four types of low-energy excitations are observed in the irradiated samples, two of which can be removed selectively by heat treatment. One set of remaining excitations gives rise to low-temperature thermal behavior characteristic of glassy (amorphous) solids. The density of these glass-like excitations can be 50% the density observed in vitreous silica, yet the sample still retains long-range atomic order. In a less-irradiated sample, glass-like excitations may be present with a density only approx. = 2.5% that observed in vitreous silica and possess a similar broad energy spectrum over 0.1 to 1 K

Anisotropy of electronic states excited in ion-atom collisions

International Nuclear Information System (INIS)

Boskamp, E.B.

1983-01-01

The author reports coincidence measurements made on the He + + Ne and He + + He systems. The complex population amplitudes for the magnetic sublevels of the investigated excited states, Ne(2p 4 3s 2 ) 1 D and He(2p 2 ) 1 D, were completely determined and possible excitation mechanisms are described. (Auth.)

Switchable directional excitation surface plasmon polaritons with dielectric nanoantennas

DEFF Research Database (Denmark)

Sinev, I.; Komissarenko, F.; Bogdanov, A.

2017-01-01

We demonstrate directional launching of surface plasmon polaritons on thin goldfilm with a single silicon nanosphere. The directivity pattern of the excited surface waves exhibits rapid switching from forward to backward excitation, which is driven by the mutual interference of magnetic and elect...... and electric dipole moments supported by the dielectric nanoantenna....

Excitation of multipolar surface plasmon resonance in plasmonic nanoparticles by complex accelerating beams

International Nuclear Information System (INIS)

Yang, Yang; Li, Jiafang; Li, Zhi-Yuan; Chen, Yue-Gang

2015-01-01

In this paper, through a vector-spherical harmonics approach, we investigate the optical spectra of plasmonic Au nanoparticles excited by two special accelerating beams: a non-paraxial Airy beam and a Bessel beam. We systematically analyze the impacts of the beam profile, phase, and helical wave front of the electromagnetic fields on the optical spectrum and the excitation of the surface plasmon resonance (SPR). We find that the high-order phase in the Airy beam would result in strong plasmonic oscillations in the optical spectra, while the cone angle and orbital angular momentum carried by the Bessel beam could be employed to engineer the plasmon modes excited in Au nanoparticles. Furthermore, the optical spectrum excited by a combined Airy–Bessel–Gauss beam is discussed. The study could help to deeply explore new ways to manipulate SPR in metal nanoparticles via the wave front engineering of optical beams for enhancing light–matter interaction and optical sensing performance. (paper)

Excitation of multipolar surface plasmon resonance in plasmonic nanoparticles by complex accelerating beams

Science.gov (United States)

Yang, Yang; Li, Jiafang; Li, Zhi-Yuan; Chen, Yue-Gang

2015-07-01

In this paper, through a vector-spherical harmonics approach, we investigate the optical spectra of plasmonic Au nanoparticles excited by two special accelerating beams: a non-paraxial Airy beam and a Bessel beam. We systematically analyze the impacts of the beam profile, phase, and helical wave front of the electromagnetic fields on the optical spectrum and the excitation of the surface plasmon resonance (SPR). We find that the high-order phase in the Airy beam would result in strong plasmonic oscillations in the optical spectra, while the cone angle and orbital angular momentum carried by the Bessel beam could be employed to engineer the plasmon modes excited in Au nanoparticles. Furthermore, the optical spectrum excited by a combined Airy-Bessel-Gauss beam is discussed. The study could help to deeply explore new ways to manipulate SPR in metal nanoparticles via the wave front engineering of optical beams for enhancing light-matter interaction and optical sensing performance.