Spin Density Wave Phase Diagram in Thin Cr(110) Films
NASA Astrophysics Data System (ADS)
Rotenberg, Eli; Freelon, B. K.; Koh, H.; Rossnagel, K.; Kevan, S. D.
2004-03-01
Using angle-resolved photoemission, we have mapped the antiferromagnetic phase diagram of Cr(110) thin films grown on Mo(110) and W(110) substrates systematically as a function of both film thickness and temperature. We find commensurate and incommensurate spin density wave and paramagnetic phases that are separated by nearly continuous transitions. We determine how the spin density wave band gap evolves near the Fermi level through these phases. Our results suggest a simple model to explain the delicate interplay between commensurate and incommensurate phases that involves a balance between spin density wave stabilization energy and surface and interface magnetic anisotropies.
Field-induced spin-density wave in (TMTSF)2NO3
NASA Astrophysics Data System (ADS)
Vignolles, David; Audouard, Alain; Nardone, Marc; Brossard, Luc; Bouguessa, Sabrina; Fabre, Jean-Marc
2005-01-01
Interlayer magnetoresistance of the Bechgaard salt (TMTSF)2NO3 is investigated up to 50 T under pressures of a few kilobars. This compound, the Fermi surface of which is quasi-two-dimensional at low temperature, is a semimetal under pressure. Nevertheless, a field-induced spin-density wave is evidenced at 8.5 kbars above ˜20T . This state is characterized by a drastically different spectrum of the quantum oscillations compared to the low-pressure spin-density wave state.
Electrical effects of spin density wave quantization and magnetic domain walls in chromium.
Kummamuru, Ravi K; Soh, Yeong-Ah
2008-04-17
The role of magnetic domains (and the walls between domains) in determining the electrical properties of ferromagnetic materials has been investigated in great detail for many years, not least because control over domains offers a means of manipulating electron spin to control charge transport in 'spintronic' devices. In contrast, much less attention has been paid to the effects of domains and domain walls on the electrical properties of antiferromagnets: antiferromagnetic domains show no net external magnetic moment, and so are difficult to manipulate or probe. Here we describe electrical measurements on chromium--a simple metal and quintessential spin density wave antiferromagnet--that show behaviour directly related to spin density wave formation and the presence of antiferromagnetic domains. Two types of thermal hysteresis are seen in both longitudinal and Hall resistivity: the first can be explained by the quantization of spin density waves due to the finite film thickness (confirmed by X-ray diffraction measurements) and the second by domain-wall scattering of electrons. We also observe the striking influence of the electrical lead configuration (a mesoscopic effect) on the resistivity of macroscopic samples in the spin density wave state. Our results are potentially of practical importance, in that they reveal tunable electrical effects of film thickness and domain walls that are as large as the highest seen for ferromagnets.
Field-induced spin-density wave beyond hidden order in URu2Si2
Knafo, W.; Duc, F.; Bourdarot, F.; Kuwahara, K.; Nojiri, H.; Aoki, D.; Billette, J.; Frings, P.; Tonon, X.; Lelièvre-Berna, E.; Flouquet, J.; Regnault, L.-P.
2016-01-01
URu2Si2 is one of the most enigmatic strongly correlated electron systems and offers a fertile testing ground for new concepts in condensed matter science. In spite of >30 years of intense research, no consensus on the order parameter of its low-temperature hidden-order phase exists. A strong magnetic field transforms the hidden order into magnetically ordered phases, whose order parameter has also been defying experimental observation. Here, thanks to neutron diffraction under pulsed magnetic fields up to 40 T, we identify the field-induced phases of URu2Si2 as a spin-density-wave state. The transition to the spin-density wave represents a unique touchstone for understanding the hidden-order phase. An intimate relationship between this magnetic structure, the magnetic fluctuations and the Fermi surface is emphasized, calling for dedicated band-structure calculations. PMID:27762260
Unconventional spin-density wave in Bechgaard salt (TMTSF)2NO3
NASA Astrophysics Data System (ADS)
Basletić, Mario; Korin-Hamzić, Bojana; Maki, Kazumi; Tomić, Silvia
2007-02-01
Among many Bechgaard salts, (TMTSF)2NO3 , where TMTSF denotes tetramethyltetraselenafulvalene, exhibits very anomalous low-temperature properties. Unlike the case of the conventional spin-density wave (SDW), (TMTSF)2NO3 undergoes the SDW transition at TC≈9.5K and the low-temperature quasiparticle excitations are gapless. Also, it is known that (TMTSF)2NO3 does not exhibit superconductivity even under pressure, while a field-induced SDW is found in (TMTSF)2NO3 only for P=8.5kbar and B>20T . Here we show that both the angle-dependent magnetoresistance data and the nonlinear Hall resistance of (TMTSF)2NO3 at ambient pressure are interpreted satisfactorily in terms of an unconventional spin-density wave. Based on these facts, we propose a new phase diagram for Bechgaard salts.
Field-induced spin-density wave beyond hidden order in URu2Si2
NASA Astrophysics Data System (ADS)
Knafo, W.; Duc, F.; Bourdarot, F.; Kuwahara, K.; Nojiri, H.; Aoki, D.; Billette, J.; Frings, P.; Tonon, X.; Lelièvre-Berna, E.; Flouquet, J.; Regnault, L.-P.
2016-10-01
URu2Si2 is one of the most enigmatic strongly correlated electron systems and offers a fertile testing ground for new concepts in condensed matter science. In spite of >30 years of intense research, no consensus on the order parameter of its low-temperature hidden-order phase exists. A strong magnetic field transforms the hidden order into magnetically ordered phases, whose order parameter has also been defying experimental observation. Here, thanks to neutron diffraction under pulsed magnetic fields up to 40 T, we identify the field-induced phases of URu2Si2 as a spin-density-wave state. The transition to the spin-density wave represents a unique touchstone for understanding the hidden-order phase. An intimate relationship between this magnetic structure, the magnetic fluctuations and the Fermi surface is emphasized, calling for dedicated band-structure calculations.
Spin-density-wave antiferromagnetism of Cr in Fe/Cr(001) superlattices
Fullerton, E.E.; Bader, S.D.; Robertson, J.L.
1996-10-01
The antiferromagnetic spin-density-wave (SDW) order of Cr layers in Fe/Cr(001) superlattices was investigated by neutron scattering. For Cr thickness 51-190 {Angstrom}, a transverse SDW is formed for all temperatures below Neel temperature with a single wavevector Q normal to the layers. A coherent magnetic structure forms with the nodes of the SDW near the Fe-Cr interfaces. For thinner Cr layers, the magnetic scattering can be described by commensurate antiferromagnetic order.
Field-induced spin density wave and spiral phases in a layered antiferromagnet
Stone, Matthew B.; Lumsden, Mark D.; Garlea, Vasile O.; ...
2015-07-28
Here we determine the low-field ordered magnetic phases of the S=1 dimerized antiferromagnet Ba3Mn2O8 using single crystal neutron diffraction. We find that for magnetic fields between μ0H=8.80 T and 10.56 T applied along themore » $$1\\bar{1}0$$ direction the system exhibits spin density wave order with incommensurate wave vectors of type (η,η,ε). For μ0H > 10.56 T, the magnetic order changes to a spiral phase with incommensurate wave vectors only along the [hh0] direction. For both field induced ordered phases, the magnetic moments are lying in the plane perpendicular to the field direction. Finally, the nature of these two transitions is fundamentally different: the low-field transition is a second order transition to a spin-density wave ground state, while the one at higher field, toward the spiral phase, is of first order.« less
Field-induced spin density wave and spiral phases in a layered antiferromagnet
Stone, Matthew B.; Lumsden, Mark D.; Garlea, Vasile O.; Grenier, B.; Ressouche, E.; Samulon, Eric C.; Fisher, Ian R.
2015-07-28
Here we determine the low-field ordered magnetic phases of the S=1 dimerized antiferromagnet Ba_{3}Mn_{2}O_{8} using single crystal neutron diffraction. We find that for magnetic fields between μ_{0}H=8.80 T and 10.56 T applied along the $1\\bar{1}0$ direction the system exhibits spin density wave order with incommensurate wave vectors of type (η,η,ε). For μ_{0}H > 10.56 T, the magnetic order changes to a spiral phase with incommensurate wave vectors only along the [hh0] direction. For both field induced ordered phases, the magnetic moments are lying in the plane perpendicular to the field direction. Finally, the nature of these two transitions is fundamentally different: the low-field transition is a second order transition to a spin-density wave ground state, while the one at higher field, toward the spiral phase, is of first order.
The η-Pairing Superconductivity in Spin-Density Wave Background
NASA Astrophysics Data System (ADS)
X, M. Qiu; Z, J. Wang
1993-10-01
In this letter, we propose a modified attractive Hubbard model at half filling that can exhibit superconductivity through η-pairing mechanism in spin-density wave representation and derive a concise relationship between the energy disparity and the single-particle energy spectrum. This relationship, in the two limits of U, clearly shows that the system does not display superconductivity for very low doping concentration. but demonstrates superconductivity when the doping concentration exceeds a certain critical value. This conclusion is in qualitative agreement with the familiar experiments on high-Tc superconductivity.
Superconductivity and magnetic field induced spin density waves in the (TMTTF)2X family
NASA Astrophysics Data System (ADS)
Balicas, L.; Behnia, K.; Kang, W.; Canadell, E.; Auban-Senzier, P.; Jérome, D.; Ribault, M.; Fabre, J. M.
1994-10-01
We report magnetotransport measurements in the quasi one dimensional (Q-1-D) organic conductor (TMTTF)2Br at pressures up to 26 kbar, clown to 0.45 K in magnetic fields up to 19 T along the c^{ast} direction. It is found that a superconducting ground state is stabilized under 26 kbar at T_C = 0.8 K. No magnetic field induced spin density wave (FISDW) transitions are observed below 19T unlike other Q-1-D superconductors pertaining to the selenium series. The computed amplitude of the interchain coupling along transverse directions is unable to explain the missing; FISDW instability.
Nodal quasiparticles and the onset of spin-density-wave order in cuprate superconductors.
Pelissetto, Andrea; Sachdev, Subir; Vicari, Ettore
2008-07-11
We present a theory for the onset of spin-density-wave order in the superconducting ground state of the cuprates. We compute the scaling dimensions of allowed perturbations of a "relativistic" fixed point with O4 x O(3) symmetry, including those associated with the fermionic nodal Bogoliubov quasiparticles. Analyses of up to six loops show that all perturbations with square lattice symmetry are likely irrelevant. We demonstrate that the fermion spectral functions are primarily damped by the coupling to fluctuations of a composite field with Ising nematic order. A number of other experimental implications are also discussed.
Controlling Spin-Density Wave Periodicity in Thin Cr1-x Vx Films
NASA Astrophysics Data System (ADS)
Krupin, Oleg; Rotenberg, Eli; Kevan, S. D.
2007-03-01
Chromium is an itinerant antiferromagnet with a spin-density wave (SDW) ground state driven by a nesting of Fermi surface sheets around the Gamma and H points of the Brillouin zone. Periodicity of the SDW plays an important role in mediating magnetic interactions in magnetic multilayer structures providing a giant magnetoresistance effect and potentially interesting for application in spintronic devices. Therefore control of SDW in thin chromium films is of the high importance. It requires a detailed understanding of phenomena related to stabilization of SDW. We used angle-resolved photoemission to characterize spin-density wave and Fermi surface topology in thin Cr1-x Vx films as a function of the film thickness, temperature, composition and hydrogen surface coverage. A key feature of our results is the ability to control the magnetic structure of thin films of Cr with an external perturbation: balancing the surface energetic interactions favored commensurate state of SDW vs. the energy associated with Fermi surface topology stabilizing SDW incommensurate phase in the bulk.
Physics in Superconductors with a Spin Density Wave: Quasiclassical Description of a two-band Model
NASA Astrophysics Data System (ADS)
Moor, Andreas; Volkov, Anatoly; Efetov, Konstantin
2014-03-01
Using a simple model of a two-band superconductor with a spin density wave we investigate the physics in the coexistence regime of the two order parameters, i.e., the spin density wave (SDW) and the superconductivity (SC). We use the quasiclassical Green's functions approach. Our findings concern, i.a., the Knight shift, the proximity and the Josephson effects, and the time and spatial dependence of the magnetic order parameter near the quantum critical point. In particular we find a solution of the stationary equation which describes a domain wall in the magnetic structure. In the center of the domain wall we find a local enhancement of SC. Investigating the stability of a uniform commensurate SDW we obtain the values of the doping parameter at which the first order transition into the state with m = 0 takes place or to the state with an inhomogeneous SDW occurs. We appreciate the financial support from the DFG by the Project EF 11/8-1.
Electronic and magnetic properties of spiral spin-density-wave states in transition-metal chains
NASA Astrophysics Data System (ADS)
Tanveer, M.; Ruiz-Díaz, P.; Pastor, G. M.
2016-09-01
The electronic and magnetic properties of one-dimensional (1D) 3 d transition-metal nanowires are investigated in the framework of density functional theory. The relative stability of collinear and noncollinear (NC) ground-state magnetic orders in V, Mn, and Fe monoatomic chains is quantified by computing the frozen-magnon dispersion relation Δ E (q ⃗) as a function of the spin-density-wave vector q ⃗. The dependence on the local environment of the atoms is analyzed by varying systematically the lattice parameter a of the chains. Electron correlation effects are explored by comparing local spin-density and generalized-gradient approximations to the exchange and correlation functional. Results are given for Δ E (q ⃗) , the local magnetic moments μ⃗i at atom i , the magnetization-vector density m ⃗(r ⃗) , and the local electronic density of states ρi σ(ɛ ) . The frozen-magnon dispersion relations are analyzed from a local perspective. Effective exchange interactions Ji j between the local magnetic moments μ⃗i and μ⃗j are derived by fitting the ab initio Δ E (q ⃗) to a classical 1D Heisenberg model. The dominant competing interactions Ji j at the origin of the NC magnetic order are identified. The interplay between the various Ji j is revealed as a function of a in the framework of the corresponding magnetic phase diagrams.
Influence of the antiferromagnetic spin density wave on the magnetoresistance of Cr
NASA Astrophysics Data System (ADS)
Soh, Yeong-Ah; Kummamuru, Ravi
2007-03-01
We have performed magnetotransport measurements on Cr films that are 350, 56, 43 and 18 nm thick. The magnetoresistance with the field perpendicular to the film plane shows a clear increase below the Neel temperature and is accompanied by an anomalous negative magnetoresistance at the Neel temperature. The orbital magnetoresistance satisfies the Kohler's rule in the paramagnetic state but violates it in the Neel state. The Hall resistance shows temperature dependence in the paramagnetic state, which was previously suggested to be indicative of a pseudogap [1]. We explain the above phenomena by the evolution of the electronic structure due to the formation of antiferromagnetic spin density wave, the influence of antiferromagnetic domain walls, and the existence of more than one scattering time. [1] ``Quantum phase transition in a common metal'', A. Yeh, Y-A. Soh, J. Brooke, G. Aeppli, T. F. Rosenbaum, and S. M. Hayden, Nature (London) 419, 459 (2002).
Dynamical spin-density waves in a spin-orbit-coupled Bose-Einstein condensate
NASA Astrophysics Data System (ADS)
Li, Yan; Qu, Chunlei; Zhang, Yongsheng; Zhang, Chuanwei
2015-07-01
Synthetic spin-orbit (SO) coupling, an important ingredient for quantum simulation of many exotic condensed matter physics, has recently attracted considerable attention. The static and dynamic properties of a SO-coupled Bose-Einstein condensate (BEC) have been extensively studied in both theory and experiment. Here we numerically investigate the generation and propagation of a dynamical spin-density wave (SDW) in a SO-coupled BEC using a fast moving Gaussian-shaped barrier. We find that the SDW wavelength is sensitive to the barrier's velocity while varies slightly with the barrier's peak potential or width. We qualitatively explain the generation of SDW by considering a rectangular barrier in a one-dimensional system. Our results may motivate future experimental and theoretical investigations of rich dynamics in the SO-coupled BEC induced by a moving barrier.
Tunneling spectroscopy of normal metals with charge-density or spin-density waves
Gabovich, A.M.; Voitenko, A.I.
1995-09-01
Tunneling current-voltage characteristics (CVC) are calculated for symmetrical and nonsymmetrical junctions made up of metals with charge-density or spin-density waves and a distortion of the Fermi-surface nesting sections described by the order parameter {Sigma}. For the symmetrical junction the CVC are odd functions of the bias voltage {ital V} and do not depend on the sign of {Sigma}. The differential conductivities have root singularities at {ital eV}={Sigma} and jumps at {ital eV}=2{Sigma}. For the nonsymmetrical junction the CVC depend on the sign of {Sigma}. Relevant differential conductivities are nonsymmetrical, with one branch being smooth and another having a root singularity at {ital eV}={Sigma}. A qualitative agreement exists with the tunneling and point-contact spectroscopy measurements for layered dichalcogenides, NbSe{sub 3}, and URu{sub 2}Si{sub 2}.
Polarization in a Rashba strip coupled with a spiral spin density wave.
Zhang, Zhi-Yong; Chen, Lang
2010-06-02
The magnetoelectric effect in a Rashba strip is studied, which is coupled to a spiral spin density wave (SDW). The polarization, if it can be induced, must be perpendicular to the plane constructed by the helix axis and the wavevector of the SDW. With a gate voltage on the strip varied, the polarization fluctuates quickly and can be switched from a positive to a negative value or vice versa. Furthermore, reversing either the helix axis or the wavevector leads to the reversal of polarization. The main contributions to the polarization come from the eigenstates in the vicinity of the von Hove singularities. At half-filling, contributions from different eigenstates offset each other exactly. With the Rashba spin-orbit coupling increased, the averaged polarization displays an oscillatory behavior due to the spin precession, whereas with the exchange coupling increased, the averaged polarization increases first then decreases. Considering the size effect on the polarization, the spin precession length is an important characteristic length.
^77Se NMR in the Spin Density Wave state of (TMTSF)_2PF_6
NASA Astrophysics Data System (ADS)
Valfells, S.; Kuhns, P.; Kleinhammes, A.; Moulton, W.; Brooks, J. S.; Anzai, H.; Takasaki, S.; Yamada, J.
1996-03-01
We have measured the linewidth, T1 and T2 of the ^77Se nuclei in the quasi-1D conductor (TMTSF)_2PF6 above and below the Spin Density Wave transition temperature, T_SDW ≈ 12 K, at ambient pressure. We observe four distinct lines at T>T_SDW attributable to four non-equivalent Selenium sites and shifted by Δ ω / ω ≈ 0.7, 1.9, 3.8 and 4.5 × 10^4, respectively; they broaden to form a single, broad (≈ 900 kHz) line below T_SDW. The data, however, show no evidence of additional phase transitions at T
NASA Astrophysics Data System (ADS)
Dey, Santanu; Sensarma, Rajdeep
2016-12-01
We propose an experimental setup using ultracold atoms to implement a bilayer honeycomb lattice with Bernal stacking. In the presence of a potential bias between the layers and at low densities, fermions placed in this lattice form an annular Fermi sea. The presence of two Fermi surfaces leads to interesting patterns in Friedel oscillations and RKKY interactions in the presence of impurities. Furthermore, a repulsive fermion-fermion interaction leads to a Stoner instability towards an incommensurate spin density wave order with a wave vector equal to the thickness of the Fermi sea. The instability occurs at a critical interaction strength which goes down with the density of the fermions. We find that the instability survives interaction renormalization due to vertex corrections and discuss how this can be seen in experiments. We also track the renormalization group flows of the different couplings between the fermionic degrees of freedom, and find that there are no perturbative instabilities, and that Stoner instability is the strongest instability which occurs at a critical threshold value of the interaction. The critical interaction goes to zero as the chemical potential is tuned towards the band bottom.
Electron states and the spin density wave phase diagram in Cr(1 1 0) films
NASA Astrophysics Data System (ADS)
Rotenberg, Eli; Freelon, B. K.; Koh, H.; Bostwick, A.; Rossnagel, K.; Schmid, Andreas; Kevan, S. D.
2005-04-01
Chromium films offer an excellent system to study the impact of dimensional confinement on physical properties associated with the spin-density-wave (SDW) ground state observed in bulk materials. These properties are also of some technological importance since chromium is a common component of thin film magnetic structures. We prepared chromium (1 1 0) films of high crystalline quality on a W(1 1 0) substrate with a wedge-shaped thickness profile so that the impact of confinement can be systematically studied. We have characterized these films using a combination of low-energy electron diffraction and microscopy as well as high-resolution angle-resolved photoemission spectroscopy. We have probed the Fermi surface and the nesting vectors therein that are relevant to the SDW ground state. We find these to predict accurately the observed bulk SDW periodicity. We have also characterized the SDW periodicity in the film directly by measuring the splitting between backfolded bands, and we find that this periodicity deviates markedly from the bulk periodicity for thinner films at higher temperatures. We have systematically mapped the SDW incommensurability and phase diagram as a function of both film thickness and temperature. We find commensurate and incommensurate phases that are separated by nearly continuous transitions. Our results suggest a simple model to explain the delicate interplay between commensurate and incommensurate phases that involves a balance between SDW stabilization energy and surface and interface energetics.
Optical observation of spin-density-wave fluctuations in Ba122 iron-based superconductors
NASA Astrophysics Data System (ADS)
Xu, B.; Dai, Y. M.; Xiao, H.; Shen, B.; Ye, Z. R.; Forget, A.; Colson, D.; Feng, D. L.; Wen, H. H.; Qiu, X. G.; Lobo, R. P. S. M.
2016-08-01
In iron-based superconductors, a spin-density-wave (SDW) magnetic order is suppressed with doping, and unconventional superconductivity appears in close proximity to the SDW instability. The optical response of the SDW order shows clear gap features: substantial suppression in the low-frequency optical conductivity, alongside a spectral weight transfer from low to high frequencies. Here, we study the detailed temperature dependence of the optical response in three different series of the Ba122 system [Ba1 -xKxFe2As2 , Ba (Fe1-xCox) 2As2 , and BaFe2(As1-xPx) 2 ]. Intriguingly, we find that the suppression of the low-frequency optical conductivity and spectral weight transfer appear at a temperature T* much higher than the SDW transition temperature TSDW. Since this behavior has the same optical feature and energy scale as the SDW order, we attribute it to SDW fluctuations. Furthermore, T* is suppressed with doping, closely following the doping dependence of the nematic fluctuations detected by other techniques. These results suggest that the magnetic and nematic orders have an intimate relationship, in favor of the magnetic-fluctuation-driven nematicity scenario in iron-based superconductors.
Incommensurate Spin Density Wave state in metamagnetic Fe3Ga4
NASA Astrophysics Data System (ADS)
Wu, Yan; Cao, Huibo; Dos Santos, António; McCandless, Greg; Chan, Julia; Karki, Amar; Jin, Rongying; Ditusa, John
Fe3Ga4 displays a rich competition between magnetic states without structural transitions: a ferromagnetic(FM) ground state transitions to an antiferromagnetic(AFM) intermediate state above 68 K followed by a reemergence of the FM state above room temprature(T). The reentrance of the FM state hints of a coupling of the magnetic degrees of freedom to other modes. To explore the nature of the magnetic states, we have performed extensive single crystal neutron diffraction measurements over a wide range of T and pressure. These measurements revealed two very different magnetic states with the low T FM state having magnetic moments along the c-axis while we discovered that the AFM state is in an incommensurate spin density wave(SDW) order with moments mostly along the a-axis. However, there is still considerable non-collinear and non-coplanar contributions along the b- and c-axial directions. This non-coplanar moment is likely to be the origin of the very large anomalous Hall effect(HE) including a substantial topological HE that we discovered in Fe3Ga4. Study of the effect of hydrostatic pressure indicates a reduction of the Tc and a destabilization of the SDW phase.
Quantum critical properties of a metallic spin-density-wave transition
NASA Astrophysics Data System (ADS)
Gerlach, Max H.; Schattner, Yoni; Berg, Erez; Trebst, Simon
2017-01-01
We report on numerically exact determinantal quantum Monte Carlo simulations of the onset of spin-density-wave (SDW) order in itinerant electron systems captured by a sign-problem-free two-dimensional lattice model. Extensive measurements of the SDW correlations in the vicinity of the phase transition reveal that the critical dynamics of the bosonic order parameter are well described by a dynamical critical exponent z =2 , consistent with Hertz-Millis theory, but are found to follow a finite-temperature dependence that does not fit the predicted behavior of the same theory. The presence of critical SDW fluctuations is found to have a strong impact on the fermionic quasiparticles, giving rise to a dome-shaped superconducting phase near the quantum critical point. In the superconducting state we find a gap function that has an opposite sign between the two bands of the model and is nearly constant along the Fermi surface of each band. Above the superconducting Tc, our numerical simulations reveal a nearly temperature and frequency independent self-energy causing a strong suppression of the low-energy quasiparticle weight in the vicinity of the hot spots on the Fermi surface. This indicates a clear breakdown of Fermi liquid theory around these points.
Competing orders and spin density wave instabilities in FeAs-based systems
NASA Astrophysics Data System (ADS)
Wang, Nan Lin
2009-03-01
The discovery of superconductivity with Tc up to 55 K in layered FeAs-based compounds has generated tremendous interest in the scientific community. Except for relatively high Tc, the Fe pnictides display many interesting properties. Among others, the presence of competing orders is one of the most intriguing phenomena. In the early stage of our study on the compounds, we identified a spin-density-wave (SDW) ordered state for the parent compound with a stripe (or collinear) type spin structure based on the transport, specific heat, optical spectroscopy measurements and the first- principle calculations. The proposed spin structure from a nesting of the Fermi surfaces is confirmed by subsequent neutron experiments. However, it could also be explained by a local superexchange picture. In this talk I shall focus on our recent optical data on single crystal samples, trying to address the debating issue about itinerant or localized approaches to the SDW order. We found that the undoped compounds are quite metallic with relatively high plasma frequencies above TSDW. Upon entering the SDW ordered state, a large part of the Drude component is removed by the gapping of Fermi surfaces. Meanwhile, the carrier scattering rate is even more dramatically reduced. Those observations favor an itinerant description for the driving mechanism of SDW instability. Nevertheless, our experiments also indicate that Fe pnictides are not simple metals. A high energy gap-like feature is present even above TSDW, which seems to be linked with the antiferromagnetic spin fluctuations. For the superconducting samples, a superconducting pairing energy gap is clearly observed in the far-infrared reflectance measurement. The Ferrell-Glover- Tinkham sum rule is satisfied at a low energy scale. Work done in collaboration with: G. F. Chen, J. L. Luo, Z. Fang, X. Dai, W. Z. Hu, J. Dong, G. Li, Z. Li, P. Dai, J. Lynn, H. Q. Yuang, J. Singleton.
Ferroelectricity Induced by Acentric Spin-Density Waves in YMn{sub 2}O{sub 5}
Chapon, L.C.; Radaelli, P.G.; Blake, G.R.; Park, S.; Cheong, S.-W.
2006-03-10
The commensurate and incommensurate magnetic structures of the magnetoelectric system YMn{sub 2}O{sub 5}, as determined from neutron diffraction, were found to be spin-density waves lacking a global center of symmetry. We propose a model, based on a simple magnetoelastic coupling to the lattice, which enables us to predict the polarization based entirely on the observed magnetic structure. Our data accurately reproduce the temperature dependence of the spontaneous polarization, particularly its sign reversal at the commensurate-incommensurate transition.
NASA Astrophysics Data System (ADS)
Fernandes, R. M.; Kivelson, S. A.; Berg, E.
2016-01-01
Recent experiments in optimally hole-doped iron arsenides have revealed a novel magnetically ordered ground state that preserves tetragonal symmetry, consistent with either a charge-spin density wave (CSDW), which displays a nonuniform magnetization, or a spin-vortex crystal (SVC), which displays a noncollinear magnetization. Here we show that, similarly to the partial melting of the usual stripe antiferromagnet into a nematic phase, either of these phases can also melt in two stages. As a result, intermediate paramagnetic phases with vestigial order appears: a checkerboard charge density wave for the CSDW ground state, characterized by an Ising-like order parameter, and a remarkable spin-vorticity density wave for the SVC ground state—a triplet d -density wave characterized by a vector chiral order parameter. We propose experimentally detectable signatures of these phases, show that their fluctuations can enhance the superconducting transition temperature, and discuss their relevance to other correlated materials.
Boundary-induced spin-density waves in linear Heisenberg antiferromagnetic spin chains with S ≥1
NASA Astrophysics Data System (ADS)
Dey, Dayasindhu; Kumar, Manoranjan; Soos, Zoltán G.
2016-10-01
Linear Heisenberg antiferromagnets (HAFs) are chains of spin-S sites with isotropic exchange J between neighbors. Open and periodic boundary conditions return the same ground-state energy per site in the thermodynamic limit, but not the same spin SG when S ≥1 . The ground state of open chains of N spins has SG=0 or S , respectively, for even or odd N . Density-matrix renormalization-group calculations with different algorithms for even and odd N are presented up to N =500 for the energy and spin densities ρ (r ,N ) of edge states in HAFs with S =1 , 3/2, and 2. The edge states are boundary-induced spin density waves (BI-SDWs) with ρ (r ,N ) ∝(-1) r -1 for r =1 ,2 ,...,N . The SDWs are in phase when N is odd, are out of phase when N is even, and have finite excitation energy Γ (N ) that decreases exponentially with N for integer S and faster than 1 /N for half integer S . The spin densities and excitation energy are quantitatively modeled for integer S chains longer than 5 ξ spins by two parameters, the correlation length ξ and the SDW amplitude, with ξ =6.048 for S =1 and 49.0 for S =2 . The BI-SDWs of S =3 /2 chains are not localized and are qualitatively different for even and odd N . Exchange between the ends for odd N is mediated by a delocalized effective spin in the middle that increases |Γ (N )| and weakens the size dependence. The nonlinear sigma model (NL σ M ) has been applied to the HAFs, primarily to S =1 with even N , to discuss spin densities and exchange between localized states at the ends as Γ (N ) ∝(-1) Nexp(-N /ξ ) . S =1 chains with odd N are fully consistent with the NL σ M ; S =2 chains have two gaps Γ (N ) with the same ξ as predicted whose ratio is 3.45 rather than 3; the NL σ M is more approximate for S =3 /2 chains with even N and is modified for exchange between ends for odd N .
Yi, M.
2010-06-02
Through a systematic high-resolution angle-resolved photoemission study of the iron pnictide compounds (Ba,Sr)Fe{sub 2}As{sub 2}, we show that the electronic structures of these compounds are significantly reconstructed across the spin density wave transition, which cannot be described by a simple folding scenario of conventional density wave ordering. Moreover, we find that LDA calculations with an incorporated suppressed magnetic moment of 0.5{mu}{sub B} can match well the details in the reconstructed electronic structure, suggesting that the nature of magnetism in the pnictides is more itinerant than local, while the origin of suppressed magnetic moment remains an important issue for future investigations.
NASA Astrophysics Data System (ADS)
Suzuki, Kenta M.; Ichioka, Masanori; Machida, Kazushige
2011-04-01
A spin-density-wave (SDW) instability mechanism enhanced by vortices under fields is proposed to explain the high field and low-temperature phase in CeCoIn5. In the vortex state strong Pauli effect and nodal gap conspire to enhance the momentum-resolved density of states over the normal state value exclusively along the nodal direction, providing a favorable nesting condition for SDW with Q=(2kF,2kF,0.5) only at high fields (H). We can consistently understand observed mysteries of the field-induced SDW confined below Hc2, such as facts that Q is directed to the nodal direction independent of H, SDW diminishes under tilting field from the ab plane, and the SDW transition line in (H,T) has a positive slope.
NASA Astrophysics Data System (ADS)
Levchenko, A.; Vavilov, M. G.; Khodas, M.; Chubukov, A. V.
2013-04-01
Recent measurements of the doping dependence of the London penetration depth λ(x) at low T in clean samples of isovalent BaFe2(As1-xPx)2 at T≪Tc [Hashimoto et al., Science 336, 1554 (2012)SCIEAS0036-8075] revealed a peak in λ(x) near optimal doping x=0.3. The observation of the peak at T≪Tc, points to the existence of a quantum critical point beneath the superconducting dome. We associate such a quantum critical point with the onset of a spin-density-wave order and show that the renormalization of λ(x) by critical magnetic fluctuations gives rise to the observed feature. We argue that the case of pnictides is conceptually different from a one-component Galilean invariant Fermi liquid, for which correlation effects do not cause the renormalization of the London penetration depth at T=0.
Accurate ab Initio Spin Densities.
Boguslawski, Katharina; Marti, Konrad H; Legeza, Ors; Reiher, Markus
2012-06-12
We present an approach for the calculation of spin density distributions for molecules that require very large active spaces for a qualitatively correct description of their electronic structure. Our approach is based on the density-matrix renormalization group (DMRG) algorithm to calculate the spin density matrix elements as a basic quantity for the spatially resolved spin density distribution. The spin density matrix elements are directly determined from the second-quantized elementary operators optimized by the DMRG algorithm. As an analytic convergence criterion for the spin density distribution, we employ our recently developed sampling-reconstruction scheme [J. Chem. Phys.2011, 134, 224101] to build an accurate complete-active-space configuration-interaction (CASCI) wave function from the optimized matrix product states. The spin density matrix elements can then also be determined as an expectation value employing the reconstructed wave function expansion. Furthermore, the explicit reconstruction of a CASCI-type wave function provides insight into chemically interesting features of the molecule under study such as the distribution of α and β electrons in terms of Slater determinants, CI coefficients, and natural orbitals. The methodology is applied to an iron nitrosyl complex which we have identified as a challenging system for standard approaches [J. Chem. Theory Comput.2011, 7, 2740].
NASA Astrophysics Data System (ADS)
Ohkawa, Fusayoshi J.
2002-06-01
A theory of Kondo lattices is applied to studying possible magnetic and charge structures of itinerant-electron antiferromagnets. Even helical spin structures can be stabilized when the nesting of the Fermi surface is not sharp and the superexchange interaction, which arises from the virtual exchange of pair excitations across the Mott-Hubbard gap, is mainly responsible for magnetic instability. Sinusoidal spin structures or spin-density waves (SDW's) are only stabilized when the nesting of the Fermi surface is sharp enough or when an exchange interaction arising from that of pair excitations of quasiparticles is mainly responsible for magnetic instability. In particular, multiple SDW's are stabilized when their incommensurate ordering wave numbers +/-Q are multiple; magnetizations of different +/-Q components are orthogonal to each other in double and triple SDW's when magnetic anisotropy is weak enough. Unless +/-2Q are commensurate, charge-density waves (CDW's) with +/-2Q coexist with SDW's with +/-Q. Because the quenching of magnetic moments by the Kondo effect or local quantum spin fluctuations depends on local numbers of electrons, the phase of CDW's or electron densities is such that magnetic moments are large where the quenching is weak. It is proposed that the so-called stripe order must be the coexisting state of double incommensurate SDW's and CDW's in tetragonal cuprate-oxide high temperature superconductors, in particular, those with the square CuO2 lattices.
NASA Astrophysics Data System (ADS)
Farrell, Aaron; Wu, P.-K.; Kao, Y.-J.; Pereg-Barnea, T.
2016-12-01
On a square lattice, the Hubbard model at half filling reduces to the Heisenberg model and exhibits antiferromagnetism. When doped away from half filling this model gives rise to d -wave superconductivity. This behavior is reminiscent of the phenomenology of the cuprate family with their high Tcd -wave superconductivity and their antiferromagnetic parent compound. It is therefore interesting to study an extension of the Hubbard model which includes spin orbit coupling. We have previously studied this model away from half filling [see, for example, Farrell and Pereg-Barnea, Phys. Rev. B 89, 035112 (2014), 10.1103/PhysRevB.89.035112] and found that the addition of spin-orbit coupling and Zeeman field leads to topological superconductivity with d +i d pairing function. In this paper we are interested in the `parent compound' of this state. Namely, we study the half filling, strong coupling limit of the square lattice Hubbard model with spin orbit coupling and Zeeman field. The strong coupling expansion of the model is a spin model which contains compass anisotropy and Dzyaloshinsky-Moriya interaction on top of the usual Heisenberg term. We analyze this spin model classically and find an incommensurate spin density wave (ISDW) for low Zeeman fields. This ISDW has a wave vector Q ⃗ which deviates from (π ,π ) by an amount which is proportional to the spin-orbit coupling and can therefore serve as a signature. We study the stability of the ISDW phase using spin wave theory and find a stable and an unstable region. At higher but moderate Zeeman fields we find a tilted antiferromagnet and a ferromagnet at high Zeeman fields.
NASA Astrophysics Data System (ADS)
Kawaguchi, Genta; Maesato, Mitsuhiko; Komatsu, Tokutaro; Imakubo, Tatsuro; Kitagawa, Hiroshi
2016-02-01
We present the results of high-pressure transport measurements on the anion-mixed molecular conductors (DIETSe)2M Br2Cl2 [DIETSe = diiodo(ethylenedithio)tetraselenafulvalene; M =Fe , Ga]. They undergo a metal-insulator (M-I) transition below 9 K at ambient pressure, which is suppressed by applying pressure, indicating a spin-density-wave (SDW) transition caused by a nesting instability of the quasi-one-dimensional (Q1D) Fermi surface, as observed in the parent compounds (DIETSe)2M Cl4 (M =Fe , Ga). In the metallic state, the existence of the Q1D Fermi surface is confirmed by observing the Lebed resonance. The critical pressures of the SDW, Pc, of the M Br2Cl2 (M =Fe , Ga) salts are significantly lower than those of the the M Cl4 (M = Fe, Ga) salts, suggesting chemical pressure effects. Above Pc, field-induced SDW transitions appear, as evidenced by kink structures in the magnetoresistance (MR) in both salts. The FeBr2Cl2 salt also shows antiferromagnetic (AF) ordering of d spins at 4 K, below which significant spin-charge coupling is observed. A large positive MR change up to 150% appears above the spin-flop field at high pressure. At low pressure, in particular below Pc, a dip or kink structure appears in MR at the spin-flop field, which shows unconventionally large hysteresis at low temperature (T <1 K). The hysteresis region clearly decreases with increasing pressure towards Pc, strongly indicating that the coexisting SDW plays an important role in the enhancement of magnetic hysteresis besides the random exchange interaction.
Field-controlled spin-density-wave order and quantum critically in Sr3 Ru2 O7
NASA Astrophysics Data System (ADS)
Hayden, Stephen
The quasi-2D metamagnetic perovskite metal Sr3Ru2O7 has been an enigma for the last decade. The application of a large magnetic field of 8T parallel to the c-axis creates a new phase at low temperatures. This phase shows ``electronic nematic'' properties in that strong anisotropy its resistivity can be created by tilting the field away from the c-axis. In addition, measurement of transport and thermodynamic properties suggest that the phase is at the centre of a quantum critical region. Here we use neutron scattering to show that the magnetic field actually induces spin-density-wave magnetic order in the proximity of a metamagnetic critical endpoint. In fact, Sr3Ru2O7 can be tuned through two magnetically-ordered SDW states which exist over relatively small ranges in field (< 0.4 T). Their origin is probably due to the electronic fine structure near the Fermi energy. The magnetic field direction is shown to control the SDW domain populations which naturally explains the strong resistivity anisotropy or ''electronic nematic'' behaviour observed in this material. We find that Sr3Ru2O7 is also unique in that its the quantum critical region is controlled by overdamped incommensurate low-energy spin fluctuations with a diverging relaxation time. The low-energy electronic properties reflect the presence of these fluctuations and, in particular, the field-dependent low-temperature specific heat is proportional to the spin relaxation rate. [Based on C. Lester, S. Ramos, R. S. Perry at el. Natural Materials 14, 373 (2015).
NASA Astrophysics Data System (ADS)
Moor, Andreas; Volkov, Anatoly F.; Efetov, Konstantin B.
2014-12-01
On the basis of coupled Ginzburg-Landau equations we study nonhomogeneous states in systems with two order parameters (OPs). Superconductors with a superconducting OP Δ and a charge- or spin-density wave with amplitude W are examples of such systems. When one OP, say Δ , has a form of a topological defect, like, e.g., a vortex or domain wall between the domains with the phases 0 and π , the other OP W is determined by the Gross-Pitaevskii equation and is localized at the center of the defect. We consider in detail the domain-wall defect for Δ and show that the shape of the associated solution for W depends on temperature and doping (or on the curvature of the Fermi surface) μ . It turns out that, provided the temperature or doping level is close to some discrete values Tn and μn, the spatial dependence of the function W (x ) is determined by the form of the eigenfunctions of the linearized Gross-Pitaevskii equation. The spatial dependence of W0 corresponding to the ground state has the form of a soliton, while other possible solutions Wn(x ) have nodes. The inverse situation when W (x ) has the form of a topological defect and Δ (x ) is localized at the center of this defect is also possible. In particular, we predict a surface or interfacial superconductivity in a system where a superconductor is in contact with a material that suppresses W . This superconductivity should have rather unusual temperature dependence existing only in certain intervals of temperature. Possible experimental realizations of such nonhomogeneous states of OPs are discussed.
Stabilization of the spin density wave structure with rare-earth substitution in Ca3Co2O6
NASA Astrophysics Data System (ADS)
Jain, Anil; Yusuf, S. M.; Meena, S. S.; Ritter, Clemens
2013-03-01
We report the structural and magnetic properties of rare-earth substituted spin-chain compounds Ca2.75R0.25Co2O6 (R = Dy and Lu). The Rietveld refinement of neutron and x-ray powder diffraction patterns confirms the single-phase formation of both compounds in the rhombohedral structure (space group R3¯c). The derived values (from the analysis of the neutron diffraction patterns at 50 K) of the bond-valence sum indicate a reduction in the oxidation state of the cobalt ions at the trigonal prism (TP) site (6a) with R substitution, which is further supported by low temperature neutron diffraction [where a zero value of the ordered moment at the 6b site and a reduction in the values of the maximum ordered moment at the TP site have been observed] and dc magnetization studies. In the neutron diffraction patterns, additional Bragg peaks appear for both compounds below Néel temperature (TN) of ˜16 K, indicating the onset of an antiferromagnetic ordering of cobalt spin chains on the triangular lattice. The magnetic structure corresponds to a spin density wave (SDW) structure [with a propagation vector k={0,0,1.02}], having c axis as a direction of both moment and modulation. For both compounds, the refined values of the ordered moment at the 18e, 6b, and 6a sites are ˜0.03(2),0.02(2), and 4.2 (2) μB, respectively. Unlike the parent compound Ca3Co2O6, no temperature dependence as well as no time dependence in the intensity of the strongest antiferromagnetic reflection (10 τ), corresponding to the propagation vector k = {0, 0, 1.02}, has been observed down to 1.5 K confirming that the SDW structure is stabilized by the substitution with rare-earth ions. The stabilization of the SDW structure and the observed decrease in the values of TN could be due to a decrease in the value of positive FM intrachain exchange interaction J with the rare-earth substitution in a system with competing intrachain and interchain exchange interactions.
Giner, Emmanuel Angeli, Celestino
2015-09-28
The aim of this paper is to unravel the physical phenomena involved in the calculation of the spin density of the CuCl{sub 2} and [CuCl{sub 4}]{sup 2−} systems using wave function methods. Various types of wave functions are used here, both variational and perturbative, to analyse the effects impacting the spin density. It is found that the spin density on the chlorine ligands strongly depends on the mixing between two types of valence bond structures. It is demonstrated that the main difficulties found in most of the previous studies based on wave function methods come from the fact that each valence bond structure requires a different set of molecular orbitals and that using a unique set of molecular orbitals in a variational procedure leads to the removal of one of them from the wave function. Starting from these results, a method to compute the spin density at a reasonable computational cost is proposed.
Shape of spin density wave versus temperature in AFe2As2 (A = Ca, Ba, Eu): A Mössbauer study
NASA Astrophysics Data System (ADS)
Błachowski, A.; Ruebenbauer, K.; Żukrowski, J.; Rogacki, K.; Bukowski, Z.; Karpinski, J.
2011-04-01
Parent compounds AFe2As2 (A = Ca, Ba, Eu) of the 122 family of the iron-based superconductors have been studied by Fe57 Mössbauer spectroscopy in the temperature range 4.2-˜300 K. Spin density waves (SDW) have been found with some confidence. They are either incommensurate with the lattice period or the ratio of the respective periods is far away from the ratio of small integers. SDW shape is very unconventional (i.e., differs from the sinusoidal shape). Magnetic order starts with lowered temperature as narrow sheets of the significant electron spin density separated by areas with very small spin density. Magnetic sheets are likely to be ordered in the alternate antiferromagnetic fashion as the material as a whole behaves similarly to the collinear antiferromagnet. A further lowering of temperature simply expands sheet thickness leading to the near triangular SDW. Finally, sheets fill the whole available space and the almost rectangular shape of the SDW is reached. The substantial maximum amplitude of SDW appears at the temperature just below the magnetic onset temperature, and this maximum amplitude increases slightly with lowering temperature. The square root from the mean squared hyperfine field behaves versus temperature according to the universality class (1,2) (i.e., with the electronic spin space having dimensionality equal to unity and the real space having dimensionality equal to 2). The more or less pronounced tail above transition temperature due to the development of incoherent SDW is seen.
NASA Astrophysics Data System (ADS)
Minamidate, T.; Matsunaga, N.; Nomura, K.; Sasaki, T.
2016-08-01
Magnetoresistance and Hall resistance measurements were conducted in the field-induced spin-density-wave (FISDW) phase of (TMTSF)2ReO4 above 1.0 GPa, with an anion ordering specified by Q_\\text{AO}=(0, 1/2, 1/2) . The quantized Hall resistance shows the sequence N = 0, 1, 2, -2, 4, -4, -6, -8, \\cdots , with decreasing field that is successfully explained by the “extended standard model”. Consequently, we demonstrate that the difference between the chemical and hydrostatic pressures is linked to the appearance of the peculiar FISDW phase of the TMTSF salts with Q_\\text{AO}=(0, 1/2, *) .
NASA Astrophysics Data System (ADS)
Cankurtaran, M.; Saunders, G. A.; Wang, Q.; Ford, P. J.; Alberts, H. L.
1992-12-01
A comprehensive experimental study has been made of the elastic and nonlinear acoustic behavior of a dilute Cr alloy as it undergoes a commensurate (C)-incommensurate (I) spin-density-wave transition. Simultaneous measurements of the temperature dependence of ultrasonic wave velocity and attenuation of longitudinal and shear 10-MHz ultrasonic waves propagated along both the [100] and the [110] direction of Cr-0.3 at. % Ru alloy single crystal have been made in the temperature range 200-300 K. The temperature dependence of ultrasonic attenuation for each mode is characterized by a spikelike peak centered at TCI (=238.6 K) (on cooling) and at TIC (=255.6 K) (on warming). The velocities of both longitudinal and shear ultrasonic waves exhibit a large and steep increase at TCI on cooling and a similar drop at TIC on warming with a pronounced hysteresis between TIC and TCI. These observations show that the transition between the commensurate and incommensurate phases is first order. Measurements of the effects of hydrostatic pressure (up to 0.15 GPa) on the velocities of ultrasonic waves, which were made at several fixed temperatures between 248 and 297 K, show similar features: a steep increase at PCI (increasing pressure) and a similar drop at PIC (decreasing pressure) with a well-defined hysteresis. Both TCI and TIC increase strongly and approximately linearly with pressure, the mean values of dTCI/dP and dTIC/dP being (333+/-3) K/GPa and (277+/-5) K/GPa, respectively. The pressure and temperature dependencies of the anomalies in the ultrasonic wave velocity have been used to locate both the C-I and I-C boundaries on the magnetic P-T phase diagram. There is a triple point (at about 315 K and 0.22 GPa) where the paramagnetic, commensurate, and incommensurate spin-density-wave phases coexist. Results for the complete sets of the elastic stiffness tensor components and their hydrostatic pressure derivatives have been used to evaluate the acoustic-mode Gr
Opening a nodal gap by fluctuating spin-density wave in lightly doped La2 -xSrxCuO4
NASA Astrophysics Data System (ADS)
Kapon, Itzik; Ellis, David S.; Drachuck, Gil; Bazalitski, Galina; Weschke, Eugen; Schierle, Enrico; Strempfer, Jörg; Niedermayer, Christof; Keren, Amit
2017-03-01
We investigate whether the spin or charge degrees of freedom are responsible for the nodal gap in underdoped cuprates by performing inelastic neutron scattering and x-ray diffraction measurements on La2 -xSrxCuO4 , which is on the edge of the antiferromagnetic phase. We found that a fluctuating incommensurate spin-density wave (SDW) with a bottom part of an hourglass dispersion exists even in this magnetic sample. The strongest component of these fluctuations diminishes at the same temperature where the nodal gap opens. X-ray scattering measurements on the same crystal show no signature of a charge-density wave (CDW). Therefore, we suggest that the nodal gap in the electronic band of this cuprate opens due to fluctuating SDW with no contribution from CDW.
Willenberg, B; Schäpers, M; Wolter, A U B; Drechsler, S-L; Reehuis, M; Hoffmann, J-U; Büchner, B; Studer, A J; Rule, K C; Ouladdiaf, B; Süllow, S; Nishimoto, S
2016-01-29
Low-temperature neutron diffraction and NMR studies of field-induced phases in linarite are presented for magnetic fields H∥b axis. A two-step spin-flop transition is observed, as well as a transition transforming a helical magnetic ground state into an unusual magnetic phase with sine-wave-modulated moments ∥H. An effective J[over ˜]_{1}-J[over ˜]_{2} single-chain model with a magnetization-dependent frustration ratio α_{eff}=-J[over ˜]_{2}/J[over ˜]_{1} is proposed. The latter is governed by skew interchain couplings and shifted to the vicinity of the ferromagnetic critical point. It explains qualitatively the observation of a rich variety of exotic longitudinal collinear spin-density wave, SDW_{p}, states (9≥p≥2).
NASA Astrophysics Data System (ADS)
Holder, Tobias; Metzner, Walter
2014-10-01
We analyze the influence of quantum critical fluctuations on single-particle excitations at the onset of incommensurate 2kF charge- or spin-density wave order in two-dimensional metals. The case of a single pair of hot spots at high symmetry positions on the Fermi surface needs to be distinguished from the case of two hot spot pairs. We compute the fluctuation propagator and the electronic self-energy perturbatively in leading order. The energy dependence of the single-particle decay rate at the hot spots obeys non-Fermi-liquid power laws, with an exponent 2/3 in the case of a single hot spot pair, and exponent one for two hot spot pairs. The prefactors of the linear behavior obtained in the latter case are not particle-hole symmetric.
Incommensurate spin-density wave and magnetic lock-in transition in CaFe{sub 4}As{sub 3}.
Manuel, P.; Chapon, L. C.; Todorov, I. S.; Chung, D. Y.; Castellan, J.-P.; Rosenkranz, S.; Osborn, R.; Toledano, P.; Kanatzidis, M. G.; Materials Science Division; Rutherford Appleton Lab.; Univ. of Picardie; Northwestern Univ.
2010-05-01
The magnetic structure for the recently synthesized iron-arsenide compound CaFe4As3 has been studied by neutron-powder diffraction. Long-range magnetic order is detected below 85 K, with an incommensurate modulation described by the propagation vector k=(0,?,0), ??0.39. Below ?25 K, our measurements detect a first-order phase transition where ? locks into the commensurate value 3/8. A model of the magnetic structure is proposed for both temperature regimes, based on Rietveld refinements of the powder data and symmetry considerations. The structures correspond to longitudinal spin-density waves with magnetic moments directed along the b axis. A Landau analysis captures the change in thermodynamic quantities observed at the two magnetic transitions, in particular, the drop in resistivity at the lock-in transition.
NASA Astrophysics Data System (ADS)
Zhang, W.-L.; Yin, Z. P.; Ignatov, A.; Bukowski, Z.; Karpinski, Janusz; Sefat, Athena S.; Ding, H.; Richard, P.; Blumberg, G.
2016-05-01
We present a polarization-resolved and temperature-dependent Raman scattering study of A Fe2As2 (A =Ca , Eu). In the spin-density-wave phase, spectral weight redistribution is observed in the fully symmetric and nonsymmetric scattering channels at different energies. An anisotropic Raman response is observed in the fully symmetric channel in spontaneously detwinned CaFe2As2 samples. We calculate the orbital-resolved electronic structures using a combination of density functional theory and dynamical mean field theory. We identify the electronic transitions corresponding to these two spectral features and find that the anisotropic Raman response originates from the lifted degeneracy of the dx z /y z orbitals in the broken-symmetry phase.
Evidence of spin-density-wave order in RFeAsO1-xFx from measurements of thermoelectric power
NASA Astrophysics Data System (ADS)
Matusiak, M.; Plackowski, T.; Bukowski, Z.; Zhigadlo, N. D.; Karpinski, J.
2009-06-01
Data on the magnetothermopower and specific heat of three compounds belonging to “1111” oxypnictides family are reported. One specimen (SmAsFeO0.8F0.2) is a superconductor with Tc=53K , while two others (SmAsFeO and NdAsFeO) are nonsuperconducting parent compounds. Our results confirm that spin-density-wave (SDW) order is present in SmAsFeO and NdAsFeO. In these two samples a strict connection between the thermoelectric power and electronic specific heat is found in the vicinity of SDW transition, which indicates that the chemical potential of charge carriers strongly depends on temperature in this region. Low-temperature data suggest presence of significant contribution magnon drag to the thermoelectric power.
Audouard, A.; Goze, F.; Ulmet, J.; Brossard, L.; Askenazy, S. , Laboratoire de Physique des Solides , Complexe Scientifique de Rangueil, 31077 Toulouse ); Fabre, J. )
1994-11-01
The transverse magnetoresistance of the Bechgaard salt (TMTSF)[sub 2]NO[sub 3] has been measured up to 37 T at ambient pressure in the temperature range from 2 to 77 K. When the magnetic field is parallel to the lowest conductivity direction [ital c][sup *] and for temperatures higher than [similar to]12 K, the data can be accounted for by a power law, the exponent of which decreases as the anion ordering takes place. At lower temperatures, the magnetic field increases the spin-density-wave (SDW) transition temperature, in overall agreement with theoretical predictions for the imperfect-nesting case. Two oscillation series, both linked to the SDW state, have been observed in the 2--10 K range. Their temperature-independent frequencies, measured from 2 to 8 K, are at (63[plus minus]2) and (248[plus minus]5) T, respectively. These oscillations have been studied (at 4.2 K) as a function of the field direction. They were found to deviate from the two-dimensional model since, in particular, their behavior differs according to whether the field is tilted on one side of the [ital c][sup *] direction or on the other. The oscillation data are discussed on the basis of recent calculations of Yakovenko.
Yi, M; Zhang, Y; Liu, Z-K; Ding, X; Chu, J-H; Kemper, A F; Plonka, N; Moritz, B; Hashimoto, M; Mo, S-K; Hussain, Z; Devereaux, T P; Fisher, I R; Wen, H H; Shen, Z-X; Lu, D H
2014-04-25
An intriguing aspect of unconventional superconductivity is that it always appears in the vicinity of other competing phases, whose suppression brings the full emergence of superconductivity. In the iron pnictides, these competing phases are marked by a tetragonal-to-orthorhombic structural transition and a collinear spin-density wave (SDW) transition. There has been macroscopic evidence for competition between these phases and superconductivity as the magnitude of both the orthorhombicity and magnetic moment are suppressed in the superconducting state. Here, using angle-resolved photoemission spectroscopy on detwinned underdoped Ba(1-x)K(x)Fe2As2, we observe a coexistence of both the SDW gap and superconducting gap in the same electronic structure. Furthermore, our data reveal that following the onset of superconductivity, the SDW gap decreases in magnitude and shifts in a direction consistent with a reduction of the orbital anisotropy. This observation provides direct spectroscopic evidence for the dynamic competition between superconductivity and both SDW and electronic nematic orders in these materials.
NASA Astrophysics Data System (ADS)
Mertelj, T.; Kusar, P.; Kabanov, V. V.; Stojchevska, L.; Zhigadlo, N. D.; Katrych, S.; Bukowski, Z.; Karpinski, J.; Weyeneth, S.; Mihailovic, D.
2010-06-01
We investigate the quasiparticle (QP) relaxation and low-energy electronic structure in undoped SmFeAsO and near-optimally doped SmFeAsO0.8F0.2 single crystals-exhibiting spin-density wave (SDW) ordering and superconductivity, respectively-using pump-probe femtosecond spectroscopy. In the undoped single crystals a single relaxation process is observed, showing a remarkable critical slowing down of the QP relaxation dynamics at the SDW transition temperature TSDW≃125K . In the superconducting (SC) crystals multiple relaxation processes are present with distinct SC-state quasiparticle recombination dynamics exhibiting a BCS-like T -dependent superconducting gap, and a pseudogap (PG)-like feature with an onset above 180 K indicating the existence of a pseudogap of magnitude 2ΔPG≃120meV above Tc . From the pump-photon energy dependence we conclude that the SC state and PG relaxation channels are independent, implying the presence of two separate electronic subsystems. We discuss the data in terms of spatial inhomogeneity and multiband scenarios, finding that the latter is more consistent with the present data.
Selective substitution of Cr in CaFe{sub 4}As{sub 3} and its effect on the spin density wave.
Todorov, I.; Chung, D. Y.; Claus, H.; Gray, K. E.; Li, Q.; Schlueter, J.; Bakas, T.; Douvalis, A.; Gutmann, M.; Kanatzidis, M. G.; Materials Science Division; Northwestern Univ.; Univ. of Ioannina; Rutherford Appleton Lab.
2010-08-11
Single crystals of CaCr{sub 0.84}Fe{sub 3.16}As{sub 3}, a Cr substituted analog of CaFe{sub 4}As{sub 3}, were grown from Sn flux and characterized with single crystal neutron diffraction. CaCr{sub 0.84}Fe{sub 3.16}As{sub 3} crystallizes in the orthorhombic space group Pnma with a three-dimensional framework, where Fe, Cr, and As form a covalent channel-like network with Ca{sup 2+} cations residing in the channels. CaCr{sub 0.84}Fe{sub 3.16}As{sub 3} has a unit cell of a = 12.057(4) {angstrom}, b = 3.7374(13) {angstrom}, and c = 11.694(3) {angstrom}, as determined by room temperature single crystal neutron diffraction (R{sub 1} = 0.0747, wR{sub 2} = 0.1825). Structural data was also collected at 10 K. The single crystal neutron data showed that Cr selectively occupies a particular metal site, Fe(4). The antiferromagnetic transition associated with spin density wave (SDW) in the parent compound is preserved and shifts from 96 to 103 K with the selective Cr doping. Moessbauer, magnetic, and electrical resistivity measurements are reported.
NASA Astrophysics Data System (ADS)
Kishigi, Keita; Hasegawa, Yasumasa
2009-08-01
The successive transitions of the field-induced spin-density wave, which is labeled by the quantum number N of the Hall conductivity and the nesting vector, are known to depend on the shape of the quasi-one-dimensional Fermi surface. We study the condition for the appearance of the negative N states, where the quantized Hall conductivity changes the sign. We obtain the phase diagram for the negative N states in the parameter space of the higher harmonics in the Fermi surface ( tb' , t3 , and t4 ) to be stabilized with and without the periodic anion potential V in the perpendicular direction to the conducting axis, which are the cases in (TMTSF)2ClO4 and (TMTSF)2PF6 , respectively. The negative N phase is shown to be stabilized for the smaller values of t3 and t4 in the case of the finite V . Comparing with the experiment by Matsunaga [J. Phys. IV 131, 269 (2005)], where the quantum Hall effect is observed in (TMTSF)2ClO4 with various cooling rates, we obtain the parameter regions of t3 and t4 for (TMTSF)2ClO4 ( 0.06≲t3/tb'≲0.23 , 0≲t4/tb'≲0.08 , and V/tb'≲2.0 ).
NASA Astrophysics Data System (ADS)
Kishigi, Keita; Hasegawa, Yasumasa
2007-06-01
We show that in (TMTSF)2ClO4 the field-induced spin-density wave (FISDW) with negative quantum number (N=-2) of the nesting vector is stabilized in some region in the parameters of magnetic field and the strength of the anion potential, which corresponds to the very recently observed phase diagram of (TMTSF)2ClO4 in the parameter plane of magnetic field vs cooling rate by Matsunaga [J. Phys. IV 131, 269 (2005)]. The spin-density wave is induced by the magnetic field in the quasi-one-dimensional conductors such as (TMTSF)2PF6 and (TMTSF)2ClO4 . The wave vector of the FISDW is quantized and the Hall conductivity is quantized corresponding to the quantum number (N) of the wave vector. In (TMTSF)2ClO4 , the ordering of the anion ClO4 makes the periodic potential, which has been known to drastically affect the FISDW. We study the instability to the FISDW by taking the eigenstates in the magnetic field numerically, with the periodic potential being treated nonperturbatively. We obtain the phase diagram of the quantum number N for FISDW in the quasi-one-dimensional systems in the parameter plane of magnetic field and the strength of the periodic potential, which can be controlled by the cooling rate.
Li, Hai-Feng; Cao, Chongde; Wildes, Andrew; Schmidt, Wolfgang; Schmalzl, Karin; Hou, Binyang; Regnault, Louis-Pierre; Zhang, Cong; Meuffels, Paul; Löser, Wolfgang; Roth, Georg
2015-01-01
Identifying the nature of magnetism, itinerant or localized, remains a major challenge in condensed-matter science. Purely localized moments appear only in magnetic insulators, whereas itinerant moments more or less co-exist with localized moments in metallic compounds such as the doped-cuprate or the iron-based superconductors, hampering a thorough understanding of the role of magnetism in phenomena like superconductivity or magnetoresistance. Here we distinguish two antiferromagnetic modulations with respective propagation wave vectors at Q± = (H ± 0.557(1), 0, L ± 0.150(1)) and QC = (H ± 0.564(1), 0, L), where (H, L) are allowed Miller indices, in an ErPd2Si2 single crystal by neutron scattering and establish their respective temperature- and field-dependent phase diagrams. The modulations can co-exist but also compete depending on temperature or applied field strength. They couple differently with the underlying lattice albeit with associated moments in a common direction. The Q± modulation may be attributed to localized 4f moments while the QC correlates well with itinerant conduction bands, supported by our transport studies. Hence, ErPd2Si2 represents a new model compound that displays clearly-separated itinerant and localized moments, substantiating early theoretical predictions and providing a unique platform allowing the study of itinerant electron behavior in a localized antiferromagnetic matrix. PMID:25608949
Special relativity and reduced spin density matrices
Gonera, Cezary; Kosinski, Piotr; Maslanka, Pawel
2004-09-01
We derive the general formula for Lorentz-transformed spin density matrix. It is shown that an appropriate Lorentz transformation can produce totally unpolarized state out of pure one. Further properties, as depurification by an arbitrary Lorentz boost and its relation to the localization properties are also discussed.
Spin density in first-row diatomic hydrides from the Hiller-Sucher-Feinberg identity
NASA Astrophysics Data System (ADS)
Rassolov, Vitaly A.; Chipman, Daniel M.
1995-12-01
The delta function and Hiller-Sucher-Feinberg (HSF) operators are compared for calculation of electronic spin density at the nucleus. New methods are designed and implemented for evaluation of the difficult molecular integrals over the HSF operator. Calculations are carried out with wave functions that include spin polarization effects using Gaussian basis sets and, to estimate the complete basis set limit, with a seminumerical procedure. Results are reported for the diatomic hydrides CH, NH, and OH in their ground states. While the HSF operator gives much better total densities at the heavy atoms, the delta function and HSF operators are found to perform overall about equally well for spin densities.
Pérez-Jiménez, Angel J; Pérez-Jordá, José M; Illas, Francesc
2004-01-01
A new method to improve the excess spin density obtained from unrestricted Hartree-Fock wave functions in terms of natural orbitals is proposed. Using this modified excess spin density to evaluate the correlation energy by means of density functionals leads to large improvements in the computed magnetic coupling constants of several materials without need to modify the exchange contribution. This is important because it reconciles the density functional theory description with the one provided by multi-determinant wave functions. Using the present approach, the leading contribution to the magnetic coupling constant arises from electron correlation effects. The performance of the new method is illustrated on various materials including high-critical-temperature superconductors parent compounds.
Goedel cosmology in Riemann-Cartan spacetime with spin density
NASA Technical Reports Server (NTRS)
Smalley, L. L.
1985-01-01
It is shown that the Goedel metric for a rotating cosmology is compatible with the self-consistent formulation of the Einstein-Cartan metric-torsion theory for a spinning fluid. In the model presented, the only changes are that the cosmological constant becomes slightly more negative, and the sense of rotation is flipped. If the Goedel model were a viable model, experimentally it would be difficult to distinguish between the two models unless the spin density could be measured directly.
Zhou, Tao; Gao, Yi; Zhu, Jian -Xin
2015-03-07
Recenmore » tly it was revealed that the whole Fermi surface is fully gapped for several families of underdoped cuprates. The existence of the finite energy gap along the d-wave nodal lines (nodal gap) contrasts the common understanding of the d-wave pairing symmetry, which challenges the present theories for the high-Tcsuperconductors. Here we propose that the incommensurate diagonal spin-density-wave order can account for the above experimental observation. The Fermi surface and the local density of states are also studied. Our results are in good agreement with many important experiments in high-Tcsuperconductors.« less
Spin Density Matrices for Nuclear Density Functionals with Parity Violation
NASA Astrophysics Data System (ADS)
Barrett, Bruce; Giraud, Bertrand
2010-11-01
Within the context of the radial density functional [1], we apply the spin density matrix (SDM) used in atomic and molecular physics [2] to nuclear physics. The vector part of the SDM defines a ``hedgehog'' situation, which exists only if nuclear states contain some amount of parity violation. Thus, looking for the vector profile of the SDM could be used as a test for parity violation in nuclei. The difference between the scalar profile and the vector profile of the SDM will be illustrated by a toy model. [4pt] [1] B. G. Giraud, Phys. Rev. C 78, 014307 (2008).[0pt] [2] A. Goerling, Phys. Rev. A 47, 2783 (1993).
Vernarsky, Brian J.
2014-01-01
In an effort towards a ''complete'' experiment for the ω meson, we present studies from an experiment with an unpolarized target and a circularly polarized photon beam (g1c), carried out using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. The experiment was analyzed using an extended maximum likelihood fit with partial wave amplitudes. New likelihood functions were calculated to account for the polarization of the photon beam. Both circular and linear polarizations are explored. The results of these fits are then used to project out the spin density matrix for the {omega}. First measurements of the {rho}{sup 3} spin density matrix elements will be presented using this method.
NASA Astrophysics Data System (ADS)
Singh, D.; Clougherty, D. P.; MacLaren, J. M.; Albers, R. C.; Wang, C. S.
1991-10-01
The influence of local-spin-dependent correlation effects on the predicted stable ground-state phase of iron is reexamined with use of general-potential linearized augmented-plane-wave calculations. Differences in the form of the Vosko-Wilk-Nusair (VWN) local-spin-density functional used in previous studies are noted, since in previous studies significant additional approximations were made with respect to those of Vosko, Wilk, and Nusan [Can. J. Phys. 58, 1200 (1980)] and of MacLaren, Clougherty, and Albers [Phys. Rev. B 42, 3205 (1990)]. While the results of previous linear muffin-tin orbital calculations using the VWN functional predict a bcc ferromagnetic ground state, the present calculations show that the VWN spin-correlation effects fail to stabilize a bcc ground state. Considerable sensitivity to the form of the spin interpolation is found.
Testing for parity violation in nuclei using spin density matrices for nuclear density functionals
NASA Astrophysics Data System (ADS)
Barrett, B. R.; Giraud, B. G.
2015-06-01
The spin density matrix (SDM) used in atomic and molecular physics is revisited for nuclear physics, in the context of the radial density functional theory. The vector part of the SDM defines a ‘hedgehog’ situation, which exists only if nuclear states contain some amount of parity violation. A toy model is given as an illustrative example.
Optimized unrestricted Kohn-Sham potentials from ab initio spin densities
NASA Astrophysics Data System (ADS)
Boguslawski, Katharina; Jacob, Christoph R.; Reiher, Markus
2013-01-01
The reconstruction of the exchange-correlation potential from accurate ab initio electron densities can provide insights into the limitations of the currently available approximate functionals and provide guidance for devising improved approximations for density-functional theory (DFT). For open-shell systems, the spin density is introduced as an additional fundamental variable in spin-DFT. Here, we consider the reconstruction of the corresponding unrestricted Kohn-Sham (KS) potentials from accurate ab initio spin densities. In particular, we investigate whether it is possible to reconstruct the spin exchange-correlation potential, which determines the spin density in unrestricted KS-DFT, despite the numerical difficulties inherent to the optimization of potentials with finite orbital basis sets. We find that the recently developed scheme for unambiguously singling out an optimal optimized potential [Ch. R. Jacob, J. Chem. Phys. 135, 244102 (2011), 10.1063/1.3670414] can provide such spin potentials accurately. This is demonstrated for two test cases, the lithium atom and the dioxygen molecule, and target (spin) densities from full configuration interaction and complete active space self-consistent field calculations, respectively.
Spin-density distribution in the partially magnetized organic quantum magnet F2PNNNO
Zheludev, Andrey I; Garlea, Vasile O; Nishihara, S.; Hosokoshi, Y.; Cousson, Alain; Gukasov, Arsen; Inoue, K.
2007-01-01
Polarized neutron diffraction experiments on an organic magnetic material reveal a highly skewed distribution of spin density within the magnetic molecular unit. The very large magnitude of the observed effect is due to quantum spin fluctuations. The data are in quantitative agreement with direct diagonalization results for a model spin Hamiltonian, and provide insight on the actual microscopic origin of the relevant exchange interactions.
Existence of minimizers for Kohn-Sham within the local spin density approximation
NASA Astrophysics Data System (ADS)
Gontier, David
2015-01-01
The purpose of this article is to extend the work by Anantharaman and Cancès (2009 Ann. Inst. Henri Poincaré (C) 26 2425-55) and prove the existence of minimizers for the spin-polarized Kohn-Sham model in the presence of a magnetic field within the local spin density approximation. We show that for any magnetic field that vanishes at infinity, the existence of minimizers is ensured for neutral or positively charged systems. The proof relies on classical concentration-compactness techniques.
Electron affinities for rare gases and some actinides from local-spin-density-functional theory
Guo, Y.; Wrinn, M.C.; Whitehead, M.A. )
1989-12-01
The negative ions of the rare gases (He, Ne, Ar, Kr, Xe, and Rn) and some actinides (Pu, Am, Bk, Cf, and Es) have been calculated self-consistently by the generalized exchange local-spin-density-functional theory with self-interaction correction and correlation. The electron affinities were obtained as the differences between the statistical total energies of the negative ions and neutral atoms; the electron affinities were positive around several millirydbergs. Consequently, the negative ions are predicted stable for the rare gases and actinides.
Ionization potentials of cobalt and nickel ions in the local-spin-density approximation
Dhar, S. ); Kestner, N.R. )
1990-06-15
In this article we report on the ionization potentials of all configurations of the Co{sup {ital n}+} and Ni{sup {ital n}+} ions obtained via transition-state calculations using local-spin-density (LSD) potentials. The calculations were performed numerically with and without modifications of the local exchange potential for fractional occupation numbers. When the exchange potential is corrected for noninteger occupation numbers, a more consistent picture of the ionization process is obtained than that given by the LSD Kohn-Sham exchange. The agreement with experimental results is also significantly improved.
Self-consistent Goedel cosmology with spin-density in Riemann-Cartan spacetime
NASA Technical Reports Server (NTRS)
Smalley, L. L.
1986-01-01
It is shown that the Goedel metric (GM) for a rotating cosmology is compatible with the self-consistent formulation of the Einstein-Cartan (EC) metric-torsion theory for a spinning fluid. The proposed calculation shows, within the context of an EC theory, how to self-consistently incorporate a perfect fluid with spin density into the GM without changing the metric. It is found that the only changes produced in the GM parameters in connection with a spinning fluid are that the cosmological constant becomes slightly more negative and the sense of rotation is flipped 180 deg.
Thermoelectric transport and spin density of graphene nanoribbons with Rashba spin-orbit interaction
NASA Astrophysics Data System (ADS)
Cheng, Xinjun; Sun, Guo-Ya
2017-03-01
In the present paper, we have theoretically investigated thermoelectric transport properties of armchair and zigzag graphene nanoribbons with Rashba spin-orbit interaction, as well as dephasing scattering processes by applying the nonequilibrium Green function method. Behaviors of electronic and thermal currents, as well as thermoelectric coefficients are studied. It is found that both electronic and thermal currents decrease, and thermoelectric properties been suppressed, with increasing strength of Rashba spin-orbit interaction. We have also studied spin split and spin density induced by Rashba spin-orbit interaction in the graphene nanoribbons.
NASA Astrophysics Data System (ADS)
Gao Xianlong; Asgari, Reza
2008-03-01
We numerically study imbalanced two component Fermi gases with attractive interactions in highly elongated harmonic traps. An accurate parametrization formula for the ground state energy is presented for a spin-polarized attractive Gaudin-Yang model. Our studies are based on an accurate microscopic spin-density-functional theory through the Kohn-Sham scheme which employs the one-dimensional homogeneous Gaudin-Yang model with a Luther-Emery-liquid ground-state correlation as a reference system. A Thomas-Fermi approximation is examined incorporating the exchange-correlation interaction. By studying the charge and spin density profiles of the system based on these methods, we gain a quantitative understanding of the role of attractive interactions and polarization on the formation of the two-shell structure, with the coexisted Fulde-Ferrell-Larkin-Ovchinnikov-type phase in the center of the trap and either the BCS superfluid phase or the normal phase at the edges of the trap. Our results are in good agreement with the recent theoretical consequences.
NASA Astrophysics Data System (ADS)
Solovyeva, Alisa; Pavanello, Michele; Neugebauer, Johannes
2012-05-01
Subsystem density-functional theory (DFT) is a powerful and efficient alternative to Kohn-Sham DFT for large systems composed of several weakly interacting subunits. Here, we provide a systematic investigation of the spin-density distributions obtained in subsystem DFT calculations for radicals in explicit environments. This includes a small radical in a solvent shell, a π-stacked guanine-thymine radical cation, and a benchmark application to a model for the special pair radical cation, which is a dimer of bacteriochlorophyll pigments, from the photosynthetic reaction center of purple bacteria. We investigate the differences in the spin densities resulting from subsystem DFT and Kohn-Sham DFT calculations. In these comparisons, we focus on the problem of overdelocalization of spin densities due to the self-interaction error in DFT. It is demonstrated that subsystem DFT can reduce this problem, while it still allows to describe spin-polarization effects crossing the boundaries of the subsystems. In practical calculations of spin densities for radicals in a given environment, it may thus be a pragmatic alternative to Kohn-Sham DFT calculations. In our calculation on the special pair radical cation, we show that the coordinating histidine residues reduce the spin-density asymmetry between the two halves of this system, while inclusion of a larger binding pocket model increases this asymmetry. The unidirectional energy transfer in photosynthetic reaction centers is related to the asymmetry introduced by the protein environment.
The dipole moment of the spin density as a local indicator for phase transitions
Schmitz, D.; Schmitz-Antoniak, C.; Warland, A.; Darbandi, M.; Haldar, S.; Bhandary, S.; Eriksson, O.; Sanyal, B.; Wende, H.
2014-01-01
The intra-atomic magnetic dipole moment - frequently called 〈Tz〉 term - plays an important role in the determination of spin magnetic moments by x-ray absorption spectroscopy for systems with nonspherical spin density distributions. In this work, we present the dipole moment as a sensitive monitor to changes in the electronic structure in the vicinity of a phase transiton. In particular, we studied the dipole moment at the Fe2+ and Fe3+ sites of magnetite as an indicator for the Verwey transition by a combination of x-ray magnetic circular dichroism and density functional theory. Our experimental results prove that there exists a local change in the electronic structure at temperatures above the Verwey transition correlated to the known spin reorientation. Furthermore, it is shown that measurement of the dipole moment is a powerful tool to observe this transition in small magnetite nanoparticles for which it is usually screened by blocking effects in classical magnetometry. PMID:25041757
Self-interaction-corrected local-spin-density calculations for rare earth materials
Svane, A.; Temmerman, W.M.; Szotek, Z.; Laegsgaard, J.; Winter, H.
2000-04-20
The ab initio self-interaction-corrected (SIC) local-spin-density (LSD) approximation is discussed with emphasis on the ability to describe localized f-electron states in rare earth solids. Two methods for minimizing the SIC-LSD total energy functional are discussed, one using a unified Hamiltonian for all electron states, thus having the advantages of Bloch's theorem, the other one employing an iterative scheme in real space. Results for cerium and cerium compounds as well as other rare earths are presented. For the cerium compounds the onset of f-electron delocalization can be accurately described, including the intricate isostructural phase transitions in elemental cerium and CeP. In Pr and Sm the equilibrium lattice constant and zero temperature equation of state is greatly improved in comparison with the LSD results.
Alkali-metal electron spin density shift induced by a helium nanodroplet
NASA Astrophysics Data System (ADS)
Koch, Markus; Callegari, Carlo; Ernst, Wolfgang E.
2010-04-01
Helium (He) nanodroplets provide a cold and virtually unperturbing environment for the study of weakly bound molecules and van der Waals aggregates. High resolution microwave spectroscopy and the detection of electron spin transitions in doped He droplets have recently become possible. Measurements of hyperfine-resolved electron spin resonance in potassium (39K) and rubidium (85Rb) atoms on the surface of He droplets show small line shifts relative to the bare atoms. These shifts were recorded for all 2I + 1 components (I is the nuclear spin) of a transition at high accuracy for He droplets ranging in size from 1000 to 15,000 He atoms. Evaluation of the spectra yields the influence of the He environment on the electron spin density at the alkali-metal nucleus. A semi-empirical model is presented that shows good qualitative agreement with the measured droplet size dependent increase of Fermi contact interaction at the nuclei of dopant K and Rb.
The dipole moment of the spin density as a local indicator for phase transitions.
Schmitz, D; Schmitz-Antoniak, C; Warland, A; Darbandi, M; Haldar, S; Bhandary, S; Eriksson, O; Sanyal, B; Wende, H
2014-07-21
The intra-atomic magnetic dipole moment - frequently called ⟨Tz⟩ term - plays an important role in the determination of spin magnetic moments by x-ray absorption spectroscopy for systems with nonspherical spin density distributions. In this work, we present the dipole moment as a sensitive monitor to changes in the electronic structure in the vicinity of a phase transiton. In particular, we studied the dipole moment at the Fe(2+) and Fe(3+) sites of magnetite as an indicator for the Verwey transition by a combination of x-ray magnetic circular dichroism and density functional theory. Our experimental results prove that there exists a local change in the electronic structure at temperatures above the Verwey transition correlated to the known spin reorientation. Furthermore, it is shown that measurement of the dipole moment is a powerful tool to observe this transition in small magnetite nanoparticles for which it is usually screened by blocking effects in classical magnetometry.
Calculations with the quasirelativistic local-spin-density-functional theory for high-Z atoms
Guo, Y.; Whitehead, M.A.
1988-10-01
The generalized-exchange local-spin-density-functional theory (LSD-GX) with relativistic corrections of the mass velocity and Darwin terms has been used to calculate statistical total energies for the neutral atoms, the positive ions, and the negative ions for high-Z elements. The effect of the correlation and relaxation correction on the statistical total energy is discussed. Comparing the calculated results for the ionization potentials and electron affinities for the atoms (atomic number Z from 37 to 56 and 72 to 80) with experiment, shows that for the atoms rubidium to barium both the LSD-GX and the quasirelativistic LSD-GX, with self-interaction correction, Gopinathan, Whitehead, and Bogdanovic's Fermi-hole parameters (Phys. Rev. A 14, 1 (1976)), and Vosko, Wilk, and Nusair's correlation correction (Can. J. Phys. 58, 1200 (1980)), are very good methods for calculating ionization potentials and electron affinities. For the atoms hafnium to mercury the relativistic effect has to be considered.
Density versus spin-density functional in DFT+U and DFT+DMFT
NASA Astrophysics Data System (ADS)
Park, Hyowon; Millis, Andrew; Marianetti, Chris
2015-03-01
The construction of multi-variable effective action theories such as DFT+U and DFT+DMFT requires the choice of a local subspace of correlated orbitals and an additional variable being either the charge density or spin density. This talk examines the differences between using charge-only and spin-dependent exchange-correlation functionals with the aim of providing guidance for constructing more sophisticated beyond-density functional theories. The widely used spin-dependent approximations to the exchange-correlation functional are found to lead to a large and in some cases unphysical effective exchange coupling within the correlated subspace. Additionally, the differences between Wannier and Projector based definitions of the correlated orbitals are examined, and only small differences are found provided that the orbitals are orthonormal and strongly localized. These results are documented in the context of the rare earth nickelates. This work is supported under the Grant DOE-ER-046169 and under the FAME grant, one of six centers of STARnet, a Semiconductor Research Corporation program sponsored by MARCO and DARPA.
Spin-density functional theory treatment of He+-He collisions
NASA Astrophysics Data System (ADS)
Baxter, Matthew; Kirchner, Tom; Engel, Eberhard
2016-09-01
The He+-He collision system presents an interesting challenge to theory. On one hand, a full treatment of the three-electron dynamics constitutes a massive computational problem that has not been attempted yet; on the other hand, simplified independent-particle-model based descriptions may only provide partial information on either the transitions of the initial target electrons or on the transitions of the projectile electron, depending on the choice of atomic model potentials. We address the He+-He system within the spin-density functional theory framework on the exchange-only level. The Krieger-Li-Iafrate (KLI) approximation is used to calculate the exchange potentials for the spin-up and spin-down electrons, which ensures the correct asymptotic behavior of the effective (Kohn-Sham) potential consisting of exchange, Hartree and nuclear Coulomb potentials. The orbitals are propagated with the two-center basis generator method. In each time step, simplified versions of them are fed into the KLI equations to calculate the Kohn-Sham potential, which, in turn, is used to generate the orbitals in the next time step. First results for the transitions of all electrons and the resulting charge-changing total cross sections will be presented at the conference. Work supported by NSERC, Canada.
Analytical O (αs) corrections to the beam frame double-spin density matrix elements of e+e-→t t ¯
NASA Astrophysics Data System (ADS)
Kaldamäe, L.; Groote, S.; Körner, J. G.
2016-12-01
We provide analytical results for the O (αs) corrections to the double-spin density matrix elements in the reaction e+e-→t t ¯ . These concern the elements l l , l t , l n , t t , t n , and n n of the double-spin density matrix elements where l , t , n stand for longitudinal, transverse and normal orientations with respect to the beam frame spanned by the electron and the top quark momentum.
NASA Astrophysics Data System (ADS)
Dias, Jerry Ray
2008-12-01
By the resonance-theoretic method zigzag graphene nanoribbons are predicted to have an antiferromagnetic ground state with a Mulliken spin density of 0.33 on the edge atoms and the armchair graphene nanoribbons are predicted to have a nonmagnetic ground state. Similar calculations predict that sawtooth graphene nanoribbons have a weakly antiferromagnetic ground state with edge atoms having a Mulliken spin density of 0.16 on the edge atoms.
NASA Astrophysics Data System (ADS)
Xianlong, Gao
2010-03-01
We calculate the nonequilibrium dynamic evolution of a one-dimensional system of two-component fermionic atoms after a strong local quench by using a time-dependent spin-density-functional theory. The interaction quench is also considered to see its influence on the spin-charge separation. It is shown that the charge velocity is larger than the spin velocity for the system of on-site repulsive interaction (Luttinger liquid), and vise versa for the system of on-site attractive interaction (Luther-Emery liquid). We find that both the interaction quench and polarization suppress the spin-charge separation.
NASA Astrophysics Data System (ADS)
Muzafarova, M. V.; Il'in, I. V.; Anisimov, A. N.; Mokhov, E. N.; Soltamov, V. A.; Baranov, P. G.
2016-12-01
The discovery of unique magnetooptical properties of paramagnetic centers in silicon carbide, which make it possible to control spins of small arrays of centers of atomic sizes to single centers at room temperatures, using the techniques of optical detection of the magnetic resonance, posed a number of problems, among which one of the main ones is the creation of conditions under which spin relaxation effects are minimized. As studies of properties of spin nitrogen-vacancy centers in diamond showed, the main contribution to spin relaxation is made by the interaction with nitrogen donors, being a major impurity in diamond. A similar problem exists for silicon carbide, since nitrogen donors are also basic background impurities. The objective of this work is to study the spatial distribution of the spin density of nitrogen donors in two basic silicon carbide polytypes, i.e., 4 H-SiC and 6 H-SiC, to use this information for minimizing the interaction of nitrogen donors with paramagnetic centers in silicon carbide. The results of the study are analyzed by magnetic resonance methods; the spin density distribution on the nearest coordination spheres of nitrogen donors occupying carbon sites in silicon carbide is determined. It is concluded that paramagnetic centers in the 4 H-SiC polytype, including silicon vacancies, can be more stable to the interactions with unpaired donor electrons, since electrons are not localized on the coordination sphere closest to the paramagnetic center in this case.
Spin density wave (SDW) transition in Ru doped BaFeAs2 investigated by AC steady state calorimetry
NASA Astrophysics Data System (ADS)
Vinod, K.; Sharma, Shilpam; Sundar, C. S.; Bharathi, A.
2015-06-01
Heat capacity measurements were done on sub-micron sized BaFe2-xRuxAs2 single crystals using thin film membrane based the AC steady state calorimetry technique. Noticeable thermal hysteresis is observed in the heat capacity of the BaFe2-xRuxAs2 during cooling and warming cycles, indicating first order nature of the SDW transition.
Vinod, K. Sharma, Shilpam; Sundar, C. S.; Bharathi, A.
2015-06-24
Heat capacity measurements were done on sub-micron sized BaFe{sub 2−x}Ru{sub x}As{sub 2} single crystals using thin film membrane based the AC steady state calorimetry technique. Noticeable thermal hysteresis is observed in the heat capacity of the BaFe{sub 2−x}Ru{sub x}As{sub 2} during cooling and warming cycles, indicating first order nature of the SDW transition.
Coherent charge and spin density waves in underdoped HgBa2CuO4+δ
NASA Astrophysics Data System (ADS)
Lee, Jeongseop A.; Xin, Yizhou; Halperin, W. P.; Reyes, A. P.; Kuhns, P. L.; Chan, M. K.
2017-03-01
Charge order in cuprate superconductors appears to be a universal characteristic, often associated with pseudogap behavior in the normal state. The central question is whether such charge ordering or the pseudogap are required for the existence of high temperature superconductivity and embody its mechanism. An important but phenomenological approach to this question is to examine whether these phenomena extend over various members of the cuprate family. Recent nuclear magnetic resonance (NMR) measurements on oxygen chain-ordered single crystals of YBa2Cu3O6+y (Y123) have demonstrated temperature and magnetic field induced charge ordering that was confirmed in x-ray experiments. In the present work on high-quality single crystals of the tetragonal compound, HgBa2CuO4+δ , we use 17O NMR to investigate the interplay between charge and spin order deduced from the full quadrupolar-split NMR spectrum over a wide range of temperature and magnetic field. We have found evidence for a coherent modulation of charge and spin order in this compound. However, neither temperature nor magnetic field induced ordering was observed and we infer that this aspect of high temperature superconductivity is not universal.
Lerayer, Emmanuel; Renaut, Patrice; Brandès, Stéphane; Cattey, Hélène; Fleurat-Lessard, Paul; Bouhadir, Ghenwa; Bourissou, Didier; Hierso, Jean-Cyrille
2017-02-20
The reaction of nonsubstituted alkali metal cyclopentadienides with haloboranes leads to ∼90:10 mixtures of isomeric diene products that can be deprotonated to give simple boryl cyclopentadienides. We extended this transformation to the sterically hindered lithium tert-butylcyclopentadienide 1 using FBMes2 (Mes = 2,4,6-trimethylphenyl) and ClBCy2 as electrophiles. The boryl group is selectively introduced in the remote position to minimize steric congestion. The new boryl dienes are obtained as mixtures of isomers, and subsequent deprotonation with MeLi or LiHMDS affords the lithium 1,3-disubstituted cyclopentadienides 5a,b in yields over 95%. Direct assembling of tert-butylated boryl cyclopentadienides with MCl2 (M = Fe, Co) selectively leads to 1,1'-planar chiral ferrocenes 6a,b and cobaltocene 7. To shed light into the diastereoselective formation of 6a, DFT calculations were performed. The potential energy surface was scrutinized so as to identify and compare its diastereoisomers and conformers. This stereoselectivity is attributed to minimized steric repulsions between the tert-butyl and the BMes2 groups in the eclipsed conformation of the racemic diastereoisomers. The X-ray structures of boryl diene 2a and diboryl ferrocene 6a are reported. The electronic structure of cobaltocene 7 was analyzed by EPR and DFT calculations. The spin density of this unique open-shell complex is mainly localized on the Co center, but significant spin density is also found on the boron atoms, indicating substantial delocalization of the unpaired electron over the Lewis acid moieties. Consistently, the singly occupied molecular orbital is a combination of a Co-centered 3d orbital with π(BC) orbitals on each CpBMes2 rings. There is only weak, if any, direct M···B interaction in 6 and 7.
Singlet-triplet energy gaps for diradicals from fractional-spin density-functional theory.
Ess, Daniel H; Johnson, Erin R; Hu, Xiangqian; Yang, Weitao
2011-01-13
Open-shell singlet diradicals are difficult to model accurately within conventional Kohn-Sham (KS) density-functional theory (DFT). These methods are hampered by spin contamination because the KS determinant wave function is neither a pure spin state nor an eigenfunction of the S(2) operator. Here we present a theoretical foray for using single-reference closed-shell ground states to describe diradicals by fractional-spin DFT (FS-DFT). This approach allows direct, self-consistent calculation of electronic properties using the electron density corresponding to the proper spin eigenfunction. The resulting FS-DFT approach is benchmarked against diradical singlet-triplet gaps for atoms and small molecules. We have also applied FS-DFT to the singlet-triplet gaps of hydrocarbon polyacenes.
Singlet-Triplet Energy Gaps for Diradicals from Fractional-Spin Density-Functional Theory
Ess, Daniel H.; Johnson, E. R.; Hu, Xiangqian; Yang, W. T.
2010-12-09
Open-shell singlet diradicals are difficult to model accurately within conventional Kohn-Sham (KS) density-functional theory (DFT). These methods are hampered by spin contamination because the KS determinant wave function is neither a pure spin state nor an eigenfunction of the S2 operator. Here we present a theoretical foray for using single-reference closed-shell ground states to describe diradicals by fractional-spin DFT (FS-DFT). This approach allows direct, self-consistent calculation of electronic properties using the electron density corresponding to the proper spin eigenfunction. The resulting FS-DFT approach is benchmarked against diradical singlet-triplet gaps for atoms and small molecules. We have also applied FS-DFT to the singlet-triplet gaps of hydrocarbon polyacenes.
NASA Astrophysics Data System (ADS)
Malček, Michal; Bučinský, Lukáš; Biskupič, Stanislav; Jayatilaka, Dylan
2013-08-01
The Infinite Order Two Component quasirelativistic Hartree-Fock contact and effective electron/spin densities of Cu, Ag, Au atoms and the chemical shifts of HgF2, Cu+, Ag+ and Au+ are presented. The effective densities for the Gaussian nucleus model based on the weighted product of electron/spin density with the Gaussian distribution of the nucleus are reported for the first time. The effective (average) electron density obtained via the derivative of the energy of the system with respect to the size of the nucleus is shown for comparison. The finite-field difference method to obtain the derivative of the energy is also considered.
Zhou, Tao; Gao, Yi; Zhu, Jian -Xin
2015-03-07
Recently it was revealed that the whole Fermi surface is fully gapped for several families of underdoped cuprates. The existence of the finite energy gap along the $d$-wave nodal lines (nodal gap) contrasts the common understanding of the $d$-wave pairing symmetry, which challenges the present theories for the high-${T}_{c}$superconductors. Here we propose that the incommensurate diagonal spin-density-wave order can account for the above experimental observation. The Fermi surface and the local density of states are also studied. Our results are in good agreement with many important experiments in high-${T}_{c}$superconductors.
Arnold, Thorsten; Siegmund, Marc; Pankratov, Oleg
2011-08-24
We apply exact-exchange spin-density functional theory in the Krieger-Li-Iafrate approximation to interacting electrons in quantum rings of different widths. The rings are threaded by a magnetic flux that induces a persistent current. A weak space and spin symmetry breaking potential is introduced to allow for localized solutions. As the electron-electron interaction strength described by the dimensionless parameter r(S) is increased, we observe-at a fixed spin magnetic moment-the subsequent transition of both spin sub-systems from the Fermi liquid to the Wigner crystal state. A dramatic signature of Wigner crystallization is that the persistent current drops sharply with increasing r(S). We observe simultaneously the emergence of pronounced oscillations in the spin-resolved densities and in the electron localization functions indicating a spatial electron localization showing ferrimagnetic order after both spin sub-systems have undergone the Wigner crystallization. The critical r(S)(c) at the transition point is substantially smaller than in a fully spin-polarized system and decreases further with decreasing ring width. Relaxing the constraint of a fixed spin magnetic moment, we find that on increasing r(S) the stable phase changes from an unpolarized Fermi liquid to an antiferromagnetic Wigner crystal and finally to a fully polarized Fermi liquid.
NASA Astrophysics Data System (ADS)
Stevens, Martin J.; Bhat, R. D. R.; Pan, X. Y.; van Driel, H. M.; Sipe, J. E.; Smirl, Arthur L.
2005-05-01
Phase- and polarization-dependent optical processes involving pulses with frequencies ω and 2ω can be used to independently control electron and spin density in zinc-blende semiconductors such as GaAs. One such process is quantum interference control (QUIC) where interference between transition amplitudes associated with one- and two-photon absorption alters the carrier/spin generation rate. A second process, which has been acknowledged but not utilized, is cascaded second-harmonic (CASH) generation in which phase-dependent upconversion/downconversion between the two pulses modulates the 2ω pulse intensity and/or polarization and hence modulates the carrier or spin generation rate by single-photon absorption at 2ω. Here we report the use of (110)-oriented GaAs /AlGaAs quantum wells with a 500-nmAlGaAs buffer layer to enhance CASH and to allow independent control of spin and carrier densities. Experiments conducted with 100-fs pulses at 775 and 1550nm or at 715 and 1430nm, with different polarization states and with different sample orientations, show how QUIC and CASH processes vary with excitation frequency and demonstrate the dominant role played by CASH. We point the way to achieving nearly 100% control through CASH.
Chernick, Erin T; Mi, Qixi; Vega, Amy M; Lockard, Jenny V; Ratner, Mark A; Wasielewski, Michael R
2007-06-21
A t-butylphenylnitroxide (BPNO*) stable radical is attached to an electron donor-bridge-acceptor (D-B-A) system having well-defined distances between the components: MeOAn-6ANI-Ph(BPNO*)-NI, where MeOAn=p-methoxyaniline, 6ANI=4-(N-piperidinyl)naphthalene-1,8-dicarboximide, Ph=phenyl, and NI=naphthalene-1,8:4,5-bis(dicarboximide). MeOAn-6ANI, BPNO*, and NI are attached to the 1, 3, and 5 positions of the Ph bridge, respectively. Time-resolved optical and EPR spectroscopy show that BPNO* influences the spin dynamics of the photogenerated triradical states 2,4(MeOAn+*-6ANI-Ph(BPNO*)-NI-*), resulting in slower charge recombination within the triradical, as compared to the corresponding biradical lacking BPNO*. The observed spin-spin exchange interaction between the photogenerated radicals MeOAn+* and NI-* is not altered by the presence of BPNO*. However, the increased spin density on the bridge greatly increases radical pair (RP) intersystem crossing from the photogenerated singlet RP to the triplet RP. Rapid formation of the triplet RP makes it possible to observe a biexponential decay of the total RP population with components of tau=740 ps (0.75) and 104 ns (0.25). Kinetic modeling shows that the faster decay rate is due to rapid establishment of an equilibrium between the triplet RP and the neutral triplet state resulting from charge recombination, whereas the slower rate monitors recombination of the singlet RP to ground state.
Martin, Erik; Samoilova, Rimma I; Narasimhulu, Kupala V; Lin, Tzu-Jen; O'Malley, Patrick J; Wraight, Colin A; Dikanov, Sergei A
2011-04-13
In the photosynthetic reaction center from Rhodobacter sphaeroides, the primary (Q(A)) and secondary (Q(B)) electron acceptors are both ubiquinone-10, but with very different properties and functions. To investigate the protein environment that imparts these functional differences, we have applied X-band HYSCORE, a 2D pulsed EPR technique, to characterize the exchangeable protons around the semiquinone (SQ) in the Q(A) and Q(B) sites, using samples of (15)N-labeled reaction centers, with the native high spin Fe(2+) exchanged for diamagnetic Zn(2+), prepared in (1)H(2)O and (2)H(2)O solvent. The powder HYSCORE method is first validated against the orientation-selected Q-band ENDOR study of the Q(A) SQ by Flores et al. (Biophys. J.2007, 92, 671-682), with good agreement for two exchangeable protons with anisotropic hyperfine tensor components, T, both in the range 4.6-5.4 MHz. HYSCORE was then applied to the Q(B) SQ where we found proton lines corresponding to T ≈ 5.2, 3.7 MHz and T ≈ 1.9 MHz. Density functional-based quantum mechanics/molecular mechanics (QM/MM) calculations, employing a model of the Q(B) site, were used to assign the observed couplings to specific hydrogen bonding interactions with the Q(B) SQ. These calculations allow us to assign the T = 5.2 MHz proton to the His-L190 N(δ)H···O(4) (carbonyl) hydrogen bonding interaction. The T = 3.7 MHz spectral feature most likely results from hydrogen bonding interactions of O1 (carbonyl) with both Gly-L225 peptide NH and Ser-L223 hydroxyl OH, which possess calculated couplings very close to this value. The smaller 1.9 MHz coupling is assigned to a weakly bound peptide NH proton of Ile-L224. The calculations performed with this structural model of the Q(B) site show less asymmetric distribution of unpaired spin density over the SQ than seen for the Q(A) site, consistent with available experimental data for (13)C and (17)O carbonyl hyperfine couplings. The implications of these interactions for Q
Density functional calculations of spin-wave dispersion curves.
NASA Astrophysics Data System (ADS)
Kleinman, Leonard; Niu, Qian
1998-03-01
Extending the density functional method of Kubler et al( J. Kubler et al, J. Phys. F 18, 469 (1983) and J. Phys. Condens. Matter 1, 8155 (1989). ) for calcuating spin density wave ground states (but not making their atomic sphere approximation which requires a constant spin polarization direction in each WS sphere) we dicuss the calculation of frozen spin-wave eigenfunctions and their total energies. From these and the results of Niu's talk, we describe the calculation of spin-wave frequencies.
NASA Astrophysics Data System (ADS)
Park, Hyowon; Millis, Andrew J.; Marianetti, Chris A.
2015-07-01
Modern extensions of density functional theory such as the density functional theory plus U and the density functional theory plus dynamical mean field theory require choices, including selection of variable (charge vs spin density) for the density functional and specification of the correlated subspace. This paper examines these issues in the context of the "plus U" extensions of density functional theory, in which additional correlations on specified correlated orbitals are treated using a Hartree-Fock approximation. Differences between using charge-only or spin-density-dependent exchange-correlation functionals and between Wannier and projector-based definitions of the correlated orbitals are considered on the formal level and in the context of the structural energetics of the rare-earth nickelates. It is demonstrated that theories based on spin-dependent exchange-correlation functionals can lead to large and in some cases unphysical effective on-site exchange couplings. Wannier and projector-based definitions of the correlated orbitals lead to similar behavior near ambient pressure, but substantial differences are observed at large pressures. Implications for other beyond density functional methods such as the combination of density functional and dynamical mean field theory are discussed.
Aliabadi, Azar; Zaripov, Ruslan; Salikhov, Kev; Voronkova, Violeta; Vavilova, Evgeniya; Abdulmalic, Mohammad A; Rüffer, Tobias; Büchner, Bernd; Kataev, Vladislav
2015-10-29
We have applied the pulse ELDOR detected NMR (EDNMR) technique to determine the tensors of the transferred Cu (S = 1/2) - (14)N (I = 1) hyperfine (HF) interaction in single crystals of diamagnetically diluted mononuclear o-phenylenebis(N(R)-oxamide) complexes of [(n)Bu4N]2[Cu(opboR2)] (R = Et 1, (n)Pr 2) (1%) in a host lattice of [(n)Bu4N]2[Ni(opboR2)] (R = Et 3, (n)Pr 4) (99%) (1@3 and 2@4)). To facilitate the analysis of our EDNMR data and to analyze possible manifestations of the nuclear quadrupole interaction in the EDNMR spectra, we have treated a model electron-nuclear system of the coupled S = 1/2 and I = 1 spins using the spin density matrix formalism. It appears that this interaction yields a peculiar asymmetry of the EDMR spectra that manifests not only in the shift of the positions of the EDNMR lines that correspond to the forbidden EPR transitions, as expected, but also in the intensities of the EDNMR lines. The symmetric shape of the experimental spectra suggests the conclusion that, in the studied complexes, the quadrupole interaction is negligible. This has simplified the analysis of the spectra. The HF tensors of all four N donor atoms could be accurately determined. On the basis of the HF tensors, an estimate of the spin density transferred from the central paramagnetic Cu(II) ion to the N donor atoms reveals its unequal distribution. We discuss possible implications of our estimates for the magnetic exchange paths and interaction strengths in respective trinuclear complexes [Cu3(opboR2) (pmdta)2](NO3)2 (R = Et 6, (n)Pr 7).
Dhar, S.
1989-02-01
In electronic-structure calculations for finite systems using the local-spin-density (LSD) approximation, it is assumed that the eigenvalues of the Kohn-Sham equation should obey Fermi-Dirac (FD) statistics. In order to comply with this assumption for some of the transition-metal atoms, a nonintegral occupation number is used which also minimizes the total energy. It is shown here that for finite systems it is not necessary that the eigenvalues of the Kohn-Sham equation obey FD statistics. It is also shown that the Kohn-Sham exchange potential used in all LSD models is correct only for integer occupation number. With a noninteger occupation number the LSD exchange potential will be smaller than that given by the Kohn-Sham potential. Ab initio self-consistent spin-polarized calculations have been performed numerically for the total energy of an iron atom. It is found that the ground state belongs to the 3d/sup 6/4s/sup 2/ configuration. The ionization potentials of all the Fe/sup n//sup +/ ions are reported and are in agreement with experiment.
NASA Astrophysics Data System (ADS)
Dey, B.; Meyer, C. A.; Bellis, M.; Williams, M.; Adhikari, K. P.; Adikaram, D.; Aghasyan, M.; Amaryan, M. J.; Anderson, M. D.; Anefalos Pereira, S.; Ball, J.; Baltzell, N. A.; Battaglieri, M.; Bedlinskiy, I.; Biselli, A. S.; Bono, J.; Boiarinov, S.; Briscoe, W. J.; Brooks, W. K.; Burkert, V. D.; Carman, D. S.; Celentano, A.; Chandavar, S.; Colaneri, L.; Cole, P. L.; Contalbrigo, M.; Cortes, O.; Crede, V.; D'Angelo, A.; Dashyan, N.; De Vita, R.; De Sanctis, E.; Deur, A.; Djalali, C.; Doughty, D.; Dugger, M.; Dupre, R.; El Alaoui, A.; El Fassi, L.; Elouadrhiri, L.; Fedotov, G.; Fegan, S.; Fleming, J. A.; Garçon, M.; Gevorgyan, N.; Ghandilyan, Y.; Gilfoyle, G. P.; Giovanetti, K. L.; Girod, F. X.; Glazier, D. I.; Goetz, J. T.; Gothe, R. W.; Griffioen, K. A.; Guidal, M.; Hafidi, K.; Hanretty, C.; Harrison, N.; Hattawy, M.; Hicks, K.; Ho, D.; Holtrop, M.; Hyde, C. E.; Ilieva, Y.; Ireland, D. G.; Ishkhanov, B. S.; Jenkins, D.; Jo, H. S.; Joo, K.; Keller, D.; Khandaker, M.; Kim, A.; Kim, W.; Klein, A.; Klein, F. J.; Koirala, S.; Kubarovsky, V.; Kuhn, S. E.; Kuleshov, S. V.; Lenisa, P.; Livingston, K.; Lu, H.; MacGregor, I. J. D.; Markov, N.; Mayer, M.; McCracken, M. E.; McKinnon, B.; Mineeva, T.; Mirazita, M.; Mokeev, V.; Montgomery, R. A.; Moriya, K.; Moutarde, H.; Munevar, E.; Munoz Camacho, C.; Nadel-Turonski, P.; Niccolai, S.; Niculescu, G.; Niculescu, I.; Osipenko, M.; Pappalardo, L. L.; Paremuzyan, R.; Park, K.; Pasyuk, E.; Peng, P.; Phillips, J. J.; Pisano, S.; Pogorelko, O.; Pozdniakov, S.; Price, J. W.; Procureur, S.; Protopopescu, D.; Puckett, A. J. R.; Rimal, D.; Ripani, M.; Ritchie, B. G.; Rizzo, A.; Rossi, P.; Roy, P.; Sabatié, F.; Saini, M. S.; Schott, D.; Schumacher, R. A.; Seder, E.; Senderovich, I.; Sharabian, Y. G.; Simonyan, A.; Smith, E. S.; Sober, D. I.; Sokhan, D.; Stepanyan, S. S.; Stoler, P.; Strakovsky, I. I.; Strauch, S.; Sytnik, V.; Taiuti, M.; Tang, W.; Tkachenko, S.; Ungaro, M.; Vernarsky, B.; Vlassov, A. V.; Voskanyan, H.; Voutier, E.; Walford, N. K.; Watts, D. P.; Zachariou, N.; Zana, L.; Zhang, J.; Zhao, Z. W.; Zonta, I.; CLAS Collaboration
2014-05-01
High-statistics measurements of differential cross sections and spin density matrix elements for the reaction γp →ϕp have been made using the CLAS detector at Jefferson Lab. We cover center-of-mass energies (√s ) from 1.97 to 2.84 GeV, with an extensive coverage in the ϕ production angle. The high statistics of the data sample made it necessary to carefully account for the interplay between the ϕ natural lineshape and effects of the detector resolution, that are found to be comparable in magnitude. We study both the charged- (ϕ →K+K-) and neutral- (ϕ →KS0KL0) KK ¯ decay modes of the ϕ. Further, for the charged mode, we differentiate between the cases where the final K- track is directly detected or its momentum reconstructed as the total missing momentum in the event. The two charged-mode topologies and the neutral-mode have different resolutions and are calibrated against each other. Extensive usage is made of kinematic fitting to improve the reconstructed ϕ mass resolution. Our final results are reported in 10- and mostly 30-MeV-wide √s bins for the charged- and the neutral-modes, respectively. Possible effects from K+Λ* channels with pKK ¯ final states are discussed. These present results constitute the most precise and extensive ϕ photoproduction measurements to date and in conjunction with the ω photoproduction results recently published by CLAS, will greatly improve our understanding of low energy vector meson photoproduction.
Dey, B.; Meyer, C. A.; Bellis, M.; ...
2014-05-27
High-statistics measurements of differential cross sections and spin density matrix elements for the reaction γ p → Φp have been made using the CLAS detector at Jefferson Lab. We cover center-of-mass energies (√s) from 1.97 to 2.84 GeV, with an extensive coverage in the Φ production angle. The high statistics of the data sample made it necessary to carefully account for the interplay between the Φ natural lineshape and effects of the detector resolution, that are found to be comparable in magnitude. We study both the charged- (Φ → K⁺K⁻) and neutral- (Φ → K0SK0L)more » $$K\\bar{K}$$ decay modes of the Φ. Further, for the charged mode, we differentiate between the cases where the final K⁻ track is directly detected or its momentum reconstructed as the total missing momentum in the event. The two charged-mode topologies and the neutral-mode have different resolutions and are calibrated against each other. Extensive usage is made of kinematic fitting to improve the reconstructed Φ mass resolution. Our final results are reported in 10- and mostly 30-MeV-wide √s bins for the charged- and the neutral-mode, respectively. Possible effects from K⁺Λ* channels with p$$K\\bar{K}$$ final-states are discussed. These present results constitute the most precise and extensive Φ photoproduction measurements to date and in conjunction with the ω photoproduction results recently published by CLAS, will greatly improve our understanding of low energy vector meson photoproduction.« less
Dey, B.; Meyer, C. A.; Bellis, M.; Williams, M.; Adhikari, K. P.; Adikaram, D.; Aghasyan, M.; Amaryan, M. J.; Anderson, M. D.; Anefalos Pereira, S.; Ball, J.; Baltzell, N. A.; Battaglieri, M.; Bedlinskiy, I.; Biselli, A. S.; Bono, J.; Boiarinov, S.; Briscoe, W. J.; Brooks, W. K.; Burkert, V. D.; Carman, D. S.; Celentano, A.; Chandavar, S.; Colaneri, L.; Cole, P. L.; Contalbrigo, M.; Cortes, O.; Crede, V.; D'Angelo, A.; Dashyan, N.; De Vita, R.; De Sanctis, E.; Deur, A.; Djalali, C.; Doughty, D.; Dugger, M.; Dupre, R.; El Alaoui, A.; El Fassi, L.; Elouadrhiri, L.; Fedotov, G.; Fegan, S.; Fleming, J. A.; Garçon, M.; Gevorgyan, N.; Ghandilyan, Y.; Gilfoyle, G. P.; Giovanetti, K. L.; Girod, F. X.; Glazier, D. I.; Goetz, J. T.; Gothe, R. W.; Griffioen, K. A.; Guidal, M.; Hafidi, K.; Hanretty, C.; Harrison, N.; Hattawy, M.; Hicks, K.; Ho, D.; Holtrop, M.; Hyde, C. E.; Ilieva, Y.; Ireland, D. G.; Ishkhanov, B. S.; Jenkins, D.; Jo, H. S.; Joo, K.; Keller, D.; Khandaker, M.; Kim, A.; Kim, W.; Klein, A.; Klein, F. J.; Koirala, S.; Kubarovsky, V.; Kuhn, S. E.; Kuleshov, S. V.; Lenisa, P.; Livingston, K.; Lu, H.; MacGregor, I. J.D.; Markov, N.; Mayer, M.; McCracken, M. E.; McKinnon, B.; Mineeva, T.; Mirazita, M.; Mokeev, V.; Montgomery, R. A.; Moriya, K.; Moutarde, H.; Munevar, E.; Munoz Camacho, C.; Nadel-Turonski, P.; Niccolai, S.; Niculescu, G.; Niculescu, I.; Osipenko, M.; Pappalardo, L. L.; Paremuzyan, R.; Park, K.; Pasyuk, E.; Peng, P.; Phillips, J. J.; Pisano, S.; Pogorelko, O.; Pozdniakov, S.; Price, J. W.; Procureur, S.; Protopopescu, D.; Puckett, A. J. R.; Rimal, D.; Ripani, M.; Ritchie, B. G.; Rizzo, A.; Rossi, P.; Roy, P.; Sabatié, F.; Saini, M. S.; Schott, D.; Schumacher, R. A.; Seder, E.; Senderovich, I.; Sharabian, Y. G.; Simonyan, A.; Smith, E. S.; Sober, D. I.; Sokhan, D.; Stepanyan, S. S.; Stoler, P.; Strakovsky, I. I.; Strauch, S.; Sytnik, V.; Taiuti, M.; Tang, W.; Tkachenko, S.; Ungaro, M.; Vernarsky, B.; Vlassov, A. V.; Voskanyan, H.; Voutier, E.; Watts, D. P.; Zachariou, N.; Zana, L.; Zhang, J.; Zhao, Z. W.; Zonta, I.
2014-05-27
High-statistics measurements of differential cross sections and spin density matrix elements for the reaction γ p → Φp have been made using the CLAS detector at Jefferson Lab. We cover center-of-mass energies (√s) from 1.97 to 2.84 GeV, with an extensive coverage in the Φ production angle. The high statistics of the data sample made it necessary to carefully account for the interplay between the Φ natural lineshape and effects of the detector resolution, that are found to be comparable in magnitude. We study both the charged- (Φ → K⁺K⁻) and neutral- (Φ → K^{0}_{S}K^{0}_{L}) $K\\bar{K}$ decay modes of the Φ. Further, for the charged mode, we differentiate between the cases where the final K⁻ track is directly detected or its momentum reconstructed as the total missing momentum in the event. The two charged-mode topologies and the neutral-mode have different resolutions and are calibrated against each other. Extensive usage is made of kinematic fitting to improve the reconstructed Φ mass resolution. Our final results are reported in 10- and mostly 30-MeV-wide √s bins for the charged- and the neutral-mode, respectively. Possible effects from K⁺Λ* channels with p$K\\bar{K}$ final-states are discussed. These present results constitute the most precise and extensive Φ photoproduction measurements to date and in conjunction with the ω photoproduction results recently published by CLAS, will greatly improve our understanding of low energy vector meson photoproduction.
Datta, Dipayan; Gauss, Jürgen
2015-07-07
We report analytical calculations of isotropic hyperfine-coupling constants in radicals using a spin-adapted open-shell coupled-cluster theory, namely, the unitary group based combinatoric open-shell coupled-cluster (COSCC) approach within the singles and doubles approximation. A scheme for the evaluation of the one-particle spin-density matrix required in these calculations is outlined within the spin-free formulation of the COSCC approach. In this scheme, the one-particle spin-density matrix for an open-shell state with spin S and MS = + S is expressed in terms of the one- and two-particle spin-free (charge) density matrices obtained from the Lagrangian formulation that is used for calculating the analytic first derivatives of the energy. Benchmark calculations are presented for NO, NCO, CH2CN, and two conjugated π-radicals, viz., allyl and 1-pyrrolyl in order to demonstrate the performance of the proposed scheme.
Novel itinerant transverse spin waves
NASA Astrophysics Data System (ADS)
Feldmann, John Delaney
wavelengths, or can lead to spin waves that are characterized by a square root dependence on the wave number at long wavelength. The author also presents new results for spin waves in a fermi liquid that has a spin density wave in its ground state. A spin density wave is characterized by a spiral magnetization in the ground state, and is observed to occur in materials such as MnSi.
NASA Astrophysics Data System (ADS)
Chen, Jiqiang; Krieger, J. B.; Li, Yan; Iafrate, G. J.
1996-11-01
We have investigated the accuracy of the local-spin-density approximation with orbital-density-dependent self-interaction correction (LSDSIC) as proposed by Perdew and Zunger within a Kohn-Sham approach in which electrons with a given spin projection all move in a single optimized effective potential (OEP). We have also studied the accuracy of the Krieger-Li-Iafrate (KLI) approximation to the OEP for the same energy functional in order to assess its applicability to systems in which the integral equation for the OEP cannot be reduced to a one-dimensional problem, e.g., molecules. Self-consistent Kohn-Sham LSDSIC calculations have been performed for atoms with atomic number Z=1-20 in the exchange-only case for the total energy, the highest-occupied orbital energy ɛm, and the expectation value of r2. In addition, the structure of the resulting exchange potential is examined and compared with the exact exchange-only density-functional theory (OEP method with Hartree-Fock exchange-energy functional) results. Furthermore, we display ɛm, the ionization potential I, and the electron affinity A when both exchange and correlation energy effects are included. Finally, we also consider the results of evaluating the LSDSIC energy functional by employing the exact (in the central-field approximation) single particle orbitals as proposed by Harrison. We find that the LSDSIC energy functional generally leads to calculated values that are superior to those provided by the LSD approximation and that the KLI approximation yields results in excellent agreement with the corresponding exact OEP results for this energy functional. In particular, quantities strongly related to the behavior of the valence electrons are nearly identical in both the OEP and KLI calculations, i.e., the difference between the
Hwang, S H; Hicks, K; Ahn, J K; Nakano, T; Ahn, D S; Chang, W C; Chen, J Y; Daté, S; Ejiri, H; Fujimura, H; Fujiwara, M; Fukui, S; Gohn, W; Hotta, T; Imai, K; Ishikawa, T; Joo, K; Kato, Y; Kohri, H; Kon, Y; Lee, H S; Maeda, Y; Miyabe, M; Mibe, T; Morino, Y; Muramatsu, N; Nakatsugawa, Y; Niiyama, M; Noumi, H; Oh, Y; Ohashi, Y; Ohta, T; Oka, M; Parker, J; Rangacharyulu, C; Ryu, S Y; Sawada, T; Sugaya, Y; Sumihama, M; Tsunemi, T; Uchida, M; Ungaro, M; Yosoi, M
2012-03-02
The exclusive reaction γp→K(+)π(-)Σ(+) was measured for the first time using linearly polarized photons at beam energies from 1.85 to 2.96 GeV. Angular distributions in the rest frame of the K(+)π(-) system were fitted to extract spin-density matrix elements of the K(*0) decay. The measured parity spin asymmetry shows that natural-parity exchange is dominant in this reaction. This result clearly indicates the need for t-channel exchange of the κ(800) scalar meson.
Datta, Dipayan Gauss, Jürgen
2015-07-07
We report analytical calculations of isotropic hyperfine-coupling constants in radicals using a spin-adapted open-shell coupled-cluster theory, namely, the unitary group based combinatoric open-shell coupled-cluster (COSCC) approach within the singles and doubles approximation. A scheme for the evaluation of the one-particle spin-density matrix required in these calculations is outlined within the spin-free formulation of the COSCC approach. In this scheme, the one-particle spin-density matrix for an open-shell state with spin S and M{sub S} = + S is expressed in terms of the one- and two-particle spin-free (charge) density matrices obtained from the Lagrangian formulation that is used for calculating the analytic first derivatives of the energy. Benchmark calculations are presented for NO, NCO, CH{sub 2}CN, and two conjugated π-radicals, viz., allyl and 1-pyrrolyl in order to demonstrate the performance of the proposed scheme.
Williams, G V M; Jurkutat, M; Rybicki, D; Haase, J
2011-02-23
We report the results from a (63)Cu nuclear magnetic resonance (NMR) study of the electron-doped high temperature superconducting cuprate (HTSC) Pr(1.85)Ce(0.15)Cu(1-x)Ni(x)O(4). We find that Ni induces a magnetic broadening of the (63)Cu NMR spectra that can be interpreted in terms of an induced spin density oscillation about the Ni site, similar to that reported from (63)Cu NMR measurements on the hole-doped HTSCs when Zn is partially substituted for Cu. There is also an additional temperature-dependent contribution to the (63)Cu spin-lattice relaxation rate that can be interpreted in terms of an Ni-induced modification of the low energy spin fluctuations. Furthermore, the spin fluctuations are intrinsically spatially inhomogeneous and additional inhomogeneities are induced by Ni.
NASA Technical Reports Server (NTRS)
Bradas, James C.; Fennelly, Alphonsus J.; Smalley, Larry L.
1987-01-01
It is shown that a generalized (or 'power law') inflationary phase arises naturally and inevitably in a simple (Bianchi type-I) anisotropic cosmological model in the self-consistent Einstein-Cartan gravitation theory with the improved stress-energy-momentum tensor with the spin density of Ray and Smalley (1982, 1983). This is made explicit by an analytical solution of the field equations of motion of the fluid variables. The inflation is caused by the angular kinetic energy density due to spin. The model further elucidates the relationship between fluid vorticity, the angular velocity of the inertially dragged tetrads, and the precession of the principal axes of the shear ellipsoid. Shear is not effective in damping the inflation.
Direct Observation of Spin- and Charge-Density Waves in a Luttinger Liquid
NASA Astrophysics Data System (ADS)
Cao, Chenglin; Marcum, Andrew; Mawardi Ismail, Arif; Fonta, Francisco; O'Hara, Kenneth
2016-05-01
At low energy, interacting fermions in one dimension (e.g. electrons in quantum wires or fermionic atoms in 1D waveguides) should behave as Luttinger liquids. In stark contrast to Fermi liquids, the low-energy elementary excitations in Luttinger liquids are collective sound-like modes that propagate independently as spin-density and/or charge-density (i.e. particle-density) waves with generally unequal, and interaction-dependent, velocities. Here we aim to unambiguously confirm this hallmark feature of the Luttinger liquid - the phenomenon of spin-charge separation - by directly observing in real space the dynamics of spin-density and ``charge''-density waves excited in an ultracold gas of spin-1/2 fermions confined in an array of 1D optical waveguides. Starting from a two-component mixture of 6 Li atoms harmonically confined along each of the 1D waveguides, we excite low lying normal modes of the trapped system - namely the spin dipole and density dipole and quadrupole modes - and measure their frequency as a function of interaction strength. Luttinger liquid theory predicts that the spin dipole frequency is strongly dependent on interaction strength whereas the density dipole and quadrupole mode frequencies are relatively insensitive. We will also discuss extending our approach to exciting localized spin density and particle density wavepackets which should propagate at different velocities. Supported by AFOSR and NSF.
Interplay between charge density wave and antiferromagnetic order in GdNiC2
NASA Astrophysics Data System (ADS)
Hanasaki, N.; Shimomura, S.; Mikami, K.; Nogami, Y.; Nakao, H.; Onodera, H.
2017-02-01
The correlation between the charge density wave (CDW) and f local moments is observed in GdNiC2 by means of x-ray diffraction in a magnetic field. Various kinds of electronic states exist in the magnetic field. The intensity of the CDW peak changes in the successive transitions and the commensurate-incommensurate transition of the CDW takes place as well. The successive transitions are explained in terms of a cooperative effect of the Peierls instability and the spin Friedel oscillation, in which the antiferromagnetic order of the f local moments is coupled to the spin density wave coexisting with the CDW of the conduction electron.
Lin, J.; Millis, A. J.
2011-03-18
We calculate the frequency-dependent longitudinal ({sigma}{sub xx}) and Hall ({sigma}{sub xy}) conductivities for two-dimensional metals with thermally disordered antiferromagnetism using a generalization of a theoretical model, involving a one-loop quasistatic fluctuation approximation, which was previously used to calculate the electron self-energy. The conductivities are calculated from the Kubo formula, with current vertex function treated in a conserving approximation satisfying the Ward identity. In order to obtain a finite dc limit, we introduce phenomenologically impurity scattering, characterized by a relaxation time {tau}. {sigma}{sub xx}({Omega}) satisfies the f-sum rule. For the infinitely peaked spin-correlation function, {chi}(q){proportional_to}{delta}(q-Q), we recover the expressions for the conductivities in the mean-field theory of the ordered state. When the spin-correlation length {zeta} is large but finite, both {sigma}{sub xx} and {sigma}{sub xy} show behaviors characteristic of the state with long-range order. The calculation runs into difficulty for {Omega} {approx}< 1/{tau}. The difficulties are traced to an inaccurate treatment of the very-low-energy density of states within the one-loop quasistatic approximation for the self-energy. The results for {sigma}{sub xx}({Omega}) and {sigma}{sub xy}({Omega}) are qualitatively consistent with data on electron-doped cuprates when {Omega} > 1/{tau}.
NASA Astrophysics Data System (ADS)
Min, Byeong June; Jeong, Hae Kyung; Lee, ChangWoo
2015-08-01
We studied via plane wave pseudopotential total-energy calculations within the local spin density approximation (LSDA) the electronic and the structural properties of amino acids (alanine, glycine, and histidine) attached to graphene oxide (GO) by peptide bonding. The HOMO-LUMO gap, the Hirshfeld charges, and the equilibrium geometrical structures exhibit distinctive variations that depend on the species of the attached amino acid. The GO-amino acid system appears to be a good candidate for a biosensor.
Alternative route to charge density wave formation in multiband systems
Eiter, Hans-Martin; Lavagnini, Michela; Hackl, Rudi; Nowadnick, Elizabeth A.; Kemper, Alexander F.; Devereaux, Thomas P.; Chu, Jiun-Haw; Analytis, James G.; Fisher, Ian R.; Degiorgi, Leonardo
2013-01-01
Charge and spin density waves, periodic modulations of the electron, and magnetization densities, respectively, are among the most abundant and nontrivial low-temperature ordered phases in condensed matter. The ordering direction is widely believed to result from the Fermi surface topology. However, several recent studies indicate that this common view needs to be supplemented. Here, we show how an enhanced electron–lattice interaction can contribute to or even determine the selection of the ordering vector in the model charge density wave system ErTe3. Our joint experimental and theoretical study allows us to establish a relation between the selection rules of the electronic light scattering spectra and the enhanced electron–phonon coupling in the vicinity of band degeneracy points. This alternative proposal for charge density wave formation may be of general relevance for driving phase transitions into other broken-symmetry ground states, particularly in multiband systems, such as the iron-based superconductors. PMID:23248317
Glaser, Rainer; Camasta, Cory
2013-10-21
The results are reported of an ab initio study of bromine dioxide BrO2, 1, and of the T-shaped trans- and cis-dihydroxides 2 and 3 of dihydrogen bromate (HO)2BrO. The thermochemistry has been explored of potential synthetic routes to (HO)2BrO involving water addition to BrO2, hydroxyl addition to bromous acid HOBrO, 4, protonation/reduction of bromic acid HOBrO2, 5, via tautomers 6-8 of protonated bromic acid, and by reduction/protonation of bromic acid via radical anion [HOBrO2](-), 9. The potential energy surface analyses were performed at the MP2(full)/6-311G* level (or better) and with the consideration of aqueous solvation at the SMD(MP2(full)/6-311G*) level (or better), and higher-level energies were computed at levels up to QCISD(full,T)/6-311++G(2df,2pd)//MP2. The addition of RO radical to bromous acid or bromite esters and the reduction of protonated bromic acid or protonated bromate esters are promising leads for possible synthetic exploration. Spin density distributions and molecular electrostatic potentials were computed at the QCISD(full)/6-311G*//MP2(full)/6-311G* level to characterize the electronic structures of 1-3. Both radicals employ maximally occupied (pseudo) π-systems to transfer electron density from bromine to the periphery. While the formation of the (3c-5e) π-system suffices to avoid hypervalency in 1, the formation of the (4c-7e) π-system in 2 or 3 still leaves the bromine formally hypervalent and (HO)2BrO requires delocalization of bromine density into σ*-SMOs over the trans O-Br-O moiety. Molecular orbital theory is employed to describe the mechanisms for the avoidance of hypervalency and for spin delocalization and spin polarization. The (4c-7e) π-system in 2 is truly remarkable in that it contains five π-symmetric spin molecular orbitals (SMO) with unique shapes.
Itinerant density wave instabilities at classical and quantum critical points
NASA Astrophysics Data System (ADS)
Feng, Yejun; van Wezel, Jasper; Wang, Jiyang; Flicker, Felix; Silevitch, D. M.; Littlewood, P. B.; Rosenbaum, T. F.
2015-10-01
Charge ordering in metals is a fundamental instability of the electron sea, occurring in a host of materials and often linked to other collective ground states such as superconductivity. What is difficult to parse, however, is whether the charge order originates among the itinerant electrons or whether it arises from the ionic lattice. Here we employ high-resolution X-ray diffraction, combined with high-pressure and low-temperature techniques and theoretical modelling, to trace the evolution of the ordering wavevector Q in charge and spin density wave systems at the approach to both thermal and quantum phase transitions. The non-monotonic behaviour of Q with pressure and the limiting sinusoidal form of the density wave point to the dominant role of the itinerant instability in the vicinity of the critical points, with little influence from the lattice. Fluctuations rather than disorder seem to disrupt coherence.
Roles of Hund's rule coupling in excitonic density-wave states
NASA Astrophysics Data System (ADS)
Kaneko, Tatsuya; Ohta, Yukinori
2014-12-01
Excitonic density-wave states realized by the quantum condensation of electron-hole pairs (or excitons) are studied in the two-band Hubbard model with Hund's rule coupling and the pair hopping term. Using the variational cluster approximation, we calculate the grand potential of the system and demonstrate that Hund's rule coupling always stabilizes the excitonic spin-density-wave state and destabilizes the excitonic charge-density-wave state and that the pair hopping term enhances these effects. The characteristics of these excitonic density-wave states are discussed using the calculated single-particle spectral function, density of states, condensation amplitude, and pair coherence length. Implications of our results in the materials' aspects are also discussed.
NASA Astrophysics Data System (ADS)
Johnson, R. D.; Khalyavin, D. D.; Manuel, P.; Bombardi, A.; Martin, C.; Chapon, L. C.; Radaelli, P. G.
2016-05-01
Through a combination of neutron diffraction and Landau theory we describe the spin ordering in the ground state of the quadruple perovskite manganite CaMn7O12 —a magnetic multiferroic supporting an incommensurate orbital density wave that onsets above the magnetic ordering temperature, TN 1=90 K. The multi-k magnetic structure in the ground state was found to be a nearly-constant-moment helix with modulated spin helicity, which oscillates in phase with the orbital occupancies on the Mn3 + sites via trilinear magneto-orbital coupling. Our phenomenological model also shows that, above TN 2=48 K, the primary magnetic order parameter is locked into the orbital wave by an admixture of helical and collinear spin density wave structures. Furthermore, our model naturally explains the lack of a sharp dielectric anomaly at TN 1 and the unusual temperature dependence of the electrical polarization.
Quantum mechanisms of density wave transport
Miller, John H.; Wijesinghe, Asanga I.
2012-01-01
We report on new developments in the quantum picture of correlated electron transport in charge and spin density waves. The model treats the condensate as a quantum fluid in which charge soliton domain wall pairs nucleate above a Coulomb blockade threshold field. We employ a time-correlated soliton tunneling model, analogous to the theory of time-correlated single electron tunneling, to interpret the voltage oscillations and nonlinear current-voltage characteristics above threshold. An inverse scaling relationship between threshold field and dielectric response, originally proposed by Grüner, emerges naturally from the model. Flat dielectric and other ac responses below threshold in NbSe3 and TaS3, as well as small density wave phase displacements, indicate that the measured threshold is often much smaller than the classical depinning field. In some materials, the existence of two distinct threshold fields suggests that both soliton nucleation and classical depinning may occur. In our model, the ratio of electrostatic charging to pinning energy helps determine whether soliton nucleation or classical depinning dominates. PMID:22711979
Superconducting pairing and density-wave instabilities in quasi-one-dimensional conductors
NASA Astrophysics Data System (ADS)
Nickel, J. C.; Duprat, R.; Bourbonnais, C.; Dupuis, N.
2006-04-01
Using a renormalization group approach, we determine the phase diagram of an extended quasi-one-dimensional electron gas model that includes interchain hopping, nesting deviations, and both intrachain and interchain repulsive interactions. d -wave superconductivity, which dominates over the spin-density-wave (SDW) phase at large nesting deviations, becomes unstable to the benefit of a triplet f -wave phase for a weak repulsive interchain backscattering term g1⊥>0 , despite the persistence of dominant SDW correlations in the normal state. Antiferromagnetism becomes unstable against the formation of a charge-density-wave state when g1⊥ exceeds some critical value. While these features persist when both Umklapp processes and interchain forward scattering (g2⊥) are taken into account, the effect of g2⊥ alone is found to frustrate nearest-neighbor interchain d - and f -wave pairing and instead favor next-nearest-neighbor interchain singlet or triplet pairing. We argue that the close proximity of SDW and charge-density-wave phases, singlet d -wave, and triplet f -wave superconducting phases in the theoretical phase diagram provides a possible explanation for recent puzzling experimental findings in the Bechgaard salts, including the coexistence of SDW and charge-density-wave phases and the possibility of a triplet pairing in the superconducting phase.
Magnetic catalysis and axionic charge density wave in Weyl semimetals
NASA Astrophysics Data System (ADS)
Roy, Bitan; Sau, Jay D.
2015-09-01
Three-dimensional Weyl and Dirac semimetals can support a chiral-symmetry-breaking, fully gapped, charge-density-wave order even for sufficiently weak repulsive electron-electron interactions, when placed in strong magnetic fields. In the former systems, due to the natural momentum space separation of Weyl nodes the ordered phase lacks the translational symmetry and represents an axionic phase of matter, while that in a Dirac semimetal (neglecting the Zeeman coupling) is only a trivial insulator. We present the scaling of this spectral gap for a wide range of subcritical (weak) interactions as well as that of the diamagnetic susceptibility with the magnetic field. A similar mechanism for charge-density-wave ordering at weak coupling is shown to be operative in double- and triple-Weyl semimetals, where the dispersion is linear (quadratic and cubic, respectively) for the z (planar) component(s) of the momentum. We here also address the competition between the charge-density-wave and a spin-density-wave orders, both of which breaks the chiral symmetry and leads to gapped spectrum, and show that at least in the weak coupling regime the former is energetically favored. The anomalous surface Hall conductivity, role of topological defects such as axion strings, existence of one-dimensional gapless dispersive modes along the core of such defects, and anomaly cancellation through the Callan-Harvey mechanism are discussed.
NASA Astrophysics Data System (ADS)
Nazarenko, Sergey
2015-07-01
Wave turbulence is the statistical mechanics of random waves with a broadband spectrum interacting via non-linearity. To understand its difference from non-random well-tuned coherent waves, one could compare the sound of thunder to a piece of classical music. Wave turbulence is surprisingly common and important in a great variety of physical settings, starting with the most familiar ocean waves to waves at quantum scales or to much longer waves in astrophysics. We will provide a basic overview of the wave turbulence ideas, approaches and main results emphasising the physics of the phenomena and using qualitative descriptions avoiding, whenever possible, involved mathematical derivations. In particular, dimensional analysis will be used for obtaining the key scaling solutions in wave turbulence - Kolmogorov-Zakharov (KZ) spectra.
Crossover from spin waves to diffusive spin excitations in underdoped Ba(Fe1-xCox)2 As2
Tucker, G S; Fernandes, R M; Pratt, D K; Thaler, A; Ni, N; Marty, K; Christianson, A D; Lumsden, M D; Sales, B C; Sefat, A S; Bud'ko, S L; Canfield, P C; Kreyssig, A; Goldman, A I; McQueeney, R J
2014-05-01
Using inelastic neutron scattering, we show that the onset of superconductivity in underdoped Ba(Fe1-xCox)2As2 coincides with a crossover from well-defined spin waves to overdamped and diffusive spin excitations. This crossover occurs despite the presence of long-range stripe antiferromagnetic order for samples in a compositional range from x=0.04 to 0.055, and is a consequence of the shrinking spin-density wave gap and a corresponding increase in the particle-hole (Landau) damping. The latter effect is captured by a simple itinerant model relating Co doping to changes in the hot spots of the Fermi surface. We argue that the overdamped spin fluctuations provide a pairing mechanism for superconductivity in these materials.
Atmospheric Science Data Center
2013-04-19
article title: Gravity Waves Ripple over Marine Stratocumulus Clouds ... Imaging SpectroRadiometer (MISR), a fingerprint-like gravity wave feature occurs over a deck of marine stratocumulus clouds. Similar ... that occur when a pebble is thrown into a still pond, such "gravity waves" sometimes appear when the relatively stable and stratified air ...
Skyrmions in a Density-Wave State: A Mechanism for Chiral Superconductivity
NASA Astrophysics Data System (ADS)
Chakravarty, Sudip; Hsu, Chen-Hsuan
Broken symmetry states characterizing density waves of higher angular momentum in correlated electronic systems are intriguing objects. In the scheme of characterization by angular momentum, conventional charge and spin density waves correspond to zero angular momentum. Here we explore a class of exotic density wave states that have topological properties observed in recently discovered topological insulators. These rich topological density wave states deserve closer attention in not only high temperature superconductors but in other correlated electron states, as in heavy fermions, of which an explicit example will be discussed. The state discussed has non-trivial charge 2e skyrmionic spin texture. These skyrmions can condense into a charged superfluid. Alternately, they can fractionalize into merons and anti-merons. The fractionalized particles that are confined in skyrmions in the insulating phase, can emerge at a deconfined quantum critical point, which separates the insulating and the superconducting phases. These fractional particles form a two-component spin-singlet chiral (dx2-y2 ± idxy) wave superconducting state that breaks time reversal symmetry. Possible connections of this exotic order to the superconducting state in the heavy-fermion material URu2Si2 are suggested. The direct evidence of such a chiral superconducting state is polar Kerr effect that was observed recently.
NASA Astrophysics Data System (ADS)
Kruse, Karsten
2017-01-01
Traveling waves propagating along surfaces play an important role for intracellular organization. Such waves can appear spontaneously in reaction-diffusion systems, but only few general criteria for their existence are known. Analyzing the dynamics of the Min proteins in Escherichia coli, Levine and Kessler (2016 New J. Phys. 18 122001) now identified a new mechanism for the emergence of traveling waves that relies on conservation laws. From their analysis one can expect traveling waves to be a generic feature of systems made of proteins that have a cytoplasmic and a membrane-bound state.
Spin Densities in Flavin Analogs within a Flavoprotein
Martínez, Jesús Ignacio; Frago, Susana; Lans, Isaías; Alonso, Pablo Javier; García-Rubio, Inés; Medina, Milagros
2016-01-01
Characterization by electron paramagnetic resonance techniques of several variants of Anabaena flavodoxin, where the naturally occurring FMN cofactor is substituted by different analogs, makes it possible to improve the details of the spin distribution map in the isoallosazine ring in its semiquinone state. The analyzed variants were selected to monitor the effects of intrinsic changes in the flavin ring electronic structure, as well as perturbations in the apoflavodoxin-flavin interaction, on the spin populations. When these effects were analyzed together with the functional properties of the different flavodoxin variants, a relationship between spin population and biochemical parameters, as the reduction potential, could be envisaged. PMID:26840722
1989-06-15
following surprising situation. Namely associated with the integrable nonlinear Schrodinger equations are standard numerical schemes which exhibit at...36. An Initial Boundary Value Problem for the Nonlinear Schrodinger Equations , A.S. Fokas, Physica D March 1989. 37. Evolution Theory, Periodic... gravity waves and wave excitation phenomena related to moving pressure distributions; numerical approximation and computation; nonlinear optics; and
Utz, Marcel; Begley, Matthew R.; Haj-Hariri, Hossein
2012-01-01
The propagation of pressure waves in fluidic channels with elastic covers is discussed in view of applications to flow control in microfluidic devices. A theory is presented which describes pressure waves in the fluid that are coupled to bending waves in the elastic cover. At low frequencies, the lateral bending of the cover dominates over longitudinal bending, leading to propagating, non-dispersive longitudinal pressure waves in the channel. The theory addresses effects due to both the finite viscosity and compressibility of the fluid. The coupled waves propagate without dispersion, as long as the wave length is larger than the channel width. It is shown that in channels of typical microfluidic dimensions, wave velocities in the range of a few 10 m s−1 result if the channels are covered by films of a compliant material such as PDMS. The application of this principle to design microfluidic band pass filters based on standing waves is discussed. Characteristic frequencies in the range of a few kHz are readily achieved with quality factors above 30. PMID:21966667
NASA Technical Reports Server (NTRS)
Fritts, David
1987-01-01
Gravity waves contributed to the establishment of the thermal structure, small scale (80 to 100 km) fluctuations in velocity (50 to 80 m/sec) and density (20 to 30%, 0 to peak). Dominant gravity wave spectrum in the middle atmosphere: x-scale, less than 100 km; z-scale, greater than 10 km; t-scale, less than 2 hr. Theorists are beginning to understand middle atmosphere motions. There are two classes: Planetary waves and equatorial motions, gravity waves and tidal motions. The former give rise to variability at large scales, which may alter apparent mean structure. Effects include density and velocity fluctuations, induced mean motions, and stratospheric warmings which lead to the breakup of the polar vortex and cooling of the mesosphere. On this scale are also equatorial quasi-biennial and semi-annual oscillations. Gravity wave and tidal motions produce large rms fluctuations in density and velocity. The magnitude of the density fluctuations compared to the mean density is of the order of the vertical wavelength, which grows with height. Relative density fluctuations are less than, or of the order of 30% below the mesopause. Such motions may cause significant and variable convection, and wind shear. There is a strong seasonal variation in gravity wave amplitude. Additional observations are needed to address and quantify mean and fluctuation statistics of both density and mean velocity, variability of the mean and fluctuations, and to identify dominant gravity wave scales and sources as well as causes of variability, both temporal and geographic.
NASA Technical Reports Server (NTRS)
Thompson, B. J.
1999-01-01
"Moreton waves," named for the observer who popularized them, are a solar phenomenon also known in scientific literature as "Moreton-Ramsey wave," "flare waves," "flare-associated waves," "MHD blast waves," "chromospheric shock fronts" and various other combinations of terms which connote violently propagating impulsive disturbances. It is unclear whether all of the observations to which these terms have been applied pertain to a single physical phenomenon: there has perhaps been some overlap between the observations and the assumed physical properties of the observed occurrence. Moreton waves are ideally observed in the wings of H alpha, and appear as semi-circular fronts propagating at speeds ranging from several hundred to over a thousand km/sec. They form an arc, or "brow shape" which can span up to 180 degrees. Extrapolating the speed and locations of the arc indicates that the phenomenon's origin intersects well with the impulsive phase of the associated H alpha flare (if the flare exhibits an impulsive phase). However, the arc may not form or may not be observable until it is tens of megameters from the flaring region, and subsequently can propagate to distances exceeding 100 megameters. The high speeds and distances of propagation, plus the associated radio and energetic particle observations, provided strong evidence of a coronal, rather than a chromospheric origin. The H alpha manifestation of the wave is assumed to be the "ground track" or "skirt" of a three-dimensional disturbance.
NASA Technical Reports Server (NTRS)
2007-01-01
With its Multispectral Visible Imaging Camera (MVIC), half of the Ralph instrument, New Horizons captured several pictures of mesoscale gravity waves in Jupiter's equatorial atmosphere. Buoyancy waves of this type are seen frequently on Earth - for example, they can be caused when air flows over a mountain and a regular cloud pattern forms downstream. In Jupiter's case there are no mountains, but if conditions in the atmosphere are just right, it is possible to form long trains of these small waves. The source of the wave excitation seems to lie deep in Jupiter's atmosphere, below the visible cloud layers at depths corresponding to pressures 10 times that at Earth's surface. The New Horizons measurements showed that the waves move about 100 meters per second faster than surrounding clouds; this is about 25% of the speed of sound on Earth and is much greater than current models of these waves predict. Scientists can 'read' the speed and patterns these waves to learn more about activity and stability in the atmospheric layers below.
NASA Astrophysics Data System (ADS)
Murthy, Ganpathy
2000-01-01
It is well known that the ν = 2/5 state is unpolarized at zero Zeeman energy, while it is fully polarized at large Zeeman energies. A novel state with a charge/spin density wave order for composite fermions is proposed to exist at intermediate values of the Zeeman coupling for ν = 2/5. This state has half the maximum possible polarization, and can be extended to other incompressible fractions. A Hartree-Fock calculation based on the new approach for all fractional quantum Hall states developed by R. Shankar and the author is used to demonstrate the stability of this state to single-particle excitations and to compute gaps. A very recent experiment shows direct evidence for this state.
Murthy
2000-01-10
It is well known that the nu = 2/5 state is unpolarized at zero Zeeman energy, while it is fully polarized at large Zeeman energies. A novel state with a charge/spin density wave order for composite fermions is proposed to exist at intermediate values of the Zeeman coupling for nu = 2/5. This state has half the maximum possible polarization, and can be extended to other incompressible fractions. A Hartree-Fock calculation based on the new approach for all fractional quantum Hall states developed by R. Shankar and the author is used to demonstrate the stability of this state to single-particle excitations and to compute gaps. A very recent experiment shows direct evidence for this state.
Coexistence of the spini-density-wave and superconductivity in the Ba1-xKxFe2As2
Bao, Wei; Chen, H; Ren, Y; Qiu, Y; Liu, R; Wu, G H; Wu, T; Xie, Y L; Wang, F; Huang, Q; Chen, X H
2008-01-01
The relation between the spin-density-wave (SDW) and superconducting order is a central topic in current research on the FeAs-based high T{sub c} superconductors. Conflicting results exist in the LaFeAs(O,F)-class of materials, for which whether the SDW and superconductivity are mutually exclusive or they can coexist has not been settled. Here we show that for the (Ba,K)Fe{sub 2}As{sub 2} system, the SDW and superconductivity can coexist in an extended range of compositions. The availability of single crystalline samples and high value of the energy gaps would make the materials a model system to investigate the high T{sub c} ferropnictide superconductivity.
Modulation of short waves by long waves. [ocean wave interactions
NASA Technical Reports Server (NTRS)
Reece, A. M., Jr.
1978-01-01
Wave-tank experiments were performed to investigate the cyclic short-wave energy changes, related in phase to an underlying long wave, which occur during active generation of the short-wave field by wind. Measurements of time series of the short-wave slope were made by a laser-optical system, where the basic long-wave parameters were controlled and wind speeds were accurately reproducible. The short-wave slope variances were found to exhibit cyclic variations that are related to the phase of the long wave. The variations result from two combined effects: (1) the short wave frequency is varied by the long-wave orbital velocity; (2) the energy of the short waves is modulated by the actions of aerodynamic and hydrodynamic couplings that operate on the short waves in a manner related to the long-wave phase.
ERIC Educational Resources Information Center
Hindes, Victoria A.; Hom, Keri; Brookshaw, Keith
About 46% of high school graduates enrolled in California State Universities need remedial courses in both math and English to prepare them for college level. These students typically earned B averages in their high school math and English classes. In order to address this issue, Shasta College launched Operation WAVES (Win by Achieving Valuable…
Ignatovich, V. K.
2009-01-15
It is shown that neutron surface waves do not exist. The difference between the neutron wave mechanics and the wave physics of electromagnetic and acoustic processes, which allows the existence of surface waves, is analyzed.
NASA Technical Reports Server (NTRS)
Vanzandt, T. E.
1985-01-01
Atmospheric parameters fluctuate on all scales. In the mesoscale these fluctuations are occasionally sinusoidal so that they can be interpreted as gravity waves. Usually, however, the fluctuations are noise like, so that their cause is not immediately evident. Results of mesoscale observations in the 20 to 120 m altitude range that are suitable for incorporation into a model atmosphere are very limited. In the stratosphere and lower mesosphere observations are sparse and very little data has been summarized into appropriate form. There is much more data in the upper mesosphere and lower thermosphere, but again very little of it has been summarized. The available mesoscale spectra of horizontal wind u versus vertical wave number m in the 20 to 120 km altitude range are shown together with a spectrum from the lower atmosphere for comparison. Further information about these spectra is given. In spite of the large range of altitudes and latitudes, the spectra from the lower atmosphere (NASA, 1971 and DEWAN, 1984) are remarkably similar in both shape and amplitude. The mean slopes of -2.38 for the NASA spectrum and -2.7 for the Dewan spectra are supported by the mean slope of -2.75 found by ROSENBERG et al. (1974). The mesospheric spectrum is too short to establish a shape. Its amplitude is about an order of magnitude larger than the NASA spectrum in the same wave number range. The NASA and Dewan spectra suggest that the mesoscale spectra in the lower atmosphere are insensitive to meteorological conditions.
Making Waves: Seismic Waves Activities and Demonstrations
NASA Astrophysics Data System (ADS)
Braile, S. J.; Braile, L. W.
2011-12-01
The nature and propagation of seismic waves are fundamental concepts necessary for understanding the exploration of Earth's interior structure and properties, plate tectonics, earthquakes, and seismic hazards. Investigating seismic waves is also an engaging approach to learning basic principles of the physics of waves and wave propagation. Several effective educational activities and demonstrations are available for teaching about seismic waves, including the stretching of a spring to demonstrate elasticity; slinky wave propagation activities for compressional, shear, Rayleigh and Love waves; the human wave activity to demonstrate P- and S- waves in solids and liquids; waves in water in a simple wave tank; seismic wave computer animations; simple shake table demonstrations of model building responses to seismic waves to illustrate earthquake damage to structures; processing and analysis of seismograms using free and easy to use software; and seismic wave simulation software for viewing wave propagation in a spherical Earth. The use of multiple methods for teaching about seismic waves is useful because it provides reinforcement of the fundamental concepts, is adaptable to variable classroom situations and diverse learning styles, and allows one or more methods to be used for authentic assessment. The methods described here have been used effectively with a broad range of audiences, including K-12 students and teachers, undergraduate students in introductory geosciences courses, and geosciences majors.
Shats, M; Punzmann, H; Xia, H
2010-03-12
We report the first observation of extreme wave events (rogue waves) in parametrically driven capillary waves. Rogue waves are observed above a certain threshold in forcing. Above this threshold, frequency spectra broaden and develop exponential tails. For the first time we present evidence of strong four-wave coupling in nonlinear waves (high tricoherence), which points to modulation instability as the main mechanism in rogue waves. The generation of rogue waves is identified as the onset of a distinct tail in the probability density function of the wave heights. Their probability is higher than expected from the measured wave background.
1986-05-27
con- €"" straints:’. *’Permanent address: Dipartimento di Fisica . Universita di Roma 1. 00185 u 11lia. tr(a U(x)) = 0. (7a. 2469 1. Math,. PyS. 26 (10...Tenenblat Universidade de Brasilia Departamento de Matematica Brasilia, Brasil September 1985 , - . Abstract The generalized wave equation and generalized...Permanent addrems: Dipartimento di Fisica . Universita di Roma t3 U, 0. Roma. Italy The linear limit of i3) provides the most general solution ot 2614 J. MatM
Wave Dissipation and Balance - NOPP Wave Project
2014-09-30
processes that affect wind-generated ocean gravity waves. The various dissipative processes that contribute to the spectral wave evolution are isolated...over mature ocean surface wave spectra. J. Phys. Oceanogr., 34:3345–2358, 2004. K. Hasselmann. On the non-linear energy transfer in a gravity wave...P. Giovanangeli. Air flow structure over short- gravity breaking water waves. Boundary-Layer Meteorol., 126:477–705, 2008. doi: 10.1007/s10546-007
2014-10-27
2014 2. REPORT TYPE 3. DATES COVERED 00-00-2014 to 00-00-2014 4. TITLE AND SUBTITLE CMS -Wave 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM...Program CMS -Wave CMS -Wave is a two-dimensional spectral wind-wave generation and transformation model that employs a forward-marching, finite...difference method to solve the wave action conservation equation. Capabilities of CMS -Wave include wave shoaling, refraction, diffraction, reflection
Waves at Navigation Structures
2014-10-27
upgrades the Coastal Modeling System’s ( CMS ) wave model CMS -Wave, a phase-averaged spectral wave model, and BOUSS-2D, a Boussinesq-type nonlinear wave...provided by this work unit address these critical needs of the Corps’ navigation mission. Description Issue Addressed CMS -Wave application at Braddock...Bay, NY WaveNet application in Gulf of Mexico CMS -Wave and BOUSS-2D are two numerical wave models, and WaveNet and TideNet are two web-based
NASA Technical Reports Server (NTRS)
2000-01-01
The pattern on the right half of this image of the Bay of Bengal is the result of two opposing wave trains colliding. This ASTER sub-scene, acquired on March 29, 2000, covers an area 18 kilometers (13 miles) wide and 15 kilometers (9 miles) long in three bands of the reflected visible and infrared wavelength region. The visible and near-infrared bands highlight surface waves due to specular reflection of sunlight off of the wave faces.
Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) is one of five Earth-observing instruments launched December 18, 1999, on NASA's Terra satellite. The instrument was built by Japan's Ministry of International Trade and Industry. A joint U.S./Japan science team is responsible for validation and calibration of the instrument and the data products. Dr. Anne Kahle at NASA's Jet Propulsion Laboratory, Pasadena, California, is the U.S. science team leader; Moshe Pniel of JPL is the project manager. ASTER is the only high-resolution imaging sensor on Terra. The primary goal of the ASTER mission is to obtain high-resolution image data in 14 channels over the entire land surface, as well as black and white stereo images. With revisit time of between 4 and 16 days, ASTER will provide the capability for repeat coverage of changing areas on Earth's surface. Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) is one of five Earth-observing instruments launched December 18, 1999, on NASA's Terra satellite. The instrument was built by Japan's Ministry of International Trade and Industry. A joint U.S./Japan science team is responsible for validation and calibration of the instrument and the data products. Dr. Anne Kahle at NASA's Jet Propulsion Laboratory, Pasadena, California, is the U.S. science team leader; Moshe Pniel of JPL is the project manager. ASTER is the only high-resolution imaging sensor on Terra. The primary goal of the ASTER mission is to obtain high-resolution image data in 14 channels
ERIC Educational Resources Information Center
Frashure, K. M.; Chen, R. F.; Stephen, R. A.; Bolmer, T.; Lavin, M.; Strohschneider, D.; Maichle, R.; Micozzi, N.; Cramer, C.
2007-01-01
Demonstrating wave processes quantitatively in the classroom using standard classroom tools (such as Slinkys and wave tanks) can be difficult. For example, waves often travel too fast for students to actually measure amplitude or wavelength. Also, when teaching propagating waves, reflections from the ends set up standing waves, which can confuse…
NASA Technical Reports Server (NTRS)
Anderson, D. L.
1984-01-01
Vertically polarized shear wave velocity (VSV), determined primarily from fundamental mode Rayleigh waves, and the difference between the velocity of horizontally polarized shear waves (VSH) and VSV, therefore a measure of anisotropy, are shown.
NASA Technical Reports Server (NTRS)
Gurnett, Donald A.
1989-01-01
A review is given of auroral plasma wave phenomena, starting with the earliest ground-based observations and ending with the most recent satellite observations. Two types of waves are considered, electromagnetic and electrostatic. Electromagnetic waves include auroral kilometric radiation, auroral hiss, ELF noise bands, and low-frequency electric and magnetic noise. Electrostatic waves include upper hybrid resonance emissions, electron cyclotron waves, lower hybrid waves, ion cyclotron waves and broadband electrostatic noise. In each case, a brief overview is given describing the observations, the origin of the instability, and the role of the waves in the physics of the auroral acceleration region.
Dispersive wave emission from wave breaking.
Conforti, Matteo; Trillo, Stefano
2013-10-01
We show that pulses undergoing wave breaking in nonlinear weakly dispersive fibers radiate, owing to phase-matching (assisted by higher-order dispersion) of linear dispersive waves with the shock-wave front. Our theoretical results perfectly explain the radiation observed recently from pulses propagating in the normal dispersion (i.e., nonsolitonic) regime.
Andreev, Pavel A
2015-03-01
The quantum hydrodynamic (QHD) model of charged spin-1/2 particles contains physical quantities defined for all particles of a species including particles with spin-up and with spin-down. Different populations of states with different spin directions are included in the spin density (the magnetization). In this paper I derive a QHD model, which separately describes spin-up electrons and spin-down electrons. Hence electrons with different projections of spins on the preferable direction are considered as two different species of particles. It is shown that the numbers of particles with different spin directions do not conserve. Hence the continuity equations contain sources of particles. These sources are caused by the interactions of the spins with the magnetic field. Terms of similar nature arise in the Euler equation. The z projection of the spin density is no longer an independent variable. It is proportional to the difference between the concentrations of the electrons with spin-up and the electrons with spin-down. The propagation of waves in the magnetized plasmas of degenerate electrons is considered. Two regimes for the ion dynamics, the motionless ions and the motion of the degenerate ions as the single species with no account of the spin dynamics, are considered. It is shown that this form of the QHD equations gives all solutions obtained from the traditional form of QHD equations with no distinction of spin-up and spin-down states. But it also reveals a soundlike solution called the spin-electron acoustic wave. Coincidence of most solutions is expected since this derivation was started with the same basic equation: the Pauli equation. Solutions arise due to the different Fermi pressures for the spin-up electrons and the spin-down electrons in the magnetic field. The results are applied to degenerate electron gas of paramagnetic and ferromagnetic metals in the external magnetic field. The dispersion of the spin-electron acoustic waves in the partially spin
ERIC Educational Resources Information Center
Temiz, Burak Kagan; Yavuz, Ahmet
2015-01-01
This study was done to develop a simple and inexpensive wave driver that can be used in experiments on string waves. The wave driver was made using a battery-operated toy car, and the apparatus can be used to produce string waves at a fixed frequency. The working principle of the apparatus is as follows: shortly after the car is turned on, the…
NASA Astrophysics Data System (ADS)
Fuster, Andrea; Pabst, Cornelia
2016-11-01
In this work we present Finsler gravitational waves. These are a Finslerian version of the well-known p p -waves, generalizing the very special relativity line element. Our Finsler p p -waves are an exact solution of Finslerian Einstein's equations in vacuum and describe gravitational waves propagating in an anisotropic background.
ERIC Educational Resources Information Center
Reid, John S.
1977-01-01
Discussed are how the thermal vibrations of a solid are described in terms of lattice waves, how these waves interact with other waves, or with themselves, and how one is led from such a description in terms of waves to the concept of a phonon. (Author/MA)
NASA Technical Reports Server (NTRS)
Gurnett, Donald A.
1993-01-01
The primary types of plasma waves observed in the vicinity of the planets Venus, Mars, Earth, Jupiter, Saturn, Uranus, and Neptune are described. The observations are organized according to the various types of plasma waves observed, ordered according to decreasing distance from the planet, starting from the sunward side of the planet, and ending in the region near the closest approach. The plasma waves observed include: electron plasma oscillations and ion acoustic waves; trapped continuum radiation; electron cyclotron and upper hybrid waves; whistler-mode emissions; electrostatic ion cyclotron waves; and electromagnetic ion cyclotron waves.
Teleseismic S wave microseisms.
Nishida, Kiwamu; Takagi, Ryota
2016-08-26
Although observations of microseisms excited by ocean swells were firmly established in the 1940s, the source locations remain difficult to track. Delineation of the source locations and energy partition of the seismic wave components are key to understanding the excitation mechanisms. Using a seismic array in Japan, we observed both P and S wave microseisms excited by a severe distant storm in the Atlantic Ocean. Although nonlinear forcing of an ocean swell with a one-dimensional Earth model can explain P waves and vertically polarized S waves (SV waves), it cannot explain horizontally polarized S waves (SH waves). The precise source locations may provide a new catalog for exploring Earth's interior.
Robust s± -wave superconductivity against multi-impurity in iron-based superconductors
NASA Astrophysics Data System (ADS)
Huang, H. X.; Zhang, S. C.; Gao, Y.; Ren, W.
2015-04-01
Effects of disorder on electron-doped iron pnictides are investigated systematically based on self-consistent Bogoliubov-de Gennes equations. Multiply impurities with same scattering potential (SP) are randomly distributed in a square lattice. Probability distribution functions of normalized order parameters for different impurity concentrations δimp , different electron doping concentrations δ are investigated for given SPs. Samples are found to be very robust against weak SP, in which order parameters do not have qualitative change even at very large δimp . While strong SP is able to easily break down the order parameters. For moderate SP, variations of order parameters on and around impurities strongly depend on δ , however the distribution functions of normalized order parameters have similar behavior as δimp increases. Compared with superconducting (SC) order, the magnetic order is more sensitive to multi-impurity effect. The spatial spin density wave pattern has already been destroyed before the system loses its superconductivity. Dependence of SC order on temperature is similar to that of impurity-free case, with the critical temperature being remarkably suppressed for high δimp .
Structure and magnetism of bulk Fe and Cr: from plane waves to LCAO methods.
Soulairol, R; Fu, Chu-Chun; Barreteau, C
2010-07-28
Magnetic, structural and energetic properties of bulk Fe and Cr were studied using first-principles calculations within density functional theory (DFT). We aimed to identify the dependence of these properties on key approximations of DFT, namely the exchange-correlation functional, the pseudopotential and the basis set. We found a smaller effect of pseudopotentials (PPs) on Fe than on Cr. For instance, the local magnetism of Cr was shown to be particularly sensitive to the potentials representing the core electrons, i.e. projector augmented wave and Vanderbilt ultrasoft PPs predict similar results, whereas standard norm-conserving PPs tend to overestimate the local magnetic moments of Cr in bcc Cr and in dilute bcc FeCr alloys. This drawback is suggested to be closely correlated to the overestimation of Cr solution energy in the latter system. On the other hand, we point out that DFT methods with very reduced localized basis sets (LCAO: linear combination of atomic orbitals) give satisfactory results compared with more robust plane-wave approaches. A minimal-basis representation of '3d' electrons comes to be sufficient to describe non-trivial magnetic phases including spin spirals in both fcc Fe and bcc Cr, as well as the experimental magnetic ground state of bcc Cr showing a spin density wave (SDW) state. In addition, a magnetic 'spd' tight binding model within the Stoner formalism was proposed and validated for Fe and Cr. The respective Stoner parameters were obtained by fitting to DFT data. This efficient semiempirical approach was shown to be accurate enough for studying various collinear and non-collinear phases of bulk Fe and Cr. It also enabled a detailed investigation of different polarization states of SDW in bcc Cr, where the longitudinal state was suggested to be the ground state, consistent with existing experimental data.
Weakly nonlinear magnetohydrodynamic wave interactions
Webb, G.M.; Brio, M.; Kruse, M.T.; Zank, G.P.
1999-06-01
Equations describing weakly nonlinear magnetohydrodynamic (MHD) wave interactions in one Cartesian space dimension are discussed. For wave propagation in uniform media, the wave interactions of interest consist of: (a) three-wave resonant interactions in which high frequency waves, may evolve on long space and time scales if the wave phases satisfy the resonance conditions; (b) Burgers self-wave steepening for the magnetoacoustic waves, and (c) mean wave field effects, in which a particular wave interacts with the mean wave field of the other waves. For wave propagation in non-uniform media, further linear wave mixing terms appear in the equations. The equations describe four types of resonant triads: slow-fast magnetosonic wave interaction; Alfv{acute e}n-entropy wave interaction; Alfv{acute e}n-magnetosonic wave interaction; and magnetosonic-entropy wave interaction. The formalism is restricted to coherent wave interactions. {copyright} {ital 1999 American Institute of Physics.}
Wave Dissipation and Balance - NOPP Wave Project
2012-09-30
ocean with the atmosphere, land and solid Earth. Waves also define in many ways the appearance of the ocean seen by remote- sensing instruments. Beyond...waves, sediments and remote sensing systems, and to improve our forecasting and hindcasting capacity of these phenomena from the global ocean to the...feedback on the wave model quality APPROACH AND WORK PLAN By combining theoretical advances with numerical models, remote sensing and field
NASA Astrophysics Data System (ADS)
Kim, E.-H.; Boardsen, S. A.; Johnson, J. R.; Slavin, J. A.
2016-02-01
This chapter provides a brief overview of the observed characteristics of ultra-low-frequency (ULF) waves at Mercury. It shows how field-aligned propagating ULF waves at Mercury can be generated by externally driven fast compressional waves (FWs) via mode conversion at the ion-ion hybrid resonance. Then, the chapter reviews the interpretation that the strong magnetic compressional waves near and its harmonics observed with 20 of Mercury's magnetic equator could be the ion Bernstein wave (IBW) mode. A recent statistical study of ULF waves at Mercury based on MESSENGER data reported the occurrence and polarization of the detected waves. The chapter further introduces the field line resonance and the electromagnetic ion Bernstein waves to explain such waves, and shows that both theories can partially explain the observations.
NASA Astrophysics Data System (ADS)
Nihei, Kurt T.; Yi, Weidong; Myer, Larry R.; Cook, Neville G. W.; Schoenberg, Michael
1999-03-01
The properties of guided waves which propagate between two parallel fractures are examined. Plane wave analysis is used to obtain a dispersion equation for the velocities of fracture channel waves. Analysis of this equation demonstrates that parallel fractures form an elastic waveguide that supports two symmetric and two antisymmetric dispersive Rayleigh channel waves, each with particle motions and velocities that are sensitive to the normal and tangential stiffnesses of the fractures. These fracture channel waves degenerate to shear waves when the fracture stiffnesses are large, to Rayleigh waves and Rayleigh-Lamb plate waves when the fracture stiffnesses are low, and to fracture interface waves when the fractures are either very closely spaced or widely separated. For intermediate fracture stiffnesses typical of fractured rock masses, fracture channel waves are dispersive and exhibit moderate to strong localization of guided wave energy between the fractures. The existence of these waves is examined using laboratory acoustic measurements on a fractured marble plate. This experiment confirms the distinct particle motion of the fundamental antisymmetric fracture channel wave (A0 mode) and demonstrates the ease with which a fracture channel wave can be generated and detected.
NASA Technical Reports Server (NTRS)
Wiley, Scott
2008-01-01
This viewgraph document reviews some mountain wave turbulence and operational hazards while soaring. Maps, photographs, and satellite images of the meteorological phenomena are included. Additionally, photographs of aircraft that sustained mountain wave damage are provided.
Menikoff, Ralph
2015-12-14
The Zel’dovich-von Neumann-Doering (ZND) profile of a detonation wave is derived. Two basic assumptions are required: i. An equation of state (EOS) for a partly burned explosive; P(V, e, λ). ii. A burn rate for the reaction progress variable; d/dt λ = R(V, e, λ). For a steady planar detonation wave the reactive flow PDEs can be reduced to ODEs. The detonation wave profile can be determined from an ODE plus algebraic equations for points on the partly burned detonation loci with a specified wave speed. Furthermore, for the CJ detonation speed the end of the reaction zone is sonic. A solution to the reactive flow equations can be constructed with a rarefaction wave following the detonation wave profile. This corresponds to an underdriven detonation wave, and the rarefaction is know as a Taylor wave.
NASA Astrophysics Data System (ADS)
Daffron, John D.; Greenslade, Thomas B.; Stille, Dale
2010-03-01
Wave machines are a staple of demonstration lectures, and a good pair of wave machines can make the idea of transverse and longitudinal waves clearly evident to students. The demonstration apparatus collection of the University of Iowa contains examples of transverse and longitudinal wave machines that will be of interest to readers of The Physics Teacher. These machines probably date from about 1925 and may have been locally produced. You too can build them.
2015-10-30
modeling and planning missions which require metocean data ( winds , waves, tides, water levels). It allows users to access, process, and analyze wave...and wind data from different data sources (Figure 1), and provides a combination of analysis and graphical capabilities to minimize the complexity and...employs techniques to minimize complexity and uncertainty of data processing. WaveNet is a decision-support tool that provides wave and wind data
Oceanic wave measurement system
NASA Technical Reports Server (NTRS)
Holmes, J. F.; Miles, R. T. (Inventor)
1980-01-01
An oceanic wave measured system is disclosed wherein wave height is sensed by a barometer mounted on a buoy. The distance between the trough and crest of a wave is monitored by sequentially detecting positive and negative peaks of the output of the barometer and by combining (adding) each set of two successive half cycle peaks. The timing of this measurement is achieved by detecting the period of a half cycle of wave motion.
NASA Technical Reports Server (NTRS)
Hollweg, J. V.
1983-01-01
Alfven waves or Alfvenic surface waves carry enough energy into the corona to provide the coronal energy requirements. Coronal loop resonances are an appealing means by which large energy fluxes enter active region loops. The wave dissipation mechanism still needs to be elucidated, but a Kolmogoroff turbulent cascade is fully consistent with the heating requirements in coronal holes and active region loops.
NASA Astrophysics Data System (ADS)
Abramson, Guillermo
2003-03-01
A spatially extended model of the hantavirus infection in deer mice is analyzed. Traveling waves solutions of the infected and susceptible populations are studied in different regimes, controlled by an environmental parameter. The wave of infection is shown to lag behind the wave of susceptible population, and the delay between the two is analyzed numerically and through a piecewise linearization.
NASA Astrophysics Data System (ADS)
John, Sajeev; Golubentsev, Andrey
1995-01-01
It is suggested that an interacting many-electron system in a two-dimensional lattice may condense into a topological magnetic state distinct from any discussed previously. This condensate exhibits local spin-1/2 magnetic moments on the lattice sites but is composed of a Slater determinant of single-electron wave functions which exist in an orthogonal sector of the electronic Hilbert space from the sector describing traditional spin-density-wave or spiral magnetic states. These one-electron spinor wave functions have the distinguishing property that they are antiperiodic along a closed path encircling any elementary plaquette of the lattice. This corresponds to a 2π rotation of the internal coordinate frame of the electron as it encircles the plaquette. The possibility of spinor wave functions with spatial antiperiodicity is a direct consequence of the two-valuedness of the internal electronic wave function defined on the space of Euler angles describing its spin. This internal space is the topologically, doubly-connected, group manifold of SO(3). Formally, these antiperiodic wave functions may be described by passing a flux which couples to spin (rather than charge) through each of the elementary plaquettes of the lattice. When applied to the two-dimensional Hubbard model with one electron per site, this new topological magnetic state exhibits a relativistic spectrum for charged, quasiparticle excitations with a suppressed one-electron density of states at the Fermi level. For a topological antiferromagnet on a square lattice, with the standard Hartree-Fock, spin-density-wave decoupling of the on-site Hubbard interaction, there is an exact mapping of the low-energy one-electron excitation spectrum to a relativistic Dirac continuum field theory. In this field theory, the Dirac mass gap is precisely the Mott-Hubbard charge gap and the continuum field variable is an eight-component Dirac spinor describing the components of physical electron-spin amplitude on each of
Wave turbulence in annular wave tank
NASA Astrophysics Data System (ADS)
Onorato, Miguel; Stramignoni, Ettore
2014-05-01
We perform experiments in an annular wind wave tank at the Dipartimento di Fisica, Universita' di Torino. The external diameter of the tank is 5 meters while the internal one is 1 meter. The tank is equipped by two air fans which can lead to a wind of maximum 5 m/s. The present set up is capable of studying the generation of waves and the development of wind wave spectra for large duration. We have performed different tests including different wind speeds. For large wind speed we observe the formation of spectra consistent with Kolmogorv-Zakharov predictions.
Goree, J.; Ono, M.; Colestock, P.; Horton, R.; McNeill, D.; Park, H.
1985-07-01
Fast wave current drive is demonstrated in the Princeton ACT-I toroidal device. The fast Alfven wave, in the range of high ion-cyclotron harmonics, produced 40 A of current from 1 kW of rf power coupled into the plasma by fast wave loop antenna. This wave excites a steady current by damping on the energetic tail of the electron distribution function in the same way as lower-hybrid current drive, except that fast wave current drive is appropriate for higher plasma densities.
1989-03-22
with a wave follower during Marsen. J. Gophysical Res. 88, 9844-9849. 11. Hughes, B.A., 1978. The effects on internal waves on surface waves : 2...Spectra of Surface Waves K. Watson March 1989 JSR-88-130 Approved for public release; distribution unlimited. DTIC SELECTE JUN0 11989 0 JASONE The...Arlington, VA 22209 8503Z 11. TITLE (hlde Secvfty Cof.kaftn) SPECTRA OF SURFACE WAVES (U) 12. PERSONAL AUTHOfRS) K. Watson 13a. TYPE OF REPORT 13b. TIME
NASA Astrophysics Data System (ADS)
Smith, F. G. W.; Charlier, R. H.
1981-06-01
Possible means for harnessing the energy contained in ocean waves are considered. Problems associated with the low-grade nature of wave energy and the rate at which wave crests approach are pointed out, and simple devices already in use for the supply of energy to bell buoys, whistle buoys and lighted buoys are noted. Attention is then given to wave energy conversion systems based on the focusing of waves onto a narrow ramp leading to a reservoir from which water is released to power a turbine generator; a slightly submerged circular shell which directs waves into its center cavity where waves act to turn a turbine (the Dam-Atoll); a long vertical pipe with an internal valve allowing water to move in an upward direction (the Isaacs wave-energy pump); a turbine located at the bottom of an open-topped pipe (the Masuda buoy); a completely submerged closed air chamber from which runs a large pipe open to the sea; a wave piston which acts by the compression of air to drive a turbine; a massive structure with upper and lower reservoirs (the Russel rectifier); and devices which consist of floating or submerged objects which transfer wave energy to pumps (the Salter duck and Cockerell raft.) It is concluded that although wave-powered generators are not likely to become competitive in the near future or provide more than a small portion of world demand, they may be found useful under special conditions.
Wang, F C; Massart, N; Kaux, J-F; Bouquiaux, O
2011-12-01
F-waves result from the discharge of the motoneurons following their antidromic activation. The F-wave appears, as an indirect (the F-wave latency decreases when the stimulation site moves away from the muscular detection) and late response (occurring after the M response). In practice, the most useful parameter is the F-wave minimal latency, provided that at least seven distinct F-waves are evoked. When the analysis is relative either to the controlateral side, or to a former examination, this parameter is one of most sensitive in electroneuromyography. F-wave evocation implies conduction along the entire peripheral nervous system, and particularly its proximal part, which is not investigated by nervous trunks conduction velocity studies. Thus, F wave study is the most useful in plexopathies and polyradiculonevritis. In the early phase of Guillain-Barré syndrome, their absence may be the unique sign indicative of proximal conduction blocks.
Cycloidal Wave Energy Converter
Stefan G. Siegel, Ph.D.
2012-11-30
This program allowed further advancing the development of a novel type of wave energy converter, a Cycloidal Wave Energy Converter or CycWEC. A CycWEC consists of one or more hydrofoils rotating around a central shaft, and operates fully submerged beneath the water surface. It operates under feedback control sensing the incoming waves, and converts wave power to shaft power directly without any intermediate power take off system. Previous research consisting of numerical simulations and two dimensional small 1:300 scale wave flume experiments had indicated wave cancellation efficiencies beyond 95%. The present work was centered on construction and testing of a 1:10 scale model and conducting two testing campaigns in a three dimensional wave basin. These experiments allowed for the first time for direct measurement of electrical power generated as well as the interaction of the CycWEC in a three dimensional environment. The Atargis team successfully conducted two testing campaigns at the Texas A&M Offshore Technology Research Center and was able to demonstrate electricity generation. In addition, three dimensional wave diffraction results show the ability to achieve wave focusing, thus increasing the amount of wave power that can be extracted beyond what was expected from earlier two dimensional investigations. Numerical results showed wave cancellation efficiencies for irregular waves to be on par with results for regular waves over a wide range of wave lengths. Using the results from previous simulations and experiments a full scale prototype was designed and its performance in a North Atlantic wave climate of average 30kW/m of wave crest was estimated. A full scale WEC with a blade span of 150m will deliver a design power of 5MW at an estimated levelized cost of energy (LCOE) in the range of 10-17 US cents per kWh. Based on the new results achieved in the 1:10 scale experiments these estimates appear conservative and the likely performance at full scale will
Partial wave analysis of the reaction {gamma}p{yields}p{omega} and the search for nucleon resonances
Williams, M.; Applegate, D.; Bellis, M.; Meyer, C. A.; Dey, B; Dickson, R.; Krahn, Z.; McCracken, M. E.; Moriya, K.; Schumacher, R. A.; Adhikari, K. P.; Careccia, S. L.; Dodge, G. E.; Guler, N.; Klein, A.; Mayer, M.; Nepali, C. S.; Niroula, M. R.; Seraydaryan, H.; Tkachenko, S.
2009-12-15
An event-based partial wave analysis (PWA) of the reaction {gamma}p{yields}p{omega} has been performed on a high-statistics dataset obtained using the CLAS at Jefferson Lab for center-of-mass energies from threshold up to 2.4 GeV. This analysis benefits from access to the world's first high-precision spin-density matrix element measurements, available to the event-based PWA through the decay distribution of {omega}{yields}{pi}{sup +}{pi}{sup -}{pi}{sup 0}. The data confirm the dominance of the t-channel {pi}{sup 0} exchange amplitude in the forward direction. The dominant resonance contributions are consistent with the previously identified states F{sub 15}(1680) and D{sub 13}(1700) near threshold, as well as the G{sub 17}(2190) at higher energies. Suggestive evidence for the presence of a J{sup P}=5/2{sup +} state around 2 GeV, a ''missing'' state, has also been found. Evidence for other states is inconclusive.
Partial wave analysis of the reaction γp→pω and the search for nucleon resonances
Williams, M.; Applegate, D.; Bellis, M.; ...
2009-12-30
We performed an event-based partial wave analysis (PWA) of the reaction γ p -> p ω on a high-statistics dataset obtained using the CLAS at Jefferson Lab for center-of-mass energies from threshold up to 2.4 GeV. This analysis benefits from access to the world's first high precision spin density matrix element measurements, available to the event-based PWA through the decay distribution of omega-> π+ π - π0. The data confirm the dominance of the t-channel π0 exchange amplitude in the forward direction. The dominant resonance contributions are consistent with the previously identified states F[15](1680) and D[13](1700) near threshold, as wellmore » as the G[17](2190) at higher energies. Suggestive evidence for the presence of a J(P)=5/2+ state around 2 GeV, a "missing" state, has also been found. Evidence for other states is inconclusive.« less
NASA Astrophysics Data System (ADS)
Revenough, Justin
Elastic waves propagating in simple media manifest a surprisingly rich collection of phenomena. Although some can't withstand the complexities of Earth's structure, the majority only grow more interesting and more important as remote sensing probes for seismologists studying the planet's interior. To fully mine the information carried to the surface by seismic waves, seismologists must produce accurate models of the waves. Great strides have been made in this regard. Problems that were entirely intractable a decade ago are now routinely solved on inexpensive workstations. The mathematical representations of waves coded into algorithms have grown vastly more sophisticated and are troubled by many fewer approximations, enforced symmetries, and limitations. They are far from straightforward, and seismologists using them need a firm grasp on wave propagation in simple media. Linear Elastic Waves, by applied mathematician John G. Harris, responds to this need.
Wouters, L.F.
1960-08-30
Radiation waves can be detected by simultaneously measuring radiation- wave intensities at a plurality of space-distributed points and producing therefrom a plot of the wave intensity as a function of time. To this end. a detector system is provided which includes a plurality of nuclear radiation intensity detectors spaced at equal radial increments of distance from a source of nuclear radiation. Means are provided to simultaneously sensitize the detectors at the instant a wave of radiation traverses their positions. the detectors producing electrical pulses indicative of wave intensity. The system further includes means for delaying the pulses from the detectors by amounts proportional to the distance of the detectors from the source to provide an indication of radiation-wave intensity as a function of time.
Hysteresis of ionization waves
Dinklage, A.; Bruhn, B.; Testrich, H.; Wilke, C.
2008-06-15
A quasi-logistic, nonlinear model for ionization wave modes is introduced. Modes are due to finite size of the discharge and current feedback. The model consists of competing coupled modes and it incorporates spatial wave amplitude saturation. The hysteresis of wave mode transitions under current variation is reproduced. Sidebands are predicted by the model and found in experimental data. The ad hoc model is equivalent to a general--so-called universal--approach from bifurcation theory.
Millimeter Wave Ocular Effects
1987-02-20
illustrates the rabbit head in holder by photography (a), thermography (b) and thermographic profile (c). The temperature of the cornea was measured using an...and graphs of profiles of the 40 temperatures difference (final-initial) of the rabbit cornea heated by the focused beam of millimeter waves from the...antenna. 5. Cooling of the cornea by air flow. 43 6. Temperature as a function of power applied using 45 continuous wave millimeter waves of
Kinesthetic Transverse Wave Demonstration
NASA Astrophysics Data System (ADS)
Pantidos, Panagiotis; Patapis, Stamatis
2005-09-01
This is a variation on the String and Sticky Tape demonstration "The Wave Game," suggested by Ron Edge. A group of students stand side by side, each one holding a card chest high with both hands. The teacher cues the first student to begin raising and lowering his card. When he starts lowering his card, the next student begins to raise his. As succeeding students move their cards up and down, a wave such as that shown in the figure is produced. To facilitate the process, students' motions were synchronized with the ticks of a metronome (without such synchronization it was nearly impossible to generate a satisfactory wave). Our waves typically had a frequency of about 1 Hz and a wavelength of around 3 m. We videotaped the activity so that the students could analyze the motions. The (17-year-old) students had not received any prior instruction regarding wave motion and did not know beforehand the nature of the exercise they were about to carry out. During the activity they were asked what a transverse wave is. Most of them quickly realized, without teacher input, that while the wave propagated horizontally, the only motion of the transmitting medium (them) was vertical. They located the equilibrium points of the oscillations, the crests and troughs of the waves, and identified the wavelength. The teacher defined for them the period of the oscillations of the motion of a card to be the total time for one cycle. The students measured this time and then several asserted that it was the same as the wave period. Knowing the length of the waves and the number of waves per second, the next step can easily be to find the wave speed.
NASA Technical Reports Server (NTRS)
Jones, Robert E.; Kramarchuk, Ihor; Williams, Wallace D.; Pouch, John J.; Gilbert, Percy
1989-01-01
Computer-controlled thermal-wave microscope developed to investigate III-V compound semiconductor devices and materials. Is nondestructive technique providing information on subsurface thermal features of solid samples. Furthermore, because this is subsurface technique, three-dimensional imaging also possible. Microscope uses intensity-modulated electron beam of modified scanning electron microscope to generate thermal waves in sample. Acoustic waves generated by thermal waves received by transducer and processed in computer to form images displayed on video display of microscope or recorded on magnetic disk.
Solli, D R; Ropers, C; Koonath, P; Jalali, B
2007-12-13
Recent observations show that the probability of encountering an extremely large rogue wave in the open ocean is much larger than expected from ordinary wave-amplitude statistics. Although considerable effort has been directed towards understanding the physics behind these mysterious and potentially destructive events, the complete picture remains uncertain. Furthermore, rogue waves have not yet been observed in other physical systems. Here, we introduce the concept of optical rogue waves, a counterpart of the infamous rare water waves. Using a new real-time detection technique, we study a system that exposes extremely steep, large waves as rare outcomes from an almost identically prepared initial population of waves. Specifically, we report the observation of rogue waves in an optical system, based on a microstructured optical fibre, near the threshold of soliton-fission supercontinuum generation--a noise-sensitive nonlinear process in which extremely broadband radiation is generated from a narrowband input. We model the generation of these rogue waves using the generalized nonlinear Schrödinger equation and demonstrate that they arise infrequently from initially smooth pulses owing to power transfer seeded by a small noise perturbation.
Carvalho, Vanuildo S de; Freire, Hermann
2014-09-15
The two-loop renormalization group (RG) calculation is considerably extended here for the two-dimensional (2D) fermionic effective field theory model, which includes only the so-called “hot spots” that are connected by the spin-density-wave (SDW) ordering wavevector on a Fermi surface generated by the 2D t−t{sup ′} Hubbard model at low hole doping. We compute the Callan–Symanzik RG equation up to two loops describing the flow of the single-particle Green’s function, the corresponding spectral function, the Fermi velocity, and some of the most important order-parameter susceptibilities in the model at lower energies. As a result, we establish that–in addition to clearly dominant SDW correlations–an approximate (pseudospin) symmetry relating a short-range incommensurated-wave charge order to the d-wave superconducting order indeed emerges at lower energy scales, which is in agreement with recent works available in the literature addressing the 2D spin-fermion model. We derive implications of this possible electronic phase in the ongoing attempt to describe the phenomenology of the pseudogap regime in underdoped cuprates.
Oceanic-wave-measurement system
NASA Technical Reports Server (NTRS)
Holmes, J. F.; Miles, R. T.
1980-01-01
Barometer mounted on bouy senses wave heights. As wave motion raises and lowers barometer, pressure differential is proportional to wave height. Monitoring circuit samples barometer output every half cycle of wave motion and adds magnitudes of adjacent positive and negative peaks. Resulting output signals, proportional to wave height, are transmitted to central monitoring station.
ERIC Educational Resources Information Center
Newman, J. N.
1979-01-01
Discussed is the utilization of surface ocean waves as a potential source of power. Simple and large-scale wave power devices and conversion systems are described. Alternative utilizations, environmental impacts, and future prospects of this alternative energy source are detailed. (BT)
Those Elusive Gravitational Waves
ERIC Educational Resources Information Center
MOSAIC, 1976
1976-01-01
The presence of gravitational waves was predicted by Einstein in his theory of General Relativity. Since then, scientists have been attempting to develop a detector sensitive enough to measure these cosmic signals. Once the presence of gravitational waves is confirmed, scientists can directly study star interiors, galaxy cores, or quasars. (MA)
2007-10-01
24 . Measured frequency vs. set frequency for all data .............................................. 23 25. Benchmark Probe#1 wave amplitude variation...4 8 A- 24 . Wave amplitude by probe, blower speed, lip setting for 0.768 Hz on the short I b an k...frequency and wavemaker bank .................................... 24 B- 1. Coefficient of variation as percentage for all conditions for long bank and bridge
Gravitational waves from inflation
NASA Astrophysics Data System (ADS)
Guzzetti, M. C.; Bartolo, N.; Liguori, M.; Matarrese, S.
2016-09-01
The production of a stochastic background of gravitational waves is a fundamental prediction of any cosmological inflationary model. The features of such a signal encode unique information about the physics of the Early Universe and beyond, thus representing an exciting, powerful window on the origin and evolution of the Universe. We review the main mechanisms of gravitational-wave production, ranging from quantum fluctuations of the gravitational field to other mechanisms that can take place during or after inflation. These include e.g. gravitational waves generated as a consequence of extra particle production during inflation, or during the (p)reheating phase. Gravitational waves produced in inflation scenarios based on modified gravity theories and second-order gravitational waves are also considered. For each analyzed case, the expected power spectrum is given. We discuss the discriminating power among different models, associated with the validity/violation of the standard consistency relation between tensor-to-scalar ratio r and tensor spectral index nT. In light of the prospects for (directly/indirectly) detecting primordial gravitational waves, we give the expected present-day gravitational radiation spectral energy-density, highlighting the main characteristics imprinted by the cosmic thermal history, and we outline the signatures left by gravitational waves on the Cosmic Microwave Background and some imprints in the Large-Scale Structure of the Universe. Finally, current bounds and prospects of detection for inflationary gravitational waves are summarized.
Advanced Gravitational Wave Detectors
NASA Astrophysics Data System (ADS)
Blair, D. G.; Howell, E. J.; Ju, L.; Zhao, C.
2012-02-01
Part I. An Introduction to Gravitational Wave Astronomy and Detectors: 1. Gravitational waves D. G. Blair, L. Ju, C. Zhao and E. J. Howell; 2. Sources of gravitational waves D. G. Blair and E. J. Howell; 3. Gravitational wave detectors D. G. Blair, L. Ju, C. Zhao, H. Miao, E. J. Howell, and P. Barriga; 4. Gravitational wave data analysis B. S. Sathyaprakash and B. F. Schutz; 5. Network analysis L. Wen and B. F. Schutz; Part II. Current Laser Interferometer Detectors: Three Case Studies: 6. The Laser Interferometer Gravitational-Wave Observatory P. Fritschel; 7. The VIRGO detector S. Braccini; 8. GEO 600 H. Lück and H. Grote; Part III. Technology for Advanced Gravitational Wave Detectors: 9. Lasers for high optical power interferometers B. Willke and M. Frede; 10. Thermal noise, suspensions and test masses L. Ju, G. Harry and B. Lee; 11. Vibration isolation: Part 1. Seismic isolation for advanced LIGO B. Lantz; Part 2. Passive isolation J-C. Dumas; 12. Interferometer sensing and control P. Barriga; 13. Stabilizing interferometers against high optical power effects C. Zhao, L. Ju, S. Gras and D. G. Blair; Part IV. Technology for Third Generation Gravitational Wave Detectors: 14. Cryogenic interferometers J. Degallaix; 15. Quantum theory of laser-interferometer GW detectors H. Miao and Y. Chen; 16. ET. A third generation observatory M. Punturo and H. Lück; Index.
ERIC Educational Resources Information Center
Houlrik, Jens Madsen
2009-01-01
The Lorentz transformation applies directly to the kinematics of moving particles viewed as geometric points. Wave propagation, on the other hand, involves moving planes which are extended objects defined by simultaneity. By treating a plane wave as a geometric object moving at the phase velocity, novel results are obtained that illustrate the…
NASA Astrophysics Data System (ADS)
Viswanathan, Koushik; Sundaram, Narayan; Chandrasekar, Srinivasan
Stick-slip, manifest as intermittent tangential motion between two dry solid surfaces, is a friction instability that governs diverse phenomena from automobile brake squeals to earthquakes. We show, using high-speed in situ imaging of an adhesive polymer interface, that low velocity stick-slip is fundamentally of three kinds, corresponding to passage of three different surface waves -- separation pulses, slip pulses and the well-known Schallamach waves. These waves, traveling much slower than elastic waves, have clear distinguishing properties. Separation pulses and Schallamach waves involve local interface separation, and propagate in opposite directions while slip pulses are characterized by a sharp stress front and do not display any interface detachment. A change in the stick-slip mode from separation to slip pulse is effected simply by increasing the normal force. Together, these three waves constitute all possible stick-slip modes in adhesive friction and are shown to have direct analogues in muscular locomotory waves in soft bodied invertebrates. A theory for slow wave propagation is also presented which is capable of explaining the attendant interface displacements, velocities and stresses.
NASA Astrophysics Data System (ADS)
Orimolade, A. P.; Furevik, B. R.; Noer, G.; Gudmestad, O. T.; Samelson, R. M.
2016-08-01
In a rather stationary fetch, one would not expect large waves in polar low situations. However, the picture changes when one considers a moving fetch. The significant wave heights that may be associated with the recorded polar lows on the Norwegian continental shelf from December 1999 to October 2015 are estimated using a one-dimensional parametric wave model. A comparison of the measured and the forecasted significant wave heights in two recent polar low cases in the Barents Sea is presented. The estimated significant wave heights show that the values could have been up to and above 9 m. The forecasted significant wave heights considerably underestimated the measured significant wave heights in the two recent polar low cases that are considered. Furthermore, a generalization of the fetch-limited wave equation in polar lows is proposed, which allows the wind field to vary in space and time, and is shown to give results that are consistent with the one-dimensional parametric model.
ERIC Educational Resources Information Center
Rosencwaig, Allan
1982-01-01
Thermal features of and beneath the surface of a sample can be detected and imaged with a thermal-wave microscope. Various methodologies for the excitation and detection of thermal waves are discussed, and several applications, primarily in microelectronics, are presented. (Author)
Search for Gravitational Waves
NASA Astrophysics Data System (ADS)
Tsubono, K.
The current status of the experimental search for gravitational waves is reviewed here. The emphasis is on the Japanese TAMA project. We started operation of the TAMA300 laser interferometric detector in 1999, and are now collecting and analyzing observational data to search for gravitational wave signals.
Leavitt, M.A.; Lutz, I.C.
1958-08-01
An amplifier circuit is described for amplifying sigmals having an alternating current component superimposed upon a direct current component, without loss of any segnnent of the alternating current component. The general circuit arrangement includes a vibrator, two square wave amplifiers, and recombination means. The amplifier input is connected to the vibrating element of the vibrator and is thereby alternately applied to the input of each square wave amplifier. The detailed circuitry of the recombination means constitutes the novelty of the annplifier and consists of a separate, dual triode amplifier coupled to the output of each square wave amplifier with a recombination connection from the plate of one amplifier section to a grid of one section of the other amplifier. The recombination circuit has provisions for correcting distortion caused by overlapping of the two square wave voltages from the square wave amplifiers.
Experiments on excitation waves
NASA Astrophysics Data System (ADS)
Müller, S. C.
Recent trends in the experimentation on chemical and biochemical excitation waves are presented. In the Belousov-Zhabotinsky reaction, which is the most suitable chemical laboratory system for the study of wave propagation in excitable medium, the efficient control of wave dynamics by electrical fields and by light illumination is illustrated. In particular, the effects of a feedback control are shown. Further new experiments in this system are concerned with three-dimensional topologies and boundary effects. Important biological applications are found in the aggregation of slime mould amoebae, in proton waves during oscillatory glycolysis, and in waves of spreading depression in neuronal tissue as studied by experiments in chicken retina. Numerical simulations with appropriate reaction-diffusion models complement a large number of these experimental findings.
NASA Astrophysics Data System (ADS)
Yan, Zhenya
2011-11-01
The coupled nonlinear volatility and option pricing model presented recently by Ivancevic is investigated, which generates a leverage effect, i.e., stock volatility is (negatively) correlated to stock returns, and can be regarded as a coupled nonlinear wave alternative of the Black-Scholes option pricing model. In this Letter, we analytically propose vector financial rogue waves of the coupled nonlinear volatility and option pricing model without an embedded w-learning. Moreover, we exhibit their dynamical behaviors for chosen different parameters. The vector financial rogue wave (rogon) solutions may be used to describe the possible physical mechanisms for the rogue wave phenomena and to further excite the possibility of relative researches and potential applications of vector rogue waves in the financial markets and other related fields.
NASA Astrophysics Data System (ADS)
Busswell, Geoff; Ash, Ellis; Piolle, Jean-Francois; Poulter, David J. S.; Snaith, Helen; Collard, Fabrice; Sheera, Harjit; Pinnock, Simon
2010-12-01
The ESA GlobWave project is a three year initiative, funded by ESA and CNES, to service the needs of satellite wave product users across the globe. Led by Logica UK, with support from CLS, IFREMER, SatOC and NOCS, the project will provide free access to satellite wave data and products in a common format, both historical and in near real time, from various European and American SAR and altimeter missions. Building on the successes of similar projects for Sea Surface Temperature and ocean colour, the project aims to stimulate increased use and analysis of satellite wave products. In addition to common-format satellite data the project will provide comparisons with in situ measurements, interactive data analysis tools and a pilot spatial wave forecast verification scheme for operational forecast production centres. The project will begin operations in January 2010, with direction from regular structured user consultation.
Electromagnetic wave energy converter
NASA Technical Reports Server (NTRS)
Bailey, R. L. (Inventor)
1973-01-01
Electromagnetic wave energy is converted into electric power with an array of mutually insulated electromagnetic wave absorber elements each responsive to an electric field component of the wave as it impinges thereon. Each element includes a portion tapered in the direction of wave propagation to provide a relatively wideband response spectrum. Each element includes an output for deriving a voltage replica of the electric field variations intercepted by it. Adjacent elements are positioned relative to each other so that an electric field subsists between adjacent elements in response to the impinging wave. The electric field results in a voltage difference between adjacent elements that is fed to a rectifier to derive dc output power.
NASA Astrophysics Data System (ADS)
Grishchuk, Leonid Petrovich
The article concerns astronomical phenomena , related with discovery of gravitational waves of various nature: 1) primordial (relic) gravitational waves, analogous to MWBR 2) gravitational waves due to giant collisions in the Universe between 2a) Macroscopic black Holes in the centers of Galaxies 2b) Tidal disruption of neutron stars by Black holes 2c) deformations of the space-time by stellar mass Black Holes moving near giant Black Holes in the centers of Galaxies 2d) Supernovae phenomena 2e) accretion phenomena on Black Holes and Neutron stars. The Earth based interferometric technics (LIGO Project) to detect gravitational waves is described as well as the perspectiva for a space Laser Interferometric Antena (LISA)is discussed. The article represents a modified text of the Plenary talk "Gravity-Wave astronomy" given at the XI International gravitational Conference (July 1986, Stockholm, Sweden).
Sculpting Waves (Presentation Recording)
NASA Astrophysics Data System (ADS)
Engheta, Nader
2015-09-01
In electronics controlling and manipulating flow of charged carriers has led to design of numerous functional devices. In photonics, by analogy, this is done through controlling photons and optical waves. However, the challenges and opportunities are different in these two fields. Materials control waves, and as such they can tailor, manipulate, redirect, and scatter electromagnetic waves and photons at will. Recent development in condensed matter physics, nanoscience, and nanotechnology has made it possible to tailor materials with unusual parameters and extreme characteristics and with atomic precision and thickness. One can now construct structures much smaller than the wavelengths of visible light, thus ushering in unprecedented possibilities and novel opportunities for molding fields and waves at the nanoscale with desired functionalities. At such subwavelength scales, sculpting optical fields and waves provides a fertile ground for innovation and discovery. I will discuss some of the exciting opportunities in this area, and forecast some future directions and possibilities.
Spatial equation for water waves
NASA Astrophysics Data System (ADS)
Dyachenko, A. I.; Zakharov, V. E.
2016-02-01
A compact spatial Hamiltonian equation for gravity waves on deep water has been derived. The equation is dynamical and can describe extreme waves. The equation for the envelope of a wave train has also been obtained.
Standing Waves on a Shoestring.
ERIC Educational Resources Information Center
Hendrix, Laura
1992-01-01
Describes the construction of a wave generator used to review the algebraic relationships of wave motion. Students calculate and measure the weight needed to create tension to generate standing waves at the first eight harmonics. (MDH)
Dynamics of baroclinic wave systems
NASA Technical Reports Server (NTRS)
Barcilon, Albert; Weng, Hengyi
1989-01-01
The research carried out in the past year dealt with nonlinear baroclinic wave dynamics. The model consisted of an Eady baroclinic basic state and uneven Elkman dissipation at the top and bottom boundaries with/without slopes. The method of solution used a truncated spectral expansion with three zonal waves and one or two meridional modes. Numerical experiments were performed on synoptic scale waves or planetary scale waves with/without wave-wave interaction.
NASA Astrophysics Data System (ADS)
Löhner-Böttcher, Johannes
2016-03-01
Context: The dynamic atmosphere of the Sun exhibits a wealth of magnetohydrodynamic (MHD) waves. In the presence of strong magnetic fields, most spectacular and powerful waves evolve in the sunspot atmosphere. Allover the sunspot area, continuously propagating waves generate strong oscillations in spectral intensity and velocity. The most prominent and fascinating phenomena are the 'umbral flashes' and 'running penumbral waves' as seen in the sunspot chromosphere. Their nature and relation have been under intense discussion in the last decades. Aims: Waves are suggested to propagate upward along the magnetic field lines of sunspots. An observational study is performed to prove or disprove the field-guided nature and coupling of the prevalent umbral and penumbral waves. Comprehensive spectroscopic observations at high resolution shall provide new insights into the wave characteristics and distribution across the sunspot atmosphere. Methods: Two prime sunspot observations were carried out with the Dunn Solar Telescope at the National Solar Observatory in New Mexico and with the Vacuum Tower Telescope at the Teide Observatory on Tenerife. The two-dimensional spectroscopic observations were performed with the interferometric spectrometers IBIS and TESOS. Multiple spectral lines are scanned co-temporally to sample the dynamics at the photospheric and chromospheric layers. The time series (1 - 2.5 h) taken at high spatial and temporal resolution are analyzed according to their evolution in spectral intensities and Doppler velocities. A wavelet analysis was used to obtain the wave power and dominating wave periods. A reconstruction of the magnetic field inclination based on sunspot oscillations was developed. Results and conclusions: Sunspot oscillations occur continuously in spectral intensity and velocity. The obtained wave characteristics of umbral flashes and running penumbral waves strongly support the scenario of slow-mode magnetoacoustic wave propagation along the
Lucia, L.V.
1982-03-16
A wave action power plant powered by the action of water waves has a drive shaft rotated by a plurality of drive units, each having a lever pivotally mounted on and extending from said shaft and carrying a weight, in the form of a float, which floats on the waves and rocks the lever up and down on the shaft. A ratchet mechanism causes said shaft to be rotated in one direction by the weight of said float after it has been raised by wave and the wave has passed, leaving said float free to move downwardly by gravity and apply its full weight to pull down on the lever and rotate the drive shaft. There being a large number of said drive units so that there are always some of the weights pulling down on their respective levers while other weights are being lifted by waves and thereby causing continuous rotation of the drive shaft in one direction. The said levers are so mounted that they may be easily raised to bring the weights into a position wherein they are readily accessible for cleaning the bottoms thereof to remove any accumulation of barnacles, mollusks and the like. There is also provided means for preventing the weights from colliding with each other as they independently move up and down on the waves.
Shoaling internal solitary waves
NASA Astrophysics Data System (ADS)
Sutherland, B. R.; Barrett, K. J.; Ivey, G. N.
2013-09-01
The evolution and breaking of internal solitary waves in a shallow upper layer as they approach a constant bottom slope is examined through laboratory experiments. The waves are launched in a two-layer fluid through the standard lock-release method. In most experiments, the wave amplitude is significantly larger than the depth of the shallow upper layer so that they are not well described by Korteweg-de Vries theory. The dynamics of the shoaling waves are characterized by the Iribarren number, Ir, which measures the ratio of the topographic slope to the square root of the characteristic wave slope. This is used to classify breaking regimes as collapsing, plunging, surging, and nonbreaking for increasing values of Ir. For breaking waves, the maximum interface descent, Hi
Undamped electrostatic plasma waves
Valentini, F.; Perrone, D.; Veltri, P.; Califano, F.; Pegoraro, F.; Morrison, P. J.; O'Neil, T. M.
2012-09-15
Electrostatic waves in a collision-free unmagnetized plasma of electrons with fixed ions are investigated for electron equilibrium velocity distribution functions that deviate slightly from Maxwellian. Of interest are undamped waves that are the small amplitude limit of nonlinear excitations, such as electron acoustic waves (EAWs). A deviation consisting of a small plateau, a region with zero velocity derivative over a width that is a very small fraction of the electron thermal speed, is shown to give rise to new undamped modes, which here are named corner modes. The presence of the plateau turns off Landau damping and allows oscillations with phase speeds within the plateau. These undamped waves are obtained in a wide region of the (k,{omega}{sub R}) plane ({omega}{sub R} being the real part of the wave frequency and k the wavenumber), away from the well-known 'thumb curve' for Langmuir waves and EAWs based on the Maxwellian. Results of nonlinear Vlasov-Poisson simulations that corroborate the existence of these modes are described. It is also shown that deviations caused by fattening the tail of the distribution shift roots off of the thumb curve toward lower k-values and chopping the tail shifts them toward higher k-values. In addition, a rule of thumb is obtained for assessing how the existence of a plateau shifts roots off of the thumb curve. Suggestions are made for interpreting experimental observations of electrostatic waves, such as recent ones in nonneutral plasmas.
NASA Astrophysics Data System (ADS)
Chen, P. F.
2016-02-01
After the Solar and Heliospheric Observatory (SOHO) was launched in 1996, the aboard Extreme Ultraviolet Imaging Telescope (EIT) observed a global coronal wave phenomenon, which was initially named ``EIT wave" after the telescope. The bright fronts are immediately followed by expanding dimmings. It has been shown that the brightenings and dimmings are mainly due to plasma density increase and depletion, respectively. Such a spectacular phenomenon sparked long-lasting interest and debates. The debates were concentrated on two topics, one is about the driving source, and the other is about the nature of this wavelike phenomenon. The controversies are most probably because there may exist two types of large-scale coronal waves that were not well resolved before the Solar Dynamics Observatory (SDO) was launched: one is a piston-driven shock wave straddling over the erupting coronal mass ejection (CME), and the other is an apparently propagating front, which may correspond to the CME frontal loop. Such a two-wave paradigm was proposed more than 13 years ago, and now is being recognized by more and more colleagues. In this paper, we review how various controversies can be resolved in the two-wave framework and how important it is to have two different names for the two types of coronal waves.
Kerschensteiner, Daniel
2016-01-01
Spontaneous activity patterns propagate through many parts of the developing nervous system and shape the wiring of emerging circuits. Prior to vision, waves of activity originating in the retina propagate through the lateral geniculate nucleus (LGN) of the thalamus to primary visual cortex (V1). Retinal waves have been shown to instruct the wiring of ganglion cell axons in LGN and of thalamocortical axons in V1 via correlation-based plasticity rules. Across species, retinal waves mature in three stereotypic stages (I–III), in which distinct circuit mechanisms give rise to unique activity patterns that serve specific functions in visual system refinement. Here, I review insights into the patterns, mechanisms, and functions of stage III retinal waves, which rely on glutamatergic signaling. As glutamatergic waves spread across the retina, neighboring ganglion cells with opposite light responses (ON vs. OFF) are activated sequentially. Recent studies identified lateral excitatory networks in the inner retina that generate and propagate glutamatergic waves, and vertical inhibitory networks that desynchronize the activity of ON and OFF cells in the wavefront. Stage III wave activity patterns may help segregate axons of ON and OFF ganglion cells in the LGN, and could contribute to the emergence of orientation selectivity in V1. PMID:27242446
Wave-wave interactions in solar type III radio bursts
Thejappa, G.; MacDowall, R. J.
2014-02-11
The high time resolution observations from the STEREO/WAVES experiment show that in type III radio bursts, the Langmuir waves often occur as localized magnetic field aligned coherent wave packets with durations of a few ms and with peak intensities well exceeding the strong turbulence thresholds. Some of these wave packets show spectral signatures of beam-resonant Langmuir waves, down- and up-shifted sidebands, and ion sound waves, with frequencies, wave numbers, and tricoherences satisfying the resonance conditions of the oscillating two stream instability (four wave interaction). The spectra of a few of these wave packets also contain peaks at f{sub pe}, 2f{sub pe} and 3 f{sub pe} (f{sub pe} is the electron plasma frequency), with frequencies, wave numbers and bicoherences (computed using the wavelet based bispectral analysis techniques) satisfying the resonance conditions of three wave interactions: (1) excitation of second harmonic electromagnetic waves as a result of coalescence of two oppositely propagating Langmuir waves, and (2) excitation of third harmonic electromagnetic waves as a result of coalescence of Langmuir waves with second harmonic electromagnetic waves. The implication of these findings is that the strong turbulence processes play major roles in beam stabilization as well as conversion of Langmuir waves into escaping radiation in type III radio bursts.
Stress wave focusing transducers
Visuri, S.R., LLNL
1998-05-15
Conversion of laser radiation to mechanical energy is the fundamental process behind many medical laser procedures, particularly those involving tissue destruction and removal. Stress waves can be generated with laser radiation in several ways: creation of a plasma and subsequent launch of a shock wave, thermoelastic expansion of the target tissue, vapor bubble collapse, and ablation recoil. Thermoelastic generation of stress waves generally requires short laser pulse durations and high energy density. Thermoelastic stress waves can be formed when the laser pulse duration is shorter than the acoustic transit time of the material: {tau}{sub c} = d/c{sub s} where d = absorption depth or spot diameter, whichever is smaller, and c{sub s} = sound speed in the material. The stress wave due to thermoelastic expansion travels at the sound speed (approximately 1500 m/s in tissue) and leaves the site of irradiation well before subsequent thermal events can be initiated. These stress waves, often evolving into shock waves, can be used to disrupt tissue. Shock waves are used in ophthalmology to perform intraocular microsurgery and photodisruptive procedures as well as in lithotripsy to fragment stones. We have explored a variety of transducers that can efficiently convert optical to mechanical energy. One such class of transducers allows a shock wave to be focused within a material such that the stress magnitude can be greatly increased compared to conventional geometries. Some transducer tips could be made to operate regardless of the absorption properties of the ambient media. The size and nature of the devices enable easy delivery, potentially minimally-invasive procedures, and precise tissue- targeting while limiting thermal loading. The transducer tips may have applications in lithotripsy, ophthalmology, drug delivery, and cardiology.
Demonstration of Shear Waves, Lamb Waves, and Rayleigh Waves by Mode Conversion.
ERIC Educational Resources Information Center
Leung, W. P.
1980-01-01
Introduces an experiment that can be demonstrated in the classroom to show that shear waves, Rayleigh waves, and Lamb waves can be easily generated and observed by means of mode conversion. (Author/CS)
Towards Gravitational Wave Astronomy
NASA Astrophysics Data System (ADS)
Losurdo, Giovanni
This chapter is meant to introduce the reader to the forthcoming network of second-generation interferometric detectors of gravitational waves, at a time when their construction is close to completion and there is the ambition to detect gravitational waves for the first time in the next few years and open the way to gravitational wave astronomy. The legacy of first-generation detectors is discussed before giving an overview of the technology challenges that have been faced to make advanced detectors possible. The various aspects outlined here are then discussed in more detail in the subsequent chapters of the book.
Kedziora, David J; Ankiewicz, Adrian; Akhmediev, Nail
2011-11-01
Using the Darboux transformation technique and numerical simulations, we study the hierarchy of rational solutions of the nonlinear Schrödinger equation that can be considered as higher order rogue waves in this model. This analysis reveals the existence of rogue wave clusters with a high level of symmetry in the (x,t) plane. These structures arise naturally when the shifts in the Darboux scheme are taken to be eigenvalue dependent. We have found single-shell structures where a central higher order rogue wave is surrounded by a ring of first order peaks on the (x,t) plane.
Lattice Waves, Spin Waves, and Neutron Scattering
DOE R&D Accomplishments Database
Brockhouse, Bertram N.
1962-03-01
Use of neutron inelastic scattering to study the forces between atoms in solids is treated. One-phonon processes and lattice vibrations are discussed, and experiments that verified the existence of the quantum of lattice vibrations, the phonon, are reviewed. Dispersion curves, phonon frequencies and absorption, and models for dispersion calculations are discussed. Experiments on the crystal dynamics of metals are examined. Dispersion curves are presented and analyzed; theory of lattice dynamics is considered; effects of Fermi surfaces on dispersion curves; electron-phonon interactions, electronic structure influence on lattice vibrations, and phonon lifetimes are explored. The dispersion relation of spin waves in crystals and experiments in which dispersion curves for spin waves in Co-Fe alloy and magnons in magnetite were obtained and the reality of the magnon was demonstrated are discussed. (D.C.W)
Dark- and bright-rogue-wave solutions for media with long-wave-short-wave resonance.
Chen, Shihua; Grelu, Philippe; Soto-Crespo, J M
2014-01-01
Exact explicit rogue-wave solutions of intricate structures are presented for the long-wave-short-wave resonance equation. These vector parametric solutions feature coupled dark- and bright-field counterparts of the Peregrine soliton. Numerical simulations show the robustness of dark and bright rogue waves in spite of the onset of modulational instability. Dark fields originate from the complex interplay between anomalous dispersion and the nonlinearity driven by the coupled long wave. This unusual mechanism, not available in scalar nonlinear wave equation models, can provide a route to the experimental realization of dark rogue waves in, for instance, negative index media or with capillary-gravity waves.
Wave Dissipation and Balance - NOPP Wave Project
2011-09-01
with a common structure , and now estimating the “cumulative term” with the breaking probabilities used for the main dissipation term. This has led to a...captured by the new parameterizations, but that will require the analysis of more detailed measurement campaigns Ardhuin et al. (2011b). These result have...much more flat bias as a function of wave height (figure 1). A detailed case study of the February 2011 storm Quirin, in the North Atlantic, has shown
Measurement of high frequency waves using a wave follower
NASA Technical Reports Server (NTRS)
Tang, S.; Shemdin, O. H.
1983-01-01
High frequency waves were measured using a laser-optical sensor mounted on a wave follower. Measured down-wind wave slope spectra are shown to be wind speed dependent; the mean square wave-slopes are generally larger than those measured by Cox and Munk (1954) using the sun glitter method.
Resonance wave pumping with surface waves
NASA Astrophysics Data System (ADS)
Carmigniani, Remi; Gharib, Morteza; Violeau, Damien; Caltech-ENPC Collaboration
2015-11-01
The valveless impedance pump enables the production or amplification of a flow without the use of integrated mobile parts, thus delaying possible failures. It is usually composed of fluid-filled flexible tubing, closed by solid tubes. The flexible tube is pinched at an off-centered position relative to the tube ends. This generates a complex wave dynamic that results in a pumping phenomenon. It has been previously reported that pinching at intrinsic resonance frequencies of the system results in a strong pulsating flow. A case of a free surface wave pump is investigated. The resonance wave pump is composed of a rectangular tank with a submerged plate separating the water into a free surface and a recirculation rectangular section connected through two openings at each end of the tank. A paddle placed at an off-center position above the submerged plate is controlled in a heaving motion with different frequencies and amplitudes. Similar to the case of valveless impedance pump, we observed that near resonance frequencies strong pulsating flow is generated with almost no oscillations. A linear theory is developed to pseudo-analytically evaluate these frequencies. In addition, larger scale applications were simulated using Smoothed Particle Hydrodynamic codes.
Hietala, Vincent M.; Vawter, Gregory A.
1993-01-01
The traveling-wave photodetector of the present invention combines an absorptive optical waveguide and an electrical transmission line, in which optical absorption in the waveguide results in a photocurrent at the electrodes of the electrical transmission line. The optical waveguide and electrical transmission line of the electrically distributed traveling-wave photodetector are designed to achieve matched velocities between the light in the optical waveguide and electrical signal generated on the transmission line. This velocity synchronization provides the traveling-wave photodetector with a large electrical bandwidth and a high quantum efficiency, because of the effective extended volume for optical absorption. The traveling-wave photodetector also provides large power dissipation, because of its large physical size.
Hietala, V.M.; Vawter, G.A.
1993-12-14
The traveling-wave photodetector of the present invention combines an absorptive optical waveguide and an electrical transmission line, in which optical absorption in the waveguide results in a photocurrent at the electrodes of the electrical transmission line. The optical waveguide and electrical transmission line of the electrically distributed traveling-wave photodetector are designed to achieve matched velocities between the light in the optical waveguide and electrical signal generated on the transmission line. This velocity synchronization provides the traveling-wave photodetector with a large electrical bandwidth and a high quantum efficiency, because of the effective extended volume for optical absorption. The traveling-wave photodetector also provides large power dissipation, because of its large physical size. 4 figures.
Turbulence generation by waves
Kaftori, D.; Nan, X.S.; Banerjee, S.
1995-12-31
The interaction between two-dimensional mechanically generated waves, and a turbulent stream was investigated experimentally in a horizontal channel, using a 3-D LDA synchronized with a surface position measuring device and a micro-bubble tracers flow visualization with high speed video. Results show that although the wave induced orbital motion reached all the way to the wall, the characteristics of the turbulence wall structures and the turbulence intensity close to the wall were not altered. Nor was the streaky nature of the wall layer. On the other hand, the mean velocity profile became more uniform and the mean friction velocity was increased. Close to the free surface, the turbulence intensity was substantially increased as well. Even in predominantly laminar flows, the introduction of 2-D waves causes three dimensional turbulence. The turbulence enhancement is found to be proportional to the wave strength.
... heat has caused more deaths than all other weather events, including floods. A heat wave is a ... care for heat- related emergencies … ❏ Listen to local weather forecasts and stay aware of upcoming temperature changes. ❏ ...
Nonlinear thermal surface waves
NASA Astrophysics Data System (ADS)
Gradov, O. M.; Stenflo, L.
1984-09-01
It is shown that density profile modifications near a plasma surface can survive at moving localized spots because of the radiation pressure of leaking wave field fluctuations. The properties of these luminous surface cavitons are studied.
Weinstein, Alla
2011-11-01
Presentation from the 2011 Water Peer Review includes in which principal investigator Alla Weinstein discusses project progress in development of a floating offshore wind structure - the WindFloat - and incorporation therin of a Spherical Wave Energy Device.
Magnetoresistive waves in plasmas
NASA Astrophysics Data System (ADS)
Felber, F. S.; Hunter, R. O., Jr.; Pereira, N. R.; Tajima, T.
1982-10-01
The self-generated magnetic field of a current diffusing into a plasma between conductors can magnetically insulate the plasma. Propagation of magnetoresistive waves in plasmas is analyzed. Applications to plasma opening switches are discussed.
Sound wave transmission (image)
When sounds waves reach the ear, they are translated into nerve impulses. These impulses then travel to the brain where they are interpreted by the brain as sound. The hearing mechanisms within the inner ear, can ...
ERIC Educational Resources Information Center
Fisher, Arthur
1983-01-01
Physicists and engineers advance the state of several arts in the design of gravitational-wave detection equipment. Provides background information and discusses the equipment (including laser interferometer), its use, and results of several experimental studies. (JN)
2016-06-07
to breaking waves described using the roller concept (Lippmann and Thornton, 1999), alongshore wind stress, cross-shore advection of mean momentum of...Lippmann and Thornton, 1999), and O[10] percent improvement by including the momentum mixing by the advection of the longshore current momentum by the mean...process modeling of breaking waves, momentum mixing due to the interaction of longshore and cross-shore vertical mean profiles, and bottom shear stress
NASA Astrophysics Data System (ADS)
López Ariste, A.; Centeno, R.; Khomenko, E.
2016-06-01
Context. Waves in the magnetized solar atmosphere are one of the favourite means of transferring and depositing energy into the solar corona. The study of waves brings information not just on the dynamics of the magnetized plasma, but also on the possible ways in which the corona is heated. Aims: The identification and analysis of the phase singularities or dislocations provide us with a complementary approach to the magnetoacoustic and Aflvén waves propagating in the solar atmosphere. They allow us to identify individual wave modes, shedding light on the probability of excitation or the nature of the triggering mechanism. Methods: We use a time series of Doppler shifts measured in two spectral lines, filtered around the three-minute period region. The data show a propagating magnetoacoustic slow mode with several dislocations and, in particular, a vortex line. We study under what conditions the different wave modes propagating in the umbra can generate the observed dislocations. Results: The observed dislocations can be fully interpreted as a sequence of sausage and kink modes excited sequentially on average during 15 min. Kink and sausage modes appear to be excited independently and sequentially. The transition from one to the other lasts less than three minutes. During the transition we observe and model the appearance of superoscillations inducing large phase gradients and phase mixing. Conclusions: The analysis of the observed wave dislocations leads us to the identification of the propagating wave modes in umbrae. The identification in the data of superoscillatory regions during the transition from one mode to the other may be an important indicator of the location of wave dissipation.
Sound Waves Levitate Substrates
NASA Technical Reports Server (NTRS)
Lee, M. C.; Wang, T. G.
1982-01-01
System recently tested uses acoustic waves to levitate liquid drops, millimeter-sized glass microballoons, and other objects for coating by vapor deposition or capillary attraction. Cylindrical contactless coating/handling facility employs a cylindrical acoustic focusing radiator and a tapered reflector to generate a specially-shaped standing wave pattern. Article to be processed is captured by the acoustic force field under the reflector and moves as reflector is moved to different work stations.
1989-09-01
components of the total velocity field, negligible measurement noise, and a completely linear wave field. Yefimov and Khristoforov (1971) have investigated...The directional spreading of the real wave field must also be considered ([82] and [3]). Yefimov and Khristoforov concluded that the spectrum of the...different. As observed by Yefimov and Khristoforov the upper linit of high coherence decreased with increasing depth (Figure 9). The horizontal
McCandless, Kathleen; Petersson, Anders; Nilsson, Stefan; Sjogreen, Bjorn
2007-01-08
WPP is a massively parallel, 3D, C++, finite-difference elastodynamic wave propagation code. Typical applications for wave propagation with WPP include: evaluation of seismic event scenarios and damage from earthquakes, non-destructive evaluation of materials, underground facility detection, oil and gas exploration, predicting the electro-magnetic fields in accelerators, and acoustic noise generation. For more information, see Users Manual [1].
2014-10-27
Studies (WIS), Coastal Data Information Program (CDIP), Great Lakes Observing System (GLOS), Great Lakes Coastal Forecasting System (GLCFS), and...Army Engineer Research and Development Center,CIRP - The Coastal Inlets Research Program,3909 Halls Ferry Road,Vicksburg,MS,39180 8. PERFORMING... Coastal Inlets Research Program WaveNet WaveNet is a web-based, Graphical-User-Interface (GUI) data management tool developed for the Corps’ coastal
Millimeter Wave Nonreciprocal Devices.
1983-01-03
gradients of the dc bias field saturation magnetization , or magnetic anisotrophy can control mode properties of magnetostatic waves (MSW) propagating in...measures microwave magnetic field patterns of magnetostatic waves in LPE- YIG thin films has been developed. The probe’s sensing element is either a... magnetic resonance mode of a YIG sphere. Theoretical analyses show that there is a critical ratio between the -4-Ai p. , , . , l!~ mj radius of the
Périnet, Nicolas; Falcón, Claudio; Chergui, Jalel; Juric, Damir; Shin, Seungwon
2016-06-01
We report on the numerical and theoretical study of the subcritical bifurcation of parametrically amplified waves appearing at the interface between two immiscible incompressible fluids when the layer of the lower fluid is very shallow. As a critical control parameter is surpassed, small amplitude surface waves bifurcate subcritically toward highly nonlinear ones with twice their amplitude. We relate this hysteresis with the change of shear stress using a simple stress balance, in agreement with numerical results.
Ultrasonic Lamb wave tomography
NASA Astrophysics Data System (ADS)
Leonard, Kevin R.; Malyarenko, Eugene V.; Hinders, Mark K.
2002-12-01
Nondestructive evaluation (NDE) of aerospace structures using traditional methods is a complex, time-consuming process critical to maintaining mission readiness and flight safety. Limited access to corrosion-prone structure and the restricted applicability of available NDE techniques for the detection of hidden corrosion or other damage often compound the challenge. In this paper we discuss our recent work using ultrasonic Lamb wave tomography to address this pressing NDE technology need. Lamb waves are ultrasonic guided waves, which allow large sections of aircraft structures to be rapidly inspected for structural flaws such as disbonds, corrosion and delaminations. Because the velocity of Lamb waves depends on thickness, for example, the travel times of the fundamental Lamb modes can be converted into a thickness map of the inspection region. However, extracting quantitative information from Lamb wave data has always involved highly trained personnel with a detailed knowledge of mechanical waveguide physics. Our work focuses on tomographic reconstruction to produce quantitative maps that can be easily interpreted by technicians or fed directly into structural integrity and lifetime prediction codes. Laboratory measurements discussed here demonstrate that Lamb wave tomography using a square perimeter array of transducers with algebraic reconstruction tomography is appropriate for detecting flaws in aircraft materials. The speed and fidelity of the reconstruction algorithms as well as practical considerations for person-portable array-based systems are discussed in this paper.
NASA Technical Reports Server (NTRS)
Kory, Carol L.
1998-01-01
The traveling-wave tube (TWT) is a vacuum device invented in the early 1940's used for amplification at microwave frequencies. Amplification is attained by surrendering kinetic energy from an electron beam to a radio frequency (RF) electromagnetic wave. The demand for vacuum devices has been decreased largely by the advent of solid-state devices. However, although solid state devices have replaced vacuum devices in many areas, there are still many applications such as radar, electronic countermeasures and satellite communications, that require operating characteristics such as high power (Watts to Megawatts), high frequency (below 1 GHz to over 100 GHz) and large bandwidth that only vacuum devices can provide. Vacuum devices are also deemed irreplaceable in the music industry where musicians treasure their tube-based amplifiers claiming that the solid-state and digital counterparts could never provide the same "warmth" (3). The term traveling-wave tube includes both fast-wave and slow-wave devices. This article will concentrate on slow-wave devices as the vast majority of TWTs in operation fall into this category.
Ocean wave electric generators
Rosenberg, H.R.
1986-02-04
This patent describes an apparatus for generating electricity from ocean waves. It consists of: 1.) a hollow buoyant duck positioned in the path of waves including a core about the center axis of which the duck rotates, a lower chamber portion having liquid therein and an upper chamber portion having air therein. The air is alternately compressed and expanded by the liquid in the chamber during the rotational motion of the duck caused by waves. A turbine mounted in the upper portion of the duck is driven by the compressed and expanded air. A generator is coupled to the turbine and operated to produce electrical energy and an air bulb; 2.) a spine having a transverse axial shaft anchoring the spine to the ocean floor. The upper portion of the spine engages the duck to maintain the duck in position. The spine has a curved configuration to concentrate and direct wave energy. The spine configuration acts as a scoop to increase the height of wave peaks and as a foil to increase the depth of wave troughs.
NASA Astrophysics Data System (ADS)
Kağan Temiz, Burak; Yavuz, Ahmet
2015-08-01
This study was done to develop a simple and inexpensive wave driver that can be used in experiments on string waves. The wave driver was made using a battery-operated toy car, and the apparatus can be used to produce string waves at a fixed frequency. The working principle of the apparatus is as follows: shortly after the car is turned on, the wheel starts to turn at a constant angular speed. A rod that is fixed on the wheel turns at the same constant angular speed, too. A tight string that the wave will be created on is placed at a distance where the rod can touch the string. During each rotation of the wheel, the rod vibrates the string up and down. The vibration frequency of this rod equals the wheel’s rotation frequency, and this frequency value can be measured easily with a small magnet and a bicycle speedometer. In this way, the frequency of the waves formed in the rope can also be measured.
NASA Astrophysics Data System (ADS)
Conklin, John
2016-03-01
With the expected direct detection of gravitational waves by Advanced LIGO and pulsar timing arrays in the near future, and with the recent launch of LISA Pathfinder this can arguably be called the decade of gravitational waves. Low frequency gravitational waves in the mHz range, which can only be observed from space, provide the richest science and complement high frequency observatories on the ground. A space-based observatory will improve our understanding of the formation and growth of massive black holes, create a census of compact binary systems in the Milky Way, test general relativity in extreme conditions, and enable searches for new physics. LISA, by far the most mature concept for detecting gravitational waves from space, has consistently ranked among the nation's top priority large science missions. In 2013, ESA selected the science theme ``The Gravitational Universe'' for its third large mission, L3, under the Cosmic Visions Program, with a planned launch date of 2034. NASA has decided to join with ESA on the L3 mission as a junior partner and has recently assembled a study team to provide advice on how NASA might contribute to the European-led mission. This talk will describe these efforts and the activities of the Gravitational Wave Science Interest Group and the L3 Study Team, which will lead to the first space-based gravitational wave observatory.
Wave Momentum Flux Parameter: A Descriptor for Nearshore Waves
2004-07-16
characterizing the wave nonlinearity. D 2004 Elsevier B.V. All rights reserved. Keywords: Coastal structures; Iribarren number; Nonlinear waves; Solitary...Local Iribarren number, n tanaffiffiffiffiffiffi H=L p Deepwater Iribarren number, no tanaffiffiffiffiffiffiffiffiffi Ho=Lo p or...solitary waves, although there are some definitions for solitary wave length which would allow use of the other wave parameters.2. The Iribarren number One
Rain waves-wind waves interaction application to scatterometry
NASA Technical Reports Server (NTRS)
Kharif, C.; Giovanangeli, J. P.; Bliven, L.
1989-01-01
Modulation of a rain wave pattern by longer waves has been studied. An analytical model taking into account capillarity effects and obliquity of short waves has been developed. Modulation rates in wave number and amplitude have been computed. Experiments were carried out in a wave tank. First results agree with theoretical models, but higher values of modulation rates are measured. These results could be taken into account for understanding the radar response from the sea surface during rain.
Invariants of 4-wave interactions
NASA Astrophysics Data System (ADS)
Balk, A.; Ferapontov, E.
1993-05-01
We give a complete description of one-dimensional 4-wave resonance interactions in which some extra quantities (besides momentum, energy, number of quasiparticles) are conserved. In this way we obtain new consideration laws for the kinetic equations for waves. In particular, we consider waves in optical fibers, the system of four resonantly interacting wave packets, long wave interactions of annihilation-creation type, various wave systems with quadratic dispersion laws. The results can be important for various problems concerning nonlinear wave dynamics, e.g. for nonlinear optics of waveguides.
Raychaudhuri equation in the self-consistent Einstein-Cartan theory with spin-density
NASA Technical Reports Server (NTRS)
Fennelly, A. J.; Krisch, Jean P.; Ray, John R.; Smalley, Larry L.
1988-01-01
The physical implications of the Raychaudhuri equation for a spinning fluid in a Riemann-Cartan spacetime is developed and discussed using the self-consistent Lagrangian based formulation for the Einstein-Cartan theory. It was found that the spin-squared terms contribute to expansion (inflation) at early times and may lead to a bounce in the final collapse. The relationship between the fluid's vorticity and spin angular velocity is clarified and the effect of the interaction terms between the spin angular velocity and the spin in the Raychaudhuri equation investigated. These results should prove useful for studies of systems with an intrinsic spin angular momentum in extreme astrophysical or cosmological problems.
Spin densities for Ni, Pt_3Cr, and Pd_3Cr
NASA Astrophysics Data System (ADS)
Chau, Hung T.; Lu, Z. W.; Klein, Barry M.
1997-03-01
Recent ab-initio calculations^1 demonstrated that the L12 ordering in Pt_3Cr is a direct consequence of spin-polarization, i.e., magnetic moment formation in the L12 structure stabilizes it over its rival DO_22 structure (which is more stable in a non magnetic calculation). Here we present calculations of the magnetic structures of Pt_3Cr and Pd_3Cr in the L12 structure. We use fcc Ni calculations as a benchmark system since its magnetic structure has been well studied experimentally and theoretically. Our LSDA-calculated Ni magnetic structure factors are in good accord with experiment as well as with previous theoretical results. Our calculated magnetic structure factors for Pt_3Cr are in fair agreement with experiment.^2 The calculated local magnetic moment at the Pt site ( ~ 0) differs somewhat from the early experimental estimate of -0.27 μB ^2 but is, however, closer to the recent circular X-ray dichroism experimental value^3 of -0.1 μ_B. We also find that the contribution of the orbital polarization to the Pt-site local moment is negligible. We will also show magnetic structure factors of Pd_3Cr in the L12 structure, for which no experimental data are yet available for comparison. Work supported by a grant from Sandia National Laboratories ^1Z. W. Lu, B. M. Klein, A. Zunger, Phys. Rev. Lett. 75, 1320 (1995). ^2S. K. Burke, et al., J. of Magn. Magn. Mat. 15, 505 (1980). ^3H. Maruyama, et al, J. of Magn. Magn. Mat. 140, 43 (1995).
Optical Polarization Möbius Strips and Points of Purely Transverse Spin Density
NASA Astrophysics Data System (ADS)
Bauer, Thomas; Neugebauer, Martin; Leuchs, Gerd; Banzer, Peter
2016-07-01
Tightly focused light beams can exhibit complex and versatile structured electric field distributions. The local field may spin around any axis including a transverse axis perpendicular to the beams' propagation direction. At certain focal positions, the corresponding local polarization ellipse can even degenerate into a perfect circle, representing a point of circular polarization or C point. We consider the most fundamental case of a linearly polarized Gaussian beam, where—upon tight focusing—those C points created by transversely spinning fields can form the center of 3D optical polarization topologies when choosing the plane of observation appropriately. Because of the high symmetry of the focal field, these polarization topologies exhibit nontrivial structures similar to Möbius strips. We use a direct physical measure to find C points with an arbitrarily oriented spinning axis of the electric field and experimentally investigate the fully three-dimensional polarization topologies surrounding these C points by exploiting an amplitude and phase reconstruction technique.
Optical Polarization Möbius Strips and Points of Purely Transverse Spin Density.
Bauer, Thomas; Neugebauer, Martin; Leuchs, Gerd; Banzer, Peter
2016-07-01
Tightly focused light beams can exhibit complex and versatile structured electric field distributions. The local field may spin around any axis including a transverse axis perpendicular to the beams' propagation direction. At certain focal positions, the corresponding local polarization ellipse can even degenerate into a perfect circle, representing a point of circular polarization or C point. We consider the most fundamental case of a linearly polarized Gaussian beam, where-upon tight focusing-those C points created by transversely spinning fields can form the center of 3D optical polarization topologies when choosing the plane of observation appropriately. Because of the high symmetry of the focal field, these polarization topologies exhibit nontrivial structures similar to Möbius strips. We use a direct physical measure to find C points with an arbitrarily oriented spinning axis of the electric field and experimentally investigate the fully three-dimensional polarization topologies surrounding these C points by exploiting an amplitude and phase reconstruction technique.
Longitudinal shear wave and transverse dilatational wave in solids.
Catheline, S; Benech, N
2015-02-01
Dilatation wave involves compression and extension and is known as the curl-free solution of the elastodynamic equation. Shear wave on the contrary does not involve any change in volume and is the divergence-free solution. This letter seeks to examine the elastodynamic Green's function through this definition. By separating the Green's function in divergence-free and curl-free terms, it appears first that, strictly speaking, the longitudinal wave is not a pure dilatation wave and the transverse wave is neither a pure shear wave. Second, not only a longitudinal shear wave but also a transverse dilatational wave exists. These waves are shown to be a part of the solution known as coupling terms. Their special motion is carefully described and illustrated.
Reflection and Refraction of Acoustic Waves by a Shock Wave
NASA Technical Reports Server (NTRS)
Brillouin, J.
1957-01-01
The presence of sound waves in one or the other of the fluid regions on either side of a shock wave is made apparent, in the region under superpressure, by acoustic waves (reflected or refracted according to whether the incident waves lie in the region of superpressure or of subpressure) and by thermal waves. The characteristics of these waves are calculated for a plane, progressive, and uniform incident wave. In the case of refraction, the refracted acoustic wave can, according to the incidence, be plane, progressive, and uniform or take the form of an 'accompanying wave' which remains attached to the front of the shock while sliding parallel to it. In all cases, geometrical constructions permit determination of the kinematic characteristics of the reflected or refractive acoustic waves. The dynamic relationships show that the amplitude of the reflected wave is always less than that of the incident wave. The amplitude of the refracted wave, whatever its type, may in certain cases be greater than that of the incident wave.
Potential changes of wave steepness and occurrence of rogue waves
NASA Astrophysics Data System (ADS)
Bitner-Gregersen, Elzbieta M.; Toffoli, Alessandro
2015-04-01
Wave steepness is an important characteristic of a sea state. It is also well established that wave steepness is one of the parameter responsible for generation of abnormal waves called also freak or rogue waves. The study investigates changes of wave steepness in the past and future wave climate in the North Atlantic. The fifth assessment report IPCC (2013) uses four scenarios for future greenhouse gas concentrations in the atmosphere called Representative Concentration Pathways (RCP). Two of these scenarios RCP 4.5 and RCP 8.5 have been selected to project future wave conditions in the North Atlantic. RCP 4.5 is believed to achieve the political target of a maximum global mean temperature increase of 2° C while RPC 8.5 is close to 'business as usual' and expected to give a temperature increase of 4° C or more. The analysis includes total sea, wind sea and swell. Potential changes of wave steepness for these wave systems are shown and compared with wave steepness derived from historical data. Three historical data sets with different wave model resolutions are used. The investigations show also changes in the mean wind direction as well as in the relative direction between wind sea and swell. Consequences of wave steepness changes for statistics of surface elevation and generation of rogue waves are demonstrated. Uncertainties associated with wave steepness projections are discussed.
NASA Astrophysics Data System (ADS)
Frisquet, Benoit; Kibler, Bertrand; Morin, Philippe; Baronio, Fabio; Conforti, Matteo; Millot, Guy; Wabnitz, Stefan
2016-02-01
Photonics enables to develop simple lab experiments that mimic water rogue wave generation phenomena, as well as relativistic gravitational effects such as event horizons, gravitational lensing and Hawking radiation. The basis for analog gravity experiments is light propagation through an effective moving medium obtained via the nonlinear response of the material. So far, analogue gravity kinematics was reproduced in scalar optical wave propagation test models. Multimode and spatiotemporal nonlinear interactions exhibit a rich spectrum of excitations, which may substantially expand the range of rogue wave phenomena, and lead to novel space-time analogies, for example with multi-particle interactions. By injecting two colliding and modulated pumps with orthogonal states of polarization in a randomly birefringent telecommunication optical fiber, we provide the first experimental demonstration of an optical dark rogue wave. We also introduce the concept of multi-component analog gravity, whereby localized spatiotemporal horizons are associated with the dark rogue wave solution of the two-component nonlinear Schrödinger system.
Hurricane, O A; Hammer, J H
2005-10-11
Radiation driven heat waves (Marshak Waves) are ubiquitous in astrophysics and terrestrial laser driven high energy density plasma physics (HEDP) experiments. Generally, the equations describing Marshak waves are so nonlinear, that solutions involving more than one spatial dimension require simulation. However, in this paper we show how one may analytically solve the problem of the two-dimensional nonlinear evolution of a Marshak wave, bounded by lossy walls, using an asymptotic expansion in a parameter related to the wall albedo and a simplification of the heat front equation of motion. Three parameters determine the nonlinear evolution, a modified Markshak diffusion constant, a smallness parameter related to the wall albedo, and the spacing of the walls. The final nonlinear solution shows that the Marshak wave will be both slowed and bent by the non-ideal boundary. In the limit of a perfect boundary, the solution recovers the original diffusion-like solution of Marshak. The analytic solution will be compared to a limited set of simulation results and experimental data.
Frisquet, Benoit; Kibler, Bertrand; Morin, Philippe; Baronio, Fabio; Conforti, Matteo; Millot, Guy; Wabnitz, Stefan
2016-02-11
Photonics enables to develop simple lab experiments that mimic water rogue wave generation phenomena, as well as relativistic gravitational effects such as event horizons, gravitational lensing and Hawking radiation. The basis for analog gravity experiments is light propagation through an effective moving medium obtained via the nonlinear response of the material. So far, analogue gravity kinematics was reproduced in scalar optical wave propagation test models. Multimode and spatiotemporal nonlinear interactions exhibit a rich spectrum of excitations, which may substantially expand the range of rogue wave phenomena, and lead to novel space-time analogies, for example with multi-particle interactions. By injecting two colliding and modulated pumps with orthogonal states of polarization in a randomly birefringent telecommunication optical fiber, we provide the first experimental demonstration of an optical dark rogue wave. We also introduce the concept of multi-component analog gravity, whereby localized spatiotemporal horizons are associated with the dark rogue wave solution of the two-component nonlinear Schrödinger system.
NASA Astrophysics Data System (ADS)
McGourty, L.; Rideout, K.
2005-12-01
"Waves in Motion" This teaching unit was created by Leslie McGourty and Ken Rideout under the Research Experience for Teachers (RET) program at MIT Haystack Observatory during the summer of 2005. The RET program is funded by a grant from the National Science Foundation. The goals of this teaching unit are to deepen students' understanding about waves, wave motion, and the electromagnetic spectrum as a whole. Specifically students will comprehend the role radio waves play in our daily lives and in the investigation of the universe. The lessons can be used in a high school physics, earth science or astronomy curriculum. The unit consists of a series of interlocking lectures, activities, and investigations that can be used as stand alone units to supplement a teacher's existing curriculum, as an independent investigation for a student, or as a long exploration into radio astronomy with a theme of waves in space: how and where they carry their information. Special emphasis is given to the Relativity theories in honor of the "World Year of Physics" to celebrate Einstein's 1905 contributions. The lessons are currently being implemented at the high school level, the preliminary results of which will be presented. At the end of the academic year, the units will be evaluated and updated, reflecting student input and peer review after which they will be posted on the internet for teachers to use in their classrooms.
Rupture, waves and earthquakes.
Uenishi, Koji
2017-01-01
Normally, an earthquake is considered as a phenomenon of wave energy radiation by rupture (fracture) of solid Earth. However, the physics of dynamic process around seismic sources, which may play a crucial role in the occurrence of earthquakes and generation of strong waves, has not been fully understood yet. Instead, much of former investigation in seismology evaluated earthquake characteristics in terms of kinematics that does not directly treat such dynamic aspects and usually excludes the influence of high-frequency wave components over 1 Hz. There are countless valuable research outcomes obtained through this kinematics-based approach, but "extraordinary" phenomena that are difficult to be explained by this conventional description have been found, for instance, on the occasion of the 1995 Hyogo-ken Nanbu, Japan, earthquake, and more detailed study on rupture and wave dynamics, namely, possible mechanical characteristics of (1) rupture development around seismic sources, (2) earthquake-induced structural failures and (3) wave interaction that connects rupture (1) and failures (2), would be indispensable.
Frisquet, Benoit; Kibler, Bertrand; Morin, Philippe; Baronio, Fabio; Conforti, Matteo; Millot, Guy; Wabnitz, Stefan
2016-01-01
Photonics enables to develop simple lab experiments that mimic water rogue wave generation phenomena, as well as relativistic gravitational effects such as event horizons, gravitational lensing and Hawking radiation. The basis for analog gravity experiments is light propagation through an effective moving medium obtained via the nonlinear response of the material. So far, analogue gravity kinematics was reproduced in scalar optical wave propagation test models. Multimode and spatiotemporal nonlinear interactions exhibit a rich spectrum of excitations, which may substantially expand the range of rogue wave phenomena, and lead to novel space-time analogies, for example with multi-particle interactions. By injecting two colliding and modulated pumps with orthogonal states of polarization in a randomly birefringent telecommunication optical fiber, we provide the first experimental demonstration of an optical dark rogue wave. We also introduce the concept of multi-component analog gravity, whereby localized spatiotemporal horizons are associated with the dark rogue wave solution of the two-component nonlinear Schrödinger system. PMID:26864099
Rupture, waves and earthquakes
NASA Astrophysics Data System (ADS)
Uenishi, Koji
2017-01-01
Normally, an earthquake is considered as a phenomenon of wave energy radiation by rupture (fracture) of solid Earth. However, the physics of dynamic process around seismic sources, which may play a crucial role in the occurrence of earthquakes and generation of strong waves, has not been fully understood yet. Instead, much of former investigation in seismology evaluated earthquake characteristics in terms of kinematics that does not directly treat such dynamic aspects and usually excludes the influence of high-frequency wave components over 1 Hz. There are countless valuable research outcomes obtained through this kinematics-based approach, but "extraordinary" phenomena that are difficult to be explained by this conventional description have been found, for instance, on the occasion of the 1995 Hyogo-ken Nanbu, Japan, earthquake, and more detailed study on rupture and wave dynamics, namely, possible mechanical characteristics of (1) rupture development around seismic sources, (2) earthquake-induced structural failures and (3) wave interaction that connects rupture (1) and failures (2), would be indispensable.
NASA Astrophysics Data System (ADS)
Goree, J.; Ono, M.; Colestock, P.; Horton, R.; McNeill, D.; Park, H.
1985-07-01
Experiments on the fast wave in the range of high ion cyclotron harmonics in the ACT-1 device show that current drive is possible with the fast wave just as it is for the lower hybrid wave, except that it is suitable for higher plasma densities. A 140° loop antenna launched the high ion cyclotron harmonic fast wave [ω/Ω=O(10)] into a He+ plasma with ne≂4×1012 cm-3 and B=4.5 kG. Probe and magnetic loop diagnostics and FIR laser scattering confirmed the presence of the fast wave, and the Rogowski loop indicated that the circulating plasma current increased by up to 40A with 1 kW of coupled power, which is comparable to lower hybrid current drive in the same device with the same unidirectional fast electron beam used as the target for the rf. A phased antenna array would be used for FWCD in a tokamak without the E-beam.
NASA Astrophysics Data System (ADS)
Bush, John W. M.
2015-01-01
Yves Couder, Emmanuel Fort, and coworkers recently discovered that a millimetric droplet sustained on the surface of a vibrating fluid bath may self-propel through a resonant interaction with its own wave field. This article reviews experimental evidence indicating that the walking droplets exhibit certain features previously thought to be exclusive to the microscopic, quantum realm. It then reviews theoretical descriptions of this hydrodynamic pilot-wave system that yield insight into the origins of its quantum-like behavior. Quantization arises from the dynamic constraint imposed on the droplet by its pilot-wave field, and multimodal statistics appear to be a feature of chaotic pilot-wave dynamics. I attempt to assess the potential and limitations of this hydrodynamic system as a quantum analog. This fluid system is compared to quantum pilot-wave theories, shown to be markedly different from Bohmian mechanics and more closely related to de Broglie's original conception of quantum dynamics, his double-solution theory, and its relatively recent extensions through researchers in stochastic electrodynamics.
NASA Astrophysics Data System (ADS)
McNutt, David; Milson, Robert; Coley, Alan
2013-03-01
We discuss the invariant classification of vacuum Kundt waves using the Cartan-Karlhede algorithm and determine the upper bound on the number of iterations of the Karlhede algorithm to classify the vacuum Kundt waves (Collins (1991 Class. Quantum Grav. 8 1859-69), Machado Ramos (1996 Class. Quantum Grav. 13 1589)). By choosing a particular coordinate system we partially construct the canonical coframe used in the classification to study the functional dependence of the invariants arising at each iteration of the algorithm. We provide a new upper bound, q ⩽ 4, and show that this bound is sharp by analyzing the subclass of Kundt waves with invariant count beginning with (0, 1,…) to show that the class with invariant count (0, 1, 3, 4, 4) exists. This class of vacuum Kundt waves is shown to be unique as the only set of metrics requiring the fourth covariant derivatives of the curvature. We conclude with an invariant classification of the vacuum Kundt waves using a suite of invariants.
Tango waves in a bidomain model of fertilization calcium waves
NASA Astrophysics Data System (ADS)
Li, Yue-Xian
2003-12-01
Fertilization of an egg cell is marked by one or several Ca 2+ waves that travel across the intra-cellular space, called fertilization Ca 2+ waves. Patterns of Ca 2+ waves observed in mature or immature oocytes include traveling fronts and pulses as well as concentric and spiral waves. These patterns have been studied in other excitable media in physical, chemical, and biological systems. Here, we report the discovery of a new wave phenomenon in the numerical study of a bidomain model of fertilization Ca 2+ waves. This wave is a front that propagates in a back-and-forth manner that resembles the movement of tango dancers, thus is called a tango wave. When the medium is excitable, a forward-moving tango wave can generate traveling pulses that propagate down the space without reversal. The study shows that the occurrence of tango waves is related to spatial inhomogeneity in the local dynamics. This is tested and confirmed by simulating similar waves in a medium with stationary spatial inhomogeneity. Similar waves are also obtained in a FitzHugh-Nagumo system with a linear spatial ramp. In both the bidomain model of Ca 2+ waves and the FitzHugh-Nagumo system, the front is stable when the slope of a linear ramp is large. As the slope decreases beyond a critical value, front oscillations occur. The study shows that tango waves facilitate the dispersion of localized Ca 2+. Key features of the bidomain model underlying the occurrence of tango waves are revealed. These features are commonly found in egg cells of a variety of species. Thus, we predict that tango waves can occur in real egg cells provided that a slowly varying inhomogeneity does occur following the sperm entry. The observation of tango wave-like waves in nemertean worm and ascidian eggs seems to support such a prediction.
Neural field theory of nonlinear wave-wave and wave-neuron processes
NASA Astrophysics Data System (ADS)
Robinson, P. A.; Roy, N.
2015-06-01
Systematic expansion of neural field theory equations in terms of nonlinear response functions is carried out to enable a wide variety of nonlinear wave-wave and wave-neuron processes to be treated systematically in systems involving multiple neural populations. The results are illustrated by analyzing second-harmonic generation, and they can also be applied to wave-wave coalescence, multiharmonic generation, facilitation, depression, refractoriness, and other nonlinear processes.
Graham, T. B.
2010-04-01
The IR Hot Wave{trademark} furnace is a breakthrough heat treatment system for manufacturing metal components. Near-infrared (IR) radiant energy combines with IR convective heating for heat treating. Heat treatment is an essential process in the manufacture of most components. The controlled heating and cooling of a metal or metal alloy alters its physical, mechanical, and sometimes chemical properties without changing the object's shape. The IR Hot Wave{trademark} furnace offers the simplest, quickest, most efficient, and cost-effective heat treatment option for metals and metal alloys. Compared with other heat treatment alternatives, the IR Hot Wave{trademark} system: (1) is 3 to 15 times faster; (2) is 2 to 3 times more energy efficient; (3) is 20% to 50% more cost-effective; (4) has a {+-}1 C thermal profile compared to a {+-}10 C thermal profile for conventional gas furnaces; and (5) has a 25% to 50% smaller footprint.
Lucas, Timothy S.
1991-01-01
A compressor for compression-evaporation cooling systems, which requires no moving parts. A gaseous refrigerant inside a chamber is acoustically compressed and conveyed by means of a standing acoustic wave which is set up in the gaseous refrigerant. This standing acoustic wave can be driven either by a transducer, or by direct exposure of the gas to microwave and infrared sources, including solar energy. Input and output ports arranged along the chamber provide for the intake and discharge of the gaseous refrigerant. These ports can be provided with optional valve arrangements, so as to increase the compressor's pressure differential. The performance of the compressor in either of its transducer or electromagnetically driven configurations, can be optimized by a controlling circuit. This controlling circuit holds the wavelength of the standing acoustical wave constant, by changing the driving frequency in response to varying operating conditions.
Tuck, J.L.
1955-03-01
This patent relates to means for ascertaining the instant of arrival of a shock wave in an exploslve charge and apparatus utilizing this means to coordinate the timing of two operations involving a short lnterval of time. A pair of spaced electrodes are inserted along the line of an explosive train with a voltage applied there-across which is insufficient to cause discharge. When it is desired to initiate operation of a device at the time the explosive shock wave reaches a particular point on the explosive line, the device having an inherent time delay, the electrodes are located ahead of the point such that the ionization of the area between the electrodes caused by the traveling explosive shock wave sends a signal to initiate operation of the device to cause it to operate at the proper time. The operated device may be photographic equipment consisting of an x-ray illuminating tube.
NASA Astrophysics Data System (ADS)
Périnet, Nicolas; Falcón, Claudio; Chergui, Jalel; Shin, Seungwon; Juric, Damir
2016-11-01
We study with numerical simulations the two-dimensional Faraday waves in two immiscible incompressible fluids when the lower fluid layer is shallow. After the appearance of the well known subharmonic stationary waves, a further instability is observed while the control parameter passes a secondary threshold. A new state then arises, composed of stationary waves with about twice the original pattern amplitude. The bifurcation presents hysteresis: there exists a finite range of the control parameter in which both states are stable. By means of a simple stress balance, we show that a change of the shear stress can explain this hysteresis. Our predictions based on this model are in agreement with our numerical results. Project funded by FONDECYT Grants 1130354, 3140522 and the National Research Foundation of Korea (NRF- 2014R1A2A1A11051346). Computations supported by the supercomputing infrastructures of the NLHPC (ECM-02) and GENCI (IDRIS).
The gravitational wave experiment
NASA Technical Reports Server (NTRS)
Bertotti, B.; Ambrosini, R.; Asmar, S. W.; Brenkle, J. P.; Comoretto, G.; Giampieri, G.; Less, L.; Messeri, A.; Wahlquist, H. D.
1992-01-01
Since the optimum size of a gravitational wave detector is the wave length, interplanetary dimensions are needed for the mHz band of interest. Doppler tracking of Ulysses will provide the most sensitive attempt to date at the detection of gravitational waves in the low frequency band. The driving noise source is the fluctuations in the refractive index of interplanetary plasma. This dictates the timing of the experiment to be near solar opposition and sets the target accuracy for the fractional frequency change at 3.0 x 10 exp -14 for integration times of the order of 1000 sec. The instrumentation utilized by the experiment is distributed between the radio systems on the spacecraft and the seven participating ground stations of the Deep Space Network and Medicina. Preliminary analysis is available of the measurements taken during the Ulysses first opposition test.
Communication at millimeter waves
NASA Astrophysics Data System (ADS)
Kamal, A. K.; Christopher, P. F.
The advantage and disadvantages of millimeter waves for terrestrial and satellite communications are enumerated. Atmospheric attenuation is discussed in detail, with brief attention given to signal loss in particulates, sandstorms, snow, hail, and fog. Short closed forms are then found for gaseous attenuation on ground-satellite paths. An exponential rain loss probability density function is used in generating atmospheric loss at arbitrary required availability. It is pointed out that this loss (as a function of frequency) can be used to pick optimum carrier frequencies as a function of location, required availability, elevation angle, and system cost. An estimate is made of the rate-of-change of millimeter wave device availability. Special attention is given to GaAs FETs, not only because they will be useful, but because one phase of their millimeter wave performance is predictable: their noise performance as a function of frequency can be estimated with the aid of a Fukui equation.
Discrete wave equation upscaling
NASA Astrophysics Data System (ADS)
Fichtner, Andreas; Hanasoge, Shravan M.
2017-01-01
We present homogenisation technique for the uniformly discretised wave equation, based on the derivation of an effective equation for the low-wavenumber component of the solution. The method produces a down-sampled, effective medium, thus making the solution of the effective equation less computationally expensive. Advantages of the method include its conceptual simplicity and ease of implementation, the applicability to any uniformly discretised wave equation in one, two or three dimensions, and the absence of any constraints on the medium properties. We illustrate our method with a numerical example of wave propagation through a one-dimensional multiscale medium, and demonstrate the accurate reproduction of the original wavefield for sufficiently low frequencies.
Yerganian, Simon Scott
2003-02-11
A piezoelectric motor having a stator in which piezoelectric elements are contained in slots formed in the stator transverse to the desired wave motion. When an electric field is imposed on the elements, deformation of the elements imposes a force perpendicular to the sides of the slot, deforming the stator. Appropriate frequency and phase-shifting of the electric field will produce a wave in the stator and motion in a rotor. In a preferred aspect, the piezoelectric elements are configured so that deformation of the elements in the direction of an imposed electric field, generally referred to as the d.sub.33 direction, is utilized to produce wave motion in the stator. In a further aspect, the elements are compressed into the slots so as to minimize tensile stresses on the elements in use.
Yerganian, Simon Scott
2001-07-17
A piezoelectric motor having a stator in which piezoelectric elements are contained in slots formed in the stator transverse to the desired wave motion. When an electric field is imposed on the elements, deformation of the elements imposes a force perpendicular to the sides of the slot, deforming the stator. Appropriate frequency and phase shifting of the electric field will produce a wave in the stator and motion in a rotor. In a preferred aspect, the piezoelectric elements are configured so that deformation of the elements in direction of an imposed electric field, generally referred to as the d.sub.33 direction, is utilized to produce wave motion in the stator. In a further aspect, the elements are compressed into the slots so as to minimize tensile stresses on the elements in use.
NASA Technical Reports Server (NTRS)
Gurnett, Donald A.
1995-01-01
An overview is given of spacecraft observations of plasma waves in the solar system. In situ measurements of plasma phenomena have now been obtained at all of the planets except Mercury and Pluto, and in the interplanetary medium at heliocentric radial distances ranging from 0.29 to 58 AU. To illustrate the range of phenomena involved, we discuss plasma waves in three regions of physical interest: (1) planetary radiation belts, (2) planetary auroral acceleration regions and (3) the solar wind. In each region we describe examples of plasma waves that are of some importance, either due to the role they play in determining the physical properties of the plasma, or to the unique mechanism involved in their generation.
NASA Technical Reports Server (NTRS)
Goertz, C. K.
1986-01-01
Three planets, the earth, Jupiter and Saturn are known to emit nonthermal radio waves which require coherent radiation processes. The characteristic features (frequency spectrum, polarization, occurrence probability, radiation pattern) are discussed. Radiation which is externally controlled by the solar wind is distinguished from internally controlled radiation which only originates from Jupiter. The efficiency of the externally controlled radiation is roughly the same at all three planets (5 x 10 to the -6th) suggesting that similar processes are active there. The maser radiation mechanism for the generation of the radio waves and general requirements for the mechanism which couples the power generator to the region where the radio waves are generated are briefly discussed.
NASA Astrophysics Data System (ADS)
Farkas, I.; Helbing, D.; Vicsek, T.
2003-12-01
Mexican wave first widely broadcasted during the 1986 World Cup held in Mexico, is a human wave moving along the stands of stadiums as one section of spectators stands up, arms lifting, then sits down as the next section does the same. Here we use variants of models originally developed for the description of excitable media to demonstrate that this collective human behaviour can be quantitatively interpreted by methods of statistical physics. Adequate modelling of reactions to triggering attempts provides a deeper insight into the mechanisms by which a crowd can be stimulated to execute a particular pattern of behaviour and represents a possible tool of control during events involving excited groups of people. Interactive simulations, video recordings and further images are available at the webpage dedicated to this work: http://angel.elte.hu/wave.
The Virtual Wave Observatory (VWO)
NASA Technical Reports Server (NTRS)
Fung, Shing F.
2008-01-01
Heliophysics wave data are currently not easily searchable by computers, making identifying pertinent wave data features for analyses and cross comparisons difficult and laborious. Since wave data analysis requires specialized knowledge about waves, which spans the spectrum of microphysics to macrophysics, researchers having varied expertise cannot easily use wave data. To resolve these difficulties and to allow wave data to contribute more fully to Heliophysics research, we are developing a Virtual Wave Observatory (VWO) whose goal is to enable all Heliophysics wave data to become searchable, understandable and usable by the Heliophysics community. The VWO objective is to enable search of multiple and distributed wave data (from both active and passive measurements). This presentation provides and overview of the VWO, a new VxO component within the emerging distributed Heliophysics data and model environment.
Marsh, S.P.
1988-03-08
An explosive plane-wave air lens which enables a spherical wave form to be converted to a planar wave without the need to specially machine or shape explosive materials is described. A disc-shaped impactor having a greater thickness at its center than around its periphery is used to convert the spherical wave into a plane wave. When the wave reaches the impactor, the center of the impactor moves first because the spherical wave reaches the center of the impactor first. The wave strikes the impactor later in time as one moves radially along the impactor. Because the impactor is thinner as one moves radially outward, the velocity of the impactor is greater at the periphery than at the center. An acceptor explosive is positioned so that the impactor strikes the acceptor simultaneously. Consequently, a plane detonation wave is propagated through the acceptor explosive. 4 figs.
Marsh, Stanley P.
1988-01-01
An explosive plane-wave air lens which enables a spherical wave form to be converted to a planar wave without the need to specially machine or shape explosive materials is described. A disc-shaped impactor having a greater thickness at its center than around its periphery is used to convert the spherical wave into a plane wave. When the wave reaches the impactor, the center of the impactor moves first because the spherical wave reaches the center of the impactor first. The wave strikes the impactor later in time as one moves radially along the impactor. Because the impactor is thinner as one moves radially outward, the velocity of the impactor is greater at the periphery than at the center. An acceptor explosive is positioned so that the impactor strikes the acceptor simultaneously. Consequently, a plane detonation wave is propagated through the acceptor explosive.
Marsh, S.P.
1987-03-12
An explosive plane-wave air lens which enables a spherical wave form to be converted to a planar wave without the need to specially machine or shape explosive materials is described. A disc-shaped impactor having a greater thickness at its center than around its periphery is used to convert the spherical wave into a plane wave. When the wave reaches the impactor, the center of the impactor moves first because the spherical wave reaches the center of the impactor first. The wave strikes the impactor later in time as one moves radially along the impactor. Because the impactor is thinner as one moves radially outward, the velocity of the impactor is greater at the periphery than at the center. An acceptor explosive is positioned so that the impactor strikes the acceptor simultaneously. Consequently, a plane detonation wave is propagated through the acceptor explosive. 3 figs., 3 tabs.
Adaptive multiconfigurational wave functions
Evangelista, Francesco A.
2014-03-28
A method is suggested to build simple multiconfigurational wave functions specified uniquely by an energy cutoff Λ. These are constructed from a model space containing determinants with energy relative to that of the most stable determinant no greater than Λ. The resulting Λ-CI wave function is adaptive, being able to represent both single-reference and multireference electronic states. We also consider a more compact wave function parameterization (Λ+SD-CI), which is based on a small Λ-CI reference and adds a selection of all the singly and doubly excited determinants generated from it. We report two heuristic algorithms to build Λ-CI wave functions. The first is based on an approximate prescreening of the full configuration interaction space, while the second performs a breadth-first search coupled with pruning. The Λ-CI and Λ+SD-CI approaches are used to compute the dissociation curve of N{sub 2} and the potential energy curves for the first three singlet states of C{sub 2}. Special attention is paid to the issue of energy discontinuities caused by changes in the size of the Λ-CI wave function along the potential energy curve. This problem is shown to be solvable by smoothing the matrix elements of the Hamiltonian. Our last example, involving the Cu{sub 2}O{sub 2}{sup 2+} core, illustrates an alternative use of the Λ-CI method: as a tool to both estimate the multireference character of a wave function and to create a compact model space to be used in subsequent high-level multireference coupled cluster computations.
On the generation of internal wave modes by surface waves
NASA Astrophysics Data System (ADS)
Harlander, Uwe; Kirschner, Ian; Maas, Christian; Zaussinger, Florian
2016-04-01
Internal gravity waves play an important role in the ocean since they transport energy and momentum and the can lead to mixing when they break. Surface waves and internal gravity waves can interact. On the one hand, long internal waves imply a slow varying shear current that modifies the propagation of surface waves. Surface waves generated by the atmosphere can, on the other hand, excite internal waves by nonlinear interaction. Thereby a surface wave packet consisting of two close frequencies can resonate with a low frequency internal wave (Phillips, 1966). From a theoretical point of view, the latter has been studied intensively by using a 2-layer model, i.e. a surface layer with a strong density contrast and an internal layer with a comparable weak density contrast (Ball, 1964; Craig et al., 2010). In the present work we analyse the wave coupling for a continuously stratified fluid using a fully non-linear 2D numerical model (OpenFoam) and compare this with laboratory experiments (see Lewis et al. 1974). Surface wave modes are used as initial condition and the time development of the dominant surface and internal waves are studied by spectral and harmonic analysis. For the simple geometry of a box, the results are compared with analytical spectra of surface and gravity waves. Ball, F.K. 1964: Energy transfer between external and internal gravity waves. J. Fluid Mech. 19, 465. Craig, W., Guyenne, P., Sulem, C. 2010: Coupling between internal and surface waves. Natural Hazards 57, 617-642. Lewis, J.E., Lake, B.M., Ko, D.R.S 1974: On the interaction of internal waves and surfacr gravity waves, J. Fluid Mech. 63, 773-800. Phillips, O.M. 1966: The dynamics of the upper ocean, Cambridge University Press, 336pp.
Shear wave transmissivity measurement by color Doppler shear wave imaging
NASA Astrophysics Data System (ADS)
Yamakoshi, Yoshiki; Yamazaki, Mayuko; Kasahara, Toshihiro; Sunaguchi, Naoki; Yuminaka, Yasushi
2016-07-01
Shear wave elastography is a useful method for evaluating tissue stiffness. We have proposed a novel shear wave imaging method (color Doppler shear wave imaging: CD SWI), which utilizes a signal processing unit in ultrasound color flow imaging in order to detect the shear wave wavefront in real time. Shear wave velocity is adopted to characterize tissue stiffness; however, it is difficult to measure tissue stiffness with high spatial resolution because of the artifact produced by shear wave diffraction. Spatial average processing in the image reconstruction method also degrades the spatial resolution. In this paper, we propose a novel measurement method for the shear wave transmissivity of a tissue boundary. Shear wave wavefront maps are acquired by changing the displacement amplitude of the shear wave and the transmissivity of the shear wave, which gives the difference in shear wave velocity between two mediums separated by the boundary, is measured from the ratio of two threshold voltages required to form the shear wave wavefronts in the two mediums. From this method, a high-resolution shear wave amplitude imaging method that reconstructs a tissue boundary is proposed.
The role of Biot slow waves in electroseismic wave phenomena.
Pride, Steven R; Garambois, Stéphane
2002-02-01
The electromagnetic fields that are generated as a spherical seismic wave (either P or S) traverses an interface separating two porous materials are numerically modeled both with and without the generation of Biot slow waves at the interface. In the case of an incident fast-P wave, the predicted electric-field amplitudes when slow waves are neglected can easily be off by as much as an order of magnitude. In the case of an incident S wave, the error is much smaller (typically on the order of 10% or less) because not much S-wave energy gets converted into slow waves. In neglecting the slow waves, only six plane waves (reflected and transmitted fast-P, S, and EM waves) are available with which to match the eight continuity conditions that hold at each interface. This overdetermined problem is solved by placing weights on the eight continuity conditions so that those conditions that are most important for obtaining the proper response are emphasized. It is demonstrated that when slow waves are neglected, it is best to also neglect the continuity of the Darcy flow and fluid pressure across an interface. The principal conclusion of this work is that to properly model the electromagnetic (EM) fields generated at an interface by an incident seismic wave, the full Biot theory that allows for generation of slow waves must be employed.
Wouters, L.F.
1958-10-28
The detection of the shape and amplitude of a radiation wave is discussed, particularly an apparatus for automatically indicating at spaced lntervals of time the radiation intensity at a flxed point as a measure of a radiation wave passing the point. The apparatus utilizes a number of photomultiplier tubes surrounding a scintillation type detector, For obtainlng time spaced signals proportional to radiation at predetermined intervals the photolnultiplier tubes are actuated ln sequence following detector incidence of a predetermined radiation level by electronic means. The time spaced signals so produced are then separately amplified and relayed to recording means.
1942-05-04
and progresses through .an explosive. Such a theory must explain how the head of the detonation wave initiates· the reaction (and the detonation ... theory of detonation is based on the assumption that the actual value of 9’ is this lower limit Cf1 ! This is tho so-called hypothesis of’ Chapman and...DEVELOP!i!ENT Progress Report on 11 Theory of Detonation Waves 11 to April 1, 1942 by John von Nounr.n Institute for Adv&nccd Study Princeton
1991-04-01
13. Directional wave spectra: 14a. Con. wind data: Y 14b. Location sensor: Narwhal Island 14c. Period of record: 07/78-10/78 isa. Con. current data: Y... Narwhal Island 14c. Period of record: 07/78-10/78 15a. Con. current data: Y 15b. Location meters: S. of Cross Island & W of Stockton Island at Newport...10. Sample: 11. Burst sampling: 12. Burst Interval: 13. Directional wave spectra: 14a. Con. wind data: Y 14b. Location sensor: Narwhal Island 14c
NASA Astrophysics Data System (ADS)
Moore, C. I.; Hafizi, B.; Ting, A.; Burris, H. R.; Sprangle, P.; Esarey, E.; Ganguly, A.; Hirshfield, J. L.
1997-11-01
The Vacuum Beat Wave Accelerator (VBWA) is a particle acceleration scheme which uses the non-linear ponderomotive beating of two different frequency laser beams to accelerate electrons. A proof-of-principle experiment to demonstrate the VBWA is underway at the Naval Research Laboratory (NRL). This experiment will use the beating of a 1054 nm and 527 nm laser pulse from the NRL T-cubed laser to generate the beat wave and a 4.5 MeV RF electron gun as the electron source. Simulation results and the experimental design will be presented. The suitability of using axicon or higher order Gaussian laser beams will also be discussed.
Ultrasonic shear wave couplant
Kupperman, David S.; Lanham, Ronald N.
1985-01-01
Ultrasonically testing of an article at high temperatures is accomplished by the use of a compact layer of a dry ceramic powder as a couplant in a method which involves providing an ultrasonic transducer as a probe capable of transmitting shear waves, coupling the probe to the article through a thin compact layer of a dry ceramic powder, propagating a shear wave from the probe through the ceramic powder and into the article to develop echo signals, and analyzing the echo signals to determine at least one physical characteristic of the article.
Mechanics, Waves and Thermodynamics
NASA Astrophysics Data System (ADS)
Ranjan Jain, Sudhir
2016-05-01
Figures; Preface; Acknowledgement; 1. Energy, mass, momentum; 2. Kinematics, Newton's laws of motion; 3. Circular motion; 4. The principle of least action; 5. Work and energy; 6. Mechanics of a system of particles; 7. Friction; 8. Impulse and collisions; 9. Central forces; 10. Dimensional analysis; 11. Oscillations; 12. Waves; 13. Sound of music; 14. Fluid mechanics; 15. Water waves; 16. The kinetic theory of gases; 17. Concepts and laws of thermodynamics; 18. Some applications of thermodynamics; 19. Basic ideas of statistical mechanics; Bibliography; Index.
Quantum positron acoustic waves
Metref, Hassina; Tribeche, Mouloud
2014-12-15
Nonlinear quantum positron-acoustic (QPA) waves are investigated for the first time, within the theoretical framework of the quantum hydrodynamic model. In the small but finite amplitude limit, both deformed Korteweg-de Vries and generalized Korteweg-de Vries equations governing, respectively, the dynamics of QPA solitary waves and double-layers are derived. Moreover, a full finite amplitude analysis is undertaken, and a numerical integration of the obtained highly nonlinear equations is carried out. The results complement our previously published results on this problem.
THERMOPLASTIC WAVES IN MAGNETARS
Beloborodov, Andrei M.; Levin, Yuri E-mail: yuri.levin@monash.edu.au
2014-10-20
Magnetar activity is generated by shear motions of the neutron star surface, which relieve internal magnetic stresses. An analogy with earthquakes and faults is problematic, as the crust is permeated by strong magnetic fields which greatly constrain crustal displacements. We describe a new deformation mechanism that is specific to strongly magnetized neutron stars. The magnetically stressed crust begins to move because of a thermoplastic instability, which launches a wave that shears the crust and burns its magnetic energy. The propagating wave front resembles the deflagration front in combustion physics. We describe the conditions for the instability, the front structure, and velocity, and discuss implications for observed magnetar activity.
NASA Astrophysics Data System (ADS)
de Rham, Claudia; Motohashi, Hayato
2017-03-01
We study the development of caustics in shift-symmetric scalar field theories by focusing on simple waves with an S O (p )-symmetry in an arbitrary number of space dimensions. We show that the pure Galileon, the DBI-Galileon, and the extreme-relativistic Galileon naturally emerge as the unique set of caustic-free theories, highlighting a link between the caustic-free condition for simple S O (p )-waves and the existence of either a global Galilean symmetry or a global (extreme-)relativistic Galilean symmetry.
Triangular rogue wave cascades.
Kedziora, David J; Ankiewicz, Adrian; Akhmediev, Nail
2012-11-01
By numerically applying the recursive Darboux transformation technique, we study high-order rational solutions of the nonlinear Schrödinger equation that appear spatiotemporally as triangular arrays of Peregrine solitons. These can be considered as rogue wave cascades and complement previously discovered circular cluster forms. In this analysis, we reveal a general parametric restriction for their existence and investigate the interplay between cascade and cluster forms. As a result, we demonstrate how to generate many more hybrid rogue wave solutions, including semicircular clusters that resemble claws.
NASA Astrophysics Data System (ADS)
Hietala, N.; Hänninen, R.; Salman, H.; Barenghi, C. F.
2016-12-01
Two vortex rings can form a localized configuration whereby they continually pass through one another in an alternating fashion. This phenomenon is called leapfrogging. Using parameters suitable for superfluid helium-4, we describe a recurrence phenomenon that is similar to leapfrogging, which occurs for two coaxial straight vortex filaments with the same Kelvin wave mode. For small-amplitude Kelvin waves we demonstrate that our full Biot-Savart simulations closely follow predictions obtained from a simplified model that provides an analytical approximation developed for nearly parallel vortices. Our results are also relevant to thin-cored helical vortices in classical fluids.
Rogue wave observation in a water wave tank.
Chabchoub, A; Hoffmann, N P; Akhmediev, N
2011-05-20
The conventional definition of rogue waves in the ocean is that their heights, from crest to trough, are more than about twice the significant wave height, which is the average wave height of the largest one-third of nearby waves. When modeling deep water waves using the nonlinear Schrödinger equation, the most likely candidate satisfying this criterion is the so-called Peregrine solution. It is localized in both space and time, thus describing a unique wave event. Until now, experiments specifically designed for observation of breather states in the evolution of deep water waves have never been made in this double limit. In the present work, we present the first experimental results with observations of the Peregrine soliton in a water wave tank.
Continuous-wave Submillimeter-wave Gyrotrons
Han, Seong-Tae; Griffin, Robert G.; Hu, Kan-Nian; Joo, Chan-Gyu; Joye, Colin D.; Mastovsky, Ivan; Shapiro, Michael A.; Sirigiri, Jagadishwar R.; Temkin, Richard J.; Torrezan, Antonio C.; Woskov, Paul P.
2007-01-01
Recently, dynamic nuclear polarization enhanced nuclear magnetic resonance (DNP/NMR) has emerged as a powerful technique to obtain significant enhancements in spin spectra from biological samples. For DNP in modern NMR systems, a high power continuous-wave source in the submillimeter wavelength range is necessary. Gyrotrons can deliver tens of watts of CW power at submillimeter wavelengths and are well suited for use in DNP/NMR spectrometers. To date, 140 GHz and 250 GHz gyrotrons are being employed in DNP spectrometer experiments at 200 MHz and 380 MHz at MIT. A 460 GHz gyrotron, which has operated with 8 W of CW output power, will soon be installed in a 700 MHz NMR spectrometer. High power radiation with good spectral and spatial resolution from these gyrotrons should provide NMR spectrometers with high signal enhancement through DNP. Also, these tubes operating at submillimeter wavelengths should have important applications in research in physics, chemistry, biology, materials science and medicine. PMID:17404605
Localized coherence of freak waves
NASA Astrophysics Data System (ADS)
Latifah, Arnida L.; van Groesen, E.
2016-09-01
This paper investigates in detail a possible mechanism of energy convergence leading to freak waves. We give examples of a freak wave as a (weak) pseudo-maximal wave to illustrate the importance of phase coherence. Given a time signal at a certain position, we identify parts of the time signal with successive high amplitudes, so-called group events, that may lead to a freak wave using wavelet transform analysis. The local coherence of the critical group event is measured by its time spreading of the most energetic waves. Four types of signals have been investigated: dispersive focusing, normal sea condition, thunderstorm condition and an experimental irregular wave. In all cases presented in this paper, it is shown that a high correlation exists between the local coherence and the appearance of a freak wave. This makes it plausible that freak waves can be developed by local interactions of waves in a wave group and that the effect of waves that are not in the immediate vicinity is minimal. This indicates that a local coherence mechanism within a wave group can be one mechanism that leads to the appearance of a freak wave.
Elandt, Ryan B; Shakeri, Mostafa; Alam, Mohammad-Reza
2014-02-01
Here we show that a nonlinear resonance between oceanic surface waves caused by small seabed features (the so-called Bragg resonance) can be utilized to create the equivalent of lenses and curved mirrors for surface gravity waves. Such gravity wave lenses, which are merely small changes to the seafloor topography and therefore are surface noninvasive, can focus or defocus the energy of incident waves toward or away from any desired focal point. We further show that for a broadband incident wave spectrum (i.e., a wave group composed of a multitude of different-frequency waves), a polychromatic topography (occupying no more than the area required for a monochromatic lens) can achieve a broadband lensing effect. Gravity wave lenses can be utilized to create localized high-energy wave zones (e.g., for wave energy harvesting or creating artificial surf zones) as well as to disperse waves in order to create protected areas (e.g., harbors or areas near important offshore facilities). In reverse, lensing of oceanic waves may be caused by natural seabed features and may explain the frequent appearance of very high amplitude waves in certain bodies of water.
"Hearing" Electromagnetic Waves
ERIC Educational Resources Information Center
Rojo, Marta; Munoz, Juan
2014-01-01
In this work, an educational experience is described in which a microwave communication link is used to make students aware that all electromagnetic waves have the same physical nature and properties. Experimental demonstrations are linked to theoretical concepts to increase comprehension of the physical principles underlying electromagnetic…
Resonant Alfven Wave Excitation
NASA Astrophysics Data System (ADS)
Hameiri, Eliezer
1999-11-01
Much of the theory of the Alfven wave resonance phenomenon was developed for a tokamak configuration where the magnetic field winds around the torus without entering the boundary. Thus, boundary conditions did not have to be considered.( J. Tataronis and W. Grossmann, Z. Phys. 261), 203 (1973). In most space plasma situations such as the magnetosphere or the Sun, as well as in the scrape-off layer of a divertor tokamak, this is not the case. When boundary conditions are considered, it is generally assumed for simplicity that the boundary is perfectly conducting, which implies that the Alfven wave bounce frequencies are real and the resonance phenomenon can be detected by some singularity in the equations. The nature of the singularity is usually described in terms of a Frobenius series.( A.N. Wright and M.J. Thompson, Phys. Plamsas 1), 691 (1994). In this work we consider resistive boundaries, which imply that the fast wave eigenfrequency is real, but the Alfven frequency is not. Thus, there is no exact resonance and no singularity in the equations. The solution of the problem is carried out asymptotically by finding an exact Laplace integral representation for the solution and then matching various regions. The energy transferred to the Alfven wave appears to be rather small.
Gravitational waves from technicolor
Jaervinen, Matti; Sannino, Francesco; Kouvaris, Chris
2010-03-15
We investigate the production and possible detection of gravitational waves stemming from the electroweak phase transition in the early universe in models of minimal walking technicolor. In particular we discuss the two possible scenarios in which one has only one electroweak phase transition and the case in which the technicolor dynamics allows for multiple phase transitions.
Nonclassical Matter Wave Sources
2007-11-02
Broglie to Heisenberg ”, invited talk, Alexander von Humboldt 18th Symposium, “100 Years Werner Heisenberg --- Works and Impact”, Bamberg, Germany, 2001...From de Broglie waves to Heisenberg ferromagnets”, Fortschritte der Physik 50, 664 (2002). 17. C. P. Search, H. Pu, W. Zhang, B. P. Anderson and P
ERIC Educational Resources Information Center
Bennett, J.
1973-01-01
Discusses wave patterns on the surfaces of ripening wheat and barley crops when the wind is moderately strong. Examines the structure of the turbulence over such natural surfaces and conditions under which the crop may be damaged by the wind. (JR)
NASA Astrophysics Data System (ADS)
Ayers, R. Dean; Inan, Nader
2003-10-01
Introductory treatments of waves usually emphasize undamped traveling waves and ideal standing waves with perfect nodes. Those are just special cases from a larger class of waves in which the crests perform a characteristic ``lurching'' or ``galloping'' motion. The variation of a terminal reflection coefficient and the constant for damping in propagation generates a continuum of more realistic behaviors that connect the special, simple cases. Attempts to develop this larger class verbally and mathematically might seem abstract and complicated, but the use of kinetic computer graphics in an interactive mode makes their introduction straightforward. Preliminary observations and explorations with these images can then lead naturally to a mathematical treatment at a level appropriate for the audience. Software from DPGraph has been particularly convenient for the development of the figures. The fact that programming must be done using analytic expressions and no iterations is a valuable constraint; it forces the user to stay close to fundamentals in the physics and mathematics. Exploratory studies then encourage the programmer to ask analytic questions that might not have been considered otherwise. Several representative figures will be presented. [Work supported by the Paul S. Veneklasen Research Foundation and the CSULB Scholarly and Creative Activities Committee.
Menikoff, Ralph
2012-04-03
Shock initiation in a plastic-bonded explosives (PBX) is due to hot spots. Current reactive burn models are based, at least heuristically, on the ignition and growth concept. The ignition phase occurs when a small localized region of high temperature (or hot spot) burns on a fast time scale. This is followed by a growth phase in which a reactive front spreads out from the hot spot. Propagating reactive fronts are deflagration waves. A key question is the deflagration speed in a PBX compressed and heated by a shock wave that generated the hot spot. Here, the ODEs for a steady deflagration wave profile in a compressible fluid are derived, along with the needed thermodynamic quantities of realistic equations of state corresponding to the reactants and products of a PBX. The properties of the wave profile equations are analyzed and an algorithm is derived for computing the deflagration speed. As an illustrative example, the algorithm is applied to compute the deflagration speed in shock compressed PBX 9501 as a function of shock pressure. The calculated deflagration speed, even at the CJ pressure, is low compared to the detonation speed. The implication of this are briefly discussed.
Submillimeter wave heterodyne receiver
NASA Technical Reports Server (NTRS)
Chattopadhyay, Goutam (Inventor); Manohara, Harish (Inventor); Siegel, Peter H. (Inventor); Ward, John (Inventor)
2011-01-01
In an embodiment, a submillimeter wave heterodyne receiver includes a finline ortho-mode transducer comprising thin tapered metallic fins deposited on a thin dielectric substrate to separate a vertically polarized electromagnetic mode from a horizontally polarized electromagnetic mode. Other embodiments are described and claimed.
ERIC Educational Resources Information Center
Tucker, Vance A.
1971-01-01
Capillary and gravity water waves are related to the position, wavelength, and velocity of an object in flowing water. Water patterns are presented for ships and the whirling beetle with an explanation of how the design affects the objects velocity and the observed water wavelengths. (DS)
NASA Technical Reports Server (NTRS)
Ray, Richard D.
1999-01-01
Oceanic internal tides are internal waves with tidal periodicities. They are ubiquitous throughout the ocean, although generally more pronounced near large bathymetric features such as mid-ocean ridges and continental slopes. The internal vertical displacements associated with these waves can be extraordinarily large. Near some shelf breaks where the surface tides are strong, internal displacements (e.g., of an isothermal surface) can exceed 200 meters. Displacements of 10 meters in the open ocean are not uncommon. The associated current velocities are usually comparable to or larger than the currents of the surface tide. On continental shelves internal tides can occasionally generate packets of internal solitons, which are detectable in remote sensing imagery. Other common nonlinear features are generation of higher harmonics (e.g., 6-hr waves) and wave breaking. Internal tides are known to be an important energy source for mixing of shelf waters. Recent research suggests that they may also be a significant energy source for deep-ocean mixing.
NASA Astrophysics Data System (ADS)
Piel, Alexander; Arp, Oliver; Menzel, Kristoffer; Klindworth, Markus
2007-11-01
We report on experimental observations of dust density waves in a complex (dusty) plasma under microgravity. The plasma is produced in a radio-frequency parallel-plate discharge (argon, p=15Pa, U=65Vpp). Different sizes of dust particles were used (3.4 μm and 6.4μm diameter). The low-frequency (f 11Hz) dust density waves are naturally unstable modes, which are driven by the ion flow in the plasma. Surprisingly, the wave propagation direction is aligned with the ion flow direction in the bulk plasma but becomes oblique at the boundary of the dust cloud with an inclination of 60^o with respect to the plasma boundary. The experimental results are compared with a kinetic model in the electrostatic approximation [1] and a fluid model [2]. Moreover, the role of dust surface waves is discussed. [1] M. Rosenberg, J. Vac. Sci. Technol. A 14, 631 (1996) [2] A. Piel et al, Phys. Rev. Lett. 97, 205009 (2006)
1980-07-01
Fendell (1970) to finite Mach numbers, and uncovered the existence of very slow deflagration waves. JI.. -2- 2. The governing equations The governing...FlapmSI,$ Cambridge University Press. 2. Buckmaster, J. 1976. The quenching of deflagration vaves. Combust. Flme. 26, 151-162. 3. Bush, W.B. & Fendell , F.E
Coded excitation plane wave imaging for shear wave motion detection.
Song, Pengfei; Urban, Matthew W; Manduca, Armando; Greenleaf, James F; Chen, Shigao
2015-07-01
Plane wave imaging has greatly advanced the field of shear wave elastography thanks to its ultrafast imaging frame rate and the large field-of-view (FOV). However, plane wave imaging also has decreased penetration due to lack of transmit focusing, which makes it challenging to use plane waves for shear wave detection in deep tissues and in obese patients. This study investigated the feasibility of implementing coded excitation in plane wave imaging for shear wave detection, with the hypothesis that coded ultrasound signals can provide superior detection penetration and shear wave SNR compared with conventional ultrasound signals. Both phase encoding (Barker code) and frequency encoding (chirp code) methods were studied. A first phantom experiment showed an approximate penetration gain of 2 to 4 cm for the coded pulses. Two subsequent phantom studies showed that all coded pulses outperformed the conventional short imaging pulse by providing superior sensitivity to small motion and robustness to weak ultrasound signals. Finally, an in vivo liver case study on an obese subject (body mass index = 40) demonstrated the feasibility of using the proposed method for in vivo applications, and showed that all coded pulses could provide higher SNR shear wave signals than the conventional short pulse. These findings indicate that by using coded excitation shear wave detection, one can benefit from the ultrafast imaging frame rate and large FOV provided by plane wave imaging while preserving good penetration and shear wave signal quality, which is essential for obtaining robust shear elasticity measurements of tissue.
Gravitational-Wave Detection (ii). Current Gravitational Wave Detector Results
NASA Astrophysics Data System (ADS)
Kanda, Nobuyuki
2005-11-01
The workshop session C1ii was focused on the results of recent operating detectors. 10 speakers presented the latest results of each experiments: ALLEGRO, GEO, LIGO, TAMA and VIRGO experiments. There were reports about searches for gravitational waves in analysis of observation data. The results are of no detection of gravitational waves, but observational upper-limits of gravitational waves are improved.
Hermes, Matthew R.; Hirata, So
2015-09-14
One-dimensional (1D) solids exhibit a number of striking electronic structures including charge-density wave (CDW) and spin-density wave (SDW). Also, the Peierls theorem states that at zero temperature, a 1D system predicted by simple band theory to be a metal will spontaneously dimerize and open a finite fundamental bandgap, while at higher temperatures, it will assume the equidistant geometry with zero bandgap (a Peierls transition). We computationally study these unique electronic structures and transition in polyyne and all-trans polyacetylene using finite-temperature generalizations of ab initio spin-unrestricted Hartree–Fock (UHF) and spin-restricted coupled-cluster doubles (CCD) theories, extending upon previous work [He et al., J. Chem. Phys. 140, 024702 (2014)] that is based on spin-restricted Hartree–Fock (RHF) and second-order many-body perturbation (MP2) theories. Unlike RHF, UHF can predict SDW as well as CDW and metallic states, and unlike MP2, CCD does not diverge even if the underlying RHF reference wave function is metallic. UHF predicts a gapped SDW state with no dimerization at low temperatures, which gradually becomes metallic as the temperature is raised. CCD, meanwhile, confirms that electron correlation lowers the Peierls transition temperature. Furthermore, we show that the results from all theories for both polymers are subject to a unified interpretation in terms of the UHF solutions to the Hubbard–Peierls model using different values of the electron-electron interaction strength, U/t, in its Hamiltonian. The CCD wave function is shown to encompass the form of the exact solution of the Tomonaga–Luttinger model and is thus expected to describe accurately the electronic structure of Luttinger liquids.
Transformation method and wave control
NASA Astrophysics Data System (ADS)
Chang, Zheng; Hu, Jin; Hu, Geng-Kai
2010-12-01
Transformation method provides an efficient way to control wave propagation by materials. The transformed relations for field and material during a transformation are essential to fulfill this method. We propose a systematic method to derive the transformed relations for a general physic process, the constraint conditions are obtained by considering geometrical and physical constraint during a mapping. The proposed method is applied to Navier's equation for elastodynamics, Helmholtz's equation for acoustic wave and Maxwell's equation for electromagnetic wave, the corresponding transformed relations are derived, which can be used in the framework of transformation method for wave control. We show that contrary to electromagnetic wave, the transformed relations are not uniquely determined for elastic wave and acoustic wave, so we have a freedom to choose them differently. Using the obtained transformed relations, we also provide some examples for device design, a concentrator for elastic wave, devices for illusion acoustic and illusion optics are conceived and validated by numerical simulations.
Gravitational Waves: The Evidence Mounts
ERIC Educational Resources Information Center
Wick, Gerald L.
1970-01-01
Reviews the work of Weber and his colleagues in their attempts at detecting extraterrestial gravitational waves. Coincidence events recorded by special detectors provide the evidence for the existence of gravitational waves. Bibliography. (LC)
NASA Astrophysics Data System (ADS)
Globke, Wolfgang; Leistner, Thomas
2016-10-01
We show that every n-dimensional locally homogeneous pp-wave is a plane wave, provided it is indecomposable and its curvature operator, when acting on 2-forms, has rank greater than one. As a consequence we obtain that indecomposable, Ricci-flat locally homogeneous pp-waves are plane waves. This generalises a classical result by Jordan, Ehlers and Kundt in dimension 4. Several examples show that our assumptions on indecomposability and the rank of the curvature are essential.
Evaluation of ADCP Wave Measurements
2006-12-01
pitch , roll , and heave motions that can place a ship’s stability in jeopardy (Beal, 1991). Wave conditions can also change rapidly and this can...measure the horizontal buoy displacements (yielding wave direction). Another type of buoy known as a “ pitch and roll buoy” (Longuet-Higgins et al...1963) measures tilt angles or pitch and roll to calculate wave direction. Newer buoys use global positioning systems (GPS) to obtain wave height and
Extreme events in Faraday waves
NASA Astrophysics Data System (ADS)
Punzmann, Horst; Shats, Michael; Xia, Hua
2014-05-01
Observations of extreme wave events in the ocean are rare due to their low statistical probability. In the laboratory however, the evolution of extreme wave events can be studied in great detail with high spatial and temporal resolution. The reported surface wave experiments in the short wavelength gravity-capillary range aim to contribute to the understanding of some of the underlying mechanisms for rogue wave generation. In this talk, we report on extreme wave events in parametrically excited Faraday waves. Faraday waves appear if a fluid is accelerated (normal to the fluid surface) above a critical threshold. A variety of novel tools have been deployed to characterize the 2D surface elevation. The results presented show spatio-temporal and statistical data on the surface wave conditions leading up to extreme wave events. The peak in wave amplitude during such an event is shown to exceed six times the standard deviation of the average wave field with significantly increased statistical probability compared to the background wave field [1]. The experiments also show that parametrically excited waves can be viewed as assembles of oscillons [2] (or oscillating solitons) where modulation instability seems to play a crucial role in their formation. More detailed studies on the oscillon dynamics reveal that the onset of an increased probability of extreme wave events correlates with the increase in the oscillons mobility and merger [3]. Reference: 1. Xia H., Maimbourg T., Punzmann H., and Shats M., Oscillon dynamics and rogue wave generation in Faraday surface ripples, Physical Review Letters 109, 114502 (2012) 2. Shats M., Xia H., and Punzmann H., Parametrically excited water surface ripples as ensembles of oscillons, Physical Review Letters 108, 034502 (2012) 3. Shats M., Punzmann H., Xia H., Capillary rogue waves, Physical Review Letters, 104, 104503 (2010)
Observed Statistics of Extreme Waves
2006-12-01
9 Figure 5. An energy stealing wave as a solution to the NLS equation . (From: Dysthe and...shown that nonlinear interaction between four colliding waves can produce extreme wave behavior. He utilized the NLS equation in his numerical ...2000) demonstrated the formation of extreme waves using the Korteweg de Vries ( KdV ) equation , which is valid in shallow water. It was shown in the
Are Rogue Waves Really Unexpected?
NASA Astrophysics Data System (ADS)
Fedele, Francesco
2016-05-01
An unexpected wave is defined by Gemmrich & Garrett (2008) as a wave that is much taller than a set of neighboring waves. Their definition of "unexpected" refers to a wave that is not anticipated by a casual observer. Clearly, unexpected waves defined in this way are predictable in a statistical sense. They can occur relatively often with a small or moderate crest height, but large unexpected waves that are rogue are rare. Here, this concept is elaborated and statistically described based on a third-order nonlinear model. In particular, the conditional return period of an unexpected wave whose crest exceeds a given threshold is developed. This definition leads to greater return periods or on average less frequent occurrences of unexpected waves than those implied by the conventional return periods not conditioned on a reference threshold. Ultimately, it appears that a rogue wave that is also unexpected would have a lower occurrence frequency than that of a usual rogue wave. As specific applications, the Andrea and WACSIS rogue wave events are examined in detail. Both waves appeared without warning and their crests were nearly $2$-times larger than the surrounding $O(10)$ wave crests, and thus unexpected. The two crest heights are nearly the same as the threshold~$h_{0.3\\cdot10^{6}}\\sim1.6H_{s}$ exceeded on average once every~$0.3\\cdot 10^{6}$ waves, where $H_s$ is the significant wave height. In contrast, the Andrea and WACSIS events, as both rogue and unexpected, would occur slightly less often and on average once every~$3\\cdot10^{6}$ and~$0.6\\cdot10^6$ waves respectively.
Observations of running penumbral waves.
NASA Technical Reports Server (NTRS)
Zirin, H.; Stein, A.
1972-01-01
Quiet sunspots with well-developed penumbrae show running intensity waves with period running around 300 sec. The waves appear connected with umbral flashes of exactly half the period. Waves are concentric, regular, with velocity constant around 10 km/sec. They are probably sound waves and show intensity fluctuation in H alpha centerline or wing of 10 to 20%. The energy is tiny compared to the heat deficit of the umbra.
Modeling Seismic Noise Body Waves
NASA Astrophysics Data System (ADS)
Stutzmann, E.; Farra, V.; Gualtieri, L.; Schimmel, M.; Ardhuin, F.
2014-12-01
Secondary microseismic noise is generated by non-linear interactions between ocean waves at the ocean surface. The sources correspond to pressure fluctuations close to the ocean surface. They generate acoustic waves in the ocean, which are then converted into P, SV, and Rayleigh waves in the deeper Earth layers. Rayleigh waves are the most energetic noise signal but body wave amplitude can be extracted using beamforming analysis. We analyze several typhoons recorded by the Southern California Seismic Network and we show that the detected P-wave amplitudes are frequency dependent. In order to understand the body wave generation mechanism, we model the P-wave amplitude. The sources are the power spectral density of the pressure derived from the ocean wave interaction model. They are distributed along the ocean surface and they are frequency dependent. We then compute the site effect of the ocean layer upon body waves generated by the noise sources. The site effect can be described as the constructive interference of multiply reflected P waves in the ocean that are then converted to P waves at the ocean-crust interface. It varies with frequency and ocean depth. Finally we compute the propagation from the source area to the network by taking into account seismic attenuation and geometrical spreading. We show that the modeled P-wave amplitude reproduce well the frequency dependent variations of the measured P-wave. This frequency dependent effect is due to both the source and site effect. We define the effective source as the product of the power spectral density of the pressure close to the surface and the site effect. We show that its maximum is consistent with the source location obtained by back projecting the slowness derived from the beamforming analysis. Finally, we show that body wave analysis enable to efficiently constrain the amount of sources generated by ocean wave reflected at the coast.
ULF waves in the magnetosphere
Takahashi, Kazue )
1991-01-01
Research efforts in the area of magnetospheric ULF waves in the 1987-1990 period are reviewed. Attention is given to externally excited hydromagnetic waves including field line resonance, the global cavity mode, bow-shock-associated upstream waves, and Kelvin-Helmholtz waves. Consideration is given to internally excited Pc 4-5 pulsations and the role of these pulsations in the diffusion of ring-current ions based on the observed properties of the pulsations. 154 refs.
Nonlinear Waves on Stochastic Support: Calcium Waves in Astrocyte Syncytia
NASA Astrophysics Data System (ADS)
Jung, P.; Cornell-Bell, A. H.
Astrocyte-signaling has been observed in cell cultures and brain slices in the form of Calcium waves. Their functional relevance for neuronal communication, brain functions and diseases is, however, not understood. In this paper, the propagation of intercellular calcium waves is modeled in terms of waves in excitable media on a stochastic support. We utilize a novel method to decompose the spatiotemporal patterns into space-time clusters (wave fragments). Based on this cluster decomposition, a statistical description of wave patterns is developed.
Wave/current interaction model
NASA Technical Reports Server (NTRS)
Liu, A. K.
1988-01-01
The wave-current interaction for the application to remote sensing data via numerical simulations and data comparison is modelled. Using the field data of surface current shear, wind condition and ambient wave spectrum, the numerical simulations of directional wave spectrum evolution were used to interpret and to compare with the aircraft data from Radar Ocean Wave Spectrometer (ROWS) and Surface Contour Radar (SCR) across the front during Frontal Air Sea Interaction Experiment (FASINEX). The wave-ice interaction was inspired by the observation of large amplitude waves hundreds of kms inside the ice pack in the Weddell Sea, resulting in breakup of the ice pack. The developed analysis of processes includes the refraction of waves at the pack edge, the effects of pack compression on wave propagation, wave train stability and buckling stability in the ice pack. Sources of pack compression and interaction between wave momentum and pack compression are investigated. Viscous camping of propagating waves in the marginal ice zone are also studied. The analysis suggests an explanation for the change in wave dispersion observed from the ship and the sequence of processes that cause ice pack breakup, pressure ridge formation and the formation of open bands of water.
ERIC Educational Resources Information Center
Ng, Chiu-king
2010-01-01
When one end of a taut horizontal elastic string is shaken repeatedly up and down, a transverse wave (assume sine waveform) will be produced and travel along it. College students know this type of wave motion well. They know when the wave passes by, each element of the string will perform an oscillating up-down motion, which in mechanics is termed…
Modelling seismic noise body waves
NASA Astrophysics Data System (ADS)
Stutzmann, Éléonore; Gualtieri, Lucia; Farra, Veronique; Capdeville, Yann; Schimmel, Martin; Ardhuin, Fabrice; Morelli, Andrea
2014-05-01
Secondary microseismic noise is generated by non-linear interactions between ocean waves at the ocean surface. We present the theory for computing the site effect of the ocean layer upon body waves generated by noise sources distributed along the ocean surface. We show that the ocean site effect can be described as the constructive interference of multiply reflected P-waves in the ocean that are then converted to either P-waves or SV-waves at the ocean-crust interface.The site effect varies strongly with period and ocean depth and that it is is stronger for P-waves than for S-waves. We validate our computation by comparing the theoretical noise body-wave sources with the sources inferred from beamforming analysis of the three seismogram components recorded by the Southern California Seismic Network. We use rotated traces for the beamforming analysis, and we show that we clearly detect P-waves generated by ocean gravity wave interactions along the track of typhoon Ioke (September 2006). We model the variability of the recorded P-waves associated with the typhon. We do not detect the corresponding SV-waves, and we demonstrate that this is because their amplitude is too weak to be detected.
Wave-particle dynamics of wave breaking in the self-excited dust acoustic wave.
Teng, Lee-Wen; Chang, Mei-Chu; Tseng, Yu-Ping; I, Lin
2009-12-11
The wave-particle microdynamics in the breaking of the self-excited dust acoustic wave growing in a dusty plasma liquid is investigated through directly tracking dust micromotion. It is found that the nonlinear wave growth and steepening stop as the mean oscillating amplitude of dust displacement reaches about 1/k (k is the wave number), where the vertical neighboring dust trajectories start to crossover and the resonant wave heating with uncertain crest trapping onsets. The dephased dust oscillations cause the abrupt dropping and broadening of the wave crest after breaking, accompanied by the transition from the liquid phase with coherent dust oscillation to the gas phase with chaotic dust oscillation. Corkscrew-shaped phase-space distributions measured at the fixed phases of the wave oscillation cycle clearly indicate how dusts move in and constitute the evolving waveform through dust-wave interaction.
Wave motions and wave heating in the upper solar atmosphere
NASA Astrophysics Data System (ADS)
Poletto, G.
The experimental and theoretical evidence favoring the wave heating mechanism in the low chromosphere is briefly reviewed, and the possibility of maintaining this mechanism, with proper modifications, in the higher layer is studied. Wave mode candidates for heating at high levels are analyzed, including gravity waves and Alfven waves. Waves in the upper chromosphere and the transition region are considered, showing power spectra of oscillations in lines forming at increasing heights in the solar atmosphere, fluctuations in UV line intensity, the predicted relationship between velocity and intensity modulation for acoustic waves, and sample results from UV spectrometer and polarimeter observations. It is concluded that in the upper chromosphere and transition regions, observations fail to reveal an acoustic flux adequate to compensate for the energy losses in these layers. Alfven waves, observed in the solar wind, could supply the required energy flux, but their presence cannot either be confirmed or ruled out.
Wave-particle dualism of spiral waves dynamics.
Biktasheva, I V; Biktashev, V N
2003-02-01
We demonstrate and explain a wave-particle dualism of such classical macroscopic phenomena as spiral waves in active media. That means although spiral waves appear as nonlocal processes involving the whole medium, they respond to small perturbations as effectively localized entities. The dualism appears as an emergent property of a nonlinear field and is mathematically expressed in terms of the spiral waves response functions, which are essentially nonzero only in the vicinity of the spiral wave core. Knowledge of the response functions allows quantitatively accurate prediction of the spiral wave drift due to small perturbations of any nature, which makes them as fundamental characteristics for spiral waves as mass is for the condensed matter.
Resonance wave pumping: wave mass transport pumping
NASA Astrophysics Data System (ADS)
Carmigniani, Remi; Violeau, Damien; Gharib, Morteza
2016-11-01
It has been previously reported that pinching at intrinsic resonance frequencies a valveless pump (or Liebau pump) results in a strong pulsating flow. A free-surface version of the Liebau pump is presented. The experiment consists of a closed tank with a submerged plate separating the water into a free-surface and a recirculation section connected through two openings at each end of the tank. A paddle is placed at an off-centre position at the free-surface and controlled in a heaving motion with different frequencies and amplitudes. Near certain frequencies identified as resonance frequencies through a linear potential theory analysis, the system behaves like a pump. Particle Image Velocimetry (PIV) is performed in the near free surface region and compared with simulations using Volume of Fluid (VOF) method. The mean eulerian mass flux field (ρ) is extracted. It is observed that the flow is located in the vicinity of the surface layer suggesting Stokes Drift (or Wave Mass Transport) is the source of the pumping. A model is developped to extend the linear potential theory to the second order to take into account these observations. The authors would like to acknowledge the Gordon and Betty Moore Foundation for their generous support.
NASA Astrophysics Data System (ADS)
Finn, L. S.
Astronomers rely on a multiplicity of observational perspectives in order to infer the nature of the Universe. Progress in astronomy has historically been associated with new or improved observational perspectives. Gravitational wave detectors now under construction will provide us with a perspective on the Universe fundamentally different from any we have come to know. With this new perspective comes the hope of new insights and understanding, not just of exotic astrophysical processes, but of "bread-and-butter" astrophysics: e.g., stars and stellar evolution, galaxy formation and evolution, neutron star structure, and cosmology. In this report the author discusses briefly a small subset of the areas of conventional, "bread-and-butter" astrophysics where we can reasonably hope that gravitational wave observations will provide us with valuable new insights and understandings.
Gravity wave initiated convection
NASA Technical Reports Server (NTRS)
Hung, R. J.
1990-01-01
The vertical velocity of convection initiated by gravity waves was investigated. In one particular case, the convective motion-initiated and supported by the gravity wave-induced activity (excluding contributions made by other mechanisms) reached its maximum value about one hour before the production of the funnel clouds. In another case, both rawinsonde and geosynchronous satellite imagery were used to study the life cycles of severe convective storms. Cloud modelling with input sounding data and rapid-scan imagery from GOES were used to investigate storm cloud formation, development and dissipation in terms of growth and collapse of cloud tops, as well as, the life cycles of the penetration of overshooting turrets above the tropopause. The results based on these two approaches are presented and discussed.
Yin, Jun; Zhang, Zhuhua; Li, Xuemei; Yu, Jin; Zhou, Jianxin; Chen, Yaqing; Guo, Wanlin
2014-05-06
Nanoscale materials offer much promise in the pursuit of high-efficient energy conversion technology owing to their exceptional sensitivity to external stimulus. In particular, experiments have demonstrated that flowing water over carbon nanotubes can generate electric voltages. However, the reported flow-induced voltages are in wide discrepancy and the proposed mechanisms remain conflictive. Here we find that moving a liquid-gas boundary along a piece of graphene can induce a waving potential of up to 0.1 V. The potential is proportional to the moving velocity and the graphene length inserted into ionic solutions, but sharply decreases with increasing graphene layers and vanishes in other materials. This waving potential arises from charge transfer in graphene driven by a moving boundary of an electric double layer between graphene and ionic solutions. The results reveal a unique electrokinetic phenomenon and open prospects for functional sensors, such as tsunami monitors.
Nonlinear Hysteretic Torsional Waves
NASA Astrophysics Data System (ADS)
Cabaret, J.; Béquin, P.; Theocharis, G.; Andreev, V.; Gusev, V. E.; Tournat, V.
2015-07-01
We theoretically study and experimentally report the propagation of nonlinear hysteretic torsional pulses in a vertical granular chain made of cm-scale, self-hanged magnetic beads. As predicted by contact mechanics, the torsional coupling between two beads is found to be nonlinear hysteretic. This results in a nonlinear pulse distortion essentially different from the distortion predicted by classical nonlinearities and in a complex dynamic response depending on the history of the wave particle angular velocity. Both are consistent with the predictions of purely hysteretic nonlinear elasticity and the Preisach-Mayergoyz hysteresis model, providing the opportunity to study the phenomenon of nonlinear dynamic hysteresis in the absence of other types of material nonlinearities. The proposed configuration reveals a plethora of interesting phenomena including giant amplitude-dependent attenuation, short-term memory, as well as dispersive properties. Thus, it could find interesting applications in nonlinear wave control devices such as strong amplitude-dependent filters.
Nonlinear Hysteretic Torsional Waves.
Cabaret, J; Béquin, P; Theocharis, G; Andreev, V; Gusev, V E; Tournat, V
2015-07-31
We theoretically study and experimentally report the propagation of nonlinear hysteretic torsional pulses in a vertical granular chain made of cm-scale, self-hanged magnetic beads. As predicted by contact mechanics, the torsional coupling between two beads is found to be nonlinear hysteretic. This results in a nonlinear pulse distortion essentially different from the distortion predicted by classical nonlinearities and in a complex dynamic response depending on the history of the wave particle angular velocity. Both are consistent with the predictions of purely hysteretic nonlinear elasticity and the Preisach-Mayergoyz hysteresis model, providing the opportunity to study the phenomenon of nonlinear dynamic hysteresis in the absence of other types of material nonlinearities. The proposed configuration reveals a plethora of interesting phenomena including giant amplitude-dependent attenuation, short-term memory, as well as dispersive properties. Thus, it could find interesting applications in nonlinear wave control devices such as strong amplitude-dependent filters.
Bergshoeff, E.A. ); Kallosh, R.; Ortin, T. )
1993-06-15
We present plane-wave-type solutions of the lowest-order superstring effective action which have unbroken space-time supersymmetries. They are given by a stringy generalization of the Brinkmann metric, dialton, axion, and gauge fields. Some conspiracy between the metric and the axion field is required. The [alpha][prime] stringy corrections to the effective on-shell action, to the equations of motion (and therefore to the solutions themselves), and to the supersymmetry transformations are shown to vanish for a special class of these solutions that we call supersymmetric string waves (SSW's). In the SSW solutions, there exists a conspiracy not only between the metric and the axion field, but also between the gauge fields and the metric, since the embedding of the spin connection in the gauge group is required.
Wave transformation over coral reefs
NASA Astrophysics Data System (ADS)
Young, Ian R.
1989-07-01
Ocean wave attenuation on coral reefs is discussed using data obtained from a preliminary field experiment and from the Seasat altimeter. Marked attenuation of the waves is observed, the rate being consistent with existing theories of bottom friction and wave breaking decay. In addition, there is a significant broadening of the spectrum during propagation across reefs. Three-dimensional effects, such as refraction and defraction, can also lead to substantial wave height reduction for significant distances adjacent to coral reefs. As a result, a matrix of such reefs provides significantly more wave attenuation than may initially be expected.
NASA Astrophysics Data System (ADS)
Miles, John
2001-09-01
The eigenvalue problem for gravity waves on a shear flow of depth h and non-inflected velocity profile U(y) (typically parabolic) is revisited, following Burns (1953) and Yih (1972). Complementary variational formulations that provide upper and lower bounds to the Froude number F as a function of the wave speed c and wavenumber k are constructed. These formulations are used to improve Burns's long-wave approximation and to determine Yih's critical wavenumber k[low asterisk], for which the wave is stationary (c = 0) and to which k must be inferior for the existence of an upstream running wave.
Stigloher, J; Decker, M; Körner, H S; Tanabe, K; Moriyama, T; Taniguchi, T; Hata, H; Madami, M; Gubbiotti, G; Kobayashi, K; Ono, T; Back, C H
2016-07-15
We report the experimental observation of Snell's law for magnetostatic spin waves in thin ferromagnetic Permalloy films by imaging incident, refracted, and reflected waves. We use a thickness step as the interface between two media with different dispersion relations. Since the dispersion relation for magnetostatic waves in thin ferromagnetic films is anisotropic, deviations from the isotropic Snell's law known in optics are observed for incidence angles larger than 25° with respect to the interface normal between the two magnetic media. Furthermore, we can show that the thickness step modifies the wavelength and the amplitude of the incident waves. Our findings open up a new way of spin wave steering for magnonic applications.
Wave Engine Topping Cycle Assessment
NASA Technical Reports Server (NTRS)
Welch, Gerard E.
1996-01-01
The performance benefits derived by topping a gas turbine engine with a wave engine are assessed. The wave engine is a wave rotor that produces shaft power by exploiting gas dynamic energy exchange and flow turning. The wave engine is added to the baseline turboshaft engine while keeping high-pressure-turbine inlet conditions, compressor pressure ratio, engine mass flow rate, and cooling flow fractions fixed. Related work has focused on topping with pressure-exchangers (i.e., wave rotors that provide pressure gain with zero net shaft power output); however, more energy can be added to a wave-engine-topped cycle leading to greater engine specific-power-enhancement The energy addition occurs at a lower pressure in the wave-engine-topped cycle; thus the specific-fuel-consumption-enhancement effected by ideal wave engine topping is slightly lower than that effected by ideal pressure-exchanger topping. At a component level, however, flow turning affords the wave engine a degree-of-freedom relative to the pressure-exchanger that enables a more efficient match with the baseline engine. In some cases, therefore, the SFC-enhancement by wave engine topping is greater than that by pressure-exchanger topping. An ideal wave-rotor-characteristic is used to identify key wave engine design parameters and to contrast the wave engine and pressure-exchanger topping approaches. An aerodynamic design procedure is described in which wave engine design-point performance levels are computed using a one-dimensional wave rotor model. Wave engines using various wave cycles are considered including two-port cycles with on-rotor combustion (valved-combustors) and reverse-flow and through-flow four-port cycles with heat addition in conventional burners. A through-flow wave cycle design with symmetric blading is used to assess engine performance benefits. The wave-engine-topped turboshaft engine produces 16% more power than does a pressure-exchanger-topped engine under the specified topping
NASA Astrophysics Data System (ADS)
Stigloher, J.; Decker, M.; Körner, H. S.; Tanabe, K.; Moriyama, T.; Taniguchi, T.; Hata, H.; Madami, M.; Gubbiotti, G.; Kobayashi, K.; Ono, T.; Back, C. H.
2016-07-01
We report the experimental observation of Snell's law for magnetostatic spin waves in thin ferromagnetic Permalloy films by imaging incident, refracted, and reflected waves. We use a thickness step as the interface between two media with different dispersion relations. Since the dispersion relation for magnetostatic waves in thin ferromagnetic films is anisotropic, deviations from the isotropic Snell's law known in optics are observed for incidence angles larger than 25 ° with respect to the interface normal between the two magnetic media. Furthermore, we can show that the thickness step modifies the wavelength and the amplitude of the incident waves. Our findings open up a new way of spin wave steering for magnonic applications.
Spatiotemporal chaos involving wave instability
NASA Astrophysics Data System (ADS)
Berenstein, Igal; Carballido-Landeira, Jorge
2017-01-01
In this paper, we investigate pattern formation in a model of a reaction confined in a microemulsion, in a regime where both Turing and wave instability occur. In one-dimensional systems, the pattern corresponds to spatiotemporal intermittency where the behavior of the systems alternates in both time and space between stationary Turing patterns and traveling waves. In two-dimensional systems, the behavior initially may correspond to Turing patterns, which then turn into wave patterns. The resulting pattern also corresponds to a chaotic state, where the system alternates in both space and time between standing wave patterns and traveling waves, and the local dynamics may show vanishing amplitude of the variables.
Introduction to the Physics of Waves
NASA Astrophysics Data System (ADS)
Freegarde, Tim
2012-11-01
Preface; 1. The essence of wave motion; 2. Wave equations and their solution; 3. Further wave equations; 4. Sinusoidal waveforms; 5. Complex wavefunctions; 6. Huygens wave propagation; 7. Geometrical optics; 8. Interference; 9. Fraunhofer diffraction; 10. Longitudinal waves; 11. Continuity conditions; 12. Boundary conditions; 13. Linearity and superpositions; 14. Fourier series and transforms; 15. Waves in three dimensions; 16. Operators for wave motions; 17. Uncertainty and quantum mechanics; 18. Waves from moving sources; 19. Radiation from moving charges; Appendix: vector mathematics; Index.
A statistical study of EMIC waves observed by Cluster. 1. Wave properties. EMIC Wave Properties
Allen, R. C.; Zhang, J. -C.; Kistler, L. M.; Spence, H. E.; Lin, R. -L.; Klecker, B.; Dunlop, M. W.; André, M.; Jordanova, V. K.
2015-07-23
Electromagnetic ion cyclotron (EMIC) waves are an important mechanism for particle energization and losses inside the magnetosphere. In order to better understand the effects of these waves on particle dynamics, detailed information about the occurrence rate, wave power, ellipticity, normal angle, energy propagation angle distributions, and local plasma parameters are required. Previous statistical studies have used in situ observations to investigate the distribution of these parameters in the magnetic local time versus L-shell (MLT-L) frame within a limited magnetic latitude (MLAT) range. In our study, we present a statistical analysis of EMIC wave properties using 10 years (2001–2010) of data from Cluster, totaling 25,431 min of wave activity. Due to the polar orbit of Cluster, we are able to investigate EMIC waves at all MLATs and MLTs. This allows us to further investigate the MLAT dependence of various wave properties inside different MLT sectors and further explore the effects of Shabansky orbits on EMIC wave generation and propagation. Thus, the statistical analysis is presented in two papers. OUr paper focuses on the wave occurrence distribution as well as the distribution of wave properties. The companion paper focuses on local plasma parameters during wave observations as well as wave generation proxies.
A statistical study of EMIC waves observed by Cluster. 1. Wave properties. EMIC Wave Properties
Allen, R. C.; Zhang, J. -C.; Kistler, L. M.; ...
2015-07-23
Electromagnetic ion cyclotron (EMIC) waves are an important mechanism for particle energization and losses inside the magnetosphere. In order to better understand the effects of these waves on particle dynamics, detailed information about the occurrence rate, wave power, ellipticity, normal angle, energy propagation angle distributions, and local plasma parameters are required. Previous statistical studies have used in situ observations to investigate the distribution of these parameters in the magnetic local time versus L-shell (MLT-L) frame within a limited magnetic latitude (MLAT) range. In our study, we present a statistical analysis of EMIC wave properties using 10 years (2001–2010) of datamore » from Cluster, totaling 25,431 min of wave activity. Due to the polar orbit of Cluster, we are able to investigate EMIC waves at all MLATs and MLTs. This allows us to further investigate the MLAT dependence of various wave properties inside different MLT sectors and further explore the effects of Shabansky orbits on EMIC wave generation and propagation. Thus, the statistical analysis is presented in two papers. OUr paper focuses on the wave occurrence distribution as well as the distribution of wave properties. The companion paper focuses on local plasma parameters during wave observations as well as wave generation proxies.« less
1987-06-20
69 4.2.1 Data of Peregrine . ..... ......... .69 4.2.2 Lituya Bay Landslide Wave .. ........ .. 69 1......................7 6...iii LIST OF ILLUSTIATIONS Figure la: Map of Lituya Bay Showing Forest Trimline .......... (Miller, 1960) Figure Ib: Photo ra h of Lituya Bay Before...have felt it appropriate to present some new results even here, as will be shown later. Lituya Bay is situated on the Gulf of Alaska south of Yakutat
NASA Technical Reports Server (NTRS)
2006-01-01
Internal waves are waves that travel within the interior of a fluid. The waves propagate at the interface or boundary between two layers with sharp density differences, such as temperature. They occur wherever strong tides or currents and stratification occur in the neighborhood of irregular topography. They can propagate for several hundred kilometers. The ASTER false-color VNIR image off the island of Tsushima in the Korea Strait shows the signatures of several internal wave packets, indicating a northern propagation direction.
With its 14 spectral bands from the visible to the thermal infrared wavelength region, and its high spatial resolution of 15 to 90 meters (about 50 to 300 feet), ASTER images Earth to map and monitor the changing surface of our planet.
ASTER is one of five Earth-observing instruments launched December 18, 1999, on NASA's Terra satellite. The instrument was built by Japan's Ministry of Economy, Trade and Industry. A joint U.S./Japan science team is responsible for validation and calibration of the instrument and the data products.
The broad spectral coverage and high spectral resolution of ASTER provides scientists in numerous disciplines with critical information for surface mapping, and monitoring of dynamic conditions and temporal change. Example applications are: monitoring glacial advances and retreats; monitoring potentially active volcanoes; identifying crop stress; determining cloud morphology and physical properties; wetlands evaluation; thermal pollution monitoring; coral reef degradation; surface temperature mapping of soils and geology; and measuring surface heat balance.
The U.S. science team is located at NASA's Jet Propulsion Laboratory, Pasadena, Calif. The Terra mission is part of NASA's Science Mission Directorate.
Size: 60 by 120 kilometers (37.2 by 74.4 miles) Location: 34.6 degrees North latitude, 129.5 degrees East longitude Orientation: North at top Image Data: ASTER bands 3, 2, and 1
1987-11-23
generalized wave equation (GWE) when (z) 0 (1-Z2)/2: - X(z). (1.5) The compatibility condition required for the existence of solutions to these B~icklund...Phys. tion of a class of nonlocal nonlinear evolution equations , A 15 (1982) 781. INS *47, Clarkson University (1985), to be published in J. Math... semilinear form. The above approach will fail if there exist linearizable quasilinear equations which can not be mapped to a semilinear from. It is shown in
NASA Astrophysics Data System (ADS)
Tian, Jing
2001-03-01
The telecom wave is sweeping the globe; however, many of us feel caught in backwater disciplines. How does one leverage her skills to become a player in a fast-growing field? This talk will suggest some strategies and share some personal experiences: in transitioning from established companies (electronics and biotech) to a very early stage telecom start-up; in choosing an appropriate industry segment and the right startup; and in preparing for immersing oneself in the start up environment.
Millimeter Wave Antenna Technology,
1984-09-30
development work will be required. Milli- meter wave antennas play a key role in the rationale for millimeter system designs beas ihspatial resolution...results in their popularity for multiple bea applications. In their design, care ust be exercised to minimize reflection losses at the lens surfaces...Alternatively, the radome surface may be treated to repel the water, and rivulet flow results. Since the water is more randomly distribu- ted, the gain loss is
Wave rotor demonstrator engine assessment
NASA Technical Reports Server (NTRS)
Snyder, Philip H.
1996-01-01
The objective of the program was to determine a wave rotor demonstrator engine concept using the Allison 250 series engine. The results of the NASA LERC wave rotor effort were used as a basis for the wave rotor design. A wave rotor topped gas turbine engine was identified which incorporates five basic requirements of a successful demonstrator engine. Predicted performance maps of the wave rotor cycle were used along with maps of existing gas turbine hardware in a design point study. The effects of wave rotor topping on the engine cycle and the subsequent need to rematch compressor and turbine sections in the topped engine were addressed. Comparison of performance of the resulting engine is made on the basis of wave rotor topped engine versus an appropriate baseline engine using common shaft compressor hardware. The topped engine design clearly demonstrates an impressive improvement in shaft horsepower (+11.4%) and SFC (-22%). Off design part power engine performance for the wave rotor topped engine was similarly improved including that at engine idle conditions. Operation of the engine at off design was closely examined with wave rotor operation at less than design burner outlet temperatures and rotor speeds. Challenges identified in the development of a demonstrator engine are discussed. A preliminary design was made of the demonstrator engine including wave rotor to engine transition ducts. Program cost and schedule for a wave rotor demonstrator engine fabrication and test program were developed.
NASA Astrophysics Data System (ADS)
Golenitskii, K. Â. Yu.; Koshelev, K. Â. L.; Bogdanov, A. Â. A.
2016-10-01
In this work we develop a theory of surface electromagnetic waves localized at the interface of periodic metal-dielectric structures. We have shown that the anisotropy of plasma frequency in metal layers lifts the degeneracy of plasma oscillations and opens a series of photonic band gaps. This results in appearance of surface waves with singular density of states—we refer to them as Tamm-Langmuir waves. Such naming is natural since we have found that their properties are very similar to the properties of both bulk Langmuir and surface Tamm waves. Depending on the anisotropy parameters, Tamm-Langmuir waves can be either forward or backward waves. Singular density of states and high sensitivity of the dispersion to the anisotropy of the structure makes Tamm-Langmuir waves very promising for potential applications in nanophotonics and biosensing.
NASA Technical Reports Server (NTRS)
Lee, Jeongwoo W.
1993-01-01
In this paper we analyze the generation of waves in a sunspot by extending Stein's hydrodynamic approach to the turbulent medium permeated by a strong uniform magnetic field oriented parallel to the gravity. For wave sources appropriate to the sunspot, we consider magnetic perturbations and entropy changes as well as turbulent convection. To describe the anisotropy imposed by the sunspot, we use a one-dimensional correlation function relating the turbulent eddies separated along the symmetry axis of the spot. This treatment yields several interesting possibilities for wave generation in a sunspot. First, it is demonstrated that the entropy change and magnetic perturbation can lead to a relative enhancement of acoustic wave emission. Second, the energy flux of Alfven waves may be comparable to that of acoustic waves in sunspots. Third, the anisotropy of the sunspot dynamics can lead to wave energy spectrum in a form which may explain the origin of umbral atmospheric oscillations.
Turbulent Shear and Internal Waves
NASA Astrophysics Data System (ADS)
Munroe, James; Sutherland, Bruce
2008-11-01
A series of experiments is presented that model the generation of non-hydrostatic internal gravity waves in upper ocean by the forcing of wind driven turbulent eddies in the surface mixed layer. A turbulent shear layer is forced by a conveyor belt with affixed flat plates near the surface of a stratified fluid and downward propagating internal waves are generated. The turbulence in the shear layer is characterized using particle image velocimetry to measure the kinetic energy as well as length and time scales. The internal waves are measured using synthetic schlieren to determine the amplitudes, frequencies, momentum fluxes, and the energy of the generated waves. The fraction of energy that leaks from the mixed layer to the internal wave field is presented. Consistent with other studies, it is found that the frequencies of internal waves generated by turbulence are an approximate constant fraction of the buoyancy frequency. Implications to internal waves propagating into the deep ocean will be discussed.
Assessing wave energy effects on biodiversity: the wave hub experience.
Witt, M J; Sheehan, E V; Bearhop, S; Broderick, A C; Conley, D C; Cotterell, S P; Crow, E; Grecian, W J; Halsband, C; Hodgson, D J; Hosegood, P; Inger, R; Miller, P I; Sims, D W; Thompson, R C; Vanstaen, K; Votier, S C; Attrill, M J; Godley, B J
2012-01-28
Marine renewable energy installations harnessing energy from wind, wave and tidal resources are likely to become a large part of the future energy mix worldwide. The potential to gather energy from waves has recently seen increasing interest, with pilot developments in several nations. Although technology to harness wave energy lags behind that of wind and tidal generation, it has the potential to contribute significantly to energy production. As wave energy technology matures and becomes more widespread, it is likely to result in further transformation of our coastal seas. Such changes are accompanied by uncertainty regarding their impacts on biodiversity. To date, impacts have not been assessed, as wave energy converters have yet to be fully developed. Therefore, there is a pressing need to build a framework of understanding regarding the potential impacts of these technologies, underpinned by methodologies that are transferable and scalable across sites to facilitate formal meta-analysis. We first review the potential positive and negative effects of wave energy generation, and then, with specific reference to our work at the Wave Hub (a wave energy test site in southwest England, UK), we set out the methodological approaches needed to assess possible effects of wave energy on biodiversity. We highlight the need for national and international research clusters to accelerate the implementation of wave energy, within a coherent understanding of potential effects-both positive and negative.
Generation of rogue waves in a wave tank
NASA Astrophysics Data System (ADS)
Lechuga, A.
2012-04-01
Rogue waves have been reported as causing damages and ship accidents all over the oceans of the world. For this reason in the past decades theoretical studies have been carried out with the double aim of improving the knowledge of their main characteristics and of attempting to predict its sudden appearance. As an effort on this line we are trying to generate them in a water tank. The description of the procedure to do that is the objective of this presentation. After Akhmediev et al. (2011) we use a symmetric spectrum as input on the wave maker to produce waves with a rate(Maximun wave height/ significant wave height) of 2.33 and a kurtosis of 4.77, clearly between the limits of rogue waves. As it was pointed out by Janssen (2003), Onorato et al. (2006) and Kharif, Pelinovsky and Slunyaev (2009) modulation instability is enhanced when waves depart from Gaussian statistics (i.e. big kurtosis) and therefore both numbers enforce the criterion that we are generating genuine rogue waves. The same is confirmed by Shemer (2010) and Dudley et al.(2009) from a different perspective. If besides being symmetrical the spectrum is triangular, following Akhmediev(2011),the generated waves are even more conspicuously rogue waves.
Shear wave speed recovery in sonoelastography using crawling wave data.
Lin, Kui; McLaughlin, Joyce; Renzi, Daniel; Thomas, Ashley
2010-07-01
The crawling wave experiment, in which two harmonic sources oscillate at different but nearby frequencies, is a development in sonoelastography that allows real-time imaging of propagating shear wave interference patterns. Previously the crawling wave speed was recovered and used as an indicator of shear stiffness; however, it is shown in this paper that the crawling wave speed image can have artifacts that do not represent a change in stiffness. In this paper, the locations and shapes of some of the artifacts are exhibited. In addition, a differential equation is established that enables imaging of the shear wave speed, which is a quantity strongly correlated with shear stiffness change. The full algorithm is as follows: (1) extract the crawling wave phase from the spectral variance data; (2) calculate the crawling wave phase wave speed; (3) solve a first-order PDE for the phase of the wave emanating from one of the sources; and (4) compute and image the shear wave speed on a grid in the image plane.
Pan Xiaoyin; Slamet, Marlina; Sahni, Viraht
2010-04-15
We extend our prior work on the construction of variational wave functions {psi} that are functionals of functions {chi}:{psi}={psi}[{chi}] rather than simply being functions. In this manner, the space of variations is expanded over those of traditional variational wave functions. In this article we perform the constrained search over the functions {chi} chosen such that the functional {psi}[{chi}] satisfies simultaneously the constraints of normalization and the exact expectation value of an arbitrary single- or two-particle Hermitian operator, while also leading to a rigorous upper bound to the energy. As such the wave function functional is accurate not only in the region of space in which the principal contributions to the energy arise but also in the other region of the space represented by the Hermitian operator. To demonstrate the efficacy of these ideas, we apply such a constrained search to the ground state of the negative ion of atomic hydrogen H{sup -}, the helium atom He, and its positive ions Li{sup +} and Be{sup 2+}. The operators W whose expectations are obtained exactly are the sum of the single-particle operators W={Sigma}{sub i}r{sub i}{sup n},n=-2,-1,1,2, W={Sigma}{sub i{delta}}(r{sub i}), W=-(1/2){Sigma}{sub i{nabla}i}{sup 2}, and the two-particle operators W={Sigma}{sub n}u{sup n},n=-2,-1,1,2, where u=|r{sub i}-r{sub j}|. Comparisons with the method of Lagrangian multipliers and of other constructions of wave-function functionals are made. Finally, we present further insights into the construction of wave-function functionals by studying a previously proposed construction of functionals {psi}[{chi}] that lead to the exact expectation of arbitrary Hermitian operators. We discover that analogous to the solutions of the Schroedinger equation, there exist {psi}[{chi}] that are unphysical in that they lead to singular values for the expectations. We also explain the origin of the singularity.
Relevance of Infragravity Waves in a Wave Dominated Shallow Inlet
NASA Astrophysics Data System (ADS)
Olabarrieta, M.; Bertin, X.
2014-12-01
Infragravity (IG) waves have received a growing attention over the last decade and they have been shown to partly control dune erosion, barrier breaching, development of seiches in harbors or the circulation on fringing reefs. Although the relevance IG waves in surf and swash zone dynamics is well recognized, their dynamics and effects on tidal inlets and estuaries have not been analyzed. This study investigates the importance of IG waves at Albufeira Lagoon Inlet, a shallow wave-dominated inlet located on the western Coast of Portugal. Water levels and currents were measured synchronously during a two-day field experiment carried out at Albufeira Lagoon Inlet in September 2010. Apart from the tidally induced gravity wave modulations and wave induced setup inside the lagoon, an important IG wave contribution was identified. Low frequency oscillations were noticeable in the free surface elevation records and produced fluctuations of up to 100% in current intensities. While IG waves in the ebb shoal were present during the whole tidal cycle, the absence of IG waves characterized the ebbing tide inside the lagoon. The energy in the IG frequency band gradually increased from low tide to high tide, and disappeared during the ebbing tide. The modeling system Xbeach was applied to hindcast the hydrodynamics during the field experiment period. The model captures the main physics related with the IG wave generation and propagation inside the inlet, and reproduced the IG blocking during the ebb as identified in the measurements. This behavior was explained by the combination of advection and wave blocking induced by opposing tidal currents. Both measurements and numerical results suggested the bound wave release as the dominant mechanism responsible for IG wave generation. The fact that IG waves only propagate at flood tide has strong implications on the sediment balance of the inlet and contribute to inlet infilling under energetic wave conditions. It is expected that IG
Coexisting rogue waves within the (2+1)-component long-wave-short-wave resonance.
Chen, Shihua; Soto-Crespo, Jose M; Grelu, Philippe
2014-09-01
The coexistence of two different types of fundamental rogue waves is unveiled, based on the coupled equations describing the (2+1)-component long-wave-short-wave resonance. For a wide range of asymptotic background fields, each family of three rogue wave components can be triggered by using a slight deterministic alteration to the otherwise identical background field. The ability to trigger markedly different rogue wave profiles from similar initial conditions is confirmed by numerical simulations. This remarkable feature, which is absent in the scalar nonlinear Schrödinger equation, is attributed to the specific three-wave interaction process and may be universal for a variety of multicomponent wave dynamics spanning from oceanography to nonlinear optics.
Introduction to Wave Turbulence Formalisms for Incoherent Optical Waves
NASA Astrophysics Data System (ADS)
Picozzi, Antonio; Garnier, Josselin; Xu, Gang; Rica, Sergio
We provide an introduction to different wave turbulence formalisms describing the propagation of partially incoherent optical waves in nonlinear media. We consider the nonlinear Schrödinger equation as a representative model accounting for a nonlocal or a noninstantaneous nonlinearity, as well as higher-order dispersion effects. We discuss the wave turbulence kinetic equation describing, e.g., wave condensation or wave thermalization through supercontinuum generation; the Vlasov formalism describing incoherent modulational instabilities and the formation of large scale incoherent localized structures in analogy with long-range gravitational systems; and the weak Langmuir turbulence formalism describing spectral incoherent solitons, as well as spectral shock or collapse singularities. Finally, recent developments and some open questions are discussed, in particular in relation with a wave turbulence formulation of laser systems and different mechanisms of breakdown of thermalization.
WAVE DELAYING STRUCTURE FOR RECTANGULAR WAVE-GUIDES
Robertson-Shersby-Harvie, R.B.; Dain, J.
1956-11-13
This patent relates to wave-guides and in particular describes wave delaying structure located within a wave-guide. The disclosed wave-guide has an elongated fiat metal sheet arranged in a central plane of the guide and formed with a series of transverse inductive slots such that each face presents an inductive impedance to the guide. The sheet is thickened in the area between slots to increase the self capacity of the slots. Experimental results indicate that in a wave-guide loaded in accordance with the invention the guided wavelength changes more slowly as the air wavelength is changed than the guided wavelength does in wave-guides loaded by means of corrugations.
Coded Excitation Plane Wave Imaging for Shear Wave Motion Detection
Song, Pengfei; Urban, Matthew W.; Manduca, Armando; Greenleaf, James F.; Chen, Shigao
2015-01-01
Plane wave imaging has greatly advanced the field of shear wave elastography thanks to its ultrafast imaging frame rate and the large field-of-view (FOV). However, plane wave imaging also has decreased penetration due to lack of transmit focusing, which makes it challenging to use plane waves for shear wave detection in deep tissues and in obese patients. This study investigated the feasibility of implementing coded excitation in plane wave imaging for shear wave detection, with the hypothesis that coded ultrasound signals can provide superior detection penetration and shear wave signal-to-noise-ratio (SNR) compared to conventional ultrasound signals. Both phase encoding (Barker code) and frequency encoding (chirp code) methods were studied. A first phantom experiment showed an approximate penetration gain of 2-4 cm for the coded pulses. Two subsequent phantom studies showed that all coded pulses outperformed the conventional short imaging pulse by providing superior sensitivity to small motion and robustness to weak ultrasound signals. Finally, an in vivo liver case study on an obese subject (Body Mass Index = 40) demonstrated the feasibility of using the proposed method for in vivo applications, and showed that all coded pulses could provide higher SNR shear wave signals than the conventional short pulse. These findings indicate that by using coded excitation shear wave detection, one can benefit from the ultrafast imaging frame rate and large FOV provided by plane wave imaging while preserving good penetration and shear wave signal quality, which is essential for obtaining robust shear elasticity measurements of tissue. PMID:26168181
Rogue waves emerging from the resonant interaction of three waves.
Baronio, Fabio; Conforti, Matteo; Degasperis, Antonio; Lombardo, Sara
2013-09-13
We introduce a novel family of analytic solutions of the three-wave resonant interaction equations for the purpose of modeling unique events, i.e., "amplitude peaks" which are isolated in space and time. The description of these solutions is likely to be a crucial step in the understanding and forecasting of rogue waves in a variety of multicomponent wave dynamics, from oceanography to optics and from plasma physics to acoustics.
Complementary optical rogue waves in parametric three-wave mixing.
Chen, Shihua; Cai, Xian-Ming; Grelu, Philippe; Soto-Crespo, J M; Wabnitz, Stefan; Baronio, Fabio
2016-03-21
We investigate the resonant interaction of two optical pulses of the same group velocity with a pump pulse of different velocity in a weakly dispersive quadratic medium and report on the complementary rogue wave dynamics which are unique to such a parametric three-wave mixing. Analytic rogue wave solutions up to the second order are explicitly presented and their robustness is confirmed by numerical simulations, in spite of the onset of modulation instability activated by quantum noise.
Wave and particle dynamics of the beat-wave accelerator
Gibbon, P. )
1989-10-15
We present two-dimensional wave-envelope studies of the interaction between a plasma beat-wave and the laser pumps which drive it. A new method of focusing is demonstrated which requires the plasma wave to be driven slightly below its resonant frequency. Test particles are employed to investigate possible means of extending the accelerator stage length. {copyright} 1989 American Institute of Physics
Scattering and Depolarization of Electromagnetic Waves--Full Wave Solutions.
1984-01-01
Analysis," Proceedings of the International Union of Radio Science URSI Conference at Ciudad Universitaria , Madrid, August 1983, in press. . . 13...rough land and seat3 J. The full wave approach was also used to determine the scattering and depolarization of radio waves in irregular spheroidal struc...Full Wave Solutions," Radio Science, Vol. 17, No. 5, September-October 1982, pp. 1055-1066. 4. "Scattering and Depolarization by Rough Surfaces: Full
Parametric wave phase conjugation of nonlinear ultrasound waves
NASA Astrophysics Data System (ADS)
Brysev, Andrew; Mikhalevich, Vladislav; Streltsov, Vladimir
2003-10-01
Real time acoustic wave phase conjugation (WPC), based on parametric self-consistent physical mechanisms, was realized up to the present time only for the monochromatic waves [A. P. Brysev et al., Phys.-Usp. 41, 793 (1998)]. Here the possibility of WPC of nonmonochromatic ultrasound waves is considered. For simultaneous WPC of the entire series of spectral components generated by nonlinear propagation of the incident wave we propose the use of phonon-plasmon interaction in piezosemiconductors. WPC of nonlinear acoustic waves can be accomplished by modulation of the electron density provided by a sequence of short laser pulses pumping the sample. If the periodicity of the optical pulses is half the period of the fundamental component of the acoustic wave, such wide-band, excitation leads to self-synchronized parametric conjugation of each spectral component in the incident wave. The conjugation efficiency depends sharply on relations between acoustical frequency content, laser pulse duration, and interband relaxation time. It is shown that under certain conditions the time profile of the conjugate wave may be efficiently controlled by varying the duration of the laser pulses. The time profile of the conjugate wave is investigated for some physical conditions of practical interest.
Helical localized wave solutions of the scalar wave equation.
Overfelt, P L
2001-08-01
A right-handed helical nonorthogonal coordinate system is used to determine helical localized wave solutions of the homogeneous scalar wave equation. Introducing the characteristic variables in the helical system, i.e., u = zeta - ct and v = zeta + ct, where zeta is the coordinate along the helical axis, we can use the bidirectional traveling plane wave representation and obtain sets of elementary bidirectional helical solutions to the wave equation. Not only are these sets bidirectional, i.e., based on a product of plane waves, but they may also be broken up into right-handed and left-handed solutions. The elementary helical solutions may in turn be used to create general superpositions, both Fourier and bidirectional, from which new solutions to the wave equation may be synthesized. These new solutions, based on the helical bidirectional superposition, are members of the class of localized waves. Examples of these new solutions are a helical fundamental Gaussian focus wave mode, a helical Bessel-Gauss pulse, and a helical acoustic directed energy pulse train. Some of these solutions have the interesting feature that their shape and localization properties depend not only on the wave number governing propagation along the longitudinal axis but also on the normalized helical pitch.
Conversion of borehole Stoneley waves to channel waves in coal
Johnson, P.A.; Albright, J.N.
1987-01-01
Evidence for the mode conversion of borehole Stoneley waves to stratigraphically guided channel waves was discovered in data from a crosswell acoustic experiment conducted between wells penetrating thin coal strata located near Rifle, Colorado. Traveltime moveout observations show that borehole Stoneley waves, excited by a transmitter positioned at substantial distances in one well above and below a coal stratum at 2025 m depth, underwent partial conversion to a channel wave propagating away from the well through the coal. In an adjacent well the channel wave was detected at receiver locations within the coal, and borehole Stoneley waves, arising from a second partial conversion of channel waves, were detected at locations above and below the coal. The observed channel wave is inferred to be the third-higher Rayleigh mode based on comparison of the measured group velocity with theoretically derived dispersion curves. The identification of the mode conversion between borehole and stratigraphically guided waves is significant because coal penetrated by multiple wells may be detected without placing an acoustic transmitter or receiver within the waveguide. 13 refs., 6 figs., 1 tab.
Rossby wave, drift wave and zonal flow turbulence
NASA Astrophysics Data System (ADS)
Quinn, Brenda E.
An extensive qualitative and quantitative study of Rossby wave, drift wave and zonal flow turbulence in the Charney-Hasegawa-Mima model is presented. This includes details of two generation mechanisms of the zonal flows, evidence of the nonlocal nature of this turbulence and of the energy exchange between the small and large scales. The modulational instability study shows that for strong primary waves the most unstable modes are perpendicular to the primary wave, which corresponds to the generation of a zonal flow if the primary wave is purely meridional. For weak waves, the maximum growth occurs for off-zonal modulations that are close to being in three-wave resonance with the primary wave. Nonlinear jet pinching is observed for all nonlinearity levels but the subsequent dynamics differ between strong and weak primary waves. The jets of the former further roll up into Karman-like vortex streets and saturate, while for the latter, the growth of the unstable mode reverses and the system oscillates between a dominant jet and a dominant primary wave. A critical level of nonlinearity is defined which separates the two regimes. Some of these characteristics are captured by truncated models. Numerical proof of the extra invariant in Rossby and drift wave turbulence is presented. While the theoretical derivations of this invariant stem from the wave kinetic equation which assumes weak wave amplitudes, it is shown to be relatively-well conserved for higher nonlinearities also. Together with the energy and enstrophy, these three invariants cascade into anisotropic sectors in the k-space as predicted by the Fjortoft argument. The cascades are characterised by the zonostrophy pushing the energy to the zonal scales. A small scale instability forcing applied to the model has demonstrated the wellknown drift wave - zonal flow feedback loop. The drift wave turbulence is generated from this primary instability. The zonal flows are then excited by either one of the generation
Gabor Wave Packet Method to Solve Plasma Wave Equations
A. Pletzer; C.K. Phillips; D.N. Smithe
2003-06-18
A numerical method for solving plasma wave equations arising in the context of mode conversion between the fast magnetosonic and the slow (e.g ion Bernstein) wave is presented. The numerical algorithm relies on the expansion of the solution in Gaussian wave packets known as Gabor functions, which have good resolution properties in both real and Fourier space. The wave packets are ideally suited to capture both the large and small wavelength features that characterize mode conversion problems. The accuracy of the scheme is compared with a standard finite element approach.
Partial wave analysis of the reaction $\gamma p\to p\omega $ and the search for nucleon resonances
Williams, M.; Applegate, D.; Bellis, M.; Meyer, C. A.; Adhikari, K. P.; Anghinolfi, M.; Baghdasaryan, H.; Ball, J.; Battaglieri, M.; Bedlinskiy, I.; Berman, B. L.; Biselli, A. S.; Briscoe, W. J.; Brooks, W. K.; Burkert, V. D.; Careccia, S. L.; Carman, D. S.; Cole, P. L.; Collins, P.; Crede, V.; D’Angelo, A.; Daniel, A.; De Vita, R.; De Sanctis, E.; Deur, A.; Dey, B.; Dhamija, S.; Dickson, R.; Djalali, C.; Dodge, G. E.; Doughty, D.; Dugger, M.; Dupre, R.; Alaoui, A. El; Elouadrhiri, L.; Eugenio, P.; Fedotov, G.; Fegan, S.; Fradi, A.; Gabrielyan, M. Y.; Garçon, M.; Gilfoyle, G. P.; Giovanetti, K. L.; Girod, F. X.; Gohn, W.; Golovatch, E.; Gothe, R. W.; Griffioen, K. A.; Guidal, M.; Guler, N.; Guo, L.; Hafidi, K.; Hakobyan, H.; Hanretty, C.; Hassall, N.; Hicks, K.; Holtrop, M.; Ilieva, Y.; Ireland, D. G.; Ishkhanov, B. S.; Isupov, E. L.; Jawalkar, S. S.; Jo, H. S.; Johnstone, J. R.; Joo, K.; Keller, D.; Khandaker, M.; Khetarpal, P.; Kim, W.; Klein, A.; Klein, F. J.; Krahn, Z.; Kubarovsky, V.; Kuleshov, S. V.; Kuznetsov, V.; Livingston, K.; Lu, H. Y.; Mayer, M.; McAndrew, J.; McCracken, M. E.; McKinnon, B.; Mirazita, M.; Mokeev, V.; Moreno, B.; Moriya, K.; Morrison, B.; Munevar, E.; Nadel-Turonski, P.; Nepali, C. S.; Niccolai, S.; Niculescu, G.; Niculescu, I.; Niroula, M. R.; Niyazov, R. A.; Osipenko, M.; Ostrovidov, A. I.; Paris, M.; Park, K.; Park, S.; Pasyuk, E.; Pereira, S. Anefalos; Perrin, Y.; Pisano, S.; Pogorelko, O.; Pozdniakov, S.; Price, J. W.; Procureur, S.; Protopopescu, D.; Ricco, G.; Ripani, M.; Ritchie, B. G.; Rosner, G.; Rossi, P.; Sabatié, F.; Saini, M. S.; Salamanca, J.; Salgado, C.; Schott, D.; Schumacher, R. A.; Seraydaryan, H.; Sharabian, Y. G.; Smith, E. S.; Sober, D. I.; Sokhan, D.; Stepanyan, S. S.; Stoler, P.; Strakovsky, I. I.; Strauch, S.; Taiuti, M.; Tedeschi, D. J.; Tkachenko, S.; Ungaro, M.; Vineyard, M. F.; Voutier, E.; Watts, D. P.; Weygand, D. P.; Wood, M. H.; Zhang, J.; Zhao, B.
2009-12-30
We performed an event-based partial wave analysis (PWA) of the reaction γ p -> p ω on a high-statistics dataset obtained using the CLAS at Jefferson Lab for center-of-mass energies from threshold up to 2.4 GeV. This analysis benefits from access to the world's first high precision spin density matrix element measurements, available to the event-based PWA through the decay distribution of omega-> π^{+} π^{ -} π^{0}. The data confirm the dominance of the t-channel π^{0} exchange amplitude in the forward direction. The dominant resonance contributions are consistent with the previously identified states F[15](1680) and D[13](1700) near threshold, as well as the G[17](2190) at higher energies. Suggestive evidence for the presence of a J(P)=5/2^{+} state around 2 GeV, a "missing" state, has also been found. Evidence for other states is inconclusive.
NASA Astrophysics Data System (ADS)
Xie, Hang
The theme of this thesis is the study of wave phenomena in complex systems. In particular, the following three topics constitute the foci of my research. The first topic involves the generalization of an electronic transport mechanism commonly observed in disordered media, fluctuation induced tunneling conduction, by considering tunneling through not just insulating potential barriers, but also narrow conducting channels. Here the wave nature of the electron implies that a narrow conduction channel can act as an electronic waveguide, with a cutoff transverse dimension that is half the Fermi wavelength. My research involves the study of electronic transport through finite-length conducting channels with transverse dimensions below the cutoff. Such narrow conduction channel may be physically realized by chains of single conducting atoms, for example. At small voltage bias across the conduction channel, only tunneling transport is possible at zero temperature. But at finite temperatures some of the electrons with energies above the Fermi level can ballistically transport across the channel. By considering both tunneling and thermal activation mechanisms, with thermally-generated (random) voltage bias across the narrow channel, we obtained a temperature-dependent conductivity behavior that is in good agreement with the measured two-lead conductance of RuO2 and IrO2 nanowires. Furthermore, by considering high applied voltage across the nano conduction channels, our model predicts interesting electronic Fabry-Perot behavior whose experimental verification is presently underway. The second topic involves the study of the Hall effect in mesoscopic samples. In particular, we are interested in the possibility of enhancing the Hall effect by nano-patterning samples of 2D electron gas. Through numerical solution of the Schrodinger equation in the presence of a magnetic field, mesoscopic transport behavior is obtained for samples with given geometric patterns of the
Passive millimeter wave imaging
NASA Astrophysics Data System (ADS)
Pergande, Al; Dean, Donald D.; O'Donnell, Daniel J.
1996-05-01
Passive millimeter wave (MMW) imaging provides a breakthrough capability for driver vision enhancement to counter the blinding effects of inclement weather. This type of sensor images in a manner analogous to an infrared or visible camera, but receives its energy from the MMW portion of the electromagnetic spectrum. Technology has progressed to the point where MMW radiometric systems offer advantages to a number of vision applications. We report on our developmental 94 GHz radiometric testbed, and the eventual technological evolutions that will help MMW radiometers and radars meet military and commercial market needs.
2015-02-16
The four-dimensional scattering function S(Q,w) obtained by inelastic neutron scattering measurements provides unique "dynamical fingerprints" of the spin state and interactions present in complex magnetic materials. Extracting this information however is currently a slow and complex process that may take an expert -depending on the complexity of the system- up to several weeks of painstaking work to complete. Spin Wave Genie was created to abstract and automate this process. It strives to both reduce the time to complete this analysis and make these calculations more accessible to a broader group of scientists and engineers.
2005-01-01
Acoust. Soc. Am., 93, 1736–1742 (1993). Ericksen, C. C., T. J. Osse, R. D. Light, T. Wen, T. W. Lehman, P. L. Sabin, J. W. Ballard, and A. M . Chiodi ...profiles were then low-pass filtered to remove high wave number variability. Typically, below the mixed layer, length scales smaller than 20–30 m were...Atlantic Bight location (39.25°N, 72.4°W) was 200 m with a sandy bottom. For the acoustic geometry a point source at 50 m with 20 km range was assumed
1985-06-01
blork number) The millimeter wave vircator has achieved a frequency in excess of 39.9 GHz and a peak power of the order of 21 kilowatts (fZ26.35 GHz ) for...achieved a frequency in excess of 39.9 GHz and a peak power of the order of 21 kilowatts (f>26.35 Gf.z) for a pulse duration of as short as 5 ns full...upon the experience of the NRL quasi-optical gyrotron ,2 we can make some reasonable estimates. Based upon an output power of 1MW, the 0 of the cavity
Lipscombe, O. J.; Chen, G. F.; Fang, Chen; Perring, T. G.; Abernathy, Douglas L; Christianson, Andrew D; Egami, Takeshi; Wang, Nanlin; Hu, Jiangping; Dai, Pengcheng
2011-01-01
We use neutron scattering to show that spin waves in the iron chalcogenide Fe{sub 1.05}Te display novel dispersion clearly different from both the first principles density functional calculations and recent observations in the related iron pnictide CaFe{sub 2}As{sub 2}. By fitting to a Heisenberg Hamiltonian, we find that although the nearest-neighbor exchange couplings in the two systems are quite different, their next-nearest-neighbor (NNN) couplings are similar. This suggests that superconductivity in the pnictides and chalcogenides share a common magnetic origin that is intimately associated with the NNN magnetic coupling between the irons.
NASA Technical Reports Server (NTRS)
Kelly, Bernard J.
2010-01-01
Einstein's General Theory of Relativity is our best classical description of gravity, and informs modern astronomy and astrophysics at all scales: stellar, galactic, and cosmological. Among its surprising predictions is the existence of gravitational waves -- ripples in space-time that carry energy and momentum away from strongly interacting gravitating sources. In my talk, I will give an overview of the properties of this radiation, recent breakthroughs in computational physics allowing us to calculate the waveforms from galactic mergers, and the prospect of direct observation with interferometric detectors such as LIGO and LISA.
Iterated multidimensional wave conversion
Brizard, A. J.; Tracy, E. R.; Johnston, D.; Kaufman, A. N.; Richardson, A. S.; Zobin, N.
2011-12-23
Mode conversion can occur repeatedly in a two-dimensional cavity (e.g., the poloidal cross section of an axisymmetric tokamak). We report on two novel concepts that allow for a complete and global visualization of the ray evolution under iterated conversions. First, iterated conversion is discussed in terms of ray-induced maps from the two-dimensional conversion surface to itself (which can be visualized in terms of three-dimensional rooms). Second, the two-dimensional conversion surface is shown to possess a symplectic structure derived from Dirac constraints associated with the two dispersion surfaces of the interacting waves.
Holographic charge density waves
NASA Astrophysics Data System (ADS)
Donos, Aristomenis; Gauntlett, Jerome P.
2013-06-01
We show that strongly coupled holographic matter at finite charge density can exhibit charge density wave phases which spontaneously break translation invariance while preserving time-reversal and parity invariance. We show that such phases are possible within Einstein-Maxwell-dilaton theory in general spacetime dimensions. We also discuss related spatially modulated phases when there is an additional coupling to a second vector field, possibly with nonzero mass. We discuss how these constructions, and others, should be associated with novel spatially modulated ground states.
Riley, Nathan; Geissel, Matthias; Lewis, Sean M; Porter, John L.
2015-03-01
The data described in this document consist of image files of shadowgraphs of astrophysically relevant laser driven blast waves. Supporting files include Mathematica notebooks containing design calculations, tabulated experimental data and notes, and relevant publications from the open research literature. The data was obtained on the Z-Beamlet laser from July to September 2014. Selected images and calculations will be published as part of a PhD dissertation and in associated publications in the open research literature, with Sandia credited as appropriate. The authors are not aware of any restrictions that could affect the release of the data.
Crespo, Antonio; García, Javier; Manuel, Fernando
2013-01-01
A simple analytical expression has been derived to calculate the characteristics of a wave that reflects at a stent implanted in a uniform vessel. The stent is characterized by its length and the wave velocity in the stented region. The reflected wave is proportional to the time derivative of the incident wave. The reflection coefficient is a small quantity of the order of the length of the stent divided by the wavelength of the unstented vessel. The results obtained coincide with those obtained numerically by Charonko et al. The main simplifications used are small amplitude of the waves so that equations can be linearized and that the length of the stent is small enough so that the values of the wave functions are nearly uniform along the stent. Both assumptions hold in typical situations.
Discrete wave mechanics: An introduction
Wall, Frederick T.
1986-01-01
Discrete wave mechanics is formulated for particles in one-dimensional systems by use of a simple finite difference equation. The solutions involve wave vectors (instead of wave functions) as well as a newly defined “wave vector energy.” In the limit, as c → ∞, the treatment reduces to that of Schrödinger's wave mechanics. Specific calculations are made for completely free particles as well as for particles confined to a one-dimensional box. The results exhibit a striking compatibility with relativistic considerations. The wave vectors show properties that can be identified with particles and anti-particles—each possess identical probability distributions with energies that add up to zero. PMID:16593732
Investigation of Pressurized Wave Bearings
NASA Technical Reports Server (NTRS)
Keith, Theo G., Jr.; Dimofte, Florin
2003-01-01
The wave bearing has been pioneered and developed by Dr. Dimofte over the past several years. This bearing will be the main focus of this research. It is believed that the wave bearing offers a number of advantages over the foil bearing, which is the bearing that NASA is currently pursuing for turbomachinery applications. The wave bearing is basically a journal bearing whose film thickness varies around the circumference approximately sinusoidally, with usually 3 or 4 waves. Being a rigid geometry bearing, it provides precise control of shaft centerlines. The wave profile also provides good load capacity and makes the bearing very stable. Manufacturing techniques have been devised that should allow the production of wave bearings almost as cheaply as conventional full-circular bearings.
Plasma waves near the magnetopause
NASA Technical Reports Server (NTRS)
Anderson, R. R.; Eastman, T. E.; Harvey, C. C.; Hoppe, M. M.; Tsurutani, B. T.; Etcheto, J.
1982-01-01
Plasma waves associated with the magnetosphere from the magnetosheath to the outer magnetosphere are investigated to obtain a clear definition of the boundaries and regions, to characterize the waves observed in these regions, to determine which wave modes are present, and to determine their origin. Emphasis is on high time resolution data and a comparison between measurements by different antenna systems. It is shown that the magnetosheath flux transfer events, the magnetopause current layer, the outer magnetosphere, and the boundary layer can be identified by their magnetic field and plasma wave characteristics, as well as by their plasma and energetic particle signatures. The plasma wave characteristics in the current layer and in the boundary layer are very similar to the features in the flux transfer events, and upon entry into their outer magnetosphere, the plasma wave spectra are dominated by intense electromagnetic chorus bursts and electrostatic emissions.
WINDII atmospheric wave airglow imaging
Armstrong, W.T.; Hoppe, U.-P.; Solheim, B.H.; Shepherd, G.G.
1996-12-31
Preliminary WINDII nighttime airglow wave-imaging data in the UARS rolldown attitude has been analyzed with the goal to survey gravity waves near the upper boundary of the middle atmosphere. Wave analysis is performed on O[sub 2](0,0) emissions from a selected 1[sup 0] x 1[sup 0] oblique view of the airglow layer at approximately 95 km altitude, which has no direct earth background and only an atmospheric background which is optically thick for the 0[sub 2](0,0) emission. From a small data set, orbital imaging of atmospheric wave structures is demonstrated, with indication of large variations in wave activity across land and sea. Comparison ground-based imagery is discussed with respect to similarity of wave variations across land/sea boundaries and future orbital mosaic image construction.
Random focusing of tsunami waves
NASA Astrophysics Data System (ADS)
Degueldre, Henri; Metzger, Jakob J.; Geisel, Theo; Fleischmann, Ragnar
2016-03-01
Tsunamis exhibit surprisingly strong height fluctuations. An in-depth understanding of the mechanisms that lead to these variations in wave height is a prerequisite for reliable tsunami forecasting. It is known, for example, that the presence of large underwater islands or the shape of the tsunami source can affect the wave heights. Here we show that the consecutive effect of even tiny fluctuations in the profile of the ocean floor (the bathymetry) can cause unexpectedly strong fluctuations in the wave height of tsunamis, with maxima several times higher than the average wave height. A novel approach combining stochastic caustic theory and shallow water wave dynamics allows us to determine the typical propagation distance at which the strongly focused waves appear. We demonstrate that owing to this mechanism the small errors present in bathymetry measurements can lead to drastic variations in predicted tsunami heights. Our results show that a precise knowledge of the ocean's bathymetry is absolutely indispensable for reliable tsunami forecasts.
NASA Astrophysics Data System (ADS)
Ding, Yingchun; Zhang, Bin; Feng, Qi; Tang, Xin; Liu, Zhongxuan; Chen, Zhaoyang; Lin, Chengyou
2017-01-01
The formation of extreme localization structures in nonlinear dispersive media (water or optical fibres) can be explained and described by the focusing nonlinear Schrödinger equation (NLSE). The NLSE is especially important in understanding how solitons on a condensate background (SCB) appear from a small perturbation through modulation instability. We have studied theoretically SCB solutions solved with the dressing method. A class of bipolar-rogue-wave structures that are constructed by collisions between elementary SCB or bipolar solitonic solutions was found. Besides, we have also found a new class of regular bright solitonic rogue waves that are originated from the collision between two bipolar-rogue-wave structures. The bipolar-rogue-wave structures can be considered to provide a new prototype for rogue-waves dynamics modeling. Our results extend previous studies in the area of rogue waves and may be important in the study of oceanography and optics.
WINDII atmospheric wave airglow imaging
NASA Technical Reports Server (NTRS)
Armstrong, W. T.; Hoppe, U.-P.; Solheim, B. H.; Shepherd, G. G.
1996-01-01
Preliminary WINDII nighttime airglow wave-imaging data in the UARS rolldown attitude has been analyzed with the goal to survey gravity waves near the upper boundary of the middle atmosphere. Wave analysis is performed on O[sub 2](0,0) emissions from a selected 1[sup 0] x 1[sup 0] oblique view of the airglow layer at approximately 95 km altitude, which has no direct earth background and only an atmospheric background which is optically thick for the 0[sub 2](0,0) emission. From a small data set, orbital imaging of atmospheric wave structures is demonstrated, with indication of large variations in wave activity across land and sea. Comparison ground-based imagery is discussed with respect to similarity of wave variations across land/sea boundaries and future orbital mosaic image construction.
Turbulent Structure Under Short Fetch Wind Waves
2015-12-01
partitioned into wave growth , wave breaking, and wave forcing of the ocean surface layer. The purpose of this study was to support the ONR Coupled Boundary...complicated by the presence of surface waves. Wind momentum and energy are partitioned into wave growth , wave breaking, and wave forcing of the ocean surface...subrange, beyond which will display a rapid exponential decay through the dissipation range as shown in Figure 1. There are six properties that best
Waves and instabilities in plasmas
Chen, L.
1987-01-01
The contents of this book are: Plasma as a Dielectric Medium; Nyquist Technique; Absolute and Convective Instabilities; Landau Damping and Phase Mixing; Particle Trapping and Breakdown of Linear Theory; Solution of Viasov Equation via Guilding-Center Transformation; Kinetic Theory of Magnetohydrodynamic Waves; Geometric Optics; Wave-Kinetic Equation; Cutoff and Resonance; Resonant Absorption; Mode Conversion; Gyrokinetic Equation; Drift Waves; Quasi-Linear Theory; Ponderomotive Force; Parametric Instabilities; Problem Sets for Homework, Midterm and Final Examinations.
Wave energy: a Pacific perspective.
Paasch, Robert; Ruehl, Kelley; Hovland, Justin; Meicke, Stephen
2012-01-28
This paper illustrates the status of wave energy development in Pacific rim countries by characterizing the available resource and introducing the region's current and potential future leaders in wave energy converter development. It also describes the existing licensing and permitting process as well as potential environmental concerns. Capabilities of Pacific Ocean testing facilities are described in addition to the region's vision of the future of wave energy.
Calcium wave of Brain Astrocytes
NASA Astrophysics Data System (ADS)
Cornell Bell, A. H.
1997-03-01
Time lapse confocal scanning laser microscopy was used to study hippocampal astrocyte cultures loaded with a calcium indicator, Fluo3-AM (4 uM). kThe neurotransmitter kainate (100uM) overwhelms the Na+-buffering capacity of astrocytes within 100 sec resulting in reversal of the Na+/Ca2+ exchanger. This results in a subcellular site where Ca2+ entering the cytoplasm contributes to a long-distance Ca2+ wave which travels at 20 um/sec without decrement. Image analysis has shown calcium waves not only at a high Kainate dose, but also at a low Kainate dose, e.g. 10uM. These are, however, shortlived and burried in an extremely noisy background and only detectable by analyzing the calcium waves images for spatio-temporal coherence. As the kainate dose increases, more large scale coherent structures with visible geometric features (spiral waves and target waves) can be observed. Multiple spiral waves are produced when the Kainate dose increases to 100 uM. These waves travel at a constant velocity across entire microscope fields for long time periods (>30 mins). Na+ channels have no effect on the Kainate wave. Voltage-gated Ca2+ channels are not involved and Ca2+ enters through reversal of the exchanger. Ca2+ release from stores does not contribute to the kainate wave. Removal of Na+ or Ca2+ from outside and the specific Na+/Ca2+ exchange inhibitor benzamil (10 uM) inhibit the kainate wave. A functional antibody to alpha6-Integrin which is localized to membrane regions between cells inhibits the spread of the kainate wave in a dose and time-dependent manner. Fluorescence Recovery after Photobleach (FRAP) techniques indicate that gap junctions remain open between cells. This would imply that Ca2+ or IP3 need not pass through the gap junction, but reversal of the exchanger would propel the Ca2+ wave at the cell surface.
Quantum Emulation of Gravitational Waves
Fernandez-Corbaton, Ivan; Cirio, Mauro; Büse, Alexander; Lamata, Lucas; Solano, Enrique; Molina-Terriza, Gabriel
2015-01-01
Gravitational waves, as predicted by Einstein’s general relativity theory, appear as ripples in the fabric of spacetime traveling at the speed of light. We prove that the propagation of small amplitude gravitational waves in a curved spacetime is equivalent to the propagation of a subspace of electromagnetic states. We use this result to propose the use of entangled photons to emulate the evolution of gravitational waves in curved spacetimes by means of experimental electromagnetic setups featuring metamaterials. PMID:26169801
Infragravity waves across the oceans
NASA Astrophysics Data System (ADS)
Rawat, Arshad; Ardhuin, Fabrice; Aucan, Jerome
2014-05-01
The propagation of transoceanic Infragravity (IG) wave was investigated using a global spectral wave model together with deep-ocean pressure recorders. IG waves are generated mostly at the shorelines due to non-linear hydrodynamic effects that transfer energy from the main windsea and swell band, with periods of 1 to 25 s, to periods up to 500 s. IG waves are important for the study of near-shore processes and harbor agitation, and can also be a potential source of errors in satellite altimetry measurements. Setting up a global IG model was motivated by the investigation of these errors for the future planned SWOT mission. Despite the fact that the infragravity waves exhibit much smaller vertical amplitudes than the usual high frequency wind-driven waves, of the order of 1 cm in the deep oceans, their propagation throughout the oceans and signature in the wave spectrum can be clearly observed. Using a simplified empirical parameterization of the nearshore source of free IG waves as a function of the incoming wave parameters we extended to WAVEWATCH III model, used so far for windseas and swell, to the IG band, up to periods of 300 s. The spatial and temporal variability of the modeled IG energy was well correlated to the DART station records, making it useful to interpret the records of IG waves. Open ocean IG wave records appear dominated by trans-oceanic events with well defined sources concentrated on a few days, usually on West coasts, and affecting the entire ocean basin, with amplitude patterns very similar to those of tsunamis. Three particular IG bursts during 2008 are studied, 2 in the Pacific Ocean and 1 in the North Atlantic. It was observed that the liberated IG waves can travel long distances often crossing whole oceans with negligible dissipation. The IG signatures are clearly observed at sensors along their propagation paths.
Quantitative wave-particle duality
NASA Astrophysics Data System (ADS)
Qureshi, Tabish
2016-07-01
The complementary wave and particle character of quantum objects (or quantons) was pointed out by Niels Bohr. This wave-particle duality, in the context of the two-slit experiment, is here described not just as two extreme cases of wave and particle characteristics, but in terms of quantitative measures of these characteristics, known to follow a duality relation. A very simple and intuitive derivation of a closely related duality relation is presented, which should be understandable to the introductory student.
Gravitational lensing of gravitational wave
NASA Astrophysics Data System (ADS)
Kei Wong, Wang; Ng, Kwan Yeung
2017-01-01
Gravitational lensing phenomena are widespread in electromagnetic astrophysics, and in principle may also be uncovered with gravitational waves. We examine gravitational wave events lensed by elliptical galaxies in the limit of geometric optics, where we expect to see multiple signals from the same event with different arrival times and amplitudes. By using mass functions for compact binaries from population-synthesis simulations and a lensing probability calculated from Planck data, we estimate the rate of lensed signals for future gravitational wave missions.
Effects of Wave Nonlinearity on Wave Attenuation by Vegetation
NASA Astrophysics Data System (ADS)
Wu, W. C.; Cox, D. T.
2014-12-01
The need to explore sustainable approaches to maintain coastal ecological systems has been widely recognized for decades and is increasingly important due to global climate change and patterns in coastal population growth. Submerged aquatic vegetation and emergent vegetation in estuaries and shorelines can provide ecosystem services, including wave-energy reduction and erosion control. Idealized models of wave-vegetation interaction often assume rigid, vertically uniform vegetation under the action of waves described by linear wave theory. A physical model experiment was conducted to investigate the effects of wave nonlinearity on the attenuation of random waves propagating through a stand of uniform, emergent vegetation in constant water depth. The experimental conditions spanned a relative water depth from near shallow to near deep water waves (0.45 < kh <1.49) and wave steepness from linear to nonlinear conditions (0.03 < ak < 0.18). The wave height to water depth ratios were in the range 0.12 < Hs/h < 0.34, and the Ursell parameter was in the range 2 < Ur < 68. Frictional losses from the side wall and friction were measured and removed from the wave attenuation in the vegetated cases to isolate the impact of vegetation. The normalized wave height attenuation decay for each case was fit to the decay equation of Dalrymple et al. (1984) to determine the damping factor, which was then used to calculate the bulk drag coefficients CD. This paper shows that the damping factor is dependent on the wave steepness ak across the range of relative water depths from shallow to deep water and that the damping factor can increase by a factor of two when the value of ak approximately doubles. In turn, this causes the drag coefficient CD to decrease on average by 23%. The drag coefficient can be modeled using the Keulegan-Carpenter number using the horizontal orbital wave velocity estimate from linear wave theory as the characteristic velocity scale. Alternatively, the Ursell
Tropical Cyclogenesis in a Tropical Wave Critical Layer: Easterly Waves
NASA Technical Reports Server (NTRS)
Dunkerton, T. J.; Montgomery, M. T.; Wang, Z.
2009-01-01
The development of tropical depressions within tropical waves over the Atlantic and eastern Pacific is usually preceded by a "surface low along the wave" as if to suggest a hybrid wave-vortex structure in which flow streamlines not only undulate with the waves, but form a closed circulation in the lower troposphere surrounding the low. This structure, equatorward of the easterly jet axis, is identified herein as the familiar critical layer of waves in shear flow, a flow configuration which arguably provides the simplest conceptual framework for tropical cyclogenesis resulting from tropical waves, their interaction with the mean flow, and with diabatic processes associated with deep moist convection. The recirculating Kelvin cat's eye within the critical layer represents a sweet spot for tropical cyclogenesis in which a proto-vortex may form and grow within its parent wave. A common location for storm development is given by the intersection of the wave's critical latitude and trough axis at the center of the cat's eye, with analyzed vorticity centroid nearby. The wave and vortex live together for a time, and initially propagate at approximately the same speed. In most cases this coupled propagation continues for a few days after a tropical depression is identified. For easterly waves, as the name suggests, the propagation is westward. It is shown that in order to visualize optimally the associated Lagrangian motions, one should view the flow streamlines, or stream function, in a frame of reference translating horizontally with the phase propagation of the parent wave. In this co-moving frame, streamlines are approximately equivalent to particle trajectories. The closed circulation is quasi-stationary, and a dividing streamline separates air within the cat's eye from air outside.
Martinez, D.; Hartigan, P.; Frank, A.; Hansen, E.; Yirak, K.; Liao, A. S.; Graham, P.; Foster, J.; Wilde, B.; Blue, B.; Rosen, P.; Farley, D.; Paguio, R.
2016-06-01
Supersonic outflows from objects as varied as stellar jets, massive stars, and novae often exhibit multiple shock waves that overlap one another. When the intersection angle between two shock waves exceeds a critical value, the system reconfigures its geometry to create a normal shock known as a Mach stem where the shocks meet. Mach stems are important for interpreting emission-line images of shocked gas because a normal shock produces higher postshock temperatures, and therefore a higher-excitation spectrum than does an oblique shock. In this paper, we summarize the results of a series of numerical simulations and laboratory experiments designed to quantify how Mach stems behave in supersonic plasmas that are the norm in astrophysical flows. The experiments test analytical predictions for critical angles where Mach stems should form, and quantify how Mach stems grow and decay as intersection angles between the incident shock and a surface change. While small Mach stems are destroyed by surface irregularities and subcritical angles, larger ones persist in these situations and can regrow if the intersection angle changes to become more favorable. Furthermore, the experimental and numerical results show that although Mach stems occur only over a limited range of intersection angles and size scales, within these ranges they are relatively robust, and hence are a viable explanation for variable bright knots observed in Hubble Space Telescope images at the intersections of some bow shocks in stellar jets.
Martinez, D.; Hartigan, P.; Frank, A.; ...
2016-06-01
Supersonic outflows from objects as varied as stellar jets, massive stars, and novae often exhibit multiple shock waves that overlap one another. When the intersection angle between two shock waves exceeds a critical value, the system reconfigures its geometry to create a normal shock known as a Mach stem where the shocks meet. Mach stems are important for interpreting emission-line images of shocked gas because a normal shock produces higher postshock temperatures, and therefore a higher-excitation spectrum than does an oblique shock. In this paper, we summarize the results of a series of numerical simulations and laboratory experiments designed tomore » quantify how Mach stems behave in supersonic plasmas that are the norm in astrophysical flows. The experiments test analytical predictions for critical angles where Mach stems should form, and quantify how Mach stems grow and decay as intersection angles between the incident shock and a surface change. While small Mach stems are destroyed by surface irregularities and subcritical angles, larger ones persist in these situations and can regrow if the intersection angle changes to become more favorable. Furthermore, the experimental and numerical results show that although Mach stems occur only over a limited range of intersection angles and size scales, within these ranges they are relatively robust, and hence are a viable explanation for variable bright knots observed in Hubble Space Telescope images at the intersections of some bow shocks in stellar jets.« less
Surface waves affect frontogenesis
NASA Astrophysics Data System (ADS)
Suzuki, Nobuhiro; Fox-Kemper, Baylor; Hamlington, Peter E.; Van Roekel, Luke P.
2016-05-01
This paper provides a detailed analysis of momentum, angular momentum, vorticity, and energy budgets of a submesoscale front undergoing frontogenesis driven by an upper-ocean, submesoscale eddy field in a Large Eddy Simulation (LES). The LES solves the wave-averaged, or Craik-Leibovich, equations in order to account for the Stokes forces that result from interactions between nonbreaking surface waves and currents, and resolves both submesoscale eddies and boundary layer turbulence down to 4.9 m × 4.9 m × 1.25 m grid scales. It is found that submesoscale frontogenesis differs from traditional frontogenesis theory due to four effects: Stokes forces, momentum and kinetic energy transfer from submesoscale eddies to frontal secondary circulations, resolved turbulent stresses, and unbalanced torque. In the energy, momentum, angular momentum, and vorticity budgets for the frontal overturning circulation, the Stokes shear force is a leading-order contributor, typically either the second or third largest source of frontal overturning. These effects violate hydrostatic and thermal wind balances during submesoscale frontogenesis. The effect of the Stokes shear force becomes stronger with increasing alignment of the front and Stokes shear and with a nondimensional scaling. The Stokes shear force and momentum transfer from submesoscale eddies significantly energize the frontal secondary circulation along with the buoyancy.
1935-01-01
It is submitted that the thermal action of short-wave therapy does not account for the therapeutic results obtained. The theory is put forward that many of the results obtained can be better explained by the disruptive and dispersive action of the impact of the electromagnetic vibrations. An analogy, indicating such disruptive effects at high frequency, is drawn from the molecular vibrations—transmitted through transformer oil, and excited by the application of high frequency currents to the layers of quartz in the piezo-electric oscillator of quartz. It is submitted that these disruptive and dispersive effects will be greatest where the conductivity of the tissues is low, such as in bones and fat, and it is shown that it is in these regions that the therapeutic action of these currents is most obvious. It is also pointed out that, if effects, comparable to those obtained in the subcutaneous area, are obtained in the deeper tissues and organs, the application of deep-wave therapy would be attended by serious risk. PMID:19990107
Rarefaction wave gun propulsion
NASA Astrophysics Data System (ADS)
Kathe, Eric Lee
A new species of gun propulsion that dramatically reduces recoil momentum imparted to the gun is presented. First conceived by the author on 18 March 1999, the propulsion concept is explained, a methodology for the design of a reasonable apparatus for experimental validation using NATO standard 35mm TP anti-aircraft ammunition is developed, and the experimental results are presented. The firing results are juxtaposed by a simple interior ballistic model to place the experimental findings into a context within which they may better be understood. Rarefaction wave gun (RAVEN) propulsion is an original contribution to the field of armament engineering. No precedent is known, and no experimental results of such a gun have been published until now. Recoil reduction in excess of 50% was experimentally achieved without measured loss in projectile velocity. RAVEN achieves recoil reduction by means of a delayed venting of the breech of the gun chamber that directs the high enthalpy propellant gases through an expansion nozzle to generate forward thrust that abates the rearward momentum applied to the gun prior to venting. The novel feature of RAVEN, relative to prior recoilless rifles, is that sufficiently delayed venting results in a rarefaction wave that follows the projectile though the bore without catching it. Thus, the projectile exits the muzzle without any compromise to its propulsion performance relative to guns that maintain a sealed chamber.
Smith, R.W.
1980-08-01
Several new aspects of nonlinear or wave mixing spectroscopy were investigated utilizing the polarization properties of the nonlinear output field and the dependence of this field upon the occurrence of multiple resonances in the nonlinear susceptibility. First, it is shown theoretically that polarization-sensitive detection may be used to either eliminate or controllably reduce the nonresonant background in coherent anti-Stokes Raman spectroscopy, allowing weaker Raman resonances to be studied. The features of multi-resonant four-wave mixing are examined in the case of an inhomogeneously broadened medium. It is found that the linewidth of the nonlinear output narrows considerably (approaching the homogeneous width) when the quantum mechanical expressions for the doubly- and triply-resonant susceptibilities are averaged over a Doppler or strain broadened profile. Experimental studies of nonlinear processes in Pr/sup +3/:LaF/sub 3/ verify this linewidth narrowing, but indicate that this strain broadened system cannot be treated with a single broadening parameter as in the case of Doppler broadening in a gas. Several susceptibilities are measured from which are deduced dipole matrix elements and Raman polarizabilities related to the /sup 3/H/sub 4/, /sup 3/H/sub 6/, and /sup 3/P/sub 0/ levels of the praseodymium ions.
Gravity Forcing Of Surface Waves
NASA Astrophysics Data System (ADS)
Kenyon, K. E.
2005-12-01
Surface waves in deep water are forced entirely by gravity at the air-sea interface when no other forces act tangent to the surface. Then according to Newton's second law, the fluid acceleration parallel to the surface must equal the component of gravity parallel to the surface. Between crest and trough the fluid accelerates; between trough and crest the fluid decelerates. By replacing Bernoulli's law, gravity forcing becomes the dynamic boundary condition needed to solve the mathematical problem of these waves. Irrotational waves with a sinusoidal profile satisfy the gravity forcing condition, with the usual dispersion relation, provided the slope is small compared to one, as is true also of the Stokes development. However, the exact wave shape can be calculated using the gravity forcing method in a way that is less complex and less time consuming than that of the Stokes perturbation expansion. To the second order the surface elevation is the same as the Stokes result; the third order calculation has not been made yet. Extensions of the gravity forcing method can easily be carried out for multiple wave trains, solitary waves and bores, waves in finite constant mean depths, and internal waves in a two-layer system. For shoaling surface waves gravity forcing provides a physical understanding of the progressive steepening often observed near shore.
Measurement of Helmholtz wave fields
Alonso
2000-07-01
A simple formalism is found for the measurement of wave fields that satisfy the Helmholtz equation in free space. This formalism turns out to be analogous to the well-known theory of measurements for quantum-mechanical wave functions: A measurement corresponds to the squared magnitude of the inner product (in a suitable Hilbert space) of the wave field and a field that is associated with the detector. The measurement can also be expressed as an overlap in phase space of a special form of the Wigner function that is tailored for Helmholtz wave fields.
Wave-equation dispersion inversion
NASA Astrophysics Data System (ADS)
Li, Jing; Feng, Zongcai; Schuster, Gerard
2017-03-01
We present the theory for wave-equation inversion of dispersion curves, where the misfit function is the sum of the squared differences between the wavenumbers along the predicted and observed dispersion curves. The dispersion curves are obtained from Rayleigh waves recorded by vertical-component geophones. Similar to wave-equation traveltime tomography, the complicated surface wave arrivals in traces are skeletonized as simpler data, namely the picked dispersion curves in the phase-velocity and frequency domains. Solutions to the elastic wave equation and an iterative optimization method are then used to invert these curves for 2-D or 3-D S-wave velocity models. This procedure, denoted as wave-equation dispersion inversion (WD), does not require the assumption of a layered model and is significantly less prone to the cycle-skipping problems of full waveform inversion. The synthetic and field data examples demonstrate that WD can approximately reconstruct the S-wave velocity distributions in laterally heterogeneous media if the dispersion curves can be identified and picked. The WD method is easily extended to anisotropic data and the inversion of dispersion curves associated with Love waves.
Guided acoustic wave inspection system
Chinn, Diane J.
2004-10-05
A system for inspecting a conduit for undesirable characteristics. A transducer system induces guided acoustic waves onto said conduit. The transducer system detects the undesirable characteristics of the conduit by receiving guided acoustic waves that contain information about the undesirable characteristics. The conduit has at least two sides and the transducer system utilizes flexural modes of propagation to provide inspection using access from only the one side of the conduit. Cracking is detected with pulse-echo testing using one transducer to both send and receive the guided acoustic waves. Thinning is detected in through-transmission testing where one transducer sends and another transducer receives the guided acoustic waves.
Wave energy and intertidal productivity.
Leigh, E G; Paine, R T; Quinn, J F; Suchanek, T H
1987-03-01
In the northeastern Pacific, intertidal zones of the most wave-beaten shores receive more energy from breaking waves than from the sun. Despite severe mortality from winter storms, communities at some wave-beaten sites produce an extraordinary quantity of dry matter per unit area of shore per year. At wave-beaten sites of Tatoosh Island, WA, sea palms, Postelsia palmaeformis, can produce > 10 kg of dry matter, or 1.5 x 10(8) J, per m(2) in a good year. Extraordinarily productive organisms such as Postelsia are restricted to wave-beaten sites. Intertidal organisms cannot transform wave energy into chemical energy, as photosynthetic plants transform solar energy, nor can intertidal organisms "harness" wave energy. Nonetheless, wave energy enhances the productivity of intertidal organisms. On exposed shores, waves increase the capacity of resident algae to acquire nutrients and use sunlight, augment the competitive ability of productive organisms, and protect intertidal residents by knocking away their enemies or preventing them from feeding.
Wave energy and intertidal productivity
Leigh, E.G. Jr.; Paine, R.T.; Quinn, J.F.; Suchanek, T.H.
1987-03-01
In the northern Pacific, intertidal zones of the most wave-beaten shores receive more energy from breaking waves than from the sun. Despite severe mortality from winter storms, communities at some wave-beaten sites produce an extraordinary quantity of dry matter per unit area of shore per year. At wave-beaten sites of Tatoosh Island, WA, sea palms, Postelsia palmaeformis, can produce > 10 kg of dry matter, or 1.5 x 10/sup 8/ J, per m/sup 2/ in a good year. Extraordinarily productive organisms such as Postelsia are restricted to wave-beaten sites. Intertidal organisms cannot transform wave energy into chemical energy, as photosynthetic plants transform solar energy, nor can intertidal organisms harness wave energy. Nonetheless, wave energy enhances the productivity of intertidal organisms. On exposed shores, waves increase the capacity of resident algae to acquire nutrients and use sunlight, augment the competitive ability of productive organism, and protect intertidal residents by knocking away their enemies or preventing them from feeding.
Wave energy and intertidal productivity
Leigh, Egbert G.; Paine, Robert T.; Quinn, James F.; Suchanek, Thomas H.
1987-01-01
In the northeastern Pacific, intertidal zones of the most wave-beaten shores receive more energy from breaking waves than from the sun. Despite severe mortality from winter storms, communities at some wave-beaten sites produce an extraordinary quantity of dry matter per unit area of shore per year. At wave-beaten sites of Tatoosh Island, WA, sea palms, Postelsia palmaeformis, can produce > 10 kg of dry matter, or 1.5 × 108 J, per m2 in a good year. Extraordinarily productive organisms such as Postelsia are restricted to wave-beaten sites. Intertidal organisms cannot transform wave energy into chemical energy, as photosynthetic plants transform solar energy, nor can intertidal organisms “harness” wave energy. Nonetheless, wave energy enhances the productivity of intertidal organisms. On exposed shores, waves increase the capacity of resident algae to acquire nutrients and use sunlight, augment the competitive ability of productive organisms, and protect intertidal residents by knocking away their enemies or preventing them from feeding. PMID:16593813
NASA Astrophysics Data System (ADS)
James, H. G.
1993-10-01
Active wave experiments in the 0-5 MHz range were carried out using a synchronized transmitter-receiver pair on the tethered sounding rocket payload OEDIPUS A. At full tether extension, the transmitter-receiver separation was 958 m. Although the transmitter power was modest (2.5 W), the receiver recorded strong propagation in tether-guided sheath-wave and plane-wave electromagnetic modes. After a summary of two principal wave results from the OEDIPUS experiment, these results are compared with related phenomena from the topside sounder spacecraft. The sheath-wave spectra clearly suggest that sheath waves are damped by electrostatic cyclotron waves. This is consistent with ideas in the topside-sounder literature that discuss how electrostatic waves transfer energy to the surrounding plasma. The transmission efficiency of slow Z-mode plane waves between the plasma and upper-hybrid resonance frequencies depends on guiding by density irregularities, which have produced related signatures in the monostatic sounder records.
Wave-wave interactions due to scattering by electrons.
NASA Technical Reports Server (NTRS)
Nishikawa, K.
1971-01-01
The kinetic wave equation which describes the nonlinear wave-particle interaction in a plasma is considered, and a method which uses the picture of quantized plasmons interacting with particles for the description of nonlinear wave-particle interactions is briefly described. In this method an assumption is made of the Markoffian character of the equation. It is shown that the Markoffian assumption can be justified at least for the case when the plasma is close to a stable stationary state. The diagram method developed by Nishikawa (1966) is used to derive an explicit expression for the kinetic equation. The application of the result to the case of interaction between an electron-wave and an ion-wave is discussed.
NASA Astrophysics Data System (ADS)
Ghezali, S.; Taleb, A.
2008-09-01
A research project at the "Laboratoire d'électronique quantique" consists in a theoretical study of the reflection and diffraction phenomena via an atomic mirror. This poster presents the principle of an atomic mirror. Many groups in the world have constructed this type of atom optics experiments such as in Paris-Orsay-Villetaneuse (France), Stanford-Gaithersburg (USA), Munich-Heidelberg (Germany), etc. A laser beam goes into a prism with an incidence bigger than the critical incidence. It undergoes a total reflection on the plane face of the prism and then exits. The transmitted resulting wave out of the prism is evanescent and repulsive as the frequency detuning of the laser beam compared to the atomic transition δ = ωL-ω0 is positive. The cold atomic sample interacts with this evanescent wave and undergoes one or more elastic bounces by passing into backward points in its trajectory because the atoms' kinetic energy (of the order of the μeV) is less than the maximum of the dipolar potential barrier ℏΩ2/Δ where Ω is the Rabi frequency [1]. In fact, the atoms are cooled and captured in a magneto-optical trap placed at a distance of the order of the cm above the prism surface. The dipolar potential with which interact the slow atoms is obtained for a two level atom in a case of a dipolar electric transition (D2 Rubidium transition at a wavelength of 780nm delivered by a Titane-Saphir laser between a fundamental state Jf = l/2 and an excited state Je = 3/2). This potential is corrected by an attractive Van der Waals term which varies as 1/z3 in the Lennard-Jones approximation (typical atomic distance of the order of λ0/2π where λ0 is the laser wavelength) and in 1/z4 if the distance between the atom and its image in the dielectric is big in front of λ0/2π. This last case is obtained in a quantum electrodynamic calculation by taking into account an orthornormal base [2]. We'll examine the role of spontaneous emission for which the rate is inversely
Standing wave tube electro active polymer wave energy converter
NASA Astrophysics Data System (ADS)
Jean, Philippe; Wattez, Ambroise; Ardoise, Guillaume; Melis, C.; Van Kessel, R.; Fourmon, A.; Barrabino, E.; Heemskerk, J.; Queau, J. P.
2012-04-01
Over the past 4 years SBM has developed a revolutionary Wave Energy Converter (WEC): the S3. Floating under the ocean surface, the S3 amplifies pressure waves similarly to a Ruben's tube. Only made of elastomers, the system is entirely flexible, environmentally friendly and silent. Thanks to a multimodal resonant behavior, the S3 is capable of efficiently harvesting wave energy from a wide range of wave periods, naturally smoothing the irregularities of ocean wave amplitudes and periods. In the S3 system, Electro Active Polymer (EAP) generators are distributed along an elastomeric tube over several wave lengths, they convert wave induced deformations directly into electricity. The output is high voltage multiphase Direct Current with low ripple. Unlike other conventional WECs, the S3 requires no maintenance of moving parts. The conception and operating principle will eventually lead to a reduction of both CAPEX and OPEX. By integrating EAP generators into a small scale S3, SBM achieved a world first: direct conversion of wave energy in electricity with a moored flexible submerged EAP WEC in a wave tank test. Through an extensive testing program on large scale EAP generators, SBM identified challenges in scaling up to a utility grid device. French Government supports the consortium consisting of SBM, IFREMER and ECN in their efforts to deploy a full scale prototype at the SEMREV test center in France at the horizon 2014-2015. SBM will be seeking strategic as well as financial partners to unleash the true potentials of the S3 Standing Wave Tube Electro Active Polymer WEC.
Optimization of one-way wave equations.
Lee, M.W.; Suh, S.Y.
1985-01-01
The theory of wave extrapolation is based on the square-root equation or one-way equation. The full wave equation represents waves which propagate in both directions. On the contrary, the square-root equation represents waves propagating in one direction only. A new optimization method presented here improves the dispersion relation of the one-way wave equation. -from Authors
Regularity of rotational travelling water waves.
Escher, Joachim
2012-04-13
Several recent results on the regularity of streamlines beneath a rotational travelling wave, along with the wave profile itself, will be discussed. The survey includes the classical water wave problem in both finite and infinite depth, capillary waves and solitary waves as well. A common assumption in all models to be discussed is the absence of stagnation points.
NASA Astrophysics Data System (ADS)
Mahadevan, A.; Richards, K.
2004-05-01
We examine the fluid-structure interaction between submerged flexible grass stems and unidirectional flow in a channel. The stems deform in response to the drag force imposed by the flow. The drag, however, varies non-linearly with the fluid velocity and it's angle of incidence with the stems' axis. An increase in fluid velocity increases drag that consequently decelerates the fluid, but also bends the stems further and reduces drag. Such a drag-induced feedback mechanism between the plant structures and water results in an instability that is responsible for the synchronous waving of aquatic grasses in a flow field that is initially uniform. We construct a model for this phenomenon to explore its dependence on parameters. Experiments are also in progress. We further propose to test the applicability of similar mechanisms to sediment transport over deformable beds.
NASA Astrophysics Data System (ADS)
Leble, Sergei B.
S.B. Leble's book deals with nonlinear waves and their propagation in metallic and dielectric waveguides and media with stratification. The underlying nonlinear evolution equations (NEEs) are derived giving also their solutions for specific situations. The reader will find new elements to the traditional approach. Various dispersion and relaxation laws for different guides are considered as well as the explicit form of projection operators, NEEs, quasi-solitons and of Darboux transforms. Special points relate to: 1. the development of a universal asymptotic method of deriving NEEs for guide propagation; 2. applications to the cases of stratified liquids, gases, solids and plasmas with various nonlinearities and dispersion laws; 3. connections between the basic problem and soliton- like solutions of the corresponding NEEs; 4. discussion of details of simple solutions in higher- order nonsingular perturbation theory.
NASA Technical Reports Server (NTRS)
1999-01-01
This map from the MGS Horizon Sensor Assembly (HORSE) shows middle atmospheric temperatures near the 1 mbar level of Mars between Ls 170 to 175 (approx. July 14 - 23, 1999). Local Mars times between 1:30 and 4:30 AM are included. Infrared radiation measured by the Mars Horizon Sensor Assembly was used to make the map. That device continuously views the 'limb' of Mars in four directions, to help orient the spacecraft instruments to the nadir: straight down.
The map shows thermal wave phenomena that are caused by the large topographic variety of Mars' surface, as well the latitudinally symmetric behavior expected at this time of year near the equinox.
Localized wave pulse experiments
Chambers, D L; Henderson, T L; Krueger, K L; Lewis, D K; Zilkowski, R N
1999-06-01
The Localized Wave project of the Strategic System Support Program has recently finished an experiment in cooperation with the Advanced SONAR group of the Applied Research Laboratory of the University of Texas at Austin. The purpose of the experiment was three-fold. They wanted to see if (1) the LW pulse could propagate over significant distances, to see if (2) a new type of array and drive system specifically designed for the pulse would increase efficiency over single frequency tone bursts, and to see if (3) the complexity of our 24 channel drivers resulted in better efficiency than a single equivalent pulse driving a piston. In the experiment, several LW pulses were launched from the Lake Travis facility and propagated over distances of either 100 feet or 600 feet, through a thermocline for the 600 foot measurements. The results show conclusively that the Localized Wave will propagate past the near field distance. The LW pulses resulted in extremely broad frequency band width pulses with narrow spatial beam patterns and unmeasurable side lobes. Their array gain was better than most tone bursts and further, were better than their equivalent piston pulses. This marks the first test of several Low Diffraction beams against their equivalent piston pulses, as well as the first propagation of LW pulses over appreciable distances. The LW pulse is now proven a useful tool in open water, rather than a laboratory curiosity. The experimental system and array were built by ARL, and the experiments were conducted by ARL staff on their standard test range. The 600 feet measurements were made at the farthest extent of that range.
Monolithic Millimeter Wave Oscillator
NASA Astrophysics Data System (ADS)
Wang, Nan-Lei
There is an increasing interest in the millimeter -wave spectrum for use in communications and for military and scientific applications. The concept of monolithic integration aims to produce very-high-frequency circuits in a more reliable, reproducible way than conventional electronics, and also at lower cost, with smaller size and lighter weight. In this thesis, a negative resistance device is integrated monolithically with a resonator to produce an effective oscillator. This work fills the void resulting from the exclusion of the local oscillator from the monolithic millimeter-wave integrated circuit (MMMIC) receiver design. For convenience a microwave frequency model was used to design the resonator circuit. A 5 GHz hybrid oscillator was first fabricated to test the design; the necessary GaAs process technology was developed for the fabrication. Negative resistance devices and oscillator theory were studied, and a simple but practical model of the Gunn diode was devised to solve the impedance matching problem. Monolithic oscillators at the Ka band (35 GHz) were built and refined. All devices operated in CW mode. By means of an electric-field probe, the output power was coupled into a metallic waveguide for measurement purposes. The best result was 3.63 mW of power output, the highest efficiency was 0.43% and the frequency stability was better than 10-4. In the future, an IMPATT diode could replace the Gunn device to give much higher power and efficiency. A varactor-tuned circuit also suitable for large-scale integration is under study.
SPHERICAL SHOCK WAVES IN SOLIDS
Contents: Introduction-Reasons for Studying Spherical Shock Waves, Physics of Cavity Expansion due to Explosive Impact, General Nature of Shock Waves...Governing Differential Equation of Self-Similar Motion; Application of the Theory of Self-Similar Motion to the Problem of Expansion of a Spherical
ERIC Educational Resources Information Center
Shipman, Bob
2006-01-01
When children first hear the term "sound wave" perhaps they might associate it with the way a hand waves or perhaps the squiggly line image on a television monitor when sound recordings are being made. Research suggests that children tend to think sound somehow travels as a discrete package, a fast-moving invisible thing, and not something that…
Compressive passive millimeter wave imager
Gopalsami, Nachappa; Liao, Shaolin; Elmer, Thomas W; Koehl, Eugene R; Heifetz, Alexander; Raptis, Apostolos C
2015-01-27
A compressive scanning approach for millimeter wave imaging and sensing. A Hadamard mask is positioned to receive millimeter waves from an object to be imaged. A subset of the full set of Hadamard acquisitions is sampled. The subset is used to reconstruct an image representing the object.
The Waves and Tsunamis Project
NASA Astrophysics Data System (ADS)
Lavin, M.; Strohschneider, D.; Maichle, R.; Frashure, K.; Micozzi, N.; Stephen, R. A.
2005-12-01
The goals of the Waves and Tsunamis Project are "to make waves real" to middle school students and to teach them some fundamental concepts of waves. The curriculum was designed in Fall 2004 (before the Sumatra Tsunami) and involves an ocean scientist classroom visit, hands-on demonstrations, and an interactive website designed to explain ocean wave properties. The website is called 'The Plymouth Wave Lab' and it has had more than 40,000 hits since the Sumatra event. One inexpensive and interesting demonstration is based on a string composed of alternating elastic bands and paper clips. Washers can be added to the paper clips to construct strings with varying mass. For example, a tapered string with mass decreasing in the wave propagation direction is an analog of tsunami waves propagating from deep to shallow water. The Waves and Tsunamis Project evolved as a collaborative effort involving an ocean science researcher and middle school science teachers. It was carried out through the direction of the Centers of Ocean Science Education Excellence New England (COSEE-NE) Ocean Science Education Institute (OSEI). COSEE-NE is involved in developing models for sustainable involvement of ocean science researchers in K-12 education ( http://necosee.net ). This work is supported by the National Science Foundation.
Exciting cytoskeleton-membrane waves
NASA Astrophysics Data System (ADS)
Shlomovitz, R.; Gov, N. S.
2008-10-01
Propagating waves on the surface of cells, over many micrometers, involve active forces. We investigate here the mechanical excitation of such waves when the membrane is perturbed by an external oscillatory force. The external perturbation may trigger the propagation of such waves away from the force application. This scheme is then suggested as a method to probe the properties of the excitable medium of the cell, and learn about the mechanisms that drive the wave propagation. We then apply these ideas to a specific model of active cellular membrane waves, demonstrating how the response of the system to the external perturbation depends on the properties of the model. The most outstanding feature that we find is that the excited waves exhibit a resonance phenomenon at the frequency corresponding to the tendency of the system to develop a linear instability. Mechanical excitation of membrane waves in cells at different frequencies can therefore be used to characterize the properties of the mechanism underlying the existence of these waves.
Rogue Waves and Modulational Instability
NASA Astrophysics Data System (ADS)
Zakharov, V. E.; Dyachenko, A.
2015-12-01
The most plausible cause of rogue wave formation in a deep ocean is development of modulational instability of quasimonochromatic wave trains. An adequate model for study of this phenomenon is the Euler equation for potential flow of incompressible fluid with free surface in 2-D geometry. Numerical integration of these equations confirms completely the conjecture of rogue wave formation from modulational instability but the procedure is time consuming for determination of rogue wave appearance probability for a given shape of wave energy spectrum. This program can be realized in framework of simpler model using replacement of the exact interaction Hamiltonian by more compact Hamiltonian. There is a family of such models. The popular one is the Nonlinear Schrodinger equation (NLSE). This model is completely integrable and suitable for numerical simulation but we consider that it is oversimplified. It misses such important phenomenon as wave breaking. Recently, we elaborated much more reliable model that describes wave breaking but is as suitable as NLSE from the point of numerical modeling. This model allows to perform massive numerical experiments and study statistics of rogue wave formation in details.
Book review: Extreme ocean waves
Geist, Eric L.
2017-01-01
“Extreme Ocean Waves”, edited by E. Pelinovsky and C. Kharif, second edition, Springer International Publishing, 2016; ISBN: 978-3-319-21574-7, ISBN (eBook): 978-3-319-21575-4The second edition of “Extreme Ocean Waves” published by Springer is an update of a collection of 12 papers edited by Efim Pelinovsky and Christian Kharif following the April 2007 meeting of the General Assembly of the European Geosciences Union. In this edition, three new papers have been added and three more have been substantially revised. Color figures are now included, which greatly aids in reading several of the papers, and is especially helpful in visualizing graphs as in the paper on symbolic computation of nonlinear wave resonance (Tobisch et al.). A note on terminology: extreme waves in this volume broadly encompass different types of waves, including deep-water and shallow-water rogue waves (which are alternatively termed freak waves), and internal waves. One new paper on tsunamis (Viroulet et al.) is now included in the second edition of this volume. Throughout the book, the reader will find a combination of laboratory, theoretical, and statistical/empirical treatment necessary for the complete examination of this subject. In the Introduction, the editors underscore the importance of studying extreme waves, documenting a dramatic instance of damaging extreme waves that recently occurred in 2014.
Inhomogeneous plane waves and cylindrical waves in anisotropic anelastic media
NASA Astrophysics Data System (ADS)
Krebes, E. S.; Le, Lawrence H. T.
1994-12-01
In isotropic anelastic media, the phase velocity of an inhomogeneous plane body wave, which is a function of Q and the degree of inhomogeneity gamma, is significantly less than the corresponding homogeneous wave phase velocity typically only if gamma is very large (unless Q is unusually low). Here we investigate inhomogeneous waves in anisotropic anelastic media, where phase velocities are also functions of the direction of phase propagation theta, and find that (1) the low phase velocities can occur at values of gamma which are substantially less than the isotropic values and that they occur over a limited range of oblique directions theta, and (2) for large positive values of gamma, there are ranges of oblique directions theta in which the inhomogeneous waves cannot propagate at all because there is no physically acceptable solution to the dispersion relation. We show examples of how the waves of case 1 can occur in practice and cause a number of anomalous wave propagation effects. The waves of case 2, though, do not arise in practice (they do not correspond to any points on the horizontal slowness plate). We also show that in the decomposition of a cylindrical wave into plane waves, inhomogeneous plane waves occur whose amplitudes grow in the direction of phase propagation and that this direction is away from the receiver to which they are contributing. The energy in these waves does, however, travel toward the receiver, and their amplitudes decay in the direction of energy propagation. We also show that if the commonly used definition for the quality factor in an isotropic medium, Q = -Re(mu)/Im(mu) where mu is a complex modulus, is applied to an anisotropic anelastic medium in order to study absorption anisotropy, a generally unreliable measure of the anelasticity of inhomogeneous wave propagation in a given arbitrary direction is obtained. The more fundamental definition based on energy loss (i.e., 2pi/Q = Delta E/E) should be used in general, and we present
Multichannel analysis of surface waves
Park, C.B.; Miller, R.D.; Xia, J.
1999-01-01
The frequency-dependent properties of Rayleigh-type surface waves can be utilized for imaging and characterizing the shallow subsurface. Most surface-wave analysis relies on the accurate calculation of phase velocities for the horizontally traveling fundamental-mode Rayleigh wave acquired by stepping out a pair of receivers at intervals based on calculated ground roll wavelengths. Interference by coherent source-generated noise inhibits the reliability of shear-wave velocities determined through inversion of the whole wave field. Among these nonplanar, nonfundamental-mode Rayleigh waves (noise) are body waves, scattered and nonsource-generated surface waves, and higher-mode surface waves. The degree to which each of these types of noise contaminates the dispersion curve and, ultimately, the inverted shear-wave velocity profile is dependent on frequency as well as distance from the source. Multichannel recording permits effective identification and isolation of noise according to distinctive trace-to-trace coherency in arrival time and amplitude. An added advantage is the speed and redundancy of the measurement process. Decomposition of a multichannel record into a time variable-frequency format, similar to an uncorrelated Vibroseis record, permits analysis and display of each frequency component in a unique and continuous format. Coherent noise contamination can then be examined and its effects appraised in both frequency and offset space. Separation of frequency components permits real-time maximization of the S/N ratio during acquisition and subsequent processing steps. Linear separation of each ground roll frequency component allows calculation of phase velocities by simply measuring the linear slope of each frequency component. Breaks in coherent surface-wave arrivals, observable on the decomposed record, can be compensated for during acquisition and processing. Multichannel recording permits single-measurement surveying of a broad depth range, high levels of
Large amplitude relativistic plasma waves
Coffey, Timothy
2010-05-15
Relativistic, longitudinal plasma oscillations are studied for the case of a simple water bag distribution of electrons having cylindrical symmetry in momentum space with the axis of the cylinder parallel to the velocity of wave propagation. The plasma is required to obey the relativistic Vlasov-Poisson equations, and solutions are sought in the wave frame. An exact solution for the plasma density as a function of the electrostatic field is derived. The maximum electric field is presented in terms of an integral over the known density. It is shown that when the perpendicular momentum is neglected, the maximum electric field approaches infinity as the wave phase velocity approaches the speed of light. It is also shown that for any nonzero perpendicular momentum, the maximum electric field will remain finite as the wave phase velocity approaches the speed of light. The relationship to previously published solutions is discussed as is some recent controversy regarding the proper modeling of large amplitude relativistic plasma waves.
Decay of capillary wave turbulence.
Deike, Luc; Berhanu, Michael; Falcon, Eric
2012-06-01
We report on the observation of freely decaying capillary wave turbulence on the surface of a fluid. The capillary wave turbulence spectrum decay is found to be self-similar in time with the same power law exponent as the one found in the stationary regime, in agreement with weak turbulence predictions. The amplitude of all Fourier modes are found to decrease exponentially with time at the same damping rate. The longest wavelengths involved in the system are shown to be damped by a viscous surface boundary layer. These long waves play the role of an energy source during the decay that sustains nonlinear interactions to keep capillary waves in a wave turbulent state.
Korneev, Valeri A [LaFayette, CA
2009-05-05
The detailed analysis of cross well seismic data for a gas reservoir in Texas revealed two newly detected seismic wave effects, recorded approximately 2000 feet above the reservoir. A tube-wave (150) is initiated in a source well (110) by a source (111), travels in the source well (110), is coupled to a geological feature (140), propagates (151) through the geological feature (140), is coupled back to a tube-wave (152) at a receiver well (120), and is and received by receiver(s) (121) in either the same (110) or a different receiving well (120). The tube-wave has been shown to be extremely sensitive to changes in reservoir characteristics. Tube-waves appear to couple most effectively to reservoirs where the well casing is perforated, allowing direct fluid contact from the interior of a well case to the reservoir.
Korneev, Valeri A.; Bakulin, Andrey
2009-10-13
The detailed analysis of cross well seismic data for a gas reservoir in Texas revealed two newly detected seismic wave effects, recorded approximately 2000 feet above the reservoir. A tube-wave (150) is initiated in a source well (110) by a source (111), travels in the source well (110), is coupled to a geological feature (140), propagates (151) through the geological feature (140), is coupled back to a tube-wave (152) at a receiver well (120), and is and received by receiver(s) (121) in either the same (110) or a different receiving well (120). The tube-wave has been shown to be extremely sensitive to changes in reservoir characteristics. Tube-waves appear to couple most effectively to reservoirs where the well casing is perforated, allowing direct fluid contact from the interior of a well case to the reservoir.
Tropical cyclogenesis in a tropical wave critical layer: easterly waves
NASA Astrophysics Data System (ADS)
Dunkerton, T. J.; Montgomery, M. T.; Wang, Z.
2009-08-01
The development of tropical depressions within tropical waves over the Atlantic and eastern Pacific is usually preceded by a "surface low along the wave" as if to suggest a hybrid wave-vortex structure in which flow streamlines not only undulate with the waves, but form a closed circulation in the lower troposphere surrounding the low. This structure, equatorward of the easterly jet axis, is identified herein as the familiar critical layer of waves in shear flow, a flow configuration which arguably provides the simplest conceptual framework for tropical cyclogenesis resulting from tropical waves, their interaction with the mean flow, and with diabatic processes associated with deep moist convection. The recirculating Kelvin cat's eye within the critical layer represents a sweet spot for tropical cyclogenesis in which a proto-vortex may form and grow within its parent wave. A common location for storm development is given by the intersection of the wave's critical latitude and trough axis at the center of the cat's eye, with analyzed vorticity centroid nearby. The wave and vortex live together for a time, and initially propagate at approximately the same speed. In most cases this coupled propagation continues for a few days after a tropical depression is identified. For easterly waves, as the name suggests, the propagation is westward. It is shown that in order to visualize optimally the associated Lagrangian motions, one should view the flow streamlines, or stream function, in a frame of reference translating horizontally with the phase propagation of the parent wave. In this co-moving frame, streamlines are approximately equivalent to particle trajectories. The closed circulation is quasi-stationary, and a dividing streamline separates air within the cat's eye from air outside. The critical layer equatorward of the easterly jet axis is important to tropical cyclogenesis because its cat's eye provides (i) a region of cyclonic vorticity and weak deformation by the
Wave-particle interaction in the Faraday waves.
Francois, N; Xia, H; Punzmann, H; Shats, M
2015-10-01
Wave motion in disordered Faraday waves is analysed in terms of oscillons or quasi-particles. The motion of these oscillons is measured using particle tracking tools and it is compared with the motion of fluid particles on the water surface. Both the real floating particles and the oscillons, representing the collective fluid motion, show Brownian-type dispersion exhibiting ballistic and diffusive mean squared displacement at short and long times, respectively. While the floating particles motion has been previously explained in the context of two-dimensional turbulence driven by Faraday waves, no theoretical description exists for the random walk type motion of oscillons. It is found that the r.m.s velocity ⟨μ̃(osc)⟩(rms) of oscillons is directly related to the turbulent r.m.s. velocity ⟨μ̃⟩(rms) of the fluid particles in a broad range of vertical accelerations. The measured ⟨μ̃(osc)⟩(rms) accurately explains the broadening of the frequency spectra of the surface elevation observed in disordered Faraday waves. These results suggest that 2D turbulence is the driving force behind both the randomization of the oscillons motion and the resulting broadening of the wave frequency spectra. The coupling between wave motion and hydrodynamic turbulence demonstrated here offers new perspectives for predicting complex fluid transport from the knowledge of wave field spectra and vice versa.
Relevance of infragravity waves in a wave-dominated inlet
NASA Astrophysics Data System (ADS)
Bertin, Xavier; Olabarrieta, Maitane
2016-08-01
This study investigates the relevance of infragravity (IG) waves at Albufeira Lagoon Inlet, a shallow wave-dominated inlet located on the western coast of Portugal. A field experiment carried out in September 2010 revealed the occurrence of low-frequency oscillations (i.e., 25-300 s) in water levels and current velocities. While these fluctuations were present over the ebb-tidal delta along the whole tidal cycle, they only appeared between the beginning of the flood and up to 2 h after high tide inside the lagoon. The XBeach modeling system was applied to Albufeira Lagoon Inlet and reproduced the generation and propagation of IG waves and their blocking during the ebb. This behavior was explained by blocking due to opposing tidal currents reaching 2.5 m s-1 in shallow water depths. Numerical results suggest that the breakpoint mechanism and the long bound wave shoaling mechanisms contributed significantly to the generation of IG waves in the inlet. IG waves induced fluctuations in flood currents inside the lagoon reaching temporarily 100% of their magnitude. The fact that these fluctuations occur mostly at flood and not at ebb could promote flood dominance in the lagoon. This hypothesis will have to be verified, namely under storm wave conditions.
Wave chaotic experiments and models for complicated wave scattering systems
NASA Astrophysics Data System (ADS)
Yeh, Jen-Hao
Wave scattering in a complicated environment is a common challenge in many engineering fields because the complexity makes exact solutions impractical to find, and the sensitivity to detail in the short-wavelength limit makes a numerical solution relevant only to a specific realization. On the other hand, wave chaos offers a statistical approach to understand the properties of complicated wave systems through the use of random matrix theory (RMT). A bridge between the theory and practical applications is the random coupling model (RCM) which connects the universal features predicted by RMT and the specific details of a real wave scattering system. The RCM gives a complete model for many wave properties and is beneficial for many physical and engineering fields that involve complicated wave scattering systems. One major contribution of this dissertation is that I have utilized three microwave systems to thoroughly test the RCM in complicated wave systems with varied loss, including a cryogenic system with a superconducting microwave cavity for testing the extremely-low-loss case. I have also experimentally tested an extension of the RCM that includes short-orbit corrections. Another novel result is development of a complete model based on the RCM for the fading phenomenon extensively studied in the wireless communication fields. This fading model encompasses the traditional fading models as its high-loss limit case and further predicts the fading statistics in the low-loss limit. This model provides the first physical explanation for the fitting parameters used in fading models. I have also applied the RCM to additional experimental wave properties of a complicated wave system, such as the impedance matrix, the scattering matrix, the variance ratio, and the thermopower. These predictions are significant for nuclear scattering, atomic physics, quantum transport in condensed matter systems, electromagnetics, acoustics, geophysics, etc.
Firpo, M.-C.; Leyvraz, F.; Attuel, G.
2006-12-15
Under the conditions of weak Langmuir turbulence, a self-consistent wave-particle Hamiltonian models the effective nonlinear interaction of a spectrum of M waves with N resonant out-of-equilibrium tail electrons. In order to address its intrinsically nonlinear time-asymptotic behavior, a Monte Carlo code was built to estimate its equilibrium statistical mechanics in both the canonical and microcanonical ensembles. First, the single wave model is considered in the cold beam-plasma instability and in the O'Neil setting for nonlinear Landau damping. O'Neil's threshold, which separates nonzero time-asymptotic wave amplitude states from zero ones, is associated with a second-order phase transition. These two studies provide both a testbed for the Monte Carlo canonical and microcanonical codes, with the comparison with exact canonical results, and an opportunity to propose quantitative results to longstanding issues in basic nonlinear plasma physics. Then, the properly speaking weak turbulence framework is considered through the case of a large spectrum of waves. Focusing on the small coupling limit as a benchmark for the statistical mechanics of weak Langmuir turbulence, it is shown that Monte Carlo microcanonical results fully agree with an exact microcanonical derivation. The wave spectrum is predicted to collapse towards small wavelengths together with the escape of initially resonant particles towards low bulk plasma thermal speeds. This study reveals the fundamental discrepancy between the long-time dynamics of single waves, which can support finite amplitude steady states, and of wave spectra, which cannot.
Wave Kinematics and Sediment Suspension at Wave Breaking Point.
1982-06-01
is the fall velocity in oscillatory flow and W is the amplitude I of vertical velocity component. Equating Eqs. (3-30) I and (3-31) and solving the w...of the waves. The I cnoidal wave model was developed by Korteweg and DeVries (1895).. At the limits, the cnoidal wave approaches the I I I I I 119I I...experimental data. At present, sediment suspension in a fluid media Lis treated as a diffusion-dispersion process, and the [governing equation takes the
Tropical cyclogenesis in a tropical wave critical layer: easterly waves
NASA Astrophysics Data System (ADS)
Dunkerton, T. J.; Montgomery, M. T.; Wang, Z.
2008-06-01
The development of tropical depressions within tropical waves over the Atlantic and eastern Pacific is usually preceded by a "surface low along the wave" as if to suggest a hybrid wave-vortex structure in which flow streamlines not only undulate with the waves, but form a closed circulation in the lower troposphere surrounding the low. This structure, equatorward of the easterly jet axis, resembles the familiar critical layer of waves in shear flow, a flow configuration which arguably provides the simplest conceptual framework for tropical cyclogenesis resulting from tropical waves, their interaction with the mean flow, and with diabatic processes associated with deep moist convection. The critical layer represents a sweet spot for tropical cyclogenesis in which a proto-vortex may form and grow within its parent wave. A common location for storm development within the critical layer is given by the intersection of the wave's critical latitude and trough axis, with analyzed vorticity centroid nearby. The wave and vortex live together for a time, and initially propagate at approximately the same speed. In most cases this coupled propagation continues for a few days after a tropical depression is identified. For easterly waves, as the name suggests, the propagation is westward. It is shown that in order to visualize optimally this "marsupial paradigm" one should view the flow streamlines, or stream function, in a frame of reference translating horizontally with the phase propagation of the parent wave. This translation requires an appropriate "gauge" that renders translating streamlines and isopleths of translating stream function approximately equivalent to flow trajectories. In the translating frame, the closed circulation is stationary, and a dividing streamline effectively separates air within the critical layer from air outside. The critical layer equatorward of the easterly jet axis is important to tropical cyclogenesis because it provides (i) a region of
Dichromatic Langmuir waves in degenerate quantum plasma
Dubinov, A. E. Kitayev, I. N.
2015-06-15
Langmuir waves in fully degenerate quantum plasma are considered. It is shown that, in the linear approximation, Langmuir waves are always dichromatic. The low-frequency component of the waves corresponds to classical Langmuir waves, while the high-frequency component, to free-electron quantum oscillations. The nonlinear problem on the profile of dichromatic Langmuir waves is solved. Solutions in the form of a superposition of waves and in the form of beatings of its components are obtained.
Ultrasonic guided wave nondestructive evaluation using generalized anisotropic interface waves
NASA Astrophysics Data System (ADS)
Gardner, Michael D.
The motivation for this work is a goal to inspect interfaces between thick layers of materials that can be anisotropic. The specific application is a thick composite bonded to a metal substrate. The interface is inspected for disbonds between the metal and composite. The large thickness allows the problem to be modeled as a half space. The theory behind guided waves in plates is presented. This theory includes the calculation and analysis of dispersion curves and the resulting wave structure. It is noted that for high frequency-thickness values, certain modes will converge to the half-space waves, e.g. the Rayleigh wave and the Stoneley wave. Points of high energy, especially shear energy, at the interface are desirable for interfacial inspection. Therefore, the wave structure for all modes and frequencies is searched for ideal inspection points. Interface waves are inherently good modes to use for interface inspection. Results from the dispersion curves and wave structures are verified in the finite element model software package called Abaqus. It is confirmed that the group speeds and wave structures of the modes match the predicted values. A theoretical development of interface waves is given wherein Rayleigh, Stoneley, and generalized interface waves are discussed. This is applied to both isotropic and anisotropic materials. It is shown that the Stoneley wave only exists for a certain range of material parameters. Because the Stoneley wave is the interface wave between two solid half spaces, it might appear that only certain pairs of solids would allow for inspection via interface wave. However, it is shown that for perturbations of the Stoneley-wave-valid material properties, interface waves which leak energy away from the interface can still propagate. They can also be used for inspection. Certain choices of materials will leak less energy and will therefore allow for longer inspection distances. The solutions to the isotropic leaky wave problem exist on
Wave dissipation by muddy seafloors
NASA Astrophysics Data System (ADS)
Elgar, Steve; Raubenheimer, Britt
2008-04-01
Muddy seafloors cause tremendous dissipation of ocean waves. Here, observations and numerical simulations of waves propagating between 5- and 2-m water depths across the muddy Louisiana continental shelf are used to estimate a frequency- and depth-dependent dissipation rate function. Short-period sea (4 s) and swell (7 s) waves are shown to transfer energy to long-period (14 s) infragravity waves, where, in contrast with theories for fluid mud, the observed dissipation rates are highest. The nonlinear energy transfers are most rapid in shallow water, consistent with the unexpected strong increase of the dissipation rate with decreasing depth. These new results may explain why the southwest coast of India offers protection for fishing (and for the 15th century Portuguese fleet) only after large waves and strong currents at the start of the monsoon move nearshore mud banks from about 5- to 2-m water depth. When used with a numerical nonlinear wave model, the new dissipation rate function accurately simulates the large reduction in wave energy observed in the Gulf of Mexico.
Dark Matter, Waves, and Identification
NASA Astrophysics Data System (ADS)
Wagner, Orvin
2011-10-01
In 1994 I wrote article for Physics Essays (Waves in Dark Matter) showing how the solar system is organized and stabilized by dark matter standing waves from the dark matter oscillating sun. Wave velocity is apparently inversely proportional to the square root of the dark matter density. At the sun's surface the wave velocity is near 1.25 m/s. More recently I have found local dark matter waves that appear to travel near 25 m/s near April 1 and appear to organize plants. They travel between plants and artificial transmitters and receivers, and penetrate my local hill. From my measurements the local dark matter density is a function of the time of year. The data indicate that dark matter interacts much more than just with gravity as others have surmised. I present experimental proofs and a local dark matter density equation in terms of the measured velocity. The waves and the earth's location may be very important for nature's organization. The observed behavior appears to go a long way towards dark matter identification. These waves also may explain the rings of the gaseous planets in terms of oscillating layers. See the ring article on the web site Darkmatterwaves.com.
Solitary waves in the atmosphere
NASA Technical Reports Server (NTRS)
Rottman, James W.; Einaudi, Franco
1993-01-01
The weakly nonlinear theory for internal solitary waves is reviewed, and theoretical results of the vertical and horizontal structure of temperature, vertical displacements, and vertical and horizontal perturbations to the wind field associated with steadily propagating solitary waves are presented in two idealized atmospheric configurations. One configuration is representative of solitary waves observed in the lower troposphere and the other of solitary waves that occupy the entire troposphere. The important results of the theory are presented in a form that can be readily used by observationalists. The results obtained are then analyzed using actual rawinsonde data for two well-documented observations of atmospheric solitary waves, which are analogous to the two idealized configurations. The importance and difficulties of properly identifying the waveguide within which the solitary wave is confined are discussed. The fundamental role of a critical level in ducting the disturbances and thus in defining the thickness of the waveguide is illustrated in the example dealing with the solitary wave occupying the entire troposphere. Together, these two examples illustrate the decisions and compromises that must be made in applying the theory to the real atmosphere.
Constitutive modeling of fracture waves
NASA Astrophysics Data System (ADS)
Resnyansky, A. D.; Romensky, E. I.; Bourne, N. K.
2003-02-01
A fracture wave (FW) in a brittle material is a narrow transition region (border) of a continuous fracture zone, which may be associated with the damage accumulation process initiated by propagation of shock waves. In multidimensional structures the fracture wave may behave in an unusual way. The high-speed photography of penetration of a borosilicate (Pyrex) glass block [N. K. Bourne, L. Forde, and J. E. Field, Proc. SPIE 2869, 626 (1997)] shows a visible fracture zone with an apparent flat front although the projectile is a hemispherically nosed rod. A strain-rate-sensitive model is being developed and employed for analysis of the role of the complex stress state and kinetic description of the damage accumulation to describe the process of the impact. Numerical analysis is conducted with a one-dimensional wave propagation code employing the model and with the LS-DYNA2D hydrocode in which the model has been implemented. The analysis demonstrates that (i) the second (plastic) shock wave is superseded by quicker FW relaxing stress behind the elastic precursor, and (ii) the FW front flattening is apparently caused by the change in the acoustic directional properties. This change is associated with the phase-like transition due to the damage accumulation within the FW. In particular, the FW transition separates a highly anisotropic zone of material characterized acoustically by longitudinal and shear waves in front of the FW from a nearly isotropic region of the material characterized only by bulk waves behind the FW.
Kinematic dynamo of inertial waves
NASA Astrophysics Data System (ADS)
Herreman, Wietze; Le Gal, Patrice; Le Dizes, Stephane
2008-11-01
Inertial waves are natural oscillatory tridimensional perturbations in rapidly rotating flows. They can be driven to high amplitudes by an external oscillatory forcing such as precession, or by a parametric instability such as in the elliptical instability. Inertial waves were observed in a MHD-flow (Gans, 1971, JFM ; Kelley et al., 2008, GAFD) and could be responsable of dynamo action. For travelling waves, a constructive alpha-effect was identified (Moffatt, 1970, JFM), but it does not apply to confined inertial wave flows. Yet, recent numerical work demonstrated that precession driven MHD flows can sustain magnetic fields (Tilgner, 2005, POF; Wu & Roberts, 2008, GAFD). This motivates us to study more precisely how inertial waves can exhibit dynamo action. Using a numerical code in cylindrical geometry, we find that standing inertial waves can generate a kinematic dynamo. We show that the dynamo-action results from a second order interaction of the diffusive eigenmodes of the magnetic field with the inertial wave. Scaling laws are obtained, which allows us to to apply the results to flows of geophysical interest.
Head wave correlations in ambient noise.
Gebbie, John; Siderius, Martin
2016-07-01
Ambient ocean noise is processed with a vertical line array to reveal coherent time-separated arrivals suggesting the presence of head wave multipath propagation. Head waves, which are critically propagating water waves created by seabed waves traveling parallel to the water-sediment interface, can propagate faster than water-only waves. Such eigenrays are much weaker than water-only eigenrays, and are often completely overshadowed by them. Surface-generated noise is different whereby it amplifies the coherence between head waves and critically propagating water-only waves, which is measured by cross-correlating critically steered beams. This phenomenon is demonstrated both experimentally and with a full wave simulation.
Diffracted and head waves associated with waves on nonseparable surfaces
NASA Technical Reports Server (NTRS)
Barger, Raymond L.
1992-01-01
A theory is presented for computing waves radiated from waves on a smooth surface. With the assumption that attention of the surface wave is due only to radiation and not to dissipation in the surface material, the radiation coefficient is derived in terms of the attenuation factor. The excitation coefficient is determined by the reciprocity condition. Formulas for the shape and the spreading of the radiated wave are derived, and some sample calculations are presented. An investigation of resonant phase matching for nonseparable surfaces is presented with a sample calculation. A discussion of how such calculations might be related to resonant frequencies of nonseparable thin shell structures is included. A description is given of nonseparable surfaces that can be modeled in the vector that facilitates use of the appropriate formulas of differential geometry.
Zeta waves: a special type of slow delta waves.
Magnus, O; Van der Holst, M
1987-08-01
A special type of delta waves with a duration of 1-3 sec which, because of their saw-tooth or zed shape in the EEG, we have named 'zeta waves' has been described. They occur particularly in cases with rather severe brain lesions, usually with an acute or subacute onset and a space occupying character. In a period of 2 years during which 2500 EEGs have been reported we have seen zeta waves in 20 patients in whom 76 EEGs have been recorded. The characteristics of these waves and the types of lesions with which they occurred are described. The importance of an adequate recording technique for proper presentation of this EEG pattern is emphasized.
How Forgetful are Seismic Waves ?
NASA Astrophysics Data System (ADS)
Milkereit, B.
2005-05-01
3D surface seismic and vertical seismic profiling (VSP) techniques can be employed to image crustal structures in complex geological settings. The effects of heterogeneities on seismic wave propagation can be described in terms of different propagation regimes (Wu, 1989): quasi-homogeneous for heterogeneities too small to be seen by seismic waves, Rayleigh scattering, Mie scattering and small-angle scattering. These scattering regimes cause characteristic amplitude, phase and travel time fluctuation, which can be used to obtain estimates of scale length. Horizontal resolution of exploration seismic data is often discussed in terms of Fresnel zone. For surface and VSP data, the Fresnel radius increases with increasing depth of investigation. In addition, the lateral resolution is limited by the effective frequency content of the seismic signal. Based on strong contrast in petrophysical data, crustal exploration targets (such as gas-hydrates, permafrost or massive sulfide ores) should make strong P-wave, S-wave and converted wave reflectors against most background velocity models. In the context of realistic geological models, 3D numerical simulations are required to better assess elastic wave interactions with high acoustic impedance targets. In addition, it is important to study the influence of composition and shape of high acoustic impedance targets on the full scattered wavefield through a series of numerical modeling experiments based on the 3D elastic finite-difference (FD) method. Massive sulfide ores consisting of the end-member sulfide minerals pyrite, sphalerite, and galena, which span the full range of observed P- and S- wave velocities and densities in ore rocks, as well as gabbro inclusions, are investigated for different shapes which represent the complex morphologies often observed for ore deposits. 3D FD modeling reveals that large ore deposits lead to a strong and complex scattering response that is often dominated by shear-wave events (Bohlen et al
Density waves in granular flow
NASA Astrophysics Data System (ADS)
Herrmann, H. J.; Flekkøy, E.; Nagel, K.; Peng, G.; Ristow, G.
Ample experimental evidence has shown the existence of spontaneous density waves in granular material flowing through pipes or hoppers. Using Molecular Dynamics Simulations we show that several types of waves exist and find that these density fluctuations follow a 1/f spectrum. We compare this behaviour to deterministic one-dimensional traffic models. If positions and velocities are continuous variables the model shows self-organized criticality driven by the slowest car. We also present Lattice Gas and Boltzmann Lattice Models which reproduce the experimentally observed effects. Density waves are spontaneously generated when the viscosity has a nonlinear dependence on density which characterizes granular flow.
Recirculation in multiple wave conversions
Kaufman, A. N.; Brizard, A.J.; Kaufman, A.N.; Tracy, E.R.
2008-07-30
A one-dimensional multiple wave-conversion model is constructed that allows energy recirculation in ray phase space. Using a modular eikonal approach, the connection coefficients for this model are calculated by ray phase-space methods. Analytical results (confirmed numerically) show that all connection coefficients exhibit interference effects that depend on an interference phase, calculated from the coupling constants and the area enclosed by the intersecting rays. This conceptual model, which focuses on the topology of intersecting rays in phase space, is used to investigate how mode conversion between primary and secondary waves is modified by the presence of a tertiary wave.
1991-10-01
PL-TR--91-1045 /’--"PL-TR-- AD-A243 555 91-1045 WAVEGUIDE FOUR -WAVE MIXING Thomas B. Simpson Jia-ming Liu JAYCOR San Diego, CA 92186-5154 October...Final Report; May 88 - Mar 91 4. TITLE AND SUBTITLE 5. FUNDING NUMBERS WAVEGUIDE FOUR -WAVE MIXING C: F29601-88-C-0023 PE: 62601F PR: 3326 6. AUTHOR(S...for public release; distribution unlimited. 13. ABSTRACT (Maximum 200 words) This program has investigated four -wave mixing (4-win) in non- linear
Surface acoustic wave microfluidics.
Ding, Xiaoyun; Li, Peng; Lin, Sz-Chin Steven; Stratton, Zackary S; Nama, Nitesh; Guo, Feng; Slotcavage, Daniel; Mao, Xiaole; Shi, Jinjie; Costanzo, Francesco; Huang, Tony Jun
2013-09-21
The recent introduction of surface acoustic wave (SAW) technology onto lab-on-a-chip platforms has opened a new frontier in microfluidics. The advantages provided by such SAW microfluidics are numerous: simple fabrication, high biocompatibility, fast fluid actuation, versatility, compact and inexpensive devices and accessories, contact-free particle manipulation, and compatibility with other microfluidic components. We believe that these advantages enable SAW microfluidics to play a significant role in a variety of applications in biology, chemistry, engineering and medicine. In this review article, we discuss the theory underpinning SAWs and their interactions with particles and the contacting fluids in which they are suspended. We then review the SAW-enabled microfluidic devices demonstrated to date, starting with devices that accomplish fluid mixing and transport through the use of travelling SAW; we follow that by reviewing the more recent innovations achieved with standing SAW that enable such actions as particle/cell focusing, sorting and patterning. Finally, we look forward and appraise where the discipline of SAW microfluidics could go next.
Cavallero, C; Cicogna, P; Natale, V; Occhionero, M; Zito, A
1992-12-01
Fifty volunteers slept two nonconsecutive nights in a sleep laboratory under electropolygraphic control. They were awakened for one report per night. Awakenings were made, in counterbalanced order, from slow wave sleep (SWS--stage 3-4 and stage 4) and rapid eye movement (REM) sleep. Following dream reporting, subjects were asked to identify memory sources of their dream imagery. Two independent judges reliably rated mentation reports for temporal units and for several content and structural dimensions. The same judges also categorized memory sources as autobiographical episodes, abstract self-references, or semantic knowledge. We found that REM reports were significantly longer than SWS reports. Minor content SWS-REM differences were also detected. Moreover, semantic knowledge was more frequently mentioned as a dream source for REM than for SWS dream reports. These findings are interpreted as supporting the hypothesis that dreaming is a continuous process that is not unique to REM sleep. Different levels of engagement of the cognitive system are responsible for the few SWS-REM differences that have been detected.
Modeling Regional Seismic Waves
1992-03-24
Source Paramneters of the, Sierra . Madre Farthquake from Hc’gioal awl Local Bodv \\Wave’s. (;ophys. 1?(,.;. 1.I0.. 18. 201(7)- 2018. I)reger, D. S. and D...04 4.0 15.04 a " " A.S. 19 91/05/20 3.7 14.20 4 San Jacinto II 16:19: 4.8 16.19 a " " A.S. 20 91/06/28 5.4 17.41 f Sierra Madre 92/05/06 4.5 15.87 a...It " A.S. 21 15:37: 3.9 14.61 f S. Madre A.S. 92/05/12 4.4 15.60 a .. . A.S. 22 17:00: 4.3 15.60 f S. Madre A.S. 92/05/18 3.5 14.39 a " " A.S. 23 91/06
NASA Technical Reports Server (NTRS)
2007-01-01
This plot tells astronomers that a fifth planet is in orbit around the star 55 Cancri, making the star the record-holder for hosting the most known exoplanets.
As planets circle around their stars, they cause the stars to wobble back and forth in a regular pattern. By looking for this motion in a star, scientists can find planets that can't be seen with telescopes.
The wobble caused by the fifth planet discovered around 55 Cancri is represented here by the sinuous line in blue. The actual data points are yellow and error bars are the lines above and below the yellow dots. The cycle of the wobble indicates that the planet circles around its star about every 260 days. The amplitude of the wobble indicates that the planet is a giant at least 45 times the mass of Earth.
The wobbles caused by the other four planets has been removed from this plot, to reveal that caused by the fifth. The departure from a perfect sine wave suggests the planet's orbit is not perfectly circular.
Because 55 Cancri has multiple planets, the star had to be observed for a long time before astronomers could find and confirm its fifth planet. These data were collected over a period of 18 years using both the Lick Observatory near San Jose, Calif., and the W.M. Keck Observatory in Hawaii.
Surface acoustic wave microfluidics
Ding, Xiaoyun; Li, Peng; Lin, Sz-Chin Steven; Stratton, Zackary S.; Nama, Nitesh; Guo, Feng; Slotcavage, Daniel; Mao, Xiaole; Shi, Jinjie; Costanzo, Francesco; Huang, Tony Jun
2014-01-01
The recent introduction of surface acoustic wave (SAW) technology onto lab-on-a-chip platforms has opened a new frontier in microfluidics. The advantages provided by such SAW microfluidics are numerous: simple fabrication, high biocompatibility, fast fluid actuation, versatility, compact and inexpensive devices and accessories, contact-free particle manipulation, and compatibility with other microfluidic components. We believe that these advantages enable SAW microfluidics to play a significant role in a variety of applications in biology, chemistry, engineering, and medicine. In this review article, we discuss the theory underpinning SAWs and their interactions with particles and the contacting fluids in which they are suspended. We then review the SAW-enabled microfluidic devices demonstrated to date, starting with devices that accomplish fluid mixing and transport through the use of travelling SAW; we follow that by reviewing the more recent innovations achieved with standing SAW that enable such actions as particle/cell focusing, sorting, and patterning. Finally, we look forward and appraise where the discipline of SAW microfluidics could go next. PMID:23900527
Internal Waves in Straits (IWISE): Observations of Wave Generation
2012-09-30
deployment of a 2-D array of pressure-sensor-equipped inverted echo sounders (PIES) so as to observe the generation of internal waves by tidal...east of the strait to the westernmost deployments. Fig. 1 Deployment locations of Pressure sensor equipped Inverted Echo Sounders [PIES] in South...measurements of nonlinear internal waves using the inverted echo sounder , J. Atmos. Oceanic Technology, 26, 2228−2242. David M Farmer, Li, Qiang & Jae-Hun
Wave - fluid particle interaction in the Faraday waves
NASA Astrophysics Data System (ADS)
Francois, Nicolas; Xia, Hua; Punzmann, Horst; Shats, Michael
2016-11-01
Faraday waves are parametrically excited perturbations that appear on a liquid surface when the latter is vertically vibrated. Recently it has been discovered that: 1) such wave field can be described as a disordered lattice made of localised oscillating excitations, termed oscillons, 2) the horizontal motion of fluid particles on the water surface reproduces in detail the motion of fluid in two-dimensional turbulence. Here we report experimental measurements of the motion of both entities using Particle Image Velocimetry and Particle Tracking Velocimetry techniques. Those techniques allow to measure Lagrangian and Eulerian features of the oscillon motion and compare them with those of the fluid motion. A strong coupling is uncovered between the erratic motion of the waves and the turbulent agitation of the fluid particles. Both motions show Brownian-type dispersion and the r.m.s velocity of oscillons is directly related to the r.m.s. velocity of the fluid particles in a broad range of vertical accelerations. These results offer new perspectives for predicting surface fluid transport from the knowledge of the wave fields and vice versa. In particular, the broadening of the wave spectra at high wave amplitude can be predicted if the 2D turbulence energy is known. This work was supported by the Australian Research Council's Discovery Projects funding scheme (DP150103468 and DP160100863). NF acknowledges support by the Australian Research Council's DECRA Award (DE160100742).
Whistler wave propagation in a large magnetoplasma
NASA Technical Reports Server (NTRS)
Stenzel, R. L.
1976-01-01
A large collisionless quiescent plasma source is developed for investigating the phase and amplitude distribution of antenna-launched whistler waves in a specified parameter regime relating wave frequency to electron cyclotron frequency. Wave dispersion is studied both by interferometer techniques with monochromatic waves and by propagation of short phase-coherent wave bursts. The wave damping mechanism is examined by propagating perfectly ducted whistler waves. The dispersion of single frequency waves and wave packets is demonstrated. Trough ducting for wave frequency to electron cyclotron frequency ratio greater than 1/2 is verified, and new eigenmodes in nonuniform plasmas at ratio values less than 1/2 are observed. It is shown that geometric effects due to ray divergence and wave refraction dominate over collisional damping.
Trend analysis of the wave storminess: the wave direction
NASA Astrophysics Data System (ADS)
Casas Prat, M.; Sierra, J. P.; Mösso, C.; Sánchez-Arcilla, A.
2009-09-01
Climate change has an important role in the current scientific research because of its possible future negative consequences. Concerning the climate change in the coastal engineering field, the apparent sea level rise is one of the key parameters as well as the wave height and the wave direction temporal variations. According to the IPCC (2007), during the last century the sea level has been increasing with a mean rate of 1.7 ± 0.5 mm/yr. However, at local/regional scale the tendency significantly differs from the global trend since the local pressure and wind field variations become more relevant. This appears to be particularly significant in semi-enclosed areas in the Mediterranean Sea (Cushman-Roisin et al., 2001). Even though the existing unsolved questions related to the sea level rise, the uncertainty concerning the wave height is even larger, in which stormy conditions are especially important because they are closely related to processes such as coastal erosion, flooding, etc. Therefore, it is necessary to identify possible existing tendencies of storm related parameters. In many studies, only the maximum wave height and storm duration are analysed, remaining the wave direction in a second term. Note that a possible rotation of the mean wave direction may involve severe consequences since most beach and harbour defence structures have been designed assuming a constant predominant wave incidence. Liste et al. (2004) illustrated this fact with an example in which a rotation of only 2 degrees of the mean energy flux vector could produce a beach retreat of 20 m. Another possible consequence would be a decrease of the harbour operability: increased frequency of storms in the same direction as the harbour entrance orientation would influence the navigability. The present study, which focuses in the Catalan coast (NW Mediterranean Sea), aims to improve the present knowledge of the wave storminess variations at regional scale, specially focusing on the wave
The parametric decay of Alfven waves into shear Alfven waves and dust lower hybrid waves
Jamil, M.; Shah, H. A.; Zubia, K.; Zeba, I.; Uzma, Ch.; Salimullah, M.
2010-07-15
The parametric decay instability of Alfven wave into low-frequency electrostatic dust-lower-hybrid and electromagnetic shear Alfven waves has been investigated in detail in a dusty plasma in the presence of external/ambient uniform magnetic field. Magnetohydrodynamic fluid equations of plasmas have been employed to find the linear and nonlinear response of the plasma particles for this three-wave nonlinear coupling in a dusty magnetoplasma. Here, relatively high frequency electromagnetic Alfven wave has been taken as the pump wave. It couples with other two low-frequency internal possible modes of the dusty magnetoplasma, viz., the dust-lower-hybrid and shear Alfven waves. The nonlinear dispersion relation of the dust-lower-hybrid wave has been solved to obtain the growth rate of the parametric decay instability. The growth rate is maximum for small value of external magnetic field B{sub s}. It is noticed that the growth rate is proportional to the unperturbed electron number density n{sub oe}.
Patsourakos, Spiros; Vourlidas, Angelos E-mail: vourlidas@nrl.navy.mil
2009-08-01
The nature of coronal mass ejection (CME)-associated low corona propagating disturbances, 'extreme ultraviolet (EUV) waves', has been controversial since their discovery by EIT on SOHO. The low-cadence, single-viewpoint EUV images and the lack of simultaneous inner corona white-light observations have hindered the resolution of the debate on whether they are true waves or just projections of the expanding CME. The operation of the twin EUV imagers and inner corona coronagraphs aboard STEREO has improved the situation dramatically. During early 2009, the STEREO Ahead (STA) and Behind (STB) spacecrafts observed the Sun in quadrature having a {approx}90 deg. angular separation. An EUV wave and CME erupted from active region 11012, on February 13, when the region was exactly at the limb for STA and hence at disk center for STB. The STEREO observations capture the development of a CME and its accompanying EUV wave not only with high cadence but also in quadrature. The resulting unprecedented data set allowed us to separate the CME structures from the EUV wave signatures and to determine without doubt the true nature of the wave. It is a fast-mode MHD wave after all.
Urban Heat Wave Hazard Assessment
NASA Technical Reports Server (NTRS)
Quattrochi, Dale A.; Jedlovec, Gary; Meyer, Paul J.; LaFontaine, Frank J.; Crane, Dakota L.
2016-01-01
Heat waves are the largest cause of environment-related deaths globally. On average, over 6,000 people in the United States alone are hospitalized each summer due to excessive heat. Key elements leading to these disasters are elevated humidity and the urban heat island effect, which act together to increase apparent temperature and amplify the effects of a heat wave. Urban demographics and socioeconomic factors also play a role in determining individual risk. Currently, advisories of impending heat waves are often too generalized, with limited or no spatial variability over urban regions. This frequently contributes to a lack of specific response on behalf of the population. A goal of this project is to develop a product that has the potential to provide more specific heat wave guidance invoking greater awareness and action.
Analytical approximations for spiral waves
Löber, Jakob Engel, Harald
2013-12-15
We propose a non-perturbative attempt to solve the kinematic equations for spiral waves in excitable media. From the eikonal equation for the wave front we derive an implicit analytical relation between rotation frequency Ω and core radius R{sub 0}. For free, rigidly rotating spiral waves our analytical prediction is in good agreement with numerical solutions of the linear eikonal equation not only for very large but also for intermediate and small values of the core radius. An equivalent Ω(R{sub +}) dependence improves the result by Keener and Tyson for spiral waves pinned to a circular defect of radius R{sub +} with Neumann boundaries at the periphery. Simultaneously, analytical approximations for the shape of free and pinned spirals are given. We discuss the reasons why the ansatz fails to correctly describe the dependence of the rotation frequency on the excitability of the medium.
Analytical approximations for spiral waves.
Löber, Jakob; Engel, Harald
2013-12-01
We propose a non-perturbative attempt to solve the kinematic equations for spiral waves in excitable media. From the eikonal equation for the wave front we derive an implicit analytical relation between rotation frequency Ω and core radius R(0). For free, rigidly rotating spiral waves our analytical prediction is in good agreement with numerical solutions of the linear eikonal equation not only for very large but also for intermediate and small values of the core radius. An equivalent Ω(R(+)) dependence improves the result by Keener and Tyson for spiral waves pinned to a circular defect of radius R(+) with Neumann boundaries at the periphery. Simultaneously, analytical approximations for the shape of free and pinned spirals are given. We discuss the reasons why the ansatz fails to correctly describe the dependence of the rotation frequency on the excitability of the medium.
Refraction of coastal ocean waves
NASA Technical Reports Server (NTRS)
Shuchman, R. A.; Kasischke, E. S.
1981-01-01
Refraction of gravity waves in the coastal area off Cape Hatteras, NC as documented by synthetic aperture radar (SAR) imagery from Seasat orbit 974 (collected on September 3, 1978) is discussed. An analysis of optical Fourier transforms (OFTs) from more than 70 geographical positions yields estimates of wavelength and wave direction for each position. In addition, independent estimates of the same two quantities are calculated using two simple theoretical wave-refraction models. The OFT results are then compared with the theoretical results. A statistical analysis shows a significant degree of linear correlation between the data sets. This is considered to indicate that the Seasat SAR produces imagery whose clarity is sufficient to show the refraction of gravity waves in shallow water.
Electron cyclotron harmonic wave acceleration
NASA Technical Reports Server (NTRS)
Karimabadi, H.; Menyuk, C. R.; Sprangle, P.; Vlahos, L.
1987-01-01
A nonlinear analysis of particle acceleration in a finite bandwidth, obliquely propagating electromagnetic cyclotron wave is presented. It has been suggested by Sprangle and Vlahos in 1983 that the narrow bandwidth cyclotron radiation emitted by the unstable electron distribution inside a flaring solar loop can accelerate electrons outside the loop by the interaction of a monochromatic wave propagating along the ambient magnetic field with the ambient electrons. It is shown here that electrons gyrating and streaming along a uniform, static magnetic field can be accelerated by interacting with the fundamental or second harmonic of a monochromatic, obliquely propagating cyclotron wave. It is also shown that the acceleration is virtually unchanged when a wave with finite bandwidth is considered. This acceleration mechanism can explain the observed high-energy electrons in type III bursts.
Stratospheric control of planetary waves
NASA Astrophysics Data System (ADS)
Hitchcock, Peter; Haynes, Peter H.
2016-11-01
The effects of imposing at various altitudes in the stratosphere zonally symmetric circulation anomalies associated with a stratospheric sudden warming are investigated in a mechanistic circulation model. A shift of the tropospheric jet is found even when the anomalies are imposed only above 2 hPa. Their influence is communicated downward through the planetary wave field via three distinct mechanisms. First, a significant fraction of the amplification of the upward fluxes of wave activity prior to the central date of the warming is due to the coupled evolution of the stratospheric zonal mean state and the wave field throughout the column. Second, a downward propagating region of localized wave, mean-flow interaction is active around the central date but does not penetrate the tropopause. Third, there is deep, vertically synchronous suppression of upward fluxes following the central date. The magnitude of this suppression correlates with that of the tropospheric jet shift.
Autoresonant control of drift waves
NASA Astrophysics Data System (ADS)
Shagalov, A. G.; Rasmussen, J. Juul; Naulin, V.
2017-03-01
The control of nonlinear drift waves in a magnetized plasmas column has been investigated. The studies are based on the Hasegawa–Mima model, which is solved on a disk domain with radial inhomogeneity of the plasma density. The system is forced by a rotating potential with varying frequency defined on the boundary. To excite and control the waves we apply the autoresonant effect, taking place when the amplitude of the forcing exceeds a threshold value and the waves are phase-locked with the forcing. We demonstrate that the autoresonant approach is applicable for excitation of a range of steady nonlinear waves of the lowest azimuthal mode numbers and for controlling their amplitudes and phases. We also demonstrate the excitation of zonal flows (m = 0 modes), which are controlled via the forced modes.
Tunnel effect wave energy detection
NASA Technical Reports Server (NTRS)
Kaiser, William J. (Inventor); Waltman, Steven B. (Inventor); Kenny, Thomas W. (Inventor)
1995-01-01
Methods and apparatus for measuring gravitational and inertial forces, magnetic fields, or wave or radiant energy acting on an object or fluid in space provide an electric tunneling current through a gap between an electrode and that object or fluid in space and vary that gap with any selected one of such forces, magnetic fields, or wave or radiant energy acting on that object or fluid. These methods and apparatus sense a corresponding variation in an electric property of that gap and determine the latter force, magnetic fields, or wave or radiant energy in response to that corresponding variation, and thereby sense or measure such parameters as acceleration, position, particle mass, velocity, magnetic field strength, presence or direction, or wave or radiant energy intensity, presence or direction.
Elastic waves in quasiperiodic structures
NASA Astrophysics Data System (ADS)
Velasco, V. R.; Zárate, J. E.
2001-08-01
We study the transverse and sagittal elastic waves in different quasiperiodic structures by means of the full transfer-matrix technique and surface Green-function matching method. The quasiperiodic structures follow Fibonacci, Thue-Morse and Rudin-Shapiro sequences, respectively. We consider finite structures having stress-free bounding surfaces and different generation orders, including up to more than 1000 interfaces. We obtain the dispersion relations for elastic waves and spatial localization of the different modes. The fragmentation of the spectrum for different sequences is evident for intermediate generation orders, in the case of transverse elastic waves, whereas, for sagittal elastic waves, higher generation orders are needed to show clearly the spectrum fragmentation. The results of Fibonacci and Thue-Morse sequences exhibit similarities not present in the results of Rudin-Shapiro sequences.
Mesosphere Dynamics with Gravity Wave Forcing. 2; Planetary Waves
NASA Technical Reports Server (NTRS)
Mayr, H. G.; Mengel, J. G.; Chan, K. L.; Porter, H. S.; Einaudi, Franco (Technical Monitor)
2000-01-01
We present results from a non-linear, 3D, time dependent numerical spectral model (NSM) which extends from the ground up into the thermosphere and incorporates Hines' Doppler Spread Parameterization for small-scale gravity waves (GW). Our focal point is the mesosphere where wave interactions are playing a dominant role. We discuss planetary waves in the present paper and diurnal and semi-diurnal tides in the companion paper. Without external time dependent energy or momentum sources, planetary waves (PWs) are generated in the model for zonal wavenumbers 1 to 4, which have amplitudes in the mesosphere above 50 km as large as 30 m/s and periods between 2 and 50 days. The waves are generated primarily during solstice conditions, which indicates that the baroclinic instability (associated with the GW driven reversal in the latitudinal temperature gradient) is playing an important role. Results from a numerical experiment show that GWs are also involved directly in generating the PWs. For the zonal wavenumber m = 1, the predominant wave periods in summer are around 4 days and in winter between 6 and 10 days. For m = 2, the periods are in summer and close to 2.5 and 3.5 days respectively For m = 3, 4 the predominant wave periods are in both seasons close to two days. The latter waves have the characteristics of Rossby gravity waves with meridional winds at equatorial latitudes. A common feature of the PWs (m = 1 to 4) generated in summer and winter is that their vertical wavelengths throughout the mesosphere are large which indicates that the waves are not propagating freely but are generated throughout the region. Another common feature is that the PWs propagate preferentially westward in summer and eastward in winter, being launched from the westward and eastward zonal winds that prevail respectively in summer and winter altitudes below 80 km. During spring and fall, for m = 1 and 2 eastward propagating long period PWs are generated that are launched from the smaller
Splash singularity for water waves.
Castro, Angel; Córdoba, Diego; Fefferman, Charles L; Gancedo, Francisco; Gómez-Serrano, Javier
2012-01-17
We exhibit smooth initial data for the two-dimensional (2D) water-wave equation for which we prove that smoothness of the interface breaks down in finite time. Moreover, we show a stability result together with numerical evidence that there exist solutions of the 2D water-wave equation that start from a graph, turn over, and collapse in a splash singularity (self-intersecting curve in one point) in finite time.
Apparatus Review: Cenco Wave Apparatus
NASA Astrophysics Data System (ADS)
Greenslade, Thomas B.
2009-01-01
Some apparatus from the 19th century illustrates the phenomena of physics so well that it crops up again in the 21st century. An example is the combined transverse and longitudinal wave machine in Fig. 1. This is in the current Cenco/Sargent-Welch catalog under the name of "Wave Apparatus" (Cat. No. WLS-1755-90) and sells for 49.95.
Waves, Turbulence and Boundary Layers
2005-09-30
streaming effects and compares the present three-dimensional wave- current equations with those by McWilliams and Restrepo (1999) I spent three Spring...Oceanographic Institute, scientists at the Technical University of Delft, Alan Blumberg of Stevens Institute of Tecnology and Tal Ezer and Leo Oey of...206, 265-297. McWilliams , J. C. and J. M. Restrepo, 1999: The wave-driven ocean circulation. J. Phys. Oceanogr., 29, 2523-2540. Mellor, G. L
Rhinefrank, Kenneth E.; Lenee-Bluhm, Pukha; Prudell, Joseph H.; Schacher, Alphonse A.; Hammagren, Erik J.; Zhang, Zhe
2013-07-29
The most prudent path to a full-scale design, build and deployment of a wave energy conversion (WEC) system involves establishment of validated numerical models using physical experiments in a methodical scaling program. This Project provides essential additional rounds of wave tank testing at 1:33 scale and ocean/bay testing at a 1:7 scale, necessary to validate numerical modeling that is essential to a utility-scale WEC design and associated certification.
Shock waves show icebreaking promise
Wesley, R.H.; Stowell, W.R.
1985-11-01
State-of-the-art technology that is readily applicable in other offshore areas does not function adequately in Arctic regions. The common offshore problem in the Arctic, whether it be related to transportation, construction, drilling or production, is ice. Technology utilizing the phenomenal characteristics of the shock wave now exists that will allow relief from the ice problem in all of these categories. The feasibility of using shock waves for icebreaking is discussed.
Magnetic field waves at Uranus
NASA Technical Reports Server (NTRS)
Smith, Charles W.; Goldstein, Melvyn L.; Lepping, Ronald P.; Mish, William H.; Wong, Hung K.
1994-01-01
The research efforts funded by the Uranus Data Analysis Program (UDAP) grant to the Bartol Research Institute (BRI) involved the study of magnetic field waves associated with the Uranian bow shock. Upstream wave studies are motivated as a study of the physics of collisionless shocks. Collisionless shocks in plasmas are capable of 'reflecting' a fraction of the incoming thermal particle distribution and directing the resulting energetic particle motion back into the upstream region. Once within the upstream region, the backward streaming energetic particles convey information of the approaching shock to the supersonic flow. This particle population is responsible for the generation of upstream magnetic and electrostatic fluctuations known as 'upstream waves', for slowing the incoming wind prior to the formation of the shock ramp, and for heating of the upstream plasma. The waves produced at Uranus not only differed in several regards from the observations at other planetary bow shocks, but also gave new information regarding the nature of the reflected particle populations which were largely unmeasurable by the particle instruments. Four distinct magnetic field wave types were observed upstream of the Uranian bow shock: low-frequency Alfven or fast magnetosonic waves excited by energetic protons originating at or behind the bow shock; whistler wave bursts driven by gyrating ion distributions within the shock ramp; and two whistler wave types simultaneously observed upstream of the flanks of the shock and argued to arise from resonance with energetic electrons. In addition, observations of energetic particle distributions by the LECP experiment, thermal particle populations observed by the PLS experiment, and electron plasma oscillations recorded by the PWS experiment proved instrumental to this study and are included to some degree in the papers and presentations supported by this grant.
Planetary waves in rotating ionosphere
Khantadze, A. G.; Jandieri, V. G.; Jandieri, G. V.
2008-06-15
The problem of propagation of ultralong planetary waves in the Earth's upper atmosphere is considered. A new exact solution to the MHD equations for the ionosphere is obtained in spherical coordinates with allowance for the geomagnetic field and Earth's rotation. A general dispersion relation is derived for planetary waves in the ionospheric E and F regions, and the characteristic features of their propagation in a weakly ionized ionospheric plasma are discussed.
Wave Detection in Acceleration Plethysmogram
2015-01-01
Objectives Acceleration plethysmogram (APG) obtained from the second derivative of photoplethysmography (PPG) is used to predict risk factors for atherosclerosis with age. This technique is promising for early screening of atherosclerotic pathologies. However, extraction of the wave indices of APG signals measured from the fingertip is challenging. In this paper, the development of a wave detection algorithm including a preamplifier based on a microcontroller that can detect the a, b, c, and d wave indices is proposed. Methods The 4th order derivative of a PPG under real measurements of an APG waveform was introduced to clearly separate the components of the waveform, and to improve the rate of successful wave detection. A preamplifier with a Sallen-Key low pass filter and a wave detection algorithm with programmable gain control, mathematical differentials, and a digital IIR notch filter were designed. Results The frequency response of the digital IIR filter was evaluated, and a pulse train consisting of a specific area in which the wave indices existed was generated. The programmable gain control maintained a constant APG amplitude at the output for varying PPG amplitudes. For 164 subjects, the mean values and standard deviation of the a wave index corresponding to the magnitude of the APG signal were 1,106.45 and ±47.75, respectively. Conclusions We conclude that the proposed algorithm and preamplifier designed to extract the wave indices of an APG in real-time are useful for evaluating vascular aging in the cardiovascular system in a simple healthcare device. PMID:25995963
2007-01-01
example, in the Bahia Blanca Estuary (Argentina), the sand wave field terminated when the surficial sand sheet became too thin (Aliotta and Perillo... Rosa Island partially breached near the present-day location of the inlet mouth, but soon closed. It was reopened in March 1929 when the local...and Perillo, 1987) Bahia Blanca Estuary mean 11˚ max 30˚ mean 4˚ (Anthony and Leth, 2002) North Sea 2-4˚ 66 Figure 24. Sand wave
Internal Wave Generation in Straits
2013-09-30
echo sounders (PIESs) so as to observe the generation of internal waves by tidal interaction with topography in Luzon Strait (Fig. 1), and to...Pressure sensor equipped Inverted Echo Sounders [PIES] (see Li et al. 2009). Five instruments were deployed in a pilot study and 13 were deployed at the...internal waves using the inverted echo sounder , J. Atmos. Oceanic Technology, 26, 2228−2242. Li Qiang & David M Farmer (2011), The Generation and
Spin waves and magnetic excitations
Borovik-Romanov, A.S.; Sinha, S.K.
1988-01-01
This book describes both simple spin waves (magnons) and complicated excitations in magnetic systems. The following subjects are covered: - various methods of magnetic excitation investigations such as neutron scattering on magnetic excitations, spin-wave excitation by radio-frequency, power light scattering on magnons and magnetic excitation observation within the light-absorption spectrum; - oscillations of magnetic electron systems coupled with phonons, nuclear spin systems and localized impurity modes: - low-dimensional magnetics, amorphous magnetics and spin glasses.
Seismic waves increase permeability.
Elkhoury, Jean E; Brodsky, Emily E; Agnew, Duncan C
2006-06-29
Earthquakes have been observed to affect hydrological systems in a variety of ways--water well levels can change dramatically, streams can become fuller and spring discharges can increase at the time of earthquakes. Distant earthquakes may even increase the permeability in faults. Most of these hydrological observations can be explained by some form of permeability increase. Here we use the response of water well levels to solid Earth tides to measure permeability over a 20-year period. At the time of each of seven earthquakes in Southern California, we observe transient changes of up to 24 degrees in the phase of the water level response to the dilatational volumetric strain of the semidiurnal tidal components of wells at the Piñon Flat Observatory in Southern California. After the earthquakes, the phase gradually returns to the background value at a rate of less than 0.1 degrees per day. We use a model of axisymmetric flow driven by an imposed head oscillation through a single, laterally extensive, confined, homogeneous and isotropic aquifer to relate the phase response to aquifer properties. We interpret the changes in phase response as due to changes in permeability. At the time of the earthquakes, the permeability at the site increases by a factor as high as three. The permeability increase depends roughly linearly on the amplitude of seismic-wave peak ground velocity in the range of 0.21-2.1 cm s(-1). Such permeability increases are of interest to hydrologists and oil reservoir engineers as they affect fluid flow and might determine long-term evolution of hydrological and oil-bearing systems. They may also be interesting to seismologists, as the resulting pore pressure changes can affect earthquakes by changing normal stresses on faults.
Millimeter Waves: Acoustic and Electromagnetic
Ziskin, Marvin C.
2012-01-01
This article is the presentation I gave at the D'Arsonval Award Ceremony on June 14, 2011 at the Bioelectromagnetics Society Annual Meeting in Halifax, Nova Scotia. It summarizes my research activities in acoustic and electromagnetic millimeter waves over the past 47 years. My earliest research involved acoustic millimeter waves, with a special interest in diagnostic ultrasound imaging and its safety. For the last 21 years my research expanded to include electromagnetic millimeter waves, with a special interest in the mechanisms underlying millimeter wave therapy. Millimeter wave therapy has been widely used in the former Soviet Union with great reported success for many diseases, but is virtually unknown to Western physicians. I and the very capable members of my laboratory were able to demonstrate that the local exposure of skin to low intensity millimeter waves caused the release of endogenous opioids, and the transport of these agents by blood flow to all parts of the body resulted in pain relief and other beneficial effects. PMID:22926874