Dynamical properties of bidirectional charge-density waves in ErTe3
NASA Astrophysics Data System (ADS)
Sinchenko, A. A.; Lejay, P.; Leynaud, O.; Monceau, P.
2016-06-01
We report a strong difference in the sliding properties of the bidirectional charge-density wave (CDW) in the two-dimensional rare-earth tritelluride ErTe3 which occurs below TCDW1=265 K with a wave vector along the c axis and below TCDW2=165 K with a wave vector along the a axis; the excess current carried by the motion of the CDW is 10 times less for the lower CDW compared with the value of the upper one. We tentatively explain this result by a stronger pinning of the lower temperature CDW intricated with the upper one, which inhibits its motion and may generate a phase slippage lattice.
Properties of Charge Density Waves in La2-xBaxCuO4
Kim,Y.; Gu, G.; Gog, T.; Casa, D.
2008-01-01
We report a comprehensive x-ray scattering study of charge density wave (stripe) ordering in La2-xBaxCuO4 (x{approx}1/8), for which the bulk superconducting Tc is greatly suppressed. Strong superlattice reflections corresponding to static ordering of charge stripes were observed in this sample. The structural modulation at the lowest temperature was deduced based on the intensity of over 70 unique superlattice positions surveyed. We found that the charge order in this sample is described with one-dimensional charge density waves, which have incommensurate wave vectors (0.23, 0, 0.5) and (0, 0.23, 0.5), respectively, on neighboring CuO2 planes. The structural modulation due to the charge density wave order is simply sinusoidal, and no higher harmonics were observed. Just below the structural transition temperature, short-range charge density wave correlation appears, which develops into a large scale charge ordering around 40 K, close to the spin density wave ordering temperature. However, this charge ordering fails to grow into a true long range order, and its correlation length saturates at {approx}230 Angstroms, and slightly decreases below about 15 K, which may be due to the onset of two-dimensional superconductivity.
Effect of high magnetic fields on the charge density wave properties of KMo 6O 17
NASA Astrophysics Data System (ADS)
Rötger, A.; Dumas, J.; Marcus, J.; Schlenker, C.; Ulmet, J. P.; Audouard, A.; Askenazy, S.
1992-03-01
The electrical resistivity of the purple bronze KMo 6O 17 has been studied between 2 and 88 K with pulsed magnetic fields up to 35 T. Several anomalies are found on the curves Δρ/ρ(B) at different temperatures. The low field results are compared with previous measurements of susceptibility and magnetization. A phase diagram which may show a field displaced charge density wave instability and field induced transitions is proposed.
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)
Global coherence of dust density waves
Killer, Carsten; Melzer, André
2014-06-15
The coherence of self-excited three-dimensional dust density waves has been experimentally investigated by comparing global and local wave properties. For that purpose, three-dimensional dust clouds have been confined in a radio frequency plasma with thermophoretic levitation. Global wave properties have been measured from the line-of-sight integrated dust density obtained from homogenous light extinction measurements. Local wave properties have been obtained from thin, two-dimensional illuminated laser slices of the cloud. By correlating the simultaneous global and local wave properties, the spatial coherence of the waves has been determined. We find that linear waves with small amplitudes tend to be fragmented, featuring an incoherent wave field. Strongly non-linear waves with large amplitudes, however, feature a strong spatial coherence throughout the dust cloud, indicating a high level of synchronization.
NASA Astrophysics Data System (ADS)
Kim, Jin Hee; Rhyee, Jong-Soo; Kwon, Yong Seung
2012-12-01
We studied the electrical, thermal, and thermoelectric properties of the polycrystalline compound of SmNiC2. The electrical resistivity and magnetization measurement show the interplay between the charge density wave at TCDW=150 K and the ferromagnetic ordering of Tc=18 K. Below the ferromagnetic transition temperature, we observed the magnon gap formation of Δ≃4.3-4.4 meV by ρ(T) and Cp(T) measurements. The charge density wave is attributed to the increase of the Seebeck coefficient resulting in the increase of the power factor S2σ. The thermal conductivity anomalously increases with increasing temperature along the whole measured temperature range, which implies the weak attribution of Umklapp phonon scattering. The thermoelectric figure of merit ZT significantly increases due to the increase of the power factor at TCDW=150 K. Here we argue that the competing interaction between electron-phonon and electron-magnon couplings exhibits the unconventional behavior of electrical and thermal properties.
Magnon gap formation and charge density wave effect on thermoelectric properties in SmNiC2 compound
NASA Astrophysics Data System (ADS)
Kim, Jin-Hee; Rhyee, Jong-Soo; Kwon, Yong Seung
2013-03-01
We studied the magnetic, electrical, and thermal properties of polycrystalline compound of SmNiC2. The electrical resistivity and magnetization measurement show the interplay between the charge density wave at TCDW = 157 K and the ferromagnetic ordering of Tc = 18 K. Below the ferromagnetic transition temperature, we observed the magnon gap formation of 4.3 ~ 4.4 meV by ρ(T) and Cp(T) measurements. The charge density wave is attributed to the increase of Seebeck coefficient resulting in the increase of power factor S2 σ . The thermoelectric figure-of-merit ZT significantly increases due to the increase of power factor at TCDW = 157 K. Here we argue that the competing interaction between electron-phonon and electron-magnon couplings exhibits the unconventional behavior of electrical and thermal properties. This research was supported by Basic Science Research Program (2011-0021335), Nano-Material Technology Development Program (2011-0030147), and Mid-career Research Program (Strategy) (No. 2012R1A2A1A03005174) through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology.
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.
Thermal properties of 1T-TaS 2 at the onset of charge density wave states
NASA Astrophysics Data System (ADS)
Balaguru Rayappan, John Bosco; Raj, S. Alfred Cecil; Lawrence, N.
2010-08-01
The crystal lattice plays an essential role in the charge density wave (CDW) phase transition together with the electron system through electron-phonon interactions. The CDW in the layered compound 1T-TaS 2 at low temperatures has a commensurate phase, which causes superlattice points to appear in the Brillouin zone of the undistorted phase. Since the effect of CDWs is to directly modulate the lattice, it is evident that an investigation that looks directly at the phonon frequencies would be most instructive in examining this phenomenon. Hence the Born-von Karman formalism, in which the equilibrium conditions are fulfilled, has been employed for the calculation of phonon frequency distribution curves of 1T-TaS 2 both in the normal and in the commensurate charge density wave (CCDW) phases. A folding technique has been adopted for the calculation in the CCDW phase. The phonon distribution and some dominant phonon frequencies for both the phases have been reported. With these results the thermal properties such as specific heat capacity, Debye Waller factor and thermal conductivity have been worked out, and are compared with the available experimental results.
Local Structure and Vibrational Properties of alpha-Pu, alpha-U, and the alpha-U Charge Density Wave
Nelson, E J; Allen, P G; Blobaum, K M; Wall, M A; Booth, C H
2004-08-10
The local atomic environment and vibrational properties of atoms in monoclinic pure {alpha}-plutonium as well as orthorhombic pure {alpha}-uranium and its low-temperature charge-density-wave (CDW) modulation are examined by extended x-ray absorption fine structure spectroscopy (EXAFS). Pu L{sub III}-edge and U L{sub III}-edge EXAFS data measured at low temperatures verify the crystal structures of {alpha}-U and {alpha}-Pu samples previously determined by x-ray diffraction and neutron scattering. Debye-Waller factors from temperature-dependent EXAFS measurements are fit with a correlated Debye model. The observed Pu-Pu bond correlated Debye temperature of {theta}{sub cD}({alpha}-Pu) = 162 {+-} 5 K for the pure {alpha}-Pu phase agrees with our previous measurement of the correlated Debye temperature of the gallium-containing {alpha}'-Pu phase in a mixed phase 1.9 at% Ga-doped {alpha}'-Pu/{delta}-Pu alloy. The temperature dependence of the U-U nearest neighbor Debye-Waller factor exhibits a sharp discontinuity in slope near T{sub CDW} = 43 K, the transition temperature at which the charge-density wave (CDW) in {alpha}-U condenses from a soft phonon mode along the (100) direction. Our measurement of the CDW using EXAFS is the first observation of the structure of the CDW in polycrystalline {alpha}-U. The different temperature dependence of the Debye-Waller factor for T < T{sub CDW} can be modeled by the change in bond length distributions resulting from condensation of the charge density wave. For T > T{sub CDW}, the observed correlated Debye temperature of {theta}{sub cD}({alpha}-U) = 199 {+-} 3 K is in good agreement with other measurements of the Debye temperature for polycrystalline {alpha}-U. CDW structural models fit to the {alpha}-U EXAFS data support a squared CDW at the lowest temperatures, with a displacement amplitude of {var_epsilon} = 0.05 {+-} 0.02 {angstrom}.
Local structure and vibrational properties of alpha-Pu, alpha-Uand the alpha-U charge density wave
Nelson, E.J.; Allen, P.G.; Blobaum, K.J.M.; Wall, W.A.; Booth, C.H.
2004-08-10
The local atomic environment and vibrational properties of atoms in monoclinic pure {alpha}-plutonium as well as orthorhombic pure a-uranium and its low-temperature charge-density-wave (CDW) modulation are examined by extended x-ray absorption fine structure spectroscopy (EXAFS). Pu L{sub III}-edge and U L{sub III}-edge EXAFS data measured at low temperatures verify the crystal structures of {alpha}-U and {alpha}-Pu samples previously determined by x-ray diffraction and neutron scattering. Debye-Waller factors from temperature-dependent EXAFS measurements are fit with a correlated Debye model. The observed Pu-Pu bond correlated Debye temperature of {theta}{sub cD}({alpha}-Pu) = 162 {+-} 5 K for the pure {alpha}-Pu phase agrees with our previous measurement of the correlated Debye temperature of the gallium-containing {alpha}{prime}-Pu phase in a mixed phase 1.9 at% Ga-doped {alpha}{prime}-Pu/{delta}-Pu alloy. The temperature dependence of the U-U nearest neighbor Debye-Waller factor exhibits a sharp discontinuity in slope near T{sub CDW} = 43 K, the transition temperature at which the charge-density wave (CDW) in {alpha}-U condenses from a soft phonon mode along the (100) direction. Our measurement of the CDW using EXAFS is the first observation of the structure of the CDW in polycrystalline {alpha}-U. The different temperature dependence of the Debye-Waller factor for T < T{sub CDW} can be modeled by the change in bond length distributions resulting from condensation of the charge density wave. For T > T{sub CDW}, the observed correlated Debye temperature of {theta}{sub cD}({alpha}-U) = 199 {+-} 3 K is in good agreement with other measurements of the Debye temperature for polycrystalline {alpha}-U. CDW structural models fit to the {alpha}-U EXAFS data support a squared CDW at the lowest temperatures, with a displacement amplitude of {var_epsilon} = 0.05 {+-} 0.02 {angstrom}.
Hellen, Adam; Matvienko, Anna; Mandelis, Andreas; Finer, Yoav; Amaechi, Bennett T
2010-12-20
Noninvasive dental diagnostics is a growing discipline since it has been established that early detection and quantification of tooth mineral loss can reverse caries lesions in their incipient state. A theoretical coupled diffuse photon density and thermal-wave model was developed and applied to photothermal radiometric frequency responses, fitted to experimental data using a multiparameter simplex downhill minimization algorithm for the extraction of optothermophysical properties from artificially demineralized human enamel. The aim of this study was to evaluate the reliability and robustness of the advanced fitting algorithm. The results showed a select group of optical and thermal transport parameters and thicknesses were reliably extracted from the computational fitting algorithm. Theoretically derived thicknesses were accurately predicted, within about 20% error, while the estimated error in the optical and thermal property evaluation was within the values determined from early studies using destructive analyses. The high fidelity of the theoretical model illustrates its efficacy, reliability, and applicability toward the nondestructive characterization of depthwise inhomogeneous sound enamel and complex enamel caries lesions. PMID:21173829
Pressure dependence of the optical properties of the charge-density-wave compound LaTe2
Lavagnini, M.; Sacchetti, A.; Degiorgi, L.; Arcangeletti, E.; Baldassarre, L.; Postorino, P.; Lupi, S.; Perucchi, A.; Shin, K.Y.; Fisher, I.R.; /Stanford U., Geballe Lab.
2009-12-14
We report the pressure dependence of the optical response of LaTe{sub 2}, which is deep in the charge-density-wave (CDW) ground state even at 300 K. The reflectivity spectrum is collected in the mid-infrared spectral range at room temperature and at pressures between 0 and 7 GPa. We extract the energy scale due to the single particle excitation across the CDW gap and the Drude weight. We establish that the gap decreases upon compressing the lattice, while the Drude weight increases. This signals a reduction in the quality of nesting upon applying pressure, therefore inducing a lesser impact of the CDW condensate on the electronic properties of LaTe{sub 2}. The consequent suppression of the CDW gap leads to a release of additional charge carriers, manifested by the shift of weight from the gap feature into the metallic component of the optical response. On the contrary, the power-law behavior, seen in the optical conductivity at energies above the gap excitation and indicating a weakly interacting limit within the Tomonaga-Luttinger liquid scenario, seems to be only moderately dependent on pressure.
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.
Optical Properties of the Charge-Density-Wave Polychalcogenide Compounds R2Te5 (R=Nd, Sm and Gd)
Pfuner, F.; Degiorgi, L.; Shin, K.Y.; Fisher, I.R.; /Stanford U., Geballe Lab.
2010-02-15
We investigate the rare-earth polychalcogenide R{sub 2}Te{sub 5} (R = Nd, Sm and Gd) charge-density-wave (CDW) compounds by optical methods. From the absorption spectrum we extract the excitation energy of the CDW gap and estimate the fraction of the Fermi surface which is gapped by the formation of the CDW condensate. In analogy to previous findings on the related RTe{sub n} (n = 2 and 3) families, we establish the progressive closing of the CDW gap and the moderate enhancement of the metallic component upon chemically compressing the lattice.
Chiral density wave in nuclear matter
NASA Astrophysics Data System (ADS)
Heinz, Achim; Giacosa, Francesco; Rischke, Dirk H.
2015-01-01
Inspired by recent work on inhomogeneous chiral condensation in cold, dense quark matter within models featuring quark degrees of freedom, we investigate the chiral density-wave solution in nuclear matter at zero temperature and nonvanishing baryon number density in the framework of the so-called extended linear sigma model (eLSM). The eLSM is an effective model for the strong interaction based on the global chiral symmetry of quantum chromodynamics (QCD). It contains scalar, pseudoscalar, vector, and axial-vector mesons as well as baryons. In the latter sector, the nucleon and its chiral partner are introduced as parity doublets in the mirror assignment. The eLSM simultaneously provides a good description of hadrons in vacuum as well as nuclear matter ground-state properties. We find that an inhomogeneous phase in the form of a chiral density wave is realized, but only for densities larger than 2.4ρ0, where ρ0 is the nuclear matter ground-state density.
Investigation of microalgae with photon density waves
NASA Astrophysics Data System (ADS)
Frankovitch, Christine; Reich, Oliver; Löhmannsröben, Hans-Gerd
2007-09-01
Phototropic microalgae have a large potential for producing valuable substances for the feed, food, cosmetics, pigment, bioremediation, and pharmacy industries as well as for biotechnological processes. Today it is estimated that the microalgal aquaculture worldwide production is 5000 tons of dry matter per year (not taking into account processed products) making it an approximately $1.25 billion U.S. per year industry. For effective observation of the photosynthetic growth processes, fast on-line sensor systems that analyze the relevant biological and technical process parameters are preferred. The optical properties of the microalgae culture influence the transport of light in the photobioreactor and can be used to extract relevant information for efficient cultivation practices. Microalgae cultivation media show a combination of light absorption and scattering, which are influenced by the concentrations and the physical and chemical properties of the different absorbing and scattering species (e.g. pigments, cell components, etc.). Investigations with frequency domain photon density waves (PDW) allow for the examination of absorption and scattering properties of turbid media, namely the absorption and reduced scattering coefficient. The reduced scattering coefficient can be used to characterize physical and morphological properties of the medium, including the cell concentration, whereas the absorption coefficient correlates with the pigment content. Nannochloropsis oculata, a single-cell species of microalgae, were examined in a nutrient solution with photon density waves. The absorption and reduced scattering coefficients were experimentally determined throughout the cultivation process, and applied to gain information about the cell concentration and average cell radius.
Unexpected properties of a density functional
Karwowski, J.; Stanke, M.
2005-02-01
An observation on a pathological behavior of an exact density functional derived from either relativistic (Dirac) or nonrelativistic (Levy-Leblond) quantum-mechanical equation is reported. As expected, in the case of a one-electron atom the variational minimum of this functional is equal to the exact ground-state energy. However, apart from the correct density, this minimum is reached also by an infinite set of densities which do not correspond to the exact wave function. This paradoxical property of the functional is related to the multicomponent structure of both Dirac and Levy-Leblond wave functions. In particular, imposing the correct boundary conditions upon the trial densities removes only a part of the fake solutions. The results of this study demonstrate that in density-functional theories derived from models based on multicomponent wave functions, one should not expect any simple relation between the accuracy of the energy and the correctness of the corresponding density.
Hussain, Zahid; Brouet, Veronique; Yang, Wanli; Zhou, Xingjiang; Hussain, Zahid; Moore, R.G.; He, R.; Lu, D. H.; Shen, Z.X.; Laverock, J.; Dugdale, S.B.; Ru, N.; Fisher, R.
2008-01-16
We present a detailed angle-resolved photoemission spectroscopy (ARPES) investigation of the RTe3 family, which sets this system as an ideal"textbook" example for the formation of a nesting driven charge density wave (CDW). This family indeed exhibits the full range of phenomena that can be associated to CDWinstabilities, from the opening of large gaps on the best nested parts of Fermi surface (up to 0.4 eV), to the existence of residual metallic pockets. ARPES is the best suited technique to characterize these features, thanks to its unique ability to resolve the electronic structure in k space. An additional advantage of RTe3 is that theband structure can be very accurately described by a simple two dimensional tight-binding (TB) model, which allows one to understand and easily reproduce many characteristics of the CDW. In this paper, we first establish the main features of the electronic structure by comparing our ARPES measurements with the linear muffin-tinorbital band calculations. We use this to define the validity and limits of the TB model. We then present a complete description of the CDW properties and of their strong evolution as a function of R. Using simple models, we are able to reproduce perfectly the evolution of gaps in k space, the evolution of the CDW wave vector with R, and the shape of the residual metallic pockets. Finally, we give an estimation of the CDWinteraction parameters and find that the change in the electronic density of states n (EF), due to lattice expansion when different R ions are inserted, has the correct order of magnitude to explain the evolution of the CDW properties.
Brouet, V.; Yang, W.L.; Zhou, X.J.; Hussain, Z.; Moore, R.G.; He, R.; Lu, D.H.; Shen, Z.X.; Laverock, J.; Dugdale, S.; Ru, N.; Fisher, I.R.
2010-02-15
We present a detailed ARPES investigation of the RTe{sub 3} family, which sets this system as an ideal 'textbook' example for the formation of a nesting driven Charge Density Wave (CDW). This family indeed exhibits the full range of phenomena that can be associated to CDW instabilities, from the opening of large gaps on the best nested parts of Fermi Surface (FS) (up to 0.4eV), to the existence of residual metallic pockets. ARPES is the best suited technique to characterize these features, thanks to its unique ability to resolve the electronic structure in k-space. An additional advantage of RTe{sub 3} is that the band structure can be very accurately described by a simple 2D tight-binding (TB) model, which allows one to understand and easily reproduce many characteristics of the CDW. In this paper, we first establish the main features of the electronic structure, by comparing our ARPES measurements with Linear Muffin-Tin Orbital band calculations. We use this to define the validity and limits of the TB model. We then present a complete description of the CDW properties and, for the first time, of their strong evolution as a function of R. Using simple models, we are able to reproduce perfectly the evolution of gaps in k-space, the evolution of the CDW wave vector with R and the shape of the residual metallic pockets. Finally, we give an estimation of the CDW interaction parameters and find that the change in the electronic density of states n(Ef), due to lattice expansion when different R ions are inserted, has the correct order of magnitude to explain the evolution of the CDW properties.
Lower hybrid wave phenomena associated with density depletions
NASA Technical Reports Server (NTRS)
Seyler, C. E.
1994-01-01
A fluid description of lower hybrid, whistler and magnetosonic waves is applied to study wave phenomena near the lower hybrid resonance associated with plasma density depletions. The goal is to understand the nature of lower hybrid cavitons and spikelets often associated with transverse ion acceleration events in the auroral ionosphere. Three-dimensional simulations show the ponderomotive force leads to the formation of a density cavity (caviton) in which lower hybrid wave energy is concentrated (spikelet) resulting in a three-dimensional collapse of the configuration. Plasma density depletions of the order of a few percent are shown to greatly modify the homogeneous linear properties of lower hybrid waves and account for many of the observed features of lower hybrid spikelets.
Density Shock Waves in Confined Microswimmers
NASA Astrophysics Data System (ADS)
Tsang, Alan Cheng Hou; Kanso, Eva
2016-01-01
Motile and driven particles confined in microfluidic channels exhibit interesting emergent behavior, from propagating density bands to density shock waves. A deeper understanding of the physical mechanisms responsible for these emergent structures is relevant to a number of physical and biomedical applications. Here, we study the formation of density shock waves in the context of an idealized model of microswimmers confined in a narrow channel and subject to a uniform external flow. Interestingly, these density shock waves exhibit a transition from "subsonic" with compression at the back to "supersonic" with compression at the front of the population as the intensity of the external flow increases. This behavior is the result of a nontrivial interplay between hydrodynamic interactions and geometric confinement, and it is confirmed by a novel quasilinear wave model that properly captures the dependence of the shock formation on the external flow. These findings can be used to guide the development of novel mechanisms for controlling the emergent density distribution and the average population speed, with potentially profound implications on various processes in industry and biotechnology, such as the transport and sorting of cells in flow channels.
Density Shock Waves in Confined Microswimmers.
Tsang, Alan Cheng Hou; Kanso, Eva
2016-01-29
Motile and driven particles confined in microfluidic channels exhibit interesting emergent behavior, from propagating density bands to density shock waves. A deeper understanding of the physical mechanisms responsible for these emergent structures is relevant to a number of physical and biomedical applications. Here, we study the formation of density shock waves in the context of an idealized model of microswimmers confined in a narrow channel and subject to a uniform external flow. Interestingly, these density shock waves exhibit a transition from "subsonic" with compression at the back to "supersonic" with compression at the front of the population as the intensity of the external flow increases. This behavior is the result of a nontrivial interplay between hydrodynamic interactions and geometric confinement, and it is confirmed by a novel quasilinear wave model that properly captures the dependence of the shock formation on the external flow. These findings can be used to guide the development of novel mechanisms for controlling the emergent density distribution and the average population speed, with potentially profound implications on various processes in industry and biotechnology, such as the transport and sorting of cells in flow channels. PMID:26871357
Oblique interactions of dust density waves
Li Yangfang; Wang Zhehui; Hou Lujing; Jiang Ke; Thomas, Hubertus M.; Morfill, Gregor E.; Wu Dejin
2010-06-16
Self-excited dust density waves (DDWs) are studied in a striped electrode device. In addition to the usual perpendicularly (with respect to the electrode) propagating DDWs, which have been frequently observed in dusty plasma experiments on the ground, a low-frequency oblique mode is also observed. This low-frequency oblique DDW has a frequency much lower than the dust plasma frequency and its spontaneous excitation is observed even with a very low dust density. It is found that the low-frequency oblique mode can exist either separately or together with the usual perpendicular mode. In the latter case, a new mode arises as a result of the interactions between the perpendicular and the oblique modes. The experiments show that these three modes satisfy the wave coupling conditions in both the frequencies and the wave-vectors.
Oblique interactions of dust density waves
Wang, Zhelchui; Li, Yang - Fang; Hou, Lujing; Jiang, Ke; Wu, De - Jin; Thomas, Hubertus M; Morfill, Gregor E
2010-01-01
Self-excited dust density waves (DDWs) are studied in a striped electrode device. In addition to the usual perpendicularly (with respect to the electrode) propagating DDWs, which have been frequently observed in dusty plasma experiments on the ground, a low-frequency oblique mode is also observed. This low-frequency oblique DDW has a frequency much lower than the dust plasma frequency and its spontaneous excitation is observed even with a very low dust density. It is found that the low-frequency oblique mode can exist either separately or together with the usual perpendicular mode. In the latter case, a new mode arises as a result of the interactions between the perpendicular and the oblique modes. The experiments show that these three modes satisfy the wave coupling conditions in both the frequencies and the wave-vectors.
Obliquely propagating dust-density waves
NASA Astrophysics Data System (ADS)
Piel, A.; Arp, O.; Klindworth, M.; Melzer, A.
2008-02-01
Self-excited dust-density waves are experimentally studied in a dusty plasma under microgravity. Two types of waves are observed: a mode inside the dust volume propagating in the direction of the ion flow and another mode propagating obliquely at the boundary between the dusty plasma and the space charge sheath. The dominance of oblique modes can be described in the frame of a fluid model. It is shown that the results fom the fluid model agree remarkably well with a kinetic electrostatic model of Rosenberg [J. Vac. Sci. Technol. A 14, 631 (1996)]. In the experiment, the instability is quenched by increasing the gas pressure or decreasing the dust density. The critical pressure and dust density are well described by the models.
Density waves in the Calogero model - revisited
Bardek, V. Feinberg, J. Meljanac, S.
2010-03-15
The Calogero model bears, in the continuum limit, collective excitations in the form of density waves and solitary modulations of the density of particles. This sector of the spectrum of the model was investigated, mostly within the framework of collective-field theory, by several authors, over the past 15 years or so. In this work we shall concentrate on periodic solutions of the collective BPS-equation (also known as 'finite amplitude density waves'), as well as on periodic solutions of the full static variational equations which vanish periodically (also known as 'large amplitude density waves'). While these solutions are not new, we feel that our analysis and presentation add to the existing literature, as we explain in the text. In addition, we show that these solutions also occur in a certain two-family generalization of the Calogero model, at special points in parameter space. A compendium of useful identities associated with Hilbert transforms, including our own proofs of these identities, appears in Appendix A. In Appendix B we also elucidate in the present paper some fine points having to do with manipulating Hilbert-transforms, which appear ubiquitously in the collective field formalism. Finally, in order to make this paper self-contained, we briefly summarize in Appendix C basic facts about the collective field formulation of the Calogero model.
Interplay of pair density wave and charge density wave order in the cuprate pseudogap phase
NASA Astrophysics Data System (ADS)
Agterberg, Daniel; Amin, Adil
Recent x-ray measurements in the cuprate YBCO suggest that the charge density wave (CDW) order seen at high-field has a different c-axis structure than that seen at zero-field and further suggests that CDW order breaks the c-axis mirror plane symmetry of the CuO2 layers. We examine pair density wave order that induces CDW order consistent with these observations.
Ru, N.; Chu, J.-H.; Fisher, I.R.; /Stanford U., Geballe Lab.
2009-12-14
The antiferromagnetic transition is investigated in the rare-earth (R) tritelluride RTe{sub 3} family of charge density wave (CDW) compounds via specific heat, magnetization and resistivity measurements. Observation of the opening of a superzone gap in the resistivity of DyTe{sub 3} indicates that additional nesting of the reconstructed Fermi surface in the CDW state plays an important role in determining the magnetic structure.
Excitation of turbulence by density waves
NASA Technical Reports Server (NTRS)
Tichen, C. M.
1985-01-01
A nonlinear system describes the microdynamical state of turbulence that is excited by density waves. It consists of an equation of propagation and a master equation. A group-scaling generates the scaled equations of many interacting groups of distribution functions. The two leading groups govern the transport processes of evolution and eddy diffusivity. The remaining sub-groups represent the relaxation for the approach of diffusivity to equilibrium. In strong turbulence, the sub-groups disperse themselves and the ensemble acts like a medium that offers an effective damping to close the hierarchy. The kinetic equation of turbulence is derived. It calculates the eddy viscosity and identifies the effective damping of the assumed medium self-consistently. It formulates the coupling mechanism for the intensification of the turbulent energy at the expense of the wave energy, and the transfer mechanism for the cascade. The spectra of velocity and density fluctuations find the power law k sup-2 and k sup-4, respectively.
Correlated quantum transport of density wave electrons.
Miller, J H; Wijesinghe, A I; Tang, Z; Guloy, A M
2012-01-20
Recently observed Aharonov-Bohm quantum interference of the period h/2e in charge density wave rings strongly suggests that correlated density wave electron transport is a cooperative quantum phenomenon. The picture discussed here posits that quantum solitons nucleate and transport current above a Coulomb blockade threshold field. We propose a field-dependent tunneling matrix element and use the Schrödinger equation, viewed as an emergent classical equation as in Feynman's treatment of Josephson tunneling, to compute the evolving macrostate amplitudes, finding excellent quantitative agreement with voltage oscillations and current-voltage characteristics in NbSe(3). A proposed phase diagram shows the conditions favoring soliton nucleation versus classical depinning. PMID:22400766
Cassini Radio Science Observations of Density Waves in Saturn's Rings
NASA Astrophysics Data System (ADS)
McGhee, C. A.; French, R. G.; Rappaport, N. J.; Marouf, E. A.; Dawson, R.; Stack, K.
2006-08-01
Saturn's ring system is an elegant celestial mechanical laboratory for studying the interactions between a host of small and large moons, and the rings themselves. Resonances between the satellites and the ring particles result in spiral density waves whose detailed characteristics can be used to determine the physical properties of the rings. Over the past year, the Cassini Radio Science Team has obtained nearly a dozen exquisite radial profiles of the structure of Saturn's rings from occultations at three radio wavelengths (0.9 cm, 3 cm, and 12 cm), at sub-km resolution, after correction for the effects of diffraction. The optical depth profiles of the rings are replete with density waves produced by Mimas, Janus, Epimetheus, Prometheus, Pandora, and even smaller moons. Using wavelet decomposition as well as direct model fitting, we have determined the surface mass density and viscosity of the ring particles from weak (linear) density waves, primarily in the A ring. These are essential ingredients for dynamical models of the rings that include the effects of self-gravity and inelastic particle collisions. Future radio science occultation experiments throughout the Cassini orbital tour of Saturn will probe the rings at a range of ring opening angles, providing both additional measurements of density waves and other ring features.
Transport and Structure of Charge Density Waves
NASA Astrophysics Data System (ADS)
Dicarlo, David Anthony
Experimental studies are presented concerning the transport properties and structure of charge-density waves (CDWs) in rm NbSe_3 and rm K_{0.3}MoO_3. Transport measurements were performed to determine how charged impurities affect the CDW and how the narrow -band noise is created in sliding CDWs. Ti-doped rm NbSe_3 is shown to have a weakly pinned CDW even though Ti is incorporated as a charged impurity. The narrow-band-noise amplitude versus sample volume and impurity concentration is consistent with the narrow-band-noise being generated in the bulk by impurities and a weakly pinned CDW. X-ray scattering measurements were performed to determine how impurities, temperature, normal carriers, and electric fields affect the CDW structure. The periodic CDW scatters x-rays and the sharpness of the scattering is a reflection of the CDW structure. The CDW correlation function and its characteristic length are determined through the competition between the disordering impurity forces and the ordering elastic forces. Added impurities and high temperatures decrease the correlations by increasing the disorder forces and decreasing the CDW order parameter Delta , respectively. For rm NbSe_3, the correlation length l was much greater than the average impurity spacing and depends on impurity density n _{i} and temperature as l ~ Delta^2/n_{i}. In addition, the CDW correlation function decays exponentially in real space;
Solar-Driven Neutral Density Waves
NASA Technical Reports Server (NTRS)
Blum, P.; Gangopadhyay, P.; Ogawa, H. S.; Judge, D. L.
1993-01-01
Interstellar neutral hydrogen atoms flowing into the solar system are attracted by the solar gravitational force, repelled by solar hydrogen Ly-alpha radiation pressure, and are ionized, primarily, through charge exchange with the solar wind protons. The solar cycle variation of the radiation pressure causes the net central solar force to fluctuate between attraction and repulsion resulting in the modulation of the neutral hydrogen density about the usual time independent model. The calculation presented here shows that the time dependent downstream density is strongly modulated by a large number of travelling neutral density waves. The waves possess a continuous range of wavelengths as is to be expected for a Maxwellian gas subjected to several eleven year cycle variations during its journey through the solar system. The amplitudes of the density modulation were found to be quite large. The backscattered glow was found to depend on the position of the detector and the phase of the solar cycle. At the most favorable condition a deviation of the order of 25% from the time dependent glow might be observed.
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.
Complex density of a suspension in an oscillatiory wave process
NASA Astrophysics Data System (ADS)
Fedotovskii, V. S.; Orlov, A. I.; Lunina, S. V.; Pil'shchikova, E. A.
2014-03-01
The effective viscous inertia properties exhibited by suspensions in the presence of oscillatory wave processes are considered. A cell model of a concentrated suspension is used to derive the dependence for the complex density, whose real and imaginary parts characterize the effective inertia and the bulk viscous resistance to oscillatory motion, respectively. From hydrodynamic models of low-frequency and high-frequency translatory oscillations of spherical inclusions in the host liquid, estimates are obtained for the internal dynamic parameters of the suspension, namely, the apparent mass factor and the inclusion relaxation time, which specify the general formulas for the complex density.
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
Sati, Priti; Tripathi, V. K.
2012-12-15
Parametric decay of a large amplitude electromagnetic wave into two electromagnetic modes in a rippled density plasma channel is investigated. The channel is taken to possess step density profile besides a density ripple of axial wave vector. The density ripple accounts for the momentum mismatch between the interacting waves and facilitates nonlinear coupling. For a given pump wave frequency, the requisite ripple wave number varies only a little w.r.t. the frequency of the low frequency decay wave. The radial localization of electromagnetic wave reduces the growth rate of the parametric instability. The growth rate decreases with the frequency of low frequency electromagnetic wave.
Effects of unequal particle number densities on Alfven waves
NASA Technical Reports Server (NTRS)
Cairns, I. H.
1989-01-01
Analytic plasma theory and numerical solutions of the dispersion equation are used to show that the assumption that the linear properties of the waves are determined by a charge-neutral plasma in the absence of the nonthermal particles, while the nonthermal particles cause growth or additional damping superposed onto the background, is seriously flawed even for stable plasmas. Even when the nonthermal particles do not contribute significantly to the dispersion equation, unequal thermal electron and ion number densities (due to the presence of the nonthermal particles) may cause fundamental low wave number modifications to the Alfven modes, including the creation of a new resonance and severely modified dispersion. These results are found for both cold and warm plasmas. Previous work on Alfven waves should be reevaluated in view of these results.
Transportation of pinned charge density waves
NASA Astrophysics Data System (ADS)
Koo, Je Huan; Jeong, Jae Yoon; Cho, Guangsup
2009-01-01
We investigated the transport of pinned charge density waves (CDWs) that is observed in low dimensional materials. We treated pinned CDWs as moving CDWs that were confined within a typical quantum well amongst the many different types where pinning occurs at the barrier. We calculated the current flowing out of the quantum well by confined CDWs. The calculated conductivity is in good correspondence with experimental data in TTF-TCNQ, where the measured Fröhlich-Peierls temperature is 60 K much higher than the theoretical value of 20 K. The voltage dependence of the conductivity was calculated, where this is easily transformed into the dependence of electric field. The magnetic susceptibility was also calculated with a similar trend of experimental data. The susceptibility is a diamagnetic contribution by CDWs in addition to the constant background Pauli paramagnetic part.
Diffuse Waves and Energy Densities Near Boundaries
NASA Astrophysics Data System (ADS)
Sanchez-Sesma, F. J.; Rodriguez-Castellanos, A.; Campillo, M.; Perton, M.; Luzon, F.; Perez-Ruiz, J. A.
2007-12-01
Green function can be retrieved from averaging cross correlations of motions within a diffuse field. In fact, it has been shown that for an elastic inhomogeneous, anisotropic medium under equipartitioned, isotropic illumination, the average cross correlations are proportional to the imaginary part of Green function. For instance coda waves are due to multiple scattering and their intensities follow diffusive regimes. Coda waves and the noise sample the medium and effectively carry information along their paths. In this work we explore the consequences of assuming both source and receiver at the same point. From the observable side, the autocorrelation is proportional to the energy density at a given point. On the other hand, the imaginary part of the Green function at the source itself is finite because the singularity of Green function is restricted to the real part. The energy density at a point is proportional with the trace of the imaginary part of Green function tensor at the source itself. The Green function availability may allow establishing the theoretical energy density of a seismic diffuse field generated by a background equipartitioned excitation. We study an elastic layer with free surface and overlaying a half space and compute the imaginary part of the Green function for various depths. We show that the resulting spectrum is indeed closely related to the layer dynamic response and the corresponding resonant frequencies are revealed. One implication of present findings lies in the fact that spatial variations may be useful in detecting the presence of a target by its signature in the distribution of diffuse energy. These results may be useful in assessing the seismic response of a given site if strong ground motions are scarce. It suffices having a reasonable illumination from micro earthquakes and noise. We consider that the imaginary part of Green function at the source is a spectral signature of the site. The relative importance of the peaks of
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.; 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 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
Ducted kinetic Alfven waves in plasma with steep density gradients
Houshmandyar, Saeid; Scime, Earl E.
2011-11-15
Given their high plasma density (n {approx} 10{sup 13} cm{sup -3}), it is theoretically possible to excite Alfven waves in a conventional, moderate length (L {approx} 2 m) helicon plasma source. However, helicon plasmas are decidedly inhomogeneous, having a steep radial density gradient, and typically have a significant background neutral pressure. The inhomogeneity introduces regions of kinetic and inertial Alfven wave propagation. Ion-neutral and electron-neutral collisions alter the Alfven wave dispersion characteristics. Here, we present the measurements of propagating kinetic Alfven waves in helium helicon plasma. The measured wave dispersion is well fit with a kinetic model that includes the effects of ion-neutral damping and that assumes the high density plasma core defines the radial extent of the wave propagation region. The measured wave amplitude versus plasma radius is consistent with the pile up of wave magnetic energy at the boundary between the kinetic and inertial regime regions.
Red density perturbations and inflationary gravitational waves
Pagano, Luca; Melchiorri, Alessandro; Cooray, Asantha; Kamionkowski, Marc E-mail: acooray@uci.edu E-mail: kamion@tapir.caltech.edu
2008-04-15
We study the implications of recent indications from the Wilkinson Microwave Anisotropy Probe (WMAP) and other cosmological data for a red spectrum of primordial density perturbations for the detection of inflationary gravitational waves (IGWs) with forthcoming cosmic microwave background experiments. We consider a variety of single-field power-law, chaotic, spontaneous symmetry-breaking and Coleman-Weinberg inflationary potentials which are expected to provide a sizable tensor component and quantify the expected tensor-to-scalar ratio given existing constraints from WMAP on the tensor-to-scalar ratio and the power spectrum tilt. We discuss the ability of the near-future Planck satellite to detect the IGW background in the framework of those models. We find that the proposed satellite missions of the Cosmic Vision and Inflation Probe programs will be able to detect IGWs from all the models we have surveyed at better than 5{sigma} confidence level. We also provide an example of what is required if the IGW background is to remain undetected even by these latter experiments.
STANDING WAVE PROBES FOR DIMENSIONAL METROLOGY OF LOW DENSITY FOAMS
Seugling, R M; Woody, S C; Bauza, M B
2010-03-23
Typically, parts and geometries of interest to LLNL are made from a combination of complex geometries and a wide array of different materials ranging from metals and ceramics to low density foams and plastic foils. These parts are combined to develop physics experiments for studying material properties, equation of state (EOS) and radiation transport. Understanding the dimensional uncertainty of the parts contained within an experiment is critical to the physical understanding of the phenomena being observed and represents the motivation for developing probe metrology capability that can address LLNL's unique problems. Standing wave probes were developed for measuring high aspect ratio, micrometer scaled features with nanometer resolution. Originally conceived of for the use in the automotive industry for characterizing fuel injector bores and similar geometries, this concept was investigated and improved for use on geometries and materials important to LLNL needs within target fabrication. As part of the original project, detailed understanding of the probe dynamics and interactions with the surface of the sample was investigated. In addition, the upgraded system was utilized for measuring fuel injector bores and micro-lenses as a means of demonstrating capability. This report discusses the use of the standing wave probe for measuring features in low density foams, 55 mg/cc SiO{sub 2} and 982 mg/cc (%6 relative density) copper foam respectively. These two foam materials represent a difficult metrology challenge because of their material properties and surface topography. Traditional non-contact metrology systems such as normal incident interferometry and/or confocal microscopy have difficulty obtaining a signal from the relatively absorptive characteristics of these materials. In addition to the foam samples, a solid copper and plastic (Rexolite{trademark}) sample of similar geometry was measured with the standing wave probe as a reference for both conductive and
Modelling of Resonantly Forced Density Waves in Dense Planetary Rings
NASA Astrophysics Data System (ADS)
Lehmann, M.; Schmidt, J.; Salo, H.
2014-04-01
Density wave theory, originally proposed to explain the spiral structure of galactic disks, has been applied to explain parts of the complex sub-structure in Saturn's rings, such as the wavetrains excited at the inner Lindblad resonances (ILR) of various satellites. The linear theory for the excitation and damping of density waves in Saturn's rings is fairly well developed (e.g. Goldreich & Tremaine [1979]; Shu [1984]). However, it fails to describe certain aspects of the observed waves. The non-applicability of the linear theory is already indicated by the "cusplike" shape of many of the observed wave profiles. This is a typical nonlinear feature which is also present in overstability wavetrains (Schmidt & Salo [2003]; Latter & Ogilvie [2010]). In particular, it turns out that the detailed damping mechanism, as well as the role of different nonlinear effects on the propagation of density waves remain intransparent. First attemps are being made to investigate the excitation and propagation of nonlinear density waves within a hydrodynamical formalism, which is also the natural formalism for describing linear density waves. A simple weakly nonlinear model, derived from a multiple-scale expansion of the hydrodynamic equations, is presented. This model describes the damping of "free" spiral density waves in a vertically integrated fluid disk with density dependent transport coefficients, where the effects of the hydrodynamic nonlinearities are included. The model predicts that density waves are linearly unstable in a ring region where the conditions for viscous overstability are met, which translates to a steep dependence of the shear viscosity with respect to the disk's surface density. The possibility that this dependence could lead to a growth of density waves with increasing distance from the resonance, was already mentioned in Goldreich & Tremaine [1978]. Sufficiently far away from the ILR, the surface density perturbation caused by the wave, is predicted to
Density gradient effects on transverse shear driven lower hybrid waves
DuBois, Ami M.; Thomas, Edward; Amatucci, William E.; Ganguli, Gurudas
2014-06-15
Shear driven instabilities are commonly observed in the near-Earth space, particularly in boundary layer plasmas. When the shear scale length (L{sub E}) is much less than the ion gyro-radius (ρ{sub i}) but greater than the electron gyro-radius (ρ{sub e}), the electrons are magnetized in the shear layer, but the ions are effectively un-magnetized. The resulting shear driven instability, the electron-ion hybrid (EIH) instability, is investigated in a new interpenetrating plasma configuration in the Auburn Linear EXperiment for Instability Studies. In order to understand the dynamics of magnetospheric boundary layers, the EIH instability is studied in the presence of a density gradient located at the boundary layer between two plasmas. This paper reports on a recent experiment in which electrostatic lower hybrid waves are identified as the EIH instability, and the effect of a density gradient on the instability properties are investigated.
Density waves in a system of non-interacting particles
NASA Astrophysics Data System (ADS)
Kolmes, E. J.; Geyko, V. I.; Fisch, N. J.
2016-09-01
An ensemble of non-interacting bouncing balls being acted on by a constant gravitational force, starting at rest from a uniform density distribution, will develop a structure of sharply peaked density waves. We describe these waves by computing the density profile of such a system analytically, and we find that the analytical results are in good agreement with numerical findings. We suggest that in a real system, these density waves could be used to produce measurements of the strength of a gravitational field.
NASA Astrophysics Data System (ADS)
Matveev, Oleg; Shvaika, Andrij; Devereaux, Thomas; Freericks, James
The charge-density-wave phase of the Falicov-Kimball model displays a number of anomalous behavior including the appearance of subgap density of states as the temperature increases. These subgap states should have a significant impact on transport properties, particularly the nonlinear response of the system to a large dc electric field. Using the Kadanoff-Baym-Keldysh formalism, we employ nonequilibrium dynamical mean-field theory to exactly solve for this nonlinear response. We examine both the current and the order parameter of the conduction electrons as the ordered system is driven by a dc electric field. Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, Lviv, Ukraine.
Whistler wave mode conversion to lower hybrid waves at a density striation
Bamber, J.F.; Gekelman, W.; Maggs, J.E. )
1994-11-28
The first observation of mode conversion of whistler waves to lower hybrid waves at a density striation has been made in a laboratory plasma. The observed lower hybrid wavelength is consistent with that predicted by linear mode coupling. The lower hybrid waves have amplitudes up to 20% of the incident whistler waves.
Continuous Dependence on the Density for Stratified Steady Water Waves
NASA Astrophysics Data System (ADS)
Chen, Robin Ming; Walsh, Samuel
2016-02-01
There are two distinct regimes commonly used to model traveling waves in stratified water: continuous stratification, where the density is smooth throughout the fluid, and layer-wise continuous stratification, where the fluid consists of multiple immiscible strata. The former is the more physically accurate description, but the latter is frequently more amenable to analysis and computation. By the conservation of mass, the density is constant along the streamlines of the flow; the stratification can therefore be specified by prescribing the value of the density on each streamline. We call this the streamline density function. Our main result states that, for every smoothly stratified periodic traveling wave in a certain small-amplitude regime, there is an L ∞ neighborhood of its streamline density function such that, for any piecewise smooth streamline density function in that neighborhood, there is a corresponding traveling wave solution. Moreover, the mapping from streamline density function to wave is Lipschitz continuous in a certain function space framework. As this neighborhood includes piecewise smooth densities with arbitrarily many jump discontinues, this theorem provides a rigorous justification for the ubiquitous practice of approximating a smoothly stratified wave by a layered one. We also discuss some applications of this result to the study of the qualitative features of such waves.
{alpha}-cluster structure and density waves in oblate nuclei
Kanada-En'yo, Yoshiko; Hidaka, Yoshimasa
2011-07-15
Pentagon and triangle shapes in {sup 28}Si and {sup 12}C are discussed in relation to nuclear density waves. In the antisymmetrized molecular dynamics calculations, the K{sup {pi}=}5{sup -} band in {sup 28}Si and the K{sup {pi}=}3{sup -} band in {sup 12}C are described by the pentagon and triangle shapes, respectively. These negative-parity bands can be interpreted as the parity partners of the K{sup {pi}=}0{sup +} ground bands and they are constructed from the parity-asymmetric-intrinsic states. The pentagon and the triangle shapes originate in 7{alpha}- and 3{alpha}-cluster structures, respectively. In a mean-field picture, they are described also by the static one-dimensional density waves at the edge of the oblate states. In analyses with ideal {alpha}-cluster models using Brink-Bloch cluster wave functions and that with a simplified model, we show that the static edge density waves for the pentagon and triangle shapes can be understood by spontaneous breaking of axial symmetry, i.e., the instability of the oblate states with respect to the edge density waves. The density wave is enhanced in the Z=N nuclei due to the proton-neutron coherent density waves, while it is suppressed in Z{ne}N nuclei.
Nonlinear density waves in the single-wave model
Marinov, Kiril B.; Tzenov, Stephan I.
2011-03-15
The single-wave model equations are transformed to an exact hydrodynamic closure by using a class of solutions to the Vlasov equation corresponding to the waterbag model. The warm fluid dynamic equations are then manipulated by means of the renormalization group method. As a result, amplitude equations for the slowly varying wave amplitudes are derived. Since the characteristic equation for waves has in general three roots, two cases are examined. If all the three roots of the characteristic equation are real, the amplitude equations for the eigenmodes represent a system of three coupled nonlinear equations. In the case where the dispersion equation possesses one real and two complex conjugate roots, the amplitude equations take the form of two coupled equations with complex coefficients. The analytical results are then compared to the exact system dynamics obtained by solving the hydrodynamic equations numerically.
Nonlinear upper hybrid waves and the induced density irregularities
Kuo, Spencer P.
2015-08-15
Upper hybrid waves are excited parametrically by the O-mode high-frequency heater waves in the ionospheric heating experiments. These waves grow to large amplitudes and self-induced density perturbations provide nonlinear feedback. The lower hybrid resonance modifies the nonlinear feedback driven by the ponderomotive force; the nonlinear equation governing the envelope of the upper hybrid waves is derived. Solutions in symmetric alternating functions, in non-alternating periodic functions, as well as in solitary functions are shown. The impact of lower hybrid resonance on the envelope of the upper hybrid waves is explored; the results show that both the spatial period and amplitude are enlarged. The average fluctuation level of induced density irregularities is also enhanced. In the soliton form, the induced density cavity is widened considerably.
Magnetic Fluctuations in Pair-Density-Wave Superconductors
NASA Astrophysics Data System (ADS)
Christensen, Morten H.; Jacobsen, Henrik; Maier, Thomas A.; Andersen, Brian M.
2016-04-01
Pair-density-wave superconductivity constitutes a novel electronic condensate proposed to be realized in certain unconventional superconductors. Establishing its potential existence is important for our fundamental understanding of superconductivity in correlated materials. Here we compute the dynamical magnetic susceptibility in the presence of a pair-density-wave ordered state and study its fingerprints on the spin-wave spectrum including the neutron resonance. In contrast to the standard case of d -wave superconductivity, we show that the pair-density-wave phase exhibits neither a spin gap nor a magnetic resonance peak, in agreement with a recent neutron scattering experiment on underdoped La1.905 Ba0.095 CuO4 [Z. Xu et al., Phys. Rev. Lett. 113, 177002 (2014)].
Magnetic Fluctuations in Pair-Density-Wave Superconductors.
Christensen, Morten H; Jacobsen, Henrik; Maier, Thomas A; Andersen, Brian M
2016-04-22
Pair-density-wave superconductivity constitutes a novel electronic condensate proposed to be realized in certain unconventional superconductors. Establishing its potential existence is important for our fundamental understanding of superconductivity in correlated materials. Here we compute the dynamical magnetic susceptibility in the presence of a pair-density-wave ordered state and study its fingerprints on the spin-wave spectrum including the neutron resonance. In contrast to the standard case of d-wave superconductivity, we show that the pair-density-wave phase exhibits neither a spin gap nor a magnetic resonance peak, in agreement with a recent neutron scattering experiment on underdoped La_{1.905}Ba_{0.095}CuO_{4} [Z. Xu et al., Phys. Rev. Lett. 113, 177002 (2014)]. PMID:27152819
Brouet, V.; Yang, W.L.; Zhou, X.J.; Hussain, Z.; Moore, R.G.; He, R.; Lu, D.H.; Shen, Z.X.; Laverock, J.; Dugdale, S.B.; Ru, N.; Fisher, I.R.
2009-05-12
We present a detailed angle-resolved photoemission spectroscopy (ARPES) investigation of the RTe{sub 3} family, which sets this system as an ideal 'textbook' example for the formation of a nesting driven charge density wave (CDW). This family indeed exhibits the full range of phenomena that can be associated to CDW instabilities, from the opening of large gaps on the best nested parts of Fermi surface (up to 0.4 eV), to the existence of residual metallic pockets. ARPES is the best suited technique to characterize these features, thanks to its unique ability to resolve the electronic structure in k space. An additional advantage of RTe{sub 3} is that the band structure can be very accurately described by a simple two dimensional tight-binding (TB) model, which allows one to understand and easily reproduce many characteristics of the CDW. In this paper, we first establish the main features of the electronic structure by comparing our ARPES measurements with the linear muffin-tin orbital band calculations. We use this to define the validity and limits of the TB model. We then present a complete description of the CDW properties and of their strong evolution as a function of R. Using simple models, we are able to reproduce perfectly the evolution of gaps in k space, the evolution of the CDW wave vector with R, and the shape of the residual metallic pockets. Finally, we give an estimation of the CDW interaction parameters and find that the change in the electronic density of states n(E{sub F}), due to lattice expansion when different R ions are inserted, has the correct order of magnitude to explain the evolution of the CDW properties.
Spatial Frequency Clustering in Nonlinear Dust-Density Waves
Menzel, K. O.; Arp, O.; Piel, A.
2010-06-11
Self-excited density waves were studied in a strongly coupled dusty plasma of a radio-frequency discharge under microgravity conditions. The spatiotemporal evolution of the complicated three-dimensional wave field was investigated and analyzed for two different situations. The reconstructed instantaneous phase information of the wave field revealed a partial synchronization within multiple distinct domains. The boundaries of these regions coincide with the locations of topological defects.
The Mass of Saturn's B ring from hidden density waves
NASA Astrophysics Data System (ADS)
Hedman, M. M.; Nicholson, P. D.
2015-12-01
The B ring is Saturn's brightest and most opaque ring, but many of its fundamental parameters, including its total mass, are not well constrained. Elsewhere in the rings, the best mass density estimates come from spiral waves driven by mean-motion resonances with Saturn's various moons, but such waves have been hard to find in the B ring. We have developed a new wavelet-based technique, for combining data from multiple stellar occultations that allows us to isolate the density wave signals from other ring structures. This method has been applied to 5 density waves using 17 occultations of the star gamma Crucis observed by the Visual and Infrared Mapping Spectrometer (VIMS) onboard the Cassini spacecraft. Two of these waves (generated by the Janus 2:1 and Mimas 5:2 Inner Lindblad Resonances) are visible in individual occultation profiles, but the other three wave signatures ( associated with the Janus 3:2, Enceladus 3:1 and Pandora 3:2 Inner Lindblad Resonances ) are not visible in individual profiles and can only be detected in the combined dataset. Estimates of the ring's surface mass density derived from these five waves fall between 40 and 140 g/cm^2. Surprisingly, these mass density estimates show no obvious correlation with the ring's optical depth. Furthermore, these data indicate that the total mass of the B ring is probably between one-third and two-thirds the mass of Saturn's moon Mimas.
Yuan Chengxun; Zhou Zhongxiang; Zhang, Jingwen W.; Sun Hongguo; Wang He; Du Yanwei; Xiang Xiaoli
2011-03-15
Propagation properties of terahertz (THz) waves in a bounded atmospheric-pressure microplasma (AMP) are analyzed in this study. A modified Epstein profile model is used to simulate the electron density distribution caused by the plasma sheaths. By introducing the dielectric constant of a Drude-Lorentz model and using the method of dividing the plasma into a series of subslabs with uniform electron density, the coefficients of power reflection, transmission, and absorption are derived for a bounded microplasma structure. The effects of size of microplasma, electron density profile, and collision frequency on the propagation of THz waves are analyzed numerically. The results indicate that the propagation of THz waves in AMPs depend greatly on the above three parameters. It is demonstrated that the THz wave can play an important role in AMPs diagnostics; meanwhile, the AMP can be used as a novel potential tool to control THz wave propagation.
GyPSuM: A Detailed Tomographic Model of Mantle Density and Seismic Wave Speeds
Simmons, N A; Forte, A M; Boschi, L; Grand, S P
2010-03-30
GyPSuM is a tomographic model fo mantle seismic shear wave (S) speeds, compressional wave (P) speeds and detailed density anomalies that drive mantle flow. the model is developed through simultaneous inversion of seismic body wave travel times (P and S) and geodynamic observations while considering realistic mineral physics parameters linking the relative behavior of mantle properties (wave speeds and density). Geodynamic observations include the (up to degree 16) global free-air gravity field, divergence of the tectonic plates, dynamic topography of the free surface, and the flow-induced excess ellipticity of the core-mantle boundary. GyPSuM is built with the philosophy that heterogeneity that most closely resembles thermal variations is the simplest possible solution. Models of the density field from Earth's free oscillations have provided great insight into the density configuration of the mantle; but are limited to very long-wavelength solutions. Alternatively, simply scaling higher resolution seismic images to density anomalies generates density fields that do not satisfy geodynamic observations. The current study provides detailed density structures in the mantle while directly satisfying geodynamic observations through a joint seismic-geodynamic inversion process. Notable density field observations include high-density piles at the base of the superplume structures, supporting the fundamental results of past normal mode studies. However, these features are more localized and lower amplitude than past studies would suggest. When we consider all seismic anomalies in GyPSuM, we find that P and S-wave speeds are strongly correlated throughout the mantle. However, correlations between the high-velocity S zones in the deep mantle ({approx} 2000 km depth) and corresponding P-wave anomalies are very low suggesting a systematic divergence from simplified thermal effects in ancient subducted slab anomalies. Nevertheless, they argue that temperature variations are the
Numerical Simulation of Low-Density Shock-Wave Interactions
NASA Technical Reports Server (NTRS)
Glass, Christopher E.
1999-01-01
Computational Fluid Dynamics (CFD) numerical simulations of low-density shock-wave interactions for an incident shock impinging on a cylinder have been performed. Flow-field density gradient and surface pressure and heating define the type of interference pattern and corresponding perturbations. The maximum pressure and heat transfer level and location for various interaction types (i.e., shock-wave incidence with respect to the cylinder) are presented. A time-accurate solution of the Type IV interference is employed to demonstrate the establishment and the steadiness of the low-density flow interaction.
Constraints on primordial density perturbations from induced gravitational waves
Assadullahi, Hooshyar; Wands, David
2010-01-15
We consider the stochastic background of gravitational waves produced during the radiation-dominated hot big bang as a constraint on the primordial density perturbation on comoving length scales much smaller than those directly probed by the cosmic microwave background or large-scale structure. We place weak upper bounds on the primordial density perturbation from current data. Future detectors such as BBO and DECIGO will place much stronger constraints on the primordial density perturbation on small scales.
Generation of ramp waves using variable areal density flyers
NASA Astrophysics Data System (ADS)
Winter, R. E.; Cotton, M.; Harris, E. J.; Chapman, D. J.; Eakins, D.
2015-02-01
Ramp loading using graded density impactors as flyers in gas-gun-driven plate impact experiments can yield new and useful information about the equation of state and the strength properties of the loaded material. Selective Laser Melting, an additive manufacture technique, was used to manufacture a graded density flyer, termed the "bed-of-nails" (BON). A 2.5-mm-thick × 99.4-mm-diameter solid disc of stainless steel formed a base for an array of tapered spikes of length 5.5 mm and spaced 1 mm apart. The two experiments to test the concept were performed at impact velocities of 900 and 1100 m/s using the 100-mm gas gun at the Institute of Shock Physics at Imperial College London. In each experiment, a BON flyer was impacted onto a copper buffer plate which helped to smooth out perturbations in the wave profile. The ramp delivered to the copper buffer was in turn transmitted to three tantalum targets of thicknesses 3, 5 and 7 mm, which were mounted in contact with the back face of the copper. Heterodyne velocimetry (Het-V) was used to measure the velocity-time history, at the back faces of the tantalum discs. The wave profiles display a smooth increase in velocity over a period of ˜ 2.5 \\upmu s, with no indication of a shock jump. The measured profiles have been analysed to generate a stress vs. volume curve for tantalum. The results have been compared with the predictions of the Sandia National Laboratories hydrocode, CTH.
Spiral density waves in M81. I. Stellar spiral density waves
Feng, Chien-Chang; Lin, Lien-Hsuan; Wang, Hsiang-Hsu; Taam, Ronald E.
2014-04-20
Aside from the grand-design stellar spirals appearing in the disk of M81, a pair of stellar spiral arms situated well inside the bright bulge of M81 has been recently discovered by Kendall et al. The seemingly unrelated pairs of spirals pose a challenge to the theory of spiral density waves. To address this problem, we have constructed a three-component model for M81, including the contributions from a stellar disk, a bulge, and a dark matter halo subject to observational constraints. Given this basic state for M81, a modal approach is applied to search for the discrete unstable spiral modes that may provide an understanding for the existence of both spiral arms. It is found that the apparently separated inner and outer spirals can be interpreted as a single trailing spiral mode. In particular, these spirals share the same pattern speed 25.5 km s{sup –1} kpc{sup –1} with a corotation radius of 9.03 kpc. In addition to the good agreement between the calculated and the observed spiral pattern, the variation of the spiral amplitude can also be naturally reproduced.
NASA Astrophysics Data System (ADS)
Venderbos, J. W. F.
2016-03-01
In this work we introduce a symmetry classification for electronic density waves which break translational symmetry due to commensurate wave-vector modulations. The symmetry classification builds on the concept of extended point groups: symmetry groups which contain, in addition to the lattice point group, translations that do not map the enlarged unit cell of the density wave to itself, and become "nonsymmorphic"-like elements. Multidimensional representations of the extended point group are associated with degenerate wave vectors. Electronic properties such as (nodal) band degeneracies and topological character can be straightforwardly addressed, and often follow directly. To further flesh out the idea of symmetry, the classification is constructed so as to manifestly distinguish time-reversal invariant charge (i.e., site and bond) order, and time-reversal breaking flux order. For the purpose of this work, we particularize to spin-rotation invariant density waves. As a first example of the application of the classification we consider the density waves of a simple single- and two-orbital square lattice model. The main objective, however, is to apply the classification to two-dimensional (2D) hexagonal lattices, specifically the triangular and the honeycomb lattices. The multicomponent density waves corresponding to the commensurate M -point ordering vectors are worked out in detail. To show that our results generally apply to 2 D hexagonal lattices, we develop a general low-energy SU(3 ) theory of (spinless) saddle-point electrons.
The impact of density heterogeneities on seismic wave propagation
NASA Astrophysics Data System (ADS)
Płonka, Agnieszka; Fichtner, Andreas
2014-05-01
Using 3D numerical simulations of seismic wave propagation in heterogeneous media, we systematically compare the imprints of heterogeneities of different type (and particularly density heterogeneities) on synthetic seismograms. Lateral density variations are the source of mass transport in the Earth at all scales, acting as drivers of convective motion in the mantle. However, the density structure of the Earth remains largely unknown since classic seismic observables and gravity provide only weak constraints with strong trade-offs. Current density models are therefore often based on velocity scaling, making strong assumptions on the origin of structural heterogeneities, which may not necessarily be true. We propose to develop a seismic tomography technique that directly inverts for density, using complete seismograms rather than arrival times of certain waves only. The first task in this challenge is to systematically study the imprints of density on synthetic seismograms. In this context, our study aims to compare the significance of density heterogeneities relative to velocity heterogeneities, and to design a numerical experiment with a source-receiver configuration particularly sensitive to density. To compute the full seismic wavefield in a 3D heterogeneous medium without making significant approximations, we use numerical wave propagation based on a spectral-element discretization of the seismic wave equation. We consider a 2000 by 1000 km wide and 500 km deep spherical section, with the 1D Earth model ak135 as a background. Onto this we superimpose 3D Gaussian-shaped perturbations of different type (P, SV, SH velocities and density) for depths in the range from 10 km to 70 km. The choice of depth in which the 3D heterogeneities were placed (10 km - 70 km) was dictated by the surface wave sensitivity to density. For each depth we perform 4 wave propagation simulations corresponding to 4 different types of heterogeneities, and calculate surface wave sensitivity
Searching for spectroscopic signatures of density wave correlations in cuprates
NASA Astrophysics Data System (ADS)
He, Rui-Hua
2015-03-01
Recent developments in the research on high-temperature cuprate superconductors highlight the relevance of some density wave correlations to the superconductivity and its normal state in this generic class of materials. Depending on specific cuprate systems, these density wave correlations can have diverse manifestations in different (charge, spin, pairing) sectors and likely break (time reversal, space inversion, point group, gauge) symmetries in addition to the lattice translation. A unified understanding of their microscopic nature hinges on further characterizations using direct (imaging scattering) probes for these correlations themselves, as well as indirect probes for their interplay with other degrees of freedom in the system. ARPES can provide information about a density wave order through probing modifications in the electron structure it induces, while other spectroscopy techniques can shed unique lights on the broken symmetry aspect of the order. In this talk, I will review the density-wave signatures that have been or yet to be found in ARPES mainly in terms of the spectral weight, energy gap, and renormalized band dispersions. These experimental observations/proposals, coupled with simple theoretical modeling, promise new insights into the (wavevector, order parameter, form factor) characters of associated density wave correlations. Time permitting, I will introduce a novel x-ray spectroscopy technique that can detect broken time-reversal versus space-inversion symmetry of an electronic order in a way complementary to the polar Kerr effect.
Properties of resonance wave functions.
NASA Technical Reports Server (NTRS)
More, R. M.; Gerjuoy, E.
1973-01-01
Construction and study of resonance wave functions corresponding to poles of the Green's function for several illustrative models of theoretical interest. Resonance wave functions obtained from the Siegert and Kapur-Peierls definitions of the resonance energies are compared. The comparison especially clarifies the meaning of the normalization constant of the resonance wave functions. It is shown that the wave functions may be considered renormalized in a sense analogous to that of quantum field theory. However, this renormalization is entirely automatic, and the theory has neither ad hoc procedures nor infinite quantities.
Momentum-space properties from coordinate-space electron density
Harbola, Manoj K.; Zope, Rajendra R.; Kshirsagar, Anjali; Pathak, Rajeev K.
2005-05-22
Electron density and electron momentum density, while independently tractable experimentally, bear no direct connection without going through the many-electron wave function. However, invoking a variant of the constrained-search formulation of density-functional theory, we develop a general scheme (valid for arbitrary external potentials) yielding decent momentum-space properties, starting exclusively from the coordinate-space electron density. A numerical illustration of the scheme is provided for the closed-shell atomic systems He, Be, and Ne in their ground state and for 1s{sup 1} 2s{sup 1} singlet electronic excited state for helium by calculating the Compton profiles and the
expectation values derived from given coordinate-space electron densities.
Scattering of radio frequency waves by cylindrical density filaments in tokamak plasmas
NASA Astrophysics Data System (ADS)
Ram, Abhay K.; Hizanidis, Kyriakos
2016-02-01
In tokamak fusion plasmas, coherent fluctuations in the form of blobs or filaments are routinely observed in the scrape-off layer. Radio frequency (RF) electromagnetic waves, excited by antenna structures placed near the wall of a tokamak, have to propagate through the scrape-off layer before reaching the core of the plasma. While the effect of fluctuations on the properties of RF waves has not been quantified experimentally, it is of interest to carry out a theoretical study to determine if fluctuations can affect the propagation characteristics of RF waves. Usually, the difference between the plasma density inside the filament and the background plasma density is sizable, the ratio of the density difference to the background density being of order one. Generally, this precludes the use of geometrical optics in determining the effect of fluctuations, since the relevant ratio has to be much less than one, typically, of the order of 10% or less. In this paper, a full-wave, analytical model is developed for the scattering of a RF plane wave by a cylindrical plasma filament. It is assumed that the plasma inside and outside the filament is cold and uniform and that the major axis of the filament is aligned along the toroidal magnetic field. The ratio of the density inside the filament to the density of the background plasma is not restricted. The theoretical framework applies to the scattering of any cold plasma wave. In order to satisfy the boundary conditions at the interface between the filament and the background plasma, the electromagnetic fields inside and outside the filament need to have the same k∥ , the wave vector parallel to the ambient magnetic field, as the incident plane wave. Consequently, in contrast to the scattering of a RF wave by a spherical blob [Ram et al., Phys. Plasmas 20, 056110-1-056110-10 (2013)], the scattering by a field-aligned filament does not broaden the k∥ spectrum. However, the filament induces side-scattering leading to surface
Propagation of radio frequency waves through density filaments
NASA Astrophysics Data System (ADS)
Ram, Abhay K.; Hizanidis, Kyriakos
2015-12-01
In tokamak fusion plasmas, coherent fluctuations in the form of blobs or filaments are routinely observed in the scrape-off layer. In this paper we develop an analytical formalism for the scattering of radio frequency waves by filaments which are cylindrical with their major axis aligned along the toroidal magnetic field lines. Since the magnitude of the ratio of the density inside the filaments to the background density is generally of order 1, the geometric optics approximation cannot be used to describe the scattering. A full-wave model is formulated which assumes that the plasma is cold and that the plasma in the cylindrical filament has uniform density. The background plasma, in which the filament is present, is also assumed to be cold and uniform. The theoretical framework applies to the scattering of any plasma wave.
Propagation of radio frequency waves through density filaments
Ram, Abhay K.; Hizanidis, Kyriakos
2015-12-10
In tokamak fusion plasmas, coherent fluctuations in the form of blobs or filaments are routinely observed in the scrape-off layer. In this paper we develop an analytical formalism for the scattering of radio frequency waves by filaments which are cylindrical with their major axis aligned along the toroidal magnetic field lines. Since the magnitude of the ratio of the density inside the filaments to the background density is generally of order 1, the geometric optics approximation cannot be used to describe the scattering. A full-wave model is formulated which assumes that the plasma is cold and that the plasma in the cylindrical filament has uniform density. The background plasma, in which the filament is present, is also assumed to be cold and uniform. The theoretical framework applies to the scattering of any plasma wave.
Properties of materials using acoustic waves
NASA Astrophysics Data System (ADS)
Apfel, R. E.
1984-10-01
Our goal of characterizing materials using acoustic waves was forwarded through a number of projects: (1) We have refined our modulated radiation pressure technique for characterizing the interfaces between liquids so that we can automatically track changes in interfacial tension over time due to contaminants, surfactants, etc. (2) We have improved and simplified our acoustic scattering apparatus for measuring distributions of the properties of microparticle samples, which will allow us to distinguish particulates in liquids by size, compressibility, and density. (3) We are continuing work on theoretical approaches to nonlinear acoustics which should permit us to cast problems with geometric and other complexities into a manageable form. (4) Our studies of cavitation have enabled us to derive an analytic expression which predicts the acoustic pressure threshold for cavitation at the micrometer scale - where surface tension effects are important. This work has relevance to the consideration of possible bioeffects from diagnostic ultrasound. (5) Other projects include the calibration of hydrophones using acoustically levitated samples, and the investigation of solitary waves of the sort discovered by Wu, Keolian and Rudnick.
Resonantly driven nonlinear density waves in protostellar disks
NASA Technical Reports Server (NTRS)
Yuan, Chi; Cassen, Pat
1994-01-01
Recent observations of binary, pre-main-sequence, solar-type stars provide evidence that such systems may coexist with circumstellar disks. The binary disk systems, besides being of general interest for the study of star formation, potentially provide useful tests of companion-disk interaction theories prominent in current hypotheses of planet formation. In this paper, we apply an asymptotic analysis of the nonlinear, resonant interaction of a stellar companion with a disk to understand the dependence of such interactions on the properties of the system: the binary mass ratio, the physical properties of the disk, and the effective dissipation (treated herein as viscosity). The method is based on a WKBJ approximation and exploits the conditions that the disk is thin and much less massive than the primary, but does not require that the companion-induced disturbance be small. Both isothermal and adiabatic responses are treated. Only circular orbit resonances are considered in this paper. It is demonstrated that the temperature of the disk as well as the relative mass of the companion affects the degree of nonlinearity, and that nonlinearity promotes high wave compression ratios, long wavelengths, and increased propagation distances. Nevertheless, the total torque exerted between the companion and the disk is well represented by linear theory. The amplitudes of density disturbances are reduced by viscosity and nonisothermality. Because resonant interactions are generally strong and capable of driving rapid evolution, one might expect observations of systems undergoing strong, resonant-driven evolution to be rare. In this connection, it is pointed out that the m = 1 resonance is distinguished by being anomalously weaker than the others and is therefore of observational interest. It is speculated that, in conditions of intrinsically small dissipation, the propagation of resonant-driven density waves is limited by the tendency of their wavelength to diminish with distance
Meissner effect without superconductivity from a chiral d -density wave
NASA Astrophysics Data System (ADS)
Kotetes, P.; Varelogiannis, G.
2008-12-01
We demonstrate that the formation of a chiral d -density wave state generates a topological Meissner effect (TME) in the absence of any kind of superconductivity. The TME is identical to the usual superconducting Meissner effect, but it appears only for magnetic fields perpendicular to the plane while it is absent for in-plane fields. The observed enhanced diamagnetic signals in the nonsuperconducting pseudogap regime of the cuprates may find an alternative interpretation in terms of the TME, originating from a chiral d -density wave pseudogap.
Ion cyclotron waves at Mars: Occurrence and wave properties
NASA Astrophysics Data System (ADS)
Wei, H. Y.; Cowee, M. M.; Russell, C. T.; Leinweber, H. K.
2014-07-01
Ion cyclotron waves (ICWs) are generated during the interaction between the solar wind and the Martian exosphere in a process called ion pickup. Mars Global Surveyor (MGS) detected waves near the proton gyrofrequency, indicating pickup of the exospheric hydrogen. To analyze these waves, we first improve the zero levels of the MGS magnetic field data taken during the first aerobreaking phase and then perform a statistical study of the ICWs observed from just outside the Martian bow shock to over 14 Mars radii away. These ICW events typically last for 5 to 30 min but can occasionally last for hours. The wave power decreases slowly with distance on both the upstream and downstream sides. From the variation of wave properties with the strength of the background field, we find that there are likely still remaining offsets in at least some the data sets even after applying our calibration technique. Thus, we use the events with a strong background field to examine the wave properties that depend on an accurate determination of the field direction and strength. We find the pickup angle associated with the largest occurrence rate of ICWs to be around 45°, but neither the wave amplitude, nor wave frequency, nor wave duration appear to vary with pickup angle. Finally, we find the waves with background field strength greater than 4 nT occur on both the positive and negative electric field sides of Mars but have a larger occurrence rate on the side of Mars in the positive electric field direction (which is defined as the direction of the cross product of the magnetic field vector and solar wind flow vector).
The impact of crustal density variations on seismic wave propagation
NASA Astrophysics Data System (ADS)
Plonka, A.; Fichtner, A.
2014-12-01
Lateral density variations are the source of mass transport in the Earth at all scales, acting as drivers of convective motion. However, the density structure of the Earth remains largely unknown since classic seismic observables and gravity provide only weak constraints with strong trade-offs. Current density models are therefore often based on velocity scaling, making strong assumptions on the origin of structural heterogeneities, which may not necessarily be correct.We propose to develop a seismic tomography technique that directly inverts for density, using complete seismograms rather than arrival times of certain waves only. The first task in this challenge is to systematically study the imprints of density on synthetic seismograms.To compute the full seismic wavefield in a 3D heterogeneous medium without making significant approximations, we usenumerical wave propagation based on a spectral-element discretization of the seismic wave equation. We consider a 2000 by 1000 km wide and 500 km deep spherical section, with the 1D Earth model PREM (with 40 km crust thickness) as a background. Onto this (in the uppermost 40 km) we superimpose 3D randomly generated velocity and density heterogeneities of various magnitudes and correlation lenghts. We use different random realizations of heterogeneity distribution.We compare the synthetic seismograms for 3D velocity and density structure with 3D velocity structure and with the 1D background, calculating relative amplitude differences and timeshifts as functions of time and frequency.Our analyses indicate that reasonably sized density variations within the crust can leave a strong imprint on both traveltimes and amplitudes. This suggests (1) that crustal tomography can be significantly biased when density heterogeneities are not properly accounted for, and (2) that the solution of the seismic inverse problem for density may become feasible.
NASA Astrophysics Data System (ADS)
Kurth, W. S.; De Pascuale, S.; Faden, J. B.; Kletzing, C. A.; Hospodarsky, G. B.; Thaller, S.; Wygant, J. R.
2015-02-01
The twin Van Allen Probe spacecraft, launched in August 2012, carry identical scientific payloads. The Electric and Magnetic Field Instrument Suite and Integrated Science suite includes a plasma wave instrument (Waves) that measures three magnetic and three electric components of plasma waves in the frequency range of 10 Hz to 12 kHz using triaxial search coils and the Electric Fields and Waves triaxial electric field sensors. The Waves instrument also measures a single electric field component of waves in the frequency range of 10 to 500 kHz. A primary objective of the higher-frequency measurements is the determination of the electron density ne at the spacecraft, primarily inferred from the upper hybrid resonance frequency fuh. Considerable work has gone into developing a process and tools for identifying and digitizing the upper hybrid resonance frequency in order to infer the electron density as an essential parameter for interpreting not only the plasma wave data from the mission but also as input to various magnetospheric models. Good progress has been made in developing algorithms to identify fuh and create a data set of electron densities. However, it is often difficult to interpret the plasma wave spectra during active times to identify fuh and accurately determine ne. In some cases, there is no clear signature of the upper hybrid band, and the low-frequency cutoff of the continuum radiation is used. We describe the expected accuracy of ne and issues in the interpretation of the electrostatic wave spectrum.
Properties of Mirror Mode Waves observed in the Kronian Magnetosphere
NASA Astrophysics Data System (ADS)
Rodriguez-Martinez, M. R.; Blanco-Cano, X.; Russell, C. T.; Aguilar-Rodriguez, E.; Wilson, R. J.; Dougherty, M. K.
2014-12-01
Mirror Mode Waves (MMW) were observed with Cassini spacecraft in the Kronian middle magnetosphere. They are compressive waves characterized by strong deeps in the magnetic field magnitude and anti-correlated with density. Furthermore, MMW share a common origin with the Ion Cyclotron Waves (ICW), requiring the condition of anisotropy in the plasma temperature (pressure) (T⊥/T‖>>1). In this work we analyze four Cassini's orbits, with low inclination angle <0.5º, of 2005. The data were obtained from MAG and CAPS instruments. We perform a study about the wave properties and their region of occurrence. We found that the MMW can appear between 6 Rs and 6.9 Rs, with respect to Saturn's center, indicating that they are further away than ICW. Finally, we use linear kinetic theory, using WHAMP code, in order to determine conditions for wave growth in a plasma resembling the regions where these modes were observed.
Pair density wave superconducting states and statistical mechanics of dimers
NASA Astrophysics Data System (ADS)
Soto Garrido, Rodrigo Andres
The following thesis is divided in two main parts. Chapters 2, 3 and 4 are devoted to the study of the so called pair-density-wave (PDW) superconducting state and some of its connections to electronic liquid crystal (ELC) phases, its topological aspects in a one dimensional model and its appearance in a quasi-one dimensional system. On the other hand, chapter 5 is focused on the investigation of the classical statistical mechanics properties of dimers, in particular, the dimer model on the Aztec diamond graph and its relation with the octahedron equation. In chapter 2 we present a theory of superconducting states where the Cooper pairs have a nonzero center-of-mass momentum, inhomogeneous superconducting states known as a pair-density-waves (PDWs) states. We show that in a system of spin-1/2 fermions in two dimensions in an electronic nematic spin-triplet phase where rotational symmetry is broken in both real and spin space PDW phases arise naturally in a theory that can be analysed using controlled approximations. We show that several superfluid phases that may arise in this phase can be treated within a controlled BCS mean field theory, with the strength of the spin-triplet nematic order parameter playing the role of the small parameter of this theory. We find that in a spin-triplet nematic phase, in addition to a triplet p-wave and spin-singlet d-wave (or s depending on the nematic phase) uniform superconducting states, it is also possible to have a d-wave (or s) PDW superconductor. The PDW phases found here can be either unidirectional, bidirectional, or tridirectional depending on the spin-triplet nematic phase and which superconducting channel is dominant. In addition, a triple-helix state is found in a particular channel. We show that these PDW phases are present in the weak-coupling limit, in contrast to the usual Fulde-Ferrell-Larkin-Ovchinnikov phases, which require strong coupling physics in addition to a large magnetic field (and often both). In chapter
Density Waves in Systems of Non-Interacting Particles
NASA Astrophysics Data System (ADS)
Kolmes, E. J.; Geyko, V. I.; Fisch, N. J.
2015-11-01
Under certain conditions, systems of non-interacting particles can give rise to density waves. In general, these waves do not require any particular perturbations in the initial density or velocity distributions, but they do tend to be strongly dependent on the boundary conditions of the system; one of the simplest examples is a collection of non-interacting particles bouncing in a constant gravitational field. A wide variety of different potentials can produce density waves, which change in both shape and behavior as the potential changes. We examine the structure and origin of these waves numerically and analytically. We also analyze the sensitivity of these waves to changes in different parameters of the system, including the effects of interparticle interactions on these structures. Strong interparticle interactions tend to disrupt the structure that develops in the non-interacting-particle case. We discuss possible experimental consequences of these phenomena. This work was supported by the U.S. Defense Threat Reduction Agency, and by the NNSA SSAA Program through DOE Research Grant No. DE-FG52-08NA28553.
Scattering of radio frequency waves by density fluctuations
NASA Astrophysics Data System (ADS)
Ram, A. K.; Hizanidis, K.; Ioannidis, Z.; Tigelis, I.
2015-11-01
The scattering of radio frequency waves by density fluctuations in magnetized fusion plasmas is studied theoretically and computationally. For coherent fluctuations, such as filaments in the edge region, we use a full-wave model for which the theory is similar to that for Mie scattering of electromagnetic waves by dielectric objects. The filaments are considered to be cylindrical with their axes aligned along the magnetic field. The results from the theoretical model are compared with numerical simulations using COMSOL. The simulations are extended to plasma conditions that are beyond the scope of the theoretical model, e.g., multiple filaments and filaments with density gradients. For incoherent planar fluctuations, which can be either in the core of the plasma or in the edge region, our theory is based on the Kirchhoff approach in tandem with Huygen's principle. The coherent and incoherent fluctuations scatter the incident plane wave, as well as couple some of the power to different plasma waves. The scattered spectrum is affected by the size of the fluctuations, the frequency, and the direction of propagation of the incident wave.
Pressure induced Superconductivity in the Charge Density Wave Compound Tritelluride
Hamlin, J.J.; Zocco, D.A.; Sayles, T.A.; Maple, M.B.; Chu, J.-H.; Fisher, I.R.; /Stanford U., Geballe Lab.
2010-02-15
A series of high-pressure electrical resistivity measurements on single crystals of TbTe{sub 3} reveal a complex phase diagram involving the interplay of superconducting, antiferromagnetic and charge density wave order. The onset of superconductivity reaches a maximum of almost 4 K (onset) near {approx} 12.4 GPa.
Density inhomogeneity driven electrostatic shock waves in planetary rings
Masood, W.; Siddiq, M.; Rizvi, H.; Haque, Q.; Hasnain, H.
2011-05-15
Dust inertia and background density driven dust drift shock waves are theoretically studied in a rotating planetary environment and are subsequently applied to the planetary rings where the collisional effects are pronounced. It has been found that the system under consideration admits significant shock formation if the collision frequency is of the order of or less than the rotational frequency of the Saturn's rings.
Akhmediev, N; Soto-Crespo, J M; Devine, N
2016-08-01
Turbulence in integrable systems exhibits a noticeable scientific advantage: it can be expressed in terms of the nonlinear modes of these systems. Whether the majority of the excitations in the system are breathers or solitons defines the properties of the turbulent state. In the two extreme cases we can call such states "breather turbulence" or "soliton turbulence." The number of rogue waves, the probability density functions of the chaotic wave fields, and their physical spectra are all specific for each of these two situations. Understanding these extreme cases also helps in studies of mixed turbulent states when the wave field contains both solitons and breathers, thus revealing intermediate characteristics. PMID:27627303
Whistler-Mode Waves inside Density Ducts Observed by the Van Allen Probes
NASA Astrophysics Data System (ADS)
Rosborough, S.; Bengtson, M.; Stein, R. L.; Streltsov, A. V.
2015-12-01
The Van Allen Probes satellites launched by NASA in 2012 are currently orbiting in Earth's radiation belts collecting data about electromagnetic waves and charged particles in the near-earth space environment. Whistler-mode waves are naturally occurring right-hand polarized, very-low frequency waves (< 30 kHz), that can efficiently interact with the energetic electrons in the earth's radiation belts magnetosphere and remediate them from the magnetosphere by precipitating these particles into the atmosphere. The important property of the whistler-mode waves is that they can be guided by density inhomogeneities extended along the ambient magnetic field and localized in the direction perpendicular to the field. Such density channels can be formed by the density enhancement or depletion and they are called ducts. The primary goal of our research is to find density duct and whistler waves in the data recorded by the Van Allen Probes satellites in the magnetosphere, and to reproduce these data with numerical simulations of time-dependent, two-dimensional electron MHD model. In this paper, we present results from our analysis of the observations performed by the Van Allen Probes satellites on 15 October 2014. Data from the probes show the electric and magnetic fields and plasma density. In this event whistler-mode waves were observed from 01:42 to 01:54 UT inside the localized density enhancement coincided with the flux of energetic electrons. Short time intervals, high concentrated electron density, and electron flux gradient activity make this event very interesting for the investigation. Numerical simulations of the electron MHD model revels reasonable quantitative agreement between numerical results and satellite observations, suggesting that the electromagnetic disturbances recorded by the Van Allen Probes satellites, are the whistler-mode waves indeed.
The imprint of crustal density heterogeneities on seismic wave propagation
NASA Astrophysics Data System (ADS)
Plonka, A.; Fichtner, A.
2015-12-01
We present the results of a set of numerical experiments designed to observe the imprint of three-dimensional density heterogeneities on a seismogram. To compute the full seismic wavefield in a three-dimensional heterogeneous medium, we use numerical wave propagation based on a spectral-element discretization of the seismic wave equation. We consider a 2000 by 1000 km wide and 500 km deep spherical section, with the one-dimensional Earth model PREM, altered so that the crust is 40 km thick and all the parameters in the crust are constant, as a background. Onto the uppermost 40 km of the underlying one-dimensional model we superimpose three-dimensional randomly generated velocity and density heterogeneities of various correlation lengths. We use different random realizations of heterogeneity distribution. We compare the synthetic seismograms for three-dimensional velocity and density structure with three-dimensional velocity structure and one-dimensional density kept as PREM, calculating relative amplitude differences and time shifts as functions of time and frequency. The misfits in time shift and amplitude for different frequency bands, epicentral distances and medium complexities are then stacked into histograms and statistically analysed. We observe strong dependency on frequency of density-related amplitude difference. We also conclude potential sensitivity to distant density structures, and that scattering is essential to observe significant density imprint on a seismogram. The possible density-related bias in velocity and attenuation for regional tomographic models is calculated using mean misfit values for given epicentral distances. Whereas the bias in velocity does not exceed 0.5% of the model value, the density-related change in attenuation may be as big as 71% of the model value for the mean amplitude difference in the highest frequency band. The results suggest that density imprint on a seismogram is not negligible and with further theoretical
Shock-wave-based density down ramp for electron injection
NASA Astrophysics Data System (ADS)
Wang, Chunmei; Li, Ji; Sun, Jun; Luo, Xisheng
2012-02-01
We demonstrate a sharp density transition for electron injection in laser wakefield acceleration through numerical study. This density transition is generated by a detached shock wave induced by a cylinder inserted into a supersonic helium gas flow. In a Mach 1.5 flow, the scale length of the density transition Lgrad can approximately equal to plasma wavelength λp at the shock front, and can be further reduced with an increase of the flow Mach number. A density down ramp with Lgrad≥λp can reduce the phase velocity of the wakefield and lower the energy threshold for the electrons to be trapped. Moreover, the quality of the accelerated beam may be greatly improved by precisely controlling of Lgrad to be one λp. For an even sharper density down ramp with Lgrad≪λp, the oscillating electrons in the plasma wave will up shift their phase when crossing the ramp, therefore a fraction of the electrons are injected into the accelerating field. For this injection mechanism, there is no threshold requirement for the pump laser intensity to reach wave breaking, which is a big advantage as compared with other injection mechanisms.
Observations of ULF wave related equatorial electrojet and density fluctuations
NASA Astrophysics Data System (ADS)
Yizengaw, E.; Zesta, E.; Biouele, C. M.; Moldwin, M. B.; Boudouridis, A.; Damtie, B.; Mebrahtu, A.; Anad, F.; Pfaff, R. F.; Hartinger, M.
2013-10-01
We report on Pc5 wave related electric field and vertical drift velocity oscillations at the equator as observed by ground magnetometers for an extended period on 9 August 2008. We show that the magnetometer-estimated equatorial E×B drift oscillates with the same frequency as ULF Pc5 waves, creating significant ionospheric density fluctuations. We also show ionospheric density fluctuations during the period when we observed ULF wave activity. At the same time, we detect the ULF activity on the ground using ground-based magnetometer data from the African Meridian B-field Education and Research (AMBER) and the South American Meridional B-field Array (SAMBA). From space, we use magnetic field observations from the GOES 12 and the Communication/Navigation Outage and Forecast System (C/NOFS) satellites. Upstream solar wind conditions are provided by the ACE spacecraft. We find that the wave power observed on the ground also occurs in the upstream solar wind and in the magnetosphere. All these observations demonstrate that Pc5 waves with a likely driver in the solar wind can penetrate to the equatorial ionosphere and modulate the equatorial electrodynamics. While no direct drift measurements from equatorial radars exist for the 9 August 2008 event, we used JULIA 150 km radar drift velocities observed on 2 May 2010 and found similar fluctuations with the period of 5-8 min, as a means of an independent confirmation of our magnetometer derived drift dynamics.
Properties of Nonlinear Dynamo Waves
NASA Technical Reports Server (NTRS)
Tobias, S. M.
1997-01-01
Dynamo theory offers the most promising explanation of the generation of the sun's magnetic cycle. Mean field electrodynamics has provided the platform for linear and nonlinear models of solar dynamos. However, the nonlinearities included are (necessarily) arbitrarily imposed in these models. This paper conducts a systematic survey of the role of nonlinearities in the dynamo process, by considering the behaviour of dynamo waves in the nonlinear regime. It is demonstrated that only by considering realistic nonlinearities that are non-local in space and time can modulation of the basic dynamo wave he achieved. Moreover, this modulation is greatest when there is a large separation of timescales provided by including a low magnetic Prandtl number in the equation for the velocity perturbations.
Transverse modulation of the positron beam density by using the laser standing wave
NASA Astrophysics Data System (ADS)
Babaev, A. A.; Dabagov, S. B.
2016-07-01
Recently it was shown that charged particles motion in the field of standing electromagnetic wave can undergo the features similar to the particles channeling in crystals. When a charged particle enters the channels formed by electromagnetic standing waves at a small angle to the node (anti-node) planes its motion represents namely the oscillations between two neighboring planes. The phenomenon is mostly known as channeling in a lattice of the standing waves. Obviously, this effect can be used to handle beams in accelerator physics, more general, for the beam shaping with the specific properties. The advantage of the plane wave channeling is the absence of inelastic scattering that takes place in a crystal. The possibility to re-distribute the current density of particles in the beam by means of the laser standing wave is demonstrated.
Spontaneous K-Complex Density in Slow-Wave Sleep
Zannat, Wassilatul; Pandi-Perumal, Seithikurippu R.; BaHammam, Ahmed S.; Hussain, M. Ejaz
2016-01-01
Purpose To study spontaneous K-complex (KC) densities during slow-wave sleep. The secondary objective was to estimate intra-non-rapid eye movement (NREM) sleep differences in KC density. Materials and Methods It is a retrospective study using EEG data included in polysomnographic records from the archive at the sleep research laboratory of the Centre for Physiotherapy and Rehabilitation Sciences, Jamia Millia Islamia, India. The EEG records of 4459 minutes were used. The study presents a manual identification investigation of KCs in 17 healthy young adult male volunteers (age = 23.82±3.40 years and BMI = 23.42±4.18 kg/m2). Results N3 had a higher KC density than N2 (Z = -2.485, p = 0.013) for all of the probes taken together. Four EEG probes had a higher probe-specific KC density during N3. The inter-probe KC density differed significantly during N2 (χ2 = 67.91, p < .001), N3 (χ2 = 70.62, p < .001) and NREM (χ2 = 68.50, p < .001). The percent distribution of KC decreased uniformly with sleep cycles. Conclusion The inter-probe differences during N3 establish the fronto-central dominance of the KC density regardless of sleep stage. This finding supports one local theory of KC generation. The significantly higher KC density during N3 may imply that the neuro-anatomical origin of slow-wave activity and KC is the same. This temporal alignment with slow-wave activity supports the sleep-promoting function of the KC. PMID:26963714
A gravitational test of wave reinforcement versus fluid density models
NASA Technical Reports Server (NTRS)
Johnson, Jacqueline Umstead
1990-01-01
Spermatozoa, protozoa, and algae form macroscopic patterns somewhat analogous to thermally driven convection cells. These bioconvective patterns have attracted interest in the fluid dynamics community, but whether in all cases these waves were gravity driven was unknown. There are two conflicting theories, one gravity dependent (fluid density model), the other gravity independent (wave reinforcement theory). The primary objectives of the summer faculty fellows were to: (1) assist in sample collection (spermatozoa) and preparation for the KC-135 research airplane experiment; and (2) to collaborate on ground testing of bioconvective variables such as motility, concentration, morphology, etc., in relation to their macroscopic patterns. Results are very briefly given.
Photoinduced Enhancement of the Charge Density Wave Amplitude.
Singer, A; Patel, S K K; Kukreja, R; Uhlíř, V; Wingert, J; Festersen, S; Zhu, D; Glownia, J M; Lemke, H T; Nelson, S; Kozina, M; Rossnagel, K; Bauer, M; Murphy, B M; Magnussen, O M; Fullerton, E E; Shpyrko, O G
2016-07-29
Symmetry breaking and the emergence of order is one of the most fascinating phenomena in condensed matter physics. It leads to a plethora of intriguing ground states found in antiferromagnets, Mott insulators, superconductors, and density-wave systems. Exploiting states of matter far from equilibrium can provide even more striking routes to symmetry-lowered, ordered states. Here, we demonstrate for the case of elemental chromium that moderate ultrafast photoexcitation can transiently enhance the charge-density-wave (CDW) amplitude by up to 30% above its equilibrium value, while strong excitations lead to an oscillating, large-amplitude CDW state that persists above the equilibrium transition temperature. Both effects result from dynamic electron-phonon interactions, providing an efficient mechanism to selectively transform a broad excitation of the electronic order into a well-defined, long-lived coherent lattice vibration. This mechanism may be exploited to transiently enhance order parameters in other systems with coupled degrees of freedom. PMID:27517781
Photoinduced Enhancement of the Charge Density Wave Amplitude
NASA Astrophysics Data System (ADS)
Singer, A.; Patel, S. K. K.; Kukreja, R.; Uhlíř, V.; Wingert, J.; Festersen, S.; Zhu, D.; Glownia, J. M.; Lemke, H. T.; Nelson, S.; Kozina, M.; Rossnagel, K.; Bauer, M.; Murphy, B. M.; Magnussen, O. M.; Fullerton, E. E.; Shpyrko, O. G.
2016-07-01
Symmetry breaking and the emergence of order is one of the most fascinating phenomena in condensed matter physics. It leads to a plethora of intriguing ground states found in antiferromagnets, Mott insulators, superconductors, and density-wave systems. Exploiting states of matter far from equilibrium can provide even more striking routes to symmetry-lowered, ordered states. Here, we demonstrate for the case of elemental chromium that moderate ultrafast photoexcitation can transiently enhance the charge-density-wave (CDW) amplitude by up to 30% above its equilibrium value, while strong excitations lead to an oscillating, large-amplitude CDW state that persists above the equilibrium transition temperature. Both effects result from dynamic electron-phonon interactions, providing an efficient mechanism to selectively transform a broad excitation of the electronic order into a well-defined, long-lived coherent lattice vibration. This mechanism may be exploited to transiently enhance order parameters in other systems with coupled degrees of freedom.
Internal wave pressure, velocity, and energy flux from density perturbations
NASA Astrophysics Data System (ADS)
Allshouse, Michael R.; Lee, Frank M.; Morrison, Philip J.; Swinney, Harry L.
2016-05-01
Determination of energy transport is crucial for understanding the energy budget and fluid circulation in density varying fluids such as the ocean and the atmosphere. However, it is rarely possible to determine the energy flux field J =p u , which requires simultaneous measurements of the pressure and velocity perturbation fields p and u , respectively. We present a method for obtaining the instantaneous J (x ,z ,t ) from density perturbations alone: A Green's function-based calculation yields p ; u is obtained by integrating the continuity equation and the incompressibility condition. We validate our method with results from Navier-Stokes simulations: The Green's function method is applied to the density perturbation field from the simulations and the result for J is found to agree typically to within 1% with J computed directly using p and u from the Navier-Stokes simulation. We also apply the Green's function method to density perturbation data from laboratory schlieren measurements of internal waves in a stratified fluid and the result for J agrees to within 6 % with results from Navier-Stokes simulations. Our method for determining the instantaneous velocity, pressure, and energy flux fields applies to any system described by a linear approximation of the density perturbation field, e.g., to small-amplitude lee waves and propagating vertical modes. The method can be applied using our matlab graphical user interface EnergyFlux.
Wave induced density modification in RF sheaths and close to wave launchers
Van Eester, D.; Lu, Ling-Feng
2015-12-10
With the return to full metal walls - a necessary step towards viable fusion machines - and due to the high power densities of current-day ICRH (Ion Cyclotron Resonance Heating) or RF (radio frequency) antennas, there is ample renewed interest in exploring the reasons for wave-induced sputtering and formation of hot spots. Moreover, there is experimental evidence on various machines that RF waves influence the density profile close to the wave launchers so that waves indirectly influence their own coupling efficiency. The present study presents a return to first principles and describes the wave-particle interaction using a 2-time scale model involving the equation of motion, the continuity equation and the wave equation on each of the time scales. Through the changing density pattern, the fast time scale dynamics is affected by the slow time scale events. In turn, the slow time scale density and flows are modified by the presence of the RF waves through quasilinear terms. Although finite zero order flows are identified, the usual cold plasma dielectric tensor - ignoring such flows - is adopted as a first approximation to describe the wave response to the RF driver. The resulting set of equations is composed of linear and nonlinear equations and is tackled in 1D in the present paper. Whereas the former can be solved using standard numerical techniques, the latter require special handling. At the price of multiple iterations, a simple ’derivative switch-on’ procedure allows to reformulate the nonlinear problem as a sequence of linear problems. Analytical expressions allow a first crude assessment - revealing that the ponderomotive potential plays a role similar to that of the electrostatic potential arising from charge separation - but numerical implementation is required to get a feeling of the full dynamics. A few tentative examples are provided to illustrate the phenomena involved.
Wave induced density modification in RF sheaths and close to wave launchers
NASA Astrophysics Data System (ADS)
Van Eester, D.; Crombé, K.; Lu, Ling-Feng
2015-12-01
With the return to full metal walls - a necessary step towards viable fusion machines - and due to the high power densities of current-day ICRH (Ion Cyclotron Resonance Heating) or RF (radio frequency) antennas, there is ample renewed interest in exploring the reasons for wave-induced sputtering and formation of hot spots. Moreover, there is experimental evidence on various machines that RF waves influence the density profile close to the wave launchers so that waves indirectly influence their own coupling efficiency. The present study presents a return to first principles and describes the wave-particle interaction using a 2-time scale model involving the equation of motion, the continuity equation and the wave equation on each of the time scales. Through the changing density pattern, the fast time scale dynamics is affected by the slow time scale events. In turn, the slow time scale density and flows are modified by the presence of the RF waves through quasilinear terms. Although finite zero order flows are identified, the usual cold plasma dielectric tensor - ignoring such flows - is adopted as a first approximation to describe the wave response to the RF driver. The resulting set of equations is composed of linear and nonlinear equations and is tackled in 1D in the present paper. Whereas the former can be solved using standard numerical techniques, the latter require special handling. At the price of multiple iterations, a simple 'derivative switch-on' procedure allows to reformulate the nonlinear problem as a sequence of linear problems. Analytical expressions allow a first crude assessment - revealing that the ponderomotive potential plays a role similar to that of the electrostatic potential arising from charge separation - but numerical implementation is required to get a feeling of the full dynamics. A few tentative examples are provided to illustrate the phenomena involved.
Kurth, W S; De Pascuale, S; Faden, J B; Kletzing, C A; Hospodarsky, G B; Thaller, S; Wygant, J R
2015-01-01
The twin Van Allen Probe spacecraft, launched in August 2012, carry identical scientific payloads. The Electric and Magnetic Field Instrument Suite and Integrated Science suite includes a plasma wave instrument (Waves) that measures three magnetic and three electric components of plasma waves in the frequency range of 10 Hz to 12 kHz using triaxial search coils and the Electric Fields and Waves triaxial electric field sensors. The Waves instrument also measures a single electric field component of waves in the frequency range of 10 to 500 kHz. A primary objective of the higher-frequency measurements is the determination of the electron density ne at the spacecraft, primarily inferred from the upper hybrid resonance frequency fuh. Considerable work has gone into developing a process and tools for identifying and digitizing the upper hybrid resonance frequency in order to infer the electron density as an essential parameter for interpreting not only the plasma wave data from the mission but also as input to various magnetospheric models. Good progress has been made in developing algorithms to identify fuh and create a data set of electron densities. However, it is often difficult to interpret the plasma wave spectra during active times to identify fuh and accurately determine ne. In some cases, there is no clear signature of the upper hybrid band, and the low-frequency cutoff of the continuum radiation is used. We describe the expected accuracy of ne and issues in the interpretation of the electrostatic wave spectrum. PMID:26167442
Electron Densities Near Io from Galileo Plasma Wave Observations
NASA Technical Reports Server (NTRS)
Gurnett, D. A.; Persoon, A. M.; Kurth, W. S.; Roux, A.; Bolton, S. J.
2001-01-01
This paper presents an overview of electron densities obtained near Io from the Galileo plasma wave instrument during the first four flybys of Io. These flybys were Io, which was a downstream wake pass that occurred on December 7, 1995; I24, which was an upstream pass that occurred on October 11, 1999; I25, which was a south polar pass that occurred on November 26, 1999; and I27, which was an upstream pass that occurred on February 22, 2000. Two methods were used to measure the electron density. The first was based on the frequency of upper hybrid resonance emissions, and the second was based on the low-frequency cutoff of electromagnetic radiation at the electron plasma frequency. For three of the flybys, Io, I25, and I27, large density enhancements were observed near the closest approach to Io. The peak electron densities ranged from 2.1 to 6.8 x 10(exp 4) per cubic centimeters. These densities are consistent with previous radio occultation measurements of Io's ionosphere. No density enhancement was observed during the I24 flyby, most likely because the spacecraft trajectory passed too far upstream to penetrate Io's ionosphere. During two of the flybys, I25 and I27, abrupt step-like changes were observed at the outer boundaries of the region of enhanced electron density. Comparisons with magnetic field models and energetic particle measurements show that the abrupt density steps occur as the spacecraft penetrated the boundary of the Io flux tube, with the region of high plasma density on the inside of the flux tube. Most likely the enhanced electron density within the Io flux tube is associated with magnetic field lines that are frozen to Io by the high conductivity of Io's atmosphere, thereby enhancing the escape of plasma along the magnetic field lines that pass through Io's ionosphere.
Statistical properties of two sine waves in Gaussian noise.
NASA Technical Reports Server (NTRS)
Esposito, R.; Wilson, L. R.
1973-01-01
A detailed study is presented of some statistical properties of a stochastic process that consists of the sum of two sine waves of unknown relative phase and a normal process. Since none of the statistics investigated seem to yield a closed-form expression, all the derivations are cast in a form that is particularly suitable for machine computation. Specifically, results are presented for the probability density function (pdf) of the envelope and the instantaneous value, the moments of these distributions, and the relative cumulative density function (cdf).
Seasonal variation of solitary wave properties in Lake Constance
NASA Astrophysics Data System (ADS)
Preusse, M.; Freistühler, H.; Peeters, F.
2012-04-01
The properties of internal solitary waves (ISWs) depend on the stratification of the water body. In most climatic regions the stratification in lakes and oceans varies during the year, and hence the properties of the ISWs can also be expected to change over the seasons. On the basis of a long-term temperature time series recorded over 6 years, this paper investigates seasonal changes in the characteristic properties of ISWs in Lake Überlingen, a subbasin of Lake Constance. A large number of ISWs with amplitudes ranging from 3 m to 30 m were identified. More than 15% of the leading ISWs of a wave train were associated with density inversions, often indicating shear instabilities or trapped cores. For all waves the propagation depth and the value of a nonlinearity index nlp providing the degree of nonlinearity were determined, propagation depth being the rest height of the isotherm undergoing maximum displacement and nlp the ratio between wave amplitude and propagation depth. The index nlp was found to be a good parameter for predicting the occurrence of inversions. The statistical analysis of the wave properties derived from the observations revealed that the degree of nonlinearity of the ISWs changes with season. Complementary to the statistical analysis, the seasonally averaged ISW properties were compared with wave prototypes obtained numerically from the Dubreil-Jacotin-Long (DJL) and the stratified Korteweg-deVries (KdV) models. The simulations indicate that the typical stratification and its seasonal variation are responsible for the degree and the seasonality of nonlinearity of the ISWs.
Excitations of the spin-density wave in pure chromium
Werner, S.A.; Shirane, G.; Fincher, C.R.; Grier, B.H.
1981-01-01
This paper summarizes recent investigations of the magnetic excitations of the spin density wave (SDW) in pure Cr in both the low temperature longitudinally polarized phase (T < 122K) and in the higher temperature transversely polarized phase (122K < T < 312K). In both phases spin wave modes of very high velocity are observed originating from the incommensurate Bragg points. In the transversely polarized SDW phase new additional excitations are observed, centered in reciprocal space at the (1,0,0) commensurate point. These excitations are not affected by a magnetic field. Inelastic scattering in the paramagnetic phase above the Neel point (312K) is observed in a reasonably well localized region of reciprocal space near (1,0,0) indicating that there are spin-spin correlations extending over many bcc unit cells and persisting to temperatures at least as high as 1.7 T/sub N/.
Unstable waves of jet flows with density inhomogeneity
NASA Astrophysics Data System (ADS)
Fung, Yee T.
1988-09-01
The problem to be considered concerns linear unstable waves of axisymmetric jet flows in the presence of density inhomogeneities. Such flow phenomena occur when a jet is discharged into a stratified medium, e.g., pollutants and industrial waste discharged into the environment, cooling water discharged from power plants into rivers and lakes, and flow patterns generated by vehicles moving in the ocean. Investigating the instability characteristics of the flow can mean controlling the flow-patterns, for example, produced by vehicles moving in the ocean. As in the case of two-dimensional shear flows, axisymmetric jet flows may possess amplified waves due to the Kelvin-Helmhholtz mechanism except that the formulation for jet flows is complicated by the absence of the Squire transformation and the consideration of cylindrical geometry.
Resonant excitation of density waves in Saturn's rings
NASA Astrophysics Data System (ADS)
Griv, Evgeny
1996-06-01
The dynamics of regions in the Saturnian ring system with rare collisions between particles, that is, Ω 2≫ν c2, where Ω is the orbital angular frequency and νc the collision frequency, is considered. According to observations, such low optical depth regions can be found in the C ring, the inner portions of the B ring and the A ring. Kinetic theory with the Vlasov and Poisson equations is used to obtain the eigen-frequencies of oscillations propagating in the plane of the system. In the considered case of rare collisions the resulting kinetic equation for the perturbed distribution function can be solved by successive approximations, neglecting the effect of binary particle collisions in the zeroth-order approximation. An oscillating instability of the kinetic type is discussed. This instability of a particulate disk is similar to the magneto-drift instability first discovered by Krall and Rosenbluth ( Physics Fluids6, 254-265, 1963) in a nonuniform magnetic plasma, and belongs to the class of microinstabilities of an inhomogeneous plasma. The cause of the oscillating instability in Saturn's rings is a resonant interaction of drifting particles with nonaxisymmetric Jeans-stable waves at the corotation. The waves that may be produced by the corotation-resonance interaction represent non-radial normal modes of the gravitationally stable disk modified by a particle drift. It is shown that density waves are effectively excited at this resonance: the growth rate of the mode of maximum instability is large, Im ω∗˜Ω. The resonant excitation of density waves investigated in the present paper may be proposed as the cause of the irregular, small-scale ˜ 100 m structure in regions of low optical depth in Saturn's rings. It is suggested that Cassini spacecraft high-resolution images of low optical depth regions will show this kind of structure.
Metal-insulator transition by holographic charge density waves.
Ling, Yi; Niu, Chao; Wu, Jian-Pin; Xian, Zhuo-Yu; Zhang, Hongbao
2014-08-29
We construct a gravity dual for charge density waves (CDWs) in which the translational symmetry along one spatial direction is spontaneously broken. Our linear perturbation calculation on the gravity side produces the frequency dependence of the optical conductivity, which exhibits the two familiar features of CDWs, namely, the pinned collective mode and gapped single-particle excitation. These two features indicate that our gravity dual also provides a new mechanism to implement the metal to insulator phase transition by CDWs, which is further confirmed by the fact that dc conductivity decreases with the decreased temperature below the critical temperature. PMID:25215974
Multiple charge density wave transitions in Gd2Te5
Shin, K.Y.; Ru, N.; Condron, C.L.; Wu, Y.Q.; Kramer, M.J.; Toney, M.F.; Fisher, I.R.; /Stanford U., Geballe Lab. /Stanford U., Appl. Phys. Dept.
2010-02-15
Diffraction measurements performed via transmission electron microscopy and high resolution X-ray scattering reveal two distinct charge density wave transitions in Gd{sub 2}Te{sub 5} at T{sub c1} = 410(3) and T{sub c2} = 532(3) K, associated with the on-axis incommensurate lattice modulation and off-axis commensurate lattice modulation respectively. Analysis of the temperature dependence of the order parameters indicates a non-vanishing coupling between these two distinct CDW states.
Fast electronic resistance switching involving hidden charge density wave states
Vaskivskyi, I.; Mihailovic, I. A.; Brazovskii, S.; Gospodaric, J.; Mertelj, T.; Svetin, D.; Sutar, P.; Mihailovic, D.
2016-01-01
The functionality of computer memory elements is currently based on multi-stability, driven either by locally manipulating the density of electrons in transistors or by switching magnetic or ferroelectric order. Another possibility is switching between metallic and insulating phases by the motion of ions, but their speed is limited by slow nucleation and inhomogeneous percolative growth. Here we demonstrate fast resistance switching in a charge density wave system caused by pulsed current injection. As a charge pulse travels through the material, it converts a commensurately ordered polaronic Mott insulating state in 1T–TaS2 to a metastable electronic state with textured domain walls, accompanied with a conversion of polarons to band states, and concurrent rapid switching from an insulator to a metal. The large resistance change, high switching speed (30 ps) and ultralow energy per bit opens the way to new concepts in non-volatile memory devices manipulating all-electronic states. PMID:27181483
Fast electronic resistance switching involving hidden charge density wave states
NASA Astrophysics Data System (ADS)
Vaskivskyi, I.; Mihailovic, I. A.; Brazovskii, S.; Gospodaric, J.; Mertelj, T.; Svetin, D.; Sutar, P.; Mihailovic, D.
2016-05-01
The functionality of computer memory elements is currently based on multi-stability, driven either by locally manipulating the density of electrons in transistors or by switching magnetic or ferroelectric order. Another possibility is switching between metallic and insulating phases by the motion of ions, but their speed is limited by slow nucleation and inhomogeneous percolative growth. Here we demonstrate fast resistance switching in a charge density wave system caused by pulsed current injection. As a charge pulse travels through the material, it converts a commensurately ordered polaronic Mott insulating state in 1T-TaS2 to a metastable electronic state with textured domain walls, accompanied with a conversion of polarons to band states, and concurrent rapid switching from an insulator to a metal. The large resistance change, high switching speed (30 ps) and ultralow energy per bit opens the way to new concepts in non-volatile memory devices manipulating all-electronic states.
Fast electronic resistance switching involving hidden charge density wave states.
Vaskivskyi, I; Mihailovic, I A; Brazovskii, S; Gospodaric, J; Mertelj, T; Svetin, D; Sutar, P; Mihailovic, D
2016-01-01
The functionality of computer memory elements is currently based on multi-stability, driven either by locally manipulating the density of electrons in transistors or by switching magnetic or ferroelectric order. Another possibility is switching between metallic and insulating phases by the motion of ions, but their speed is limited by slow nucleation and inhomogeneous percolative growth. Here we demonstrate fast resistance switching in a charge density wave system caused by pulsed current injection. As a charge pulse travels through the material, it converts a commensurately ordered polaronic Mott insulating state in 1T-TaS2 to a metastable electronic state with textured domain walls, accompanied with a conversion of polarons to band states, and concurrent rapid switching from an insulator to a metal. The large resistance change, high switching speed (30 ps) and ultralow energy per bit opens the way to new concepts in non-volatile memory devices manipulating all-electronic states. PMID:27181483
Asaduzzaman, M; Mamun, A A
2012-07-01
A rigorous theoretical investigation has been made of the effects of nonthermal ions and polarization force (which arises due to the dust density inhomogeneity) on the propagation of dust-acoustic (DA) waves in a density-varying unmagnetized dusty plasma (consisting of nonthermal ions, Maxwellian electrons, and negatively charged mobile dust) by the normal mode analysis. It has been shown that the dispersion properties of the DA waves are significantly modified by the presence of nonthermal ions and polarization force. It has been also found that the phase speed of the DA waves, as well as the dust density perturbation, increases (decreases) with the increase of nonthermal ions (polarization force), and that the potential associated with the DA waves decreases with the increase of the equilibrium dust number density. The implications of our results in the specific situation of space environments (dust-ion plasma situation) are also briefly discussed. PMID:23005552
Probability Density Function for Waves Propagating in a Straight PEC Rough Wall Tunnel
Pao, H
2004-11-08
The probability density function for wave propagating in a straight perfect electrical conductor (PEC) rough wall tunnel is deduced from the mathematical models of the random electromagnetic fields. The field propagating in caves or tunnels is a complex-valued Gaussian random processing by the Central Limit Theorem. The probability density function for single modal field amplitude in such structure is Ricean. Since both expected value and standard deviation of this field depend only on radial position, the probability density function, which gives what is the power distribution, is a radially dependent function. The radio channel places fundamental limitations on the performance of wireless communication systems in tunnels and caves. The transmission path between the transmitter and receiver can vary from a simple direct line of sight to one that is severely obstructed by rough walls and corners. Unlike wired channels that are stationary and predictable, radio channels can be extremely random and difficult to analyze. In fact, modeling the radio channel has historically been one of the more challenging parts of any radio system design; this is often done using statistical methods. In this contribution, we present the most important statistic property, the field probability density function, of wave propagating in a straight PEC rough wall tunnel. This work only studies the simplest case--PEC boundary which is not the real world but the methods and conclusions developed herein are applicable to real world problems which the boundary is dielectric. The mechanisms behind electromagnetic wave propagation in caves or tunnels are diverse, but can generally be attributed to reflection, diffraction, and scattering. Because of the multiple reflections from rough walls, the electromagnetic waves travel along different paths of varying lengths. The interactions between these waves cause multipath fading at any location, and the strengths of the waves decrease as the distance
Shock-wave properties of brittle solids
Grady, D.E.
1995-10-01
Extensive experimental investigation in the form of large-amplitude, nonlinear wave-profile measurements which manifest the shock strength and equation-of-state properties of brittle solids has been performed. Brittle materials for which a base of dynamic property data is available include Al{sub 2}O{sub 3}, AlN, B{sub 4}C, CaCO{sub 3}, SiC, Si{sub 3}N{sub 4}, SiO{sub 2} (quartz and glass), TiB{sub 2}, WC and ZrO{sub 2}. Planar impact methods and velocity interferometry diagnostics have been used exclusively to provide the high-resolution shock-profile data. These wave-profile data are providing engineering dynamic strength and equation-of-state properties as well as controlled, shock-induced motion histories for the validation of theoretical and Computational models. Of equal importance, such data are providing a window into the physics of a newly emerging understanding of the compression and deformation behavior of high-strength brittle solids. When considered along with a rich assortment of strength and deformation data in the literature, a systematic assessment of this shock-wave data lends strong support for failure waves and concomitant high-confinement dilatancy as a general mechanism of inelastic deformation in the shock compression of ceramics. Phase transformation in selected brittle solids appears to be a critical state phenomenon strongly controlled by kinetics. The risetime and structure of deformation shock waves in brittle solids are controlled by viscous effects which at present are still poorly understood. The shockwave data also suggest that both crystalline plasticity and brittle fracture may play important and interconnected roles in the dynamic failure process.
Classification of charge density waves based on their nature
Zhu, Xuetao; Cao, Yanwei; Zhang, Jiandi; Plummer, E. W.; Guo, Jiandong
2015-01-01
The concept of a charge density wave (CDW) permeates much of condensed matter physics and chemistry. CDWs have their origin rooted in the instability of a one-dimensional system described by Peierls. The extension of this concept to reduced dimensional systems has led to the concept of Fermi surface nesting (FSN), which dictates the wave vector (q→CDW) of the CDW and the corresponding lattice distortion. The idea is that segments of the Fermi contours are connected by q→CDW, resulting in the effective screening of phonons inducing Kohn anomalies in their dispersion at q→CDW, driving a lattice restructuring at low temperatures. There is growing theoretical and experimental evidence that this picture fails in many real systems and in fact it is the momentum dependence of the electron–phonon coupling (EPC) matrix element that determines the characteristic of the CDW phase. Based on the published results for the prototypical CDW system 2H-NbSe2, we show how well the q→-dependent EPC matrix element, but not the FSN, can describe the origin of the CDW. We further demonstrate a procedure of combing electronic band and phonon measurements to extract the EPC matrix element, allowing the electronic states involved in the EPC to be identified. Thus, we show that a large EPC does not necessarily induce the CDW phase, with Bi2Sr2CaCu2O8+δ as the example, and the charge-ordered phenomena observed in various cuprates are not driven by FSN or EPC. To experimentally resolve the microscopic picture of EPC will lead to a fundamental change in the way we think about, write about, and classify charge density waves. PMID:25646420
NASA Astrophysics Data System (ADS)
Fritts, David C.; Isler, Joseph R.; Hecht, James H.; Walterscheid, Richard L.; Andreassen, Øyvind
Measurements of atmospheric structure and dynamics near the mesopause were performed using a sodium lidar, an MF radar, and a nightglow CCD camera during the CORN campaign performed in central Illinois during September 1992. The major features of the observed structure on September 27/28 include a low-frequency, large-scale wave accounting for persistent overturning of the temperature and sodium density fields, superposed higher-frequency motions, small-scale transient ripples in the nightglow images suggestive of instability structures, and large-scale wind shear near the height of apparent instability. We describe four simulations of wave breaking with a three-dimensional model designed to assist in the interpretation of these observations. Two simulations address the instability of a low-frequency wave in a background shear flow with and without higher-frequency modulation. These show higher-frequency motions to be important in assigning the spatial and temporal scales of instability structures. Two other simulations examine the instabilities accompanying a convectively unstable inertia-gravity wave with and without higher-frequency modulation without mean shear. These show the instability structure to remain aligned in the direction of wave propagation, with only weak influences by the high-frequency motion. Our results suggest that instability due to a superposition of waves accounts best for the nightglow features observed during the CORN campaign and that streamwise convective instabilities observed due to wave breaking at higher intrinsic frequencies continue to dominate instability structure for internal waves for which inertial effects are important.
Pressure dependence of the charge-density-wave gap in rare-earth tritellurides.
Sacchetti, A; Arcangeletti, E; Perucchi, A; Baldassarre, L; Postorino, P; Lupi, S; Ru, N; Fisher, I R; Degiorgi, L
2007-01-12
We investigate the pressure dependence of the optical properties of CeTe3, which exhibits an incommensurate charge-density-wave (CDW) state already at 300 K. Our data are collected in the midinfrared spectral range at room temperature and at pressures between 0 and 9 GPa. The energy for the single particle excitation across the CDW gap decreases upon increasing the applied pressure, similarly to the chemical pressure by rare-earth substitution. The broadening of the bands upon lattice compression removes the perfect nesting condition of the Fermi surface and therefore diminishes the impact of the CDW transition on the electronic properties of RTe3. PMID:17358625
Self-detection of mechanical oscillations of charge-density wave conductors
NASA Astrophysics Data System (ADS)
Pokrovskii, V. Ya.; Nikitin, M. V.; Zybtsev, S. G.
2015-03-01
Heterodyne mixing technique with frequency modulation is applied for detection of torsional resonances of whiskers of orthorhombic TaS3-a typical quasi one-dimensional conductor with charge-density wave (CDW). In contrast to the previous applications of this technique, both actuation (the torque) and detection (torsional modulation of current) are based on the intrinsic properties of the CDW systems and do not require positioning of the sample in vicinity of a gating electrode. The technique allows studies of electromechanical and elastic properties of the CDW systems at the MHz range at least.
The fine-scale density wave structure of Saturn's rings
NASA Astrophysics Data System (ADS)
Griv, E.; Gedalin, M.
2003-04-01
A self-consistent system of the Boltzmann and the Poisson equations is used to study the dynamical evolution of Saturn's main A, B, C rings composed of discrete mutually gravitating particles. The simplified case of rare collisions between identical particles, when the collision frequency is smaller than the orbital frequency, is examined by exploring in the Boltzmann equation a Krook model integral of collisions. Equations describing the quasilinear (or weakly nonlinear) stage of Jeans instability of small gravity perturbations in Saturn's rings are derived and solved analytically. The theory, as applied to Saturn's rings, predicts for several features, such as numerous irregular Jeans-unstable density wakes, with size and spacing between them of the order of 2pi h <= 100 m, where h is the typical thickness of the system. The interaction of particles with these almost aperiodically growing gravity perturbations increases both the radial spread of the disk and random velocities of particles in a very short time scale of only 2-3 disk orbital revolutions. The latter leads to an eventual stabilization of the system, unless some effective ``cooling" mechanism exists, reducing the magnitude of the relative velocity of particles. It is suggested that inelastic (dissipative) interparticle impacts provide such a cooling mechanism, leading to the recurrent density waves activity. We predict that forthcoming in 2004 Cassini spacecraft high-resolution images will reveal this fine-scale recurrent ˜ 100 m or even less spiral density wave structure in low and moderately high optical depth regions (τ <= 1, where τ is the normal optical depth) of Saturn's main rings. Acknowledgements: Partial support for this work was provided by the Israel Science Foundation and the Israeli Ministry of Immigrant Absorption.
Properties of the cosmological density distribution function
NASA Astrophysics Data System (ADS)
Bernardeau, Francis; Kofman, Lev
1995-04-01
The properties of the probability distribution function (PDF) of the cosmological continuous density field are studied. We focus our analysis on the quasi-linear regime where various calculations, based on dynamically motivated methods, have been presented: either by using the Zel'dovich approximation (ZA) or by using the perturbation theory to evaluate the behavior of the moments of the distribution function. We show how these two approaches are related to each other and that they can be used in a complementary way. For that respect, the one-dimensional dynamics, where the ZA is exact solution, has first been used as a testing ground. In particular, we show that, when the density PDF obtained with the ZA is regularized, its various moments exhibit the behavior expected by the perturbation theory applied to the ZA. We show that ZA approach can be used for arbitrary initial conditions (not only Gaussian) and that the nonlinear evolution of the moments can be obtained. The perturbation theory can be used for the exact dynamics. We take into account the final filtering of the density field both for ZA and perturbation theory. Applying these techniques, we got the generating function of the moments for the one-dimensional dynamics, the three-dimensional ZA, with and without smoothing effects. We also suggest methods to build PDFs. One is based on the Laplace inverse transform of the moment generating function. The other, the Edgeworth expansion, is obtained when the previous generating function is truncated at a given order and allows evaluation of the PDF out of limited number of moments. It provides insight on the relationship between the moments and the shape of the density PDF. In particular, it provides an alternative method to evaluate the skewness and kurtosis by measuring the PDF around its maximum. Eventually, results obtained from a numerical simulation with cold dark matter initial conditions have been used to validate the accuracy of the considered
NASA Astrophysics Data System (ADS)
Kiełczyński, P.; Szalewski, M.; Balcerzak, A.
2014-07-01
Simultaneous determination of the viscosity and density of liquids is of great importance in the monitoring of technological processes in the chemical, petroleum, and pharmaceutical industry, as well as in geophysics. In this paper, the authors present the application of Love waves for simultaneous inverse determination of the viscosity and density of liquids. The inversion procedure is based on measurements of the dispersion curves of phase velocity and attenuation of ultrasonic Love waves. The direct problem of the Love wave propagation in a layered waveguide covered by a viscous liquid was formulated and solved. Love waves propagate in an elastic layered waveguide covered on its surface with a viscous (Newtonian) liquid. The inverse problem is formulated as an optimization problem with appropriately constructed objective function that depends on the material properties of an elastic waveguide of the Love wave, material parameters of a liquid (i.e., viscosity and density), and the experimental data. The results of numerical calculations show that Love waves can be efficiently applied to determine simultaneously the physical properties of liquids (i.e., viscosity and density). Sensors based on this method can be very attractive for industrial applications to monitor on-line the parameters (density and viscosity) of process liquid during the course of technological processes, e.g., in polymer industry.
High density operation with Lower Hybrid waves in FTU tokamak
NASA Astrophysics Data System (ADS)
Pericoli Ridolfini, V.; Mirizzi, F.; Panaccione, L.; Podda, S.
2001-10-01
Since April 2001 the lower hybrid (LH) radiofrequency system in FTU (6 gyrotrons @ f=8 GHz) can deliver to the plasma about 2 MW through two equal launchers with a reflection coefficient = 10%. This value is close to the target value of 2.2 MW (net power density of 6.2 kW/cm2 on the waveguides mouth) which could be reached after further conditioning of the grill and of the transmission lines. In high density plasmas (line density *1*1020 m-3), high magnetic field (BT=7.2 T), with PLH=2 MW we drive about 75% of the total current (Ip=500 kA) and stabilise fully the sawteeth activity. The central electron temperature Te0 increases from 1.6 to 3.3 keV (steady), and the neutron rate by about 10 times. Analysis of these pulses with effective electronic heating will be presented. In post-pellet plasmas ( *6*1020 m-3), good coupling of the LH is achieved with the launcher almost flush to the walls, due to the very dense scrape off-layer. The perturbation here induced by the pellet imposes a delay to the LH of only 20 ms. The exact location of the launcher is critical in these regimes, because the high N|| (parallel index of refraction) requested (N||>2.3) for a good penetration of the waves makes more problematic a good coupling all along the poloidal extension of the grill.
Lifshitz transition in two-dimensional spin density wave models.
Lin, J.; Materials Science Division
2010-11-09
We argue that both pocket-disappearing and neck-disrupting types of Lifshitz transitions can be realized in two-dimensional spin-density wave models for underdoped cuprates, and study both types of transitions with impurity scattering treated in the self-consistent Born approximation. We first solve for the electron self-energy from the self-consistent equation, and then study the low-temperature electrical conductivity and thermopower. Close to the Lifshitz transition, the thermopower is strongly enhanced. For the pocket-disappearing type, it has a sharp peak while for the neck-disrupting type, it changes sign at the transition, with its absolute value peaked on both sides of the transition. We discuss possible applications to underdoped cuprates.
Evidence against a charge density wave on Bi(111)
Kim, T. K.; Wells, J.; Kirkegaard, C.; Li, Z.; Hoffmann, S. V.; Gayone, J. E.; Fernandez-Torrente, I.; Häberle, P.; Pascual, J. I.; Moore, K. T.; et al
2005-08-18
The Bi(111) surface was studied by scanning tunneling microscopy (STM), transmission electron microscopy (TEM) and angle-resolved photoemission (ARPES) in order to verify the existence of a recently proposed surface charge density wave (CDW). The STM and TEM results to not support a CDW scenario at low temperatures. Thus the quasiparticle interference pattern observed in STM confirms the spin-orbit split character of the surface states which prevents the formation of a CDW, even in the case of good nesting. The dispersion of the electronic states observed with ARPES agrees well with earlier findings. In particular, the Fermi contour of the electronmore » pocket at the centre of the surface Brillouin zone is found to have a hexagonal shape. However, no gap opening or other signatures of a CDW phase transition can be found in the temperature-dependent data.« less
Charge density waves in strongly correlated electron systems
NASA Astrophysics Data System (ADS)
Chen, Chih-Wei; Choe, Jesse; Morosan, E.
2016-08-01
Strong electron correlations are at the heart of many physical phenomena of current interest to the condensed matter community. Here we present a survey of the mechanisms underlying such correlations in charge density wave (CDW) systems, including the current theoretical understanding and experimental evidence for CDW transitions. The focus is on emergent phenomena that result as CDWs interact with other charge or spin states, such as magnetism and superconductivity. In addition to reviewing the CDW mechanisms in 1D, 2D, and 3D systems, we pay particular attention to the prevalence of this state in two particular classes of compounds, the high temperature superconductors (cuprates) and the layered transition metal dichalcogenides. The possibilities for quantum criticality resulting from the competition between magnetic fluctuations and electronic instabilities (CDW, unconventional superconductivity) are also discussed.
Evidence against a charge density wave on Bi(111)
Kim, T. K.; Wells, J.; Kirkegaard, C.; Li, Z.; Hoffmann, S. V.; Gayone, J. E.; Fernandez-Torrente, I.; Häberle, P.; Pascual, J. I.; Moore, K. T.; Schwartz, A. J.; He, H.; Spence, J. C. H.; Downing, K. H.; Lazar, S.; Tichelaar, F. D.; Borisenko, S. V.; Knupfer, M.; Hofmann, Ph.
2005-08-18
The Bi(111) surface was studied by scanning tunneling microscopy (STM), transmission electron microscopy (TEM) and angle-resolved photoemission (ARPES) in order to verify the existence of a recently proposed surface charge density wave (CDW). The STM and TEM results to not support a CDW scenario at low temperatures. Thus the quasiparticle interference pattern observed in STM confirms the spin-orbit split character of the surface states which prevents the formation of a CDW, even in the case of good nesting. The dispersion of the electronic states observed with ARPES agrees well with earlier findings. In particular, the Fermi contour of the electron pocket at the centre of the surface Brillouin zone is found to have a hexagonal shape. However, no gap opening or other signatures of a CDW phase transition can be found in the temperature-dependent data.
Charge density waves in strongly correlated electron systems.
Chen, Chih-Wei; Choe, Jesse; Morosan, E
2016-08-01
Strong electron correlations are at the heart of many physical phenomena of current interest to the condensed matter community. Here we present a survey of the mechanisms underlying such correlations in charge density wave (CDW) systems, including the current theoretical understanding and experimental evidence for CDW transitions. The focus is on emergent phenomena that result as CDWs interact with other charge or spin states, such as magnetism and superconductivity. In addition to reviewing the CDW mechanisms in 1D, 2D, and 3D systems, we pay particular attention to the prevalence of this state in two particular classes of compounds, the high temperature superconductors (cuprates) and the layered transition metal dichalcogenides. The possibilities for quantum criticality resulting from the competition between magnetic fluctuations and electronic instabilities (CDW, unconventional superconductivity) are also discussed. PMID:27376547
Density waves in the solar nebula - Differential Lindblad torque
NASA Technical Reports Server (NTRS)
Ward, W. R.
1986-01-01
The differential torque exerted by Lindblad resonances on a perturbing object embedded in a two-dimensional nonself-gravitating disk with density, pressure and sound speed gradients is quantified. First-order corrections are made to account for Keplerian rotation and the presence of the gradients. The total torque is calculated by summing over all resonances in the absence of local wave damping. When applied to the primordial solar nebula disk, the calculations show that disks that cool with increasing heliocentric distance will cause decay of the orbit of the perturbing object. Conditions in which the perturber will escape orbit delay are also described. The characteristic drift time will be no greater than the stochastic accretion time scales. Implications of the calculations for planetary formation are discussed.
Evidence against a charge density wave on Bi(111)
Kim, T.K.; Wells, J.; Kirkegaard, C.; Li, Z.; Hoffmann, S.V.; Gayone, J.E.; Fernancez-Torrente, I.; Haberle, P.; Pascual, J.I.; Moore,K.T.; Schwartz, A.J.; He, H.; Spence, J.C.H.; Downing, K.H.; Lazar, S.; Tichelaar, F.D.; Borisenko, S.V.; Knupfer, M.; Hofmann, Ph.
2005-05-01
The Bi(111) surface was studied by scanning tunneling microscopy (STM), transmission electron microscopy (TEM) and angle-resolved photoemission (ARPES) in order to verify the existence of a recently proposed surface charge density wave (CDW) [Ch. R. Ast and H. Hoechst Phys. Rev. Lett. 90, 016403 (2003)]. The STM and TEM results to not support a CDW scenario at low temperatures. Furthermore, the quasiparticle interference pattern observed in STM confirms the spin-orbit split character of the surface states which prevents the formation of a CDW, even in the case of good nesting. The dispersion of the electronic states observed with ARPES agrees well with earlier findings. In particular, the Fermi contour of the electron pocket at the centre of the surface Brillouin zone is found to have a hexagonal shape. However, no gap opening or other signatures of a CDW phase transition can be found in the temperature-dependent data.
Theory of charge-density-wave non-contact nanofriction
NASA Astrophysics Data System (ADS)
Tosatti, Erio; Pellegrini, Franco; Santoro, Giuseppe E.
2014-03-01
Bulk dissipation caused by charge-density-wave (CDW) voltage-induced depinning and sliding is a classic subject. We present a local, nanoscale mechanism describing the occurrence of distance-dependent dissipation in the dynamics of an atomic force microscope tip oscillating over the surface of a CDW material. A mechanical tip hysteresis is predicted in correspondence to localized 2 slips of the CDW phase, giving rise to large tip dissipation peaks at selected distances. Results of static and dynamic numerical simulations of the tip-surface interaction are believed to be relevant to recent experiments on the layer compound NbSe . Supported by SNF Contract CRSII2136287/1 and by ERC Advanced Grant 320796 - MODPHYSFRICT.
NASA Astrophysics Data System (ADS)
Pasmanik, Dmitry; Demekhov, Andrei
We study the propagation of VLF waves in the Earth's ionosphere and magnetosphere in the presence of large-scale artificial plasma inhomogeneities which can be created by HF heating facilities like HAARP and ``Sura''. A region with enhanced cold plasma density can be formed due to the action of HF heating. This region is extended along geomagnetic field (up to altitudes of several thousand km) and has rather small size across magnetic field (about 1 degree). The geometric-optical approximation is used to study wave propagation. The plasma density and ion composition are calculated with the use of SAMI2 model, which was modified to take the effect of HF heating into account. We calculate ray trajectories of waves with different initial frequency and wave-normal angles and originating at altitudes of about 100 km in the region near the heating area. The source of such waves could be the lightning discharges, modulated HF heating of the ionosphere, or VLF transmitters. Variation of the wave amplitude along the ray trajectories due to refraction is considered and spatial distribution of wave intensity in the magnetosphere is analyzed. We show that the presence of such a density disturbances can lead to significant changes of wave propagation trajectories, in particular, to efficient guiding of VLF waves in this region. This can result in a drastic increase of the VLF-wave intensity in the density duct. The dependence of wave propagation properties on parameters of heating facility operation regime is considered. We study the variation of the spatial distribution of VLF wave intensity related to the slow evolution of the artificial inhomogeneity during the heating.
NASA Astrophysics Data System (ADS)
Xing, Guangchi; Niu, Fenglin; Chen, Min; Yang, Yingjie
2016-05-01
Surface wave tomography routinely uses empirically scaled density model in the inversion of dispersion curves for shear wave speeds of the crust and uppermost mantle. An improperly selected empirical scaling relationship between density and shear wave speed can lead to unrealistic density models beneath certain tectonic formations such as sedimentary basins. Taking the Sichuan basin east to the Tibetan plateau as an example, we investigate the differences between density profiles calculated from four scaling methods and their effects on Rayleigh wave phase velocities. Analytical equations for 1-D layered models and adjoint tomography for 3-D models are used to examine the trade-off between density and S-wave velocity structures at different depth ranges. We demonstrate that shallow density structure can significantly influence phase velocities at short periods, and thereby affect the shear wave speed inversion from phase velocity data. In particular, a deviation of 25 per cent in the initial density model can introduce an error up to 5 per cent in the inverted shear velocity at middle and lower crustal depths. Therefore one must pay enough attention in choosing a proper velocity-density scaling relationship in constructing initial density model in Rayleigh wave inversion for crustal shear velocity structure.
Imaging and Spectroscopy of Tissue-Like Phantoms Using Photon Density Waves: Theory and Experiments.
NASA Astrophysics Data System (ADS)
Fishkin, Joshua Ben
The determination of the optical properties of turbid biological media is of primary importance in several areas of medicine and biotechnology. In particular, the quantitative determination and spatial localization of the optical scattering and absorbing properties of biological tissue would allow for the non-invasive and non-ionizing imaging of tissue structure and the monitoring of physiology. Until recently, such characterization of thick, highly scattering biological tissues using visible and near infrared light has been thwarted because of the inability to determine the absolute optical properties of thick tissues. This thesis presents the development of the concept, physical model, and experimental study of diffuse photon density waves in thick turbid media. The goal of this work is to determine the applicability of photon density waves to the optical tomography and spectroscopy of thick, multiply scattering media. Toward this end, analytic expressions based on the diffusion approximation to the Boltzmann transport equation are derived for the case of an isotropically emitting, sinusoidally intensity-modulated point source of light immersed in an infinite, macroscopically uniform, multiply scattering medium. These frequency-domain expressions are given in terms of the optical properties of the medium, and they predict that the photon density propagates outward from the light source as a spherical wave of constant phase velocity. Experiments are performed which support the validity of these frequency-domain expressions, and provide a basis for the understanding of photon transport in turbid media containing absorbing and/or reflecting objects. Further experiments demonstrate the feasibility of using frequency -domain data in conjunction with a frequency-domain diffusion model to determine the absolute optical parameters of thick, multiply scattering media.
Spin and charge density waves in the Lieb lattice
NASA Astrophysics Data System (ADS)
Gouveia, J. D.; Dias, R. G.
2016-05-01
We study the mean-field phase diagram of the two-dimensional (2D) Hubbard model in the Lieb lattice allowing for spin and charge density waves. Previous studies of this diagram have shown that the mean-field magnetization surprisingly deviates from the value predicted by Lieb's theorem [1] as the on-site repulsive Coulomb interaction (U) becomes smaller [2]. Here, we show that in order for Lieb's theorem to be satisfied, a more complex mean-field approach should be followed in the case of bipartite lattices or other lattices whose unit cells contain more than two types of atoms. In the case of the Lieb lattice, we show that, by allowing the system to modulate the magnetization and charge density between sublattices, the difference in the absolute values of the magnetization of the sublattices, mLieb, at half-filling, saturates at the exact value 1/2 for any value of U, as predicted by Lieb. Additionally, Lieb's relation, mLieb = 1 / 2, is verified approximately for large U, in the n ∈ [ 2 / 3 , 4 / 3 ] range. This range includes not only the ferromagnetic region of the phase diagram of the Lieb lattice (see Ref. [2]), but also the adjacent spiral regions. In fact, in this lattice, below or at half-filling, mLieb is simply the filling of the quasi-flat bands in the mean-field energy dispersion both for large and small U.
Adiabatic corrections to density functional theory energies and wave functions.
Mohallem, José R; Coura, Thiago de O; Diniz, Leonardo G; de Castro, Gustavo; Assafrão, Denise; Heine, Thomas
2008-09-25
The adiabatic finite-nuclear-mass-correction (FNMC) to the electronic energies and wave functions of atoms and molecules is formulated for density-functional theory and implemented in the deMon code. The approach is tested for a series of local and gradient corrected density functionals, using MP2 results and diagonal-Born-Oppenheimer corrections from the literature for comparison. In the evaluation of absolute energy corrections of nonorganic molecules the LDA PZ81 functional works surprisingly better than the others. For organic molecules the GGA BLYP functional has the best performance. FNMC with GGA functionals, mainly BLYP, show a good performance in the evaluation of relative corrections, except for nonorganic molecules containing H atoms. The PW86 functional stands out with the best evaluation of the barrier of linearity of H2O and the isotopic dipole moment of HDO. In general, DFT functionals display an accuracy superior than the common belief and because the corrections are based on a change of the electronic kinetic energy they are here ranked in a new appropriate way. The approach is applied to obtain the adiabatic correction for full atomization of alcanes C(n)H(2n+2), n = 4-10. The barrier of 1 mHartree is approached for adiabatic corrections, justifying its insertion into DFT. PMID:18537228
Shock-wave properties of soda-lime glass
Grady, D.E.; Chhabildas, L.C.
1996-11-01
Planar impact experiments and wave profile measurements provided single and double shock equation of state data to 30 GPa. Both compression wave wave profile structure and release wave data were used to infer time-dependent strength and equation of state properties for soda-lime glass.
Averill, Frank; Painter, Gayle S
2006-01-01
Describing materials properties and behavior over increasing scales of dimension and complexity requires an optimal balance of completeness and accuracy in solving the local density equations. In this study, the convergence properties of a set of schemes that aim to achieve increasing accuracy are systematically examined according to the hierarchical approximations upon which they are based. Specifically, the Harris density functional (HDF) and related schemes that express the total energy in terms of atomic densities and limited self-consistency are compared within a single consistent framework. Convergence of the HDF energy relative to input density is first tested by carrying out calculations within the non-self-consistent atom fragment and self-consistent atom fragment (SCAF) approximations and then by supplementing the SCAF density by increasing numbers of partial waves about each atomic site using the self-consistent partial wave (SCPW) method. The construct of the SCPW method, that solves the local density equations with controlled precision according to the number of partial waves in the site density expansions, enables this study. The rapid convergence of structural properties with an increasing number of partial waves on each site, sometimes even with only L=0 partial waves, provides additional justification for HDF-based tight-binding and molecular dynamics methods where the interatomic potentials are obtained from the superposition of atomic-like densities. The convergence of ground state structural properties is demonstrated by application to the set of molecules: carbon monoxide, water, orthosilicic acid (H{sub 4}SiO{sub 4}) , formamide (HCONH{sub 2}) , iron pentacarbonyl [Fe(CO){sub 5}] , and dimanganese decacarbonyl [Mn{sub 2}(CO){sub 10}] .
NASA Astrophysics Data System (ADS)
Venderbos, J. W. F.
2016-03-01
We study hexagonal spin-channel ("triplet") density waves with commensurate M -point propagation vectors. We first show that the three Q =M components of the singlet charge density and charge-current density waves can be mapped to multicomponent Q =0 nonzero angular momentum order in three dimensions (3D) with cubic crystal symmetry. This one-to-one correspondence is exploited to define a symmetry classification for triplet M -point density waves using the standard classification of spin-orbit coupled electronic liquid crystal phases of a cubic crystal. Through this classification we naturally identify a set of noncoplanar spin density and spin-current density waves: the chiral spin density wave and its time-reversal invariant analog. These can be thought of as 3 DL =2 and 4 spin-orbit coupled isotropic β -phase orders. In contrast, uniaxial spin density waves are shown to correspond to α phases. The noncoplanar triple-M spin-current density wave realizes a novel 2 D semimetal state with three flavors of four-component spin-momentum locked Dirac cones, protected by a crystal symmetry akin to nonsymmorphic symmetry, and sits at the boundary between a trivial and topological insulator. In addition, we point out that a special class of classical spin states, defined as classical spin states respecting all lattice symmetries up to global spin rotation, are naturally obtained from the symmetry classification of electronic triplet density waves. These symmetric classical spin states are the classical long-range ordered limits of chiral spin liquids.
NASA Astrophysics Data System (ADS)
Sotnikov, V.; Kim, T.; Lundberg, J.; Paraschiv, I.; Mehlhorn, T.
2014-09-01
The presence of plasma turbulence can strongly influence propagation properties of electromagnetic signals used for surveillance and communication. In particular, we are interested in the generation of low frequency plasma density irregularities in the form of coherent vortex structures. Interchange or flute type density irregularities in magnetized plasma are associated with Rayleigh-Taylor type instability. These types of density irregularities play important role in refraction and scattering of high frequency electromagnetic signals propagating in the earth ionosphere, in high energy density physics (HEDP) and in many other applications. We will discuss scattering of high frequency electromagnetic waves on low frequency density irregularities due to the presence of vortex density structures associated with interchange instability. We will also present PIC simulation results on EM scattering on vortex type density structures using the LSP code and compare them with analytical results. Acknowledgement: This work was supported by the Air Force Research laboratory, the Air Force Office of Scientific Research, the Naval Research Laboratory and NNSA/DOE grant no. DE-FC52-06NA27616 at the University of Nevada at Reno.
Spin density wave instabilities in the NbS2 monolayer
NASA Astrophysics Data System (ADS)
Güller, F.; Vildosola, V. L.; Llois, A. M.
2016-03-01
In the present work, we study the magnetic properties of the NbS2 monolayer by first-principles calculations. The transition metal dichalcogenides (TMDCs) are a family of laminar materials presenting exciting properties such as charge density waves (CDWs), superconductivity, and metal-insulating transitions. 2 H -NbS2 is a particular case within the family, because it is the only one that is a superconductor without exhibiting a CDW order. Although no long-range magnetic order was experimentally observed in the TMDCs, we show here that the single monolayer of NbS2 is on the verge of a spin density wave (SDW) phase. Our calculations indicate that a wavelike magnetic order is stabilized in the NbS2 monolayer in the presence of magnetic defects or within zigzag nanoribbons, due to the presence of unpaired electrons. We calculate the real part of the bare electronic susceptibility and the corresponding nesting function of the clean NbS2 monolayer, showing that there are strong electronic instabilities at the same wave vector associated with the calculated SDWs, also corresponding with one of the main nesting vectors of the Fermi surface. We conclude that the physical mechanism behind the spin-wave instabilities are the nesting properties, accentuated by the quasi-2D character of this system, and the rather strong Coulomb interactions of the 4 d band of the Nb atom. We also estimate the amplitude of the spin fluctuations and find that they are rather large, as expected for a system on the verge of a quantum critical transition.
NASA Technical Reports Server (NTRS)
Bell, T. F.; Ngo, H. D.
1990-01-01
This paper presents a theoretical model for electrostatic lower hybrid waves excited by electromagnetic whistler mode waves propagating in regions of the magnetosphere and the topside ionosphere, where small-scale magnetic-field-aligned plasma density irregularities are thought to exist. In this model, the electrostatic waves are excited by linear mode coupling as the incident electromagnetic whistler mode waves scatter from the magnetic-field-aligned plasma density irregularities. Results indicate that high-amplitude short-wavelength (5 to 100 m) quasi-electrostatic whistler mode waves can be excited when electromagnetic whistler mode waves scatter from small-scale planar magnetic-field-aligned plasma density irregularities in the topside ionosphere and magnetosphere.
Fluctuation of the charge density wave in TTF-TCNQ under high pressure
NASA Astrophysics Data System (ADS)
Murata, Keizo; Weng, Yufeng; Seno, Yuki; Rani Tamilselvan, Natarajan; Kobayashi, Kensuke; Arumugam, Sonachalam; Takashima, Yusaku; Yoshino, Harukazu; Kato, Reizo
2009-03-01
Temperature dependence of the resistivity of TTF-TCNQ along the b-(1D)- and a-axes was studied under hydrostatic pressure up to 8 GPa. A striking contrast was seen between the b-(1D)- and a-axes in the power-law dependence of resistivity ρ=ρ0Tα in the metallic region as well as the activation energy in the charge density wave (CDW) insulating state. We note that the careful terminal configuration is essentially important to obtain these properties.
Multiple charge-density-wave transitions in single-crystalline Lu2Ir3Si5
NASA Astrophysics Data System (ADS)
Sangeetha, N. S.; Thamizhavel, A.; Tomy, C. V.; Basu, Saurabh; Awasthi, A. M.; Rajak, Piu; Bhattacharyya, Somnath; Ramakrishnan, S.; Pal, D.
2015-05-01
The physical properties of the single-crystalline samples of Lu2Ir3Si5 have been investigated by magnetic susceptibility, resistivity, and heat capacity studies. We observed multiple charge-density-wave (CDW) transitions in all the measurements. A strong thermal hysteresis at these transitions suggests a possible first order CDW ordering. In addition, the first order nature is ascertained by a very narrow and a huge cusp (62 J/mol K) in the zero field specific heat data which also suggests strong electron-phonon interchain coupling.
NASA Astrophysics Data System (ADS)
Porer, M.; Ménard, J.-M.; Poellmann, C.; Dachraoui, H.; Mouchliadis, L.; Perakis, I. E.; Heinzmann, U.; Demsar, J.; Rossnagel, K.; Galopin, E.; Lemaître, A.; Amo, A.; Bloch, J.; Huber, R.
2016-05-01
Many-body correlation effects in complex quantum systems often lead to phase transitions that bear great technological potential. However, the underlying microscopic driving mechanisms or even the quantum-mechanical properties of the novel ground state often remain elusive. Here we employ phase-locked ultrabroadband terahertz (THz) pulses to disentangle two coexisting orders in the charge density wave phase 1T-TiSe2 via their individual non-equilibrium multi- THz dynamics. Furthermore, we demonstrate that few-cycle THz pulses can project out the matter part of a transient cold exciton-polariton condensate, providing novel insights into the very nature of this macroscopic quantum state.
NASA Astrophysics Data System (ADS)
Li, X. D.; O'Leary, M. A.; Boas, D. A.; Chance, Britton; Yodh, A. G.
1996-07-01
We present analytic solutions for fluorescent diffuse photon density waves originating from fluorophores distributed in thick turbid media. Solutions are derived for a homogeneous turbid medium containing a uniform distribution of fluorophores and for a system that is homogeneous except for the presence of a single spherical inhomogeneity. Generally the inhomogeneity has fluorophore concentration, and lifetime and optical properties that differ from those of the background. The analytic solutions are verified by numerical calculations and are used to determine the fluorophore lifetime and concentration changes required for the accurate detection of inhomogeneities in biologically relevant systems. The relative sensitivities of absorption and fluorescence methods are compared.
Relationship between macro-fracture density, P-wave velocity, and permeability of coal
NASA Astrophysics Data System (ADS)
Wang, Haichao; Pan, Jienan; Wang, Sen; Zhu, Haitao
2015-06-01
This study was undertaken to determine the quantitative relationship between macro-fracture density, P-wave velocity, porosity and permeability of different coal rank samples from mining areas in North China. The coal sample permeability shows an exponential growth with increasing fracture density. The relation between P-wave velocity and porosity is power function and P-wave velocity decreases with the increasing porosity. P-wave velocity linearly or nonlinearly decreases with the increase of fracture density in the selected coal samples (0.73-3.59% Ro). However, the overall trend is that P-wave velocity decreases with an increase in macro-fracture density. The permeability of coal samples linearly decreases with the increase of P-wave velocity. The quantitative relationship between P-wave velocity and permeability could provide reference for the further study of permeability predicting.
Fluctuating charge-density waves in a cuprate superconductor.
Torchinsky, Darius H; Mahmood, Fahad; Bollinger, Anthony T; Božović, Ivan; Gedik, Nuh
2013-05-01
Cuprate materials hosting high-temperature superconductivity (HTS) also exhibit various forms of charge and spin ordering whose significance is not fully understood. So far, static charge-density waves (CDWs) have been detected by diffraction probes only at particular doping levels or in an applied external field . However, dynamic CDWs may also be present more broadly and their detection, characterization and relationship with HTS remain open problems. Here we present a method based on ultrafast spectroscopy to detect the presence and measure the lifetimes of CDW fluctuations in cuprates. In an underdoped La(1.9)Sr(0.1)CuO4 film (T(c) = 26 K), we observe collective excitations of CDW that persist up to 100 K. This dynamic CDW fluctuates with a characteristic lifetime of 2 ps at T = 5 K that decreases to 0.5 ps at T = 100 K. In contrast, in an optimally doped La(1.84)Sr(0.16)CuO4 film (T(c) = 38.5 K), we detect no signatures of fluctuating CDWs at any temperature, favouring the competition scenario. This work forges a path for studying fluctuating order parameters in various superconductors and other materials. PMID:23435216
Quasiclassical description of a superconductor with a spin density wave
NASA Astrophysics Data System (ADS)
Moor, A.; Volkov, A. F.; Efetov, K. B.
2011-04-01
We derive equations for the quasiclassical Green’s functions ǧ within a simple model of a two-band superconductor with a spin density wave (SDW). The elements of the matrix ǧ are the retarded, advanced, and Keldysh functions, each of which is an 8×8 matrix in the Gor’kov-Nambu, the spin, and the band space. In equilibrium, these equations are a generalization of the Eilenberger equation. On the basis of the derived equations, we analyze the Knight shift, the proximity, and the dc Josephson effects in the superconductors under consideration. The Knight shift is shown to depend on the orientation of the external magnetic field with respect to the direction of the vector of the magnetization of the SDW. The proximity effect is analyzed for an interface between a superconductor with the SDW and a normal metal. The function describing both superconducting and magnetic correlations is shown to penetrate the normal metal or a metal with the SDW due to the proximity effect. The dc Josephson current in an SSDW/N/SSDW junction is also calculated as a function of the phase difference φ. It is shown that in our model, the Josephson current does not depend on the mutual orientation of the magnetic moments in the superconductors SSDW and is proportional to sinφ. The dissipationless spin current jsp depends on the angle α between the magnetization vectors in the same way (jsp~sinα) and is not zero above the superconducting transition temperature.
Self-gravity density waves in Saturn's rings
NASA Astrophysics Data System (ADS)
Griv, E.; Gedalin, M.
A weakly nonlinear (quasi-linear) theory is used to determine the stability of the self-gravitating, rapidly and nonuniformly rotating, three-dimensional, and collisional particulate disk against small gravity perturbations. A gas-kinetic theory approach is used by exploring the combined system of the Boltzmann and the Poisson equations. The effects of physical collisions between particles are taken into account by using in the Boltzmann kinetic equation a Krook model integral of collisions modified to allow collisions to be inelastic. Equations describing the quasi-linear stage of classical Jeans instability of small gravity perturbations in Saturn's rings (e.g., those produced by spontaneous perturbations) are derived and solved analytically. It is shown that as a direct result of the Jeans instability of gravity disturbances the disk is subdivided into numerous almost regular density waves, with size and spacing of the order of 2πh, where h is the typical thickness of the system. The present research is aimed above all at explaining the origin of various structures in highly flattened, rapidly rotating systems of mutually gravitating particles. In particular, it is suggested that Cassini spacecraft high-resolution images may reveal this kind of hyperfine ˜ 100 m or even less radial structure in the rings A, B, and C of the Saturnian ring system. This work was supported in part by the Israel Science Foundation and the Israeli Ministry of Immigrant Absorption.
Charge density wave transition in single-layer titanium diselenide
Chen, P.; Chan, Y. -H.; Fang, X. -Y.; Zhang, Y.; Chou, M. Y.; Mo, S. -K.; Hussain, Z.; Fedorov, A. -V.; Chiang, T. -C.
2015-11-16
A single molecular layer of titanium diselenide (TiSe_{2}) is a promising material for advanced electronics beyond graphene--a strong focus of current research. Such molecular layers are at the quantum limit of device miniaturization and can show enhanced electronic effects not realizable in thick films. We show that single-layer TiSe_{2} exhibits a charge density wave (CDW) transition at critical temperature T_{C}=232±5 K, which is higher than the bulk T_{C}=200±5 K. Angle-resolved photoemission spectroscopy measurements reveal a small absolute bandgap at room temperature, which grows wider with decreasing temperature T below T_{C} in conjunction with the emergence of (2 × 2) ordering. The results are rationalized in terms of first-principles calculations, symmetry breaking and phonon entropy effects. The behavior of the Bardeen-Cooper-Schrieffer (BCS) gap implies a mean-field CDW order in the single layer and an anisotropic CDW order in the bulk.
Charge Order Induced in an Orbital Density-Wave State
NASA Astrophysics Data System (ADS)
Singh, Dheeraj Kumar; Takimoto, Tetsuya
2016-04-01
Motivated by recent angle resolved photoemission measurements [D. V. Evtushinsky et al., Phys. Rev. Lett. 105, 147201 (2010)] and evidence of the density-wave state for the charge and orbital ordering [J. García et al., Phys. Rev. Lett. 109, 107202 (2012)] in La0.5Sr1.5MnO4, the issue of charge and orbital ordering in a two-orbital tight-binding model for layered manganite near half doping is revisited. We find that the charge order with the ordering wavevector 2{Q} = (π ,π ) is induced by the orbital order of d-/d+-type having B1g representation with a different ordering wavevector Q, where the orbital order as the primary order results from the strong Fermi-surface nesting. It is shown that the induced charge order parameter develops according to TCO - T by decreasing the temperature below the orbital ordering temperature TCO, in addition to the usual mean-field behavior of the orbital order parameter. Moreover, the same orbital order is found to stabilize the CE-type spin arrangement observed experimentally below TCE < TCO.
Charge density wave transition in single-layer titanium diselenide
Chen, P; Chan, Y. -H.; Fang, X. -Y.; Zhang, Y; Chou, M Y; Mo, S. -K.; Hussain, Z; Fedorov, A. -V.; Chiang, T. -C.
2015-01-01
A single molecular layer of titanium diselenide (TiSe2) is a promising material for advanced electronics beyond graphene—a strong focus of current research. Such molecular layers are at the quantum limit of device miniaturization and can show enhanced electronic effects not realizable in thick films. We show that single-layer TiSe2 exhibits a charge density wave (CDW) transition at critical temperature TC=232±5 K, which is higher than the bulk TC=200±5 K. Angle-resolved photoemission spectroscopy measurements reveal a small absolute bandgap at room temperature, which grows wider with decreasing temperature T below TC in conjunction with the emergence of (2 × 2) ordering. The results are rationalized in terms of first-principles calculations, symmetry breaking and phonon entropy effects. The observed Bardeen-Cooper-Schrieffer (BCS) behaviour of the gap implies a mean-field CDW order in the single layer and an anisotropic CDW order in the bulk. PMID:26568512
Charge density wave transition in single-layer titanium diselenide
Chen, P.; Chan, Y. -H.; Fang, X. -Y.; Zhang, Y.; Chou, M. Y.; Mo, S. -K.; Hussain, Z.; Fedorov, A. -V.; Chiang, T. -C.
2015-11-16
A single molecular layer of titanium diselenide (TiSe2) is a promising material for advanced electronics beyond graphene--a strong focus of current research. Such molecular layers are at the quantum limit of device miniaturization and can show enhanced electronic effects not realizable in thick films. We show that single-layer TiSe2 exhibits a charge density wave (CDW) transition at critical temperature TC=232±5 K, which is higher than the bulk TC=200±5 K. Angle-resolved photoemission spectroscopy measurements reveal a small absolute bandgap at room temperature, which grows wider with decreasing temperature T below TC in conjunction with the emergence of (2 × 2) ordering.more » The results are rationalized in terms of first-principles calculations, symmetry breaking and phonon entropy effects. The behavior of the Bardeen-Cooper-Schrieffer (BCS) gap implies a mean-field CDW order in the single layer and an anisotropic CDW order in the bulk.« less
NASA Astrophysics Data System (ADS)
Pokrovskii, Vadim Ya; Zybtsev, Sergey G.; Nikitin, Maksim V.; Gorlova, Irina G.; Nasretdinova, Venera F.; Zaitsev-Zotov, Sergei V.
2013-01-01
Recent results (some previously unpublished) on the physics of charge density waves (CDWs) are reviewed. The synthesis conditions and unique properties of the quasi-one-dimensional compound {NbS_3}, with highly coherent room temperature CDWs, are described. A peculiar type of 'quantization' is discussed, which is observed in micro- and nanosamples of {K_{0.3}MoO_3} and {NbSe_3} due to the discrete nature of CDW wave vector values. The electric-field-induced torsional strain (TS) in quasi-one-dimensional conductors is considered. Research results on the TS of a noise character induced by sliding CDWs are presented, along with those on the inverse effect, the modulation of the voltage induced by externally driven TS. Results on the nonlinear conduction of {TiS_3}, a quasi-one-dimensional compound not belonging to the family of classical Peierls conductors, are also described.
Himpel, Michael Killer, Carsten; Melzer, André; Bockwoldt, Tim; Piel, Alexander; Ole Menzel, Kristoffer
2014-03-15
Experiments on dust-density waves have been performed in dusty plasmas under the microgravity conditions of parabolic flights. Three-dimensional measurements of a dust density wave on a single particle level are presented. The dust particles have been tracked for many oscillation periods. A Hilbert analysis is applied to obtain trajectory parameters such as oscillation amplitude and three-dimensional velocity amplitude. While the transverse motion is found to be thermal, the velocity distribution in wave propagation direction can be explained by harmonic oscillations with added Gaussian (thermal) noise. Additionally, it is shown that the wave properties can be reconstructed by means of a pseudo-stroboscopic approach. Finally, the energy dissipation mechanism from the kinetic oscillation energy to thermal motion is discussed and presented using phase-resolved analysis.
Electron density measurement of cesium seeded negative ion source by surface wave probe
Kisaki, M.; Tsumori, K.; Nakano, H.; Ikeda, K.; Osakabe, M.; Nagaoka, K.; Shibuya, M.; Sato, M.; Sekiguchi, H.; Komada, S.; Kondo, T.; Hayashi, H.; Asano, E.; Takeiri, Y.; Kaneko, O.
2012-02-15
Electron density measurements of a large-scaled negative ion source were carried out with a surface wave probe. By comparison of the electron densities determined with the surface wave probe and a Langmuir probe, it was confirmed that the surface wave probe is highly available for diagnostic of the electron density in H{sup -} ion sources. In addition, it was found that the ratio of the electron density to the H{sup -} ion density dramatically decreases with increase of a bias voltage and the H{sup -} ions become dominant negative particles at the bias voltage of more than 6 V.
Electronic properties of solids excited with intermediate laser power densities
NASA Astrophysics Data System (ADS)
Sirotti, Fausto; Tempo Beamline Team
Intermediate laser power density up to about 100 GW/cm2 is below the surface damage threshold is currently used to induce modification in the physical properties on short time scales. The absorption of a short laser pulse induces non-equilibrium electronic distributions followed by lattice-mediated equilibrium taking place only in the picosecond range. The role of the hot electrons is particularly important in several domains as for example fast magnetization and demagnetization processes, laser induced phase transitions, charge density waves. Angular resolved photoelectron spectroscopy measuring directly energy and momentum of electrons is the most adapted tool to study the electronic excitations at short time scales during and after fast laser excitations. The main technical problem is the space charge created by the pumping laser pulse. I will present angular resolved multiphoton photoemission results obtained with 800 nm laser pulses showing how space charge electrons emitted during fast demagnetization processes can be measured. Unable enter Affiliation: CNRS-SOLEIL Synchrotron L'Orme des Merisiers , Saint Aubin 91192 Gif sur Yvette France.
NASA Astrophysics Data System (ADS)
Schoonmaker, Robert; Clark, Stewart; Lancaster, Tom; Frawley, Thomas; Hatton, Peter
Iron arsenide intersects interesting physics between novel superconductors and other helical magnetic ordering in Pnma metal arsenide materials. Recent diffraction data has found a more complex ordering than a simple helical incommensurate spin density wave. Instead iron arsenide exhibits a definite chirality to the helimagnetism, an ellipticity in the spiral not aligned with the crystal axis, and resonant diffraction peaks forbidden by the Pnma symmetry. From non-magnetic and collinear density functional theory calculations we present insight into the mechanisms for the formation of this helimagnetic state. We find that ferromagnetic superexchange is a likely mechanism for the spin ordering and that the noncollinear ordering under this regime is caused by the spins on neighbouring irons arranging to minimise direct exchange between iron atoms, and also minimize disruption of the ferromagnetic superexchange between priveleged iron-arsenic pairs. To explain the forbidden peaks in the diffraction we have performed second-order spin-orbit perturbation calculations on the nonmagnetic calculation, which finds that the orbital ordering on the iron atoms coupled to the helimagnetism will lead to the otherwise symmetry-forbidden peaks.
El-Labany, S.K.; El-Shamy, E.F.
2005-04-15
The nonlinear properties of solitary waves structures in a hot magnetized dusty plasma consisting of isothermal hot electrons, nonisothermal ions, and high negatively charged massive dust grains are reported. A modified Korteweg-de Vries (modified KdV) equation, which admits a solitary waves solution, for small but finite amplitude, is derived using a reductive perturbation theory. A nonisothermal ion distribution provides the possibility of existence of rarefactive solitary waves. On the other hand, the dynamics of solitary waves at a critical ion density is governed by KdV equation. The modification in the amplitude and width of the solitary waves structures due to the inclusion of obliqueness and external magnetic field are also investigated.
NASA Astrophysics Data System (ADS)
Sotnikov, V.; Kim, T.; Lundberg, J.; Paraschiv, I.; Mehlhorn, T. A.
2014-05-01
The presence of plasma turbulence can strongly influence propagation properties of electromagnetic signals used for surveillance and communication. In particular, we are interested in the generation of low frequency plasma density irregularities in the form of coherent vortex structures. Interchange or flute type density irregularities in magnetized plasma are associated with Rayleigh-Taylor type instability. These types of density irregularities play an important role in refraction and scattering of high frequency electromagnetic signals propagating in the earth ionosphere, in high energy density physics, and in many other applications. We will discuss scattering of high frequency electromagnetic waves on low frequency density irregularities due to the presence of vortex density structures associated with interchange instability. We will also present particle-in-cell simulation results of electromagnetic scattering on vortex type density structures using the large scale plasma code LSP and compare them with analytical results.
Sotnikov, V.; Kim, T.; Lundberg, J.; Paraschiv, I.; Mehlhorn, T. A.
2014-05-15
The presence of plasma turbulence can strongly influence propagation properties of electromagnetic signals used for surveillance and communication. In particular, we are interested in the generation of low frequency plasma density irregularities in the form of coherent vortex structures. Interchange or flute type density irregularities in magnetized plasma are associated with Rayleigh-Taylor type instability. These types of density irregularities play an important role in refraction and scattering of high frequency electromagnetic signals propagating in the earth ionosphere, in high energy density physics, and in many other applications. We will discuss scattering of high frequency electromagnetic waves on low frequency density irregularities due to the presence of vortex density structures associated with interchange instability. We will also present particle-in-cell simulation results of electromagnetic scattering on vortex type density structures using the large scale plasma code LSP and compare them with analytical results.
A restoration model of distorted electron density in wave-cutoff probe measurement
Jun, Hyun-Su Lee, Yun-Seong
2014-02-15
This study investigates the problem of electron density distortion and how the density can be restored in a wave-cutoff probe. Despite recent plasma diagnostics research using a wave-cutoff probe, the problem of electron density distortion caused by plasma conditions has not been resolved. Experimental results indicate that electron density measured using the wave-cutoff method is highly susceptible to variations in the probe tip gap. This electron density distortion is caused by the bulk plasma disturbance between probe tips, and it must be removed for calculating the absolute electron density. To do this, a detailed analytic model was developed using the power balance equation near probe tips. This model demonstrates the characteristics of plasma distortion in wave-cutoff probe measurement and successfully restored the absolute value of electron density with varying probe tip gaps.
Arregui, I.; Asensio Ramos, A.
2013-06-01
We present a Bayesian seismology inversion technique for propagating magnetohydrodynamic transverse waves observed in coronal waveguides. The technique uses theoretical predictions for the spatial damping of propagating kink waves in transversely inhomogeneous coronal waveguides. It combines wave amplitude damping length scales along the waveguide with theoretical results for resonantly damped propagating kink waves to infer the plasma density variation across the oscillating structures. Provided that the spatial dependence of the velocity amplitude along the propagation direction is measured and the existence of two different damping regimes is identified, the technique would enable us to fully constrain the transverse density structuring, providing estimates for the density contrast and its transverse inhomogeneity length scale.
NASA Astrophysics Data System (ADS)
Classen, Laura; Herbut, Igor F.; Janssen, Lukas; Scherer, Michael M.
2016-03-01
We study the competition of spin- and charge-density waves and their quantum multicritical behavior for the semimetal-insulator transitions of low-dimensional Dirac fermions. Employing the effective Gross-Neveu-Yukawa theory with two order parameters as a model for graphene and a growing number of other two-dimensional Dirac materials allows us to describe the physics near the multicritical point at which the semimetallic and the spin- and charge-density-wave phases meet. With the help of a functional renormalization group approach, we are able to reveal a complex structure of fixed points, the stability properties of which decisively depend on the number of Dirac fermions Nf. We give estimates for the critical exponents and observe crucial quantitative corrections as compared to the previous first-order ɛ expansion. For small Nf, the universal behavior near the multicritical point is determined by the chiral Heisenberg universality class supplemented by a decoupled, purely bosonic, Ising sector. At large Nf, a novel fixed point with nontrivial couplings between all sectors becomes stable. At intermediate Nf, including the graphene case (Nf=2 ), no stable and physically admissible fixed point exists. Graphene's phase diagram in the vicinity of the intersection between the semimetal, antiferromagnetic, and staggered density phases should consequently be governed by a triple point exhibiting first-order transitions.
Inferring Magnetospheric Heavy Ion Density using EMIC Waves
Kim, Eun-Hwa; Johnson, Jay R.; Kim, Hyomin; Lee, Dong-Hun
2014-05-01
We present a method to infer heavy ion concentration ratios from EMIC wave observations that result from ionion hybrid (IIH) resonance. A key feature of the ion-ion hybrid resonance is the concentration of wave energy in a field-aligned resonant mode that exhibits linear polarization. This mode converted wave is localized at the location where the frequency of a compressional wave driver matches the IIH resonance condition, which depends sensitively on the heavy ion concentration. This dependence makes it possible to estimate the heavy ion concentration ratio. In this letter, we evaluate the absorption coefficients at the IIH resonance at Earth's geosynchronous orbit for variable concentrations of He+ and field-aligned wave numbers using a dipole magnetic field. Although wave absorption occurs for a wide range of heavy ion concentrations, it only occurs for a limited range of field-aligned wave numbers such that the IIH resonance frequency is close to, but not exactly the same as the crossover frequency. Using the wave absorption and observed EMIC waves from GOES-12 satellite, we demonstrate how this technique can be used to estimate that the He+ concentration is around 4% near L = 6.6.
Stabilities of Superfluid and Density Wave States in Fermionic Mass Imbalanced Optical Lattices
NASA Astrophysics Data System (ADS)
Takemori, Nayuta; Koga, Akihisa
We study the attractive Hubbard model with different masses by means of dynamical mean-field theory with continuous-time quantum Monte Carlo simulation. Calculating the internal energy and density of states, we discuss how the interaction affects the stabilities of superfluid and density wave states at half-filling. It is found that the density wave and superfluid states are almost degenerate in a certain region. On the other hand, the genuine density wave state is stable in a wide parameter space.
Inferring magnetospheric heavy ion density using EMIC waves
NASA Astrophysics Data System (ADS)
Kim, Eun-Hwa; Johnson, Jay R.; Kim, Hyomin; Lee, Dong-Hun
2015-08-01
We present a method to infer heavy ion concentration ratios from electromagnetic ion cyclotron (EMIC) wave observations that result from ion-ion hybrid (IIH) resonance. A key feature of the IIH resonance is the concentration of wave energy in a field-aligned resonant mode that exhibits linear polarization. These mode-converted waves at the IIH resonance are localized at the location where the frequency of a compressional wave driver matches the IIH resonance condition, which depends sensitively on the heavy ion concentration. This dependence makes it possible to estimate the heavy ion concentration ratio. In this paper, we evaluate the absorption coefficients at the IIH resonance at Earth's geosynchronous orbit for variable concentrations of He+ and wave frequencies using a dipole magnetic field model. We find that the resonance only occurs over a limited range of wave frequency such that the IIH resonance frequency is close to but not exactly the same as the crossover frequency. Using the wave absorption and EMIC waves observed from the GOES 12 satellite, we demonstrate how this technique can be used to estimate the He+ concentration of around 4% near L = 6.6 assuming electron-H+-He+ plasma.
Wave-Particle Properties and Pair Formation of the Photon
Lehnert, B.
2008-10-15
Models of an individual photon having joint wave-particle properties, needle-like geometry, and spin cannot be based on conventional theory, but be deduced in terms of a revised quantum electrodynamic approach. In this paper the latter is applied to two-slit configurations and electron-positron pair formation: (a) Two-slit experiments performed earlier by Tsuchiya et al. and recently by Afshar et al. demonstrate the joint wave-particle properties of the individual photon, and agree with Einstein's argument against Complementarity. The present theory is consistent with these results, (b) The elementary electron-positron pair formation process is considered, with special attention to the involved orbits, conservation of energy, spin, and electric charge. The obtained model appears to be consistent with the process in which the created electron and positron move along two rays and have original directions along the path of the incoming photon. The nonzero electric field divergence of the theory is associated with an intrinsic local electric charge density. This may explain that the photon can decay on account of the impact from an external electric field.
Constant Density Approximations for the Flow Behind Axisymmetric Shock Waves
NASA Technical Reports Server (NTRS)
Munson, Albert G.
1961-01-01
The incompressible rotational flow equations are used to obtain solutions for the flow behind axisymmetric shock waves with conic longitudinal sections. The nonlinear part of the term due to rotation is retained in the analysis. Numerical results for standoff distance and stagnation point velocity gradient are presented for the case in which the shock wave is a paraboloid, a sphere, or an oblate or prolate ellipsoid. A similarity parameter is proposed which correlates approximately the flow behind geometrically similar shock waves at different free-stream conditions.
Time-Dependent Density Wave Theory for Co-orbital Satellites
NASA Astrophysics Data System (ADS)
Stewart, Glen R.
2009-05-01
The standard theory of density waves in planetary rings assumes that the orbit of the perturbing satellite is on a fixed orbit. However, the co-orbital satellites, Janus and Epimetheus, trade orbits every four years. Cassini images of Saturn's rings record the time evolution of the density waves excited by these satellites. Ticareno et al. (Ap. J. 651: L65-L68, 2006) attempted to model the observations by assuming the steady-state density waves shift locations in the rings instantaneously when the co-orbital satellites trade orbits. They found that certain wave-like features are observed in the evanescent region of the wave that were not predicted by the steady state theory. We will present the results of a new time-dependent density wave theory that can model the perturbations by the co-orbital satellites during their orbital exchange. Similar to our previous result for temporally modulated density waves excited by the satellite, Pandora (Stewart and Sremcevic, DDA 2008), we find that the effective sound velocity in the wave plays an important role in propagating the time-dependent signal in the wave train. Comparisons with Cassini observations as well as predictions for the next co-orbital exchange event in January 2010 will be presented. This research was supported by NASA's Outer Planets Research Program.
Time-Dependent Density Wave Theory for Co-orbital Satellites
NASA Astrophysics Data System (ADS)
Stewart, Glen R.
2008-09-01
The standard theory of density waves in planetary rings assumes that the orbit of the perturbing satellite is on a fixed orbit. However, the co-orbital satellites, Janus and Epimetheus, trade orbits every four years. Cassini images of Saturn's rings record the time evolution of the density waves excited by these satellites. Ticareno et al. (Ap. J. 651: L65-L68, 2006) attempted to model the observations by assuming the steady-state density waves shift locations in the rings instantaneously when the co-orbital satellites trade orbits. They found that certain wave-like features are observed in the evanescent region of the wave that are not predicted by the steady state theory. We will present the results of a new time-dependent density wave theory that can model the perturbations by the co-orbital satellites during their orbital exchange. Similar to our previous result for temporally modulated density waves excited by the satellite, Pandora (Stewart and Sremcevic, DDA 2008), we find that the effective sound velocity in the wave plays an important role in propagating the time-dependent signal in the wave train. Comparisons with Cassini observations as well as predictions for the next co-orbital exchange event in January 2010 will be presented.
Coronal Density Structure and its Role in Wave Damping in Loops
NASA Astrophysics Data System (ADS)
Cargill, P. J.; De Moortel, I.; Kiddie, G.
2016-05-01
It has long been established that gradients in the Alfvén speed, and in particular the plasma density, are an essential part of the damping of waves in the magnetically closed solar corona by mechanisms such as resonant absorption and phase mixing. While models of wave damping often assume a fixed density gradient, in this paper the self-consistency of such calculations is assessed by examining the temporal evolution of the coronal density. It is shown conceptually that for some coronal structures, density gradients can evolve in a way that the wave-damping processes are inhibited. For the case of phase mixing we argue that (a) wave heating cannot sustain the assumed density structure and (b) inclusion of feedback of the heating on the density gradient can lead to a highly structured density, although on long timescales. In addition, transport coefficients well in excess of classical are required to maintain the observed coronal density. Hence, the heating of closed coronal structures by global oscillations may face problems arising from the assumption of a fixed density gradient, and the rapid damping of oscillations may have to be accompanied by a separate (non-wave-based) heating mechanism to sustain the required density structuring.
Reflection properties of gravito-acoustic waves
NASA Astrophysics Data System (ADS)
Jovanović, Gordana
2016-03-01
We derive the dispersion equation for gravito-acoustic waves in an isothermal gravitationally stratified nonmagnetized atmosphere. In this model, with constant sound speed, it is possible to derive analytically the equations for gravito-acoustic waves. The large value of the viscous Reynolds number in the solar atmosphere imply that the dissipative terms in HD (hydrodynamics) equations are negligible. We consider the plane boundary z = 0 between two isothermal atmosphere regions and using the boundary conditions we derive the equation for the reflection coeffcient of gravito-acoustic waves. For the frequencies much greater than acoustic cutoff frequency, the reflection coefficient of the acoustic waves modified by gravity is the same as in the case of the pure acoustic waves. Reflection coefficient for the gravity waves is very high, R ≈ 1.
Comparison of density waves in the rings of Saturn and Uranus
NASA Technical Reports Server (NTRS)
Yanamandra-Fisher, Padmavati A.
1992-01-01
The similarity of density waves in the rings of Saturn and Uranus are addressed. It is found that all ring systems are grossly similar in that they all encircle the primary in its equatorial plane and exhibit responses to resonant satellite perturbations. The dominant response of Saturn's rings is the clearing of gaps and generation of density and bending waves. The Uranian rings appear to be confined by the presence of shepherd satellites. Three possible density waves have been identified, two in the epsilon ring and one in the delta ring.
Charge-density wave and magnetic phase diagram of chromium alloys
Fishman, R.S.; Jiang, X.W.
1996-08-08
The magnetic phase diagrams of all dilute Cr alloys can be explained by a simple theoretical model with coupled spin- and charge-density waves and a finite electron reservoir. If the charge-density wave and electron reservoir are sufficiently large, the paramagnetic to commensurate spin-density wave transition becomes strongly first order, as found in Cr{sub 1- x}Fe{sub x} and Cr{sub 1-x}Si{sub x} alloys. The observed discontinuity of the slope dT{sub N}/dx at the triple point and the bending of the CI phase boundary are also natural consequences of this model.
Liquid Water through Density-Functional Molecular Dynamics: Plane-Wave vs Atomic-Orbital Basis Sets.
Miceli, Giacomo; Hutter, Jürg; Pasquarello, Alfredo
2016-08-01
We determine and compare structural, dynamical, and electronic properties of liquid water at near ambient conditions through density-functional molecular dynamics simulations, when using either plane-wave or atomic-orbital basis sets. In both frameworks, the electronic structure and the atomic forces are self-consistently determined within the same theoretical scheme based on a nonlocal density functional accounting for van der Waals interactions. The overall properties of liquid water achieved within the two frameworks are in excellent agreement with each other. Thus, our study supports that implementations with plane-wave or atomic-orbital basis sets yield equivalent results and can be used indiscriminately in study of liquid water or aqueous solutions. PMID:27434607
Nonlinear waves on a string with inhomogeneous properties
NASA Astrophysics Data System (ADS)
Arredondo, Robert
Nonlinear waves on an infinite string with a rapid change in properties at one location are treated. The string is an idealized version of more complex configurations in both fluids and solids. This idealized version treats the property change as an interface with a discontinuity in properties. Packets of waves are then considered with a reduced model, here a set of nonlinear Schrodinger (NLS) equations. The stress and the displacement must both be matched at the interface, resulting in dynamic and kinematic interfacial conditions. The dynamic condition produces an inhomogeneous effect that cannot be treated successfully with separation-of-variables. This inhomogeneity is treated here with a time-evolution approach using Laplace transforms. The results show that this inhomogeneity creates a mean longitudinal displacement on both sides of the interface and a shift in the position of the interface as the waves transit the interface. This mean longitudinal displacement corresponds to a sustained strain in the string. The mean longitudinal displacement develops three distinct features. One feature has a length scale that is half the wave-length of the incident waves, while the lengths of the other two features have the same order as the length of the wave packet. The position of maximum strain as a result of this mean is often at the interface, depending on parameter values. These results apply to a variety of applications, such as waves in ocean ice, Rayleigh waves caused by earthquakes, internal waves in the oceans and atmosphere, as well as waves in stretched cables.
ULF waves upstream of the Venus bow shock - Properties of one-hertz waves
NASA Technical Reports Server (NTRS)
Orlowski, D. S.; Russell, C. T.
1991-01-01
Pioneer Venus Orbiter data are used here to study the properties of a class of ULF upstream waves with relatively high observed frequencies. These waves show significant similarity to 'one-Hz' waves identified at earth in the ISEE 1 and 2 observations and the whistler waves identified earlier by IMP 6 observations. The waves appear almost immediately after the spacecraft crosses the magnetic field tangent line to the bow shock surface into the region of connected field lines. The wave amplitude decreases with distance from the shock measured along the magnetic field line. Group velocities calculated using the cold plasma dispersion relation indicate that the waves have sufficient upstream velocities to propagate form the shock into the solar wind. The totality of observations seem best explained by a source of right-handed whistler mode waves at the bow shock.
Chirality density wave of the ``hidden order'' phase in URu2 Si2
NASA Astrophysics Data System (ADS)
Blumberg, Girsh
Many novel electronic ground states have been found to emerge from the hybridization between localized d - or f - electron states and conduction electron states in correlated electron materials. The heavy fermion compound URu2Si2 exhibits the coexistence of two such ground states: so-called ``hidden order'' (HO) below THO = 17.5 K and superconductivity below Tc =1.5 K. Despite 30 years of research the symmetry of the order parameter associated with HO phase below 17.5 K has remained ambiguous. Here we report results of polarization resolved Raman spectroscopy study aimed to specify the symmetry of the low energy excitations above and below the HO transition. These excitations involve transitions between interacting heavy uranium 5f orbitals, responsible for the broken symmetry in the HO phase. From the symmetry analysis of the collective mode, we determine that the HO parameter breaks local vertical and diagonal reflection symmetries at the uranium sites, resulting in crystal field states with distinct chiral properties, which order to a commensurate chirality density wave ground state. We further explore the competition between the HO phase and large moment antiferromagnetic (LMAFM) phase, and the connection between the HO chirality density wave and the unconventional superconductivity which has recently been proposed to be of a chiral d-wave type. Work was performed in collaboration with H.-H. Kung, R. Baumbach, E. Bauer, K. Haule, M. B. Maple, and J. Mydosh. Research at Rutgers was supported by DOE BES Award DE-SC0005463 and by NSF under Awards NSF DMR-1104884.
NASA Astrophysics Data System (ADS)
Wu, Ya-Jie; Li, Ning; He, Jing; Kou, Su-Peng
2016-03-01
In this paper, based on mean-field approach and random-phase-approximation, we study the magnetic properties of the repulsive Haldane-Hubbard model on a square lattice. We find antiferromagnetic order driven topological spin density waves beyond Landau’s symmetry-breaking paradigm, for which the effective low energy physics is determined by Chern-Simons-Hopf gauge field theories with different K matrices.
Chemotaxis of artificial microswimmers in active density waves
NASA Astrophysics Data System (ADS)
Geiseler, Alexander; Hänggi, Peter; Marchesoni, Fabio; Mulhern, Colm; Savel'ev, Sergey
2016-07-01
Living microorganisms are capable of a tactic response to external stimuli by swimming toward or away from the stimulus source; they do so by adapting their tactic signal transduction pathways to the environment. Their self-motility thus allows them to swim against a traveling tactic wave, whereas a simple fore-rear asymmetry argument would suggest the opposite. Their biomimetic counterpart, the artificial microswimmers, also propel themselves by harvesting kinetic energy from an active medium, but, in contrast, lack the adaptive capacity. Here we investigate the transport of artificial swimmers subject to traveling active waves and show, by means of analytical and numerical methods, that self-propelled particles can actually diffuse in either direction with respect to the wave, depending on its speed and waveform. Moreover, chiral swimmers, which move along spiraling trajectories, may diffuse preferably in a direction perpendicular to the active wave. Such a variety of tactic responses is explained by the modulation of the swimmer's diffusion inside traveling active pulses.
Chemotaxis of artificial microswimmers in active density waves.
Geiseler, Alexander; Hänggi, Peter; Marchesoni, Fabio; Mulhern, Colm; Savel'ev, Sergey
2016-07-01
Living microorganisms are capable of a tactic response to external stimuli by swimming toward or away from the stimulus source; they do so by adapting their tactic signal transduction pathways to the environment. Their self-motility thus allows them to swim against a traveling tactic wave, whereas a simple fore-rear asymmetry argument would suggest the opposite. Their biomimetic counterpart, the artificial microswimmers, also propel themselves by harvesting kinetic energy from an active medium, but, in contrast, lack the adaptive capacity. Here we investigate the transport of artificial swimmers subject to traveling active waves and show, by means of analytical and numerical methods, that self-propelled particles can actually diffuse in either direction with respect to the wave, depending on its speed and waveform. Moreover, chiral swimmers, which move along spiraling trajectories, may diffuse preferably in a direction perpendicular to the active wave. Such a variety of tactic responses is explained by the modulation of the swimmer's diffusion inside traveling active pulses. PMID:27575185
Evidence of the charge-density wave state in polypyrrole nanotubes
NASA Astrophysics Data System (ADS)
Sarma, Abhisakh; Sanyal, Milan K.; Littlewood, Peter B.
2015-04-01
We present a detailed investigation of the low-frequency dielectric and conductivity properties of conducting polymer nanowires. Our results, obtained by connecting ˜107 nanowires in parallel, show that these polypyrrole nanowires behave like conventional charge-density wave (CDW) materials, in their nonlinear and dynamic response, together with scaling of relaxation time and conductivity. The observed Arrhenius law for both these quantities gives a CDW gap of 3.5 meV in the regime of temperature (˜40 K) in which the CDW state survives. We find good agreement with a theory of weakly pinned CDW, screened by thermally excited carriers across the CDW gap. The identification of polymer nanowires as CDW provides us a model system to investigate charge ordering owing to electrostatic interaction, relevant to a variety of systems from dusty plasma to molecular biology.
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.
Rettig, L.; Cortés, R.; Chu, J.-H.; Fisher, I. R.; Schmitt, F.; Moore, R. G.; Shen, Z.-X.; Kirchmann, P. S.; Wolf, M.; Bovensiepen, U.
2016-01-01
Non-equilibrium conditions may lead to novel properties of materials with broken symmetry ground states not accessible in equilibrium as vividly demonstrated by non-linearly driven mid-infrared active phonon excitation. Potential energy surfaces of electronically excited states also allow to direct nuclear motion, but relaxation of the excess energy typically excites fluctuations leading to a reduced or even vanishing order parameter as characterized by an electronic energy gap. Here, using femtosecond time- and angle-resolved photoemission spectroscopy, we demonstrate a tendency towards transient stabilization of a charge density wave after near-infrared excitation, counteracting the suppression of order in the non-equilibrium state. Analysis of the dynamic electronic structure reveals a remaining energy gap in a highly excited transient state. Our observation can be explained by a competition between fluctuations in the electronically excited state, which tend to reduce order, and transiently enhanced Fermi surface nesting stabilizing the order. PMID:26804717
Fast plane wave density functional theory molecular dynamics calculations on multi-GPU machines
Jia, Weile; University of Chinese Academy of Sciences, Beijing ; Fu, Jiyun; University of Chinese Academy of Sciences, Beijing ; Cao, Zongyan; Wang, Long; Chi, Xuebin; Gao, Weiguo; MOE Key Laboratory of Computational Physical Sciences, Fudan University, Shanghai ; Wang, Lin-Wang
2013-10-15
Plane wave pseudopotential (PWP) density functional theory (DFT) calculation is the most widely used method for material simulations, but its absolute speed stagnated due to the inability to use large scale CPU based computers. By a drastic redesign of the algorithm, and moving all the major computation parts into GPU, we have reached a speed of 12 s per molecular dynamics (MD) step for a 512 atom system using 256 GPU cards. This is about 20 times faster than the CPU version of the code regardless of the number of CPU cores used. Our tests and analysis on different GPU platforms and configurations shed lights on the optimal GPU deployments for PWP-DFT calculations. An 1800 step MD simulation is used to study the liquid phase properties of GaInP.
Wave Properties of Equatorial Magnetosonic Waves as Observed by Cluster
NASA Astrophysics Data System (ADS)
Balikhin, M. A.; Walker, S. N.; Shprits, Y.
2014-12-01
A survey of the Cluster STAFF data set shows a number of periods in which Equatorial Magnetosonic Waves display a discrete spectrum. In some of these instances, the frequency of emissions varies in the same fashion as the background magnetic field, indicating that the wars are observed within their source region. This paper analyses the propagation characteristics of these emissions and investigates the appropriateness of the quasi-linear assumption of a gaussian spectrum used in the numerical modelling of their role in the electron dynamics within the radiation belts based in the Chirikov resonance overlap criterion.
Spectroscopic and thermal properties of minerals from density-functional perturbation theory
NASA Astrophysics Data System (ADS)
Refson, K.
2003-12-01
Ab-initio calculations based on density-functional theory have provento give a highly accurate description of structural and elastic properties of minerals under pressure. To evaluate spectroscopic, dielectric and thermal properties it is necessary to compute the second derivatives of the energy with respect to a displacement or electric field perturbation. While the Hellman-Feynmann theorem makes the computation of forces (first derivatives of the energy) straightforward, second derivatives depend on the linear response of the orbitals and density to the perturbation. I will sketch the variational formulation of density-function perturbation theory, and it's implementation in the CASTEP plane-wave code. The capabilities will be illustrated with calculation of the full phonon dispersion spectra and dielectric properties of a-quartz, ZrO2 and NaHF2.
Interaction of a plane shock wave in water with a thin layer of lower density
Bergel`son, V.I.; Nemchinov, I.V.; Orlova, T.I.; Khazins, V.M.
1992-08-01
A numerical analysis is conducted on the interaction of a plane shock wave in water with a thin layer of lower density, which is perpendicular to the wave front. Parameters are defined for the perturbed flow structure and for large-scale precursors, which arise ahead of the shock front. Possibilities are discussed of experimentally investigating this phenomena with a cylindrical shock wave using standard explosives. 4 refs., 4 figs.
Threshold Energy Density of Lower Hybrid Waves in the Freja Experiment
Popel, S. I.
2001-05-15
Data from the Freja satellite experiment on the lower hybrid turbulence in the Earth's magnetosphere are analyzed. It is shown that the observed threshold energy density of lower hybrid waves required for the excitation of localized wave packets is in good agreement with theoretical predictions.
Some properties of adiabatic blast waves in preexisting cavities
NASA Technical Reports Server (NTRS)
Cox, D. P.; Franco, J.
1981-01-01
Cox and Anderson (1982) have conducted an investigation regarding an adiabatic blast wave in a region of uniform density and finite external pressure. In connection with an application of the results of the investigation to a study of interstellar blast waves in the very hot, low-density matrix, it was found that it would be desirable to examine situations with a positive radial density gradient in the ambient medium. Information concerning such situations is needed to learn about the behavior of blast waves occurring within preexisting, presumably supernova-induced cavities in the interstellar mass distribution. The present investigation is concerned with the first steps of a study conducted to obtain the required information. A review is conducted of Sedov's (1959) similarity solutions for the dynamical structure of any explosion in a medium with negligible pressure and power law density dependence on radius.
Properties of Langmuir wave bursts associated with magnetic holes
NASA Technical Reports Server (NTRS)
MacDowall, R. J.; Lin, N.; Kellogg, P. J.; Phillips, J. L.; Neugebauer, M.; Balogh, A.; Forsyth, R. J.
1995-01-01
The radio and plasma wave receivers on the Ulysses spacecraft have detected thousands of short-duration bursts of waves at approximately the electron plasma frequency. These wave events believed to be Langmuir waves are usually less than approximately 5 minutes in duration. They occur in or at the boundaries of depletions in the magnetic field amplitude known as magnetic holes. Using the 16 sec time resolution provided by the plasma frequency receiver, it is possible to examine the density structure inside of magnetic holes. Even higher time resolutions are sometimes available from the radio receiver data. The Ulysses observations show that these wave bursts occur more frequently at high heliographic latitudes; the occurrence rates depend on both latitude and distance from the Sun. We review the statistics for the wave events, compare them to magnetic and plasma parameters, and review the reasons for the more frequent occurrence at high heliographic latitudes.
NASA Astrophysics Data System (ADS)
Xing, Guangchi; Niu, Fenglin; Chen, Min; Yang, Yingjie
2016-03-01
Surface wave tomography routinely uses empirically scaled density model in the inversion of dispersion curves for shear wavespeeds of the crust and uppermost mantle.
Density Functional Theory of Structural and Electronic Properties of III-N Semiconductors
Guerel, H. Hakan; Akinci, Oezden; Uenlue, Hilmi
2010-11-01
In this wok, we present the density functional theory (DFT) calculations of cubic III-N based semiconductors by using the full potential linear augmented plane-wave method plus local orbitals as implemented in the WIEN2k code. Our aim is to predict the pressure effect on structural and electronic properties of III-N binaries and ternaries. Results are given for structural properties (e.g., lattice constant, elastic constants, bulk modulus, and its pressure derivative) and electronic properties (e.g., band structure, density of states, band gaps and band widths) of GaAs, GaN, AlN, and InN binaries and GaAsN ternaries. The proposed model uses GGA exchange-correlation potential to determine band gaps of semiconductors at {Gamma}, L and X high symmetry points of Brillouin zone. The results are found in good agreement with available experimental data for structural and electronic properties of these semiconductors.
NASA Astrophysics Data System (ADS)
Bernard, Marie-Lise; Coutant, Olivier; Beauducel, Francois
2014-05-01
One objective of the french project Domoscan (2009-2013) was to obtain better constraints on the geological structure of La Soufriere hydrothermal system, that is the dome inner structure but also its basement that has not yet been imaged, while it may play an essential role in potential flank destabilization. In this framework, we performed a 3D gravity and P-wave travel time joint inversion to obtain density and P-wave velocity images of La Soufriere hydrothermal system (Coutant et al., 2012). The joint inversion approach was proposed to overcome the lack of resolution of the two methods taken separately. In this study, the coupling between P-wave velocity and density relies on a relationship derived from laboratory measurements on 58 samples from La Soufriere and Mt Pelee deposits. The laboratory data cover a large range of porosity (1-73%) with P wave velocity ranging from 2 to 5.4 km/s and density from 1.5 to 2.8 g/cm3 in water saturated samples. The joint inversion results show that P wave velocity model benefits from density resolution at the volcano summit, while density resolution improves at depth. The improved images allow new insights on La Soufriere structures. As an example the resistive zones that have been so far only seen by electromagnetic surveys may not be due only to argilization but may also be explained by the presence of dense massive zones, that we interpret as andesite spines resulting from 3100 B.P. or 1530 A.D eruptions. These dense bodies may have implication on the stability of the edifice and then the destabilization risks at La Soufriere of Guadeloupe. This work also shows that laboratory studies on physical properties of volcanic rocks and their relationships can be useful in the interpretation of geophysical observations on structurally complex areas such as volcano or geothermal system.
NASA Astrophysics Data System (ADS)
Yoshida, Shuhei; Kurata, Hiroyuki; Ozawa, Shohei; Okubo, Kaito; Horiuchi, Shuma; Ushiyama, Zenta; Yamamoto, Manabu; Koga, Shogo; Tanaka, Asato
2013-09-01
In this study, we propose a three-dimensional shift multiplexing technique using a spherical reference wave. By utilizing a spherical reference wave, multiplex recording is enabled in this system by simply displacing the recording medium. The utilization of a spherical reference wave makes it possible to realize three-dimensional multiplexing, which uses parallel directions of the medium surface and thickness direction. It is also expected that this approach will improve the recording density as compared with the conventional multiplex technique. We report the numerical and experimental evaluation results of our high-density recording and reproduction system based on this principle.
Wave propagation in semi-infinite bar with random imperfections of density and elasticity module
NASA Astrophysics Data System (ADS)
Náprstek, J.
2008-02-01
Mathematical modeling and properties of a linear longitudinal wave propagating in a slender bar with random imperfections of material density and Young modulus of elasticity is discussed. Fluctuation components of material properties are considered as continuous stochastic functions of the length coordinate. Two types of fluctuation and their influence on response properties have been investigated, in particular the delta correlated and a diffusion-type processes. Investigation itself is based on Markov processes and corresponding Fokker-Planck-Kolmogorov equation. The stochastic moments closure as a solution method has been used. Many effects due to the stochastic nature of the problem have been detected. Along the bar a drop of the mean value of the response with the simultaneous increase of the response variance have been observed. This effect does not represent any conventional damping, but a gradual drop of the deterministic and an increase of the stochastic components of the overall response. The rate of the response indeterminacy increases with the increase of the length coordinate. Increasing values of material imperfection variances and the rising excitation frequency can lead to a critical state when the length of the propagating wave is comparable with the correlation length of imperfections. This state will manifest itself as a radical change of the response character. The problem will pass beyond the boundaries of stochastic mechanics and lose its physical meaning. Similar effects can be observed in the FEM analysis, where there is also a certain permissible upper boundary of the excitation frequency corresponding with the size and type of the element used.
Scanning tunneling microscopy in TTF-TCNQ: Phase and amplitude modulated charge density waves
NASA Astrophysics Data System (ADS)
Wang, Z. Z.; Girard, J. C.; Pasquier, C.; Jérome, D.; Bechgaard, K.
2003-03-01
Charge density waves (CDWs) have been studied at the surface of a cleaved tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) single crystal using a low temperature scanning tunneling microscope (STM) under ultrahigh-vacuum conditions, between 300 and 33 K with molecular resolution. All CDW phase transitions of TTF-TCNQ have been identified. The measurement of the modulation wave vector along the a direction provides evidence of the existence of domains comprising single plane wave modulated structures in the temperature regime where the transverse wave vector of the CDW is temperature dependent, as hinted by the theory more than 20 years ago.
Interlaced dynamics of density waves and vortices in self-gravitating Discs
NASA Astrophysics Data System (ADS)
Mamatsashvili, G. R.
2013-04-01
Latest developments in the dynamics of density waves and vortices in selfgravitating protoplanetary discs is reviewed. It is well established by now that in discs, vortices are dynamically coupled with density waves due to the disc's differential rotation, or shear. On the other hand, density waves play a central role in the theory of self-gravitating discs and recently revealed their coupling with vortices implies that the latter can also be subject to self-gravity effects, thus taking active part in defining overall dynamics of self-gravitating discs. We describe the specific features of vortex dynamics and evolution in self-gravitating discs with and without driving by baroclinic or Rossby wave instabilities and point out differences between these two case.
Models for electrostatic drift waves with density variations along magnetic field lines
NASA Astrophysics Data System (ADS)
Garcia, O. E.; Pécseli, H. L.
2013-11-01
Drift waves with vertical magnetic fields in gravitational ionospheres are considered where the unperturbed plasma density is enhanced in a magnetic flux tube. The gravitational field gives rise to an overall decrease of plasma density for increasing altitude. Simple models predict that drift waves with finite vertical wave vector components can increase in amplitude merely due to a conservation of energy density flux of the waves. Field-aligned currents are some of the mechanisms that can give rise to fluctuations that are truly unstable. We suggest a self-consistent generator or "battery" mechanism that in the polar ionospheres can give rise to magnetic field-aligned currents even in the absence of electron precipitation. The free energy here is supplied by steady state electric fields imposed in the direction perpendicular to the magnetic field in the collisional lower parts of the ionosphere or by neutral winds that have similar effects.
Cascade properties of shear Alfven wave turbulence
NASA Technical Reports Server (NTRS)
Bondeson, A.
1985-01-01
Nonlinear three-wave interactions of linear normal modes are investigated for two-dimensional incompressible magnetohydrodynamics and the weakly three-dimensional Strauss equations in the case where a strong uniform background field B0 is present. In both systems the only resonant interaction affecting Alfven waves is caused by the shear of the background field plus the zero frequency components of the perturbation. It is shown that the Alfven waves are cascaded in wavenumber space by a mechanism equivalent to the resonant absorption at the Alfven resonance. For large wavenumbers perpendicular to B0, the cascade is described by Hamilton's ray equations, dk/dt = -(first-order) partial derivative of omega with respect to vector r, where omega includes the effects of the zero frequency perturbations.
Electron-cyclotron wave scattering by edge density fluctuations in ITER
Tsironis, Christos; Peeters, Arthur G.; Isliker, Heinz; Chatziantonaki, Ioanna; Vlahos, Loukas; Strintzi, Dafni
2009-11-15
The effect of edge turbulence on the electron-cyclotron wave propagation in ITER is investigated with emphasis on wave scattering, beam broadening, and its influence on localized heating and current drive. A wave used for electron-cyclotron current drive (ECCD) must cross the edge of the plasma, where density fluctuations can be large enough to bring on wave scattering. The scattering angle due to the density fluctuations is small, but the beam propagates over a distance of several meters up to the resonance layer and even small angle scattering leads to a deviation of several centimeters at the deposition location. Since the localization of ECCD is crucial for the control of neoclassical tearing modes, this issue is of great importance to the ITER design. The wave scattering process is described on the basis of a Fokker-Planck equation, where the diffusion coefficient is calculated analytically as well as computed numerically using a ray tracing code.
Three-dimensional structure of self-excited dust density waves under microgravity conditions
Arp, Oliver; Menzel, Kristoffer; Piel, Alexander
2008-09-07
Self-excited dust density waves in a dusty plasma, containing micrometer-sized particles, have been observed under microgravity conditions at low gas pressures and high dust densities. The waves emerge spontaneously and propagate from the void edge radially outwards to the plasma boundary. We found that the wave propagates obliquely to the local ion flow in regions with high electric fields close to the sheath, whereas it propagates parallel in the plasma bulk. So far the observation was limited to a fixed two-dimensional section through the discharge volume. Recent experiments were performed on parabolic flights in a parallel plate rf discharge, which used the technique of scanning video microscopy. This technique utilizes the high temporal coherence of the waves to reconstruct their full three-dimensional structure. The analysis yields a surprising global spatial coherence of the wave phenomenon.
NASA Astrophysics Data System (ADS)
Blanc, E.
1982-04-01
It is noted that an acoustic wave generated at ground level and propagating vertically through the lower ionosphere produces partial reflections of radio waves transmitted by a vertical sounder. The Doppler effect of the radio wave produced by the acoustic wave motion depends on the properties of the atmosphere and ionosphere. It is shown that this permits a determination of both the neutral-temperature and the electron-density profiles of the lower E region. The accuracy and the advantages offered by this method are discussed, and some experimental results are compared with those of other measurement techniques.
Electron density and gas density measurements in a millimeter-wave discharge
NASA Astrophysics Data System (ADS)
Schaub, S. C.; Hummelt, J. S.; Guss, W. C.; Shapiro, M. A.; Temkin, R. J.
2016-08-01
Electron density and neutral gas density have been measured in a non-equilibrium air breakdown plasma using optical emission spectroscopy and two-dimensional laser interferometry, respectively. A plasma was created with a focused high frequency microwave beam in air. Experiments were run with 110 GHz and 124.5 GHz microwaves at powers up to 1.2 MW. Microwave pulses were 3 μs long at 110 GHz and 2.2 μs long at 124.5 GHz. Electron density was measured over a pressure range of 25 to 700 Torr as the input microwave power was varied. Electron density was found to be close to the critical density, where the collisional plasma frequency is equal to the microwave frequency, over the pressure range studied and to vary weakly with input power. Neutral gas density was measured over a pressure range from 150 to 750 Torr at power levels high above the threshold for initiating breakdown. The two-dimensional structure of the neutral gas density was resolved. Intense, localized heating was found to occur hundreds of nanoseconds after visible plasma formed. This heating led to neutral gas density reductions of greater than 80% where peak plasma densities occurred. Spatial structure and temporal dynamics of gas heating at atmospheric pressure were found to agree well with published numerical simulations.
Mid-Latitude Plasma Density Irregularities and Electromagnetic Wave Scattering
NASA Astrophysics Data System (ADS)
Sotnikov, V.; Kim, T.; Mishin, E.; Rose, D.; Paraschiv, I.
2015-11-01
Ionospheric irregularities cause scintillations of electromagnetic signals that can severely affect navigation and transionospheric communication, in particular during space storms. At midlatitudes, such space weather events are caused mainly by subauroral electric field structures (SAID/SAPS) SAID/SAPS -related shear flows and plasma density troughs point to interchange and Kelvin-Helmholtz type instabilities as a possible source of plasma irregularities. A model of nonlinear development of these instabilities based on the two-fluid hydrodynamic description with inclusion of finite Larmor radius effects will be presented. The high-resolution simulations with continuous density and velocity profiles will be driven by the ambient conditions corresponding to the in situ Defense Meteorological Satellite Program (DMSP) satellite low-resolution data during UHF/GPS L-band subauroral scintillation events. These types of density irregularities play important roles in refraction and scattering of high frequency electromagnetic signals propagating in the Earth's ionosphere, inside the plasma sheath of reentry and hypersonic vehicles, and in many other applications.
Spin polarization driven by a charge-density wave in monolayer 1T-TaS2
NASA Astrophysics Data System (ADS)
Zhang, Qingyun; Gan, Li-Yong; Cheng, Yingchun; Schwingenschlögl, Udo
2014-08-01
Using first-principles calculations, we investigate the electronic and vibrational properties of monolayer T-phase TaS2. We demonstrate that a charge-density wave is energetically favorable at low temperature, similar to bulk 1T-TaS2. Electron-phonon coupling is found to be essential for the lattice reconstruction. The charge-density wave results in a strong localization of the electronic states near the Fermi level and consequently in spin polarization, transforming the material into a magnetic semiconductor with enhanced electronic correlations. The combination of inherent spin polarization with a semiconducting nature distinguishes the monolayer fundamentally from the bulk compound as well as from other two-dimensional transition metal dichalcogenides. Monolayer T-phase TaS2 therefore has the potential to enable two-dimensional spintronics.
Role of Gravity Waves in Determining Cirrus Cloud Properties
NASA Technical Reports Server (NTRS)
OCStarr, David; Singleton, Tamara; Lin, Ruei-Fong
2008-01-01
Cirrus clouds are important in the Earth's radiation budget. They typically exhibit variable physical properties within a given cloud system and from system to system. Ambient vertical motion is a key factor in determining the cloud properties in most cases. The obvious exception is convectively generated cirrus (anvils), but even in this case, the subsequent cloud evolution is strongly influenced by the ambient vertical motion field. It is well know that gravity waves are ubiquitous in the atmosphere and occur over a wide range of scales and amplitudes. Moreover, researchers have found that inclusion of statistical account of gravity wave effects can markedly improve the realism of simulations of persisting large-scale cirrus cloud features. Here, we use a 1 -dimensional (z) cirrus cloud model, to systematically examine the effects of gravity waves on cirrus cloud properties. The model includes a detailed representation of cloud microphysical processes (bin microphysics and aerosols) and is run at relatively fine vertical resolution so as to adequately resolve nucleation events, and over an extended time span so as to incorporate the passage of multiple gravity waves. The prescribed gravity waves "propagate" at 15 m s (sup -1), with wavelengths from 5 to 100 km, amplitudes range up to 1 m s (sup -1)'. Despite the fact that the net gravity wave vertical motion forcing is zero, it will be shown that the bulk cloud properties, e.g., vertically-integrated ice water path, can differ quite significantly from simulations without gravity waves and that the effects do depend on the wave characteristics. We conclude that account of gravity wave effects is important if large-scale models are to generate realistic cirrus cloud property climatology (statistics).
Fabrication and properties of SiNO continuous fiber reinforced BN wave-transparent composites
NASA Astrophysics Data System (ADS)
Cao, F.; Fang, Z.; Chen, F.; Shen, Q.; Zhang, C.
2012-06-01
SiNO continuous fiber reinforced boron nitride (BN) wave-transparent composites (SiNO f /BN) have been fabricated by a precursor infiltration pyrolysis (PIP) method using borazine as the precursor. The densification behavior, microstructures, mechanical properties, and dielectric properties of the composites have been investigated. After four PIP cycles, the density of the composites had increased from 1.1 g·cm-3 to 1.81 g·cm-3. A flexural strength of 128.9 MPa and an elastic modulus of 23.5 GPa were achieved. The obtained composites have relatively high density and the fracture faces show distinct fiber pull-out and interface de-bonding features. The dielectric properties of the SiNO f /BN composites, including the dielectric constant of 3.61 and the dielectric loss angle tangent of 5.7×10-3, are excellent for application as wave-transparent materials.
Studies of the linear and nonlinear properties of Alfvén waves in LAPD
NASA Astrophysics Data System (ADS)
Carter, Troy; Dorfman, Seth; Gekelman, Walter; Tripathi, Shreekrishna; van Compernolle, Bart; Vincena, Steve; Rossi, Giovanni; Jenko, Frank
2015-11-01
An overview will be given of recent experimental research into linear and nonlinear properties of Alfvén waves in the Large Plasma Device (LAPD). The nonlinear three-wave interaction process at the heart of the parametric decay instability is studied by launching counter-propagating Alfvén waves from antennas placed at either end of LAPD, producing a damped ion acoustic mode. The decay of a lone, large amplitude Alfvén wave has been observed, producing co-propagating daughter waves with characteristics consistent with kinetic Alfvén waves. The process has an amplitude threshold and the frequency of the daughter modes varies with the amplitude of the pump. A new plasma source based on LaB6 cathode has been added to LAPD, enabling much higher density (x50), electron temperature (x2) and ion temperature (x6). This provides the opportunity to study the physics of waves and instabilities with space and astrophysically relevant β. Topics under investigation include the physics of Alfvén waves in increased β plasmas, electromagnetic effects in drift-Alfvén wave turbulence and the excitation of ion-temperature-anisotropy driven modes such as the mirror and firehose. Supported by NSF and DOE.
Correlation of densities with shear wave velocities and SPT N values
NASA Astrophysics Data System (ADS)
Anbazhagan, P.; Uday, Anjali; Moustafa, Sayed S. R.; Al-Arifi, Nassir S. N.
2016-06-01
Site effects primarily depend on the shear modulus of subsurface layers, and this is generally estimated from the measured shear wave velocity (V s) and assumed density. Very rarely, densities are measured for amplification estimation because drilling and sampling processes are time consuming and expensive. In this study, an attempt has been made to derive the correlation between the density (dry and wet density) and V s/SPT (standard penetration test) N values using measured data. A total of 354 measured V s and density data sets and 364 SPT N value and density data sets from 23 boreholes have been used in the study. Separate relations have been developed for all soil types as well as fine-grained and coarse-grained soil types. The correlations developed for bulk density were compared with the available data and it was found that the proposed relation matched well with the existing data. A graphical comparison and validation based on the consistency ratio and cumulative frequency curves was performed and the newly developed relations were found to demonstrate good prediction performance. An attempt has also been made to propose a relation between the bulk density and shear wave velocity applicable for a wide range of soil and rock by considering data from this study as well as that of previous studies. These correlations will be useful for predicting the density (bulk and dry) of sites having measured the shear wave velocity and SPT N values.
Structured mass density slab as a waveguide of fast magnetoacoustic waves
NASA Astrophysics Data System (ADS)
Jelínek, P.; Karlický, M.
Coronal loops are waveguides for magnetohydrodynamic (MHD) waves. These loops are expected to be structured. Therefore, in the present paper, we numerically studied the propagation of the fast MHD waves in the structured density slab (composed from a broad density slab with one axisymmetric narrow sub-slab superposed), and analysed the wave signals. Then, this structured slab was divided into its components, i.e., to simple broad and narrow slabs and the same analysis was made. We compared results of both these cases. For the calculations we adopted a two-dimensional (2D) magnetohydrodynamic (MHD) model, in which we solved a full set of ideal time-dependent MHD equations using the FLASH code, applying the adaptive mesh refinement (AMR) method. To initiate the fast sausage magnetoacoustic waves, we used axisymmetric Gaussian velocity perturbation. Wave signals were detected in different locations along the slab and as a diagnostic tool of these waves, the wavelet analysis method has been used. We found that for the structured density slab with sufficiently sharp boundaries, i.e., for good quality waveguides (without an energy leakage), the guided waves in the structured slab behave similarly as in its separated (simple slab) components.
Quantum Hall effect in field-induced spin density wave systems
NASA Astrophysics Data System (ADS)
Tevosyan, Kahren
The research work described in this thesis is motivated by recent theoretical and experimental studies of the Quantum Hall Effect (QHE) in the quasi-one-dimensional conductors such as organic metals of the (TMTSF)sb2X family. These materials consist of weakly coupled parallel conducting chains that lie in the same plane. They exhibit very interesting behavior in the presence of a strong magnetic field which is perpendicular to the plane. At low temperatures a series of phase transitions from the metallic state to spin density wave states occur with increasing magnetic field. The latter are called the Field-Induced Spin Density Wave (FISDW) states. Within each FISDW phase, the value of the Hall resistance is quantized, signalling the presence of the Quantum Hall Effect. In contrast with the conventional QHE in isotropic two-dimensional systems, finite-width Landau bands appear naturally in the disorder-free (TMTSF)sb2X materials. In fact, the theory of the QHE in quasi-one-dimensiona1 organic conductors has so far been developed without any consideration of the effect of the disorder required to broaden Landau bands in isotropic systems. Here we address for the first time the localization properties of the quantum states in FISDW Landau bands. We employ the Thouless approach which uses the sensitivity of the eigenvalues to the choice of boundary conditions to study localization. Our results show that the localization properties of the states are very different from those of the conventional QHE systems. We find that the Thouless numbers do not decrease exponentially with the system size, indicating that states are not localized on the scales we can study. Another aspect of the dissertation deals with the edge state picture of the QHE which states that gapless excitations localized at the system edge are present whenever the quantum Hall effect occurs. We examine these properties of edge states for the FISDW systems by performing computer simulations to model the
Charge density waves in individual nanoribbons of orthorhombic-TaS₃.
Farley, Katie E; Shi, Zhenzhong; Sambandamurthy, G; Banerjee, Sarbajit
2015-07-28
Orthorhombic-TaS3 is a quasi-1D material that undergoes a Peierls' transition to become a charge density wave conductor at low temperatures. Electrical transport measurements of individual single-crystalline TaS3 nanoribbons prepared by a novel bottom-up method from elemental precursors indicate a depression of the Peierls' ordering temperature to 205 K, broadening of the electric-field-induced depinning of the charge density wave below the Peierls' transition temperature, and a greatly increased threshold voltage for nucleation of charge density wave dislocations posited to be a result of surface confinement and finite size effects. Single-nanoribbon measurements of broad-band noise indicate discrete phase slip events near the depinning threshold. Three distinct regimes are identified with the normalized noise spectrum showing a distinctive maxima near the threshold voltage for depinning of the charge density wave, corresponding to sampling of different metastable states that balance ordered and sliding charge density waves. PMID:26104129
On the density waves developed in gravity channel flows of granular materials
NASA Astrophysics Data System (ADS)
Wang, Chi-Hwa; Tong, Ziquan
2001-05-01
This paper provides insight to the transient development of density waves generated in gravity-driven flows of granular materials. The evolution of three modes of dominant linear instabilities (predicted in a previous work by Wang, Jackson & Sundaresan 1997) is examined by FFT analysis. For the first symmetric density wave (SDW1) mode, the evolution is governed by the linear instability. The second symmetric density wave (SDW2) mode undergoes a few stages of temporal development; as a result, large particle clusters gradually degenerate into a series of smaller clusters in the flow direction. For the anti-symmetric (ASDW) mode, the corresponding particle distribution shows significant development in the direction perpendicular to the flow. The present study indicates that the wall roughness may affect the structure of the density waves, but these density waves need not be triggered by the wall roughness. All the three modes of instabilities reported in this work are of inertial nature and occur only when the particle particle collisions are significantly inelastic.
Inhomogeneity of charge-density-wave order and quenched disorder in a high-Tc superconductor
NASA Astrophysics Data System (ADS)
Campi, G.; Bianconi, A.; Poccia, N.; Bianconi, G.; Barba, L.; Arrighetti, G.; Innocenti, D.; Karpinski, J.; Zhigadlo, N. D.; Kazakov, S. M.; Burghammer, M.; Zimmermann, M. V.; Sprung, M.; Ricci, A.
2015-09-01
It has recently been established that the high-transition-temperature (high-Tc) superconducting state coexists with short-range charge-density-wave order and quenched disorder arising from dopants and strain. This complex, multiscale phase separation invites the development of theories of high-temperature superconductivity that include complexity. The nature of the spatial interplay between charge and dopant order that provides a basis for nanoscale phase separation remains a key open question, because experiments have yet to probe the unknown spatial distribution at both the nanoscale and mesoscale (between atomic and macroscopic scale). Here we report micro X-ray diffraction imaging of the spatial distribution of both short-range charge-density-wave `puddles' (domains with only a few wavelengths) and quenched disorder in HgBa2CuO4 + y, the single-layer cuprate with the highest Tc, 95 kelvin (refs 26, 27, 28). We found that the charge-density-wave puddles, like the steam bubbles in boiling water, have a fat-tailed size distribution that is typical of self-organization near a critical point. However, the quenched disorder, which arises from oxygen interstitials, has a distribution that is contrary to the usually assumed random, uncorrelated distribution. The interstitial-oxygen-rich domains are spatially anticorrelated with the charge-density-wave domains, because higher doping does not favour the stripy charge-density-wave puddles, leading to a complex emergent geometry of the spatial landscape for superconductivity.
Inhomogeneity of charge-density-wave order and quenched disorder in a high-Tc superconductor.
Campi, G; Bianconi, A; Poccia, N; Bianconi, G; Barba, L; Arrighetti, G; Innocenti, D; Karpinski, J; Zhigadlo, N D; Kazakov, S M; Burghammer, M; Zimmermann, M v; Sprung, M; Ricci, A
2015-09-17
It has recently been established that the high-transition-temperature (high-Tc) superconducting state coexists with short-range charge-density-wave order and quenched disorder arising from dopants and strain. This complex, multiscale phase separation invites the development of theories of high-temperature superconductivity that include complexity. The nature of the spatial interplay between charge and dopant order that provides a basis for nanoscale phase separation remains a key open question, because experiments have yet to probe the unknown spatial distribution at both the nanoscale and mesoscale (between atomic and macroscopic scale). Here we report micro X-ray diffraction imaging of the spatial distribution of both short-range charge-density-wave 'puddles' (domains with only a few wavelengths) and quenched disorder in HgBa2CuO4 + y, the single-layer cuprate with the highest Tc, 95 kelvin (refs 26-28). We found that the charge-density-wave puddles, like the steam bubbles in boiling water, have a fat-tailed size distribution that is typical of self-organization near a critical point. However, the quenched disorder, which arises from oxygen interstitials, has a distribution that is contrary to the usually assumed random, uncorrelated distribution. The interstitial-oxygen-rich domains are spatially anticorrelated with the charge-density-wave domains, because higher doping does not favour the stripy charge-density-wave puddles, leading to a complex emergent geometry of the spatial landscape for superconductivity. PMID:26381983
Density waves in debris discs and galactic nuclei
NASA Astrophysics Data System (ADS)
Jalali, Mir Abbas; Tremaine, Scott
2012-04-01
We study the linear perturbations of collisionless near-Keplerian discs. Such systems are models for debris discs around stars and the stellar discs surrounding supermassive black holes at the centres of galaxies. Using a finite-element method, we solve the linearized collisionless Boltzmann equation and Poisson's equation for a wide range of disc masses and rms orbital eccentricities to obtain the eigenfrequencies and shapes of normal modes. We find that these discs can support large-scale 'slow' modes, in which the frequency is proportional to the disc mass. Slow modes are present for arbitrarily small disc mass so long as the self-gravity of the disc is the dominant source of apsidal precession. We find that slow modes are of two general types: parent modes and hybrid child modes, the latter arising from resonant interactions between parent modes and singular van Kampen modes. The most prominent slow modes have azimuthal wavenumbers m= 1 and m= 2. We illustrate how slow modes in debris discs are excited during a fly-by of a neighbouring star. Many of the non-axisymmetric features seen in debris discs (clumps, eccentricity, spiral waves) that are commonly attributed to planets could instead arise from slow modes; the two hypotheses can be distinguished by long-term measurements of the pattern speed of the features.
Analyzing and improving viscoelastic properties of high density polyethylene
NASA Astrophysics Data System (ADS)
Ahmed, Reaj Uddin
2011-12-01
High Density Polyethylene (HDPE) is closely packed, less branched polyethylene having higher mechanical properties, chemical resistance, and heat resistance than Low Density Polyentylene (LDPE). Better properties and cost effectiveness make it an important raw material over LDPE in packaging industries. Stacked containers made of HDPE experience static loading and deformation strain during their storage period in a warehouse. As HDPE is a viscoelastic material, dimensional stability of stacked HDPE containers depends on time dependent properties such as creep and stress relaxation. Now, light weighting is a driving force in packaging industries, which results in lower production costs but performance of the product becomes a challenge. Proper understanding of the viscoelastic properties of HDPE, with relevant FE simulation can facilitate improved designs. This research involves understanding and improving viscoelastic properties, creep behavior, and stress relaxation of HDPE. Different approaches were carried out to meet the objectives. Organic filler CaCO3 was added to HDPE at increasing weight fractions and corresponding property changes were investigated. Annealing heat treatments were also carried out for potential property improvements. The effect of ageing was also investigated on both annealed and non annealed HDPE. The related performance of different water bottles against squeeze pressure was also characterized. Both approaches, incorporation of CaCO3 and annealing, showed improvements in the properties of HDPE over neat HDPE. This research aids finding the optimum solution for improving viscoelastic properties, stress relaxation, and creep behavior of HDPE in manufacturing.
Johnston, J.E.; Christensen, N.I. . Dept. of Earth and Atmospheric Sciences)
1992-01-01
The physical properties of a sequence of Paleozoic sedimentary rocks have been examined in detail, with an emphasis on laboratory measurements of density, shear wave velocity, shear wave splitting, and Vp/Vs ratios. Seismic properties of 147 cores from 49 rock samples collected from the thorn hill sedimentary sequence of eastern Tennessee are examined in terms of implications for future seismic studies in the southern Appalachians. The shear wave velocities of these rocks are strongly influenced by the relatively high shear wave velocity of quartz. Shear wave velocity anisotropy is present in most of the lithologic groups: it is highest in the shales while being almost insignificant in the dolostones. The related phenomenon of shear wave splitting occurs to some degree in all of the lithologies studied and at high pressures originates from mineral orientation. Compressional to shear velocity (Vp/Vs) ratios of approximately 1.82 (dolostones) and 1.95 (limestones) effectively characterize the carbonates while other lithologies display wider ranges of Vp/Vs, primarily due to the influence of accessory minerals such as quartz. Densities of the sample suite range from 2.34 g/cm[sup 3] (shale) to 2.86 g/cm[sup 3] (dolostone). Normal incidence shear and compressional wave synthetic seismograms of the entire Thorn Hill section indicate that three zones of high amplitude reflections would be seen on reflection records obtained over this 3,327 meter thick sequence. differences are seen at some interfaces in the Mississippian-Devonian interval, which are more reflective to shear waves, and in the Ordovician Martinsburg Formation, which appears more reflective to compressional waves.
Computation of Thermally Perfect Properties of Oblique Shock Waves
NASA Technical Reports Server (NTRS)
Tatum, Kenneth E.
1996-01-01
A set of compressible flow relations describing flow properties across oblique shock waves, derived for a thermally perfect, calorically imperfect gas, is applied within the existing thermally perfect gas (TPG) computer code. The relations are based upon a value of cp expressed as a polynomial function of temperature. The updated code produces tables of compressible flow properties of oblique shock waves, as well as the original properties of normal shock waves and basic isentropic flow, in a format similar to the tables for normal shock waves found in NACA Rep. 1135. The code results are validated in both the calorically perfect and the calorically imperfect, thermally perfect temperature regimes through comparisons with the theoretical methods of NACA Rep. 1135, and with a state-of-the-art computational fluid dynamics code. The advantages of the TPG code for oblique shock wave calculations, as well as for the properties of isentropic flow and normal shock waves, are its ease of use, and its applicability to any type of gas (monatomic, diatomic, triatomic, polyatomic, or any specified mixture thereof).
Computation of Thermally Perfect Oblique Shock Wave Properties
NASA Technical Reports Server (NTRS)
Tatum, Kenneth E.
1997-01-01
A set of compressible flow relations describing flow properties across oblique shock waves, derived for a thermally perfect, calorically imperfect gas, is applied within the existing thermally perfect gas (TPG) computer code. The relations are based upon the specific heat expressed as a polynomial function of temperature. The updated code produces tables of compressible flow properties of oblique shock waves, as well as the original properties of normal shock waves and basic isentropic flow, in a format similar to the tables for normal shock waves found in NACA Rep. 1135. The code results are validated in both the calorically perfect and the calorically imperfect, thermally perfect temperature regimes through comparisons with the theoretical methods of NACA Rep. 1135. The advantages of the TPG code for oblique shock wave calculations, as well as for the properties of isentropic flow and normal shock waves, are its ease of use and its applicability to any type of gas (monatomic, diatomic, triatomic, polyatomic, or any specified mixture thereof).
Projector augmented-wave method: Application to relativistic spin-density functional theory
NASA Astrophysics Data System (ADS)
Dal Corso, Andrea
2010-08-01
Applying the projector augmented-wave (PAW) method to relativistic spin-density functional theory (RSDFT) we derive PAW Dirac-Kohn-Sham equations for four-component spinor pseudo-wave-functions. The PAW freedom to add a vanishing operator inside the PAW spheres allows us to transform these PAW Dirac-type equations into PAW Pauli-type equations for two-component spinor pseudo-wave-functions. With these wave functions, we get the frozen-core energy as well as the charge and magnetization densities of RSDFT, with errors comparable to the largest between 1/c2 and the transferability error of the PAW data sets. Presently, the latter limits the accuracy of the calculations, not the use of the Pauli-type equations. The theory is validated by applications to isolated atoms of Fe, Pt, and Au, and to the band structure of fcc-Pt, fcc-Au, and ferromagnetic bcc-Fe.
Density response of the mesospheric sodium layer to gravity wave perturbations
NASA Technical Reports Server (NTRS)
Shelton, J. D.; Gardner, C. S.; Sechrist, C. F., Jr.
1980-01-01
Lidar observations of the mesospheric sodium layer often reveal wavelike features moving through the layer. It is often assumed that these features are a layer density response to gravity waves. Chiu and Ching (1978) described the approximate form of the linear response of atmospheric layers to gravity waves. In this paper, their results are used to predict the response of the sodium layer to gravity waves. These simulations are compared with experimental observations and a good correlation is found between the two. Because of the thickness of the sodium layer and the density gradients found in it, a linear model of the layer response is not always adequate to describe gravity wave-sodium layer interactions. Inclusion of nonlinearities in the layer response is briefly discussed. Experimental data is seen to contain features consistent with the predicted nonlinearities.
On d+id Density Wave and Superconducting Orderings in Hole-Doped Cuprates
NASA Astrophysics Data System (ADS)
Goswami, Partha; Gahlot, Ajay Pratap Singh; Singh, Pankaj
2013-05-01
The d+id-density wave (chiral DDW) order, at the anti-ferromagnetic wave vector Q = (π, π), is assumed to represent the pseudo-gap (PG) state of a hole-doped cuprate superconductor. The pairing interaction U(k, k‧) required for d+id ordering comprises of (Ux2-y2(k, k‧), Uxy(k, k‧)), where Ux2-y2(k, k') = U1(cos kxa-cos kya)(cos k'xa- cos k'ya) and Uxy(k, k') = U2sin(kxa)sin(kya) sin(k'xa) sin(k'ya) with U1 > U2. The d-wave superconductivity (DSC), driven by an assumed attractive interaction of the form V(k, k') = -ěrt V1ěrt(cos kxa-cos kya)(cos k'xa- cos k'ya) where V1 is a model parameter, is discussed within the mean-field framework together with the d+id ordering. The single-particle excitation spectrum in the CDDW + DSC state is characterized by the Bogoluibov quasi-particle bands — a characteristic feature of SC state. The coupled gap equations are solved self-consistently together with the equation to determine the chemical potential (μ). With the pinning of the van Hove-singularities close to μ, one is able to calculate the thermodynamic and transport properties of the under-doped cuprates in a consistent manner. The electron specific heat displays non-Fermi liquid feature in the CDDW state. The CDDW and DSC are found to represent two competing orders as the former brings about a depletion of the spectral weight (and Raman response function density) available for pairing in the anti-nodal region of momentum space. It is also shown that the depletion of the spectral weight below Tc at energies larger than the gap amplitude occurs. This is an indication of the strong-coupling superconductivity in cuprates. The calculation of the ratio of the quasi-particle thermal conductivity αxx and temperature in the superconducting phase is found to be constant in the limit of near-zero quasi-particle scattering rate.
Measurements of ICRF wave-induced density fluctuations in LHD by a microwave reflectometer
NASA Astrophysics Data System (ADS)
Ejiri, A.; Tokuzawa, T.; Tsujii, N.; Saito, K.; Seki, T.; Kasahara, H.; Kamio, S.; Seki, R.; Mutoh, T.; Yamada, I.; Takase, Y.
2015-12-01
An O-mode microwave reflectometer has been developed to measure ICRF wave induced electron density fluctuations in LHD plasmas. The system has two probing frequencies (28.8 and 30.1 GHz) to measure two spatial points simultaneously. The rms density fluctuation levels are typically 0.01%. The linearity between the measured density fluctuation amplitude and the square root of the RF power is discussed. The decay length of the RF field was estimated to be 1 to 7 m under the operational condition investigated. A typical spatial distance between the two measurement points corresponding to the two probing frequencies is a few centimeters, and the fluctuation amplitudes at the two points are similar in amplitude. The phase difference between the two fluctuations show in-phase relationship on average. Out-of phase relationships, which implies a standing wave structure, are often observed when the wave absorption is expected to be poor.
Suppression of Three-Dimensional Charge Density Wave Ordering via Thickness Control
NASA Astrophysics Data System (ADS)
Kim, Gideok; Neumann, Michael; Kim, Minu; Le, Manh Duc; Kang, Tae Dong; Noh, Tae Won
2015-11-01
Barium bismuth oxide (BaBiO3 ) is the end member of two families of high-Tc superconductors, i.e., BaPb1 -xBix O3 and Ba1 -xKx BiO3 . The undoped parent compound is an insulator, exhibiting a charge density wave that is strongly linked to a static breathing distortion in the oxygen sublattice of the perovskite structure. We report a comprehensive spectroscopic and x-ray diffraction study of BaBiO3 thin films, showing that the minimum film thickness required to stabilize the breathing distortion and charge density wave is ≈11 unit cells, and that both phenomena are suppressed in thinner films. Our results constitute the first experimental observation of charge density wave suppression in bismuthate compounds without intentionally introducing dopants.
Elastic anomalies at the charge density wave transition in TbTe3
NASA Astrophysics Data System (ADS)
Saint-Paul, M.; Guttin, C.; Lejay, P.; Remenyi, G.; Leynaud, O.; Monceau, P.
2016-05-01
The set of elastic constants of the charge density wave (CDW) rare earth tritelluride TbTe3 has been measured at 15 MHz in the temperature range 300-360 K. Large anomalies in the velocity and ultrasonic attenuation of the longitudinal C11 and C33 modes are observed at the charge density wave phase transition TCDW=333 K. Anisotropic stress dependence ∂TCDW / ∂σ is found, the components ∂TCDW / ∂σ11 and ∂TCDW / ∂σ33 in the (a,c) plane are one order of magnitude larger than the component ∂TCDW / ∂σ22 perpendicular to it. The Landau theory has been used to explain the experimental data. Critical behaviour near the charge density wave phase transition is described in terms of a phenomenological dynamic scaling theory.
Long-range order and pinning of charge-density waves in competition with superconductivity
NASA Astrophysics Data System (ADS)
Caplan, Yosef; Wachtel, Gideon; Orgad, Dror
2015-12-01
Recent experiments show that charge-density-wave correlations are prevalent in underdoped cuprate superconductors. The correlations are short ranged at weak magnetic fields but their intensity and spatial extent increase rapidly at low temperatures beyond a crossover field. Here we consider the possibility of long-range charge-density-wave order in a model of a layered system where such order competes with superconductivity. We show that in the clean limit, low-temperature long-range order is stabilized by arbitrarily weak magnetic fields. This apparent discrepancy with the experiments is resolved by the presence of disorder. Like the field, disorder nucleates halos of charge-density wave, but unlike the former it also disrupts interhalo coherence, leading to a correlation length that is always finite. Our results are compatible with various experimental trends, including the onset of longer range correlations induced by interlayer coupling above a characteristic field scale.
Exotic topological density waves in cold atomic Rydberg-dressed fermions
Li, Xiaopeng; Sarma, S Das
2015-01-01
Versatile controllability of interactions in ultracold atomic and molecular gases has now reached an era where quantum correlations and unconventional many-body phases can be studied with no corresponding analogues in solid-state systems. Recent experiments in Rydberg atomic gases have achieved exquisite control over non-local interactions, allowing novel quantum phases unreachable with the usual local interactions in atomic systems. Here we study Rydberg-dressed atomic fermions in a three-dimensional optical lattice predicting the existence of hitherto unheard-of exotic mixed topological density wave phases. By varying the spatial range of the non-local interaction, we find various chiral density waves with spontaneous time-reversal symmetry breaking, whose quasiparticles form three-dimensional quantum Hall and Weyl semimetal states. Remarkably, certain density waves even exhibit mixed topologies beyond the existing topological classification. Our results suggest gapless fermionic states could exhibit far richer topology than previously expected. PMID:25972134
On the Linear Damping Relation for Density Waves in Saturn’s Rings
NASA Astrophysics Data System (ADS)
Schmidt, Jürgen; Colwell, Joshua E.; Lehmann, Marius; Marouf, Essam A.; Salo, Heikki; Spahn, Frank; Tiscareno, Matthew S.
2016-06-01
We revisit the equation for viscous damping of density waves derived from linearized theory and show that the damping is not only determined by the magnitudes of shear and bulk viscosity. Modifications arise from the dependence of the viscosity on the ring’s surface mass density. This was noted more than 30 years ago by Goldreich & Tremaine (1978b). Still, to date the consequences have not been explored. In the literature these terms have been neglected throughout when fitting the rings’ viscosity from observations of wave damping. Therefore, one must suspect that these viscosities, as well as the dispersion velocities inferred from them, suffer from systematic bias, which might be small or significant, depending on the local conditions in the ring. We show that the modified damping formula, to linear order, is related to the stability threshold for viscous overstability and argue that the appearance of density waves may be altered by this instability.
Development of spiral density waves and evaluation of their parameters: a computer experiment
Grivnev, E.M.
1985-07-01
Numerical experiments with a disk of N = 250 interacting test-particles show that the velocity field does manifest development of the spiral density waves predicted by the Lin theory. The parameters of these simulated waves are evaluated in a nonlinear treatment. Similar N-body computer models can be employed to analyze the spiral structure in loosely wound galaxies such as NGC 3310 whose underlying equilibrium state is strongly perturbed.
Prediction of crack density in porous-cracked rocks from elastic wave velocities
NASA Astrophysics Data System (ADS)
Byun, Ji-Hwan; Lee, Jong-Sub; Park, Keunbo; Yoon, Hyung-Koo
2015-04-01
The stability of structures that are built over rock is affected by cracks in the rock that result from weathering, thawing and freezing processes. This study investigates a new method for determining rock crack densities using elastic wave velocities. The Biot-Gassmann model, which consists of several elastic moduli and Poisson's ratio, was used to determine a theoretical equation to predict the crack density of rocks. Ten representative specimens were extracted from ten boreholes to highlight the spatial variability. Each specimen was characterized using X-Ray Diffraction (XRD) analysis. The specimens were carved into cylinders measuring 50 mm in diameter and 30 mm in height using an abrasion process. A laboratory test was performed to obtain the elastic wave velocity using transducers that can transmit and receive compressional and shear waves. The measured compressional wave and shear wave velocities were approximately 2955 m/s-5209 m/s and 1652 m/s-2845 m/s, respectively. From the measured elastic wave velocities, the analyzed crack density and crack porosity were approximately 0.051-0.185 and 0.03%-0.14%, respectively. The calculated values were compared with the results of previous studies, and they exhibit similar values and trends. The sensitivity of the suggested theoretical equation was analyzed using the error norm technique. The results show that the compressional wave velocity and the shear modulus of a particle are the most influential factors in this equation. The study demonstrates that rock crack density can be estimated using the elastic wave velocities, which may be useful for investigating the stability of structures that are built over rock.
Numerical Tests and Properties of Waves in Radiating Fluids
Johnson, B M; Klein, R I
2009-09-03
We discuss the properties of an analytical solution for waves in radiating fluids, with a view towards its implementation as a quantitative test of radiation hydrodynamics codes. A homogeneous radiating fluid in local thermodynamic equilibrium is periodically driven at the boundary of a one-dimensional domain, and the solution describes the propagation of the waves thus excited. Two modes are excited for a given driving frequency, generally referred to as a radiative acoustic wave and a radiative diffusion wave. While the analytical solution is well known, several features are highlighted here that require care during its numerical implementation. We compare the solution in a wide range of parameter space to a numerical integration with a Lagrangian radiation hydrodynamics code. Our most significant observation is that flux-limited diffusion does not preserve causality for waves on a homogeneous background.
Waves associated with interplanetary shocks: Types and properties
NASA Astrophysics Data System (ADS)
Goncharov, Oleksandr; Nemecek, Zdenek; Safrankova, Jana; Prech, Lubomir; Koval, Andriy; Wilson, Lynn B., III; Zastenker, Georgy N.
2016-04-01
Interplanetary (IP) shocks are often associated with high-frequency (several Hz) wave packets in both upstream and downstream regions. These waves could be resolved in Wind fast magnetic field data but the time resolution of plasma instruments is insufficient for their detection. The BMSW instrument onboard the Spektr-R spacecraft measures solar wind parameters with a resolution of 32 ms and it allows a detailed analysis of these waves. Our previous analysis of subcritical low-Mach-number fast forward shocks has shown that the both upstream and downstream waves conserve over the spacecraft separation of the order of 200 Re and their wavelengths are directly proportional to the shock ramp thickness that is controlled by the ion thermal gyroradius. Comparing observations of both Wind and Spektr-R spacecraft, we discuss a nature of these waves in both regions and their properties and their dependence on upstream solar wind and magnetic field parameters.
Effect of pulse slippage on beat wave THz generation in a rippled density magnetized plasma
NASA Astrophysics Data System (ADS)
Kumar, Manoj; Rajouria, Satish Kumar; K, Magesh Kumar K.
2013-10-01
Beat wave excitation of terahertz radiation by nonlinear mixing of two laser pulses in a ripple density magnetized plasma is investigated allowing for the effect of pulse slippage. The lasers' ponderomotive-force-induced electron drift couples with the density ripple to produce a nonlinear current that resonantly drives the terahertz at the beat frequency. Density ripple provides the phase matching while the magnetic field, transverse to the direction of laser propagation, provides a transverse component to current density. However, the group velocity mismatch between the lasers and the terahertz radiation leads to slippage of the latter behind the laser pulses leading to saturation of the terahertz amplitude.
KRONOSEISMOLOGY: USING DENSITY WAVES IN SATURN'S C RING TO PROBE THE PLANET'S INTERIOR
Hedman, M. M.; Nicholson, P. D.
2013-07-01
Saturn's C ring contains multiple spiral patterns that appear to be density waves driven by periodic gravitational perturbations. In other parts of Saturn's rings, such waves are generated by Lindblad resonances with Saturn's various moons, but most of the wave-like C-ring features are not situated near any strong resonance with any known moon. Using stellar occultation data obtained by the Visual and Infrared Mapping Spectrometer on board the Cassini spacecraft, we investigate the origin of six unidentified C-ring waves located between 80,900 and 87,200 km from Saturn's center. By measuring differences in the waves' phases among the different occultations, we are able to determine both the number of arms in each spiral pattern and the speeds at which these patterns rotate around the planet. We find that all six of these waves have between two and four arms and pattern speeds between 1660 Degree-Sign day{sup -1} and 1861 Degree-Sign day{sup -1}. These speeds are too large to be attributed to any satellite resonance. Instead, they are comparable to the predicted pattern speeds of waves generated by low-order normal-mode oscillations within the planet. The precise pattern speeds associated with these waves should therefore provide strong constraints on Saturn's internal structure. Furthermore, we identify multiple waves with the same number of arms and very similar pattern speeds, indicating that multiple m = 3 and m = 2 sectoral (l = m) modes may exist within the planet.
Driving ionospheric outflows and magnetospheric O+ energy density with Alfvén waves
NASA Astrophysics Data System (ADS)
Chaston, C. C.; Bonnell, J. W.; Reeves, G. D.; Skoug, R. M.
2016-05-01
We show how dispersive Alfvén waves observed in the inner magnetosphere during geomagnetic storms can extract O+ ions from the topside ionosphere and accelerate these ions to energies exceeding 50 keV in the equatorial plane. This occurs through wave trapping, a variant of "shock" surfing, and stochastic ion acceleration. These processes in combination with the mirror force drive field-aligned beams of outflowing ionospheric ions into the equatorial plane that evolve to provide energetic O+ distributions trapped near the equator. These waves also accelerate preexisting/injected ion populations on the same field lines. We show that the action of dispersive Alfvén waves over several minutes may drive order of magnitude increases in O+ ion pressure to make substantial contributions to magnetospheric ion energy density. These wave accelerated ions will enhance the ring current and play a role in the storm time evolution of the magnetosphere.
Determination of basic physical and mechanical properties of basaltic rocks from P-wave velocity
NASA Astrophysics Data System (ADS)
Karakuş, Askeri; Akatay, Mahmut
2013-12-01
Physical and mechanical properties of basaltic rocks used as main building material in historical buildings in Diyarbakir show great diversity depending on the place of origin. Especially, earthquake studies as well as restoration jobs and civil engineers and architects who work on building dynamics need to know basic material properties of basaltic rocks that are the main building material. In this study, the basalt samples obtained from 18 different locations of the Diyarbakir area were tested in order to estimate the main material properties of basalts used in historical buildings without collecting samples from them. Subsequently, statistical relationships between the nondestructive P-wave velocity and other properties of basalts were investigated. Consequently, highly correlated models (R2 = 0.717-0.890) were obtained between P-wave velocity and density, porosity, uniaxial compressive strength, Brazilian tensile strength, modulus of elasticity and Poisson's ratio.
NASA Technical Reports Server (NTRS)
Brophy, Thomas G.; Rosen, Paul A.
1992-01-01
A parallel examination is conducted of Voyager radio and photopolarimeter occultation observations of the Saturn A ring's density waves. The radio instrument waves exhibit an average -90 deg offset from the dynamical phase. A warping height of about 100-m amplitude can qualtitatively reproduce this phase shift, while preserving the overall model wave shape. These results may be profoundly relevant for satellite-ring torque calculations in Saturn's rings, given the deposition of all of the net torque of the standard model in the first wavelength.
Evidence for a Peierls phase-transition in a three-dimensional multiple charge-density waves solid
Mansart, Barbara; Cottet, Mathieu J. G.; Penfold, Thomas J.; Dugdale, Stephen B.; Tediosi, Riccardo; Chergui, Majed; Carbone, Fabrizio
2012-01-01
The effect of dimensionality on materials properties has become strikingly evident with the recent discovery of graphene. Charge ordering phenomena can be induced in one dimension by periodic distortions of a material’s crystal structure, termed Peierls ordering transition. Charge-density waves can also be induced in solids by strong coulomb repulsion between carriers, and at the extreme limit, Wigner predicted that crystallization itself can be induced in an electrons gas in free space close to the absolute zero of temperature. Similar phenomena are observed also in higher dimensions, but the microscopic description of the corresponding phase transition is often controversial, and remains an open field of research for fundamental physics. Here, we photoinduce the melting of the charge ordering in a complex three-dimensional solid and monitor the consequent charge redistribution by probing the optical response over a broad spectral range with ultrashort laser pulses. Although the photoinduced electronic temperature far exceeds the critical value, the charge-density wave is preserved until the lattice is sufficiently distorted to induce the phase transition. Combining this result with ab initio electronic structure calculations, we identified the Peierls origin of multiple charge-density waves in a three-dimensional system for the first time. PMID:22451898
Metwally, Khaled; Lefevre, Emmanuelle; Baron, Cécile; Zheng, Rui; Pithioux, Martine; Lasaygues, Philippe
2016-02-01
When assessing ultrasonic measurements of material parameters, the signal processing is an important part of the inverse problem. Measurements of thickness, ultrasonic wave velocity and mass density are required for such assessments. This study investigates the feasibility and the robustness of a wavelet-based processing (WBP) method based on a Jaffard-Meyer algorithm for calculating these parameters simultaneously and independently, using one single ultrasonic signal in the reflection mode. The appropriate transmitted incident wave, correlated with the mathematical properties of the wavelet decomposition, was determined using a adapted identification procedure to build a mathematically equivalent model for the electro-acoustic system. The method was tested on three groups of samples (polyurethane resin, bone and wood) using one 1-MHz transducer. For thickness and velocity measurements, the WBP method gave a relative error lower than 1.5%. The relative errors in the mass density measurements ranged between 0.70% and 2.59%. Despite discrepancies between manufactured and biological samples, the results obtained on the three groups of samples using the WBP method in the reflection mode were remarkably consistent, indicating that it is a reliable and efficient means of simultaneously assessing the thickness and the velocity of the ultrasonic wave propagating in the medium, and the apparent mass density of material. PMID:26403278
Effect of vacancies on the spin density waves onset in Fe/Cr superlattices
NASA Astrophysics Data System (ADS)
Parlebas, J. C.; Demangeat, C.; Mokrani, A.; Yartsev, S. V.; Ustinov, V. V.; Yartseva, N. S.
2011-05-01
The spin density wave's onset in Cr based superlattices is considered within proximity of Fe interlayer boundaries and the effect of randomly located vacancies in Cr monolayers is examined. The study is performed for Fe/Cr, Fe/Cr/V superlattices with odd and even number of Cr monolayers. It is shown that the number of Cr monolayer determines the spin density wave's nodes onset in the perfect Fe/Cr super lattices. Pinning of Cr magnetic moments on vacancies destroys this determination and leads to appearance or disappearance of nodes.
NASA Astrophysics Data System (ADS)
Patel, Aavishkar A.; Eberlein, Andreas
2016-05-01
We develop a theory for light-induced superconductivity in underdoped cuprates in which the competing bond-density wave order is suppressed by driving phonons with light. Close to a bond-density wave instability in a system with a small Fermi surface, such as a fractionalized Fermi liquid, we show that the coupling of electrons to phonons is strongly enhanced at the bond-density wave ordering wave vectors, leading to a strong softening of phonons at these wave vectors. For a model of classical phonons with anharmonic couplings, we show that the combination of strong softening and driving can lead to large phonon oscillations. When coupled to a phenomenological model describing the competition between bond-density wave order and superconductivity, these phonon oscillations melt bond-density wave order, thereby enhancing pairing correlations.
Properties of Longitudinal Flux Tube Waves. III; Wave Propagation in Solar and Stellar Wind Flows
NASA Technical Reports Server (NTRS)
Cuntz, M.; Suess, S. T.
2004-01-01
We discuss the analytic properties of longitudinal tube waves taking into account ambient wind flows. This is an extension of the studies of Papers I and II, which assumed a mean flow speed of zero and also dealt with a simplified horizontal pressure balance. Applications include the study of longitudinal flux tube waves in stars with significant mass loss and heating and dynamics of plumes in the solar wind. Slow magnetosonic waves, also called longitudinal waves, have been observed in solar plumes and are likely an important source of heating. We show that the inclusion of ambient wind flows considerably alters the limiting shock strength as well as the energy damping length of waves.
Properties of Longitudinal Flux Tube Waves. III; Wave Propagation in Solar and Stellar Wind FLows
NASA Technical Reports Server (NTRS)
Cuntz, M.; Suess, S. T.
2004-01-01
We discuss the analytic properties of longitudinal tube waves taking into account ambient wind flows. This is an extension of the studies of Papers I and II, which assumed a mean flow speed of zero and also dealt with a simplified horizontal pressure balance. Applications include the study of longitudinal flux tube waves in stars with significant mass loss and the heating and dynamics of plumes in the solar wind. Slow magnetosonic waves, also called longitudinal waves, have been observed in solar plumes and are likely an important source of heating. We show that the inclusion of ambient wind flows considerably alters the limiting shock strength as well as the energy damping length of the waves.
Properties of materials using acoustic waves
NASA Astrophysics Data System (ADS)
Apfel, R. E.
1985-10-01
Our goal of characterizing materials using acoustic waves was forwarded through a number of projects: (1) We have derived a theory, and tested it on tissues, for predicting the composition of composite materials using mixture rules, such as the one we derived for the nonlinear parameter two years ago; (2) We have published one article and another is in review on our use of modulated acoustic radiation pressure on levitated drops to characterize interfaces with and without surfactants. We have begun to study in a systematic way the nonlinear dynamics of drops, including drop fission: (3) we have improved apparatus for 30 MHz ultrasonic scattering from microparticles (approx. micron size), which should allow us to discriminate between different microparticles in a liquid; (4) We have begun to study the nonlinear mechanics of hydrodynamic solitons in cylindrical (2-d) geometry; and (5) We have been studying the use of acoustic levitation for transducer calibration.
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.
Properties of medium density fiberboards made from renewable biomass.
Ye, X Philip; Julson, James; Kuo, Monlin; Womac, Al; Myers, Deland
2007-03-01
The goal of this study was to determine the comparative properties of dry-formed medium density fiberboards (MDF) made from renewable biomass (wheat and soybean straw) and those from conventional soft wood fiber. The MDF properties evaluated were modulus of elasticity, modulus of rupture, internal bond strength, thickness swell, and screw holding capacity. The results show that MDF made from wheat straw fiber and soy straw fiber have weaker mechanical and water resistance properties than those made from softwood fiber. Soybean straw is comparable to wheat straw in terms of both mechanical and water resistance properties to make MDF. Water resistance of MDF decreased drastically with increasing straw fiber composition. Wheat straw fiber and soybean straw fiber should be physically or chemically treated to increase their water resistance property for MDF production. PMID:16781143