Antiferromagnetic noise correlations in optical lattices
DEFF Research Database (Denmark)
Bruun, Niels Bohr International Academy, University of Copenhagen, DK-2100 Copenhagen Ø, Denmark, Georg Morten; Syljuåsen, F. T.; Pedersen, K. G. L.;
2009-01-01
We analyze how noise correlations probed by time-of-flight experiments reveal antiferromagnetic (AF) correlations of fermionic atoms in two-dimensional and three-dimensional optical lattices. Combining analytical and quantum Monte Carlo calculations using experimentally realistic parameters, we...... show that AF correlations can be detected for temperatures above and below the critical temperature for AF ordering. It is demonstrated that spin-resolved noise correlations yield important information about the spin ordering. Finally, we show how to extract the spin correlation length and the related...
Electron-phonon interaction and antiferromagnetic correlations
Sangiovanni, G.; Gunnarsson, O.; Koch, E.; Castellani, C.; M. Capone
2006-01-01
We study effects of the Coulomb repulsion on the electron-phonon interaction (EPI) in a model of cuprates at zero and finite doping. We find that antiferromagnetic correlations strongly enhance EPI effects on the electron Green's function with respect to the paramagnetic correlated system, but the net effect of the Coulomb interaction is a moderate suppression of the EPI. Doping leads to additional suppression, due to reduced antiferromagnetic correlations. In contrast, the Coulomb interactio...
Local Spin Correlations in Heisenberg Antiferromagnets
Weihong, Zheng; Oitmaa, J.
2000-01-01
We use linked cluster series expansion methods to estimate the values of various short distance correlation functions in $S=1/2$ Heisenberg antiferromagnets at T=0, for dimension $d=1,2,3$. The method incorporates the possibility of spontaneous symmetry breaking, which is manifest in $d=2,3$. The results are important in providing a test for approximate theories of the antiferromagnetic ground state.
Spin torque antiferromagnetic nanooscillator in the presence of magnetic noise
Directory of Open Access Journals (Sweden)
H. Gomonay
2012-12-01
Full Text Available Spin-torque effects in antiferromagnetic (AFM materials are of great interest due to the possible applications as high-speed spintronic devices. In the present paper we analyze the statistical properties of the current-driven AFM nanooscillator that result from the white Gaussian noise of magnetic nature. According to the peculiarities of deterministic dynamics, we derive the Langevin and Fokker-Planck equations in the energy representation of two normal modes. We find the stationary distribution function in the subcritical and overcritical regimes and calculate the current dependence of the average energy, energy fluctuation and their ratio (quality factor. The noncritical mode shows the Boltzmann statistics with the current-dependent effective temperature in the whole range of the current values. The effective temperature of the other, i.e., soft, mode critically depends on the current in the subcritical region. Distribution function of the soft mode follows the Gaussian law above the generation threshold. In the overcritical regime, the total average energy and the quality factor grow with the current value. This raises the AFM nanooscillators to the promising candidates for active spintronic components.
Antiferromagnetic phase transition and spin correlations in NiO
DEFF Research Database (Denmark)
Chatterji, Tapan; McIntyre, G.J.; Lindgård, Per-Anker
2009-01-01
We have investigated the antiferromagnetic (AF) phase transition and spin correlations in NiO by high-temperature neutron diffraction below and above TN. We show that AF phase transition is a continuous second-order transition within our experimental resolution. The spin correlations manifested by...... process. We determined the critical exponents =0.328±0.002 and =0.64±0.03 and the Néel temperature TN=530±1 K. These critical exponents suggest that NiO should be regarded as a 3dXY system...
Correlations in the Ising antiferromagnet on the anisotropic kagome lattice
International Nuclear Information System (INIS)
We study the correlation function of middle spins, i.e. of spins on intermediate sites between two adjacent parallel lattice axes, of the spatially anisotropic Ising antiferromagnet on the kagome lattice. It is given rigorously by a Toeplitz determinant. The large-distance behaviour of this correlation function is obtained by analytic methods. For shorter distances we evaluate the Toeplitz determinant numerically. The correlation function is found to vanish exactly on a line Jd(T) in the T − J (temperature versus coupling constant) phase diagram. This disorder line divides the phase diagram into two regions. For J d(T) the correlations display the features of an unfrustrated two-dimensional Ising magnet, whereas for J > Jd(T) the correlations between the middle spins are seen to be strongly influenced by the short-range antiferromagnetic order that prevails among the spins of the adjacent lattice axes. While for J d(T) there is a region with ferrimagnetic long-range order, the model remains disordered for J > Jd(T) down to T = 0
Bootstrap equations and correlation functions for the Heisenberg XYZ antiferromagnet
Quano, Yas-Hiro
2002-01-01
Presented are two kinds of integral solutions to the quantum Knizhnik-Zamolodchikov equations for the 2n-point correlation functions of the Heisenberg XYZ antiferromagnet. Our first integral solution can be obtained from those for the cyclic SOS model by using the vertex-face correspondence. By the construction, the sum with respect to the local height variables k_0, k_1, >..., k_{2n} of the cyclic SOS model remains other than n-fold integral in the first solution. In order to perform those s...
Probing Spatial Spin Correlations of Ultracold Gases by Quantum Noise Spectroscopy
Bruun, G.; Andersen, Brian; Sørensen, Anders; Demler, Eugene A.
2009-01-01
Spin noise spectroscopy with a single laser beam is demonstrated theoretically to provide a direct probe of the spatial correlations of cold fermionic gases. We show how the generic many-body phenomena of anti-bunching, pairing, antiferromagnetic, and algebraic spin liquid correlations can be revealed by measuring the spin noise as a function of laser width, temperature, and frequency.
International Nuclear Information System (INIS)
Highlights: • In a layered 2D cuprates the long-range order antiferromagnetism is driven mainly by the Van Hove singularity. • The long-range antiferromagnetism quickly disappear with doping away from the Van Hove singularity. • For pnictides the antiferromagnetism exists as a result of the nesting condition. • Since the doping steadily changes the nesting conditions, the antiferromagnetism and superconductivity may coexist. -- Abstract: We consider the Hubbard model in terms of the perturbative diagrammatic approach (UNF⩽1) where the interaction between two electrons with antiparallel spins in the lowest order of perturbation is described by the short-range repulsive contact (on-site) interaction (U>0). We argue that in layered 2D cuprates the long-range order antiferromagnetism is driven mainly by the Van Hove singularity, whereas in the case of pnictides the antiferromagnetism exists as a result of the nesting condition. We show that when the interaction is quite strong (UNF≈1) in the case of the Van Hove singularity the electron system undergoes the antiferromagnetic phase transition with the log-range order parameter and large insulating gap. The long-range antiferromagnetism quickly disappear, as shown, with the doping away from the Van Hove singularity, but the antiferromagnetic short-range correlation persists (UNF < 1) due to Coulomb repulsive interaction which is the mechanism for superconductivity in cuprates. We argue that in the case of pnictides the antiferromagnetism appears when the nesting conditions for the Fermi surface are met. Since the doping steadily changes the nesting conditions, the antiferromagnetism and superconductivity may coexist as has been observed in pnictides. We show that the proximity of the antiferromagnetism and superconductivity implies the repulsive interaction between electrons, which turns into attractive between quasiparticles as shown by the authors in the article published on the same issue as this one and
The Berezinskii-Kosterlitz-Thouless transition and correlations in the XY kagome antiferromagnet
Cherepanov, V B; Podivilov, E V
2001-01-01
The problem of the Berezinskii-Kosterlitz-Thouless transition in the highly frustrated XY antiferromagnetic is solved. The transition temperature is found. It is shown that the spin correlation function exponentially decays with distance even in the low-temperature phase, in contrast to the order parameter correlation function, which decays algebraically with distance
Random Correlation Matrix and De-Noising
Ken-ichi Mitsui; Yoshio Tabata
2006-01-01
In Finance, the modeling of a correlation matrix is one of the important problems. In particular, the correlation matrix obtained from market data has the noise. Here we apply the de-noising processing based on the wavelet analysis to the noisy correlation matrix, which is generated by a parametric function with random parameters. First of all, we show that two properties, i.e. symmetry and ones of all diagonal elements, of the correlation matrix preserve via the de-noising processing and the...
Correlated Levy Noise in Linear Dynamical Systems
International Nuclear Information System (INIS)
Linear dynamical systems, driven by a non-white noise which has the Levy distribution, are analysed. Noise is modelled by a specific stochastic process which is defined by the Langevin equation with a linear force and the Levy distributed symmetric white noise. Correlation properties of the process are discussed. The Fokker-Planck equation driven by that noise is solved. Distributions have the Levy shape and their width, for a given time, is smaller than for processes in the white noise limit. Applicability of the adiabatic approximation in the case of the linear force is discussed. (author)
Magnetic correlations in the 2D S=5/2 honeycomb antiferromagnet MnPS3
DEFF Research Database (Denmark)
Rønnow, H.M.; Wildes, A.R.; Bramwell, S.T.
2000-01-01
MnPS3 is a quasi-2D S = 5/2 antiferromagnet on a honeycomb lattice. Using an energy integrating neutron scattering technique, we have measured the structure factor S(k) of the instantaneous magnetic fluctuations. The temperature dependence of the correlation length xi follows the Kosterlitz...
International Nuclear Information System (INIS)
Magnetic correlations in all four phases of pure and doped vanadium sesquioxide (V2O3) have been examined by magnetic thermal-neutron scattering. Specifically, we have studied the antiferromagnetic and paramagnetic phases of metallic V2-yO3, the antiferromagnetic insulating and paramagnetic metallic phases of stoichiometric V2O3, and the antiferromagnetic and paramagnetic phases of insulating V1.944Cr0.056O3. While the antiferromagnetic insulator can be accounted for by a localized Heisenberg spin model, the long-range order in the antiferromagnetic metal is an incommensurate spin-density wave, resulting from a Fermi surface nesting instability. Spin dynamics in the strongly correlated metal are dominated by spin fluctuations with a open-quotes single lobeclose quotes spectrum in the Stoner electron-hole continuum. Furthermore, our results in metallic V2O3 represent an unprecedentedly complete characterization of the spin fluctuations near a metallic quantum critical point, and provide quantitative support for the self-consistent renormalization theory for itinerant antiferromagnets in the small moment limit. Dynamic magnetic correlations for ℎωBT in the paramagnetic insulator carry substantial magnetic spectral weight. However, they are extremely short-ranged, extending only to the nearest neighbors. The phase transition to the antiferromagnetic insulator, from the paramagnetic metal and the paramagnetic insulator, introduces a sudden switching of magnetic correlations to a different spatial periodicity which indicates a sudden change in the underlying spin Hamiltonian. To describe this phase transition and also the unusual short-range order in the paramagnetic state, it seems necessary to take into account the orbital degrees of freedom associated with the degenerate d orbitals at the Fermi level in V2O3. copyright 1998 The American Physical Society
Correlated Noise Effects on Gene Expression
Institute of Scientific and Technical Information of China (English)
王先菊; 艾保全; 刘国涛; 刘良钢
2003-01-01
Based on the model describing the regulation of the PRM operator region of λ phage proposed by Hasty et al.[Proc. Nat. Acad. Sci. 97(2000)2075], we study the steady-state probability distribution properties of the model in the presence of correlated Gaussian white noise. We find that the degree of correlation of the noises can affect the form of the steady-state probability distribution. When the degree of correlation of the noises increases, the form of the steady-state probability distribution changes from a bimodal into a unimodal structure.The steady-state probability distribution extrema have also been investigated. We find that noise correlation can change the positions of the extreme value of the steady-state probability distribution of the model greatly.
Source and processing effects on noise correlations
Fichtner, Andreas
2014-05-01
We quantify the effects of spatially heterogeneous noise sources and seismic processing on noise correlation measurements and their sensitivity to Earth structure. Our analysis is based on numerical wavefield simulations in heterogeneous media. This allows us to calculate inter-station correlations for arbitrarily distributed noise sources where - as in the real Earth - different frequencies are generated in different locations. Using adjoint methods, we compute the exact structural sensitivities for a given combination of source distribution, processing scheme, and measurement technique. The key results of our study are as follows: (1) Heterogeneous noise sources and subjective processing, such as the application of spectral whitening, have profound effects on noise correlation wave forms. (2) Nevertheless, narrow-band traveltime measurements are only weakly affected by heterogeneous noise sources and processing. This result is in accord with previous analytical studies, and it explains the similarity of noise and earthquake tomographies that only exploit traveltime information. (3) Spatially heterogeneous noise sources can lead to structural sensitivities that deviate strongly from the classical cigar-shaped sensitivities. Furthermore, the frequency dependence of sensitivity kernels can go far beyond the well-know dependence of the Fresnel zone width on frequency. Our results imply that a meaningful application of modern full waveform inversion methods to noise correlations is not possible unless both the noise source distribution and the processing scheme are properly taken into account. Failure to do so can lead to erroneous misfit quantifications, slow convergence of optimisation schemes, and to the appearance of tomographic artefacts that reflect the incorrect structural sensitivity. These aspects acquire special relevance in the monitoring of subtle changes of subsurface structure that may be polluted when the time dependence of heterogeneous noise sources
DEFF Research Database (Denmark)
Lindgård, Per-Anker
1984-01-01
The correlation theory is applied to a Heisenberg antiferromagnet in a magnetic field. Special cases covered are the ferromagnet and an anisotropic Heisenberg model. The theory includes selfconsistently correlation effects in static and dynamic properties. It is a generalization of the random......-phase approximation and is applicable to the quantum spin case for any dimension and temperature. The static susceptibilities and the excitation spectrum are calculated. Besides the spin-wave excitations a central peak is found which can be understood as coming from local longitudinal fluctuations. The results of the...... theory are exemplified by numerical calculations for the onedimensional S=1 quantum antiferromagnetic chain. Qualitative agreement is found with computer simulations on a classical chain....
Correlation of Quantized Spectrally-Varying Noise
Gwinn, C R; Dougherty, S M; Rizzo, D D; Reynolds, J E; Jauncey, D L; Tzioumis, A K; Quick, J; McCulloch, P M; Hirabayashi, H; Kobayashi, H; Murata, Y
2000-01-01
We compute statistics for correlation of quantized, spectrally-varying,noise. We compare results with computer simulations and with radio-astronomicalobservations. We consider cross-correlation of two signals (or auto-correlationof one); we suppose that each signal is complex, and consists ofspectrally-varying Gaussian noise. We suppose that these signals are quantized,and then correlated. For many samples, the correlation is drawn from a Gaussiandistribution at each frequency, and is completely characterized by its averageand variance. The average is linearly related to the average correlation of theanalog signals. We present expressions for the variance, and compare resultswith computer simulations and with VLBI observations of the Vela pulsar. Wefind excellent agreement. These results are important for understanding thestatistics of radio-astronomical observations, particularly of sources thatvary with time and observing frequency.
Correlated noise unfolding on a Hadronic Calorimeter
Fiolhais, M C N; The ATLAS collaboration
2011-01-01
The correlated noise component of TileCal, the barrel hadronic calorimeter of the ATLAS experiment at the Large Hadron Collider, is studied and an algorithm is used to parametrize and unfold it from the response of the photomultipliers. It is shown that the correlated noise component can be significantly reduced and mostly removed not only for pedestal runs, but also in the presence of physics signals like minimum bias events in 900 GeV collisions and 7 TeV simulated top quark pair production events.
Physiologic correlates to background noise acceptance
Tampas, Joanna; Harkrider, Ashley; Nabelek, Anna
2001-05-01
Acceptance of background noise can be evaluated by having listeners indicate the highest background noise level (BNL) they are willing to accept while following the words of a story presented at their most comfortable listening level (MCL). The difference between the selected MCL and BNL is termed the acceptable noise level (ANL). One of the consistent findings in previous studies of ANL is large intersubject variability in acceptance of background noise. This variability is not related to age, gender, hearing sensitivity, personality, type of background noise, or speech perception in noise performance. The purpose of the current experiment was to determine if individual differences in physiological activity measured from the peripheral and central auditory systems of young female adults with normal hearing can account for the variability observed in ANL. Correlations between ANL and various physiological responses, including spontaneous, click-evoked, and distortion-product otoacoustic emissions, auditory brainstem and middle latency evoked potentials, and electroencephalography will be presented. Results may increase understanding of the regions of the auditory system that contribute to individual noise acceptance.
Cross-correlation studies with seismic noise
Hoffmann, H; Cheng, Y; Blair, D G
2002-01-01
Ocean waves interacting in shallow water at the shore generate land waves propagating inland. To study these waves vertical, horizontal and tilt seismic noise were measured simultaneously at one location. Vibration isolators designed for gravitational wave research were used for detection. Cross-correlation between the above components was calculated. We found correlations between all of them. However, only the correlation between horizontal and vertical motions could be addressed to land waves, and other correlations are thought to be due to local rigid body motion of the large building in which the experiments were located.
On the second-neighbour correlator in 1D XXX quantum antiferromagnetic spin chain
International Nuclear Information System (INIS)
We have calculated the energy per site for the ground state of the antiferromagnetic quantum spin chain with variable range exchange h(j-k) ∝ sinh2 a sinh-2 a(j-k) in the framework of the asymptotic Bethe ansatz. By expanding it in powers of e-2a, we have confirmed the value of the second-neighbour correlator for the model with nearest-neighbour exchange obtained earlier in the atomic limit of the Hubbard chain. (author). Letter-to-the-editor
Incommensurate antiferromagnetism and magnetic correlations in CeCu6-xAux
DEFF Research Database (Denmark)
Stockert, O.; Lohneysen, H. von; Schröder, A.;
1997-01-01
Magnetic ordering and correlations in single crystals of the heavy-fermion alloys CeCu5.8Au0.2 and CeCu5.9Au0.1 were investigated by elastic and inelastic neutron scattering. CeCu5.8Au0.2 orders with an incommensurate magnetic structure and a wave vector q = (+/- 0.79 0 0). Only dynamic antiferro......Magnetic ordering and correlations in single crystals of the heavy-fermion alloys CeCu5.8Au0.2 and CeCu5.9Au0.1 were investigated by elastic and inelastic neutron scattering. CeCu5.8Au0.2 orders with an incommensurate magnetic structure and a wave vector q = (+/- 0.79 0 0). Only dynamic...... antiferromagnetic correlations along a* are observed in CeCu5.9Au0.1 which evolve into a static sine modulation in CeCu5.8Au0.2....
Monitoring volcanoes using seismic noise correlations
Brenguier, Florent; Clarke, Daniel; Aoki, Yosuke; Shapiro, Nikolai M.; Campillo, Michel; Ferrazzini, Valérie
2011-01-01
In this article, we summarize some recent results of measurements of temporal changes of active volcanoes using seismic noise cross-correlations. We first present a novel approach to estimate volcano interior temporal seismic velocity changes. The proposed method allows to measure very small velocity changes (≈ 0.1%) with a time resolution as small as one day. The application of that method to Piton de la Fournaise Volcano (La Réunion Island) shows velocity decreases preceding eruptions. More...
Constructing a global noise correlation database
Ermert, L. A.; Fichtner, A.; Sleeman, R.
2013-12-01
We report on the ongoing construction of an extensive global-scale database of ambient noise cross-correlation functions spanning a frequency range from seismic hum to oceanic microseisms (roughly 2 mHz to 0.2 Hz). The database - ultimately to be hosted by ORFEUS - will be used to study the distribution of microseismic and hum sources, and to perform multiscale full waveform inversion for crustal and mantle structure. To build the database, we acquire continuous time series data from permanent and temporary networks hosted mostly at IRIS and ORFEUS. We process and correlated the time series using a fully parallelised tool based on the Python package Obspy. Processing follows two main flows: We obtain both classical cross-correlation functions and phase cross-correlation functions. Phase cross-correlation is an amplitude-independent measure of waveform similarity. Either type of correlation can be used for the inversions. We stack individual time windows linearly. Additionally, we calculate the stack of instantaneous phases of the analytic cross-correlation signal, which can be included as optional processing step. Multiplying the linear stack by the phase stack downweights those parts of the linear stack that show little phase coherency. Thus, it accelerates the emergence of weak coherent signals, which is of particular importance for the processing of data from recently deployed or temporary stations that have only been recording for a short time. Obtaining and processing data for such a massive database requires considerable computational resources, offered by the Swiss National Supercomputing Centre (CSCS) in the form of HPC clusters specifically designed for large-scale data analysis. The data set will be made available to the scientific community via ORFEUS. By separately providing classical cross-correlation, phase cross-correlation and instantaneous phase stack, the database will offer relative flexibility for application in further studies. Many current
Directory of Open Access Journals (Sweden)
E Ghasemikhah
2012-03-01
Full Text Available This study investigated the electronic properties of antiferromagnetic UBi2 metal by using ab initio calculations based on the density functional theory (DFT, employing the augmented plane waves plus local orbital method. We used the exact exchange for correlated electrons (EECE method to calculate the exchange-correlation energy under a variety of hybrid functionals. Electric field gradients (EFGs at the uranium site in UBi2 compound were calculated and compared with the experiment. The EFGs were predicted experimentally at the U site to be very small in this compound. The EFG calculated by the EECE functional are in agreement with the experiment. The densities of states (DOSs show that 5f U orbital is hybrided with the other orbitals. The plotted Fermi surfaces show that there are two kinds of charges on Fermi surface of this compound.
Institute of Scientific and Technical Information of China (English)
王会立; 陈希信
2004-01-01
The optimum state filter and fixed-interval smoother and the optimum deconvolution algorithm for system with multiplicative noise are derived upon the condition that the dynamic noise correlates itself in one-step and correlates with the measurement noise at the present step as well as one past step, and the multiplicative noise is white and statistically independent of the dynamic noise and the measurement noise. A simulation example demonstrates the effectiveness of the above-mentioned deconvolution algorithm.
Highly noise resistant multiqubit quantum correlations
International Nuclear Information System (INIS)
We analyze robustness of correlations of the N-qubit GHZ and Dicke states against white noise admixture. For sufficiently large N, the Dicke states (for any number of excitations) lead to more robust violation of local realism than the GHZ states (e.g. for N > 8 for the W state). We also identify states that are the most resistant to white noise. Surprisingly, it turns out that these states are the GHZ states augmented with fully product states. Based on our numerical analysis conducted up to N = 8, and an analytical formula derived for any N parties, we conjecture that the three-qubit GHZ state augmented with a product of (N − 3) pure qubits is the most robust against white noise admixture among any N-qubit state. As a by-product, we derive a single Bell inequality and show that it is violated by all pure entangled states of a given number of parties. This gives an alternative proof of Gisin’s theorem. (paper)
Antiferromagnetic correlations near the lower edge of superconducting dome in YBCO6+x
International Nuclear Information System (INIS)
Neutron scattering from high-quality YBCO6.334 single crystals with a Tc of 8.4 K shows that there is no coexistence with long-range antiferromagnetic order at this very low, near-critical doping of ∼0.055, in contrast to claims based on local probe techniques. We find that the neutron resonance seen in optimally doped YBCO7 and underdoped YBCO6.5, has undergone large softening and damping. It appears that the overdamped resonance, with a relaxation rate of 2 meV, is coupled to a zero-energy central mode that grows with cooling and eventually saturates with no change at or below Tc. Although a similar qualitative behaviour is found for YBCO6.35, our study shows that the central mode is stronger in YBCO6.334 than YBCO6.35. The system remains subcritical with short-ranged three dimensional correlations
Magnon squeezing in an antiferromagnet: reducing the spin noise below the standard quantum limit
Zhao, J.; Bragas, A. V.; Lockwood, D. J.; Merlin, R.
2003-01-01
At absolute zero temperature, thermal noise vanishes when a physical system is in its ground state, but quantum noise remains as a fundamental limit to the accuracy of experimental measurements. Such a limitation, however, can be mitigated by the formation of squeezed states. Quantum mechanically, a squeezed state is a time-varying superposition of states for which the noise of a particular observable is reduced below that of the ground state at certain times. Quantum squeezing has been achie...
Directory of Open Access Journals (Sweden)
G. C. Fouokeng
2014-01-01
Full Text Available We analyze the influence of a two-state autocorrelated noise on the decoherence and on the tunneling Landau-Zener (LZ transitions during a two-level crossing of a central electron spin (CES coupled to a one dimensional anisotropic-antiferomagnetic spin, driven by a time-dependent global external magnetic field. The energy splitting of the coupled spin system is found through an approach that computes the noise-averaged frequency. At low magnetic field intensity, the decoherence (or entangled state of a coupled spin system is dominated by the noise intensity. The effects of the magnetic field pulse and the spin gap antiferromagnetic material used suggest to us that they may be used as tools for the direct observation of the tunneling splitting through the LZ transitions in the sudden limit. We found that the dynamical frequencies display basin-like behavior decay with time, with the birth of entanglement, while the LZ transition probability shows Gaussian shape.
Horizontal Correlation of Ambient Noise near a Sea Route
Institute of Scientific and Technical Information of China (English)
HE Li; LI Zheng-Lin; ZHANG Ren-He; PENG Zhao-Hui
2008-01-01
Ambient noise data measured in an experiment conducted near the sea route are analysed.It is found that at low frequency,the measured horizontal correlation coeffients at different separations oscillate much larger than that predicted by the classical ambient noise model.The theoretical analyses show that the observed phenomenon is mainly caused by windy noise together with the discrete shipping noise nearby.An ambient noise model is proposed to include the effects caused by both the noise sources and can be used to forecast the ambient noise field neara sea route.
Institute of Scientific and Technical Information of China (English)
Bing Wang; Shaoping Yan
2009-01-01
Considering an optical bistable system with cross-correlated additive white noise and multiplicative colored noise,we study the effects of correlation between the noises on the correlation function C(s)using the unified colored noise approximation and the Stratonovich decoupling ansatz formalism.The effects of the self-correlation time T of the multiplicative colored noise and the correlation intensity A between the two noises are studied with numerical calculation.It is found that C(s)increases with the increase of the self-correlation time r,but decreases with the increase of the correlation intensity A.At large value of T,there is almost no change for C(s)when T changes.
The Correlation between Harmonica Indices and Noise Indicators
Directory of Open Access Journals (Sweden)
Momir Prascevic
2015-09-01
Full Text Available Environmental Noise Directive requires the use of common noise indicators in member countries of the European Union as physical quantities that describe the environment noise created by different sources of noise. The END noise indicators are expressed in decibel unit which is logarithmic in nature, and usually complicated to explain and relatively far-removed from perception of people. Two French organizations suggested a new environmental noise index called Harmonica index based on measurement data obtained by noise monitoring and take into account both the overall environmental noise load and noise peaks from sudden noise events. In order to determine adequacy of Harmonica indices and relationship between the Harmonica indices and the END noise indicators, the correlation analysis was carried out and the correlation coefficient was determined for different combination of the Harmonica indices and the END noise indicators. The results of the correlation analysis on the sample of noise monitoring data in the city of Niš are presented in this paper after overview the END noise indicators and Harmonica index.
Dugave, Maxime; Kozlowski, Karol K; Suzuki, Junji
2016-01-01
We use the form factors of the quantum transfer matrix in the zero-temperature limit in order to study the two-point ground-state correlation functions of the XXZ chain in the antiferromagnetic massive regime. We obtain novel form factor series representations of the correlation functions which differ from those derived either from the q-vertex-operator approach or from the algebraic Bethe Ansatz approach to the usual transfer matrix. We advocate that our novel representations are numerically more efficient and allow for a straightforward calculation of the large-distance asymptotic behaviour of the two-point functions. Keeping control over the temperature corrections to the two-point functions we see that these are of order $T^\\infty$ in the whole antiferromagnetic massive regime. The isotropic limit of our result yields a novel form factor series representation for the two-point correlation functions of the XXX chain at zero magnetic field.
Synchronization in a Mutualism Ecosystem Induced by Noise Correlation
Institute of Scientific and Technical Information of China (English)
ZHONG Wei-Rong; SHAO Yuan-Zhi; BIE Meng-Jie; HE Zhen-Hui
2008-01-01
Understanding the cause of the synchronization of population evolution is an important issue for ecological improvement.Here we present a Lotka-Volterra-type model driven by two correlated environmental noises and show,via theoretical analysis and direct simulation,that noise correlation can induce a synchronization of the mutualists.The time series of mutual species exhibit a chaotic-like fluctuation,which is independent of the noise correlation,however,the chaotic fluctuation of mutual species ratio decreases with the noise correlation.A quantitative parameter defined for characterizing chaotic fluctuation provides a good approach to measure when the complete synchronization happens.
System Driven by Correlated Gaussian Noises Related with Disorder
Institute of Scientific and Technical Information of China (English)
LI Jing-Hui
2007-01-01
A system driven by correlated Gaussian noises related with disorder is investigated. The Fokker-Planck equation (FPE) for the system is derived. Using the FPE derived, some systems driven by correlated Gaussian noises related with disorder can be investigated for Brownian motors, nonequilibrium transition, resonant activation,stochastic resonance, and so on. We only give one example: i.e., using the FPE derived, we study the resonant activation for a single motor protein model with correlated noises related to disorder. Since the correlated noise related to disorder usually exists with the friction, for the temperature, and so on, our results have generic physical meanings for physics, chemistry, biology and other sciences.
Partial removal of correlated noise in thermal imagery
International Nuclear Information System (INIS)
Correlated noise occurs in many imaging systems such as scanners and push-broom imagers. The sources of correlated noise can be from the detectors, pre-amplifiers and sampling circuits. Correlated noise appears as streaking along the scan direction of a scanner or in the along track direction of a push-broom imager. We have developed algorithms to simulate correlated noise and pre-filter to reduce the amount of streaking while not destroying the scene content. The pre- filter in the Fourier domain consists of the product of two filters. One filter models the correlated noise spectrum, the other is a windowing function e.g. Gaussian or Hanning window with variable width to block high frequency noise away from the origin of the Fourier Transform of the image data. We have optimized the filter parameters for various scenes and find improvements of the RMS error of the original minus the pre-filtered noisy image
Institute of Scientific and Technical Information of China (English)
Zeng Chun-Hua; Wang Hua; Wang Hui-Tao
2011-01-01
For the activated dynamics of a Brownian particle moving in a confined system with the presence of entropic barriers, this paper investigates a periodic driving and correlations between two noises. Within the two-state approximation, the explicit expressions of the mean first passage time (MFPT) and the spectral power amplification (SPA)are obtained, respectively. Based on the numerical computations, it is found that: (i) The MFPT as a function of the noise intensity exhibits a maximum with the positive correlations between two noises (λ＞0), this maximum for MFPT shows the characteristic of the entropic noise induced stability (ENIS) effect. The intensity λ of correlations between two noises can enhance the ENIS effect, (ii) The SPA as a function of the noise intensity exhibits a double-peak by tuning the noise correlation intensity λ, i.e., the existence of a double-peak behaviour is the identifying characteristic of the double entropic stochastic resonance phenomenon.
International Nuclear Information System (INIS)
With a mean field approach, the heavy Fermi liquid in the two-dimensional Kondo lattice model is carefully considered in the presence of short-range antiferromagnetic correlations. As the ratio of the local Heisenberg superexchange coupling to the Kondo coupling increases, the Fermi surface structure changes dramatically. From the analysis of the ground state energy density, multiple Lifshitz type phase transitions occur at zero temperature.
High-sensitivity correlation spectrometer for shot noise measurements
Nieminen, Teemu
2015-01-01
Shot noise measurement is an important characterization method in nanophysics research, although shot noise correlation measurement setups have gained little attention in the literature. Most of the previous setups either utilize low frequencies around 1 MHz or rely on solely analog circuitry. This thesis presents a novel correlation spectrometer for low-temperature shot noise measurements. The setup utilizes a four-channel PCI-E digitizer card with a sample rate of 125 megasamples per se...
Fluctuating Potential Barrier System with Correlated Spatial Noises
Institute of Scientific and Technical Information of China (English)
LI Jing-Hui
2004-01-01
In this paper, we study a fluctuating potential barrier system with correlated spatial noises. Study shows that for this system, there is the resonant activation over the fluctuating potential barrier, and that the correlation between the different spatial noises can enhance (or weaken) the resonant activation.
Impact of correlated noise in an energy depot model.
Zeng, Chunhua; Zeng, Jiakui; Liu, Feng; Wang, Hua
2016-01-01
Based on the depot model of the motion of active Brownian particles (ABPs), the impact of cross-correlated multiplicative and additive noises has been investigated. Using a nonlinear Langevin approach, we discuss a new mechanism for the transport of ABPs in which the energy originates from correlated noise. It is shown that the correlation between two types of noise breaks the symmetry of the potential to generate motion of the ABPs with a net velocity. The absolute maximum value of the mean velocity depends on correlated noise or multiplicative noise, whereas a monotonic decrease in the mean velocity occurs with additive noise. In the case of no correlation, the ABPs undergo pure diffusion with zero mean velocity, whereas in the case of perfect correlation, the ABPs undergo pure drift with zero diffusion. This shows that the energy stemming from correlated noise is primarily converted to kinetic energy of the intrawell motion and is eventually dissipated in drift motion. A physical explanation of the mechanisms for noise-driven transport of ABPs is derived from the effective potential of the Fokker-Planck equation. PMID:26786478
Institute of Scientific and Technical Information of China (English)
ZHU Ping; CHEN Shi-Bo; MEI Dong-Cheng
2006-01-01
We investigate the intensity correlation function C(s) and its associated relaxation time Tc for a saturation model of single-mode laser with correlated noises.The expressions of C(s) and Tc are derived by means of the projection operator method,and effects of correlations between an additive noise and a multiplicative noise are discussed by numerical calculation.Based on the calculated results,it is found that the correlation strength λ between the additive noise and the multiplicative noise can enhance the fluctuation decay of the laser intensity.
Self-tuning measurement fusion white noise deconvolution estimator with correlated noises
Institute of Scientific and Technical Information of China (English)
Xiaojun Sun; Zili Deng
2010-01-01
For the multisensor linear discrete time-invadant stochastic systems with correlated noises and unknown noise statistics,an on-line noise statistics estimator is presented by using the correlation method.Substituting it into the steady-state Riccati equation,the self-tuning Riccati equation is obtained.Using the Kalman filtering method,based on the self-tuning Riccati equation,a self-tuning weighted measurement fusion white noise deconvolution estimator is presented.By the dynamic error system analysis(DESA)method,it is proved that the self-tuning fusion white noise deconvolution estimator converges to the optimal fusion steadystate white noise deconvolution estimator in a realization,so that it has the asymptotic global optimality.A simulation example for Bernoulli-Gaussian input white noise shows its effectiveness.
Time correlation of noise pulses in a PMT
International Nuclear Information System (INIS)
Two types of time correlation of noise pulses caused by the PMT photocathode and dynodes are established using the autocorrelation delayed-coincidence time spectrometer. Time distributions of noise pulses in the XP2020, XP2232B, XP1021, FEU-85, FEU-87, FEU-93, and FEU-130 photomultiplier tubes are investigated. An exponential time component of noise pulses with a nanosecond scintillation time is found in some types of PMTs
Noise correlations in a flux qubit with tunable tunnel coupling
Gustavsson, Simon; Bylander, Jonas; Yan, Fei; Oliver, William D.; Yoshihara, Fumiki; Nakamura, Yasunobu
2011-01-01
We have measured flux-noise correlations in a tunable superconducting flux qubit. The device consists of two loops that independently control the qubit's energy splitting and tunnel coupling. Low frequency flux noise in the loops causes fluctuations of the qubit frequency and leads to dephasing. Since the noises in the two loops couple to different terms of the qubit Hamiltonian, a measurement of the dephasing rate at different bias points provides a way to extract both the amplitude and the ...
Lü, Yan; Bao, Jing-Dong
2016-07-01
Transport of overdamped particle driven by a colored Lévy noise in a static ratchet potential is investigated. We analyze the influence of the noise in the determination of the current and find that the direction of the current depends on the parameters characterizing the colored Lévy noise. In the present model, the long jumps and the noise correlation are two different factors that can break thermodynamical equilibrium and induce directional transport, the competition between the both leads to current inversion. This implies that an interesting non-equilibrium effect arises from long tail distribution of noise.
Unscented Filtering from Delayed Observations with Correlated Noises
Hermoso-Carazo, A.; Linares-Pérez, J.
2009-01-01
A filtering algorithm based on the unscented transformation is proposed to estimate the state of a nonlinear system from noisy measurements which can be randomly delayed by one sampling time. The state and observation noises are perturbed by correlated nonadditive noises, and the delay is modeled by independent Bernoulli random variables.
Unscented Filtering from Delayed Observations with Correlated Noises
Directory of Open Access Journals (Sweden)
A. Hermoso-Carazo
2009-01-01
Full Text Available A filtering algorithm based on the unscented transformation is proposed to estimate the state of a nonlinear system from noisy measurements which can be randomly delayed by one sampling time. The state and observation noises are perturbed by correlated nonadditive noises, and the delay is modeled by independent Bernoulli random variables.
Microscopic realization of cross-correlated noise processes
Shit, Anindita; Chattopadhyay, Sudip; Banik, Suman Kumar; Chaudhuri, Jyotipratim Ray
2010-01-01
We present a microscopic theory of cross-correlated noise processes, starting from a Hamiltonian system-reservoir description. In the proposed model, the system is nonlinearly coupled to a reservoir composed of harmonic oscillators, which in turn is driven by an external fluctuating force. We show that the resultant Langevin equation derived from the composite system (system+reservoir+external modulation) contains the essential features of cross-correlated noise processes.
Microscopic realization of cross-correlated noise processes.
Shit, Anindita; Chattopadhyay, Sudip; Banik, Suman Kumar; Chaudhuri, Jyotipratim Ray
2010-06-01
We present a microscopic theory of cross-correlated noise processes, starting from a Hamiltonian system-reservoir description. In the proposed model, the system is nonlinearly coupled to a reservoir composed of harmonic oscillators, which in turn is driven by an external fluctuating force. We show that the resultant Langevin equation derived from the composite system (system+reservoir+external modulation) contains the essential features of cross-correlated noise processes. PMID:20590326
Correlated Noises in a Prey-Predator Ecosystem
Institute of Scientific and Technical Information of China (English)
ZHONG Wei-Rong; SHAO Yuan-Zhi; HE Zhen-Hui
2006-01-01
@@ We investigate a Volterra ecosystem driven by correlated noises. The fluctuation in the death rate of the predator induces an increase of population density of the predators. The fluctuation in the growth rate of the prey, however,leads the predators to decay. It is reported that the predators undergo sensitivity to a random environment,whereas the preys exhibit a surprising endurance to the same stochastic factor. The predators are of better stability under strong correlation of noises.
Impact of Correlated Noises on Additive Dynamical Systems
Directory of Open Access Journals (Sweden)
Chujin Li
2014-01-01
Full Text Available Impact of correlated noises on dynamical systems is investigated by considering Fokker-Planck type equations under the fractional white noise measure, which correspond to stochastic differential equations driven by fractional Brownian motions with the Hurst parameter H>1/2. Firstly, by constructing the fractional white noise framework, one small noise limit theorem is proved, which provides an estimate for the deviation of random solution orbits from the corresponding deterministic orbits. Secondly, numerical experiments are conducted to examine the probability density evolutions of two special dynamical systems, as the Hurst parameter H varies. Certain behaviors of the probability density functions are observed.
Calibration of Correlation Radiometers Using Pseudo-Random Noise Signals
Directory of Open Access Journals (Sweden)
Sebastián Pantoja
2009-08-01
Full Text Available The calibration of correlation radiometers, and particularly aperture synthesis interferometric radiometers, is a critical issue to ensure their performance. Current calibration techniques are based on the measurement of the cross-correlation of receivers’ outputs when injecting noise from a common noise source requiring a very stable distribution network. For large interferometric radiometers this centralized noise injection approach is very complex from the point of view of mass, volume and phase/amplitude equalization. Distributed noise injection techniques have been proposed as a feasible alternative, but are unable to correct for the so-called “baseline errors” associated with the particular pair of receivers forming the baseline. In this work it is proposed the use of centralized Pseudo-Random Noise (PRN signals to calibrate correlation radiometers. PRNs are sequences of symbols with a long repetition period that have a flat spectrum over a bandwidth which is determined by the symbol rate. Since their spectrum resembles that of thermal noise, they can be used to calibrate correlation radiometers. At the same time, since these sequences are deterministic, new calibration schemes can be envisaged, such as the correlation of each receiver’s output with a baseband local replica of the PRN sequence, as well as new distribution schemes of calibration signals. This work analyzes the general requirements and performance of using PRN sequences for the calibration of microwave correlation radiometers, and particularizes the study to a potential implementation in a large aperture synthesis radiometer using an optical distribution network.
Directory of Open Access Journals (Sweden)
Xin Wang
2012-01-01
Full Text Available For the multisensor linear discrete time-invariant stochastic control systems with different measurement matrices and correlated noises, the centralized measurement fusion white noise estimators are presented by the linear minimum variance criterion under the condition that noise input matrix is full column rank. They have the expensive computing burden due to the high-dimension extended measurement matrix. To reduce the computing burden, the weighted measurement fusion white noise estimators are presented. It is proved that weighted measurement fusion white noise estimators have the same accuracy as the centralized measurement fusion white noise estimators, so it has global optimality. It can be applied to signal processing in oil seismic exploration. A simulation example for Bernoulli-Gaussian white noise deconvolution filter verifies the effectiveness.
Noise reduction algorithm for glueball correlators
Energy Technology Data Exchange (ETDEWEB)
Majumdar, Pushan, E-mail: tppm@iacs.res.in [Department of Theoretical Physics, Indian Association for the Cultivation of Science, Kolkata (India); Mathur, Nilmani, E-mail: nilmani@theory.tifr.res.in [Department of Theoretical Physics, Tata Institute of Fundamental Research, Mumbai (India); Mondal, Sourav, E-mail: tpsm5@iacs.res.in [Department of Theoretical Physics, Indian Association for the Cultivation of Science, Kolkata (India)
2014-09-07
We present an error reduction method for obtaining glueball correlators from Monte Carlo simulations of SU(3) lattice gauge theory. We explore the scalar and tensor channels at three different lattice spacings. Using this method we can follow glueball correlators to temporal separations even up to 1 fermi. We estimate the improvement over the naive method and compare our results with existing computations.
Robust filtering: Correlated noise and multidimensional observation
Crisan, D.; Diehl, J.; Friz, P. K.; Oberhauser, H.
2013-01-01
In the late seventies, Clark [In Communication Systems and Random Process Theory (Proc. 2nd NATO Advanced Study Inst., Darlington, 1977) (1978) 721–734, Sijthoff & Noordhoff] pointed out that it would be natural for $\\pi_{t}$, the solution of the stochastic filtering problem, to depend continuously on the observed data $Y=\\{Y_{s},s\\in[0,t]\\}$. Indeed, if the signal and the observation noise are independent one can show that, for any suitably chosen test function $f$, there exists a continuous...
Statistical fluctuations in a saturation laser model with correlated noises
Institute of Scientific and Technical Information of China (English)
Chen Shi-Bo; Mei Dong-Cheng
2006-01-01
We study the effects of correlations between quantum and pump noises on fluctuations of the laser intensity in a saturation laser model. An approximative Fokker-Planck equation and analytic expressions of the steady-state probability distribution function (SPD) of the laser system are derived. Based on the SPD, the normalized mean, the normalized variance, and the normalized skewness of the steady-state laser intensity are calculated numerically. The results indicate that (i) the correlation strength λ of correlated noises always enhances the fluctuation of laser intensity;(ii) the correlation time τ of correlated noises strengthens the fluctuation of laser intensity for the below-threshold case but τ weakens it for the above-threshold case.
Noise reduction algorithm for glueball correlators
Directory of Open Access Journals (Sweden)
Pushan Majumdar
2014-09-01
Full Text Available We present an error reduction method for obtaining glueball correlators from Monte Carlo simulations of SU(3 lattice gauge theory. We explore the scalar and tensor channels at three different lattice spacings. Using this method we can follow glueball correlators to temporal separations even up to 1 fermi. We estimate the improvement over the naive method and compare our results with existing computations.
Compressed Sensing with Linear Correlation Between Signal and Measurement Noise
DEFF Research Database (Denmark)
Arildsen, Thomas; Larsen, Torben
2014-01-01
Existing convex relaxation-based approaches to reconstruction in compressed sensing assume that noise in the measurements is independent of the signal of interest. We consider the case of noise being linearly correlated with the signal and introduce a simple technique for improving compressed...... sensing reconstruction from such measurements. The technique is based on a linear model of the correlation of additive noise with the signal. The modification of the reconstruction algorithm based on this model is very simple and has negligible additional computational cost compared to standard...... reconstruction algorithms, but is not known in existing literature. The proposed technique reduces reconstruction error considerably in the case of linearly correlated measurements and noise. Numerical experiments confirm the efficacy of the technique. The technique is demonstrated with application to low...
Jungwirth, T.; Marti, X.; Wadley, P.; Wunderlich, J.
2016-03-01
Antiferromagnetic materials are internally magnetic, but the direction of their ordered microscopic moments alternates between individual atomic sites. The resulting zero net magnetic moment makes magnetism in antiferromagnets externally invisible. This implies that information stored in antiferromagnetic moments would be invisible to common magnetic probes, insensitive to disturbing magnetic fields, and the antiferromagnetic element would not magnetically affect its neighbours, regardless of how densely the elements are arranged in the device. The intrinsic high frequencies of antiferromagnetic dynamics represent another property that makes antiferromagnets distinct from ferromagnets. Among the outstanding questions is how to manipulate and detect the magnetic state of an antiferromagnet efficiently. In this Review we focus on recent works that have addressed this question. The field of antiferromagnetic spintronics can also be viewed from the general perspectives of spin transport, magnetic textures and dynamics, and materials research. We briefly mention this broader context, together with an outlook of future research and applications of antiferromagnetic spintronics.
Colored Correlated Noises in Growth Model of Tumor
Mirian, Najmeh Sadat
2014-01-01
Stochastic resonance induced by external factor is considering to investigate the complex dynamics of tumor. The surrounding environment and the treatment effects on the tumor growth are considered as additive and multiplicative noises in growth model. The adaptability of tumor to treatment is presented by correlation of these two noises. The Fokker-Plank equation is deduced to study the probability distribution function and mean number of tumor cells in different conditions. The mean number ...
Effects of Perfectly Correlated and Anti-Correlated Noise in a Logistic Growth Model
Institute of Scientific and Technical Information of China (English)
ZHANG Li; CAO Li
2011-01-01
The logistic growth model with correlated additive and multipllcative Gaussian white noise is used to analyze tumor cell population. The effects of perfectly correlated and anti-correlated noise on the stationary properties of tumor cell population are studied. As in both cases the diffusion coefficient has zero point in real number field, some special features of the system are arisen. It is found that in both cases, the increase of the multiplicative noise intensity cause tumor cell extinction. In the perfectly anti-correlated case, the stationary probability distribution as a function of tumor cell population exhibit two extrema.
Effects of Perfectly Correlated and Anti-Correlated Noise in a Logistic Growth Model
International Nuclear Information System (INIS)
The logistic growth model with correlated additive and multiplicative Gaussian white noise is used to analyze tumor cell population. The effects of perfectly correlated and anti-correlated noise on the stationary properties of tumor cell population are studied. As in both cases the diffusion coefficient has zero point in real number field, some special features of the system are arisen. It is found that in both cases, the increase of the multiplicative noise intensity cause tumor cell extinction. In the perfectly anti-correlated case, the stationary probability distribution as a function of tumor cell population exhibit two extrema. (general)
Sensor Selection for Estimation with Correlated Measurement Noise
Liu, Sijia; Chepuri, Sundeep Prabhakar; Fardad, Makan; Masazade, Engin; Leus, Geert; Varshney, Pramod K.
2016-07-01
In this paper, we consider the problem of sensor selection for parameter estimation with correlated measurement noise. We seek optimal sensor activations by formulating an optimization problem, in which the estimation error, given by the trace of the inverse of the Bayesian Fisher information matrix, is minimized subject to energy constraints. Fisher information has been widely used as an effective sensor selection criterion. However, existing information-based sensor selection methods are limited to the case of uncorrelated noise or weakly correlated noise due to the use of approximate metrics. By contrast, here we derive the closed form of the Fisher information matrix with respect to sensor selection variables that is valid for any arbitrary noise correlation regime, and develop both a convex relaxation approach and a greedy algorithm to find near-optimal solutions. We further extend our framework of sensor selection to solve the problem of sensor scheduling, where a greedy algorithm is proposed to determine non-myopic (multi-time step ahead) sensor schedules. Lastly, numerical results are provided to illustrate the effectiveness of our approach, and to reveal the effect of noise correlation on estimation performance.
Estimating correlations of neighbouring frequencies in ambient seismic noise
Liu, Xin; Ben-Zion, Yehuda
2016-08-01
Extracting accurate empirical Green's functions from the ambient seismic noise field requires the noise to be fully diffuse and that different frequency components are not correlated. Calculating a matrix of correlation coefficients of power spectral samples can be used to estimate deviations from a fully diffuse random noise field in the analysed frequency range. A fully diffuse field has correlations only in a narrow region around the diagonal of the matrix, with frequency resolution inversely proportional to length of the used time window. Analysis of low-frequency data (0.005-0.6 Hz) recorded by three broad-band stations of the southern California seismic network reveals three common types of correlations, manifested in the correlation coefficient matrix as square, diagonal halo and correlated stripes. Synthetic calculations show that these types of signatures in the correlation coefficient matrix can result from certain combinations of cross-frequency correlated random components and diffuse field. The analysis of observed data indicates that the secondary microseismic peak around 0.15 Hz is correlated with its neighbouring frequencies, while the primary peak around 0.06 Hz is more diffuse. This suggests that the primary and secondary peaks may be associated with somewhat different physical origins. In addition, significant correlation of frequencies below that of the primary microseismic peak suggests that the very low frequencies noise is less scattered during propagation. The power spectra recorded by a station close to the edge of the Los Angeles basin is higher compared to data recorded by stations outside the basin perhaps because of enhanced basin reverberations and/or closer proximity to the ocean. This and other regional variations should be tested further using data from many more stations.
Sun, Xiaojuan; Perc, Matjaz; Lu, Qishao; Kurths, Jürgen
2010-01-01
In this paper, we examine the effects of correlated Gaussian noise on a two-dimensional neuronal network that is locally modeled by the Rulkov map. More precisely, we study the effects of the noise correlation on the variations of the mean firing rate and the correlations among neurons versus the noise intensity. Via numerical simulations, we show that the mean firing rate can always be optimized at an intermediate noise intensity, irrespective of the noise correlation. On the other hand, var...
Jet engine noise and infrared plume correlation field campaign
Cunio, Phillip M.; Weber, Reed A.; Knobel, Kimberly R.; Smith, Christine; Draudt, Andy
2015-09-01
Jet engine noise can be a health hazard and environmental pollutant, particularly affecting personnel working in close proximity to jet engines, such as airline mechanics. Mitigating noise could reduce the potential for hearing loss in runway workers; however, there exists a very complex relationship between jet engine design parameters, operating conditions, and resultant noise power levels, and understanding and characterizing this relationship is a key step in mitigating jet engine noise effects. We demonstrate initial results highlighting the utility of high-speed imaging (hypertemporal imaging) in correlating the infrared signatures of jet engines with acoustic noise. This paper builds on prior theoretical analysis of jet engine infrared signatures and their potential relationships to jet engine acoustic emissions. This previous work identified the region of the jet plume most likely to emit both in infrared and in acoustic domains, and it prompted the investigation of wave packets as a physical construct tying together acoustic and infrared energy emissions. As a means of verifying these assertions, a field campaign to collect relevant data was proposed, and data collection was carried out with a bank of infrared instruments imaging a T700 turboshaft engine undergoing routine operational testing. The detection of hypertemporal signatures in association with acoustic signatures of jet engines enables the use of a new domain in characterizing jet engine noise. This may in turn enable new methods of predicting or mitigating jet engine noise, which could lead to socioeconomic benefits for airlines and other operators of large numbers of jet engines.
Cross-correlations of ambient noise recorded by accelerometers.
Rábade García, S. E.; Ramirez-Guzman, L.
2014-12-01
We investigate the ambient noise cross-correlations obtained by using properly corrected accelerometric recordings, and determine velocity structure in central Mexico based on a dispersion analysis. The data used comprise ten months of continuous recordings - from April 2013 to January 2014 - of ambient seismic noise at stations operated by the National Seismological Service of Mexico and the Engineering Strong Ground Motion Network of the National Autonomous University of Mexico (UNAM). The vertical component of ambient noise was base-line corrected, filtered, and properly integrated before extracting Green's functions (GF), which were compared successfully against GF obtained using recordings from broadband velocity sensors. In order to obtain dispersion curves, we estimated group and phase velocities applying the FTAN analysis technique and obtained s-wave velocity profiles at selected regions. We conclude and highlight that the use of widely deployed accelerographs to conduct regional studies using ambient noise tomography is feasible
Power Mapping and Noise Reduction for Financial Correlations
International Nuclear Information System (INIS)
The spectral properties of financial correlation matrices can show features known from completely random matrices. A major reason is noise originating from the finite lengths of the financial time series used to compute the correlation matrix elements. In recent years, various methods have been proposed to reduce this noise, i.e. to clean the correlation matrices. This is of direct practical relevance for risk management in portfolio optimization. In this contribution, we discuss in detail the power mapping, a new shrinkage method. We show that the relevant parameter is, to a certain extent, self-determined. Due to the 'hirality' and the normalization of the correlation matrix, the optimal shrinkage parameter is fixed. We apply the power mapping and the well-known filtering method to market data and compare them by optimizing stock portfolios. We address the role of constraints by excluding short selling in the optimization. (author)
Shear wave velocities from noise correlation at local scale
De Nisco, G.; Nunziata, C.; Vaccari, F.; Panza, G. F.
2008-07-01
Cross correlations of ambient seismic noise recordings have been studied to infer shear seismic velocities with depth. Experiments have been done in the crowded and noisy historical centre of Napoli over inter-station distances from 50 m to about 400 m, whereas active seismic spreadings are prohibitive, even for just one receiver. Group velocity dispersion curves have been extracted with FTAN method from the noise cross correlations and then the non linear inversion of them has resulted in Vs profiles with depth. The information of near by stratigraphies and the range of Vs variability for samples of Neapolitan soils and rocks confirms the validity of results obtained with our expeditious procedure. Moreover, the good comparison of noise H/V frequency of the first main peak with 1D and 2D spectral amplifications encourages to continue experiments of noise cross-correlation. If confirmed in other geological settings, the proposed approach could reveal a low cost methodology to obtain reliable and detailed Vs velocity profiles.
Persistent Rabi oscillations probed via low-frequency noise correlation
Korotkov, Alexander N.
2010-01-01
The qubit Rabi oscillations are known to be non-decaying (though with a fluctuating phase) if the qubit is continuously monitored in the weak-coupling regime. In this paper we propose an experiment to demonstrate these persistent Rabi oscillations via low-frequency noise correlation. The idea is to measure a qubit by two detectors, biased stroboscopically at the Rabi frequency. The low-frequency noise depends on the relative phase between the two combs of biasing pulses, with a strong increas...
Extraction of triplicated PKP phases from noise correlations
Xia, Han H.; Song, Xiaodong; Wang, Tao
2016-04-01
Ambient noise correlation method has been widely used to extract surface waves and tomography. The extraction of body waves has been very limited, but recent reports have suggested promises for deep incident waves. Here we report our first observations of triplicated PKP phases (important phases for studying the Earth's core) and confirm observations of other body-wave core phases from noise correlations. We use dense seismic arrays in South America and China Regional Seismic Networks at distances from 145° to the antipode. We can clearly observe different PKP branches (df, bc and ab) in stacks of the station-station correlations. Both ambient noise and earthquake coda contribute to PKP phases. However, the contributions vary with frequency and with body-wave phases. At shorter periods (5-20 s), three branches of PKP (df, bc and ab) can be extracted from ambient noise and the ab phase from earthquake coda. At longer periods (15-50 s), earthquake coda are effective in generating the df branch, but not the ab branch. The generation of the PKIKP phase (df branch) from earthquake coda does not depend on earthquake focal mechanisms or focal depths. However, earthquakes far from the stations contribute more than events closer by. The best coda window is around 10 000-40 000 s and the best magnitude threshold is Mw greater than 6.8 or 6.9. The observation of triplicated PKP branches from noise correlations provides a new type of data for studying the Earth's deep interior, in particularly the inner core anisotropy, which overcomes some of the limitations of traditional earthquake-based studies (such as limited source distributions and source location errors).
Kontani, Hiroshi; Ohno, Masanori
2006-07-01
In nearly antiferromagnetic (AF) metals such as high- Tc superconductors (HTSCs), a single nonmagnetic impurity frequently causes nontrivial widespread change of the electronic states. To elucidate this long-standing issue, we study a Hubbard model with a strong onsite impurity potential based on an improved fluctuation-exchange (FLEX) approximation, which we call the GVI -FLEX method. This model corresponds to the HTSC with dilute nonmagnetic impurity concentration. We find that (i) both local and staggered susceptibilities are strongly enhanced around the impurity. By this reason, (ii) the quasiparticle lifetime as well as the local density of states are strongly suppressed in a wide area around the impurity (like a Swiss cheese hole), which causes the “huge residual resistivity” beyond the s -wave unitary scattering limit. We stress that the excess quasiparticle damping rate caused by impurities has strong k -dependence due to non- s -wave scatterings induced by many-body effects, so the structure of the “hot spot/cold spot” in the host system persists against impurity doping. This result could be examined by the ARPES measurements. In addition, (iii) only a few percent of impurities can cause a “Kondo-like” upturn of resistivity (dρ/dT<0) at low T when the system is very close to the AF quantum critical point. The results (i)-(iii) obtained in the present study, which cannot be derived by the simple FLEX approximation, naturally explain the main impurity effects in HTSCs. We also discuss the impurity effect in heavy fermion systems and organic superconductors.
The influence of noise sources on cross-correlation amplitudes
Hanasoge, Shravan M
2012-01-01
We use analytical examples and asymptotic forms to examine the mathematical structure and physical meaning of the seismic cross correlation measurement. We show that in general, cross correlations are not Green's functions of medium, and may be very different depending on the source distribution. The modeling of noise sources using spatial distributions as opposed to discrete collections of sources is emphasized. When stations are illuminated by spatially complex source distributions, cross correlations show arrivals at a variety of time lags, from zero to the maximum surface-wave arrival time. Here, we demonstrate the possibility of inverting for the source distribution using the energy of the full cross-correlation waveform. The interplay between the source distribution and wave attenuation in determining the functional dependence of cross correlation energies on station-pair distance is quantified. Without question, energies contain information about wave attenuation. However, the accurate interpretation o...
Noise cross correlation functions in a noisy region
Gaudot, I.; Beucler, E.; Mocquet, A.; Schimmel, M.; Le Feuvre, M.; Leparoux, D.; Côte, P.
2013-12-01
The geology of the western France can be roughly split into two main domains: the Armorican massif that contains imprints of the old Cadomian and Variscan orogens; and the Bay of Biscay which present signatures of more recent tectonic events closely related to the opening of North Atlantic ocean. Due to the lack of seismic stations deployment, it exists very few pictures of the deep structures below the Armorican Massif and the Bay of Biscay. Recently, a broadband array of seismometers has been deployed over the south and west of France, providing a good opportunity to get reliable images at depth. Since the region is surrounded by the seas, the seismic ambient noise tomography technique has been proposed to reveal the crustal and uppermost mantle features beneath this area. The first step consists in the computation of noise correlation functions (NCFs) between each station pairs. The ability to obtain empirical Green's functions from NCFs relies on the efficiency of the randomization. Classic ambient noise tomography studies use long-time series (typically several months) to help the randomization including all the scattering effects due to Earth's heterogeneities. However, additionnal signal processing steps such as temporal and/or spectral whitening are most often required for the signals to be representative of a random wavefield. These techniques rely on nonlinear operations which corrupt the integrity of the original record. In the literature, alternatives have been proposed to avoid, at least partially, such non linear operations. One of them is the instantaneous phase cross correlation (PCC). This correlation technique is intrinsically little sensitive to large amplitude transient signals. Using a set of data from a temporary broad band array, we explore the features of the PCC as compared to the time domain geometrically normalized cross correlation (CCGN). In the 0.02Hz-1Hz frequency band, different time series are extracted to investigate the effects of
Institute of Scientific and Technical Information of China (English)
Bing Wang; Xiuqing Wu
2008-01-01
@@ Considering a single-mode laser system with cross-correlated additive colored noise and multiplicative colored noise, we study the effects of correlation among noises on the normalized intensity correlation function C(s).C(s) is derived by means of the projection operator method.
Institute of Scientific and Technical Information of China (English)
HANLi-Bo; CAOLi; WUDa-Jin; WANGJun
2004-01-01
By using the linear approximation method, the intensity correlation function and the intensity correlation time are calculated in a gain-noise model of a single-mode laser driven by colored cross-correlated pump noise and quantum noise, each of which is colored. We detect that, when the cross-correlation between both noises is negative, the behavior of the intensity correlation function C(t) versus time t, in addition to decreasing monotonously, also exhibits several other cases, such as one maximum, one minimum, and two extrema (one maximum and one minimum), i.e., some parameters of the noises can greatly change the dependence of the intensity correlation function upon time. Moreover, we find that there is a minimum Tmin in the curve of the intensity correlation time versus the pump noise intensity, and the depth and position of Train strongly depend on the quantum noise self-correlation time T2 and cross-correlation time T3.
Asymptotically Sufficient Statistics in Nonparametric Regression Experiments with Correlated Noise
Carter, Andrew V
2009-01-01
We find asymptotically sufficient statistics that could help simplify inference in nonparametric regression problems with correlated errors. These statistics are derived from a wavelet decomposition that is used to whiten the noise process and to effectively separate high-resolution and low-resolution components. The lower-resolution components contain nearly all the available information about the mean function, and the higher-resolution components can be used to estimate the error covarianc...
Passive defect localization in reverberating plates using ambient noise correlation
Chehami, Lynda
2015-01-01
Green’s functions retrieval from ambient noise correlation has recently drawn a new interestin structural health monitoring. In this manuscript, we propose an original methodbased on this approach to detect and locate defects (cracks, holes, grooves) in a reverberantthin plate with a limited number of sensors. Flexural waves that propagate on the plateare generated by either a set of sources distributed randomly on the surface or an ambientnoise. Covariance matrices are estimated from the spa...
Metallic-thin-film instability with spatially correlated thermal noise.
Diez, Javier A; González, Alejandro G; Fernández, Roberto
2016-01-01
We study the effects of stochastic thermal fluctuations on the instability of the free surface of a flat liquid metallic film on a solid substrate. These fluctuations are represented by a stochastic noise term added to the deterministic equation for the film thickness within the long-wave approximation. Unlike the case of polymeric films, we find that this noise, while remaining white in time, must be colored in space, at least in some regimes. The corresponding noise term is characterized by a nonzero correlation length, ℓ_{c}, which, combined with the size of the system, leads to a dimensionless parameter β that accounts for the relative importance of the spatial correlation (β∼ℓ_{c}^{-1}). We perform the linear stability analysis (LSA) of the film both with and without the noise term and find that for ℓ_{c} larger than some critical value (depending on the system size), the wavelength of the peak of the spectrum is larger than that corresponding to the deterministic case, while for smaller ℓ_{c} this peak corresponds to smaller wavelength than the latter. Interestingly, whatever the value of ℓ_{c}, the peak always approaches the deterministic one for larger times. We compare LSA results with the numerical simulations of the complete nonlinear problem and find a good agreement in the power spectra for early times at different values of β. For late times, we find that the stochastic LSA predicts well the position of the dominant wavelength, showing that nonlinear interactions do not modify the trends of the early linear stages. Finally, we fit the theoretical spectra to experimental data from a nanometric laser-melted copper film and find that at later times, the adjustment requires smaller values of β (larger space correlations). PMID:26871167
Quantum Stackelberg duopoly in the presence of correlated noise
Energy Technology Data Exchange (ETDEWEB)
Khan, Salman; Ramzan, M; Khan, M Khalid, E-mail: sksafi@phys.qau.edu.p, E-mail: mramzan@phys.qau.edu.p, E-mail: mkkhan@qau.edu.p [Department of Physics, Quaid-i-Azam University, Islamabad 45320 (Pakistan)
2010-09-17
We study the influence of entanglement and correlated noise using correlated amplitude damping, depolarizing and phase damping channels on the quantum Stackelberg duopoly. Our investigations show that under the influence of an amplitude damping channel a critical point exists for an unentangled initial state at which firms get equal payoffs. The game becomes a follower advantage game when the channel is highly decohered. Two critical points corresponding to two values of the entanglement angle are found in the presence of correlated noise. Within the range of these limits of the entanglement angle, the game is a follower advantage game. In the case of a depolarizing channel, the payoffs of the two firms are strongly influenced by the memory parameter. The presence of quantum memory ensures the existence of the Nash equilibrium for the entire range of decoherence and entanglement parameters for both the channels. A local maximum in the payoffs is observed which vanishes as the channel correlation increases. Moreover, under the influence of the depolarizing channel, the game is always a leader advantage game. Furthermore, it is seen that the phase damping channel does not affect the outcome of the game.
Antiferromagnetic correlations in icosahedral R-Mg-Zn quasicrystals (R rare earth)
Energy Technology Data Exchange (ETDEWEB)
Charrier, B.; Schmitt, D. [Centre National de la Recherche Scientifique (CNRS), 38 - Grenoble (France); Ouladdiaf, B. [Institut Max von Laue - Paul Langevin (ILL), 38 - Grenoble (France)
1997-04-01
Powder neutron-diffraction experiments performed on R-Mg-Zn quasicrystals have shown for the first time the existence of magnetic ordering of the rare earth in these systems at low temperature (T{sub c} {<=} 6.5 K depending on the rare earth). Both narrow and broad magnetic diffraction peaks have been observed showing the presence of two different scales of magnetic correlations. (author). 3 refs.
Laser-noise-induced correlations and anti-correlations in Electromagnetically Induced Transparency
Cruz, L S; Gómez, J G A; Lezama, A; Martinelliinst1, M; Nussenzveig, P; Valente, P
2006-01-01
High degrees of intensity correlation between two independent lasers were observed after propagation through a rubidium vapor cell in which they generate Electromagnetically Induced Transparency (EIT). As the optical field intensities are increased, the correlation changes sign (becoming anti-correlation). The experiment was performed in a room temperature rubidium cell, using two diode lasers tuned to the $^{85}$Rb $D_2$ line ($\\lambda = 780$nm). The cross-correlation spectral function for the pump and probe fields is numerically obtained by modeling the temporal dynamics of both field phases as diffusing processes. We explored the dependence of the atomic response on the atom-field Rabi frequencies, optical detuning and Doppler width. The results show that resonant phase-noise to amplitude-noise conversion is at the origin of the observed signal and the change in sign for the correlation coefficient can be explained as a consequence of the competition between EIT and Raman resonance processes.
Infrasonic ambient noise interferometry from correlations of microbaroms
Haney, M.M.
2009-01-01
We show that microbaroms, continuous infrasound fluctuations resulting from the interaction of the ocean with the atmosphere, have long-range correlation properties that make it possible to estimate the impulse response between two microphones from passive recordings. The processing is analogous to methods employed in the emerging field of ambient noise seismology, where the random noise source is the ocean coupling with the solid Earth (microseisms) instead of the atmosphere (microbaroms). We find that time-dependent temperature fields and temperature inversions determine the character of infrasonic impulse responses at Fourpeaked Volcano in Alaska. Applications include imaging and monitoring the gross structure of the Earth's atmospheric boundary layer. Copyright 2009 by the American Geophysical Union.
Zverev, M V; Clark, J W
2001-01-01
On the basis of analysis of the Landau-Pitaevskii one has determined that antiferromagnetic transition follows fermion condensation and rearrangement of single-particle degrees of freedom. It results in the spectrum of single-particle excitations. The derived results are used to explain structure of slit in the spectrum at T = 0 in two-dimensional high-temperature superconductors with a square lattice. They may be, as well, used to describe superfluid states of strongly correlated systems with fermion condensation
Tanase-Nicola, Sorin; Warren, Patrick B.; Wolde, Pieter Rein ten
2005-01-01
Understanding cell function requires an accurate description of how noise is transmitted through biochemical networks. We present an analytical result for the power spectrum of the output signal of a biochemical network that takes into account the correlations between the noise in the input signal (the extrinsic noise) and the noise in the reactions that constitute the network (the intrinsic noise). These correlations arise from the fact that the reactions by which biochemical signals are det...
Enhanced current noise correlations in a Coulomb-Majorana device
Lü, Hai-Feng; Lu, Hai-Zhou; Shen, Shun-Qing
2016-06-01
Majorana bound states (MBSs) nested in a topological nanowire are predicted to manifest nonlocal correlations in the presence of a finite energy splitting between the MBSs. However, the signal of the nonlocal correlations has not yet been detected in experiments. A possible reason is that the energy splitting is too weak and seriously affected by many system parameters. Here we investigate the charging energy induced nonlocal correlations in a hybrid device of MBSs and quantum dots. The nanowire that hosts the MBSs is assumed in proximity to a mesoscopic superconducting island with a finite charging energy. Each end of the nanowire is coupled to one lead via a quantum dot with resonant levels. With a floating superconducting island, the devices show a negative differential conductance and giant super-Poissonian shot noise, due to the interplay between the nonlocality of the MBSs and dynamical Coulomb blockade effect. When the island is strongly coupled to a bulk superconductor, the current cross correlations at small lead chemical potentials are negative by tuning the dot energy levels. In contrast, the cross correlation is always positive in a non-Majorana setup. This difference may provide a signature for the existence of the MBSs.
Quantum correlations of identical particles subject to classical environmental noise
Beggi, Andrea; Buscemi, Fabrizio; Bordone, Paolo
2016-06-01
In this work, we propose a measure for the quantum discord of indistinguishable particles, based on the definition of entanglement of particles given in Wiseman and Vaccaro (Phys Rev Lett 91:097902, 2003. doi: 10.1103/PhysRevLett.91.097902). This discord of particles is then used to evaluate the quantum correlations in a system of two identical bosons (fermions), where the particles perform a quantum random walk described by the Hubbard Hamiltonian in a 1D lattice. The dynamics of the particles is either unperturbed or subject to a classical environmental noise—such as random telegraph, pink or brown noise. The observed results are consistent with those for the entanglement of particles, and we observe that on-site interaction between particles have an important protective effect on correlations against the decoherence of the system.
International Nuclear Information System (INIS)
This work analyzes numerically the effects of delay time τ and cross-correlation strength between noises λ on the phenomena of noise enhanced stability (NES) and resonant activation (RA) in a periodically modulated bistable system. The simulation results indicate that: (i) multiplicative noise can produce the NES effect only for the larger λ, while additive noise always induces the NES effect; (ii) for the NES phenomenon induced by additive noise, there is a characteristic value of τ, below which the increasing of τ enhances it and above which the effect of τ reverses; however, the increasing of τ can only enhance the NES effect induced by multiplicative noise; (iii) increasing λ weakens the NES effect induced by additive noise and strengthens that induced by multiplicative noise; and (iv) the RA effect becomes more and more pronounced while the RA minimum of the mean first-passage time increases with the increase of λ or τ. (paper)
Institute of Scientific and Technical Information of China (English)
Luo Xiao-Qin; Zhu Shi-Qun
2004-01-01
The phenomenon of stochastic resonance (SR) in a bistable nonlinear system with coupling between additive and multiplicative noises is investigated when the correlation between two noise terms is coloured. It is found that the signal-to-noise ratio (SNR) of the system is affected not only by the coupling strength λ between two noise terms, but also by the noise correlation time . The SNR is changed from a single peak, to two peaks with a dip, and then to a monotonically decreasing function with noise strength. The dependence of the SR on the initial conditions is entirely caused by the coupling strength λ between two noise terms.
Ermert, Laura; Afanasiev, Michael; Sager, Korbinian; Gokhberg, Alexey; Fichtner, Andreas
2016-04-01
We report on the ongoing development of a new inversion method for the space- and time-dependent power spectral density distribution of ambient seismic noise sources. The method, once complete, will mainly serve two purposes: First, it will allow us to construct more realistic forward models for noise cross-correlation waveforms, thereby opening new possibilities for waveform imaging by ambient noise tomography. Second, it may provide new insights about the properties of ambient noise sources, complementing studies based on beamforming or numerical modeling of noise based on oceanographic observations. To invert for noise sources, we consider surface wave signal energy measurements on the 'causal' (station A to B) and on the 'acausal' (station B to A) correlation branch, and the ratio between them. These and similar measurements have proven useful for locating noise sources using cross-correlations in several past studies. The inversion procedure is the following: We construct correlation forward models based on Green's functions from a spectral element wave propagation code. To construct these models efficiently, we use source-receiver reciprocity and assume spatial uncorrelation of noise sources. In such a setting, correlations can be calculated from a pre-computed set of Green's functions between the seismic receivers and sources located at the Earth's surface. We then calculate spatial sensitivity kernels for the noise source distribution with respect to the correlation signal energy measurements. These in turn allow us to construct a misfit gradient and optimize the source distribution model to fit our observed cross-correlation signal energies or energy ratios. We will present the workflow for calculation of the forward model and sensitivity kernels, as well as results for both forward modeling and kernels for an example data set of long-period noise or 'hum' at a global scale. We will also provide an outlook on the noise source inversion considering the
Mutual Information of Pauli Channels with Correlated Noise
Institute of Scientific and Technical Information of China (English)
HOU Li-zhen; FANG Mao-Fa
2007-01-01
A general formula for the mutual information of the Pauli channels with memory modelled by correlated noise is derived.It is shown that the mutual information depends on the channel shrinking factor,the input state parameter and the channel memory coefficient.The analyses based on the general formula reveal that the entanglement is always a useful resource to enhance the mutual information of some.Pauli channels,such as the bit flip channel and the bit-phase flip channel.Our analyses also show that the entanglement is not advantageous to the reliable transmission of classical information for Borne Pauli channels at any time,such as the phase flip channel and the phase damping channel.
Microseism source direction from noise cross-correlation
Chen, Zhao; Gerstoft, Peter; Bromirski, Peter D.
2016-05-01
Inhomogeneous noise sources surrounding stations produce asymmetric amplitudes in cross-correlation functions that yield preferential source directions. Here we show that preprocessing biases the dominant source direction estimate towards the source producing long-duration signals by down-weighting high-amplitude signals. Tests with both synthetic data and observations show that conventional preprocessing, where only earthquakes and local transients (e.g. trawling, fish impacts) are removed, is more sensitive to coherent energy, while one-bit preprocessing and running-absolute-mean preprocessing are more influenced by signal duration. Comparisons between different preprocessing methods are made on data from the Cascadia Initiative ocean bottom seismometer array, where we find that the total energy arriving from pelagic and coastal areas is similar. Moreover, pelagic-generated signals tend to be weaker but have longer duration, in contrast to coastal-generated signals that tend to be stronger but have shorter duration.
DEFF Research Database (Denmark)
Jiang, Jianzhong; Mørup, Steen
1997-01-01
The influence of the particle size distribution on the ratio of the peak temperature, T-peak, to the blocking temperature, T-Bm, in zero field cooled (ZFD) magnetization curves has studied for both ferromagnetic and antiferromagnetic particle systems. In both systems the ratio beta=T-peak/T-Bm do...
Institute of Scientific and Technical Information of China (English)
HAN Li-Bo; CAO Li; WU Da-Jin; WANG Jun
2004-01-01
By using the linear approximation method, the intensity correlation function and the intensity correlation time are calculated in a gain-noise model of a single-mode laser driven by colored cross-correlated pump noise and quantum noise, each of which is colored. We detect that, when the cross-correlation between both noises is negative, the behavior of the intensity correlation function C(t) versus time t, in addition to decreasing monotonously, also exhibits several other cases, such as one maximum, one minimum, and two extrema (one maximum and one minimum), i.e., some parameters of the noises can greatly change the dependence of the intensity correlation function upon time. T3.
Shoji Kawahito; Shinya Itoh; Satoshi Aoyama; Sungho Suh
2010-01-01
For low-noise complementary metal-oxide-semiconductor (CMOS) image sensors, the reduction of pixel source follower noises is becoming very important. Column-parallel high-gain readout circuits are useful for low-noise CMOS image sensors. This paper presents column-parallel high-gain signal readout circuits, correlated multiple sampling (CMS) circuits and their noise reduction effects. In the CMS, the gain of the noise cancelling is controlled by the number of samplings. It has a similar effec...
Effects of cross-correlated noises on the relaxation time of the bistable system
Institute of Scientific and Technical Information of China (English)
谢崇伟; 梅冬成
2003-01-01
The stationary correlation function and the associated relaxation time for a general system driven by crosscorrelated white noises are derived, by virtue of a Stratonovich-like ansatz. The effects of correlated noises on the relaxation time of a bistable kinetic model coupled to an additive and a multiplicative white noises are studied. It is proved that for small fluctuations the relaxation time Tc as a function of λ (the correlated intensity between noises)exhibits very different behaviours for α＜ D and for α＞ D (α and D, respectively, stand for the intensities of additive and multiplicative noises). When α＞ D, Tc increases with increasing λ. But when α＜ D, Tc increases with λ for the case of weak correlated noises and sharply decreases with λ for the case of strong correlated noises, and thus Tc-λ curve behaves with one extremum.
Institute of Scientific and Technical Information of China (English)
Wang Can-Jun; Chen Shi-Bo; Mei Dong-Cheng
2006-01-01
The steady-state properties of a bistable system are investigated when both the multiplicative noise and the coupling between additive and multiplicative noises are coloured with different values of noise correlation times τ1 and 72. After introducing a dimensionless parameter R(R = α/D, D is the intensity of the multiplicative noise and α is the intensity of the additive noise), and performing the numerical computations, we find the following points: (1) For the case ofR ＞ 1, λ (the intensity of correlation between additive and multiplicative noises), τ1 and τ2 can induce the stationary probability distribution (SPD) transition from bimodal to unimodal in structure, but for the cases of R ≤ 1,the bimodal structure is preserved; (2) α can also induce the SPD transition from bimodal to unimodal in structure;(3) the bimodal structure of the SPD exhibits a symmetrical structure as D increases.
Signal-to-noise ratio limitations for intensity correlation imaging.
Fried, David L; Riker, Jim; Agrawal, Brij
2014-07-01
Intensity correlation imaging (ICI) is a concept which has been considered for the task of providing images of satellites in geosynchronous orbit using ground-based equipment. This concept is based on the intensity interferometer principle first developed by Hanbury Brown and Twiss. It is the objective of this paper to establish that a sun-lit geosynchronous satellite is too faint a target object to allow intensity interferometry to be used in developing image information about it-at least not in a reasonable time and with a reasonable amount of equipment. An analytic treatment of the basic phenomena is presented. This is an analysis of one aspect of the statistics of the very high frequency random variations of a very narrow portion of the optical spectra of the incoherent (black-body like-actually reflected sunlight) radiation from the satellite, an analysis showing that the covariance of this radiation as measured by a pair of ground-based telescopes is directly proportional to the square of the magnitude of one component of the Fourier transform of the image of the satellite-the component being the one for a spatial frequency whose value is determined by the separation of the two telescopes. This analysis establishes the magnitude of the covariance. A second portion of the analysis considers shot-noise effects. It is shown that even with much less than one photodetection event (pde) per signal integration time an unbiased estimate of the covariance of the optical field's random variations can be developed. Also, a result is developed for the standard deviation to be associated with the estimated value of the covariance. From these results an expression is developed for what may be called the signal-to-noise ratio to be associated with an estimate of the covariance. This signal-to-noise ratio, it turns out, does not depend on the measurement's integration time, Δt (in seconds), or on the optical spectral bandwidth, Δν (in Hertz), utilized-so long as
SPEECH ENHANCEMENT BASED ON DYNAMIC NOISE ESTIMATION WITHIN AUTO-CORRELATION DOMAIN
Institute of Scientific and Technical Information of China (English)
吴亚栋; 吴旭辉
2002-01-01
Most noise suppression algorithms of single channel use the mean of noisy segments to estimate the characteristics of noise spectrum, ignoring the estimation of noise in speech segments. Therefore, when the energy level of noise varies with the time, the performance of removing noise will be degraded. To solve this problem, a speech enhancement approach based on dynamic noise estimation within correlation domain was proposed. This method exploits the characteristics that noise energy mainly concentrates on 0 th-order correlation coefficients, signal is auto-correlated but signal and noise, noise and noise are uncorrelated, then estimates and decomposes the noise, thus helps to solve the above-mentioned problem. The results of recognition experiments on speech signals of 15 Chinese cities' names corrupted by noise of exhibition hall shows, this approach is better than SS (Spectral Subtraction) method, adapts better to the variances of energy levels of speech signal corrupted by noise, has some practicability to improve the robustness of recognition systems under noisy environment.
Stochastic resonance in the growth of a tumor induced by correlated noises
Institute of Scientific and Technical Information of China (English)
ZHONG Weirong; SHAO Yuanzhi; HE Zhenhui
2005-01-01
Multiplicative noise is found to divide the growth law of tumors into two parts in a logistic model, which is driven by additive and multiplicative noises simultaneously. The Fokker-Planck equation was also derived to explain the fact that the influence of the intensity of multiplicative noise on the growth of tumor cells has a stochastic resonance-like characteristic. An appropriate intensity of multiplicative noise is benefit to the growth of the tumor cells. The correlation between two sorts of noises weakens the stochastic resonance-like characteristic. Homologous noises promote the growth of the tumor cells.
Escape over a potential barrier driven by colored noise: Large but finite correlation times
International Nuclear Information System (INIS)
The recent theory of Tsironis and Grigolini for the mean first-passage time from one metastable state to another of a bistable potential for long correlation times of the noise is extended to large but finite correlation times
3-D surface wave tomography of the Piton de la Fournaise volcano using seismic noise correlations
Brenguier, Florent; M. Shapiro, Nikolai; Campillo, Michel; Nercessian, Alexandre; Ferrazzini, Valérie
2007-01-01
[1] We invert Rayleigh waves reconstructed from cross-correlations of 18 months of ambient seismic noise recorded by permanent seismological stations run by the Piton de la Fournaise Volcanological Observatory. By correlating noise records between 21 receivers, we reconstruct Rayleigh waves with sufficient signal-to-noise ratio for 210 inter-station paths. We use the reconstructed waveforms to measure group velocity dispersion curves at periods between 1.5 and 4.5 s. The obtained measurements...
Widjaja, Joewono
2015-11-01
A new method is proposed for recognizing noise corrupted low-contrast retinal images that employs joint wavelet transform correlator with compressed reference and target. Noise robustness is achieved by correlating wavelet-transformed retinal target and reference images. Simulation results show that besides being robust to noise, its recognition performance can become independent upon compression qualities when low spatial-frequency components of joint power spectrum are enhanced by appropriately dilated wavelet filter.
International Nuclear Information System (INIS)
We numerically investigate the influences of the time delay τ simultaneously existing in both the deterministic and fluctuating forces, the time delay τr existing only in the fluctuating force and the cross-correlation strength λ on the enhancement of the mean first-passage time (MFPT) as a function of the additive D and the multiplicative α noise intensities in a metastable system. The results indicate that both the multiplicative and additive noises can induce the noise-enhanced stability (NES) effect. An increase of λ can enhance or weaken the NES effect induced by the additive noise, depending on the value of τ. However, it weakens the NES effect induced by the multiplicative noise with a suppression of the effect of λ caused by increasing τ. The τ-induced critical behavior on both NES effects can be observed, i.e. an increase of τ can enhance or restrain the NES effects induced by the two kinds of noises. With an increase of λ and τ, MFPT versus D shows a transition from one peak to two peaks and finally one peak, implying the multiple NES effect caused by λ and τ. An increase of τr can enhance the NES effect induced by the additive noise and weaken the NES effect induced by the multiplicative noise.
Quantum metrology subject to spatially correlated Markovian noise: restoring the Heisenberg limit
Jeske, Jan; Cole, Jared H.; Huelga, Susana F.
2014-07-01
Environmental noise can hinder the metrological capabilities of entangled states. While the use of entanglement allows for Heisenberg-limited resolution, the largest permitted by quantum mechanics, deviations from strictly unitary dynamics quickly restore the standard scaling dictated by the central limit theorem. Product and maximally entangled states become asymptotically equivalent when the noisy evolution is both local and strictly Markovian. However, temporal correlations in the noise have been shown to lift this equivalence while fully (spatially) correlated noise allows for the identification of decoherence-free subspaces. Here we analyze precision limits in the presence of noise with finite correlation length and show that there exist robust entangled state preparations which display persistent Heisenberg scaling despite the environmental decoherence, even for small correlation length. Our results emphasize the relevance of noise correlations in the study of quantum advantage and could be relevant beyond metrological applications.
Investigation of the spatial correlations of flow noise in vector hydrophone towed linear array
Institute of Scientific and Technical Information of China (English)
YANG Xiuting; SUN Guiqing; LI Mini; LI Qihu
2008-01-01
Following the wall pressure spectrum of the turbulent boundary layer developed by Corcos, a method in the frequency-wavenumber space was presented to analyze the flow noise in the vector hydrophone towed linear array. The general forms of the acoustic pressure and particle velocity in the flow noise field were obtained, and the spatial correlations of the flow noise were calculated. The numerical analysis results based on wavenumber integration show that: (1) The spatial correlations of flow noise drops rapidly with increasing axial separation between the elements, so the flow noise received by different vector hydrophones usually sampled in a half-wavelength rate can be considered as independent; (2) The flow noise is highly correlated in the radial direction at low frequency, and only those of high frequency componet can be neglected.
Intensity and phase noise correlations in a dual-frequency VECSEL operating at telecom wavelength
De, Syamsundar; Bouchoule, Sophie; Alouini, Mehdi; Bretenaker, Fabien
2015-01-01
The amplitude and phase noises of a dual-frequency vertical-external-cavity surface-emitting laser (DF-VECSEL) operating at telecom wavelength are theoretically and experimentally investigated in detail. In particular, the spectral behavior of the correlation between the intensity noises of the two modes of the DF-VECSEL is measured. Moreover, the correlation between the phase noise of the radio-frequency (RF) beatnote generated by optical mixing of the two laser modes with the intensity noises of the two modes is investigated. All these spectral behaviors of noise correlations are analyzed for two different values of the nonlinear coupling between the laser modes. We find that to describe the spectral behavior of noise correlations between the laser modes, it is of utmost importance to have a precise knowledge about the spectral behavior of the pump noise, which is the dominant source of noise in the frequency range of our interest (10 kHz to 35 MHz). Moreover, it is found that the noise correlation also dep...
Fast direction of arrival estimation of wideband sources in unknown correlated noise fields
Institute of Scientific and Technical Information of China (English)
DAI Zhengjian; LIU Yun; LI Zhishun
2006-01-01
A computational efficient wideband Direction of Arrival (DOA) estimation method in the presence of unknown correlated noise is presented. A fast Two-sided Correlation Transformation (TCT) focusing matrix that transforms only the signal subspace is developed firstly,and then the propagator method is utilized to compute the focusing matrix and noise correlation matrix. In contrast to conventional wideband DOA estimation method, the proposed method requires only linear operation but does not involve any eigenvelue-decomposition to estimate the focusing matrix; it has a lower computational load, especially when the sensor number is greater than the source number. Because noise correlation matrix is estimated and eliminated from the array correlation matrix, the accuracy of DOA estimation is improved even in the presence of unknown correlation noise. Computer simulation results verified the efficiency of the method.
Moment Equations in a Lotka--Volterra Extended System with Time Correlated Noise
Valenti, D.; Schimansky-Geier, L.; Sailer, X.; Spagnolo, B.; Iacomi, M.
2007-05-01
A spatially extended Lotka--Volterra system of two competing species in the presence of two correlated noise sources is analyzed: (i) an external multiplicative time correlated noise, which mimics the interaction between the system and the environment; (ii) a dichotomous stochastic process, whose jump rate is a periodic function, which represents the interaction parameter between the species. The moment equations for the species densities are derived in Gaussian approximation, using a mean field approach. Within this formalism we study the effect of the external time correlated noise on the ecosystem dynamics. We find that the time behavior of the 1st order moments are independent on the multiplicative noise source. However, the behavior of the 2nd order moments is strongly affected both by the intensity and the correlation time of the multiplicative noise. Finally we compare our results with those obtained studying the system dynamics by a coupled map lattice model.
Kargovsky, A V; Chichigina, O A; Anashkina, E I; Valenti, D; Spagnolo, B
2015-10-01
The relaxation dynamics of a system described by a Langevin equation with pulse multiplicative noise sources with different correlation properties is considered. The solution of the corresponding Fokker-Planck equation is derived for Gaussian white noise. Moreover, two pulse processes with regulated periodicity are considered as a noise source: the dead-time-distorted Poisson process and the process with fixed time intervals, which is characterized by an infinite correlation time. We find that the steady state of the system is dependent on the correlation properties of the pulse noise. An increase of the noise correlation causes the decrease of the mean value of the solution at the steady state. The analytical results are in good agreement with the numerical ones. PMID:26565201
The power spectrum and correlation of flow noise for an axisymmetric body in water
Institute of Scientific and Technical Information of China (English)
Li Xue-Gang; Yang Kun-De; Wang Yong
2011-01-01
Understanding the physical features of the flow noise for an axisymmetric body is important for improving the performance of a sonar mounted on an underwater platform. Analytical calculation and numerical analysis of the physical features of the flow noise for an axisymmetric body are presented and a simulation scheme for the noise correlation on the hydrophones is given. It is shown that the numerical values of the flow noise coincide well with the analytical values. The main physical features of flow noise are obtained. The flow noises of two different models are compared and a model with a rather optimal fore-body shape is given. The flow noise in horizontal symmetry profile of the axisymmetric body is non-uniform, but it is omni-directional and has little difference in the cross section of the body. The loss of noise diffraction has a great effect on the flow noise from boundary layer transition. Meanwhile, based on the simulation, the noise power level increases with velocity to approximately the fifth power at high frequencies,which is consistent with the experiment data reported in the literature. Furthermore, the flow noise received by the acoustic array has lower correlation at a designed central frequency, which is important for sonar system design.
International Nuclear Information System (INIS)
Purpose: To study the noise correlation properties of cone-beam CT (CBCT) projection data and to incorporate the noise correlation information to a statistics-based projection restoration algorithm for noise reduction in low-dose CBCT. Methods: In this study, we systematically investigated the noise correlation properties among detector bins of CBCT projection data by analyzing repeated projection measurements. The measurements were performed on a TrueBeam on-board CBCT imaging system with a 4030CB flat panel detector. An anthropomorphic male pelvis phantom was used to acquire 500 repeated projection data at six different dose levels from 0.1 mAs to 1.6 mAs per projection at three fixed angles. To minimize the influence of the lag effect, lag correction was performed on the consecutively acquired projection data. The noise correlation coefficient between detector bin pairs was calculated from the corrected projection data. The noise correlation among CBCT projection data was then incorporated into the covariance matrix of the penalized weighted least-squares (PWLS) criterion for noise reduction of low-dose CBCT. Results: The analyses of the repeated measurements show that noise correlation coefficients are non-zero between the nearest neighboring bins of CBCT projection data. The average noise correlation coefficients for the first- and second- order neighbors are about 0.20 and 0.06, respectively. The noise correlation coefficients are independent of the dose level. Reconstruction of the pelvis phantom shows that the PWLS criterion with consideration of noise correlation (PWLS-Cor) results in a lower noise level as compared to the PWLS criterion without considering the noise correlation (PWLS-Dia) at the matched resolution. Conclusion: Noise is correlated among nearest neighboring detector bins of CBCT projection data. An accurate noise model of CBCT projection data can improve the performance of the statistics-based projection restoration algorithm for low
International Nuclear Information System (INIS)
A Brownian particle in a spatially symmetric and Bashing periodic potential subjected to correlated noises is investigated. The exact expression of its current is analytically derived. The numerical results indicate that its current as a function of noise intensity exhibits two peaks in the case of positive correlations, and two vales in the case of negative correlations, i.e., a novel stochastic resonance (SR) phenomenon. The SR is attributed to the harmonic cooperation between the noises and the Bashing periodic potential. The conditions under which the SR occurs are also presented
Noise and correlations in genes silenced by small RNA.
Hwa, Terence; Levine, Erel
2006-03-01
Many small regulatory RNAs have been identified in prokaryotes and eukaryotes in recent years. In many cases, RNA regulation is found in critical pathways. These include stress response and quorum sensing pathways in bacteria, and cell differentiation and programmed cell death in eukaryotes. In many cases, regulation by small RNA is used in switching off a response program as long as it is not required, allowing for a fast switching on when necessary. Clearly, accidental execution of such a program may bare grave consequences on the cell, and should be avoided. Here we analyze a stochastic model for gene regulation by the most abundant class of small RNA in bacteria. This class of small RNAs acts by base pairing with target mRNAs, silencing its translation and actively promoting its degradation. Importantly, the small RNA molecule is not recycled. Our model suggests that genes silenced by sRNA exhibits smooth noise, as opposed to the bursty noise characteristic to genes repressed at the level of transcription, with coupling between intrinsic noise and global, extrinsic fluctuations. In addition, we investigate how noise propagates through the indirect coupling between different targets of the same sRNA. These features are discussed in the context of circuits exhibiting multi-stability, where protein bursts have strong implications on spontaneous switching.
Directory of Open Access Journals (Sweden)
Yu Hu
2014-02-01
Full Text Available Over repeat presentations of the same stimulus, sensory neurons show variable responses. This "noise" is typically correlated between pairs of cells, and a question with rich history in neuroscience is how these noise correlations impact the population's ability to encode the stimulus. Here, we consider a very general setting for population coding, investigating how information varies as a function of noise correlations, with all other aspects of the problem - neural tuning curves, etc. - held fixed. This work yields unifying insights into the role of noise correlations. These are summarized in the form of theorems, and illustrated with numerical examples involving neurons with diverse tuning curves. Our main contributions are as follows. (1 We generalize previous results to prove a sign rule (SR - if noise correlations between pairs of neurons have opposite signs vs. their signal correlations, then coding performance will improve compared to the independent case. This holds for three different metrics of coding performance, and for arbitrary tuning curves and levels of heterogeneity. This generality is true for our other results as well. (2 As also pointed out in the literature, the SR does not provide a necessary condition for good coding. We show that a diverse set of correlation structures can improve coding. Many of these violate the SR, as do experimentally observed correlations. There is structure to this diversity: we prove that the optimal correlation structures must lie on boundaries of the possible set of noise correlations. (3 We provide a novel set of necessary and sufficient conditions, under which the coding performance (in the presence of noise will be as good as it would be if there were no noise present at all.
Widjaja, Joewono; Kaewphaluk, Komin
2014-03-01
Noise suppression in retinal recognition by using a compression-based joint transform correlator (CBJTC) is experimentally studied. The experimental results show that the noise suppression can be done by compressing targets into a joint-photographic expert group (JPEG) format with appropriate image compression quality. In the case of the weak noise suppression, the improved recognition performance is as high as that of the classical JTC.
Observer efficiency in free-localization tasks with correlated noise
Directory of Open Access Journals (Sweden)
Craig eAbbey
2014-05-01
Full Text Available The efficiency of visual tasks involving localization has traditionally been evaluated using forced choice experiments that capitalize on independence across locations to simplify the performance of the ideal observer. However, developments in ideal observer analysis have shown how an ideal observer can be defined for free-localization tasks, where a target can appear anywhere in a defined search region and subjects respond by localizing the target. Since these tasks are representative of many real-world search tasks, it is of interest to evaluate the efficiency of observer performance in them. The central question of this work is whether humans are able to effectively use the information in a free-localization task relative to a similar task where target location is fixed. We use a yes-no detection task at a cued location as the reference for this comparison. Each of the tasks is evaluated using a Gaussian target profile embedded in four different Gaussian noise backgrounds having power-law noise power spectra with exponents ranging from 0 to 3. The free localization task had a square 6.7° search region. We report on two follow-up studies investigating efficiency in a detect-and-localize task, and the effect of processing the white-noise backgrounds. In the fixed-location detection task, we find average observer efficiency ranges from 35% to 59% for the different noise backgrounds. Observer efficiency improves dramatically in the tasks involving localization, ranging from 63% to 82% in the forced localization tasks and from 78% to 92% in the detect-and- localize tasks. Performance in white noise, the lowest efficiency condition, was improved by filtering to give them a power-law exponent of 2. Classification images, used to examine spatial frequency weights for the tasks, show better tuning to ideal weights in the free-localization tasks. The high absolute levels of efficiency suggest that observers are well-adapted to free-localization tasks.
Institute of Scientific and Technical Information of China (English)
Bing Wang; Xiuqing Wu
2007-01-01
A single-mode laser system with colored cross-correlated additive and multiplicative noise terms is considered. By the means of projection operator method, we study the effects of the cross-correlation time τ and the cross-correlation intensity λ between noises on the normalized intensity correlation function C(s). It is found that if λ＞ 0 (λ＜ 0), the normalized intensity correlation function C(s) increases (decreases) with increasing the cross-correlation time τ, and at large value of τ, the variation of the normalized intensity correlation function C(s) becomes small. With the increase of the net gain a0, C(s) exhibits a maximum when λ is larger. However, a minimum and a maximum appear on C(s) curves with the increase of a0 when λ becomes smaller and smaller.
Madurski, Christine; LeBel, Etienne P
2015-08-01
Correll (Journal of Personality and Social Psychology, 94, 48-59, 2008; Study 2) found that instructions to use or avoid race information decreased the emission of 1/f noise in a weapon identification task (WIT). These results suggested that 1/f noise in racial bias tasks reflected an effortful deliberative process, providing new insights regarding the mechanisms underlying implicit racial biases. Given the potential theoretical and applied importance of understanding the psychological processes underlying implicit racial biases - and in light of the growing demand for independent direct replications of findings to ensure the cumulative nature of our science - we attempted to replicate Correll's finding in two high-powered studies. Despite considerable effort to closely duplicate all procedural and methodological details of the original study (i.e., same cover story, experimental manipulation, implicit measure task, original stimuli, task instructions, sampling frame, population, and statistical analyses), both replication attempts were unsuccessful in replicating the original finding challenging the theoretical account that 1/f noise in racial bias tasks reflects a deliberative process. However, the emission of 1/f noise did consistently emerge across samples in each of our conditions. Hence, future research is needed to clarify the psychological significance of 1/f noise in racial bias tasks. PMID:25384891
Direct correlation between strengthening mechanisms and electrical noise in strained copper wires
Bellido, Natalia; Pautrat, Alain; Keller, Clement; Hug, Eric
2011-01-01
We have measured the resistance noise of copper metallic wires during a tensile stress. The time variation of the main resistance is continuous up to the wire breakdown, but its fluctuations reveal the intermittent and heterogeneous character of plastic flow. We show in particular direct correlations between strengthening mechanisms and noise spectra characteristics.
Passive elastography: shear-wave tomography from physiological-noise correlation in soft tissues.
Gallot, Thomas; Catheline, Stefan; Roux, Philippe; Brum, Javier; Benech, Nicolas; Negreira, Carlos
2011-06-01
Inspired by seismic-noise correlation and time reversal, a shear-wave tomography of soft tissues using an ultrafast ultrasonic scanner is presented here. Free from the need for controlled shear-wave sources, this passive elastography is based on Green's function retrieval and takes advantage of the permanent physiological noise of the human body. PMID:21693392
Measurement of Barkhausen noise and its correlation with magnetic permeability
Czech Academy of Sciences Publication Activity Database
Stupakov, Oleksandr; Pal'a, J.; Yurchenko, Vitaliy; Tomáš, Ivan; Bydžovský, J.
2008-01-01
Roč. 320, 3-4 (2008), s. 204-209. ISSN 0304-8853 R&D Projects: GA AV ČR 1QS100100508 Grant ostatní: VEGA(SK) 1/3116/06 Institutional research plan: CEZ:AV0Z10100520 Keywords : Barkhausen noise * magnetic hysteresis * magnetic non-destructive testing Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.283, year: 2008
National Aeronautics and Space Administration — A new type of calibration standard is proposed which produces a pair of microwave noise signals to aid in the characterization and calibration of correlating...
Directory of Open Access Journals (Sweden)
Shoji Kawahito
2010-10-01
Full Text Available For low-noise complementary metal-oxide-semiconductor (CMOS image sensors, the reduction of pixel source follower noises is becoming very important. Column-parallel high-gain readout circuits are useful for low-noise CMOS image sensors. This paper presents column-parallel high-gain signal readout circuits, correlated multiple sampling (CMS circuits and their noise reduction effects. In the CMS, the gain of the noise cancelling is controlled by the number of samplings. It has a similar effect to that of an amplified CDS for the thermal noise but is a little more effective for 1/f and RTS noises. Two types of the CMS with simple integration and folding integration are proposed. In the folding integration, the output signal swing is suppressed by a negative feedback using a comparator and one-bit D-to-A converter. The CMS circuit using the folding integration technique allows to realize a very low-noise level while maintaining a wide dynamic range. The noise reduction effects of their circuits have been investigated with a noise analysis and an implementation of a 1Mpixel pinned photodiode CMOS image sensor. Using 16 samplings, dynamic range of 59.4 dB and noise level of 1.9 e- for the simple integration CMS and 75 dB and 2.2 e- for the folding integration CMS, respectively, are obtained.
Improving signal-to-noise ratio performance of compressive imaging based on spatial correlation
Mao, Tianyi; Chen, Qian; He, Weiji; Zou, Yunhao; Dai, Huidong; Gu, Guohua
2016-07-01
In this paper, compressive imaging based on spatial correlation (CISC), which uses second-order correlation with the measurement matrix, is introduced to improve the signal-to-noise ratio performance of compressive imaging (CI). Numerical simulations and experiments are performed as well. Referred to the results, it can be seen that CISC performs much better than CI in three common noise environments. This provides the great opportunity to pave the way for real applications.
Correlation of Electrical Noise with Non-radiative Current for High Power QWLs
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
The characteristics of low-frequency electrical noise, voltage-current (V-I) and electrical derivation for 980nm InGaAsP/InGaAs/GaAs high power double quantum well lasers(DQWLs) are measured under different conditions. The correlation of the low-frequency electrical noise with surface non-radiative current of devices is discussed. The results indicate the low-frequency electrical noise of 980nm DQWLs with high power is mainly 1/f noise and has good relation with the device surface current at low injection.
A Noise-Correlated Cancellation Transmission Scheme for Cooperative MIMO Ad Hoc Networks
Directory of Open Access Journals (Sweden)
Wanni Liu
2014-04-01
Full Text Available A new transmission scheme based on noise-correlated cancellation (NCC is proposed, which absorbs the advantages of phase-inversion symmetric method and cooperative MIMO technology and makes full use of the correlation of noise in the adjacent channels to reduce channel noise. This paper firstly presents the implementation process of NCC transmission scheme in detail. Further, through theoretical analysis, it is showed that the signal-to-noise ratio gain which the proposed NCC transmission scheme gets is at least 4 times greater than the signal-to-noise ratio gain which the traditional cooperative MIMO transmission scheme gets. Finally, simulation experiment results also verify that the proposed NCC transmission scheme can make the channel capacity per bandwidth of cooperative MIMO Ad Hoc networks improve significantly and bit error rate (BER of the network reduce greatly, which will help to expand application scopes of cooperative MIMO Ad Hoc networks.
International Nuclear Information System (INIS)
The spin correlations ωrz, r=1,2,3, and the probability pN of finding a system in the Neel state for the antiferromagnetic ring Fe6III (the so-called 'small ferric wheel') are calculated. States with magnetization M=0 and total spin 0≤S≤15, labeled by two (out of four) one-dimensional irreducible representations (irreps) of the point symmetry group D6, are taken into account. This choice follows from importance of these irreps in analyzing low-lying states in each S multiplet. Taking into account the Clebsch-Gordan coefficients for coupling total spins of sublattices (SA=SB=(15/2)) the global Neel probability pN* can be determined. Dependences of these quantities on state energy (per bond and in the units of exchange integral J) and the total spin S are analyzed. Providing we have determined pN(S), etc., for other antiferromagnetic rings (Fe10, for instance) we could try to approximate results for the largest synthesized ferric wheel Fe18. Since thermodynamic properties of Fe6 have been investigated recently, in the present considerations they are not discussed, but only used to verify obtained values of eigenenergies. Numerical results are calculated with high precision using two main tools: (i) thorough analysis of symmetry properties including methods of algebraic combinatorics and (ii) multiple precision arithmetic library GMP. The system considered yields more than 45 000 basic states (the so-called Ising configurations), but application of the method proposed reduces this problem to 20-dimensional eigenproblem for the ground state (S=0). The largest eigenproblem has to be solved for S=4; its dimension is 60. These two facts (high precision and small resultant eigenproblems) confirm the efficiency and usefulness of such an approach, so it is briefly discussed here
The shot noise of a strongly correlated quantum dot coupled to the Luttinger liquid leads
International Nuclear Information System (INIS)
We study the shot noise of a strongly correlated quantum dot weakly coupled to Luttinger liquid leads in the Kondo regime by means of the extended equation of motion method. A general zero-frequency shot noise formula with good convergence is derived. The shot noise exhibits a non-monotonic dependence on voltage for weak intralead interaction. There is a peak around the Kondo temperature at low voltage when the interaction is very weak, and its height decreases rapidly with the intralead interaction increasing. When the interaction is moderately strong the peak disappears and the shot noise scales as a power law in bias voltage, indicating that the intralead electron interaction suppresses the shot noise. It is possible that the measurements of the shot noise spectrum can extract the information of the intralead interaction. - Highlights: • The shot noise of a dot coupled to Luttinger liquid leads in the Kondo regime. • A shot noise formula is derived. • Intralead interaction suppresses the shot noise. • The noise shows different voltage-dependence for different intralead interaction
Xue, Zhenyu; Vlachos, Pavlos P
2014-01-01
In particle image velocimetry (PIV) the measurement signal is contained in the recorded intensity of the particle image pattern superimposed on a variety of noise sources. The signal-to-noise-ratio (SNR) strength governs the resulting PIV cross correlation and ultimately the accuracy and uncertainty of the resulting PIV measurement. Hence we posit that correlation SNR metrics calculated from the correlation plane can be used to quantify the quality of the correlation and the resulting uncertainty of an individual measurement. In this paper we present a framework for evaluating the correlation SNR using a set of different metrics, which in turn are used to develop models for uncertainty estimation. The SNR metrics and corresponding models presented herein are expanded to be applicable to both standard and filtered correlations. In addition, the notion of a valid measurement is redefined with respect to the correlation peak width in order to be consistent with uncertainty quantification principles and distinct ...
Temporal Correlation-Based Spatial Filtering of Rician Noise for Functional MRIs
Institute of Scientific and Technical Information of China (English)
Amir. A. Khaliq; I. M. Qureshi; Jawad. A. Shah
2012-01-01
A novel correlation-based filter is presented for de-noising functional magnetic resonance imaging (fMRI) data. Temporal correlation-based exponential weights are defined for spatial smoothing of the data, with bias reduction using estimated noise variance. The proposed scheme is tested on simulated and real fMRI data. Finally, the results are compared with conventional filters. The method is found to be effectively suppressing the Rician noise in fMRI data, while improving the SNR.%A novel correlation-based filter is presented for de-noising functional magnetic resonance imaging (fMRI) data.Temporal correlation-based exponential weights are defined for spatial smoothing of the data,with bias reduction using estimated noise variance.The proposed scheme is tested on simulated and real fMRI data.Finally,the results are compared with conventional filters.The method is found to be effectively suppressing the Rician noise in fMRI data,while improving the SNR.
Hadziioannou, Céline; Coutant, Olivier; Roux, Philippe; Campillo, Michel
2009-01-01
Previous studies have shown that small changes can be monitored in a scattering medium by observing phase shifts in the coda. Passive monitoring of weak changes through ambient noise correlation has already been applied to seismology, acoustics and engineering. Usually, this is done under the assumption that a properly reconstructed Green function as well as stable background noise sources are necessary. In order to further develop this monitoring technique, a laboratory experiment was performed in the 2.5MHz range in a gel with scattering inclusions, comparing an active (pulse-echo) form of monitoring to a passive (correlation) one. Present results show that temperature changes in the medium can be observed even if the Green function (GF) of the medium is not reconstructed. Moreover, this article establishes that the GF reconstruction in the correlations is not a necessary condition: the only condition to monitoring with correlation (passive experiment) is the relative stability of the background noise struc...
Institute of Scientific and Technical Information of China (English)
Shuo Zhang,Yan Zhao,Min Li,; Jianhui Zhao
2015-01-01
The global y optimal recursive filtering problem is stu-died for a class of systems with random parameter matrices, stochastic nonlinearities, correlated noises and missing measure-ments. The stochastic nonlinearities are presented in the system model to reflect multiplicative random disturbances, and the addi-tive noises, process noise and measurement noise, are assumed to be one-step autocorrelated as wel as two-step cross-correlated. A series of random variables is introduced as the missing rates governing the intermittent measurement losses caused by un-favorable network conditions. The aim of the addressed filtering problem is to design an optimal recursive filter for the uncertain systems based on an innovation approach such that the filtering error is global y minimized at each sampling time. A numerical simulation example is provided to il ustrate the effectiveness and applicability of the proposed algorithm.
The correlation between serum leptin and blood pressure after exposure to noise at work
Directory of Open Access Journals (Sweden)
Muayad S Rahma
2013-01-01
Full Text Available Several epidemiologic studies have reported that exposure to noise is associated with cardiovascular disease. The increased body weight is often associated with metabolic as well as increased blood pressure. The aim of this study is to investigate the correlation between the elevation of blood pressure and serum leptin hormones due to the effects of noise in the work place. A total of 80 volunteer males where included in this study with an age range between of 20 and 45 years, they were divided in two groups equally, the 1 st group were exposed to noise in the workplace while the 2 nd group were not. The individual noise exposure was determined by using a sound level meter. The range of noise was 80-100 dBA. Body Mass Index was also taken for each individual by a standard measure, blood pressure was measured by OMRON sphygmomanometer and serum leptin was measured through venous blood sample analysis enzyme linked immunosorbent assay. Spearman rank order correlation was used to examine the correlations between Blood pressure value (Systolic, Diastolic and Leptin. All the relationships between parameters showed a positive correlation. Systolic and diastolic blood pressure values had a significant correlation to leptin hormone level in comparison to the control. There was a significant relation between leptin and blood pressure. leptin effects on the sympathetic nervous system may provide a partial explanation. Therefore, Leptin might have diverse cardiovascular actions.
A new method to estimate the noise in financial correlation matrices
International Nuclear Information System (INIS)
Companies belonging to the same industrial branch are subject to similar economical influences. Hence, the time series of their stocks can show similar trends implying a correlation. Financial correlation matrices measure the unsystematic correlations between time series of stocks. Such information is important for risk management. It has been found by Laloux et al that the correlation matrices are 'noise dressed', a major reason being the finiteness of the time series. We present a new and alternative method to estimate this noise. We introduce a power mapping of the elements in the correlation matrix which suppresses the noise and thereby effectively 'prolongs' the time series. Neither further data processing nor additional input is needed. To develop and test our method, we use a model suggested by Noh which can be viewed as a special case of a 'factor model' in economics. We perform numerical simulations for the time series and obtain correlation matrices. We support the numerics by a qualitative analytical discussion. With our approach, different correlation structures buried under this noise can be detected. Our method is general and can be applied to all systems in which time series are measured
Shot noise of a quantum dot with non-Fermi liquid correlations
Braggio, A.; Fazio, R.; Sassetti, M.
2003-01-01
The shot noise of a one-dimensional wire interrupted by two barriers shows interesting features related to the interplay between Coulomb blockade effects, Luttinger correlations and discrete excitations. At small bias the Fano factor reaches the lowest attainable value, 1/2, irrespective of the ratio of the two junction resistances. At larger voltages this asymmetry is power-law renormalized by the interaction strength. We discuss how the measurement of current and these features of the noise...
The connection between noise and quantum correlations in a double quantum dot
Bodoky, F.; Belzig, W.; Bruder, C.
2007-01-01
We investigate the current and noise characteristics of a double quantum dot system. The strong correlations induced by the Coulomb interaction create entangled two-electron states and lead to signatures in the transport properties. We show that the interaction parameter phi, which measures the admixture of the double-occupancy contribution to the singlet state and thus the degree of entanglement, can be directly accessed through the Fano factor of super-Poissonian shot noise.
Noise-correlation-time-mediated localization in random nonlinear dynamical systems
Cabrera, J L; De la Rubia, F J; Cabrera, Juan L.
1999-01-01
We investigate the behavior of the residence times density function for different nonlinear dynamical systems with limit cycle behavior and perturbed parametrically with a colored noise. We present evidence that underlying the stochastic resonancelike behavior with the noise correlation time, there is an effect of optimal localization of the system trajectories in the phase space. This phenomenon is observed in systems with different nonlinearities, suggesting a degree of universality.
On the loss-of-correlation due to PIV image noise
Scharnowski, Sven; Kähler, Christian J.
2016-07-01
The effect of image noise on the uncertainty of velocity fields measured with particle image velocimetry (PIV) is still an unsolved problem. Image noise reduces the correlation signal and thus affects the estimation of the particle image displacement. However, a systematic quantification of the effect of the noise level on the loss-of-correlation is missing. In this work, a new method is proposed to estimate the loss-of-correlation due to image noise F_{σ } from the autocorrelation function of PIV images. Furthermore, a new definition of the signal-to-noise ratio (SNR) for PIV images is suggested, which results in a bijective relation between F_{σ } and SNR. Based on the newly defined SNR, it becomes possible to estimate the signal level and the noise level itself. The presented method is very general because the estimation of F_{σ } and SNR works independently of various parameters, including the particle image intensity, the particle image density, the particle image size, the image noise distributions and the laser light-sheet profile. The findings lead to an extension of the fundamental PIV equation N=NI FI FO F_{Δ } and enable PIV users to optimize their measurement setup with respect to the image noise and not only based on the loss-of-correlation due to in-plane motion, out-of-plane motion and displacement gradients. Furthermore, the new definition of SNR allows for a characterization and comparison of PIV images. The new approaches are validated by using synthetic images, and the predictions are confirmed by using experimental data.
Institute of Scientific and Technical Information of China (English)
HAN Li-Bo; CAO Li; YANG Hong-Quan; WU Da-Jin
2005-01-01
By using the linear approximation method, the intensity correlation function is calculated for a single-mode laser modulated by a bias signal and driven by colored pump and quantum noises with colored cross-correlation. We found that, when the correlation time between the two noises is very short, the behavior of the intensity correlation function versus the time, in addition to decreasing monotonously, also exhibits several cases, such as one maximum, one minimum, and two extrema. When the correlation time between the two noises is very long, the behavior of the intensity correlation function exhibits oscillation and the envelope is similar to the case of short cross-correlation time.
Noise-induced bias for convolution-based interpolation in digital image correlation.
Su, Yong; Zhang, Qingchuan; Gao, Zeren; Xu, Xiaohai
2016-01-25
In digital image correlation (DIC), the noise-induced bias is significant if the noise level is high or the contrast of the image is low. However, existing methods for the estimation of the noise-induced bias are merely applicable to traditional interpolation methods such as linear and cubic interpolation, but are not applicable to generalized interpolation methods such as BSpline and OMOMS. Both traditional interpolation and generalized interpolation belong to convolution-based interpolation. Considering the widely use of generalized interpolation, this paper presents a theoretical analysis of noise-induced bias for convolution-based interpolation. A sinusoidal approximate formula for noise-induced bias is derived; this formula motivates an estimating strategy which is with speed, ease, and accuracy; furthermore, based on this formula, the mechanism of sophisticated interpolation methods generally reducing noise-induced bias is revealed. The validity of the theoretical analysis is established by both numerical simulations and actual subpixel translation experiment. Compared to existing methods, formulae provided by this paper are simpler, briefer, and more general. In addition, a more intuitionistic explanation of the cause of noise-induced bias is provided by quantitatively characterized the position-dependence of noise variability in the spatial domain. PMID:26832501
Institute of Scientific and Technical Information of China (English)
Chen Li-Mei; Cao Li; Wu Da-Jin
2007-01-01
Stochastic resonance (SR) is studied in a gain-noise model of a single-mode laser driven by a coloured pump noise and a quantum noise with cross-correlation between real and imaginary parts under a direct signal modulation. By using a linear approximation method, we find that the SR appears during the variation of signal-to-noise ratio (SNR)separately with the pump noise self-correlation time τ, the noise correlation coefficient between the real part and the imaginary part of the quantum noise λq, the attenuation coefficient γ and the deterministic steady-state intensity I0.In addition, it is found that the SR can be characterized not only by the dependence of SNR on the noise variables of τand λq, but also by the dependence of SNR on the laser system variables of γ and I0. Thus our investigation extends the characteristic quantity of SR proposed before.
Fujihala, M.; Zheng, X. G.; Oohara, Y.; Morodomi, H.; Kawae, T.; Matsuo, Akira; Kindo, Koichi
2012-01-01
Spin fluctuations and spin-liquid behaviors of frustrated kagome antiferromagnets have received intense recent attention. Although most severe frustration was predicted for an Ising kagome antiferromagnet, a real material system of undistorted kagome lattice has not been found so far. Here we report the frustrated magnetism of a new Ising kagome antiferromagnet, MgCo3(OH)6Cl2, which can be viewed as a Co version of the intensively researched quantum kagome antiferromagnet of Herbertsmithite ZnCu3(OH)6Cl2. Experiments of magnetization, heat capacity, μSR, and neutron scattering demonstrated a partially frozen state with persistent spin fluctuations below around T = 2.7 K. The present study has provided a real material system to study the Ising spin behaviors on undistorted kagome lattice.
Noise is all around you, from televisions and radios to lawn mowers and washing machines. Normally, you ... sensitive structures of the inner ear and cause noise-induced hearing loss. More than 30 million Americans ...
Cross-correlation measurement of quantum shot noise using homemade transimpedance amplifiers.
Hashisaka, Masayuki; Ota, Tomoaki; Yamagishi, Masakazu; Fujisawa, Toshimasa; Muraki, Koji
2014-05-01
We report a cross-correlation measurement system, based on a new approach, which can be used to measure shot noise in a mesoscopic conductor at milliKelvin temperatures. In contrast to other measurement systems in which high-speed low-noise voltage amplifiers are commonly used, our system employs homemade transimpedance amplifiers (TAs). The low input impedance of the TAs significantly reduces the crosstalk caused by unavoidable parasitic capacitance between wires. The TAs are designed to have a flat gain over a frequency band from 2 kHz to 1 MHz. Low-noise performance is attained by installing the TAs at a 4 K stage of a dilution refrigerator. Our system thus fulfills the technical requirements for cross-correlation measurements: low noise floor, high frequency band, and negligible crosstalk between two signal lines. Using our system, shot noise generated at a quantum point contact embedded in a quantum Hall system is measured. The good agreement between the obtained shot-noise data and theoretical predictions demonstrates the accuracy of the measurements. PMID:24880392
Cross-correlation measurement of quantum shot noise using homemade transimpedance amplifiers
International Nuclear Information System (INIS)
We report a cross-correlation measurement system, based on a new approach, which can be used to measure shot noise in a mesoscopic conductor at milliKelvin temperatures. In contrast to other measurement systems in which high-speed low-noise voltage amplifiers are commonly used, our system employs homemade transimpedance amplifiers (TAs). The low input impedance of the TAs significantly reduces the crosstalk caused by unavoidable parasitic capacitance between wires. The TAs are designed to have a flat gain over a frequency band from 2 kHz to 1 MHz. Low-noise performance is attained by installing the TAs at a 4 K stage of a dilution refrigerator. Our system thus fulfills the technical requirements for cross-correlation measurements: low noise floor, high frequency band, and negligible crosstalk between two signal lines. Using our system, shot noise generated at a quantum point contact embedded in a quantum Hall system is measured. The good agreement between the obtained shot-noise data and theoretical predictions demonstrates the accuracy of the measurements
Body Waves Revealed by Spatial Stacking on Long-Term Cross-Correlation of Ambient Noise
Institute of Scientific and Technical Information of China (English)
Kai Wang; Yinhe Luo; Kaifeng Zhao; Limeng Zhang
2014-01-01
ABSTRCT: Theoretical and experimental studies indicate that complete Green’s Function can be retrieved from cross-correlation in a diffuse field. High SNR (signal-to-noise ratio) surface waves have been extracted from cross-correlations of long-duration ambient noise across the globe. Body waves, not extracted in most of ambient noise studies, are thought to be more difficult to retrieve from regular ambient noise data processing. By stacking cross-correlations of ambient noise in 50 km inter-station distance bins in China, western United States and Europe, we observed coherent 20–100 s core phases (ScS, PKIKPPKIKP, PcPPKPPKP) and crustal-mantle phases (Pn, P, PL, Sn, S, SPL, SnSn, SS, SSPL) at distances ranging from 0 to 4 000 km. Our results show that these crustal-mantle phases show diverse characteristics due to different substructure and sources of body waves beneath different regions while the core phases are relatively robust and can be retrieved as long as stations are available. Further analysis indicates that the SNR of these body-wave phases depends on a compromise between stacking fold in spatial domain and the coherence of pre-stacked cross-correlations.Spatially stacked cross-correlations of seismic noise can provide new virtual seismograms for paths that complement earthquake data and that contain valuable information on the structure of the Earth. The extracted crustal-mantle phases can be used to study lithospheric heterogeneities and the robust core phases are significantly useful to study the deep structure of the Earth, such as detecting fine heterogeneities of the core-mantle boundary and constraining differential rotation of the inner core.
Interpreting Cross-correlations of One-bit Filtered Seismic Noise
Hanasoge, Shravan
2013-01-01
Seismic noise, generated by oceanic microseisms and other sources, illuminates the crust in a manner different from tectonic sources, and therefore provides independent information. The primary measurable is the two-point cross-correlation, evaluated using traces recorded at a pair of seismometers over a finite-time interval. However, raw seismic traces contain intermittent large-amplitude perturbations arising from tectonic activity and instrumental errors, which may corrupt the estimated cross-correlations of microseismic fluctuations. In order to diminish the impact of these perturbations, the recorded traces are filtered using the nonlinear one-bit digitizer, which replaces the measurement by its sign. Previous theory shows that for stationary Gaussian-distributed seismic noise fluctuations one-bit and raw correlation functions are related by a simple invertible transformation. Here we extend this to show that the simple correspondence between these two correlation techniques remains valid for {\\it non-st...
Graphene thermal transport studies via radio-frequency, cross-correlated Johnson noise thermometry
Crossno, Jesse; Liu, Xiaomeng; Wang, Ke; Harzheim, Achim; Watanabe, Kenji; Taniguchi, Takashi; Ohki, Thomas; Fong, Kin Chung; Kim, Philip
2015-03-01
The electronic temperature of a dissipative, mesoscale device can be determined by monitoring the Johnson noise power emitted over a wide frequency range. Using radiometry techniques, we have developed a high-frequency, wide bandwidth, cross-correlation Johnson noise thermometer operating from room temperature to cryogenic levels that is compatible with strong magnetic fields. Precisions ranging from 2 to 25 mK are demonstrated over the temperature range of 3 to 300 K with 1 second of integration time. This non-invasive thermometer has enabled us to perform sensitive electronic thermal transport studies in boron nitride encapsulated monolayer graphene over two orders of magnitude in temperature. This versatile technique also enables precision Fano factor measurements as well as studies of correlated noise phenomena, such as those found in layered Van der Waals heterostructures.
Probability distributions for directed polymers in random media with correlated noise.
Chu, Sherry; Kardar, Mehran
2016-07-01
The probability distribution for the free energy of directed polymers in random media (DPRM) with uncorrelated noise in d=1+1 dimensions satisfies the Tracy-Widom distribution. We inquire if and how this universal distribution is modified in the presence of spatially correlated noise. The width of the distribution scales as the DPRM length to an exponent β, in good (but not full) agreement with previous renormalization group and numerical results. The scaled probability is well described by the Tracy-Widom form for uncorrelated noise, but becomes symmetric with increasing correlation exponent. We thus find a class of distributions that continuously interpolates between Tracy-Widom and Gaussian forms. PMID:27575059
Experimental demonstration of sub-shot-noise intensity correlations in an intense twin beam
Czech Academy of Sciences Publication Activity Database
Bondani, M.; Allevi, A.; Zambra, G.; Andreoni, A.; Peřina, Jan; Křepelka, Jaromír; Peřina ml., Jan
2008-01-01
Roč. 160, č. 1 (2008), s. 33-41. ISSN 1951-6355 Institutional research plan: CEZ:AV0Z10100522 Keywords : sub- shot -noise * intensity correlation * twin beam Subject RIV: BH - Optics, Masers, Lasers Impact factor: 0.689, year: 2008
Filtering for linear systems with noise correlation and its application to singular systems
Institute of Scientific and Technical Information of China (English)
Wu Jian-Rong; Song Shi-Ji
2004-01-01
In this paper, an optimal filter for a stochastic linear system with previous stage noise correlation is designed.Based on this result, together with the decomposition techniques of the stochastic singular linear system, the design of an optimal filter for a stochastic singular linear system is given.
Theodorsen, Audun; Rypdal, Martin
2016-01-01
The filtered Poisson process is often used as a reference model for intermittent fluctuations in physical systems. Here, this process is extended by adding a noise term, either as a purely additive term to the process or as a dynamical term in a stochastic differential equation. The moments, probability density function, auto- correlation function and power spectral density are derived and used to compare the effects of the different noise terms. Monte-Carlo studies of synthetic time series are used to investigate the accuracy of parameter estimation and to identify methods for separating the noise types. It is shown that the probability density function and the three lowest moments provide accurate estimations of the parameters, but are unable to separate the noise types. The auto-correlation function and the power spectral density also provide methods for estimating the model parameters, as well as being capable of determining the noise type. The number of times the signal passes a prescribed threshold in t...
Surrogate testing of volatility series from long-range correlated noise
Nagarajan, R
2006-01-01
Detrended fluctuation analysis (DFA) [1] of the volatility series has been found to be useful in dentifying possible nonlinear/multifractal dynamics in the empirical sample [2-4]. Long-range volatile correlation can be an outcome of static as well as dynamical nonlinearity. In order to argue in favor of dynamical nonlinearity, surrogate testing is used in conjunction with volatility analysis [2-4]. In this brief communication, surrogate testing of volatility series from long-range correlated noise and their static, invertible nonlinear transforms is investigated. Long-range correlated monofractal noise is generated using FARIMA (0, d, 0) with Gaussian and non-Gaussian innovations. We show significant deviation in the scaling behavior between the empirical sample and the surrogate counterpart at large time-scales in the case of FARIMA (0, d, 0) with non-Gaussian innovations whereas no such discrepancy was observed in the case of Gaussian innovations. The results encourage cautious interpretation of surrogate t...
Ohlson, J. E.
1976-01-01
Optimum estimation (tracking) of the polarization plane of a linearly polarized electromagnetic wave is determined when the signal is a narrow-band Gaussian random process with a polarization plane angle which is also a Gaussian random process. This model is compared to previous work and is applicable to space communication. The estimator performs a correlation operation similar to an amplitude-comparison monopulse angle tracker, giving the name correlation polarimeter. Under large signal-to-noise ratio (SNR), the estimator is causal. Performance of the causal correlation polarimeter is evaluated for arbitrary SNR. Optimum precorrelation filtering is determined. With low SNR, the performance of this system is far better than that of previously developed systems. Practical implementation is discussed. A scheme is given to reduce the effect of linearly polarized noise.
Stochastic Bifurcations induced by correlated Noise in a Birhythmic van der Pol System
Yonkeu, R Mbakob; Filatrella, G; Tchawoua, C
2015-01-01
We investigate the effects of exponentially correlated noise on birhythmic van der Pol type oscillators. The analytical results are obtained applying the quasi-harmonic assumption to the Langevin equation to derive an approximated Fokker-Planck equation. This approach allows to analytically derive the probability distributions as well as the activation energies associated to switching between coexisting attractors. The stationary probability density function of the van der Pol oscillator reveals the influence of the correlation time on the dynamics. Stochastic bifurcations are discussed through a qualitative change of the stationary probability distribution, which indicates that noise intensity and correlation time can be treated as bifurcation parameters. Comparing the analytical and numerical results, we find good agreement both when the frequencies of the attractors are about equal or when they are markedly different.
Depict noise-driven nonlinear dynamic networks from output data by using high-order correlations
Chen, Yang; Chen, Tianyu; Wang, Shihong; Hu, Gang
2016-01-01
Many practical systems can be described by dynamic networks, for which modern technique can measure their output signals, and accumulate extremely rich data. Nevertheless, the network structures producing these data are often deeply hidden in these data. Depicting network structures by analysing the available data turns to be significant inverse problems. On one hand, dynamics are often driven by various unknown facts, called noises. On the other hand, network structures of practical systems are commonly nonlinear, and different nonlinearities can provide rich dynamic features and meaningful functions of realistic networks. So far, no method, both theoretically or numerically, has been found to systematically treat the both difficulties together. Here we propose to use high-order correlation computations (HOCC) to treat nonlinear dynamics; use two-time correlations to treat noise effects; and use suitable basis and correlator vectors to unifiedly depict all dynamic nonlinearities and topological interaction l...
Cross-correlation spin noise spectroscopy of heterogeneous interacting spin systems
International Nuclear Information System (INIS)
Interacting multi-component spin systems are ubiquitous in nature and in the laboratory. As such, investigations of inter-species spin interactions are of vital importance. Traditionally, they are studied by experimental methods that are necessarily perturbative: e.g., by intentionally polarizing or depolarizing one spin species while detecting the response of the other(s). Here, we describe and demonstrate an alternative approach based on multi-probe spin noise spectroscopy, which can reveal inter-species spin interactions - under conditions of strict thermal equilibrium - by detecting and cross-correlating the stochastic fluctuation signals exhibited by each of the constituent spin species. Specifically, we consider a two-component spin ensemble that interacts via exchange coupling, and we determine cross-correlations between their intrinsic spin fluctuations. The model is experimentally confirmed using 'two-color' optical spin noise spectroscopy on a mixture of interacting Rb and Cs vapors. Noise correlations directly reveal the presence of inter-species spin exchange, without ever perturbing the system away from thermal equilibrium. These non-invasive and noise-based techniques should be generally applicable to any heterogeneous spin system in which the fluctuations of the constituent components are detectable
An Optimal Energy Estimator to Reduce Correlated Noise for the EXO-200 Light Readout
Collaboration, EXO-200; :; Davis, C. G.; Hall, C; Albert, J. B.; Barbeau, P. S.; D. Beck; Belov, V.; Breidenbach, M.; Brunner, T.; Burenkov, A.; Cao, G. F.; Cen, W. R.; Chambers, C.; Cleveland, B.
2016-01-01
The energy resolution of the EXO-200 detector is limited by electronics noise in the measurement of the scintillation response. Here we present a new technique to extract optimal scintillation energy measurements for signals split across multiple channels in the presence of correlated noise. The implementation of these techniques improves the energy resolution of the detector at the neutrinoless double beta decay Q-value from $\\left[1.9641\\pm 0.0039\\right]\\%$ to $\\left[1.5820\\pm 0.0044\\right]...
An Optimal Energy Estimator to Reduce Correlated Noise for the EXO-200 Light Readout
:,; Hall, C; Albert, J B; Barbeau, P S; Beck, D; Belov, V; Breidenbach, M; Brunner, T; Burenkov, A; Cao, G F; Cen, W R; Chambers, C; Cleveland, B; Coon, M; Craycraft, A; Daniels, T; Danilov, M; Daugherty, S J; Davis, J; Delaquis, S; Der Mesrobian-Kabakian, A; DeVoe, R; Didberidze, T; Dilling, J; Dolgolenko, A; Dolinski, M J; Dunford, M; Fairbank, W; Farine, J; Feldmeier, W; Feyzbakhsh, S; Fierlinger, P; Fudenberg, D; Gornea, R; Graham, K; Gratta, G; Hughes, M; Jewell, M J; Johnson, A; Johnson, T N; Johnston, S; Karelin, A; Kaufman, L J; Killick, R; Koffas, T; Kravitz, S; Krücken, R; Kuchenkov, A; Kumar, K S; Leonard, D S; Licciardi, C; Lin, Y H; Ling, J; MacLellan, R; Marino, M G; Mong, B; Moore, D; Njoya, O; Nelson, R; Odian, A; Ostrovskiy, I; Piepke, A; Pocar, A; Prescott, C Y; Retière, F; Rowson, P C; Russell, J J; Schubert, A; Sinclair, D; Smith, E; Stekhanov, V; Tarka, M; Tolba, T; Tsang, R; Twelker, K; Vuilleumier, J -L; Waite, A; Walton, J; Walton, T; Weber, M; Wen, L J; Wichoski, U; Wood, J; Yang, L; Yen, Y -R; Zeldovich, O Ya
2016-01-01
The energy resolution of the EXO-200 detector is limited by electronics noise in the measurement of the scintillation response. Here we present a new technique to extract optimal scintillation energy measurements for signals split across multiple channels in the presence of correlated noise. The implementation of these techniques improves the energy resolution of the detector at the neutrinoless double beta decay Q-value from $\\left[1.9641\\pm 0.0039\\right]\\%$ to $\\left[1.5820\\pm 0.0044\\right]\\%$.
Institute of Scientific and Technical Information of China (English)
Xie Wen-Xian; Xu Wei; Cai Li; Jin Yan-Fei
2005-01-01
It is shown how the cross-correlation time and strength of coloured cross-correlated white noises can set an upper bound for the time derivative of entropy in a nonequilibrium system. The value of upper bound can be calculateddirectly based on the Schwartz inequality principle and the Fokker-Planck equation of the dynamical system driven by coloured cross-correlated white noises. The present calculations can be used to interpret the interplay of the dissipative constant and cross-correlation time and strength of coloured cross-correlated white noises on the upper bound.
International Nuclear Information System (INIS)
In particle image velocimetry (PIV) the measurement signal is contained in the recorded intensity of the particle image pattern superimposed on a variety of noise sources. The signal-to-noise-ratio (SNR) strength governs the resulting PIV cross correlation and ultimately the accuracy and uncertainty of the resulting PIV measurement. Hence we posit that correlation SNR metrics calculated from the correlation plane can be used to quantify the quality of the correlation and the resulting uncertainty of an individual measurement. In this paper we extend the original work by Charonko and Vlachos and present a framework for evaluating the correlation SNR using a set of different metrics, which in turn are used to develop models for uncertainty estimation. Several corrections have been applied in this work. The SNR metrics and corresponding models presented herein are expanded to be applicable to both standard and filtered correlations by applying a subtraction of the minimum correlation value to remove the effect of the background image noise. In addition, the notion of a ‘valid’ measurement is redefined with respect to the correlation peak width in order to be consistent with uncertainty quantification principles and distinct from an ‘outlier’ measurement. Finally the type and significance of the error distribution function is investigated. These advancements lead to more robust and reliable uncertainty estimation models compared with the original work by Charonko and Vlachos. The models are tested against both synthetic benchmark data as well as experimental measurements. In this work, U68.5 uncertainties are estimated at the 68.5% confidence level while U95 uncertainties are estimated at 95% confidence level. For all cases the resulting calculated coverage factors approximate the expected theoretical confidence intervals, thus demonstrating the applicability of these new models for estimation of uncertainty for individual PIV measurements. (paper)
Mean first-passage time of an asymmetric bistable system driven by colour-correlated noise
Institute of Scientific and Technical Information of China (English)
Zhang Xiao-Yan; Xu Wei
2007-01-01
In this paper, the effect of every parameter (including p, q,r, λ,τ) on the mean first-passage time (MFPT) is investigated in an asymmetric bistable system driven by colour-correlated noise. The expression of MFPT has been obtained by applying the steepest-descent approximation. Numerical results show that (1) the intensity of multiplicative noise p and the intensity of additive noise q play different roles in the MFPT of the system, (2) suppression appears on the curve of the MFPT with small λ (e.g. λ＜ 0.5) but there is a peak on the curve of the MFPT when λ is big (e.g.λ＞ 0.5), and (3) with different values of r (e.g. r = 0.1, 0.5, 1.5), the effort of τ on the MFPT is diverse.
Effects of Tropospheric Spatio-Temporal Correlated Noise on the Analysis of Space Geodetic Data
Romero-Wolf, A.; Jacobs, C. S.; Ratcliff, J. T.
2012-01-01
The standard VLBI analysis models the distribution of measurement noise as Gaussian. Because the price of recording bits is steadily decreasing, thermal errors will soon no longer dominate. As a result, it is expected that troposphere and instrumentation/clock errors will increasingly become more dominant. Given that both of these errors have correlated spectra, properly modeling the error distributions will become increasingly relevant for optimal analysis. We discuss the advantages of modeling the correlations between tropospheric delays using a Kolmogorov spectrum and the frozen flow assumption pioneered by Treuhaft and Lanyi. We then apply these correlated noise spectra to the weighting of VLBI data analysis for two case studies: X/Ka-band global astrometry and Earth orientation. In both cases we see improved results when the analyses are weighted with correlated noise models vs. the standard uncorrelated models. The X/Ka astrometric scatter improved by approx.10% and the systematic Delta delta vs. delta slope decreased by approx. 50%. The TEMPO Earth orientation results improved by 17% in baseline transverse and 27% in baseline vertical.
Influence of the angular correlation of fission neutrons on noise signatures
International Nuclear Information System (INIS)
Noise signatures, the measurement of the correlation between the fluctuating parts of the signals coming from neutron detectors, are commonly used to measure nuclear parameters (reactivities, mean lives) and to monitor nuclear systems. Several techniques are used, such as the correlation or analog signals in time or frequency domains or the statistical analysis of detection events. Apart from the experimental method, the useful components of the stochastic descriptors is related to the detection of neutrons that have ancestors born in the same fission event. Despite an early work opened to the inclusion of the n - n angular correlations of neutrons coming from the same fission, practically all the theoretical applications ignore this additional complication by making the implicit or explicit hypothesis that fission neutrons are born uncorrelated. However, there are direct measurements that show angular and energy correlation for the two-fission-neutron distribution. The first attempt to include this experimental evidence into the theory of neutron noise was the calculation of the ratio of spectral densities related to the 252Cf method of measuring reactivities under the simplest condition: two neutron detectors monitoring a 252Cf-plated fission chamber. The objective of this communication is to show how noise signatures of more complex systems are sensitive to the joint distribution γ(v,v '), of two neutrons coming from the same fission with velocities v and v'
International Nuclear Information System (INIS)
Highlights: ► Significant increase of the noise amplitude was observed in PWRs. ► Coolant flow with more coherent characteristics could be an explanation. ► The dependence of the noise amplitude on radial correlation length was investigated. ► The noise amplitude increases with the increased spatial correlation length. - Abstract: The dependence of the amplitude of the neutron noise in PWRs on the radial correlation length of the noise source, that is the inlet temperature fluctuations, is investigated. The motivation for this work comes from the recent observation that the noise amplitude has increased significantly in certain Spanish PWRs. The reason of this increase has not yet been satisfactorily identified, although there are a few assumptions. One new hypothesis, put forward in this paper, is that a coolant flow with more coherent characteristics, which has actually been observed, could explain the increase of the noise amplitude. A more coherent flow leads to a longer spatial (radial) correlation length of the inlet temperature fluctuations, which in turn, in case the APSD of the temperature noise is unchanged, will lead to the increase of the neutron noise APSD. The mechanism behind this phenomenon is the same as the reason of the failure of the traditional noise based method for the determination of the Moderator Temperature Coefficient (MTC), and is related to the characteristics of the spatially randomly distributed noise sources. In this paper the relationship between the radial correlation length of the inlet temperature fluctuations and the neutron noise amplitude is investigated quantitatively and the increase of the noise amplitude with the increased spatial correlation of the inlet temperature fluctuations is demonstrated
Towards a global-scale ambient noise cross-correlation data base
Ermert, Laura; Fichtner, Andreas; Sleeman, Reinoud
2014-05-01
We aim to obtain a global-scale data base of ambient seismic noise correlations. This database - to be made publicly available at ORFEUS - will enable us to study the distribution of microseismic and hum sources, and to perform multi-scale full waveform inversion for crustal and mantle structure. Ambient noise tomography has developed into a standard technique. According to theory, cross-correlations equal inter-station Green's functions only if the wave field is equipartitioned or the sources are isotropically distributed. In an attempt to circumvent these assumptions, we aim to investigate possibilities to directly model noise cross-correlations and invert for their sources using adjoint techniques. A data base containing correlations of 'gently' preprocessed noise, excluding preprocessing steps which are explicitly taken to reduce the influence of a non-isotropic source distribution like spectral whitening, is a key ingredient in this undertaking. Raw data are acquired from IRIS/FDSN and ORFEUS. We preprocess and correlate the time series using a tool based on the Python package Obspy which is run in parallel on a cluster of the Swiss National Supercomputing Centre. Correlation is done in two ways: Besides the classical cross-correlation function, the phase cross-correlation is calculated, which is an amplitude-independent measure of waveform similarity and therefore insensitive to high-energy events. Besides linear stacks of these correlations, instantaneous phase stacks are calculated which can be applied as optional weight, enhancing coherent portions of the traces and facilitating the emergence of a meaningful signal. The _STS1 virtual network by IRIS contains about 250 globally distributed stations, several of which have been operating for more than 20 years. It is the first data collection we will use for correlations in the hum frequency range, as the STS-1 instrument response is flat in the largest part of the period range where hum is observed, up to a
Effects of cross-correlated noises on the intensity fluctuation of the single-mode laser system
Institute of Scientific and Technical Information of China (English)
Bing Wang; Shuwen Dai; Shuping Ge
2006-01-01
@@ A single-mode laser model with cross-correlated additive and multiplicative noise terms is considered, and the effects of correlation between noises on the relaxation time and the intensity correlation function are studied. Using the projection operator method and taking into account the effects of the memory kernels of the intensity correlation function, the analytic expressions for the relaxation time and the correlation function are derived. Based on numerical computations, it is found that the self-correlation time and the cross-correlation time have the same effects on the single-mode laser system.
Tobey, R. I.; Wall, S.; Foerst, M.; Bromberger, H.; Khanna, V.; Turner, J. J.; Schlotter, W.; Trigo, M.; Krupin, O.; Lee, W. S.; Chuang, Y. -D.; Moore, R.; Cavalieri, A. L.; Wilkins, S. B.; Zheng, H.; Mitchell, J. F.; Dhesi, S. S.; Cavalleri, A.; Hill, J.P.
2012-01-01
Using time-resolved resonant soft x-ray diffraction, we measure the evolution of the full three-dimensional scattering volume of the antiferromagnetic superlattice reflection in the single-layer manganite La0.5Sr1.5MnO4 on femtosecond time scales following photoexcitation. We find that the in-plane
Coarse-Grained Theory of Biological Charge Transfer with Spatially and Temporally Correlated Noise.
Liu, Chaoren; Beratan, David N; Zhang, Peng
2016-04-21
System-environment interactions are essential in determining charge-transfer (CT) rates and mechanisms. We developed a computationally accessible method, suitable to simulate CT in flexible molecules (i.e., DNA) with hundreds of sites, where the system-environment interactions are explicitly treated with numerical noise modeling of time-dependent site energies and couplings. The properties of the noise are tunable, providing us a flexible tool to investigate the detailed effects of correlated thermal fluctuations on CT mechanisms. The noise is parametrizable by molecular simulation and quantum calculation results of specific molecular systems, giving us better molecular resolution in simulating the system-environment interactions than sampling fluctuations from generic spectral density functions. The spatially correlated thermal fluctuations among different sites are naturally built-in in our method but are not readily incorporated using approximate spectral densities. Our method has quantitative accuracy in systems with small redox potential differences (
International Nuclear Information System (INIS)
Nickel and its oxides are released from the surface of steam generator tubes into the primary water. Released nickel and cobalt is activated to Co-58 and Co-60 in the reactor core by a neutron flux, respectively. These activated corrosion products are the main source of high radiation fields and occupational radiation exposure. In addition, some of the corrosion products redeposit on the fuel cladding, hinder the heat transfer, increase the corrosion rate of the fuel cladding, and finally induce an axial offset anomaly. This phenomenon can decrease core shutdown margin, and thus lead to a down-rating of a plant. Recently, many researchers have reported that the surface states of Alloy 690 tubes affect the corrosion product formation and its release in simulated primary water environments. Meanwhile, the surface states of steam generator tubes affect the noise level of eddy current testing. Noise signals arising from the tubes degrade the probability of detection and sizing accuracy of the defects. The corrosion behavior was closely correlated to the tube noise measured using a rotating probe, while it was not related to the noise measured using a bobbin probe. It is suggested that the tube noise value measured using a rotating pancake coil probe can be a decisive measure to estimate the corrosion behavior of tubing
Energy Technology Data Exchange (ETDEWEB)
Hur, Do Haeng; Choi, Myung Sik; Lee, Deok Hyun; Shim, Hee-Sang [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)
2015-05-15
Nickel and its oxides are released from the surface of steam generator tubes into the primary water. Released nickel and cobalt is activated to Co-58 and Co-60 in the reactor core by a neutron flux, respectively. These activated corrosion products are the main source of high radiation fields and occupational radiation exposure. In addition, some of the corrosion products redeposit on the fuel cladding, hinder the heat transfer, increase the corrosion rate of the fuel cladding, and finally induce an axial offset anomaly. This phenomenon can decrease core shutdown margin, and thus lead to a down-rating of a plant. Recently, many researchers have reported that the surface states of Alloy 690 tubes affect the corrosion product formation and its release in simulated primary water environments. Meanwhile, the surface states of steam generator tubes affect the noise level of eddy current testing. Noise signals arising from the tubes degrade the probability of detection and sizing accuracy of the defects. The corrosion behavior was closely correlated to the tube noise measured using a rotating probe, while it was not related to the noise measured using a bobbin probe. It is suggested that the tube noise value measured using a rotating pancake coil probe can be a decisive measure to estimate the corrosion behavior of tubing.
Spin correlations due to Dyakonov-Perel and spin noise spectroscopy in semicoductor quantum wells
Energy Technology Data Exchange (ETDEWEB)
Hartenstein, Tobias; Krauss, Michael; Schneider, Hans Christian [Department of Physics and Research Center OPTIMAS, Kaiserslautern University of Technology (Germany)
2010-07-01
We present a theoretical investigation of dynamical electronic spin-spin correlations in quantum wells resulting from the Dyakonov-Perel mechanism due to electron-impurity interactions in the presence of external magnetic fields. We set up the coupled equations of motion for the different spin-spin correlation functions, and solve them numerically. Since spin-noise measurements are sensitive to the spin-spin correlation functions, our results provide a microcscopic basis for this measurement technique, but also allow us to study how the Dyakonov-Perel relaxation mechanism affects non-trivial electronic spin correlations and correlation waves that can be induced by the absorption of non-classical polarization-squeezed light.
Li, Changbiao; Jiang, Zihai; Wang, Xiuxiu; Ahmed, Irfan; Raza, Faizan; Yang, Yiheng; Zhang, Yanpeng
2016-05-01
We observed four-wave mixing (FWM) processes in a double-Λ level of rubidium atomic system with electromagnetically induced transparency window having different polarization. The Autler-Townes splitting of FWM induced by the polarized multi-dark-state is observed. And the two-stage line shape of correlation that exhibits a sharp peak and a broad peak is also studied. The sharp peak and the broad peak are from the correlation of two spontaneous parametric FWMs and that of the vertical component and horizontal component of two coherent FWMs. Moreover we demonstrate that the intensity noise correlation and intensity-difference squeezing can be well modulated by the relative initial phase and nonlinear phase shift. Meanwhile, we also found the following of correlation (anti-correlation) by intensity-difference squeezing (anti-squeezing). The associated results may be applicable in all-optical communication and optical information processing on photonic chips.
International Nuclear Information System (INIS)
This paper investigates the stochastic resonance (SR) induced by a multiplicative periodic signal in the gene transcriptional regulatory system with correlated noises. The expression of the signal-to-noise ratio (SNR) is derived. The results indicate that the existence of a maximum in SNR vs. the additive noise intensity α, the multiplicative noise intensity D and the cross-correlated noise intensity λ is the identifying characteristic of the SR phenomenon and there is a critical phenomenon in the SNR as a function of λ, i.e., for the case of smaller values of noise intensity (α or D), the SNR decreases as λ increases; however, for the case of larger values of noise intensity (α or D), the SNR increases as λ increases. (general)
Institute of Scientific and Technical Information of China (English)
CAOLi; WANGJun; WuDa-Jin; LIANGGui-Yun
2003-01-01
Applying the approximate Fokker-Planck equation we derived, we obtain the analytic expression of the stationary laser intensity distribution Pst(l) by studying the single-mode laser cubic model subject to colored cross-correlation additive and multiplicative noise, each of which is colored. Based on it, we discuss the effects on the stationary laser intensity distribution Pot(I) by cross-correlation between noises and "color" of noises (non-Markovian effect) when the laser system is above the threshold. In detail, we analyze two cases: One is that the three correlation-times (i.e.the self-correlation and cross-correlation times of the additive and multiplicative noise) are chosen to be the same value(Tl=T2=T3=T). For this case, the effect of noise cross-correlation is investigated emphatically, and we detect that only when λ≠ 0 can the noise-induced transition occur in the Pst (I) curve, and only when T≠ 0 and λ≠0, can the "reentrant noise-induced transition" occur. The other case is that the three correlation times are not the same value,T1≠T2≠T3. For this case, we find that the noise-induced transition occurring in the Pst(I) curve is entirely different when the values of T1,T2, and T3 are changed respectively. In particular, when T2 (serf-correlation time of additive noise) is cha~g~g, the ratio of the two maximums of the Pst( I) curve R exhibits an interesting phenomenon,"reentrant noise-induced transition", which demonstrates the effect of noise "color" (non-Markovian effect).
International Nuclear Information System (INIS)
Highlights: ► Exploration of directed transport in stochastic systems with embedded nonlinearity. ► Formalism is valid for open system in the presence of arbitrary periodic potential. ► Effective temperature depends on correlation time and extent of correlation. ► Study of the directed motion in presence of external cross-correlated noises. ► Steady state current increases with increase in the extent of correlation. - Abstract: Starting from a Langevin description of a particle submerged in a heat bath that offers a state dependent dissipation, we examine the noise-induced transport of a Brownian particle in the presence of two external, mutually correlated noises and envisage that in a symmetric periodic potential, the steady state current increases with an increase in the extent of correlation. The study of inhomogeneous diffusion in the presence of colored noise makes the present development formally interesting since this brings in a direct implication that exercising control on the degree of correlation can enhance the current in a properly designed experiment. As an offshoot of this development, we also envisage an effective temperature that depends on the correlation time and the extent of correlation.
Subtraction of correlated noise in global networks of gravitational-wave interferometers
Coughlin, Michael W; De Rosa, Rosario; Fiori, Irene; Gołkowski, Mark; Guidry, Melissa; Harms, Jan; Kubisz, Jerzy; Kulak, Andrzej; Mlynarczyk, Janusz; Paoletti, Federico; Thrane, Eric
2016-01-01
The recent discovery of merging black holes suggests that a stochastic gravitational-wave background is within reach of the advanced detector network operating at design sensitivity. However, correlated magnetic noise from Schumann resonances threatens to contaminate observation of a stochastic background. In this paper, we report on the first effort to eliminate intercontinental correlated noise from Schumann resonances using Wiener filtering. Using magnetometers as proxies for gravitational-wave detectors, we demonstrate as much as a factor of two reduction in the coherence between magnetometers on different continents. While much work remains to be done, our results constitute a proof-of-principle and motivate follow-up studies with a dedicated array of magnetometers.
Institute of Scientific and Technical Information of China (English)
Chen Li-Mei; Cao Li; Wu Da-Jin; Wang Zhong-Long
2005-01-01
In this paper, the intensity correlation time T is studied for the gain-noise model of a single-mode laser driven by coloured pump noise and coloured quantum noise with coloured cross-correlation with a direct signal modulation.By using the linear approximation method, it is found that when the pump noise is modulated directly by a signal,the effects of the cross-correlation between the pump noise and the quantum noise will disappear. In addition, there exists a maximum (i.e. resonance) in the curve of the intensity correlation time T versus the pump noise self-correlation time τ1. Furthermore, when τ1 ≤τ2, the intensity correlation time T increases monotonically with the increase of D and decreases monotonically with the increase of Q, but when τ1 ＞τ2, the intensity correlation time T increases monotonically with the increase of Q and decreases monotonically with the increase of D.
Complex Dynamics of Credit Risk Contagion with Time-Delay and Correlated Noises
2014-01-01
The stochastic time-delayed system of credit risk contagion driven by correlated Gaussian white noises is investigated. Novikov’s theorem, the time-delay approximation, the path-integral approach, and first-order perturbation theory are used to derive time-delayed Fokker-Planck model and the stationary probability distribution function of the dynamical system of credit risk contagion in the financial market. Using the method of numerical simulation, the Hopf bifurcation and chaotic behaviors ...
High-Resolution Algorithm for Image Segmentation in the Presence of Correlated Noise
Jiang, Haiping; Bourennane, Salah; Fossati, Caroline
2010-01-01
Multiple line characterization is a most common issue in image processing. A specific formalism turns the contour detection issue of image processing into a source localization issue of array processing. However, the existing methods do not address correlated noise. As a result, the detection performance is degraded. In this paper, we propose to improve the subspace-based high-resolution methods by computing the fourth-order slice cumulant matrix of the received signals instead of second-orde...
The effects of correlated noise in intra-complex DSN arrays for S-band Galileo telemetry reception
Dewey, R. J.
1992-01-01
A number of the proposals for supporting a Galileo S-band (2.3-GHz) mission involve arraying several antennas to maximize the signal-to-noise ratio (and bit rate) obtainable from a given set of antennas. Arraying is no longer a new idea, having been used successfully during the Voyager encounters with Uranus and Neptune. However, arraying for Galileo's tour of Jupiter is complicated by Jupiter's strong radio emission, which produces correlated noise effects. This article discusses the general problem of correlated noise due to a planet, or other radio source, and applies the results to the specific case of an array of antennas at the DSN's Tidbinbilla, Australia, complex (DSS 42, DSS 43, DSS 45, and the yet-to-be-built DSS 34). The effects of correlated noise are highly dependent on the specific geometry of the array and on the spacecraft-planet configuration; in some cases, correlated noise effects produce an enhancement, rather than a degradation, of the signal-to-noise ratio. For the case considered here--an array of the DSN's Australian antennas observing Galileo and Jupiter--there are three regimes of interest. If the spacecraft-planet separation is approximately less than 75 arcsec, the average effect of correlated noise is a loss of signal to noise (approximately 0.2 dB as the spacecraft-planet separation approaches zero). For spacecraft-planet separations approximately greater than 75 arcsec, but approximately less than 400 arcsec, the effects of correlated noise cause signal-to-noise variations as large as several tenths of a decibel over time scales of hours or changes in spacecraft-planet separation of tens of arcseconds; however, on average its effects are small (less than 0.01 dB). When the spacecraft is more than 400 arcsec from Jupiter (as is the case for about half of Galileo's tour), correlated noise is a less than 0.05-dB effect.
Spintronics of antiferromagnetic systems
International Nuclear Information System (INIS)
Spintronics of antiferromagnetics is a new field that has developed in a fascinating research topic in physics of magnetism. Antiferromagnetics, like ferromagnetic materials experience the influence of spin-polarized current, even though they show no macroscopic magnetization. The mechanism of this phenomenon is related to spin-dependent interaction between free and localized electrons-sd-exchange. Due to the peculiarities of antiferromagnetic materials (complicated magnetic structure, essential role of the exchange interactions, lack of macroscopic magnetization) spintronics of antiferromagnets appeals to new theoretical and experimental approaches. The purpose of this review is to systemize and summarize the recent progress in this field. We start with a short introduction into the structure and dynamics of antiferromagnets and proceed with discussion of different microscopic and phenomenological theories for description of current-induced phenomena in ferro-/antiferromagnetic heterostructures. We also consider the problems of the reverse influence of antiferromagnetic ordering on current, and effectiveness of the fully antiferromagnetic spin valve. In addition, we shortly review and interpret the available experimental results.
Alexander, David B.; Narayanan, Ram M.; Himed, Braham
2016-05-01
The performance of different random array geometries is analyzed and compared. Three phased array geometries are considered: linear arrays with non-uniform randomized spacing between elements, circular arrays with non-uniform element radii, and ad hoc sensor networks with elements located randomly within a circular area. For each of these array geometries, computer simulations modeled the transmission, reflection from an arbitrary target, and reception of signals. The effectiveness of each array's beamforming techniques was measured by taking the peak cross-correlation between the received signal and a time-delayed replica of the original transmitted signal. For each array type, the correlation performance was obtained for transmission and reception of both chirp waveforms and ultra-wideband noise signals. It was found that the non-uniform linear array generally produced the highest correlation between transmitted and reflected signals. The non-uniform circular and ad hoc arrays demonstrated the most consistent performance with respect to noise signal bandwidth. The effect of scan angle was found to have a significant impact on the correlation performance of the linear arrays, where the correlation performance declines as the scan angle moves away from broadside to the array.
Experimental analysis of image noise and interpolation bias in digital image correlation
Gao, Zeren; Xu, Xiaohai; Su, Yong; Zhang, Qingchuan
2016-06-01
The popularization of the digital image correlation (DIC) method has raised urgent needs to evaluate the accuracy of this method. However, there are still some problems to be solved. Among the problems, the effects of various factors, such as the image noise caused by the camera sensors, the employed interpolation algorithm, and the structure of the speckle patterns, have become a major concern. To experimentally measure the position-dependent systematic error (i.e. interpolation bias) caused by non-ideal interpolation algorithm is an important way to evaluate the quality of the speckle patterns in the correlation method, and remains unsolved. In this work, a novel, simple and convenient method is proposed to measure the interpolation bias. In the new method which can avoid the out-of-plane displacements and the mechanical errors of translation stages, integral-pixel shifts are applied to the image shown on the screen so that sub-pixel displacements can be realized in the images captured by the camera via proper experimental settings. Besides, the fluctuations of the image noise and the sub-pixel displacement errors caused by the image noise are experimentally analyzed by employing three types of cameras commonly used in the DIC measurements. Experimental results indicate that the fluctuations of the image noise are not only proportional to the image gray value, but also dependent on the type of the employed camera. On the basis of eliminating the image noise via the image averaging technique, high-precision interpolation bias curves more than one period are experimentally obtained by the proposed method.
The bulk of the stock market correlation matrix is not pure noise
Kwapien, J; Drozdz, S
2006-01-01
We analyse the structure of the distribution of eigenvalues of the stock market correlation matrix with increasing length of the time series representing the price changes. We use 100 highly-capitalized stocks from the American market and relate result to the corresponding ensemble of Wishart random matrices. It turns out that systematically more eigenvalues stay beyond the borders prescribed by this variant of the Random Matrix Theory (RMT). This may indicate that even the bulk of the spectrum of the stock market correlation matrix carries some sort of correlations that are masked by a measurement noise when the time series used to construct the matrix are short. We also study some other characteristics of the "noisy" eigensignals, like their return distributions, temporal correlations or their multifractal spectra and the results support the above conclusions.
Reddy, V R; Reddy, T G; Reddy, P Y; Reddy, K R
2003-01-01
An AC modulation technique is described to convert stochastic signal variations into an amplitude variation and its retrieval through Fourier analysis. It is shown that this AC detection of signals of stochastic processes when processed through auto- and cross-correlation techniques improve the signal-to-noise ratio; the correlation techniques serve a similar purpose of frequency and phase filtering as that of phase-sensitive detection. A few model calculations applied to nuclear spectroscopy measurements such as Angular Correlations, Mossbauer spectroscopy and Pulse Height Analysis reveal considerable improvement in the sensitivity of signal detection. Experimental implementation of the technique is presented in terms of amplitude variations of harmonics representing the derivatives of normal spectra. Improved detection sensitivity to spectral variations is shown to be significant. These correlation techniques are general and can be made applicable to all the fields of particle counting where measurements ar...
McKee, K. F.; Waite, G. P.; Richardson, J. P.
2012-12-01
We used the Green's functions from auto-correlations and cross-correlations of seismic ambient noise to monitor temporal velocity changes in the subsurface at Villarrica Volcano in the Southern Andes of Chile. Campaigns were conducted from March to October 2010 and February to April 2011 with 8 broadband and 6 short-period stations, respectively. We prepared the data by removing the instrument response, normalizing with a root-mean-square method, whitening the spectra, and filtering from 1 to 10 Hz. This frequency band was chosen based on the relatively high background noise level in that range. Hour-long auto- and cross-correlations were computed and the Green's functions stacked by day and total time. To track the temporal velocity changes we stretched a 24 hour moving window of correlation functions from 90% to 110% of the original and cross correlated them with the total stack. The average increase in velocity gleaned from the auto-correlations during the 2010 array was 0.13%, as seen in the figure. Cross-correlations from station V01, near the summit, to the other stations show comparable increases in velocity. We attribute this change to the closing of cracks in the subsurface due either to seasonal snow loading or regional tectonics. In addition to the common increase in velocity across the stations, there are excursions in velocity on the same order lasting several days. Amplitude decreases as the station's distance from the vent increases suggesting these excursions may be attributed to changes within the volcanic edifice. Two occurrences are highlighted in the figure in which it is seen that the amplitudes at stations V06 and V07, the stations farthest from the vent, are smaller. Similar short temporal excursions were seen in the auto-correlations from 2011, however, there was little to no increase in the overall velocity.ercent change in velocity at Villarrica Volcano, Chile from March to October 2010 (stations offset by 0.2%)
Vazirani, P.
1995-01-01
The process of combining telemetry signals received at multiple antennas, commonly referred to as arraying, can be used to improve communication link performance in the Deep Space Network (DSN). By coherently adding telemetry from multiple receiving sites, arraying produces an enhancement in signal-to-noise ratio (SNR) over that achievable with any single antenna in the array. A number of different techniques for arraying have been proposed and their performances analyzed in past literature. These analyses have compared different arraying schemes under the assumption that the signals contain additive white Gaussian noise (AWGN) and that the noise observed at distinct antennas is independent. In situations where an unwanted background body is visible to multiple antennas in the array, however, the assumption of independent noises is no longer applicable. A planet with significant radiation emissions in the frequency band of interest can be one such source of correlated noise. For example, during much of Galileo's tour of Jupiter, the planet will contribute significantly to the total system noise at various ground stations. This article analyzes the effects of correlated noise on two arraying schemes currently being considered for DSN applications: full-spectrum combining (FSC) and complex-symbol combining (CSC). A framework is presented for characterizing the correlated noise based on physical parameters, and the impact of the noise correlation on the array performance is assessed for each scheme.
International Nuclear Information System (INIS)
We investigate the effects of the noise parameters and immunization strength β on the dynamical properties of a tumor growth system with both immunization and colored cross-correlated noises. The analytical expressions for the associated relaxation time TC and the normalized correlation function C(s) are derived by means of the projection operator method. The results indicate that: (i) TC as a function of the multiplicative noise intensity α shows resonance-like behavior, i.e. the curves of TC versus α exhibit a single-peak structure and its peak position changes with increasing correlation strength between noises λ, the autocorrelation time of multiplicative noise τ1, the autocorrelation time of additive noise τ2 and the cross-correlation time τ3. This behavior can be understood in terms of the noise-enhanced stability effect and the influence of the memory effects on it. (ii) The increasing λ, τ1, τ2 and the additive noise intensity D slow down the fluctuation decay of the tumor population, whereas the increasing τ3 and β speed it up. (iii) C(s) increases as λ, τ1, τ2 and β increase, while it decreases with τ3 increasing. Our study shows that the effects of some noise parameters on tumor growth can be modified due to the presence of the immunization effect.
Liu, Xin; Ben-Zion, Yehuda; Zigone, Dimitri
2015-11-01
We develop and apply an algorithm for deriving interstation seismic attenuation from cross-correlations of ambient noise recorded by linear arrays. Theoretical results on amplitude decay due to attenuation are used to form a linear least-square inversion for interstation QR values of Rayleigh surface waves propagating along linear arrays having three or more stations. The noise wave field is assumed stationary within each day and the interstation distances should be greater than the employed wavelength. The inversion uses differences of logarithmic amplitude decay curves measured at different stations from cross-correlation functions within a given frequency band. The background attenuation between noise sources and receivers is effectively cancelled with this method. The site amplification factors are assumed constant (or following similar patterns) in the frequency band of interest. The inversion scheme is validated with synthetic tests using ambient noise generated by ray-theory-based calculations with heterogeneous attenuation and homogenous velocity structure. The interstation attenuation and phase velocity dispersion curves are inverted from cross-correlations of the synthetic data. The method is then applied to triplets of stations from the regional southern California seismic network crossing the Mojave section of the San Andreas fault, and a dense linear array crossing the southern San Jacinto Fault zone. Bootstrap technique is used to derive empirical mean and confidence interval for the obtained inverse Q values. The results for the regional stations yield QR values around 25 for a frequency band 0.2-0.36 Hz. The results for the San Jacinto fault zone array give QR values of about 6-30 for frequencies in the range 15-25 Hz.
Guo, Xueshi; Li, Xiaoying; Liu, Nannan; Ou, Z. Y.
2016-01-01
One of the important functions in a communication network is the distribution of information. It is not a problem to accomplish this in a classical system since classical information can be copied at will. However, challenges arise in quantum system because extra quantum noise is often added when the information content of a quantum state is distributed to various users. Here, we experimentally demonstrate a quantum information tap by using a fiber optical parametric amplifier (FOPA) with correlated inputs, whose noise is reduced by the destructive quantum interference through quantum entanglement between the signal and the idler input fields. By measuring the noise figure of the FOPA and comparing with a regular FOPA, we observe an improvement of 0.7 ± 0.1 dB and 0.84 ± 0.09 dB from the signal and idler outputs, respectively. When the low noise FOPA functions as an information splitter, the device has a total information transfer coefficient of Ts+Ti = 1.5 ± 0.2, which is greater than the classical limit of 1. Moreover, this fiber based device works at the 1550 nm telecom band, so it is compatible with the current fiber-optical network for quantum information distribution. PMID:27458089
Institute of Scientific and Technical Information of China (English)
ZHANG Li; CAO Li; WU Da-Jin
2003-01-01
Applying the method of the unified colored noise approximation and phase lock, we study in this paper the stationary intensity distribution of the single-mode laser driven by colored pump noise with cross-correlation between the real and imaginary parts of the quantum noise. We present a thorough discussion of how the cross-correlation λq between the realand imaginary parts of the quantum noise and the self-correlation time τ of the pump noise determine the behaviors of the stationary distribution Qst(I), the mean (I), and the variance λ2(0) of the laser intensity. It is shown that cross-correlation intensity λq of the complex quantum noise can induce a first-order-like transition. When the pump noise is colored noise (τ≠ 0), improving the pump parameters monotonously will make the curves of Qst(I)exhibit reentrant phase transition. The fluctuations of laser intensity are strongly influenced by λq and τ when the laser is operated near or below threshold. Especially when τ≠ 0, the heights of the peaks of the curves of λ2(0)-a0 and λ3(0)-a0, (here a0 is the net gain coefficient) go up as λq increases. However the entire curves of λ2(0)-a0 and λ3(0)-a0are abruptly suppressed when λq = 1, in similarity to phase transition of stationary intensity distribution.
Institute of Scientific and Technical Information of China (English)
ZHANGLi; CAOLi; WUDa-Jin
2003-01-01
Applying the method of the unified colored noise approximation and phase lock, we study in this paper the stationary intensity distribution of the single-mode laser driven by colored pump noise with cross-correlation between the real and imaginary parts of the quantum noise. We present a thorough discussion of how the cross-correlation λq between the real and imaginary parts of the quantum noise and the self-correlation time τ of the pump noise determine the behaviors of the stationary distribution Qst(I), the mean (I）, and the variance λ2(0) of the laser intensity. It is shown that cross-correlation intensity λq of the complex quantum noise can induce a first-order-like transition. When the pump noise is colored noise (τ≠0), improving the pump parameters monotonously will make the curves of Qst(I) exhibit reentrant phase transition. The fluctuations of laser intensity are strongly influenced by λq and τ when the laser is operated near or below threshold. Especially when τ≠0, the heights of the peaks of the curves of λ2(0)-α0 and α3(0)-α0, (here a0 is the net gain coefficient) go up as λq increases. However the entire curves λ2(0)-α0 and λ3(0)-α0 are abruptly suppressed when λq = 1, in similarity to phase transition of stationary intensity distribution.
Effects of Time Delay on Stability of an Unstable State in a Bistable System with Correlated Noises
International Nuclear Information System (INIS)
Effects of time delay on stability of an unstable state in a time-delayed bistable system are investigated. The analytic expression of the transition rate W(xu, τ) from unstable state xu to stable state x+ is derived. The numerical calculation results of W(xu, τ) indicate that W(xu, τ) decreases with the increasing multiplicative noise intensity, the additive noise intensity and the strength of correlations between the multiplicative and the additive noise increase, but W(xu, τ) increases with increasing delay time. Namely, the multiplicative noise, the additive noise and the correlations between the multiplicative and the additive noises enhance the stability of the unstable state in the time-delayed bistable system but the stability is weakened by time delay. (general)
Method of Removing the Cross-correlation Noise for Dual-input and Dual-output SAR
Directory of Open Access Journals (Sweden)
Huang Ping-ping
2012-03-01
Full Text Available According to analysis of separating the mixed echo by suppressing the cross-correlation noise in dual-input and dual-output SAR system, a new method based on threshold filter and inverse filter was proposed. The method can eliminate the most energy of cross-correlation noise by threshold filter, which can suppress the cross-correlation noise well. The principle and implementation steps are presented in detail. The computer simulation and account for the integrated sidelobe ratio showed the effectiveness of the proposed method.
International Nuclear Information System (INIS)
A single-mode laser noise model driven by quadratic pump noise and quantum noise with cross-correlation between the real and imaginary parts of the noises is proposed. The approximate Fokker-Planck equation (AFPE) of the model for the laser phase and the laser amplitude is derived. It is found that the laser phase is controlled intensively by the correlation between the real and imaginary parts of the pump noise and that of the quantum noise. The correlation between the real and imaginary parts of quantum noise λq tends to lead the laser phase to be locked at some values and the correlation between the real and imaginary parts of the pump noise λp tends to destroy or confine the laser phase lock. Quantitative results are presented and discussed in detail. As an important application of the above-mentioned results, we take a phase lock approximation to get a Langevin equation for the laser field amplitude and an AFPE of the laser intensity
The correlation study of parallel feature extractor and noise reduction approaches
Energy Technology Data Exchange (ETDEWEB)
Dewi, Deshinta Arrova; Sundararajan, Elankovan; Prabuwono, Anton Satria [Industrial Computing Research Group, Centre for Artificial Intelligence Technology, Universiti Kebangsaan Malaysia, 43600 Bangi (Malaysia)
2015-05-15
This paper presents literature reviews that show variety of techniques to develop parallel feature extractor and finding its correlation with noise reduction approaches for low light intensity images. Low light intensity images are normally displayed as darker images and low contrast. Without proper handling techniques, those images regularly become evidences of misperception of objects and textures, the incapability to section them. The visual illusions regularly clues to disorientation, user fatigue, poor detection and classification performance of humans and computer algorithms. Noise reduction approaches (NR) therefore is an essential step for other image processing steps such as edge detection, image segmentation, image compression, etc. Parallel Feature Extractor (PFE) meant to capture visual contents of images involves partitioning images into segments, detecting image overlaps if any, and controlling distributed and redistributed segments to extract the features. Working on low light intensity images make the PFE face challenges and closely depend on the quality of its pre-processing steps. Some papers have suggested many well established NR as well as PFE strategies however only few resources have suggested or mentioned the correlation between them. This paper reviews best approaches of the NR and the PFE with detailed explanation on the suggested correlation. This finding may suggest relevant strategies of the PFE development. With the help of knowledge based reasoning, computational approaches and algorithms, we present the correlation study between the NR and the PFE that can be useful for the development and enhancement of other existing PFE.
The correlation study of parallel feature extractor and noise reduction approaches
International Nuclear Information System (INIS)
This paper presents literature reviews that show variety of techniques to develop parallel feature extractor and finding its correlation with noise reduction approaches for low light intensity images. Low light intensity images are normally displayed as darker images and low contrast. Without proper handling techniques, those images regularly become evidences of misperception of objects and textures, the incapability to section them. The visual illusions regularly clues to disorientation, user fatigue, poor detection and classification performance of humans and computer algorithms. Noise reduction approaches (NR) therefore is an essential step for other image processing steps such as edge detection, image segmentation, image compression, etc. Parallel Feature Extractor (PFE) meant to capture visual contents of images involves partitioning images into segments, detecting image overlaps if any, and controlling distributed and redistributed segments to extract the features. Working on low light intensity images make the PFE face challenges and closely depend on the quality of its pre-processing steps. Some papers have suggested many well established NR as well as PFE strategies however only few resources have suggested or mentioned the correlation between them. This paper reviews best approaches of the NR and the PFE with detailed explanation on the suggested correlation. This finding may suggest relevant strategies of the PFE development. With the help of knowledge based reasoning, computational approaches and algorithms, we present the correlation study between the NR and the PFE that can be useful for the development and enhancement of other existing PFE
V S Profiles from Noise Cross Correlation at Local and Small Scale
de Nisco, G.; Nunziata, C.
2011-03-01
Ambient noise measurements have been performed at local and small scales in the Neapolitan and surrounding areas (Campania, southern Italy) by employing two broad-band Kinemetrics Q330 stations, equipped with Episensor ES-T three component accelerometers. In both experiments frequency time analysis (FTAN method) has been performed on the vertical and radial components of noise cross correlations to retrieve the Rayleigh wave dispersion (Green's function). At local scale, over an interstation distance of about 26 km, the group velocity dispersion values have been compared with those obtained from FTAN analysis on recordings of two earthquakes with similar path. At small scale, measurements have been carried out over an interstation distance of about 440 m in the public gardens of Scampia, the northernmost quarter of Naples. The Rayleigh wave group velocity dispersion data obtained from noise cross correlation, have been combined with those from active seismic experiment along the same alignment, but shorter (120 m offset). The non linear inversion of such a dispersion curve has allowed the definition of V S models to depths of 100 m, in agreement with nearby stratigraphy. Moreover, a good agreement has resulted for the resonance frequency among the H/V ratio, the ellipticity of the fundamental mode computed for the chosen V S model, and the average two-dimensional (2D) spectral amplification computed along a cross section representative of the Scampia quarter.
Glattli, D. C.; Roulleau, P.
2016-02-01
We study the Hanbury Brown and Twiss correlation of electronic quasi-particles injected in a quantum conductor using current noise correlations and we experimentally address the effect of finite temperature. By controlling the relative time of injection of two streams of electrons it is possible to probe the fermionic antibunching, performing the electron analog of the optical Hong Ou Mandel (HOM) experiment. The electrons are injected using voltage pulses with either sine-wave or Lorentzian shape. In the latter case, we propose a set of orthogonal wavefunctions, describing periodic trains of multiply charged electron pulses, which give a simple interpretation to the HOM shot noise. The effect of temperature is then discussed and experimentally investigated. We observe a perfect electron anti-bunching for a large range of temperature, showing that, as recently predicted, thermal mixing of the states does not affect anti-bunching properties, a feature qualitatively different from dephasing. For single charge Lorentzian pulses, we provide experimental evidence of the prediction that the HOM shot noise variation versus the emission time delay is remarkably independent of the temperature.
Effects of Time Delay on Stability of an Unstable State in a Bistable System with Correlated Noises
Institute of Scientific and Technical Information of China (English)
LI Chun; MEI Dong-Cheng
2011-01-01
@@ Effects of time delay on stability of an unstable state in a time-delayed bistable system are investigated.The analytic expression of the transition rate W(xu,τ)from unstable state xu to stable state x+ is derived.The numerical calculation results of W(xu,τ)indicate that W(xu,τ)decreases with the increasing multiplicative noise intensity, the additive noise intensi by and the strength of correlations between the multiplicative and the additive noise increase, but W(xu,τ)increases with increasing delay time.Namely, the multiplicative noise, the additive noise and the correlations between the multiplicative and the additive noises enhance the stability of the unstable state in the time-delayed bistable system but the stability is weakened by time delay.%Effects of time delay on stability of an unstable state in a time-delayed bistable system are investigated. The analytic expression of the transition rate W(xu, T) from unstable state xu to stable state x+ is derived. The numerical calculation results of W(xu, T) indicate that W(xu, T) decreases with the increasing multiplicative noise intensity, the additive noise intensity and the strength of correlations between the multiplicative and the additive noise increase, but W(xu, T) increases with increasing delay time. Namely, the multiplicative noise, the additive noise and the correlations between the multiplicative and the additive noises enhance the stability of the unstable state in the time-delayed bistable system but the stability is weakened by time delay.
Nakata, Nori; Boué, Pierre; Brenguier, Florent; Roux, Philippe; Ferrazzini, Valérie; Campillo, Michel
2016-02-01
Body wave reconstruction from ambient seismic noise correlations is an important step toward improving volcano imaging and monitoring. Here we extract body and surface waves that propagate in Piton de la Fournaise volcano on La Réunion island using ambient noise cross correlation and array-processing techniques. Ambient noise was continuously recorded at three dense arrays, each comprising 49 geophones. To identify and enhance the Green's function from the ambient noise correlation, we apply a double beamforming (DBF) technique between the array pairs. The DBF allows us to separate surface and body waves, direct and reflected waves, and multipathing waves. Based on their azimuths and slownesses, we successfully extract body waves between all the combinations of arrays, including the wave that propagates through the active magmatic system of the volcano. Additionally, we identify the effects of uneven noise source distribution and interpret the surface wave reflections.
Institute of Scientific and Technical Information of China (English)
LIANG Gui-Yun; CAO Li; WANG Jun; Wu Da-Jin
2003-01-01
Applying the approximate Fokker-Planck equation we derived, we obtain the analytic expression of thestationary laser intensity distribution Pst(Ⅰ) by studying the single-mode laser cubic model subject to colored cross-correlation additive and multiplicative noise, each of which is colored. Based on it, we discuss the effects on the stationarylaser intensity distribution Pst(Ⅰ) by cross-correlation between noises and "color" of noises (non-Markovian effect) whenthe laser system is above the threshold. In detail, we analyze two cases: One is that the three correlation-times (i.e.the self-correlation and cross-correlation times of the additive and multiplicative noise) are chosen to be the same value(τ1 = τ2 = τ3 = τ). For this case, the effect of noise cross-correlation is investigated emphatically, and we detect thatonly when λ≠ 0 can the noise-induced transition occur in the Pst(Ⅰ) curve, and only when τ≠ 0 and λ≠ 0, can the"reentrant noise-induced transition" occur. The other case is that the three correlation times are not the same value,τ1 ≠τ2 ≠τ3. For this case, we find that the noise-induced transition occurring in the Pst (Ⅰ) curve is entirely differentwhen the values of τ1, τ2, and τ3 are changed respectively. In particular, when τ2 (self-correlation time of additivenoise) is changing, the ratio of the two maximums of the Pst(Ⅰ) curve R exhibits an interesting phenomenon, "reentrantnoise-induced transition", which demonstrates the effect of noise "color" (non-Markovian effect).
Influence of the angular correlation of fission neutrons on noise signatures
International Nuclear Information System (INIS)
Noise signatures, the measurement of the correlation between the fluctuating parts of the signals coming from neutron detectors, are commonly used to measure nuclear parameters (reactivities, mean lives) and to monitor nuclear systems. Several techniques are used, such as the correlation of analog signals in time or frequency domains or the statistical analysis of detection events. Independently of the experimental method, the useful component of the stochastic descriptors is related to the detection of neutrons that have ancestors born in the same fission event. Despite an early work, opened to the inclusion of the n-n angular correlations of neutrons coming from the same fission, practically all the theoretical applications ignore this additional complication by making the implicit or explicit hypothesis that fission neutrons are born uncorrelated. However, there are direct measurements that show angular and energy correlation for the two-fission-neutron distribution. The first attempt to include this experimental evidence into the theory of neutron noise was the calculation of the ratio of spectral densities related to the 252Cf method of measuring reactivities under the simplest condition: two neutron detectors monitoring a 252Cf plated fission chamber. The objective of this communication is to show how noise signatures of more complex systems are sensitive to the joint distribution of two neutrons coming from the same fission with velocities rvec v and rvec v'. To avoid mathematical complications, we are going to assume (1) that the system is monitored by two different detectors, Labels 2 and 3, distributed according to the fundamental kinetic mode, and (2) that the subcritical system contains only one fissile specie. The driver of the neutron flux is a 252Cf fission source. 5 refs
Zang, Xiaoqin; Brown, Michael G; Godin, Oleg A
2015-09-01
Theoretical studies have shown that cross-correlation functions (CFs) of time series of ambient noise measured at two locations yield approximations to the Green's functions (GFs) that describe propagation between those locations. Specifically, CFs are estimates of weighted GFs. In this paper, it is demonstrated that measured CFs in the 20-70 Hz band can be accurately modeled as weighted GFs using ambient noise data collected in the Florida Straits at ∼100 m depth with horizontal separations of 5 and 10 km. Two weighting functions are employed. These account for (1) the dipole radiation pattern produced by a near-surface source, and (2) coherence loss of surface-reflecting energy in time-averaged CFs resulting from tidal fluctuations. After describing the relationship between CFs and GFs, the inverse problem is considered and is shown to result in an environmental model for which agreement between computed and simulated CFs is good. PMID:26428771
Determination of local boiling in light water reactors by correlation of the neutron noise
International Nuclear Information System (INIS)
The power limit of swimming-pool type reactors depends on the phenomenon of the appearance of burn-out. In order to determine this limit we have attempted to detect the local boiling which usually occurs before the burn out. Local boiling has been simulated by an electrically heated plate placed in the core of the reactor Siloette. The study of local boiling, which is based on the properties of the correlation functions for the neutron noise of detectors placed in the core, shows that a privileged frequency occurs in the power spectrum of the noise. It is intended in the future to determine the influence of various parameters on this characteristic frequency. (author)
Sub-shot-noise photon-number correlation in a mesoscopic twin beam of light
International Nuclear Information System (INIS)
We demonstrate sub-shot-noise photon-number correlations in a (temporal) multimode mesoscopic (∼103 detected photons) twin beam produced by picosecond-pulsed spontaneous nondegenerate parametric down-conversion. We have separately detected the signal and idler distributions of photons collected in twin coherence areas and found that the variance of the photon-count difference goes below the shot-noise limit by 3.25 dB. The number of temporal modes contained in the twin beam, as well as the size of the twin coherence areas, depends on the pump intensity. Our scheme is based on spontaneous down-conversion and thus does not suffer from limitations due to the finite gain of the parametric process. Twin beams are also used to demonstrate the conditional preparation of a nonclassical (sub-Poissonian) state
Stochastic noise reduction upon complexification: positively correlated birth-death type systems.
Rooman, Marianne; Albert, Jaroslav; Duerinckx, Mitia
2014-08-01
Cell systems consist of a huge number of various molecules that display specific patterns of interactions, which have a determining influence on the cell׳s functioning. In general, such complexity is seen to increase with the complexity of the organism, with a concomitant increase of the accuracy and specificity of the cellular processes. The question thus arises how the complexification of systems - modeled here by simple interacting birth-death type processes - can lead to a reduction of the noise - described by the variance of the number of molecules. To gain understanding of this issue, we investigated the difference between a single system containing molecules that are produced and degraded, and the same system - with the same average number of molecules - connected to a buffer. We modeled these systems using Itō stochastic differential equations in discrete time, as they allow straightforward analytical developments. In general, when the molecules in the system and the buffer are positively correlated, the variance on the number of molecules in the system is found to decrease compared to the equivalent system without a buffer. Only buffers that are too noisy themselves tend to increase the noise in the main system. We tested this result on two model cases, in which the system and the buffer contain proteins in their active and inactive state, or protein monomers and homodimers. We found that in the second test case, where the interconversion terms are non-linear in the number of molecules, the noise reduction is much more pronounced; it reaches up to 20% reduction of the Fano factor with the parameter values tested in numerical simulations on an unperturbed birth-death model. We extended our analysis to two arbitrary interconnected systems, and found that the sum of the noise levels in the two systems generally decreases upon interconnection if the molecules they contain are positively correlated. PMID:24632443
Spinon dynamics in quantum integrable antiferromagnets
Vlijm, R.; Caux, J.-S.
2016-05-01
The excitations of the Heisenberg antiferromagnetic spin chain in zero field are known as spinons. As pairwise-created fractionalized excitations, spinons are important in the understanding of inelastic neutron scattering experiments in (quasi-)one-dimensional materials. In the present paper, we consider the real space-time dynamics of spinons originating from a local spin flip on the antiferromagnetic ground state of the (an)isotropic Heisenberg spin-1/2 model and the Babujan-Takhtajan spin-1 model. By utilizing algebraic Bethe ansatz methods at finite system size to compute the expectation value of the local magnetization and spin-spin correlations, spinons are visualized as propagating domain walls in the antiferromagnetic spin ordering with anisotropy dependent behavior. The spin-spin correlation after the spin flip displays a light cone, satisfying the Lieb-Robinson bound for the propagation of correlations at the spinon velocity.
Antiferromagnets at Low Temperatures
International Nuclear Information System (INIS)
The low-temperature properties of the Heisenberg antiferromagnet in 2+1 space-time dimensions are analyzed within the framework of effective Lagrangians. It is shown that the magnon-magnon interaction is very weak and repulsive, manifesting itself through a term proportional to five powers of the temperature in the pressure. The structure of the low-temperature series for antiferromagnets in 2+1 dimensions is compared with the structure of the analogous series for antiferromagnets in 3+1 dimensions. The model-independent and systematic effective field theory approach clearly proves to be superior to conventional condensed matter methods such as spin-wave theory.
Background noise levels and correlation with ship traffic in the Gulf of Catania
Viola, Salvatore; Buscaino, Giuseppa; Caruso, Francesco; Chierici, Francesco; Embriaco, Davide; Favali, Paolo; Giovanetti, Gabriele; Grammauta, Roasario; Larosa, Giuseppina; Pavan, Gianni; Pellegrino, Carmelo; Pulvirenti, Sara; Riccobene, Giorgio; Sciacca, Virginia; Simeone, Francesco; Beranzoli, Laura; Marinaro, Giuditta
2015-04-01
In the last decades the growing interest in the evaluation of the underwater acoustic noise for studies in the fields of geology, biology and high-energy physics is driving the scientific community to collaborate towards a multidisciplinary approach to the topic. In June 2012 in the framework of the European project EMSO, a multidisciplinary underwater observatory, named NEMO-SN1, was installed 25 km off-shore the port of Catania, at a depth of 2100 m and operated until May 2013 by INFN (Istituto Nazionale di Fisica Nucleare) and INGV (Istituto Nazionale di Geofisica e Vulcanologia). NEMO-SN1 hosted aboard geophysical, oceanographic and acoustic sensors: among these a seismic hydrophone model SMID DT-405D(V). In this work, conducted within the activity of the SMO project, the results on the evaluation of the underwater acoustic pollution in the Gulf of Catania through SMID DT-405D(V) recordings are presented. The seismic hydrophone provided a data set of about 11 months of continuous (24/7) recordings. Underwater sounds have been continuously digitized at a sampling frequency of 2 kHz and the acquired data have been stored in 10min long files for off-line analysis. To describe one-year background noise levels, the mean integrated acoustic noise was measured every second (sampling frequency 2000, NFFT 2048) in the 1/3 octave bands with centre frequency 63 Hz and for each 10 minutes-long file the 5th, the 50th and the 98th percentiles were calculated. Measured noise was correlated with the shipping traffic in the area, thanks to the data provided by an AIS receiver installed at the INFN-Laboratori Nazionali del Sud. An acoustic noise increment was measured in coincidence with the passing of crafts in the area and it was possible to identify the characteristic spectrum of each ship. A simple model for the estimation of the acoustic noise induced by the ships passing through the area was developed. The model was applied by using AIS data acquired during the operation
Crustal tomography of the Aegean-Anatolian domain using noise cross-correlations
Hubans, Fabien; Paul, Anne; Campillo, Michel; Karabulut, Hayrullah; Hatzidimitriou, Panagiotis
2010-05-01
Data of more than 150 temporary and permanent broadband seismological stations deployed in the Aegean-Anatolian domain between May 2007 and May 2009 are grouped in the SIMBAAD (Seismic Imaging of the Mantle Across the Anatolian Domain) dataset. We compute noise cross-correlations between all station pairs on a 1.5-yr duration. We obtain more than 11.000 correlations for each component of the cross-correlation tensor. We apply a MFA (Multiple Filter Analysis) method to measure group velocity dispersion curves of Rayleigh waves on 4 components of the correlation tensor (ZZ, ZR, RZ, RR) and of Love waves on the TT component, both in positive and negative times. According to the theory, a noise cross-correlation converges to the Green function if noise sources are randomly distributed around the station pair. If this condition is fulfilled, the cross-correlation should be symmetrical in time. We compare group velocity measurements between positive and negative times to evaluate the convergence of each cross-correlation to the Green function. The quality of the symmetry is used to weight the time measurements in the inversion for group velocity maps. In the last step, Rayleigh wave group velocity data are inverted for a 3-D model of S-wave velocity. This processing gives an image of the crustal structure in the area [37-41°N ; 23-33°E] with a horizontal resolution of 60 to 200 km depending on depth and station coverage. The shallowest layers clearly display the present-day thick sedimentary basins (Axios, Thrace, Marmara, Bay of Antalya, ...) and older sedimentary nappes (Lycian nappes, Miocene sediments in the Kirsehir block) as strong low velocity anomalies. At larger depth, Southwestern Anatolia is characterized by a broad low velocity anomaly which contrasts with the higher velocities of the Aegean Sea. We clearly image a West to East increase of Moho depth from 20-25 km in the Aegean Sea to 35 km in the Anatolian plateau. This increase located between 27°E and
A geometric Model for the Spatial Correlation of an Acoustic Vector Field in Surface-generated Noise
Institute of Scientific and Technical Information of China (English)
Yiwang Huang; Qunyan Ren; Ting Li
2012-01-01
Spatial correlation of sound pressure and particle velocity of the surface noise in horizontally stratified media was demonstrated,with directional noise sources uniformly distributed on the ocean surface.In the evaluation of particle velocity,plane wave approximation was applied to each incident ray.Due to the equivalence of the sound source correlation property and its directivity,solutions for the spatial correlation of the field were transformed into the integration of the coherent function generated by a single directional source.As a typical horizontally stratified media,surface noise in a perfect waveguide was investigated.Correlation coefficients given by normal mode and geometric models show satisfactory agreement.Also,the normalized covariance between sound pressure and the vertical component of particle velocity is proportional to acoustic absorption coefficient,while that of the surface noise in semi-infinitely homogeneous space is zero.
Ueli, Meier; Brenguier, Florent; M. Shapiro, N.
2010-01-01
International audience We analyze 3 years of continuous seismic records from broadband stations of the Caltech Regional Seismic Network (CI) in vicinity of the Los Angeles basin. Using correlations of ambient seismic noise, relative velocity variations in the order of 0.1 % can be measured between all inter-station pairs. It is the first time that such an extensive study between 861 inter-station pairs over such a large area has been carried out. We perform these measurements using the 'st...
Real time noise and wavelength correlations in octave-spanning supercontinuum generation
Godin, T; Sylvestre, T; Larger, L; Kudlinski, A; Mussot, A; Salem, A Ben; Zghal, M; Genty, G; Dias, F; Dudley, J M
2013-01-01
We use dispersive Fourier transformation to measure shot-to-shot spectral instabilities in femtosecond supercontinuum generation. We study both the onset phase of supercontinuum generation with distinct dispersive wave generation, as well as a highly-unstable supercontinuum regime spanning an octave in bandwidth. Wavelength correlation maps allow interactions between separated spectral components to be identified, even when such interactions are not apparent in shot-to-shot or average measurements. Experimental results are interpreted using numerical simulations. Our results show the clear advantages of dispersive Fourier transformation for studying spectral noise during supercontinuum generation.
[Correlation of ear and extra-ear effects in workers exposed to industrial noise].
Chkannikov, A N
1993-01-01
A morbidity of 600 female twister operators was exposed to a long-standing (over 20 years) study and manifold statistic analysis, data of which are represented. The vascular disorders appeared to correlate with the occupational deafness formation. Cerebral resistance recording (CRR) and EEG in 120 workers with various deafness degrees demonstrated the different grades of impaired cerebral and peripheral blood flow. The manifold analysis and CRR produced basic data so as to classify the vasculogenic lesions caused by the exposure to noise and to evaluate the occupational disablement. PMID:8061961
International Nuclear Information System (INIS)
In continuation with our effort to model the short-period micro seismic noise at the seismic array at Gauribidanur (GBA), we have examined in detail time-correlation and spectral coherence of the noise field within the array space. This has implications of maximum possible improvement in signal-to-noise ratio (SNR) relevant to event detection. The basis of this study is about a hundred representative wide-band noise samples collected from GBA throughout the year 1992. Both time-structured correlation as well as coherence of the noise waveforms are found to be practically independent of the inter element distances within the array, and they exhibit strong temporal and spectral stability. It turns out that the noise is largely incoherent at frequencies ranging upwards from 2 Hz; the coherency coefficient tends to increase in the lower frequency range attaining a maximum of 0.6 close to 0.5 Hz. While the maximum absolute cross-correlation also diminishes with increasing frequency, the zero-lag cross-correlation is found to be insensitive to frequency filtering regardless of the pass band. An extremely small value of -0.01 of the zero-lag correlation and a comparatively higher year-round average estimate at 0.15 of the maximum absolute time-lagged correlation yields an SNR improvement varying between a probable high of 4.1 and a low of 2.3 for the full 20-element array. 19 refs., 6 figs
Fault zone reverberations from cross-correlations of earthquake waveforms and seismic noise
Hillers, Gregor; Campillo, Michel
2016-03-01
Seismic wavefields interact with low-velocity fault damage zones. Waveforms of ballistic fault zone head waves, trapped waves, reflected waves and signatures of trapped noise can provide important information on structural and mechanical fault zone properties. Here we extend the class of observable fault zone waves and reconstruct in-fault reverberations or multiples in a strike-slip faulting environment. Manifestations of the reverberations are significant, consistent wave fronts in the coda of cross-correlation functions that are obtained from scattered earthquake waveforms and seismic noise recorded by a linear fault zone array. The physical reconstruction of Green's functions is evident from the high similarity between the signals obtained from the two different scattered wavefields. Modal partitioning of the reverberation wavefield can be tuned using different data normalization techniques. The results imply that fault zones create their own ambiance, and that the here reconstructed reverberations are a key seismic signature of wear zones. Using synthetic waveform modelling we show that reverberations can be used for the imaging of structural units by estimating the location, extend and magnitude of lateral velocity contrasts. The robust reconstruction of the reverberations from noise records suggests the possibility to resolve the response of the damage zone material to various external and internal loading mechanisms.
Institute of Scientific and Technical Information of China (English)
Liu Li; Zhang Liang-Ying; Cao Li
2009-01-01
The diffusion in a harmonic oscillator driven by coloured noises ζ(t) and η(t) with coloured cross-correlation in which one of the noises is modulated by a biased periodic signal is investigated. The exact expression of diffusion coefficient d as a function of noise parameter, signal parameter, and oscillator frequency is derived. The findings in this paper are as follows. 1) The curves of d versus noise intensity D and d versus noises cross-correlation time τ_3 exist as two different phases. The transition between the two phases arises from the change of the cross-correlation coefficient λ of the two Orustein-Uhlenbeck (O-U) noises. 2) Changing the value of τ3, the curves of d versus Q, the intensity of colored noise that is modulated by the signal, can transform from a phase having a minimum to a monotonic phase. 3)Changing the value of signal amplitude A, d versus Q curves can transform from a phase having a minimum to a monotonic phase. The above-mentioned results demonstrate that a like noise-induced transition appears in the model.
Farrell, J.; Lin, F. C.
2015-12-01
We present a new S-wave velocity model for the Yellowstone magmatic system derived from the inversion of Rayleigh- and Love-wave phase velocity measurements from periods from 6 to 35 s. All available data from 2007-2014 within and near the Yellowstone region was downloaded for the USArray TA network (TA), the Yellowstone Seismic Network (WY), the NOISY array (Z2), the USGS Intermountain West network (IW), the Plate Boundary Observatory Borehole Seismic Network (PB), and the USGS National Seismic Network (US). For each station, we perform daily noise pre-processing (temporal normalization and spectrum whitening) simultaneously for all three components before multi-component noise cross-correlations are calculated. Results for both Rayleigh- and Love-wave phase velocity inversions clearly show the low velocity anomaly associated with the upper-crustal magma reservoir seen previously using body wave tomography. In addition, low-velocity anomalies associated with sediment-filled basins are visible in Wyoming. Short period low Love-wave velocities are seen along the Snake River Plain, the track of the Yellowstone hotspot likely related to the shallow sediment layer. Based on the surface wave phase velocity maps, we invert for a 3D S-wave crustal model. The resulting model will be compared to previous, but spatially limited, body wave S-wave models as well as recent body wave P-wave velocity models to better constrain Vp/Vs ratios as well as the melt fraction of the magma chamber. Preliminary results using amplitude information of noise cross-correlations to calculate Rayleigh-wave ellipticity, or Rayleigh-wave H/V (horizontal to vertical) amplitude ratios to better constrain the shallow velocity structure will also be discussed.
International Nuclear Information System (INIS)
The associated relaxation time Tc and the normalized correlation function C(s) for a tumor cell growth system subjected to color noises are investigated. Using the Novikov theorem and Fox approach, the steady probability distribution is obtained. Based on them, the expressions of Tc and C(s) are derived by means of projection operator method, in which the effects of the memory kernels of the correlation function are taken into account. Performing the numerical computations, it is found: (1) With the cross-correlation intensity |λ|, the additive noise intensity α and the multiplicative noise self-correlation time τ1 increasing, the tumor cell numbers can be restrained; And the cross-correlation time τ3, the multiplicative noise intensity D can induce the tumor cell numbers increasing; However, the additive noise self-correlation time τ2 cannot affect the tumor cell numbers; The relaxation time Tc is a stochastic resonant phenomenon, and the distribution curves exhibit a single-maximum structure with D increasing. (2) The cross-correlation strength λ weakens the related activity between two states of the tumor cell numbers at different time, and enhances the stability of the tumor cell growth system in the steady state; On the contrast, τ1 and τ3 enhance the related activity between two states at different time; However, τ2 has no effect on the related activity between two states at different time
Institute of Scientific and Technical Information of China (English)
梁贵云; 曹力; 张莉; 吴大进
2003-01-01
We study a system for a single-mode laser driven by additive and multiplicative coloured noises with a coloured cross-correlation. The analytical expression of the stationary intensity distribution (SID) for the laser is derived in the case of three different correlation times. The influences of each stochastic parameter on the SID are discussed, the the skewness, λ3(O) of the single-mode laser are investigated. We find that there are colourful phase transitions for the SID above a threshold, and re-entrant transitions induced by the "colour" of the additive noises. Further research of the not only increases with the additive noise correlation time τ2 and the cross-correlation time τs, but also the quality of the output of laser beams is optimized.
Optimization of Ambient Noise Cross-Correlation Imaging Across Large Dense Array
Sufri, O.; Xie, Y.; Lin, F. C.; Song, W.
2015-12-01
Ambient Noise Tomography is currently one of the most studied topics of seismology. It gives possibility of studying physical properties of rocks from the depths of subsurface to the upper mantle depths using recorded noise sources. A network of new seismic sensors, which are capable of recording continuous seismic noise and doing the processing at the same time on-site, could help to assess possible risk of volcanic activity on a volcano and help to understand the changes in physical properties of a fault before and after an earthquake occurs. This new seismic sensor technology could also be used in oil and gas industry to figure out depletion rate of a reservoir and help to improve velocity models for obtaining better seismic reflection cross-sections. Our recent NSF funded project is bringing seismologists, signal processors, and computer scientists together to develop a new ambient noise seismic imaging system which could record continuous seismic noise and process it on-site and send Green's functions and/or tomography images to the network. Such an imaging system requires optimum amount of sensors, sensor communication, and processing of the recorded data. In order to solve these problems, we first started working on the problem of optimum amount of sensors and the communication between these sensors by using small aperture dense network called Sweetwater Array, deployed by Nodal Seismic in 2014. We downloaded ~17 day of continuous data from 2268 one-component stations between March 30-April 16 2015 from IRIS DMC and performed cross-correlation to determine the lag times between station pairs. The lag times were then entered in matrix form. Our goal is to selecting random lag time values in the matrix and assuming all other elements of the matrix either missing or unknown and performing matrix completion technique to find out how close the results from matrix completion technique would be close to the real calculated values. This would give us better idea
Institute of Scientific and Technical Information of China (English)
Li Yue-Hong; Mei Dong-Cheng
2008-01-01
This paper studies the effects of cross-correlations between the real and imaginary parts of quantum noise on the laser intensity in a saturation laser model.It derives the analytic expressions of the intensity correlation function C(Υ)and the associated relaxation time T(C) in the case of a stable locked phase resulting from the cross-correlation λq between the real and imaginary parts of quantum noise.Based on numerical computations it finds that the presence of cross correlations between the real and imaginary parts of quantum noise slow down the decay of intensity fluctuation,i.e.,it causes the increase of intensity fluctuation.
Effects of Time Delay on the Bistable System Subjected to Correlated Noises
Institute of Scientific and Technical Information of China (English)
NIE Lin-Ru; Mei Dong-Cheng
2007-01-01
The time-delayed bistable system subjected to the multiplicative and additive noises is investigated. In the condition of small delay time, the stationary probability distribution function (SPDF) is derived, and under the condition of large delay time, the SPDF is stochastically simulated. The analytical and simulative results indicate that: (i) For the case of λ= 0λ denotes the strength of correlations between the multiplicative and additive noises), the time delay affects weakly the SPDF peak structure, and the symmetrical property of the SPDF two-peak structure does not change with the increasing delay time, (ii) For the case of λ≠0, the two-peak structure changes with the increasing delay time, i.e. one peak goes up and the other go down simultaneously as the delay time increases and along with further increase of the delay time, the lower peak disappears gradually while the higher one goes up, i.e. the structure of the SPDF changes from a bimodal to a unimodal and the system becomes monostable.
Sastrawan, J.; Jones, C.; Akhalwaya, I.; Uys, H.; Biercuk, M. J.
2016-08-01
We introduce concepts from optimal estimation to the stabilization of precision frequency standards limited by noisy local oscillators. We develop a theoretical framework casting various measures for frequency standard variance in terms of frequency-domain transfer functions, capturing the effects of feedback stabilization via a time series of Ramsey measurements. Using this framework, we introduce an optimized hybrid predictive feedforward measurement protocol that employs results from multiple past measurements and transfer-function-based calculations of measurement covariance to improve the accuracy of corrections within the feedback loop. In the presence of common non-Markovian noise processes these measurements will be correlated in a calculable manner, providing a means to capture the stochastic evolution of the local oscillator frequency during the measurement cycle. We present analytic calculations and numerical simulations of oscillator performance under competing feedback schemes and demonstrate benefits in both correction accuracy and long-term oscillator stability using hybrid feedforward. Simulations verify that in the presence of uncompensated dead time and noise with significant spectral weight near the inverse cycle time predictive feedforward outperforms traditional feedback, providing a path towards developing a class of stabilization software routines for frequency standards limited by noisy local oscillators.
Noise-Driven Phenotypic Heterogeneity with Finite Correlation Time in Clonal Populations.
Directory of Open Access Journals (Sweden)
UnJin Lee
Full Text Available There has been increasing awareness in the wider biological community of the role of clonal phenotypic heterogeneity in playing key roles in phenomena such as cellular bet-hedging and decision making, as in the case of the phage-λ lysis/lysogeny and B. Subtilis competence/vegetative pathways. Here, we report on the effect of stochasticity in growth rate, cellular memory/intermittency, and its relation to phenotypic heterogeneity. We first present a linear stochastic differential model with finite auto-correlation time, where a randomly fluctuating growth rate with a negative average is shown to result in exponential growth for sufficiently large fluctuations in growth rate. We then present a non-linear stochastic self-regulation model where the loss of coherent self-regulation and an increase in noise can induce a shift from bounded to unbounded growth. An important consequence of these models is that while the average change in phenotype may not differ for various parameter sets, the variance of the resulting distributions may considerably change. This demonstrates the necessity of understanding the influence of variance and heterogeneity within seemingly identical clonal populations, while providing a mechanism for varying functional consequences of such heterogeneity. Our results highlight the importance of a paradigm shift from a deterministic to a probabilistic view of clonality in understanding selection as an optimization problem on noise-driven processes, resulting in a wide range of biological implications, from robustness to environmental stress to the development of drug resistance.
Correlated low-frequency electric and magnetic noise along the auroral field lines
Gurnett, D. A.; Huff, R. L.; Menietti, J. D.; Burch, J. L.; Winningham, J. D.; Shawhan, S. D.
1984-01-01
Dynamics Explorer 1 measurements of intense low-frequency electric and magnetic noise observed at low altitudes over the auroral zone are described. The intensity of both the electric and magnetic fields decreases rapidly with increasing frequency. Most of the energy is at frequencies below the O(+) cyclotron frequency, and some evidence is found for a cutoff or change in spectral slope near that frequency. The magnetic to electric field ratio decreases rapidly with increasing radial distance and also decreases with increasing frequency. The polarization of the electric field in a plane perpendicular to the earth's magnetic field is essentially random. The transverse electric and magnetic fields are closely correlated, with the average Poynting flux directed toward the earth. The total electromagnetic power flow associated with the noise is substantial. Two general models are discussed to interpret these observations, one based on static electric and magnetic fields imbedded in the ionosphere and the other based on Alfven waves propagating along the auroral field lines.
Kloss, Thomas; Canet, Léonie; Delamotte, Bertrand; Wschebor, Nicolás
2014-02-01
We investigate the scaling regimes of the Kardar-Parisi-Zhang (KPZ) equation in the presence of spatially correlated noise with power-law decay D(p) ∼ p(-2ρ) in Fourier space, using a nonperturbative renormalization group approach. We determine the full phase diagram of the system as a function of ρ and the dimension d. In addition to the weak-coupling part of the diagram, which agrees with the results from Europhys. Lett. 47, 14 (1999) and Eur. Phys. J. B 9, 491 (1999), we find the two fixed points describing the short-range- (SR) and long-range- (LR) dominated strong-coupling phases. In contrast with a suggestion in the references cited above, we show that, for all values of ρ, there exists a unique strong-coupling SR fixed point that can be continuously followed as a function of d. We show in particular that the existence and the behavior of the LR fixed point do not provide any hint for 4 being the upper critical dimension of the KPZ equation with SR noise. PMID:25353423
Noise and Correlations in a Spatial Population Model with Cyclic Competition
Reichenbach, Tobias; Frey, Erwin
2007-01-01
Noise and spatial degrees of freedom characterize most ecosystems. Some aspects of their influence on the coevolution of populations with cyclic interspecies competition have been demonstrated in recent experiments [e.g. B. Kerr et al., Nature {\\bf 418}, 171 (2002)]. To reach a better theoretical understanding of these phenomena, we consider a paradigmatic spatial model where three species exhibit cyclic dominance. Using an individual-based description, as well as stochastic partial differential and deterministic reaction-diffusion equations, we account for stochastic fluctuations and spatial diffusion at different levels, and show how fascinating patterns of entangled spirals emerge. We rationalize our analysis by computing the spatio-temporal correlation functions and provide analytical expressions for the front velocity and the wavelength of the propagating spiral waves.
Directory of Open Access Journals (Sweden)
Chao Tan
2014-01-01
Full Text Available In order to solve the problem of industrial sensor signal denoising, an integrated denoising method for sensor mixed noises based on wavelet packet transform and energy-correlation analysis is proposed. The architecture of proposed method is designed and the key technologies, such as wavelet packet transformation, energy-correlation analysis, and processing method of wavelet packet coefficients based on energy-correlation analysis, are presented. Finally, a simulation example for a specific signal and an application of shearer cutting current signal, which mainly contain white Gaussian noise and impact noise, are carried out, and the simulation and application results show that the proposed method is effective and is outperforming others.
Shu, Huisheng; Zhang, Sijing; Shen, Bo; Liu, Yurong
2016-07-01
This paper is concerned with the problem of simultaneous input and state estimation for a class of linear discrete-time systems with missing measurements and correlated noises. The missing measurements occur in a random way and are governed by a series of mutually independent random variables obeying a certain Bernoulli distribution. The process and measurement noises under consideration are correlated at the same time instant. Our attention is focused on the design of recursive estimators for both input and state such that, for all missing measurements and correlated noises, the estimators are unbiased and the estimation error covariances are minimized. This objective is achieved using direct algebraic operation and the design algorithm for the desired estimators is given. Finally, an illustrative example is presented to demonstrate the effectiveness of the proposed design scheme.
Liu, Yu
2015-09-01
The spectral characteristics of combustion noise are dictated by the temporal correlation of the overall change of heat release rate fluctuations which has not received sufficient attention in prior studies. In this work, the two-time correlation of the volumetric heat release rate fluctuations within the flame brush and its role in modeling combustion noise spectrum are investigated by analyzing direct numerical simulation (DNS) data of turbulent premixed V-flames. This two-time correlation can be well represented by Gaussian-type functions and it captures the slow global variation of the fluctuating heat release rate and hence the low-frequency noise sources of unsteady combustion. The resulting correlation model is applied to predict the far-field noise spectrum from test open flames, and different reference time scales are used to scale this correlation from the DNS data to the test flames. The comparison between predictions and measurements indicates that the correlation models of all reference time scales are capable of reproducing the essential spectral shape including the low- and high-frequency dependencies. Reasonable agreement in the peak frequency, peak sound pressure level, and the Strouhal number scaling of peak frequency is also achieved for two turbulent time scales. A promising convective time scale shows great potential for characterizing the spectral features, yet its predictive capabilities are to be further verified through a longer DNS signal of a bounded flame configuration.
Tunable non-local entanglement of electrons probed by noise cross-correlation measurement
Wei, Jian
2010-03-01
Nonlocal entanglement is crucial for quantum information processes. While nonlocal entanglement has been realized for photons, it is much more difficult to demonstrate for electrons. One approach that has been proposed is to use hybrid superconducting/normal-metal devices. When the distance between two normal-metal electrodes connected to a superconductor is comparable to the superconducting coherence length, theory predicts that two electrons in the normal-metal electrodes with opposite spin are entangled by Cooper pairs, leading to non-local entanglement of electrons. Such entanglement can be understood by a non-local process called crossed Andreev reflection (CAR), in which a Cooper pair splits into two coherent electrons with one in each normal-metal electrode, generating instantaneous current of the same sign, and inducing a positive current correlation. Experimentally, CAR is indicated by a negative non-local resistance. However, another non-local process, elastic cotunneling (EC), in which one electron tunnels through the superconductor from one normal-metal electrode to the other, contributes to a positive non-local resistance that cancels the contribution due to CAR, preventing us from measuring and control of the CAR component. Fortunately, EC leads to a negative current correlation with bias dependence different from that of CAR. Thus, noise correlation measurement is expected to be able to distinguish these two non-local processes. By cross-correlation measurements as well as measurements of the local and nonlocal resistance, we present here experimental evidence showing that by independently controlling the energy of electrons at the superconductor/normal-metal interfaces, nonlocal Andreev reflection, the signature of spin-entanglement, can be maximized, qualitatively in agreement with theoretical predication.
Oren, C.; Nowack, R. L.
2015-12-01
It is known that the positive lags of the auto-correlation for the seismic transmission response of a layered medium correspond to the reflection seismogram (Claerbout, 1968). In this study, we investigate the use of ambient seismic noise recorded at selected broadband USArray EarthScope Transportable Array (TA) stations to obtain effective reflection seismograms for frequencies up to 1 Hz. The goal is to determine the most suitable parameters used for the processing of ambient seismic noise for the identification of crustal and upper mantle reflections and to minimize unwanted artifacts in the noise correlations. In order to best retrieve the body-wave components of the Green's function beneath a station, a number of processing steps are required. We first remove the instrument response and apply a temporal normalization to remove the effects of the most energetic sources. Next we implement spectral whitening. We test several operators for the spectral whitening where the undulations of the power spectrum are related to the strengths of later arrivals in the auto-correlation. Different filters are then applied to the auto-correlation functions, including Gaussian and zero phase Butterworth filters, in order to reduce the effect of side lobes. Hourly auto-correlations are then stacked for up to one year. On the final stack, Automatic Gain Control (AGC) is applied to equalize the correlation amplitudes in the time domain. The robustness of the resulting ambient noise auto-correlation is first tested on selected TA stations in Nevada, where we are able to identify PmP and SmS arrivals similar to those found by Tibuleac and von Seggern (2012). We then investigate noise auto-correlations applied to selected USArray TA stations in the central US.
Antiferromagnetic spin-orbitronics
Manchon, Aurelien
2015-05-01
Antiferromagnets have long remained an intriguing and exotic state of matter, whose application has been restricted to enabling interfacial exchange bias in metallic and tunneling spin-valves [1]. Their role in the expanding field of applied spintronics has been mostly passive and the in-depth investigation of their basic properties mostly considered from a fundamental perspective.
Nanoparticles of antiferromagnetic materials
DEFF Research Database (Denmark)
Madsen, Daniel Esmarch
2008-01-01
I denne Ph.D. afhandling studeres forskellige egenskaber ved antiferromagnetiske nanopartikler. I en ideel antiferromagnet er spinnene orienteret således at der ikke er et resulterende magnetisk moment. I nanopartikler af antiferromagnetiske materialer er denne kompensation på grund af forskellig...
Tsai, V.C.
2010-01-01
Recent derivations have shown that when noise in a physical system has its energy equipartitioned into the modes of the system, there is a convenient relationship between the cross correlation of time-series recorded at two points and the Green's function of the system. Here, we show that even when energy is not fully equipartitioned and modes are allowed to be degenerate, a similar (though less general) property holds for equations with wave equation structure. This property can be used to understand why certain seismic noise correlation measurements are successful despite known degeneracy and lack of equipartition on the Earth. No claim to original US government works Journal compilation ?? 2010 RAS.
Optimal CMB map-making in presence of cross-correlated noise
de Gasperis, Giancarlo; Cabella, Paolo; de Bernardis, Paolo; Vittorio, Nicola
2016-01-01
We present an extension of the ROMA map-making algorithm for the generation of optimal CMB temperature and polarization maps. The new code takes into account a possible cross-correlated noise component among the detectors of a CMB experiment. A promising application is the forthcoming LSPE balloon experiment, devoted to the observation of CMB polarization at large angular scales. To check the reliability of the code, we tested the extended ROMA algorithm on real and simulated data of the BOOMERanG(2003) mission, in order to compare our conclusions with already established results. Hence, we performed a preliminary forecast of the LSPE/SWIPE instrument. We found that considering the cross-correlation among the detectors results in a more realistic estimate of the angular power spectra. In particular, the extended ROMA map-making algorithm provides a strong reduction of the spectra error bars. We expect that this improvement will be crucial in constraining the B component of CMB polarization at the largest scal...
International Nuclear Information System (INIS)
The stochastic resonance (SR) phenomenon induced by a multiplicative periodic signal in a bistable system with cross-correlated noises and time delay is studied. Two cases have been considered: the case of a system with no delay and the case of a system with time-delayed feedback. The expressions for the signal-to-noise ratio (SNR) are derived, for both cases. The effects of the cross-correlated noise intensity (λ) and the delay time (τ) on the SNR are discussed. It is found that the existence of a maximum in the SNR is the identifying characteristic of the SR phenomenon. In contrast with the case for the SR induced by an additive signal, here both λ and τ have critical values in SR when the SNR as a function of the noise intensities, i.e., λ (or τ), suppresses the SR for λ (or τ) below the critical value while it enhances the SR for λ (or τ) above the critical value. τ suppresses the SR in the SNR as a function of λ while it enhances the SR in the SNR as a function of the noise intensities. The SNR is not only dependent on λ, τ and the noise intensities, but also on the initial condition of the system
Ray, R. L.; Bhattarai, P.
2016-06-01
The error propagation and statistical-noise reduction method of Reid and Trainor for two-point correlation applications in high-energy collisions is extended to include particle-pair references constructed by mixing two particles from all event-pair combinations within event subsets of arbitrary size. The Reid-Trainor method is also applied to other particle-pair mixing algorithms commonly used in correlation analysis of particle production from high-energy nuclear collisions. The statistical-noise reduction, inherent in the Reid-Trainor event-mixing procedure, is shown to occur for these other event-mixing algorithms as well. Monte Carlo simulation results are presented which verify the predicted degree of noise reduction. In each case the final errors are determined by the bin-wise particle-pair number, rather than by the bin-wise single-particle count.
Ray, R L
2016-01-01
The error propagation and statistical-noise reduction method of Reid and Trainor for two-point correlation applications in high-energy collisions is extended to include particle-pair references constructed by mixing two particles from all event-pair combinations within event subsets of arbitrary size. The Reid-Trainor method is also applied to other particle-pair mixing algorithms commonly used in correlation analysis of particle production from high-energy nuclear collisions. The statistical-noise reduction, inherent in the Reid-Trainor event-mixing procedure, is shown to occur for these other event-mixing algorithms as well. Monte Carlo simulation results are presented which verify the predicted degree of noise reduction. In each case the final errors are determined by the bin-wise particle-pair number, rather than by the bin-wise single-particle count.
Correlation between dark current RTS noise and defects for AlGaInP multiple-quantum-well laser diode
International Nuclear Information System (INIS)
The correlation model between dark current RTS noise and defects for AlGaInP multiple-quantum-well laser diode is derived. Experimental results show that dark current RTS noise caused carrier number fluctuations at the interface of the heterojunction in the active region. According to this correlation model, the defect types are determined, and the defects' energy levels are quantitatively determined. The corner frequency of RTS noise power spectral density is analyzed. The experimental results are in good agreement with the theoretical. This result provided an effective method for estimating the deep-level traps in the active region of AlGaInP multiple quantum well laser diode. (semiconductor devices)
Panou, Areti; Paulssen, Hanneke; Hatzidimitriou, Panagiotis
2015-01-01
In this study we present phase velocity maps that were obtained from the cross-correlation analysis of ambient seismic noise recorded in the region of Greece.We used one year (2013) of ambient seismic data obtained from the vertical component of 64 broadband permanent seismological stations that are
Chen, Y.; Theuwissen, A.J.P.; Chae, Y.
2011-01-01
This paper presents a low noise CMOS image sensor (CIS) using 10/12 bit configurable column-parallel single slope ADCs (SS-ADCs) and digital correlated multiple sampling (CMS). The sensor used is a conventional 4T active pixel with a pinned-photodiode as photon detector. The test sensor was fabricat
Directory of Open Access Journals (Sweden)
Alaa Abousetta
2014-11-01
Full Text Available This study was conducted to determine the injurious effects of noise on the hippocampus, and to show whether Ginkgo biloba (Gb has any modulatory effect on hippocampal injury. Fifteen adult male albino rats were divided into three groups; control group, noise group and protected group. The noise group was exposed to 100 dB Sound pressure level (SPL white noise, six hours/day for four consecutive weeks. The protected group was exposed to the same noise level with the administration of Gb extract to the animals (50 mg/kg daily for 4 weeks. In the noise exposed group, both pyramidal cell layer and dentate gyrus (DG granular cell layer showed a decrease in thickness with loss and degeneration of many cells. The protected group showed preservation of many parameters as compared to the noise group i.e. increase in thickness of Cornu Ammonis area3 (CA3 & DG; increase in surface area of cells and increased vascularity. In conclusion, noise had detrimental effects on cells of Cornu Ammonis area1 (CA1, CA3 & DG of the hippocampus. In view of this finding, the clinical auditory hazardous effects in people exposed to harmful noise such as tinnitus, as well as memory disturbances and learning disabilities might have a new dimension. The administration of Gb protected the hippocampus against the injurious effect of noise. The probable mechanism and usefulness of Gb in reducing the previously mentioned effects are discussed.
Offshore Southern California lithospheric velocity structure from noise cross-correlation functions
Bowden, D. C.; Kohler, M. D.; Tsai, V. C.; Weeraratne, D. S.
2016-05-01
A new shear wave velocity model offshore Southern California is presented that images plate boundary deformation including both thickening and thinning of the crustal and mantle lithosphere at the westernmost edge of the North American continent. The Asthenospheric and Lithospheric Broadband Architecture from the California Offshore Region Experiment (ALBACORE) ocean bottom seismometer array, together with 65 stations of the onshore Southern California Seismic Network, is used to measure ambient noise correlation functions and Rayleigh wave dispersion curves which are inverted for 3-D shear wave velocities. The resulting velocity model defines the transition from continental lithosphere to oceanic, illuminating the complex history and deformation in the region. A transition to the present-day strike-slip regime between the Pacific and North American Plates resulted in broad deformation and capture of the now >200 km wide continental shelf. Our velocity model suggests the persistence of the uppermost mantle volcanic processes associated with East Pacific Rise spreading adjacent to the Patton Escarpment, which marks the former subduction of Farallon Plate underneath North America. The most prominent of these seismic structures is a low-velocity anomaly underlying the San Juan Seamount, suggesting ponding of magma at the base of the crust, resulting in thickening and ongoing adjustment of the lithosphere due to the localized loading. The velocity model also provides a robust framework for future earthquake location determinations and ground-shaking simulations for risk estimates.
Prospect for antiferromagnetic spintronics
Czech Academy of Sciences Publication Activity Database
Martí, Xavier; Fina, I.; Jungwirth, Tomáš
2015-01-01
Roč. 51, č. 4 (2015), s. 2900104. ISSN 0018-9464 R&D Projects: GA MŠk(CZ) LM2011026; GA ČR GB14-37427G Grant ostatní: ERC Advanced Grant 0MSPIN(XE) 268066 Institutional support: RVO:68378271 Keywords : spintronics * antiferromagnets Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.386, year: 2014
Antiferromagnetic crystalline topological insulators
LIU, CHAO-XING
2013-01-01
The gapless surface Dirac cone of time reversal invariant topological insulators is protected by time reversal symmetry due to the Kramers' theorem. Spin degree of freedom is usually required since Kramers' theorem only guarantees double degeneracy for spinful fermions, but not for spinless fermions. In this paper, we present an antiferromagnetic spinless model, which breaks time reversal symmetry. Similar to time reversal invariant topological insulators, this model possesses a topologically...
Directory of Open Access Journals (Sweden)
Ana Fernández-Somoano
2015-06-01
Full Text Available This study aimed to describe the degree of annoyance among pregnant women in a Spanish cohort and to examine associations with proximity to traffic, NO2 and benzene exposure. We included 2457 participants from the Spanish Childhood and Environment study. Individual exposures to outdoor NO2 and benzene were estimated, temporally adjusted for pregnancy. Interviews about sociodemographic variables, noise and air pollution were carried out. Levels of annoyance were assessed using a scale from 0 (none to 10 (strong and unbearable; a level of 8 to 10 was considered high. The reported prevalence of high annoyance levels from air pollution was 11.2% and 15.0% from noise; the two variables were moderately correlated (0.606. Significant correlations between NO2 and annoyance from air pollution (0.154 and that from noise (0.181 were observed. Annoyance owing to noise and air pollution had a low prevalence in our Spanish population compared with other European populations. Both factors were associated with proximity to traffic. In multivariate models, annoyance from air pollution was related to NO2, building age, and country of birth; annoyance from noise was only related to the first two. The health burden of these exposures can be increased by stress caused by the perception of pollution sources.
Fernández-Somoano, Ana; Llop, Sabrina; Aguilera, Inmaculada; Tamayo-Uria, Ibon; Martínez, María Dolores; Foraster, Maria; Ballester, Ferran; Tardón, Adonina
2015-06-01
This study aimed to describe the degree of annoyance among pregnant women in a Spanish cohort and to examine associations with proximity to traffic, NO2 and benzene exposure. We included 2457 participants from the Spanish Childhood and Environment study. Individual exposures to outdoor NO2 and benzene were estimated, temporally adjusted for pregnancy. Interviews about sociodemographic variables, noise and air pollution were carried out. Levels of annoyance were assessed using a scale from 0 (none) to 10 (strong and unbearable); a level of 8 to 10 was considered high. The reported prevalence of high annoyance levels from air pollution was 11.2% and 15.0% from noise; the two variables were moderately correlated (0.606). Significant correlations between NO2 and annoyance from air pollution (0.154) and that from noise (0.181) were observed. Annoyance owing to noise and air pollution had a low prevalence in our Spanish population compared with other European populations. Both factors were associated with proximity to traffic. In multivariate models, annoyance from air pollution was related to NO2, building age, and country of birth; annoyance from noise was only related to the first two. The health burden of these exposures can be increased by stress caused by the perception of pollution sources. PMID:26095869
Lai, Yi Ming
2013-07-09
We study ensembles of globally coupled, nonidentical phase oscillators subject to correlated noise, and we identify several important factors that cause noise and coupling to synchronize or desynchronize a system. By introducing noise in various ways, we find an estimate for the onset of synchrony of a system in terms of the coupling strength, noise strength, and width of the frequency distribution of its natural oscillations. We also demonstrate that noise alone can be sufficient to synchronize nonidentical oscillators. However, this synchrony depends on the first Fourier mode of a phase-sensitivity function, through which we introduce common noise into the system. We show that higher Fourier modes can cause desynchronization due to clustering effects, and that this can reinforce clustering caused by different forms of coupling. Finally, we discuss the effects of noise on an ensemble in which antiferromagnetic coupling causes oscillators to form two clusters in the absence of noise. © 2013 American Physical Society.
Feroz, F.; Hobson, M. P.
2014-02-01
GJ667C is the least massive component of a triple star system which lies at a distance of about 6.8 pc (22.1 light-year) from the Earth. GJ667C has received much attention recently due to the claims that it hosts up to seven planets including three super-Earths inside the habitable zone. We present a Bayesian technique for the analysis of radial velocity (RV) data sets in the presence of correlated noise component (`red noise'), with unknown parameters. We also introduce hyper-parameters in our model in order to deal statistically with under- or overestimated error bars on measured RVs as well as inconsistencies between different data sets. By applying this method to the RV data set of GJ667C, we show that this data set contains a significant correlated (red) noise component with correlation time-scale for HARPS data of the order of 9 d. Our analysis shows that the data only provide strong evidence for the presence of two planets: GJ667Cb and c with periods 7.19 and 28.13 d, respectively, with some hints towards the presence of a third signal with period 91 d. The planetary nature of this third signal is not clear and additional RV observations are required for its confirmation. Previous claims of the detection of additional planets in this system are due the erroneous assumption of white noise. Using the standard white noise assumption, our method leads to the detection of up to five signals in this system. We also find that with the red noise model, the measurement uncertainties from HARPS for this system are underestimated at the level of ˜50 per cent.
Institute of Scientific and Technical Information of China (English)
Jin Xing; Li Jun; Lin Shu; Zhou Zhengrong; Kang Lanchi; Ou Yiping
2008-01-01
This paper uses the 8 broad-band stations' microseism data recorded by the Seismic Monitoring Network of Fujian Province to calculate the vertical correlation coefficient between two stationsat intervals of 5 minutes. According to the time intervals technique we obtain the different coefficients and then add the correlative coefficients. Depending on this, we extract the group velocity of Rayleigh waves from the cross correlation of the ambient seismic noise between two seismic stations and figure out the group velocity' spatial distribution. The results show that the signal noise ratio (SNR) increases proportionally to the superposition times, but the results from different days are similar to one another. Synchronously, the arrival-time is also stable and there is no obvious change when coming across typhoons. It is found the velocity of the surface wave is 2.9～3. 1km/s in Fujian Province, which is close to the observationally attained value.
Makita, Shuichi; Kurokawa, Kazuhiro; Hong, Young-Joo; Miura, Masahiro; Yasuno, Yoshiaki
2016-01-01
This paper describes a complex correlation mapping algorithm for optical coherence angiography (cmOCA). The proposed algorithm avoids the signal-to-noise ratio dependence and exhibits low noise in vasculature imaging. The complex correlation coefficient of the signals, rather than that of the measured data are estimated, and two-step averaging is introduced. Algorithms of motion artifact removal based on non perfusing tissue detection using correlation are developed. The algorithms are implemented with Jones-matrix OCT. Simultaneous imaging of pigmented tissue and vasculature is also achieved using degree of polarization uniformity imaging with cmOCA. An application of cmOCA to in vivo posterior human eyes is presented to demonstrate that high-contrast images of patients’ eyes can be obtained. PMID:27446673
Barnoud, Anne; Coutant, Olivier; Bouligand, Claire; Massin, Frédérick; Stehly, Laurent
2015-04-01
We image the volcanic island of Basse-Terre, Guadeloupe, Lesser Antilles, using both earthquake travel times and noise correlations. (1) A new earthquake catalog was recently compiled for the Lesser Antilles by the CDSA/OVSG/IPGP (Massin et al., EGU General Assembly 2014) and allows us to perform classical travel time tomography to obtain smooth 3D body wave velocity models. The geometrical configuration of the volcanic arc controls the resolution of the model in our zone of interest. (2) Surface wave tomography using noise correlations was successfully applied to volcanoes (Brenguier et al., Geophys. Res. Lett. 2007). We use seismic noise recorded at 16 broad-band stations and 9 short-period stations from Basse-Terre over a period of six years (2007-2012). For each station pair, we extract a dispersion curve from the noise correlation to get surface wave velocity models. The inversion of the dispersion curves produces a 3D S-wave velocity model of the island. The spatial distribution of seismic stations accross the island is highly heterogeneous, leading to higher resolution near the dome of the Soufrière of Guadeloupe volcano. Resulting velocity models are compared with densities obtained by 3D inversion of gravimetric data (Barnoud et al., AGU Fall Meeting 2013). Further work should include simultaneous inversion of seismic and gravimetric datasets to overcome resolution limitations.
Panigrahi, Swapnesh; Fade, Julien; Alouini, Mehdi
2015-10-01
We show the use of a simplified snapshot polarimetric camera along with an adaptive image processing for optimal detection of a polarized light beacon through fog. The adaptive representation is derived using theoretical noise analysis of the data at hand and is shown to be optimal in the Maximum likelihood sense. We report that the contrast enhancing optimal representation that depends on the background noise correlation differs in general from standard representations like polarimetric difference image or polarization filtered image. Lastly, we discuss a detection strategy to reduce the false positive counts.
International Nuclear Information System (INIS)
The linear Langevin equation proposed by Edwards and Wilkinson [Proc. R. Soc. London A 381, 17 (1982)] is solved in closed form for noise of arbitrary space and time correlation. Furthermore, the temporal development of the full probability functional describing the height fluctuations is derived exactly, exhibiting an interesting evolution between two distinct Gaussian forms. We determine explicitly the dynamic scaling function for the interfacial width for any given initial condition, isolate the early-time behavior, and discover an invariance that was unsuspected in this problem of arbitrary spatiotemporal noise
Localization of Narrow-Band Sources in Unknown Spatially Correlated Noise
Directory of Open Access Journals (Sweden)
Bourennane Salah
2010-01-01
Full Text Available In subspace-based method for direction-of-arrival (DOA estimation of signal wavefronts, the additive noise term is often assumed to be spatially white or known to within a multiplicative scalar. When the noise is nonwhite but has a known covariance matrix, we can still handle the problem through prewhitening. However, the problem turns to be complex when the noise field is completely unknown. In this paper, we study the localization of the sources, when the noise covariance matrix is one unknown band matrix. An iterative denoising algorithm based on the noise subspace spanned by the eigenvectors associated with the smallest eigenvalues is developed. The performance of the proposed algorithm is evaluated by computer simulations. We also test the proposed algorithm with some experimental data recorded during an underwater acoustic experiment.
Triangular Ising antiferromagnets with quenched nonmagnetic impurities.
Tang, Huai-Lei; Zhu, Yi; Yang, Guo-Hong; Jiang, Ying
2010-05-01
In a random spin system, the cooperation of randomness and frustration will lead to a spin-glass phase. However, in geometrically frustrated spin systems, quenched nonmagnetic impurities lift frustration locally. This makes randomness and frustration in these systems as competitors rather than cooperators. By mapping the dilute triangular Ising antiferromagnetic system to elastic array of noncrossing strings, we find that the nonmagnetic impurities in the spin system play roles of pinning centers in the string system. Calculation shows that in the ground state of this system, the spin-glass correlation is power-law decayed, quite different from the standard behavior of spin glass in which spin-glass correlation between two spins at infinite distance tends to a finite value. This indicates that triangular Ising antiferromagnets with quenched nonmagnetic impurities cannot be a spin glass. Instead, in the ground states, they present properties of vortex glass. PMID:20866185
Xu, Zhen J; Song, Xiaodong
2009-08-25
Detecting temporal changes of the medium associated with major earthquakes has implications for understanding earthquake genesis. Here we report temporal changes of surface wave velocity over a large area associated with 3 major Sumatra earthquakes in 2004, 2005, and 2007. We use ambient noise correlation to retrieve empirical Green's function (EGF) of surface waves between stations. Because the process is completely repeatable, the technique is powerful in detecting possible temporal change of medium. We find that 1 excellent station pair (PSI in Indonesia and CHTO in Thailand) shows significant time shifts (up to 1.44 s) after the 2004 and 2005 events in the Rayleigh waves at 10-20 s but not in the Love waves, suggesting that the Rayleigh time shifts are not from clock error. The time shifts are frequency dependent with the largest shifts at the period band of 11-16 s. We also observe an unusual excursion approximately 1 month before the 2004 event. We obtain a total of 17 pairs for June, 2007 to June, 2008, which allow us to examine the temporal and spatial variation of the time shifts. We observed strong anomalies (up to 0.68 s) near the epicenter after the 2007 event, but not in the region further away from the source or before the event or 3 months after the event. The observations are interpreted as stress changes and subsequent relaxation in upper-mid crust in the immediate vicinity of the rupture and the broad area near the fault zone. PMID:19667205
Song, Shu-Chun; Sun, Ming-Jie; Wu, Ling-An
2016-05-01
Ghost imaging with thermal light is a topic in optical imaging that has aroused great interest in recent years. However, the imaging quality must be greatly improved before the technology can be transferred from the lab to engineering applications. By means of correspondence ghost imaging (CGI) with a pseudo-thermal light source and appropriate sorting of the intensity fluctuations of the signal and reference beams, we obtain the positive and negative Hanbury Brown and Twiss intensity correlation characteristics of the optical field. Then, for ghost imaging of a transmissive binary object, we find that by subtracting the negative from the positive fluctuation frames of the presorted reference detector signals, the signal-to-noise ratio can be effectively increased, with almost all the background noise eliminated. Our results show that, compared with the generic CGI technique, the signal-to-noise ratio can be increased by nearly 60%.
Shao, Xinxing; Dai, Xiangjun; He, Xiaoyuan
2015-08-01
The inverse compositional Gauss-Newton (IC-GN) algorithm is one of the most popular sub-pixel registration algorithms in digital image correlation (DIC). The IC-GN algorithm, compared with the traditional forward additive Newton-Raphson (FA-NR) algorithm, can achieve the same accuracy in less time. However, there are no clear results regarding the noise robustness of IC-GN algorithm and the computational efficiency is still in need of further improvements. In this paper, a theoretical model of the IC-GN algorithm was derived based on the sum of squared differences correlation criterion and linear interpolation. The model indicates that the IC-GN algorithm has better noise robustness than the FA-NR algorithm, and shows no noise-induced bias if the gray gradient operator is chosen properly. Both numerical simulations and experiments show good agreements with the theoretical predictions. Furthermore, a seed point-based parallel method is proposed to improve the calculation speed. Compared with the recently proposed path-independent method, our model is feasible and practical, and it can maximize the computing speed using an improved initial guess. Moreover, we compared the computational efficiency of our method with that of the reliability-guided method using a four-point bending experiment, and the results show that the computational efficiency is greatly improved. This proposed parallel IC-GN algorithm has good noise robustness and is expected to be a practical option for real-time DIC.
Matos, Catarina; Silveira, Graça; Custódio, Susana; Domingues, Ana; Dias, Nuno; Fonseca, João F. B.; Matias, Luís; Krueger, Frank; Carrilho, Fernando
2014-05-01
Noise cross-correlations are now widely used to extract Green functions between station pairs. But, do all the cross-correlations routinely computed produce successful Green Functions? What is the relationship between noise recorded in a couple of stations and the cross-correlation between them? During the last decade, we have been involved in the deployment of several temporary dense broadband (BB) networks within the scope of both national projects and international collaborations. From 2000 to 2002, a pool of 8 BB stations continuously operated in the Azores in the scope of the Memorandum of Understanding COSEA (COordinated Seismic Experiment in the Azores). Thanks to the Project WILAS (West Iberia Lithosphere and Astenosphere Structure, PTDC/CTE-GIX/097946/2008) we temporarily increased the number of BB deployed in mainland Portugal to more than 50 (permanent + temporary) during the period 2010 - 2012. In 2011/12 a temporary pool of 12 seismometers continuously recorded BB data in the Madeira archipelago, as part of the DOCTAR (Deep Ocean Test Array Experiment) project. Project CV-PLUME (Investigation on the geometry and deep signature of the Cape Verde mantle plume, PTDC/CTE-GIN/64330/2006) covered the archipelago of Cape Verde, North Atlantic, with 40 temporary BB stations in 2007/08. Project MOZART (Mozambique African Rift Tomography, PTDC/CTE-GIX/103249/2008), covered Mozambique, East Africa, with 30 temporary BB stations in the period 2011 - 2013. These networks, located in very distinct geographical and tectonic environments, offer an interesting opportunity to study seasonal and spatial variations of noise sources and their impact on Empirical Green functions computed from noise cross-correlation. Seismic noise recorded at different seismic stations is evaluated by computation of the probability density functions of power spectral density (PSD) of continuous data. To assess seasonal variations of ambient noise sources in frequency content, time-series of
Spectral-Ripple Resolution Correlates with Speech Reception in Noise in Cochlear Implant Users
Won, Jong Ho; Drennan, Ward R.; Rubinstein, Jay T.
2007-01-01
Speech perception ability in noise is one of the most practical measures of success with a cochlear implant; however, with experience, this ability can change dramatically over time, making it a less than ideal tool for comparing performance among different processing strategies. This study examined performance on a spectral discrimination task and compared it to speech perception in noise. An adaptive procedure was used to determine the spectral-ripple density that subjects could discriminat...
Antiferromagnetic spin Seebeck effect.
Energy Technology Data Exchange (ETDEWEB)
Wu, Stephen M.; Zhang, Wei; KC, Amit; Borisov, Pavel; Pearson, John E.; Jiang, J. Samuel; Lederman, David; Hoffmann, Axel; Bhattacharya, Anand
2016-03-03
We report on the observation of the spin Seebeck effect in antiferromagnetic MnF2. A device scale on-chip heater is deposited on a bilayer of MnF2 (110) (30nm)/Pt (4 nm) grown by molecular beam epitaxy on a MgF2(110) substrate. Using Pt as a spin detector layer, it is possible to measure the thermally generated spin current from MnF2 through the inverse spin Hall effect. The low temperature (2–80 K) and high magnetic field (up to 140 kOe) regime is explored. A clear spin-flop transition corresponding to the sudden rotation of antiferromagnetic spins out of the easy axis is observed in the spin Seebeck signal when large magnetic fields (>9T) are applied parallel to the easy axis of the MnF2 thin film. When the magnetic field is applied perpendicular to the easy axis, the spin-flop transition is absent, as expected.
Feroz, Farhan
2013-01-01
GJ667C is the least massive component of a triple star system which lies at a distance of about 6.8 pc (22.1 light-years) from Earth. GJ667C has received much attention recently due to the claims that it hosts up to seven planets including three super-Earths inside the habitable zone. We present a Bayesian technique for the analysis of radial velocity (RV) data-sets in the presence of correlated noise component ("red noise"), with unknown parameters. We also introduce hyper-parameters in our model in order to deal statistically with under or over-estimated error bars on measured RVs as well as inconsistencies between different data-sets. By applying this method to the RV data-set of GJ667C and show that this data-set contains a significant correlated (red) noise component with correlation timescale for HARPS data of order 9 days. Our analysis shows that the data only provides strong evidence for the presence of two planets: GJ667Cb and c with periods 7.19d and 28.13d respectively, with some hints towards the ...
Directory of Open Access Journals (Sweden)
Kaysser-Kranich Tamma
2004-09-01
Full Text Available Abstract Background Despite the widespread use of microarrays, much ambiguity regarding data analysis, interpretation and correlation of the different technologies exists. There is a considerable amount of interest in correlating results obtained between different microarray platforms. To date, only a few cross-platform evaluations have been published and unfortunately, no guidelines have been established on the best methods of making such correlations. To address this issue we conducted a thorough evaluation of two commercial microarray platforms to determine an appropriate methodology for making cross-platform correlations. Results In this study, expression measurements for 10,763 genes uniquely represented on Affymetrix U133A/B GeneChips® and Amersham CodeLink™ UniSet Human 20 K microarrays were compared. For each microarray platform, five technical replicates, derived from the same total RNA samples, were labeled, hybridized, and quantified according to each manufacturers' standard protocols. The correlation coefficient (r of differential expression ratios for the entire set of 10,763 overlapping genes was 0.62 between platforms. However, the correlation improved significantly (r = 0.79 when genes within noise were excluded. In addition to levels of inter-platform correlation, we evaluated precision, statistical-significance profiles, power, and noise levels for each microarray platform. Accuracy of differential expression was measured against real-time PCR for 25 genes and both platforms correlated well with r values of 0.92 and 0.79 for CodeLink and GeneChip, respectively. Conclusions As a result of this study, we recommend using only genes called 'present' in cross-platform correlations. However, as in this study, a large number of genes may be lost from the correlation due to differing levels of noise between platforms. This is an important consideration given the apparent difference in sensitivity of the two platforms. Data from
Electrical switching of an antiferromagnet
Wadley, P.; Howells, B.; Železný, J.; Andrews, C.; Hills, V.; Campion, R. P.; Novák, V.; Olejník, K.; Maccherozzi, F.; Dhesi, S. S.; Martin, S. Y.; Wagner, T.; Wunderlich, J.; Freimuth, F.; Mokrousov, Y.; Kuneš, J.; Chauhan, J. S.; Grzybowski, M. J.; Rushforth, A. W.; Edmonds, K. W.; Gallagher, B. L.; Jungwirth, T.
2016-02-01
Antiferromagnets are hard to control by external magnetic fields because of the alternating directions of magnetic moments on individual atoms and the resulting zero net magnetization. However, relativistic quantum mechanics allows for generating current-induced internal fields whose sign alternates with the periodicity of the antiferromagnetic lattice. Using these fields, which couple strongly to the antiferromagnetic order, we demonstrate room-temperature electrical switching between stable configurations in antiferromagnetic CuMnAs thin-film devices by applied current with magnitudes of order 106 ampere per square centimeter. Electrical writing is combined in our solid-state memory with electrical readout and the stored magnetic state is insensitive to and produces no external magnetic field perturbations, which illustrates the unique merits of antiferromagnets for spintronics.
Kamdem Djidjou, Thaddee; Li, Sergey; Rogachev, Andrey
2014-03-01
Carrier injection and transport mechanism in small-molecule phosphorescent organic light-emitting diodes (PhOLED) have been investigated using current noise spectroscopy. The PhOLED devices studied consist of multilayers having the structure ITO / NPB / NPB:Irphq / Balq / Bpen:CsCO3/ Al. We found that in high bias regime, the noise spectral density can be described by two terms, 1/ f1.3 and 1/f2.8. The first term disappears below 2.5 V, as does the luminance; this suggests that this term is related to bimolecular recombination in the devices. The second term is more pronounced al low frequencies and its magnitude is linearly proportional to the current in the device. This term, which exists in all bias range, is likely related to the presence of traps with a distributed time constant. For applied voltages greater than 2.4 V, the frequency-independent noise is dominated by the shot noise. The Fano factor is one in the range 2.4 - 2.5 V, and decreases to a constant value of 0.4 at higher biases. This indicates the presence of a barrier for carrier injection into the device. Our overall results confirm the utility of noise measurements for OLED characterization.
Institute of Scientific and Technical Information of China (English)
Xu Dai-Hai; Cheng Qing-Hua; Cao Li; Wu Da-Jin
2006-01-01
Using the linear approximation method, this paper studies the statistical property of a single-mode laser driven by both coloured pump noise with signal modulation and the quantum noise with cross-correlation between its real and imaginary parts, and calculates the steady-state mean normalized intensity fluctuation and intensity correlation time.It analyses the influences of the modulation signal, the net gain coefficient, the noise and its correlation form on the statistical fluctuation of the laser system respectively. It is found that the coloured pump noise modulated by the signal has a great suppressing action on the statistical fluctuation of the laser system; the pump noise self-correlation time and the specific frequency of modulation signal have the result that the statistical fluctuation tends to zero. Furthermore,the intensity of pump noise will augment the statistical fluctuation of the laser system, but the intensity of quantum noise and the coefficient of cross-correlation between its real and imaginary parts have less influence on the statistical fluctuation of the laser system. Therefore, from the conclusions of this paper the statistical property can be known and a theoretical basis for steady operation and output of the laser system can be provided.
A Measure of the Signal-to-Noise Ratio of Microarray Samples and Studies Using Gene Correlations
Venet, David; Detours, Vincent; Bersini, Hugues
2012-01-01
Background The quality of gene expression data can vary dramatically from platform to platform, study to study, and sample to sample. As reliable statistical analysis rests on reliable data, determining such quality is of the utmost importance. Quality measures to spot problematic samples exist, but they are platform-specific, and cannot be used to compare studies. Results As a proxy for quality, we propose a signal-to-noise ratio for microarray data, the “Signal-to-Noise Applied to Gene Expression Experiments”, or SNAGEE. SNAGEE is based on the consistency of gene-gene correlations. We applied SNAGEE to a compendium of 80 large datasets on 37 platforms, for a total of 24,380 samples, and assessed the signal-to-noise ratio of studies and samples. This allowed us to discover serious issues with three studies. We show that signal-to-noise ratios of both studies and samples are linked to the statistical significance of the biological results. Conclusions We showed that SNAGEE is an effective way to measure data quality for most types of gene expression studies, and that it often outperforms existing techniques. Furthermore, SNAGEE is platform-independent and does not require raw data files. The SNAGEE R package is available in BioConductor. PMID:23251415
International Nuclear Information System (INIS)
This paper investigates the stochastic resonance (SR) phenomenon induced by the multiplicative periodic signal in a cancer growth system with the cross-correlated noises and time delay. To describe the periodic change of the birth rate due to the periodic treatment, a multiplicative periodic signal is added to the system. Under the condition of small delay time, the analytical expression of the signal-to-noise ratio RSNR is derived in the adiabatic limit. By numerical calculation, the effects of the cross-correlation strength λ and the delay time τ on RSNR are respectively discussed. The existence of a peak in the curves of RSNR as a function of the noise intensities indicates the occurrence of the SR phenomenon. It is found that λ and τ play opposite role on the SR phenomenon, i.e., the SR is suppressed by increasing λ whereas it is enhanced with the increase of τ, which is different from the case where the periodic signal is additive. (general)
Glattli, D. C.; Roulleau, P.
2016-08-01
We study the Hanbury Brown and Twiss correlation of electronic quasi-particles injected in a quantum conductor using current noise correlations and we experimentally address the effect of finite temperature. By controlling the relative time of injection of two streams of electrons it is possible to probe the fermionic antibunching, performing the electron analog of the optical Hong Ou Mandel (HOM) experiment. The electrons are injected using voltage pulses with either sine-wave or Lorentzian shape. In the latter case, we propose a set of orthogonal wavefunctions, describing periodic trains of multiply charged electron pulses, which give a simple interpretation to the HOM shot noise. The effect of temperature is then discussed and experimentally investigated. We observe a perfect electron anti-bunching for a large range of temperature, showing that, as recently predicted, thermal mixing of the states does not affect anti-bunching properties, a feature qualitatively different from dephasing. For single charge Lorentzian pulses, we provide experimental evidence of the prediction that the HOM shot noise variation versus the emission time delay is remarkably independent of the temperature.
Novel algorithm on DOA estimation for correlated sources under complex symmetric Toeplitz noise
Institute of Scientific and Technical Information of China (English)
Wang Kai; Zhang Yongshun; Shi Dan
2008-01-01
To cope with the scenario where both uncorrelated sources and coherent sources coexist,a novel algorithm to direction of arrival (DOA) estimation for symmetric uniform linear array is presented.Under the condition of stationary colored noise field,the algorithm employs a spatial differencing method to eliminate the noise covariance matrix and uncorrelated sources,then a Toeplitz matrix is constructed for the remained coherent sources.After preprocessing,a propagator method (PM) is employed to find the DOAs without any eigendecomposition.The number of sources resolved by this approach can exceed the number of array elements at a lower computational complexity.Simulation results demonstrate the effectiveness and efficiency of the proposed method.
Image Subtraction Noise Reduction Using Point Spread Function Cross-correlation
Hartung, Steven
2013-01-01
Image subtraction in astronomy is a tool for transient object discovery and characterization, particularly useful in wide fields, and is well suited for moving or photometrically varying objects such as asteroids, extra-solar planets and supernovae. A convolution technique is used to match point spread functions (PSFs) between images of the same field taken at different times prior to pixel-by-pixel subtraction. Particularly suitable for large-scale images is a spatially-varying kernel, where the convolution is allowed to adapt to PSF changes as a function of position within the images. The most versatile basis for fitting the spatially-varying kernel is the Dirac delta function. However, the convolution kernel based on the delta function does not discriminate between pixel scale noise variations and the intended stellar point spread function signals. The situation can frequently lead to reduced signal to noise ratios for variable objects detectable in the resulting subtraction. This work presents a cross-cor...
RAYMOND, GARY M.; Bassingthwaighte, James B.
1999-01-01
Methods for estimating the fractal dimension, D, or the related Hurst coefficient, H, for a one-dimensional fractal series include Hurst’s method of rescaled range analysis, spectral analysis, dispersional analysis, and scaled windowed variance analysis (which is related to detrended fluctuation analysis). Dispersional analysis estimates H by using the variance of the grouped means of discrete fractional Gaussian noise series (DfGn). Scaled windowed variance analysis estimates H using the mea...
Panou, Areti; Paulssen, Hanneke; Hatzidimitriou, Panagiotis
2015-01-01
In this study we present phase velocity maps that were obtained from the cross-correlation analysis of ambient seismic noise recorded in the region of Greece.We used one year (2013) of ambient seismic data obtained from the vertical component of 64 broadband permanent seismological stations that are part of the Hellenic Unified Seismic Network. Inter-station istances between these stations ranged from 60 to 840 km and the number of station pairs was 2054. All signals were corrected for instru...
Chen, Y; Theuwissen, A.J.P.; Chae, Y
2011-01-01
This paper presents a low noise CMOS image sensor (CIS) using 10/12 bit configurable column-parallel single slope ADCs (SS-ADCs) and digital correlated multiple sampling (CMS). The sensor used is a conventional 4T active pixel with a pinned-photodiode as photon detector. The test sensor was fabricated in a 0.18 colonm CMOS image sensor process from TSMC. The ADC nonlinearity measurement result shows totally 0.58% nonlinearity. Using the proposed column-parallel SS-ADC with digital CMS techniq...
International Nuclear Information System (INIS)
The effects of time delay on the fluctuation properties of a bistable system are investigated by simulating its normalised correlation function C(s). Three cases including linear delay, cubic delay and global delay in the system are considered respectively. The simulation results indicate that the linear delay enhances the fluctuation of the system (reduces the stability of the system) while the cubic delay and global delay weaken it (enforce the stability of the system), and the effect of cubic delay is more pronounced than the linear delay and global delay. (general)
Tilley, Steven; Siewerdsen, Jeffrey H.; Zbijewski, Wojciech; Stayman, J. Webster
2016-03-01
Flat-panel cone-beam CT (FP-CBCT) is a promising imaging modality, partly due to its potential for high spatial resolution reconstructions in relatively compact scanners. Despite this potential, FP-CBCT can face difficulty resolving important fine scale structures (e.g, trabecular details in dedicated extremities scanners and microcalcifications in dedicated CBCT mammography). Model-based methods offer one opportunity to improve high-resolution performance without any hardware changes. Previous work, based on a linearized forward model, demonstrated improved performance when both system blur and spatial correlations characteristics of FP-CBCT systems are modeled. Unfortunately, the linearized model relies on a staged processing approach that complicates tuning parameter selection and can limit the finest achievable spatial resolution. In this work, we present an alternative scheme that leverages a full nonlinear forward model with both system blur and spatially correlated noise. A likelihood-based objective function is derived from this forward model and we derive an iterative optimization algorithm for its solution. The proposed approach is evaluated in simulation studies using a digital extremities phantom and resolution-noise trade-offs are quantitatively evaluated. The correlated nonlinear model outperformed both the uncorrelated nonlinear model and the staged linearized technique with up to a 86% reduction in variance at matched spatial resolution. Additionally, the nonlinear models could achieve finer spatial resolution (correlated: 0.10 mm, uncorrelated: 0.11 mm) than the linear correlated model (0.15 mm), and traditional FDK (0.40 mm). This suggests the proposed nonlinear approach may be an important tool in improving performance for high-resolution clinical applications.
Tilley, Steven; Siewerdsen, Jeffrey H.; Zbijewski, Wojciech; Stayman, J. Webster
2016-01-01
Flat-panel cone-beam CT (FP-CBCT) is a promising imaging modality, partly due to its potential for high spatial resolution reconstructions in relatively compact scanners. Despite this potential, FP-CBCT can face difficulty resolving important fine scale structures (e.g, trabecular details in dedicated extremities scanners and microcalcifications in dedicated CBCT mammography). Model-based methods offer one opportunity to improve high-resolution performance without any hardware changes. Previous work, based on a linearized forward model, demonstrated improved performance when both system blur and spatial correlations characteristics of FP-CBCT systems are modeled. Unfortunately, the linearized model relies on a staged processing approach that complicates tuning parameter selection and can limit the finest achievable spatial resolution. In this work, we present an alternative scheme that leverages a full nonlinear forward model with both system blur and spatially correlated noise. A likelihood-based objective function is derived from this forward model and we derive an iterative optimization algorithm for its solution. The proposed approach is evaluated in simulation studies using a digital extremities phantom and resolution-noise trade-offs are quantitatively evaluated. The correlated nonlinear model outperformed both the uncorrelated nonlinear model and the staged linearized technique with up to a 86% reduction in variance at matched spatial resolution. Additionally, the nonlinear models could achieve finer spatial resolution (correlated: 0.10 mm, uncorrelated: 0.11 mm) than the linear correlated model (0.15 mm), and traditional FDK (0.40 mm). This suggests the proposed nonlinear approach may be an important tool in improving performance for high-resolution clinical applications. PMID:27110051
State and parameter estimation of state-space model with entry-wise correlated uniform noise
Czech Academy of Sciences Publication Activity Database
Pavelková, Lenka; Kárný, Miroslav
2014-01-01
Roč. 28, č. 11 (2014), s. 1189-1205. ISSN 0890-6327 R&D Projects: GA TA ČR TA01030123; GA ČR GA13-13502S Institutional research plan: CEZ:AV0Z1075907 Keywords : state-space models * bounded noise * filtering problems * estimation algorithms * uncertain dynamic systems Subject RIV: BC - Control Systems Theory Impact factor: 1.346, year: 2014 http://library.utia.cas.cz/separaty/2014/AS/pavelkova-0422958.pdf
Adrián-Martínez, S; Bou-Cabo, M; Felis, I; Llorens, C; Martínez-Mora, J A; Saldaña, M
2015-01-01
The study and application of signal detection techniques based on cross-correlation method for acoustic transient signals in noisy and reverberant environments are presented. These techniques are shown to provide high signal to noise ratio, good signal discernment from very close echoes and accurate detection of signal arrival time. The proposed methodology has been tested on real data collected in environments and conditions where its benefits can be shown. This work focuses on the acoustic detection applied to tasks of positioning in underwater structures and calibration such those as ANTARES and KM3NeT deep-sea neutrino telescopes, as well as, in particle detection through acoustic events for the COUPP/PICO detectors. Moreover, a method for obtaining the real amplitude of the signal in time (voltage) by using cross correlation has been developed and tested and is described in this work.
Directory of Open Access Journals (Sweden)
Kim Pansoo
2009-01-01
Full Text Available Recent standards for wireless transmission require reliable synchronization for channels with low signal-to-noise ratio (SNR as well as with a large amount of frequency offset, which necessitates a robust correlator structure for the initial frame synchronization process. In this paper, a new correlation strategy especially targeted for low SNR regions is proposed and its performance is analyzed. By utilizing a modified energy correction term, the proposed method effectively reduces the variance of the decision variable to enhance the detection performance. Most importantly, the method is demonstrated to outperform all previously reported schemes by a significant margin, for SNRs below 5 dB regardless of the existence of the frequency offsets. A variation of the proposed method is also presented for further enhancement over the channels with small frequency errors. The particular application considered for the performance verification is the second generation digital video broadcasting system for satellites (DVB-S2.
Disambiguating the role of noise correlations when decoding neural populations together
Eyherabide, Hugo Gabriel
2016-01-01
Objective: Integrating information from populations of correlated neurons can become too complex even for the human brain. Ignoring correlations may simplify the process but also cause an information loss. This loss has been quantified using many methods, one of which has always been deemed exact due to its rigorous communication-theoretical foundations. However, we have recently shown that this method can overestimate the loss in real applications. Approach: To solve this problem, we disting...
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
We explore inelastic cotunneling through a strongly Coulomb-blockaded quantum dot attached to two ferromagnetic leads in the weak coupling limit using a generic quantum Langevin equation approach. We first develop a Bloch-type equation microscopically to describe the cotunneling-induced spin relaxation dynamics, and then develop explicit analytical expressions for the local magnetization, current, and its fluctuations. On this basis, we predict a novel zero-bias anomaly of the differential conductance in the absence of a magnetic field for the anti-parallel configuration,and asymmetric peak splitting in a magnetic field. Also, for the same system with large polarization, we find a negative zero-frequency differential shot noise in the low positive bias-voltage region. All these effects are ascribed to rapid spin-reversal due to underlying spin-flip cotunneling.
Arias, A; Shlyagin, M G; Miridonov, S V; Manuel, Rodolfo Martinez
2015-11-16
We propose and experimentally demonstrate a simple approach to realize a phase-sensitive correlation optical time-domain reflectometer (OTDR) suitable for detection and localization of dynamic perturbations along a single-mode optical fiber. It is based on the quantum phase fluctuations of a coherent light emitted by a telecom DFB diode laser. Truly random probe signals are generated by an interferometer with the optical path difference exceeding the coherence length of the laser light. Speckle-like OTDR traces were obtained by calculating cross-correlation functions between the probe light and the light intensity signals returned back from the sensing fiber. Perturbations are detected and localized by monitoring time variations of correlation amplitude along the fiber length. Results of proof-of-concept experimental testing are presented using an array of ultra-low-reflectivity fiber Bragg gratings as weak reflectors. PMID:26698514
Max-Moerbeck, W; Hovatta, T; Pavlidou, V; Pearson, T J; Readhead, A C S
2014-01-01
We present a practical implementation of a Monte Carlo method to estimate the significance of cross-correlations in unevenly sampled time series of data, whose statistical properties are modeled with a simple power-law power spectral density. This implementation builds on published methods, we introduce a number of improvements in the normalization of the cross-correlation function estimate and a bootstrap method for estimating the significance of the cross-correlations. A closely related matter is the estimation of a model for the light curves, which is critical for the significance estimates. We present a graphical and quantitative demonstration that uses simulations to show how common it is to get high cross-correlations for unrelated light curves with steep power spectral densities. This demonstration highlights the dangers of interpreting them as signs of a physical connection. We show that by using interpolation and the Hanning sampling window function we are able to reduce the effects of red-noise leak...
Observation of noise correlated by the Hawking effect in a water tank
Euvé, L -P; Parentani, R; Philbin, T G; Rousseaux, G
2015-01-01
We measure the power spectrum and two-point correlation function for the fluctuating free surface on the downstream side of a stationary flow above an obstacle with high Froude number $F \\approx 0.85$. On such a flow the scattering of incident long wavelength modes is analogous to that responsible for black hole radiation (the Hawking effect). Our measurements of the correlations clearly indicate a steady conversion of incident modes into pairs of modes of opposite energies. We then use a wave maker to measure the scattering coefficients responsible for this effect.
Institute of Scientific and Technical Information of China (English)
谢崇伟; 梅冬成
2003-01-01
We study the effects of correlations between the real and imaginary parts of quantum noise on the intensity fluctuation for a single-mode laser. The analytic expressions of the intensity correlation function C(τ) and the associated relaxation time Tc in the case of a stable locked phase resulting from the cross-correlation λq between the real and imaginary parts of quantum noise are derived by means of projection operator method. Based on numerical computations it is found that the presence of cross-correlations between the real and imaginary parts of quantum noise causes the intensity fluctuation to increase. A slowing-down phenomenon exists in the sense that Tc increases as a function of |λq|. Thus the decay of intensity fluctuation becomes slower.
Ferro- and antiferro-magnetism in (Np, Pu)BC
Czech Academy of Sciences Publication Activity Database
Klimczuk, T.; Shick, Alexander; Kozub, Agnieszka L.; Griveau, J.C.; Colineau, E.; Falmbigl, M.; Wastin, F.; Rogl, P.
2015-01-01
Roč. 3, č. 4 (2015), "041803-1"-"041803-9". ISSN 2166-532X R&D Projects: GA ČR GA15-07172S Institutional support: RVO:68378271 Keywords : ferromagetism * antiferromagnetism * magnetic anisotropy * strong electron correlations * spin-orbit coupling Subject RIV: BM - Solid Matter Physics ; Magnetism
An antiferromagnetic transverse Ising nanoisland; unconventional surface effects
Kaneyoshi, T.
2015-12-01
The phase diagrams and temperature dependences of magnetizations in a transverse Ising nanosisland with an antiferromagnetic spin configuration are studied by the use of the effective-field theory with correlations (EFT). Some novel features, such as the re-entrant phenomena with two compensation points being free from disorder induced frustration, are obtained for the magnetic properties in the system.
On the ground state of antiferromagnets at zero temperature
Mayer, I.; Angelov, S. A.
1984-02-01
The wave function describing a perfect antiferromagnetic ordering of spins at 0 K (the singlet projection of the Néel function) was proved to be not an eigenfunction of the exchange Hamiltonian: the long-range order is reduced as to permit a higher correlation between the nearest-neighbour spins.
On the Capacity of Densely Packed Arrays with Mutual Coupling and Correlated Noise
Directory of Open Access Journals (Sweden)
Vahid Dehghanian
2015-01-01
Full Text Available Capacity of a wireless link can be enhanced by increasing the number of receive antennas. However, imposed receiver physical size constraints necessitate that the antenna elements be in close proximity, which typically reduces the overall link capacity of the wireless channel. Counterintuitively, under certain conditions the capacity of the overall link can be enhanced by decreasing antenna spacings. The focus of this paper is that of identifying the fundamental mechanisms and the conditions that give rise to this excess capacity. Closed-form expressions that directly quantify this capacity gain are derived based on a representative circuit theoretic model. Interesting insights are developed about the impact of different noise and interference sources and the limiting effect of heat losses in the antenna system. The capacity analysis is subsequently generalized to encompass the effect of antenna current deformation and load mismatch due to mutual coupling, based on the standard Method of Moments (MoM analysis, demonstrating similar capacity enhancement behavior as predicted by the closed-form expressions.
Spin structures in antiferromagnetic nanoparticles
DEFF Research Database (Denmark)
Brok, Erik
In this thesis magnetic structures of antiferromagnetic nanoparticles are studied as a function of particle size and aggregation. In nanoparticles the magnetic structure can be different from that of the corresponding bulk system due to the following reasons: a) a significant surface contribution...... a detailed knowledge of it can be important for applications of antiferromagnetic nanoparticles for example combined with ferromagnetic nanoparticles in nanocomposite devices. In this thesis the magnetic structure, in particular the orientation of the spins in the antiferromagnetic sublattices......, is investigated in systems of magnetic nanoparticles using a variety of experimental techniques. The spin structure in systems with spin canting, due to magnetic atoms in low symmetry surroundings, is studied in a theoretical model that is able to quantitatively explain observations of anomalous temperature...
Quantum critical behavior in a two-layer antiferromagnet
International Nuclear Information System (INIS)
We analyze quantum Monte Carlo data in the vicinity of the quantum transition between a Neel state and a quantum paramagnet in a two-layer, square-lattice spin-1/2 Heisenberg antiferromagnet. The real-space correlation function and the universal amplitude ratio of the structure factor and the dynamic susceptibility show clear evidence of quantum critical behavior at low temperatures. The numerical results are in good quantitative agreement with 1/N calculations for the O(N) nonlinear σ model. A discrepancy, reported earlier, between the critical properties of the antiferromagnet and the σ model is resolved. We also discuss the values of prefactors of the dynamic susceptibility and the structure factor in a single-layer antiferromagnet at low T
Quantum noise of a Bose-Einstein condensate in an optical cavity, correlations and entanglement
Szirmai G.; Nagy D.; Domokos P.
2010-01-01
A Bose-Einstein condensate of ultracold atoms inside the field of a laser-driven optical cavity exhibits dispersive optical bistability. We describe this system by using mean-field approximation and by analyzing the correlation functions of the linearized quantum fluctuations around the mean-field solution. The entanglement and the statistics of the atom-field quadratures are given in the stationary state. It is shown that the mean-field solution, i.e. the Bose-Einstein condensate is robust a...
Ku, C. S.; You, S. H.; Kuo, Y. T.; Huang, B. S.; Wu, Y. M.; Chen, Y. G.; Taylor, F. W.
2015-12-01
A MW 8.1 earthquake occurred on 1 April 2007 in the western Solomon Islands. Following this event, a damaging tsunami was induced and hit the Island Gizo where the capital city of Western Province of Solomon Islands located. Several buildings of this city were destroyed and several peoples lost their lives during this earthquake. However, during this earthquake, no near source seismic instrument has been installed in this region. The seismic evaluations for the aftershock sequence, the possible earthquake early warning and tsunami warning were unavailable. For the purpose of knowing more detailed information about seismic activity in this region, we have installed 9 seismic stations (with Trillium 120PA broadband seismometer and Q330S 24bit digitizer) around the rupture zone of the 2007 earthquake since September of 2009. Within a decade, it has been demonstrated both theoretically and experimentally that the Green's function or impulse response between two seismic stations can be retrieved from the cross-correlation of ambient noise. In this study, 6 stations' observations which are more complete during 2011/10 ~ 2012/12 period, were selected for the purpose of the cross-correlation analysis of ambient seismic noise. The group velocities at period 2-20 seconds of 15 station-pairs were extracted by using multiple filter technique (MFT) method. The analyzed results of this study presented significant results of group velocities with higher frequency contents than other studies (20-60 seconds in usually cases) and opened new opportunities to study the shallow crustal structure of the western Solomon Islands.
Effects of imperfect noise correlations on decoherence-free subsystems: SU(2) diffusion model
International Nuclear Information System (INIS)
We present a model of an N-qubit channel where consecutive qubits experience correlated random rotations. Our model is an extension to the standard decoherence-free subsystems approach which assumes that all qubits experience the same disturbance. The variation of rotations acting on consecutive qubits is modeled as diffusion on the SU(2) group. The model may be applied to spins traveling in a varying magnetic field or to photons passing through a fiber whose birefringence fluctuates over the time separation between photons. We derive an explicit formula describing the action of the channel on an arbitrary N-qubit state. For N=3 we investigate the effects of diffusion on both the classical and quantum capacities of the channel. We observe that nonorthogonal states are necessary to achieve optimal classical capacity. Furthermore, we find the threshold for the diffusion parameter above which coherent information of the channel vanishes
Anomalous Magnetothermopower in a Metallic Frustrated Antiferromagnet
Arsenijević, Stevan; Ok, Jong Mok; Robinson, Peter; Ghannadzadeh, Saman; Katsnelson, Mikhail I.; Kim, Jun Sung; Hussey, Nigel E.
2016-02-01
We report the temperature T and magnetic field H dependence of the thermopower S of an itinerant triangular antiferromagnet PdCrO2 in high magnetic fields up to 32 T. In the paramagnetic phase, the zero-field thermopower is positive with a value typical of good metals with a high carrier density. In marked contrast to typical metals, however, S decreases rapidly with increasing magnetic field, approaching zero at the maximum field scale for T >70 K . We argue here that this profound change in the thermoelectric response derives from the strong interaction of the 4 d correlated electrons of the Pd ions with the short-range spin correlations of the Cr3 + spins that persist beyond the Néel ordering temperature due to the combined effects of geometrical frustration and low dimensionality.
Energy Technology Data Exchange (ETDEWEB)
Renard, F.
2003-01-01
The goal of seismic inversion is to recover an Earth model that best fits some observed data. To reach that goal, we have to minimize an objective function that measures the amplitude of the misfits according to a norm to be chosen in data space. In general, the used norm is the L2 norm. Unfortunately, such a norm is not adapted to data corrupted by correlated noise: the noise is in that case inverted as signal and the inversion results are unacceptable. The goal of this thesis is to obtain satisfactory results to the inverse problem in that situation. For this purpose, we study two inverse problems: reflection tomography and waveform inversion. In reflection tomography, we propose a new formulation of the continuum inverse problem which relies on a H1 norm in data space. This allows us to account for the correlated nature of the noise that corrupts the kinematic information. However, this norm does not give more satisfactory results than the ones obtained with the classical formalism. This is why, for sake of simplicity, we recommend to use this classical formalism. Then we try to understand how to properly sample the kinematic information so as to obtain an accurate approximation of the continuum inverse problem. In waveform inversion, we propose to directly invert data corrupted by some correlated noise. A first idea consists in rejecting the noise in the residues. In that goal, we can use a semi-norm to formulate the inverse problem. This technique gives very good results, except when the data are corrupted by random noise. Thus we propose a second method which consists in retrieving, by solving an inverse problem, the signal and the noise whose sum best fits the data. This technique gives very satisfactory results, even if some random noise pollutes the data, and is moreover solved, thanks to an original algorithm, in a very efficient way. (author)
Institute of Scientific and Technical Information of China (English)
ZHANG Li; CAO Li; WU Da-Jin
2006-01-01
A two-dimensional single-mode laser model with cross-correlation between the real and imaginary parts of the colored quadric pump noise is investigated. A novel laser amplitude Langevin equation is obtained, in which the cross-correlation λp between the real and imaginary parts of the pump noise appears. The mean, variance, and skewness of first-passage-time are calculated. It is shown that the mean, variance, and skewness of first-passage-time are strongly affected by λp.
Valence Bond Solid Order Near Impurities in Two-Dimensional Quantum Antiferromagnets
Metlitski, Max A.; Sachdev, Subir
2008-01-01
Recent scanning tunneling microscopy (STM) experiments on underdoped cuprates have displayed modulations in the local electronic density of states, which are centered on a Cu-O-Cu bond [Kohsaka et al. Science 315 1380 (2007)]. As a paradigm of the pinning of such bond-centered ordering in strongly correlated systems, we present the theory of valence bond solid (VBS) correlations near a single impurity in a square lattice antiferromagnet. The antiferromagnet is assumed to be in the vicinity of...
Drone-fermions in the two-dimensional antiferromagnet
Krivenko, S.; Khaliullin, G.
1995-02-01
Two different representations of spins - via the conventional fermions, or via the Mattis drone-fermions - are compared considering the planar antiferromagnetic Heisenberg model as an example. Mean-field spin correlation functions calculated for the uniform and flux RVB states show that the drone-fermion approach has an advantage in giving the lower energy and the enhanced AF correlations, because of the absence of unphysical spinless states in this representation.
Exchange bias in diluted-antiferromagnet/antiferromagnet bilayers
International Nuclear Information System (INIS)
The hysteresis-loop properties of a diluted-antiferromagnetic (DAF) layer exchange coupling to an antiferromagnetic (AF) layer are investigated by means of numerical simulations. Remarkable loop shift and coercivity enhancement are observed in such DAF/AF bilayers, while they are absent in the uncoupled DAF single layer. The influences of pinned domains, dilution, cooling field and DAF layer thickness on the loop shift are investigated systematically. The result unambiguously confirms an exchange bias (EB) effect in the DAF/AF bilayers. It also reveals that the EB effect originates from the pinned AF domains within the DAF layer. In contrast to conventional EB systems, frozen uncompensated spins are not found at the interface of the AF pinning layer. (paper)
Paquette, Stephen T.; Gilels, Felicia; White, Patricia M.
2016-01-01
Cochlear neuropathy resulting from unsafe noise exposure is a life altering condition that affects many people. This hearing dysfunction follows a conserved mechanism where inner hair cell synapses are lost, termed cochlear synaptopathy. Here we investigate cochlear synaptopathy in the FVB/nJ mouse strain as a prelude for the investigation of candidate genetic mutations for noise damage susceptibility. We used measurements of auditory brainstem response (ABR) and distortion product otoacoustic emissions (DPOAE) to assess hearing recovery in FVB/nJ mice exposed to two different noise levels. We also utilized confocal fluorescence microscopy in mapped whole mount cochlear tissue, in conjunction with deconvolution and three-dimensional modeling, to analyze numbers, volumes and positions of paired synaptic components. We find evidence for significant synapse reorganization in response to both synaptopathic and sub-synaptopathic noise exposures in FVB/nJ. Specifically, we find that the modulation in volume of very small synaptic ribbons correlates with the presence of reduced ABR peak one amplitudes in both levels of noise exposures. These experiments define the use of FVB/nJ mice for further genetic investigations into the mechanisms of noise damage. They further suggest that in the cochlea, neuronal-inner hair cell connections may dynamically reshape as part of the noise response. PMID:27162161
International Nuclear Information System (INIS)
Positron Emission Tomography (PET), Computed Tomography (CT), PET/CT and Single Photon Emission Tomography (SPECT) are non-invasive imaging tools used for creating two dimensional (2D) cross section images of three dimensional (3D) objects. PET and SPECT have the potential of providing functional or biochemical information by measuring distribution and kinetics of radiolabelled molecules, whereas CT visualizes X-ray density in tissues in the body. PET/CT provides fused images representing both functional and anatomical information with better precision in localization than PET alone. Images generated by these types of techniques are generally noisy, thereby impairing the imaging potential and affecting the precision in quantitative values derived from the images. It is crucial to explore and understand the properties of noise in these imaging techniques. Here we used autocorrelation function (ACF) specifically to describe noise correlation and its non-isotropic behaviour in experimentally generated images of PET, CT, PET/CT and SPECT. Experiments were performed using phantoms with different shapes. In PET and PET/CT studies, data were acquired in 2D acquisition mode and reconstructed by both analytical filter back projection (FBP) and iterative, ordered subsets expectation maximisation (OSEM) methods. In the PET/CT studies, different magnitudes of X-ray dose in the transmission were employed by using different mA settings for the X-ray tube. In the CT studies, data were acquired using different slice thickness with and without applied dose reduction function and the images were reconstructed by FBP. SPECT studies were performed in 2D, reconstructed using FBP and OSEM, using post 3D filtering. ACF images were generated from the primary images, and profiles across the ACF images were used to describe the noise correlation in different directions. The variance of noise across the images was visualised as images and with profiles across these images. The most important
Spin Structure Analyses of Antiferromagnets
International Nuclear Information System (INIS)
We have synthesized series of powder sample of incommensurate antiferromagnetic multiferroics, (Mn, Co)WO4 and Al doped Ba0.5Sr1.5Zn2Fe12O22, incommensurate antiferromagnetic multiferroics. Their spin structure was studied by using the HRPD. In addition, we have synthesized series of crystalline samples of incommensurate multiferroics, (Mn, Co)WO4 and olivines. Their spin structure was investigated using neutron diffraction under high magnetic field. As a result, we were able to draw the phase diagram of (Mn, Co)WO4 as a function of composition and temperature. We learned the how the spin structure changes with increased ionic substitution. Finally we have drawn the phase diagram of the multicritical olivine Mn2SiS4/Mn2GeS4 as a function of filed and temperature through the spin structure studies
Electrical switching of an antiferromagnet
Czech Academy of Sciences Publication Activity Database
Wadley, P.; Howells, B.; Železný, J.; Andrews, C.; Hills, V.; Campion, R. P.; Novák, Vít; Olejník, Kamil; Maccherozzi, F.; Dhesi, S.S.; Martin, S.Y.; Wagner, T.; Wunderlich, Joerg; Freimuth, F.; Mokrousov, Y.; Kuneš, Jan; Chauhan, J.S.; Grzybowski, M.J.; Rushforth, A.W.; Edmonds, K. W.; Gallagher, B. L.; Jungwirth, Tomáš
2016-01-01
Roč. 351, č. 6273 (2016), 587-590. ISSN 0036-8075 R&D Projects: GA MŠk(CZ) LM2011026; GA ČR GB14-37427G EU Projects: European Commission(XE) 268066 - 0MSPIN Institutional support: RVO:68378271 Keywords : spintronics * antiferromagnets * current induced switching Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 33.611, year: 2014
Nonequilibrium Spin Noise and Noise of Susceptibility
Schad, Pablo; Narozhny, Boris N.; Schön, Gerd; Shnirman, Alexander
2014-01-01
We analyze out-of-equilibrium fluctuations in a driven spin system and relate them to the noise of spin susceptibility. In the spirit of the linear response theory we further relate the noise of susceptibility to a $4$-spin correlation function in equilibrium. We show that, in contrast to the second noise (noise of noise), the noise of susceptibility is a direct measure of non-Gaussian fluctuations in the system. We develop a general framework for calculating the noise of susceptibility using...
Martin, Thierry
2005-01-01
This is a course on noise which covers some of the scattering theory for normal metals, Hanbury Brown and Twiss analogs for noise correlations with electrons, noise correlations in superconducting/normal metal junctions. Entanglement in such NS systems is described with a criterion for violating Bell inegalities. The last section is devoted to the perturbative derivation of noise in a particular one dimensional correlated electron system (Luttinger liquid): edge states in the fractional quant...
Thermoinduced magnetization in nanoparticles of antiferromagnetic materials
DEFF Research Database (Denmark)
Mørup, Steen; Frandsen, Cathrine
2004-01-01
We show that there is a thermoinduced contribution to the magnetic moment of nanoparticles of antiferromagnetic materials. It arises from thermal excitations of the uniform spin-precession mode, and it has the unusual property that its magnitude increases with increasing temperature. This has...... the consequence that antiferromagnetism is nonexistent in nanoparticles at finite temperatures and it explains magnetic anomalies, which recently have been reported in a number of studies of nanoparticles of antiferromagnetic materials....
Electric voltage generation by antiferromagnetic dynamics
Yamane, Yuta; Ieda, Jun'ichi; Sinova, Jairo
2016-05-01
We theoretically demonstrate dc and ac electric voltage generation due to spin motive forces originating from domain wall motion and magnetic resonance, respectively, in two-sublattice antiferromagnets. Our theory accounts for the canting between the sublattice magnetizations, the nonadiabatic electron spin dynamics, and the Rashba spin-orbit coupling, with the intersublattice electron dynamics treated as a perturbation. This work suggests a way to observe and explore the dynamics of antiferromagnetic textures by electrical means, an important aspect in the emerging field of antiferromagnetic spintronics, where both manipulation and detection of antiferromagnets are needed.
Spica, Zack; Perton, Mathieu; Calò, Marco; Legrand, Denis; Córdoba Montiel, Francisco; Iglesias, Arturo
2016-07-01
This work presents an innovative strategy to enhance the resolution of surface wave tomography obtained from ambient noise cross-correlation (C1) by bridging asynchronous seismic networks through the correlation of coda of correlations (C3). Rayleigh wave group dispersion curves show consistent results between synchronous and asynchronous stations. Rayleigh wave group travel times are inverted to construct velocity-period maps with unprecedented resolution for a region covering Mexico and the southern United States. The resulting period maps are then used to regionalize dispersion curves in order to obtain local 1-D shear velocity models (VS) of the crust and uppermost mantle in every cell of a grid of 0.4°. The 1-D structures are obtained by iteratively adding layers until reaching a given misfit, and a global tomography model is considered as an input for depths below 150 km. Finally, a high-resolution 3-D VS model is obtained from these inversions. The major structures observed in the 3-D model are in agreement with the tectonic-geodynamic features and with previous regional and local studies. It also offers new insights to understand the present and past tectonic evolution of the region.
Spica, Zack; Perton, Mathieu; Calò, Marco; Legrand, Denis; Córdoba-Montiel, Francisco; Iglesias, Arturo
2016-09-01
This work presents an innovative strategy to enhance the resolution of surface wave tomography obtained from ambient noise cross-correlation (C1) by bridging asynchronous seismic networks through the correlation of coda of correlations (C3). Rayleigh wave group dispersion curves show consistent results between synchronous and asynchronous stations. Rayleigh wave group traveltimes are inverted to construct velocity-period maps with unprecedented resolution for a region covering Mexico and the southern United States. The resulting period maps are then used to regionalize dispersion curves in order to obtain local 1-D shear velocity models (VS) of the crust and uppermost mantle in every cell of a grid of 0.4°. The 1-D structures are obtained by iteratively adding layers until reaching a given misfit, and a global tomography model is considered as an input for depths below 150 km. Finally, a high-resolution 3-D VS model is obtained from these inversions. The major structures observed in the 3-D model are in agreement with the tectonic-geodynamic features and with previous regional and local studies. It also offers new insights to understand the present and past tectonic evolution of the region.
Entanglement Perturbation Theory for Antiferromagnetic Heisenberg Spin Chains
Wang, Lihua; Chung, Sung Gong
2012-11-01
A recently developed numerical method, entanglement perturbation theory (EPT), is used to study the antiferromagnetic Heisenberg spin chains with z-axis anisotropy λ and magnetic field B. To demonstrate its accuracy, we first apply EPT to the isotropic spin-1/2 antiferromagnetic Heisenberg model, and find that EPT successfully reproduces the exact Bethe ansatz results for the ground state energy, the local magnetization, and the spin correlation functions (Bethe ansatz result is available for the first seven lattice separations). In particular, EPT confirms for the first time the asymptotic behavior of the spin correlation functions predicted by the conformal field theory, which realizes only for lattice separations larger than 1000. Next, turning on the z-axis anisotropy and the magnetic field, the 2- and 4-spin correlation functions are calculated, and the results are compared with those obtained by bosonization and density matrix renormalization group methods. Finally, for the spin-1 antiferromagnetic Heisenberg model, the ground state phase diagram in λ space is determined by Roomany--Wyld renormalization group (RG) finite size scaling. The results are in good agreement with those obtained by the level-spectroscopy method.
Electrical conduction noise and its correlation with structural properties of Cu2ZnSnS4 thin films
Zubair Ansari, Mohd; Munjal, Sandeep; Kumar, Vikram; Khare, Neeraj
2016-07-01
Cu2ZnSnS4 (CZTS) thin films have been deposited by ultrasonic assisted chemical vapor deposition in a single step process at different substrate temperatures and structural, morphological, electrical and conduction noise characteristics of the CZTS thin films have been studied. Single phase CZTS thin films are formed at 275 °C and 325 °C deposition temperatures, whereas the CZTS thin film deposited at 375 °C showed secondary phase also. The crystallinity of the films improves and resistivity decreases with the increases of the deposition temperature. The temperature dependent electrical conductivity of the films reveals that in the temperature range 300–250 K, thermally activated conduction is observed. The conduction noise in the CZTS thin films, exhibits 1/f noise in the low frequency region and found to be strongly dependent on the film deposition temperatures. The film deposited at 275 °C and 375 °C shows larger conduction noise, whereas the film deposited at 325 °C shows smaller noise. For the low frequency 1/f noise, the value of α is also found to be the minimum for the film deposited at 325 °C. The higher value of conduction noise in the film deposited at 275 °C is related to poor crystallinity and less compact morphology. For the film deposited at 375 °C, crystallinity and compactness improves, but the presence of the secondary phases seems to be responsible for generating higher noise. The smallest conduction noise of the film deposited at 325 °C is due to single phase film with better crystallinity and smaller trap density ∼5.1 × 1015 cm‑2 eV‑1.
International Nuclear Information System (INIS)
The properties of non-Markovian noises with exponentially correlated memory are discussed. Considered are dichotomic noise, white shot noise, Gaussian white noise, and Gaussian colored noise. The stationary correlation functions of the non-Markovian versions of these noises are given by linear combinations of two or three exponential functions (colored noises) or of the δ function and exponential function (white noises). The non-Markovian white noises are well defined only when the kernel of the non-Markovian master equation contains a nonzero admixture of a Markovian term. Approximate equations governing the probability densities for processes driven by such non-Markovian noises are derived, including non-Markovian versions of the Fokker-Planck equation and the telegrapher's equation. As an example, it is shown how the non-Markovian nature changes the behavior of the driven linear process
Cumulant approach to weakly doped antiferromagnets
International Nuclear Information System (INIS)
We present an approach to static and dynamical properties of holes and spins in weakly doped antiferromagnets in two dimensions. The calculations are based on a recently introduced cumulant approach to ground endash state properties of correlated electronic systems. The present method allows us to evaluate hole and spin-wave dispersion relations by considering hole or spin excitations of the ground state. Usually, these dispersions are found from time-dependent correlation functions. To demonstrate the ability of the approach we first derive the dispersion relation for the lowest single hole excitation at half-filling. However, the main purpose of this paper is to focus on the mutual influence of mobile holes and spin waves in the weakly doped system. It is shown that low-energy spin excitations strongly admix to the ground state. The coupling of spin waves and holes leads to a strong suppression of the staggered magnetization which cannot be explained by a simple rigid-band picture for the hole quasiparticles. Also the experimentally observed doping dependence of the spin-wave excitation energies can be understood within our formalism. copyright 1996 The American Physical Society
Quantum Computers: Noise Propagation and Adversarial Noise Models
Kalai, Gil
2009-01-01
In this paper we consider adversarial noise models that will fail quantum error correction and fault-tolerant quantum computation. We describe known results regarding high-rate noise, sequential computation, and reversible noisy computation. We continue by discussing highly correlated noise and the "boundary," in terms of correlation of errors, of the "threshold theorem." Next, we draw a picture of adversarial forms of noise called (collectively) "detrimental noise." Detrimental noise is mode...
Vilar, J. M. G.; Rubí Capaceti, José Miguel
2001-01-01
We have analyzed the interplay between an externally added noise and the intrinsic noise of systems that relax fast towards a stationary state, and found that increasing the intensity of the external noise can reduce the total noise of the system. We have established a general criterion for the appearance of this phenomenon and discussed two examples in detail.
Kapusta, Joseph; Mueller, Berndt; Stephanov, Misha
2012-01-01
The relativistic theory of hydrodynamic fluctuations, or noise, is derived and applied to high energy heavy ion collisions. These fluctuations are inherent in any space-time varying system and are in addition to initial state fluctuations. We illustrate the effects with the boost-invariant Bjorken solution to the hydrodynamic equations. Long range correlations in rapidity are induced by propagation of sound modes. The magnitude of these correlations are directly proportional to the viscositie...
Institute of Scientific and Technical Information of China (English)
Hu Jing-Guo; Stamps R L
2006-01-01
The rotational anisotropies in the exchange bias structures of ferromagnetism/antiferromagnetism 1/antiferromagnetism 2 are studied in this paper. Based on the model, in which the antiferromagnetism is treated with an Ising mean field theory and the rotational anisotropy is assumed to be related to the field created by the moment induced on the antiferromagnetic layer next to the ferromagnetic layer, we can explain why in experiments for ferromagnetism (FM)/antiferromagntism 1 (AFM1)/antiferromagnetism 2 (AFM2) systems the thickness-dependent rotational anisotropy value is non-monotonic, i.e. it reaches a minimum for this system at a specific thickness of the first antiferromagnetic layer and exhibits oscillatory behaviour. In addition, we find that the temperature-dependent rotational anisotropy value is in good agreement with the experimental result.
Neutron scattering studies of three one-dimensional antiferromagnets
Kenzelmann, M
2001-01-01
observed in the disordered phase of spin-1/2 chains. The magnetic order of the one-dimensional spin-1/2 XY antiferromagnet Cs sub 2 CoCl sub 4 was investigated using neutron diffraction. The magnetic structure has an ordering wave-vector (0, 0.5, 0.5) for T < 217 mK and the magnetic structure is a non-linear structure with the magnetic moments at a small angle to the b axis. Above a field of H = 2.1 T the magnetic order collapses in an apparent first order phase transition, suggesting a transition to a spin-liquid phase. Low-dimensional magnets with low-spin quantum numbers are ideal model systems for investigating strongly interacting macroscopic quantum ground states and their non-linear spin excitations. This thesis describes neutron scattering experiments of three one-dimensional low-spin antiferromagnets where strong quantum fluctuations lead to highly-correlated ground states and unconventional cooperative spin excitations. The excitation spectrum of the antiferromagnetic spin-1 Heisenberg chain CsNi...
Pressure effects on antiferromagnetism in UNiAl
International Nuclear Information System (INIS)
The temperature dependencies of the electrical resistivity ρ for current along and perpendicular to the c axis were measured on single crystalline UNiAl under various hydrostatic pressures. The ρ(T) curves at ambient pressure exhibit a Cr anomaly around the Neel temperature TN. Application of pressure causes a reduction of TN value. Linear extrapolation of low-pressure TN vs p data yields an estimate of a critical pressure for antiferromagnetism pc≅10 GPa. Measurements above 1 GPa, however, reveal a collapse of the antiferromagnetic (AF) ordering already below 3 GPa, although AF correlations seem to affect resistivity behavior ρ(T) in pressures up to 8 GPa. A sudden change of the ρ(T) curve character for i(perpendicular sign)c and TN indicates a pressure-induced change of magnetic ordering or fluctuations within the basal plane. The results are discussed in terms of the instability of the itinerant 5f-electron antiferromagnetism in UNiAl. (c) 2000 American Institute of Physics
Ana Fernández-Somoano; Sabrina Llop; Inmaculada Aguilera; Ibon Tamayo-Uria; María Dolores Martínez; Maria Foraster; Ferran Ballester; Adonina Tardón
2015-01-01
This study aimed to describe the degree of annoyance among pregnant women in a Spanish cohort and to examine associations with proximity to traffic, NO2 and benzene exposure. We included 2457 participants from the Spanish Childhood and Environment study. Individual exposures to outdoor NO2 and benzene were estimated, temporally adjusted for pregnancy. Interviews about sociodemographic variables, noise and air pollution were carried out. Levels of annoyance were assessed using a scale from 0 (...
Pedersen, H. A.; Boué, P.; Poli, P.; Colombi, A.
2015-12-01
Deviation of seismic surface waves from the great-circle between source and receiver is illustrated by the anomalies in the arrival angle, that is the difference between the observed backazimuth of the incident waves and the great-circle. Such arrival angle anomalies have been known for decades, but observations remain scattered. We present a systematic study of arrival angle anomalies of fundamental mode Rayleigh waves (20-100 s period interval) from 289 earthquakes and recorded by a broadband network LAPNET, located in northern Finland. These observations are compared with those of full waveform synthetic seismograms for the same events, calculated in a 3-D Earth and also compared with those of seismograms obtained by ambient noise correlation. The arrival angle anomalies for individual events are complex, and have significant variations with period. On average, the mean absolute deviation decreases from ˜9° at 20 s period to ˜3° at 100 s period. The synthetic seismograms show the same evolution, albeit with somewhat smaller deviations. While the arrival angle anomalies are fairly well simulated at long periods, the deviations at short periods are very poorly modelled, demonstrating the importance of the continuous improvement of global crustal models. At 20-30 s period, both event data and numerical simulations have strong multipathing, and relative amplitude changes between different waves will induced differences in deviations between very closely located events. The source mechanism has only limited influence on the deviations, demonstrating that they are directly linked to propagation effects, including near-field effects in the source area. This observation is confirmed by the comparison with seismic noise correlation records, that is where the surface waves correspond to those emitted by a point source at the surface, as the two types of observations are remarkably similar in the cases where earthquakes are located close to seismic stations. This
Synthetic antiferromagnetic nanoparticles with tunable susceptibilities
Hu, Wei; Wilson, Robert J.; Earhart, Christopher M.; Koh, Ai Leen; Sinclair, Robert; Wang, Shan X.
2009-01-01
High-moment monodisperse disk-shaped Co–Fe magnetic nanoparticles, stable in aqueous solution, were physically fabricated by using nanoimprinted templates and vacuum deposition techniques. These multilayer synthetic antiferromagnetic nanoparticles exhibit nearly zero magnetic remanence and coercivity, and susceptibilities which can be tuned by exploiting interlayer magnetic interactions. In addition, a low cost method of scaling up the production of sub-100 nm synthetic antiferromagnetic nano...
Makita, Shuichi; Kurokawa, Kazuhiro; Hong, Young-Joo; Li, En; Miura, Masahiro; Yasuno, Yoshiaki
2016-03-01
A new optical coherence angiography (OCA) method, called correlation mapping OCA (cmOCA), is presented by using the SNR-corrected complex correlation. An SNR-correction theory for the complex correlation calculation is presented. The method also integrates a motion-artifact-removal method for the sample motion induced decorrelation artifact. The theory is further extended to compute more reliable correlation by using multi- channel OCT systems, such as Jones-matrix OCT. The high contrast vasculature imaging of in vivo human posterior eye has been obtained. Composite imaging of cmOCA and degree of polarization uniformity indicates abnormalities of vasculature and pigmented tissues simultaneously.
Constructing a magnetic handle for antiferromagnetic manganites
Glavic, Artur; Dixit, Hemant; Cooper, Valentino R.; Aczel, Adam A.
2016-04-01
An intrinsic property of antiferromagnetic materials is the compensation of the magnetic moments from the individual atoms that prohibits the direct interaction of the spin lattice with an external magnetic field. To overcome this limitation we have created artificial spin structures by heteroepitaxy between two bulk antiferromagnets SrMnO3 and NdMnO3. Here, we demonstrate that charge transfer at the interface results in the creation of thin ferromagnetic layers adjacent to A -type antiferromagnetism in thick NdMnO3 layers. A novel interference based neutron diffraction technique and polarized neutron reflectometry are used to confirm the presence of ferromagnetism in the SrMnO3 layers and to probe the relative alignment of antiferromagnetic spins induced by the coupling at the ferro- to antiferromagnet interface. A density functional theory analysis of the driving forces for the exchange reveals strong ferromagnetic interfacial coupling through quantifiable short range charge transfer. These results confirm a layer-by-layer control of magnetic arrangements that constitutes a promising step on a path towards isothermal magnetic control of antiferromagnetic arrangements as would be necessary in spin-based heterostructures like multiferroic devices.
Antiferromagnetic fractons in percolating magnets
International Nuclear Information System (INIS)
We report the observations of the dynamical structure factors S(q,ω) for antiffero-magnetic fractons in diluted three-dimensional (3d) and two-dimensional (2d) Heisenberg systems, RbMn0.4Mg0.6F3 and Rb2Mn0.598Mg0.402F4, with a magnetic concentration close to the percolation concentration, which were obtained by means of high-resolution (ΔE=17.5 μeV) inelastic neutron scattering experiments. The peak intensity A(q) and the dispersion relation E(q) show the clear scaling laws following to A(q) ∝ q-y with y=2.9±0.1 and E(q) ∝ qz with z=2.5±0.1 for the 3d system, and y=2.9±0.2 and z=1.8±0.2 for the 2d system. The validity of the single-length-scaling postulate (SLSP) for S(q,ω) are demonstrated, for the first time. In addition, we show that the spectral dimension of antiferromagnetic fractons is unity independent of the embedding Euclidean dimension of the systems. These values are consistent with the theoretical predictions. (author)
Moore, C. S.; Wood, T. J.; Saunderson, J. R.; Beavis, A. W.
2015-12-01
This work assessed the appropriateness of the signal-to-noise ratio improvement factor (KSNR) as a metric for the optimisation of computed radiography (CR) of the chest. The results of a previous study in which four experienced image evaluators graded computer simulated chest images using a visual grading analysis scoring (VGAS) scheme to quantify the benefit of using an anti-scatter grid were used for the clinical image quality measurement (number of simulated patients = 80). The KSNR was used to calculate the improvement in physical image quality measured in a physical chest phantom. KSNR correlation with VGAS was assessed as a function of chest region (lung, spine and diaphragm/retrodiaphragm), and as a function of x-ray tube voltage in a given chest region. The correlation of the latter was determined by the Pearson correlation coefficient. VGAS and KSNR image quality metrics demonstrated no correlation in the lung region but did show correlation in the spine and diaphragm/retrodiaphragmatic regions. However, there was no correlation as a function of tube voltage in any region; a Pearson correlation coefficient (R) of -0.93 (p = 0.015) was found for lung, a coefficient (R) of -0.95 (p = 0.46) was found for spine, and a coefficient (R) of -0.85 (p = 0.015) was found for diaphragm. All demonstrate strong negative correlations indicating conflicting results, i.e. KSNR increases with tube voltage but VGAS decreases. Medical physicists should use the KSNR metric with caution when assessing any potential improvement in clinical chest image quality when introducing an anti-scatter grid for CR imaging, especially in the lung region. This metric may also be a limited descriptor of clinical chest image quality as a function of tube voltage when a grid is used routinely.
International Nuclear Information System (INIS)
This work assessed the appropriateness of the signal-to-noise ratio improvement factor (KSNR) as a metric for the optimisation of computed radiography (CR) of the chest. The results of a previous study in which four experienced image evaluators graded computer simulated chest images using a visual grading analysis scoring (VGAS) scheme to quantify the benefit of using an anti-scatter grid were used for the clinical image quality measurement (number of simulated patients = 80). The KSNR was used to calculate the improvement in physical image quality measured in a physical chest phantom. KSNR correlation with VGAS was assessed as a function of chest region (lung, spine and diaphragm/retrodiaphragm), and as a function of x-ray tube voltage in a given chest region. The correlation of the latter was determined by the Pearson correlation coefficient. VGAS and KSNR image quality metrics demonstrated no correlation in the lung region but did show correlation in the spine and diaphragm/retrodiaphragmatic regions. However, there was no correlation as a function of tube voltage in any region; a Pearson correlation coefficient (R) of −0.93 (p = 0.015) was found for lung, a coefficient (R) of −0.95 (p = 0.46) was found for spine, and a coefficient (R) of −0.85 (p = 0.015) was found for diaphragm. All demonstrate strong negative correlations indicating conflicting results, i.e. KSNR increases with tube voltage but VGAS decreases. Medical physicists should use the KSNR metric with caution when assessing any potential improvement in clinical chest image quality when introducing an anti-scatter grid for CR imaging, especially in the lung region. This metric may also be a limited descriptor of clinical chest image quality as a function of tube voltage when a grid is used routinely. (paper)
Bond-centered, bond-ordered stripes in doped antiferromagnets
Wrobel, P.; Maciag, A; Eder, R.
2004-01-01
Motivated by recent inelastic neutron scattering experiments on cuprates, we discuss the formation of bond order in the stripe phase. We suggest that the spin Peierls order emerges in hole-rich domain walls (DWs) formed between hole-poor regions in which long-range antiferromagnetic (AF) correlations exist. On the example of a single stripe we analyze the stability of such structures. The motion of a hole inside the DW which takes the form of a bond ordered ladder is in principle unrestricted...
A transverse Ising bilayer film with an antiferromagnetic spin configuration
Kaneyoshi, T.
2015-10-01
The phase diagrams and temperature dependences of magnetizations in a transverse Ising bilayer film with an antiferromagnetic spin configuration are studied by the uses of the effective-field theory (EFT) with correlations, in order to clarify whether the appearance of a compensation point is possible below the transition temperature in the system. From these investigations, we have found a lot of characteristic phenomena in these properties, when the value of an interlayer coupling takes a large value, such as the reentrant phenomenon free from the disorder-induced frustration and the novel types of magnetization curve with a compensation point.
International Nuclear Information System (INIS)
Background: For the intensity of high-enriched uranium's neutrons from fission is weak, the active detection method is commonly adopted. Purpose: The quality attribute of uranium components is analysed. Methods: According to the theory of neutron source-driven noise analysis method and mass measurement problem of uranium material or uranium component, Monte Carlo simulation is used to study the mass measurement of metal uranium sphere components with the same geometry and enrichment and the different masses. The time-correlation coincidence count distributions to different uranium components are obtained. Results: The source-driven time correlation coincidence measurements can provide quantities, time-dependent coincidence distributions between two detectors, which can be related to the mass of uranium components. Conclusions: By studying on the sample (radius: 4.67 cm, mass: 8 kg), it realized mass measurement to metal uranium sphere components with different masses. (authors)
Noise in electromigrated nanojunctions
Wheeler, P. J.; Chen, Ruoyu; Natelson, D.
2013-01-01
Noise measurements are a probe beyond simple electronic transport that can reveal additional information about electronic correlations and inelastic processes. Here we report noise measurements in individual electromigrated nanojunctions, examining the evolution from the many channel regime to the tunneling regime, using a radio frequency technique. While we generally observe the dependence of noise on bias expected for shot noise, in approximately 12% of junction configurations we find discr...
Antiferromagnetism and metal-insulator transition in high temperature superconductors
International Nuclear Information System (INIS)
The ground state of the three band Hubbard Hamiltonian for the CuO2 planes of high temperature superconductors is investigated using local ansatz approach which includes local correlations between holes. For sufficiently large Coulomb interaction, U, or charge transfer energy, Δ, one finds a transition from a nonmagnetic metal to an antiferromagnetic (AF) insulator. If the parameters determined by the local density approximation are used, the ground state is a charge-transfer antiferromagnet, with the magnetic moments of m=0.47μΒ and 0.56μΒ, for La2CuO4 and YBa2Cu3O6, respectively. Correlations and the presence of interoxygen hopping reduce drastically the stability of the AF long-range order which disappears at the doping of either 0.06 hole or 0.08 electron, respectively. The effective mass is enhanced by a factor less than two due to correlations. (author). 27 refs.; 5 figs
Energy Technology Data Exchange (ETDEWEB)
Deng, Xiao-Yan [Graduate School, Tianjin Polytechnic University, Tianjin 300387 (China); Dou, Jun-Ya [Department of Physics, Tianjin Polytechnic University, Tianjin 300387 (China); Liu, Guang-Hua, E-mail: liuguanghua@tjpu.edu.cn [Department of Physics, Tianjin Polytechnic University, Tianjin 300387 (China)
2015-10-15
The magnetization process of a spin-1/2 J{sub 1}–J{sub 1}–J{sub 2}–J{sub 2} tetrameric Heisenberg chain is investigated by the infinite time-evolving block decimation (iTEBD) method. A magnetization phase diagram including three different phases, i.e., a fully polarized (FP) phase, a 1/2 plateau phase, and a spin-fluid (SF) phase, is obtained. All the quantum phase transitions (QPTs) are determined to belong to the second-order category, and the central charge in the critical SF phase equals 1. In addition, a 1/2 plateau phase also exists in the classical J{sub 1}–J{sub 1}–J{sub 2}–J{sub 2} tetrameric Ising chain. The F–F–AF–AF (or AF–AF–F–F) type longitudinal correlation is found to be important and necessary for the appearance of the 1/2 plateau state in both quantum and classical cases. - Highlights: • 1/2 magnetization plateau can be realized in both quantum and classical cases. • 1/2 plateau is characterized by constant magnetization, entanglement and correlation. • Central charge of the spin-fluid phase is determined to be 1. • F–F–AF–AF correlation is important for the appearance of the 1/2 plateau.
Antiferromagnetic Spin Wave Field-Effect Transistor
Cheng, Ran; Daniels, Matthew W.; Zhu, Jian-Gang; Xiao, Di
2016-04-01
In a collinear antiferromagnet with easy-axis anisotropy, symmetry dictates that the spin wave modes must be doubly degenerate. Theses two modes, distinguished by their opposite polarization and available only in antiferromagnets, give rise to a novel degree of freedom to encode and process information. We show that the spin wave polarization can be manipulated by an electric field induced Dzyaloshinskii-Moriya interaction and magnetic anisotropy. We propose a prototype spin wave field-effect transistor which realizes a gate-tunable magnonic analog of the Faraday effect, and demonstrate its application in THz signal modulation. Our findings open up the exciting possibility of digital data processing utilizing antiferromagnetic spin waves and enable the direct projection of optical computing concepts onto the mesoscopic scale.
Energy Technology Data Exchange (ETDEWEB)
Drichko, Natalia; Hackl, Rudi; Schlueter, John A.
2015-10-15
Using Raman scattering, the quasi-two-dimensional organic superconductor kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br (T-c = 11.8 K) and the related antiferromagnet kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Cl are studied. Raman scattering provides unique spectroscopic information about magnetic degrees of freedom that has been otherwise unavailable on such organic conductors. Below T = 200 K a broad band at about 500 cm(-1) develops in both compounds. We identify this band with two-magnon excitation. The position and the temperature dependence of the spectral weight are similar in the antiferromagnet and in the metallic Fermi liquid. We conclude that antiferromagnetic correlations are similarly present in the magnetic insulator and the Fermi-liquid state of the superconductor.
... Overview » Title IV - Noise Pollution Title IV - Noise Pollution The 1990 Clean Air Act Amendments added a ... abatement 7642 Authorization of appropriations What is Noise Pollution? The traditional definition of noise is “unwanted or ...
Budi-Santoso, Agus; Lesage, Philippe
2016-07-01
We present a study of the seismic velocity variations that occurred in the structure before the large 2010 eruption of Merapi volcano. For the first time to our knowledge, the technique of coda wave interferometry is applied to both families of similar events (multiplets) and to correlation functions of seismic noise. About half of the seismic events recorded at the summit stations belong to one of the ten multiplets identified, including 120 similar events that occurred in the last 20 hr preceding the eruption onset. Daily noise cross-correlation functions (NCF) were calculated for the six pairs of short-period stations available. Using the stretching method, we estimate time-series of apparent velocity variation (AVV) for each multiplet and each pair of stations. No significant velocity change is detected until September 2010. From 10 October to the beginning of the eruption on 26 October, a complex pattern of AVV is observed with amplitude of up to ±1.5 per cent. Velocity decrease is first observed from families of deep events and then from shallow earthquakes. In the same period, AVV with different signs and chronologies are estimated from NCF calculated for various station pairs. The location in the horizontal plane of the velocity perturbations related with the AVV obtained from NCF is estimated by using an approach based on the radiative transfer approximation. Although their spatial resolution is limited, the resulting maps display velocity decrease in the upper part of the edifice in the period 12-25 October. After the eruption onset, the pattern of velocity perturbations is significantly modified with respect to the previous one. We interpret these velocity variations in the framework of a scenario of magmatic intrusion that integrates most observations. The perturbation of the stress field associated with the magma migration can induce both decrease and increase of the seismic velocity of rocks. Thus the detected AVVs can be considered as precursors of
Budi-Santoso, Agus; Lesage, Philippe
2016-04-01
We present a study of the seismic velocity variations that occurred in the structure before the large 2010 eruption of Merapi volcano. For the first time to our knowledge, the technique of Coda Wave Interferometry is applied to both families of similar events (multiplets) and to correlation functions of seismic noise. About half of the seismic events recorded at the summit stations belong to one of the ten multiplets identified, including 120 similar events that occurred in the last 20 hours preceding the eruption onset. Daily noise cross-correlation functions (NCF) were calculated for the six pairs of short-period stations available. Using the stretching method, we estimate time series of apparent velocity variation (AVV) for each multiplet and each pair of stations. No significant velocity change is detected until September 2010. From 10 October to the beginning of the eruption on 26 October, a complex pattern of AVV is observed with amplitude of up to ±1.5%. Velocity decrease is first observed from families of deep events and then from shallow earthquakes. In the same period, AVV with different signs and chronologies are estimated from NCF calculated for various station pairs. The location in the horizontal plane of the velocity perturbations related with the AVV obtained from NCF is estimated by using an approach based on the radiative transfer approximation. Although their spatial resolution is limited, the resulting maps display velocity decrease in the upper part of the edifice in the period 12-25 October. After the eruption onset, the pattern of velocity perturbations is significantly modified with respect to the previous one. We interpret these velocity variations in the framework of a scenario of magmatic intrusion that integrates most observations. The perturbation of the stress field associated with the magma migration can induce both decrease and increase of the seismic velocity of rocks. Thus the detected apparent velocity variations can be
Uranium nitride. A cubic antiferromagnet with anisotropic critical behaviour
International Nuclear Information System (INIS)
Highly anisotropic critical scattering associated with the transition at Tsub(N)=49.5K to the type-I antiferromagnetic structure has been observed in uranium nitride. The transverse susceptibility is found to be unobservably small. The longitudinal susceptibility diverges at Tsub(N) and its anisotropy shows that the spins within the (001) ferromagnetic sheets of the [001] domain are much more highly correlated than they are with the spins lying in adjacent (001) sheets. The correlation range within the sheets is much greater than that expected for a Heisenberg system with the same Tsub(N). The rod-like scattering extended along the spin and domain direction is reminiscent of two-dimensional behaviour. The results are inconsistent with a simple localized model and may reflect the itinerant nature of the 5f electrons. (author)
Antiferromagnets Structure in Adsorbed O2 Monolayers
DEFF Research Database (Denmark)
Nielsen, Mourits; McTague, J. P.
1977-01-01
Neutron diffraction from monolayers of O2 adsorbed on graphite shows structural arrangements similar to the dense planes of bulk O2. At monolayer completion and above, a magnetic superlattice reflection shows well-developed antiferromagnetic order for T ⩽ 10 K. The submonolayer phase also shows...
Magnetic Properties of Nanoparticles of Antiferromagnetic Materials
DEFF Research Database (Denmark)
Mørup, Steen; Frandsen, Cathrine; Bødker, Franz;
2003-01-01
The magnetic properties of antiferromagnetic nanoparticles have been studied by Mossbauer spectroscopy and neutron scattering. Temperature series of Mossbauer spectra of non-interacting, superparamagnetic hematite nanoparticles were fitted by use of the Blume-Tjon relaxation model. It has been fo...
Antiferromagnetic resonance in GdVO4
International Nuclear Information System (INIS)
Microwave spectroscopy is used to study gadolinium orthovanadate in the antiferromagnetic phase, from 2.2 to 1.4 K. AFMR data at 9.4 and 34.8 GHz are analyzed and the temperature dependence for the anisotropy constant is obtained. (author)
Electrical control of antiferromagnetic metal up to 15 nm
Zhang, PengXiang; Yin, GuFan; Wang, YuYan; Cui, Bin; Pan, Feng; Song, Cheng
2016-08-01
Manipulation of antiferromagnetic (AFM) spins by electrical means is on great demand to develop the AFM spintronics with low power consumption. Here we report a reversible electrical control of antiferromagnetic moments of FeMn up to 15 nm, using an ionic liquid to exert a substantial electric-field effect. The manipulation is demonstrated by the modulation of exchange spring in [Co/Pt]/FeMn system, where AFM moments in FeMn pin the magnetization rotation of Co/Pt. By carrier injection or extraction, the magnetic anisotropy of the top layer in FeMn is modulated to influence the whole exchange spring and then passes its influence to the [Co/Pt]/FeMn interface, through a distance up to the length of exchange spring that fully screens electric field. Comparing FeMn to IrMn, despite the opposite dependence of exchange bias on gate voltages, the same correlation between carrier density and exchange spring stiffness is demonstrated. Besides the fundamental significance of modulating the spin structures in metallic AFM via all-electrical fashion, the present finding would advance the development of low-power-consumption AFM spintronics.
Antiferromagnetic character of workplace stress
Watanabe, Jun-Ichiro; Akitomi, Tomoaki; Ara, Koji; Yano, Kazuo
2011-07-01
We study the nature of workplace stress from the aspect of human-human interactions. We investigated the distribution of Center for Epidemiological Studies Depression Scale scores, a measure of the degree of stress, in workplaces. We found that the degree of stress people experience when around other highly stressed people tends to be low, and vice versa. A simulation based on a model describing microlevel human-human interaction reproduced this observed phenomena and revealed that the energy state of a face-to-face communication network correlates with workplace stress macroscopically.
International Nuclear Information System (INIS)
Bipartite entanglement, entanglement spectrum, and Schmidt gap in S=1 bond-alternative antiferromagnetic Heisenberg chain are investigated by the infinite time-evolving block decimation (iTEBD) method. The quantum phase transition (QPT) from the singlet-dimer phase to the Haldane phase can be detected by the singular behavior of bipartite entanglement, the sudden change of the entanglement spectrum, and the completely vanishing of the Schmidt gap. The critical point is determined to be around rc ≃ 0.587, and the second-order character of the QPT is verified. Doubly degenerate entanglement spectra of both even and odd bonds are observed in the Haldane phase, by which one can distinguish the Haldane phase from the singlet-dimer phase easily. Nearest-neighbor antiferromagnetic correlations and next-nearest-neighbor ferromagnetic correlations are found in the whole parameter region. At the critical massless point, although exponentially decaying antiferromagnetic correlation is observed, it approaches to a constant value finally. Therefore, long-range correlations exist and the correlation length becomes divergent at the critical point. (condensed matter: electronic structure, electrical, magnetic, and optical properties)
Dimensional Reduction in Quantum Dipolar Antiferromagnets
Babkevich, P.; Jeong, M.; Matsumoto, Y.; Kovacevic, I.; Finco, A.; Toft-Petersen, R.; Ritter, C.; Mânsson, M.; Nakatsuji, S.; Rønnow, H. M.
2016-05-01
We report ac susceptibility, specific heat, and neutron scattering measurements on a dipolar-coupled antiferromagnet LiYbF4 . For the thermal transition, the order-parameter critical exponent is found to be 0.20(1) and the specific-heat critical exponent -0.25 (1 ) . The exponents agree with the 2D X Y /h4 universality class despite the lack of apparent two-dimensionality in the structure. The order-parameter exponent for the quantum phase transitions is found to be 0.35(1) corresponding to (2 +1 )D . These results are in line with those found for LiErF4 which has the same crystal structure, but largely different TN, crystal field environment and hyperfine interactions. Our results therefore experimentally establish that the dimensional reduction is universal to quantum dipolar antiferromagnets on a distorted diamond lattice.
Heisenberg antiferromagnet on the Husimi lattice
Liao, H. J.; Xie, Z. Y.; Chen, J.; Han, X. J.; Xie, H. D.; Normand, B.; Xiang, T.
2016-02-01
We perform a systematic study of the antiferromagnetic Heisenberg model on the Husimi lattice using numerical tensor-network methods based on projected entangled simplex states. The nature of the ground state varies strongly with the spin quantum number S . For S =1/2 , it is an algebraic (gapless) quantum spin liquid. For S =1 , it is a gapped, nonmagnetic state with spontaneous breaking of triangle symmetry (a trimerized simplex-solid state). For S =2 , it is a simplex-solid state with a spin gap and no symmetry breaking; both integer-spin simplex-solid states are characterized by specific degeneracies in the entanglement spectrum. For S =3/2 , and indeed for all spin values S ≥5/2 , the ground states have 120∘ antiferromagnetic order. In a finite magnetic field, we find that, irrespective of the value of S , there is always a plateau in the magnetization at m =1/3 .
Diffusive magnonic spin transport in antiferromagnetic insulators
Rezende, S. M.; Rodríguez-Suárez, R. L.; Azevedo, A.
2016-02-01
It has been shown recently that a layer of the antiferromagnetic insulator (AFI) NiO can be used to transport spin current between a ferromagnet (FM) and a nonmagnetic metal (NM). In the experiments one uses the microwave-driven ferromagnetic resonance in a FM layer to produce a spin pumped spin current that flows through an AFI layer and reaches a NM layer where it is converted into a charge current by means of the inverse spin Hall effect. Here we present a theory for the spin transport in an AFI that relies on the spin current carried by the diffusion of thermal antiferromagnetic magnons. The theory explains quite well the measured dependence of the voltage in the NM layer on the thickness of the NiO layer.
Antiferromagnetic Stabilization in Ti8O12
Yu, Xiaohu; Qian, Guangrui; Popov, Ivan A; Boldyrev, Alexander I
2015-01-01
Using the evolutionary algorithm USPEX and DFT+U calculations, we predicted a high-symmetry geometric structure of bare Ti8O12 cluster composed of 8 Ti atoms forming a cube, which O atoms are at midpoints of all of its edges, in excellent agreement with experimental results. Using Natural Bond Orbital analysis, Adaptive Natural Density Partitioning algorithm, electron localization function and partial charge plots, we find the origin of the particular stability of bare Ti8O12 cluster: unique chemical bonding where eight electrons of Ti atoms interacting with each other in antiferromagnetic fashion to lower the total energy of the system. The bare Ti8O12 is thus an unusual molecule stabilized by d-orbital antiferromagnetic coupling.
Terahertz Antiferromagnetic Spin Hall Nano-Oscillator
Cheng, Ran; Xiao, Di; Brataas, Arne
2016-05-01
We consider the current-induced dynamics of insulating antiferromagnets in a spin Hall geometry. Sufficiently large in-plane currents perpendicular to the Néel order trigger spontaneous oscillations at frequencies between the acoustic and the optical eigenmodes. The direction of the driving current determines the chirality of the excitation. When the current exceeds a threshold, the combined effect of spin pumping and current-induced torques introduces a dynamic feedback that sustains steady-state oscillations with amplitudes controllable via the applied current. The ac voltage output is calculated numerically as a function of the dc current input for different feedback strengths. Our findings open a route towards terahertz antiferromagnetic spin-torque oscillators.
... EPA Home Air and Radiation Noise Pollution Noise Pollution This page has moved. You should be immediately ... gov/clean-air-act-overview/title-iv-noise-pollution Local Navigation Air & Radiation Home Basic Information Where ...
Emergence of antiferromagnetic ordering in Mn clusters
International Nuclear Information System (INIS)
First-principles density-functional-theory investigations of small Mnn (n=2-7,13) clusters reveal a competition between ferromagnetic and antiferromagnetic ordering of atomic magnetic moments. For smaller sizes (n≤6), this competition results in a near degeneracy between the two types of orderings, whereas AF arrangements are clearly favored for larger clusters. The calculations thus predict a size-dependent transition in the magnetic ordering of Mn clusters
Transformation of spin current by antiferromagnetic insulators
Khymyn, Roman; Lisenkov, Ivan; Tiberkevich, Vasil S.; Slavin, Andrei N.; Ivanov, Boris A.
2015-01-01
It is demonstrated theoretically that a thin layer of an anisotropic antiferromagnetic (AFM) insulator can effectively conduct spin current by excitation of a pair of evanescent AFM spin wave modes. The spin current flowing through the AFM is not conserved due to the interaction between the excited AFM modes and the AFM lattice, and, depending on the excitation conditions, can be either attenuated or enhanced. When the phase difference between the excited evanescent modes is close to $\\pi/2$,...
Room-temperature antiferromagnetic memory resistor
Czech Academy of Sciences Publication Activity Database
Martí, Xavier; Fina, I.; Frontera, C.; Liu, J.; Wadley, P.; He, P.; Paull, R.J.; Clarkson, J.D.; Kudrnovský, Josef; Turek, Ilja; Kuneš, Jan; Yi, D.; Chu, J.-H.; Nelson, C.T.; You, L.; Arenholz, E.; Salahuddin, S.; Fontcuberta, J.; Jungwirth, Tomáš; Ramesh, R.
2014-01-01
Roč. 13, č. 4 (2014), s. 367-374. ISSN 1476-1122 R&D Projects: GA MŠk(CZ) LM2011026; GA ČR(CZ) GAP204/11/1228 Grant ostatní: ERC Advanced Grant 0MSPIN(XE) 268066; AV ČR(CZ) Premium Academiae Institutional support: RVO:68378271 ; RVO:68081723 Keywords : spintronics * antiferromagnets * memories Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 36.503, year: 2014
Ordered Phase in the Fermionized Heisenberg Antiferromagnet
Azakov, S.; Dilaver, M.; Oztas, A. M.
1999-01-01
Thermal properties of the ordered phase of the spin 1/2 isotropic Heisenberg Antiferromagnet on a d-dimensional hypercubical lattice are studied within the fermionic representation when the constraint of single occupancy condition is taken into account by the method suggested by Popov and Fedotov. Using saddle point approximation in path integral approach we discuss not only the leading order but also the fluctuations around the saddle point at one-loop level. The influence of taking into acc...
Phase separation of holes in antiferromagnets
International Nuclear Information System (INIS)
It is shown that dilute holes in an antiferromagnet are unstable against phase separation into a hole-rich phase and a no-hole phase. When the spin exchange interaction J exceeds a critical value Jc, one phase consists of all holes, the other all electrons. The argument is presented in detail for the t--J model but evidence of phase separation in other models is mentioned. 11 refs
Tricritical behavior of the frustrated XY antiferromagnet
Plumer, M. L.; Mailhot, A.; Caillé, A.
1994-01-01
Extensive histogram Monte-Carlo simulations of the XY antiferromagnet on a stacked triangular lattice reveal exponent estimates which strongly favor a scenario of mean-field tricritical behavior for the spin-order transition. The corresponding chiral-order transition occurs at the same temperature but appears to be decoupled from the spin-order. These results are relevant to a wide class of frustrated systems with planar-type order and serve to resolve a long-standing controversy regarding th...
Dynamic rotor mode in antiferromagnetic nanoparticles
Lefmann, K.; Jacobsen, H.; Garde, J; Hedegard, P.; Wischnewski, Andreas; Ancona, S.N.; Jacobsen, H. S.; Bahl, C R H; Theil Kuhn, L.
2015-01-01
We present experimental, numerical, and theoretical evidence for an unusual mode of antiferromagnetic dynamics in nanoparticles. Elastic neutron scattering experiments on 8-nm particles of hematite display a loss of diffraction intensity with temperature, the intensity vanishing around 150 K. However, the signal from inelastic neutron scattering remains above that temperature, indicating a magnetic system in constant motion. In addition, the precession frequency of the inelastic magnetic sign...
A quadrangular transverse Ising nanowire with an antiferromagnetic spin configuration
Kaneyoshi, T.
2015-11-01
The phase diagrams and the temperature dependences of magnetizations in a transverse Ising nanowire with an antiferromagnetic spin configuration are investigated by the use of the effective-field theory with correlations (EFT) and the core-shell concept. Many characteristic and unexpected behaviors are found for them, especially for thermal variation of total magnetization mT. The reentrant phenomenon induced by a transverse field in the core, the appearance of a compensation point, the non-monotonic variation with a compensation point, the reentrant phenomena with a compensation point and the existence of both a broad maximum and a compensation point have been found in the thermal variations of mT.
Partially informed noise traders
Aase, Knut K.; Bjuland, Terje; Øksendal, Bernt
2012-01-01
The single auction equilibrium of Kyle’s (1985) is studied, in which noise traders may be partially informed, or alternatively they can be manipulated. Unlike Kyle’s assumption that the quantity traded by the noise traders is independent of the asset value, we assume that the noise traders are able to correlate their trade with the true price. This has several implications for the equilibrium, one being that the informed trader’s expected profits decrease as the noise traders’ ability to corr...
Universality in antiferromagnetic strange metals
Maier, Stefan A.; Strack, Philipp
2016-04-01
We propose a theory of metals at the spin-density-wave quantum-critical point in spatial dimension d =2 . We provide a first estimate of the full set of critical exponents (dynamical exponent z =2.13 , correlation length ν =1.02 , spin susceptibility γ =0.96 , electronic non-Fermi liquid ητf=0.53 , spin-wave Landau damping ητb=1.06 ), which determine the universal power laws in thermodynamics and response functions in the quantum-critical regime relevant for experiments in heavy-fermion systems and iron pnictides. We present approximate numerical and analytical solutions of Polchinski-Wetterich-type flow equations with soft frequency regulators for an effective action of electrons coupled to spin-wave bosons. Performing the renormalization group in frequency instead of momentum space allows to track changes of the Fermi-surface shape and to capture Landau damping during the flow. The technique is easily generalizable from models retaining only patches of the Fermi surface to full, compact Fermi surfaces.
Vassallo, Maurizio; Festa, Gaetano; Bobbio, Antonella; Serra, Marcello
2016-06-01
We extracted the Green's functions from cross correlation of ambient noise recorded at broadband stations located across the Apennine belt, Southern Italy. Continuous records at 26 seismic stations acquired for 3 years were analyzed. We found the emergence of surface waves in the whole range of the investigated distances (10-140 km) with energy confined in the frequency band 0.04-0.09 Hz. This phase reproduces Rayleigh waves generated by earthquakes in the same frequency range. Arrival time of Rayleigh waves was picked at all the couples of stations to obtain the average group velocity along the path connecting the two stations. The picks were inverted in separated frequency bands to get group velocity maps then used to obtain an S wave velocity model. Penetration depth of the model ranges between 12 and 25 km, depending on the velocity values and on the depth of the interfaces, here associated to strong velocity gradients. We found a low-velocity anomaly in the region bounded by the two main faults that generated the 1980, M 6.9 Irpinia earthquake. A second anomaly was retrieved in the southeast part of the region and can be ascribed to a reminiscence of the Adria slab under the Apennine Chain.
International Nuclear Information System (INIS)
In this report we describe the concept of adaptive noise canceling, an alternative method of estimating signals corrupted by additive noise of interference. The method uses 'primary' input containing the corrupted signal and a 'reference' input containing noise correlated in some unknown way with the primary noise, the reference input is adaptively filtered and subtracted from the primary input to obtain the signal estimate. Adaptive filtering before subtraction allows the treatment of inputs that are deterministic or stochastic, stationary or time variable. When the reference input is free of signal and certain other conditions are met then noise in the primary input can be essentially eliminated without signal distortion. It is further shown that the adaptive filter also acts as notch filter. Simulated results illustrate the usefulness of the adaptive noise canceling technique. (author)
Ferromagnetic response of a ``high-temperature'' quantum antiferromagnet
Wang, Xin
2014-03-01
We study the antiferromagnetic phase of the ionic Hubbard model at finite temperature using dynamical mean-field theory. We find that the ionic potential plays a dual role in determining the antiferromagnetic order. A small ionic potential (compared to the Hubbard repulsion) increases the super-exchange coupling, thereby implying an increase of the Neel temperature of the system, which should facilitate observation of antiferromagnetic ordering experimentally. On the other hand, for large ionic potential, the antiferromagnetic ordering is killed and the system becomes a charge density wave with electron occupancies alternating between 0 and 2. This novel way of degrading antiferromagnetism leads to spin polarization of the low energy single particle density of states. The dynamic response of the system thus mimics ferromagnetic behavior, although the system is still an antiferromagnet in terms of the static spin order. Work done in collaboration with Rajdeep Sensarma and Sankar Das Sarma, and supported by NSF-JQI-PFC, AFOSR MURI, and ARO MURI.
Witek, M.; Kang, T. S.; van der Lee, S.
2015-12-01
We have collected three-component data from 122 Korean accelerometer stations for the month of December in 2014. We apply similar techniques described by Zha et al. (2013) to retrieve accurate station orientation angles, in order to rotate the horizontal component data into the radial and transverse frame of reference, and for subsequent measurement of Love wave group velocity dispersion. We simultaneously normalize all three components of a daily noise record via the frequency-time normalization (FTN) method. Each component is divided by the average signal envelope in an effort to retain relative amplitude information between all three components. Station orientations are found by a grid search for the orientation azimuth which maximizes the coherency between the radial-vertical cross-correlation and the Hilbert transformed vertical-vertical cross-correlation. After measuring orientation angles, we cross-correlate and rotate the data. Typically, the group velocity dispersion curves are measured using the frequency time analysis technique (FTAN), effectively producing spectrograms with significant uncertainty in the time-frequency plane. The spectrogram approach retains only the amplitude information of the short-time Fourier transform (STFT). However, Kodera et al (1976) show that by taking into account the phase information, the concepts of instantaneous frequency and group-time delay can be used to compute the first moment of the signal power in the frequency and time domains. During energy reassignment, the signal power calculated using the STFT at a point (t0,f0t_0, f_0) is reassigned to the location of the first moment (t^g,f^ihat{t}_g,hat{f}_i), where t^ghat{t}_g is the group-time delay and f^ihat{f}_i is the instantaneous frequency. We apply the method of energy reassignment to produce precise Rayleigh and Love wave group velocity measurements in the frequency range 0.1 - 1.0 Hz. Tests on synthetic data show more accurate retrieval of group velocities at
Methods for noise abatement are discussed. Noise nuisance, types of noise (continuous, fluctuating, intermittent, pulsed), and types of noise abatement (absorption, vibration damping, isolation) are defined. Rockwool panels, industrial ceiling panels, baffles, acoustic foam panels, vibration dampers, acoustic mats, sandwich panels, isolating cabins and walls, ear protectors, and curtains are presented.
Barbon, Jose L F
2014-01-01
We study the fine structure of long-time quantum noise in correlation functions of AdS/CFT systems. Under standard assumptions of quantum chaos for the dynamics and the observables, we estimate the size of exponentially small oscillations and trace them back to geometrical features of the bulk system. The noise level is highly suppressed by the amount of dynamical chaos and the amount of quantum impurity in the states. This implies that, despite their missing on the details of Poincare recurrences, `virtual' thermal AdS phases do control the overall noise amplitude even at high temperatures where the thermal ensemble is dominated by large AdS black holes. We also study EPR correlations and find that, in contrast to the behavior of large correlation peaks, their noise level is the same in TFD states and in more general highly entangled states.
Němcová, Michaela
2015-01-01
The aim of this paper is to introduce the measurement of noise and create a noise map in a geographic information system. The first part is focused on describing the physical properties of sound in space, atmospheric and physiological acoustics. It also deals with the physiological effects of noise on the human body and technology needed for measure and process noise. Other part describes the structure of a geographic information system and noise map. The last part is about the practical crea...
Liikonen, Larri; Alanko, Mikko; Jokinen, Sirpa; Niskanen, Ilkka; Virrankoski, Lauri
2007-01-01
Planning snowmobiling routes and considering the possible need for off-road traffic restrictions requires that the noise impact of snowmobile traffic is known. The objective of this report was to take off-road readings in order to determine snowmobile noise emissions and the spread of noise from snowmobile routes into the environment. Based on the readings taken, it can be said that the noise zones created by snowmobile traffic are quite narrow at current traffic levels. Noise pollution ca...
Mehran zolfaghari
1996-01-01
Various risk factors in industrial environments can affect hearing status and healthy in today’s modern society. Noise control and hearing conservation program is very crucial in preventing workers exposed to high levels of noise in the work places. In the current article we are going to discuss issues such as industrial noise control, noise characteristics and standards and techniques for noise control. Then the methods for individual hearing conservation and medical care will be described i...
Viney, Mark; Reece, Sarah E.
2013-01-01
In biology, noise implies error and disorder and is therefore something which organisms may seek to minimize and mitigate against. We argue that such noise can be adaptive. Recent studies have shown that gene expression can be noisy, noise can be genetically controlled, genes and gene networks vary in how noisy they are and noise generates phenotypic differences among genetically identical cells. Such phenotypic differences can have fitness benefits, suggesting that evolution can shape noise ...
Room temperature write-read operations in antiferromagnetic memory
Moriyama, Takahiro; Matsuzaki, Noriko; Kim, Kab-Jin; Suzuki, Ippei; Taniyama, Tomoyasu; Ono, Teruo
2015-01-01
B2-ordered FeRh has been known to exhibit antiferromagnetic-ferromagnetic (AF-F) phase transitions in the vicinity of room temperature. Manipulation of the N\\'eel order via AF-F phase transition and recent experimental observation of the anisotropic magnetoresistance in antiferromagnetic FeRh has proven that FeRh is a promising candidate for antiferromagnetic memory material. In this work, we demonstrate sequential write and read operations in antiferromagnetic memory resistors made of B2-ord...
Directory of Open Access Journals (Sweden)
V.V. Kulish
2015-06-01
Full Text Available The paper investigates the antiferromagnetic vector distribution in an antiferromagnetic film with a system of antidots. A static distribution of the antiferromagnetic vector is written and a method – based on the minimization of the antiferromagnet energy – that allows reducing the number of boundary conditions required for finding the constants of this distribution is proposed. Equations for the distribution constants are obtained for the both cases of minimizing the antiferromagnet energy by one and by two distribution constants that enter the expression for the antiferromagnet energy. The method is illustrated on a system of one isolated antidot. For such system, one additional condition – for the case when two boundary conditions on the surface of the antidot are given – and two additional conditions – for the case when one boundary condition on the surface of the antidot is given – on the distribution constants are written.
Costanzo, M. R.; Nunziata, C.
2014-09-01
Cross-correlation functions of long noise recordings with two broadband stations and earthquake recordings in the Campanian Plain have been processed with frequency time analysis to extract the fundamental mode of Rayleigh waves. Group velocities have been combined with regional group and phase velocity data in the non-linear inversion, with Hedgehog method, in order to get average shear wave velocity models for lithospheric structures extending to 73 km of depth. The structural model below the central part of the Campanian Plain is characterized by a covering of pyroclastics and alluvial sediments, about 2 km thick, on the carbonate platform with VS ranging from 2.30-2.40 to 2.85-3.15 km/s. However, the presence of lava bodies within the carbonates cannot be excluded in the light of the same density and seismic velocities. At greater depths, a main feature is represented by a sharp increment of velocity around 8-9 km of depth (VS of 3.85 km/s), which can be attributed to the presence of metamorphic rocks, overlying a low VS layer (5% velocity reduction), at about 14-15 km of depth. Such structural model resembles those found below the quiescent Roccamonfina and Colli Albani volcanoes, and can be interpreted as the signature of a cooling magma chamber. Moreover, a low VS layer is detected at 8-9 km of depth towards the Apennines and at 6 km of depth in the southernmost part of the Campanian Plain, nearby Mt. Vesuvius. Such low velocity layer seems to be a regional feature since it has been found below Roccamonfina in the North, Campi Flegrei, bay of Napoli and Mt. Vesuvius in the South, and can be explained by the widespread presence of partially melted material below the whole Campanian area.
Gu, Bo; Su, Gang; Gao, Song
2006-04-01
The magnetization process, the susceptibility, and the specific heat of the spin- 1/2 antiferromagnet (AF)-AF-ferromagnet (F) and F-F-AF trimerized quantum Heisenberg chains have been investigated by means of the transfer matrix renormalization group (TMRG) technique as well as the modified spin-wave (MSW) theory. A magnetization plateau at m=1/6 for both trimerized chains is observed at low temperature. The susceptibility and the specific heat show various behaviors for different ferromagnetic and antiferromagnetic interactions and in different magnetic fields. The TMRG results of susceptibility and the specific heat can be nicely fitted by a linear superposition of double two-level systems, where two fitting equations are proposed. Three branch excitations, one gapless excitation and two gapful excitations, for both systems are found within the MSW theory. It is observed that the MSW theory captures the main characteristics of the thermodynamic behaviors at low temperatures. The TMRG results are also compared with the possible experimental data.
Classical and quantum anisotropic Heisenberg antiferromagnets
Directory of Open Access Journals (Sweden)
W. Selke
2009-01-01
Full Text Available We study classical and quantum Heisenberg antiferromagnets with exchange anisotropy of XXZ-type and crystal field single-ion terms of quadratic and quartic form in a field. The magnets display a variety of phases, including the spin-flop (or, in the quantum case, spin-liquid and biconical (corresponding, in the quantum lattice gas description, to supersolid phases. Applying ground-state considerations, Monte Carlo and density matrix renormalization group methods, the impact of quantum effects and lattice dimension is analysed. Interesting critical and multicritical behaviour may occur at quantum and thermal phase transitions.
Switching of antiferromagnetic chains with magnetic pulses
Tao, Kun; Polyakov, Oleg P.; Stepanyuk, Valeri S.
2016-04-01
Recent experimental studies have demonstrated the possibility of information storage in short antiferromagnetic chains on an insulator substrate [S. Loth et al., Science 335, 196 (2012), 10.1126/science.1214131]. Here, using the density functional theory and atomistic spin dynamics simulations, we show that a local magnetic control of such chains with a magnetic tip and magnetic pulses can be used for fast switching of their magnetization. Furthermore, by changing the position of the tip one can engineer the magnetization dynamics of the chains.
Small antiferromagnetic spin systems-Sublattice Hamiltonians
International Nuclear Information System (INIS)
A few examples of four-spin Heisenberg systems with dominant antiferromagnetic couplings are considered. All systems can be described by the so-called sublattice Hamiltonian H=SA.SB or its modifications, where SX is the total spin of a sublattice X=A, B. In such a case (eigen)energies are simple functions of the total spin number S, total spins of sublattices SA, SB, and the Hamiltonian parameters (ratios of exchange integrals). Moreover, eigenstates are strictly determined by a coupling scheme assumed and the appropriate Clebsch-Gordan coefficients. In this sense the systems considered are classical ones.
Antiferromagnetic topological insulators in cold atomic gases
Essin, Andrew M.; Gurarie, Victor
2011-01-01
We propose a spin-dependent optical lattice potential that realizes a three-dimensional antiferromagnetic topological insulator in a gas of cold, two-state fermions such as alkaline earths, as well as a model that describes the tight-binding limit of this potential. We discuss the physically observable responses of the gas that can verify the presence of this phase. We also point out how this model can be used to obtain two-dimensional flat bands with nonzero Chern number.
The electronic structure of antiferromagnetic chromium
DEFF Research Database (Denmark)
Skriver, Hans Lomholt
1981-01-01
The author has used the local spin density formalism to perform self-consistent calculations of the electronic structure of chromium in the non-magnetic and commensurate antiferromagnetic phases, as a function of the lattice parameter. A change of a few per cent in the atomic radius brings...... the calculated ground state properties into agreement with experiment. The magnetisation is studied as function of volume in several models, and it is shown that a Stoner picture provides an extremely accurate description of the full calculation provided the sp-d hybridisation is taken into account. It is found...
Lattice distortion in disordered antiferromagnetic XY models
Institute of Scientific and Technical Information of China (English)
Li Peng-Fei; Cao Hai-Jing
2012-01-01
The behavior of lattice distortion in spin 1/2 antiferromagnetic XY models with random magnetic modulation is investigated with the consideration of spin-phonon coupling in the adiabatic limit.It is found that lattice distortion relies on the strength of the random modulation.For strong or weak enough spin-phonon couplings,the average lattice distortion may decrease or increase as the random modulation is strengthened.This may be the result of competition between the random magnetic modulation and the spin-phonon coupling.
Anisotropic magnetoresistance in an antiferromagnetic semiconductor
Czech Academy of Sciences Publication Activity Database
Fina, I.; Martí, Xavier; Yi, D.; Liu, J.; Chu, J.-H.; Rayan-Serrao, C.; Suresha, S.; Shick, Alexander; Železný, Jakub; Jungwirth, Tomáš; Fontcuberta, J.; Ramesh, R.
2014-01-01
Roč. 5, SEP (2014), "4671-1"-"4671-7". ISSN 2041-1723 R&D Projects: GA MŠk(CZ) LM2011026; GA ČR GB14-37427G; GA ČR(CZ) GAP204/10/0330 Grant ostatní: ERC Advanced Grant 0MSPIN(XE) 268066; AV ČR(CZ) Premium Academiae Institutional support: RVO:68378271 Keywords : antiferromagnets * semiconductors * spintronic s Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 11.470, year: 2014
Edge states in Open Antiferromagnetic Heisenberg Chains
Qin, Shaojin; Ng, Tai-Kai; Su, Zhao-Bin
1995-01-01
In this letter we report our results in investigating edge effects of open antiferromagnetic Heisenberg spin chains with spin magnitudes $S=1/2, 1,3/2,2$ using the density-matrix renormalization group (DMRG) method initiated by White. For integer spin chains, we find that edge states with spin magnitude $S_{edge}=S/2$ exist, in agreement with Valence-Bond-Solid model picture. For half-integer spin chains, we find that no edge states exist for $S=1/2$ spin chain, but edge state exists in $S=3/...
Noise-improved Signal Correlation in a Nonlinear Network System%一类非线性网络系统中噪声改善信号的相关性
Institute of Scientific and Technical Information of China (English)
王友国; 郑克; 陆望
2014-01-01
Based on correlation coefficient the Suprathreshold Stochastic Resonance ( SSR) phenomenon under additive and multiplicative noise in a nonlinear neural network system is studied. When the system is only affected by one kind of noise,e. g. the additive noise or multiplicative noise,under different system threshold,additive noise is easier for SSR phenomenon to occur than multiplicative noise. For a fixed threshold,the additive noise is superior to multiplicative noise for signal transmission since the resonance peak value under the ad-ditive noise is larger than that under the multiplicative noise. The increase of network threshold cuts down the efficiency of SSR,while the increase of unit number plays a positive role in the emergence and effect of SSR. The composing noise mixed by additive noise and multi-plicative noise can also arouse SSR in such a system. A reasonable threshold value and a larger unit number would lead to a more signifi-cant SSR. Fixing multiplicative noise and changing additive noise,the SSR phenomenon is more likely to happen and gets a better effect than under the contrary operation. It is an extension of noise benefits in signal processing.%基于相关系数研究了在一类非线性神经网络系统中加性和乘性噪声作用下的阈上随机共振现象。仅在加性噪声或者乘性噪声的作用下，对每一个固定的系统阈值，加性噪声下的阈上随机共振比乘性噪声下的阈上随机共振更容易发生，且相关系数所达到的峰值也比在乘性噪声下的峰值大，这说明加性噪声更有利于改善信号的相关性。系统阈值的增加会降低阈上随机共振的功效；而阈值单元数目的增多，会提高阈上随机共振的功效。加性和乘性噪声共同作用下的阈上随机共振现象同样存在，对系统阈值进行恰当选取和增加系统阈值单元数目使得阈上随机共振现象更加明显；给定乘性噪声而改变加性噪声比固定加性
一种矢量相关性的抗噪声边缘检测方法%An anti-noise edge detection method based on vector correlation
Institute of Scientific and Technical Information of China (English)
王文宁
2014-01-01
对图像中常见的高斯噪声特性进行了分析，对含有较强高斯噪声的数字图像的边缘检测方法进行了研究。分析了边缘的方向性相关特征和连续性相关特征，设计了图像特征矢量图，检测图像特征矢量相关的相似度，提取出抗噪声的图像边缘检测方法。仿真验证表明，对于含有较强高斯噪声的图像，本方法能够有效抑制噪声，而且能够提取出准确清晰的边缘。本算法在噪声图像中能很好地克服普通算子的噪声问题，而且算法简单，计算量较少。%This article analyses the Gauss noise characteristics of common image , studies the edge detection method based on digital image which contains a strong Gauss noise. It analyses directional correlation feature edges and continuity characteristics , design the image feature vector, detects similarity of image feature vector related, extract image edge detection method of anti-noise. The simulation results show that, for images with a strong Gauss noise, the proposed method can effectively suppress the noise, and can extract accurate and clear edge. This method can well overcome the noise problem of common operators in noise image , but also has a simple algorithm with less calculation.
Noise in Genotype Selection Model
Institute of Scientific and Technical Information of China (English)
AI Bao-Quan; CHEN Wei; WANG Xian-Ju; LIU Guo-Tao; WEN De-Hua; LIU Liang-Gang
2003-01-01
We study the steady state properties ofa genotype selection model in presence of correlated Gaussian whitenoise. The effect of the noise on the genotype selection model is discussed. It is found that correlated noise can breakthe balance of gene selection and induce the phase transition which can makes us select one type gene haploid from agene group.
Community reaction to noise from power stations
International Nuclear Information System (INIS)
Community reaction is a major consideration in noise control. The relationship between noise exposure and community reaction has received considerable attention in relation to railway, traffic, aircraft and impulsive noise. The results have shown a number of features in common, including: similarly shaped noise/reaction functions; similar results across different measurement techniques and cultures, noise/reaction correlations based on individual respondent data are low (mean r = 0.42 ± 0.12: Job, 1988), although correlations of .58 and above have been reported correlations based on data grouped by noise exposure are generally high and relatively unaffected by the type of noise studied whereas correlations based on individual data tend to be lower for impulsive noise than for transportation noise attitude to the noise source and sensitivity to noise shows strong correlations with reaction. This paper reports that the present study was undertaken in order toe establish over a wider range of noise exposure whether community reaction to power station noise is similar to reaction to other types of non-impulsive noise. It is possible that reaction is different given important differences in the source of the noise which may affect attitude. Attitudes towards power stations may be more positive than attitudes to aircraft or rail noise for example, because almost all respondents use electricity regularly every day. Further, the power stations in the present study provided employment for the relatively small surrounding communities
Quantum Heisenberg antiferromagnets: a survey of the activity in Firenze
International Nuclear Information System (INIS)
Over the years the research group in Firenze has produced a number of theoretical results concerning the statistical mechanics of quantum antiferromagnetic models, which range from the theory of two-magnon Raman scattering to the characterization of the phase transitions in quantum low-dimensional antiferromagnetic models. Our research activity was steadily aimed to the understanding of experimental observations
Nonequilibrium spin noise spectroscopy
Li, Fuxiang; Pershin, Yuriy V.; Slipko, Valeriy A.; Sinitsyn, Nikolai A.
2013-01-01
Spin Noise Spectroscopy (SNS) is an experimental approach to obtain correlators of mesoscopic spin fluctuations in time by purely optical means. We explore the information that this technique can provide when it is applied to a weakly non-equilibrium regime when an electric current is driven through a sample by an electric field. We find that the noise power spectrum of conducting electrons experiences a shift, which is proportional to the strength of the spin-orbit coupling for electrons mov...
Hanafy, Sherif M.
2015-08-19
We use controlled noise seismology (CNS) to generate surface waves, where we continuously record seismic data while generating artificial noise along the profile line. To generate the CNS data we drove a vehicle around the geophone line and continuously recorded the generated noise. The recorded data set is then correlated over different time windows and the correlograms are stacked together to generate the surface waves. The virtual shot gathers reveal surface waves with moveout velocities that closely approximate those from active source shot gathers.
Directory of Open Access Journals (Sweden)
P. Sahebsara
2006-09-01
Full Text Available The self-energy-functional approach is a powerful many-body tool to investigate different broken symmetry phases of strongly correlated electron systems. We use the variational cluster perturbation theory (also called the variational cluster approximation to investigate the interplay between the antiferromagnetism and d-wave superconductivity of κ-(ET2 X conductors. These compounds are described by the so-called dimer Hubbard model, with various values of the on-site repulsion U and diagonal hopping amplitude t. At strong coupling, our zero-temperature calculations show a transition from Néel antiferromagnetism to a spin-liquid phase with no long range order, at around t ~ 0.9. At lower values of U, we find d-wave superconductivity. Taking into account the point group symmetries of the lattice, we find a transition between dx2-y2 and dxy pairing symmetries, the latter happening for smaller values of U.
Molecular orbital study on antiferromagnetic coupling mechanism in a silver (I) complex
Institute of Scientific and Technical Information of China (English)
ZHANG Guiqin; HUANG Jiangen; HUANG Yuanhe; FANG Decai; ZHANG Deqing
2005-01-01
The mechanism of antiferromagnetic coupling in an Ag (I) complex of nitronyl nitroxide is investigated by means of the broken-symmetry approach within the density functional method (DFT-BS). The magneto-structural correlation and the single-occupied molecular orbital (SOMO) analysis reveal the existence of the antiferromagnetic coupling pathway along nitronyl nitroxide units via Ag (I) ion, and that the Ag (I) ion plays an important bridge role. The spin population analysis also shows the existence of spin delocalization along the ONCNO-Ag-ONCNO chain. It is found that the non-typical covalent bonds with major ionic character between Ag (I) ions and oxygen atoms of nitronyl nitroxide units can be used to mediate the spin-spin interaction of nitronyl nitroxides.
Paul Voice
2009-01-01
In this paper I argue that noise is a significant source of social harm and thoseharmed by noise often suffer not merely a misfortune but an injustice. I arguethat noise is a problem of justice in two ways; firstly, noise is a burden of socialcooperation and so the question of the distribution of this burden arises. And,secondly, some noises, although burdensome, are nevertheless just becausethey arise from practices that are ‘reasonable’. I offer a number of distinctions,between necessary an...
Wind turbine noise source characterization
International Nuclear Information System (INIS)
Wind turbine noise is a function of many parameters. Aerodynamics noise is a direct function of the rotor characteristics and wind speed, which can change rapidly with time. Mechanical noise is primarily a function of electrical power output, but the radiation of such noise is highly modified by vibration behaviour within the turbine. An experiment has been performed to isolate the behaviour of the major WTG noise sources with respect to electrical power output and wind speed. Twelve ground based microphones equispaced around the turbine gave detailed noise directionality information. Additional instrumentation was added to allow the separation of aerodynamic and mechanical noise components. Noise was found to be very well correlated to electrical power output. (author)
Spin correlations in percolating networks with fractal geometry
International Nuclear Information System (INIS)
Using neutron scattering techniques, the authors investigated the magnetic correlations in diluted antiferromagnets close to the percolation threshold in which the magnetic connectivity takes a fractal form. Recent experimental results concerning the self-similarity of the magnetic order, and magnetic excitations in two-dimensional Ising and three-dimensional Heisenberg antiferromagnets are presented
Spin correlations in percolating networks with fractal geometry
Energy Technology Data Exchange (ETDEWEB)
Ikeda, H.; Iwasa, K. [Keio Univ., Hiyoshi (Japan); Fernandez-Baca, J.A.; Nicklow, R.M. [Oak Ridge National Lab., TN (United States)
1994-07-28
Using neutron scattering techniques, the authors investigated the magnetic correlations in diluted antiferromagnets close to the percolation threshold in which the magnetic connectivity takes a fractal form. Recent experimental results concerning the self-similarity of the magnetic order, and magnetic excitations in two-dimensional Ising and three-dimensional Heisenberg antiferromagnets are presented.
Enhanced antiferromagnetic coupling in dual-synthetic antiferromagnet with Co2FeAl electrodes
Zhang, D. L.; Xu, X. G.; Wu, Y.; Li, X. Q.; Miao, J.; Jiang, Y.
2012-05-01
We study dual-synthetic antiferromagnets (DSyAFs) using Co2FeAl (CFA) Heusler electrodes with a stack structure of Ta/CFA/Ru/CFA/Ru/CFA/Ta. When the thicknesses of the two Ru layers are 0.45 nm, 0.65 nm or 0.45 nm, 1.00 nm, the CFA-based DSyAF has a strong antiferromagnetic coupling between adjacent CFA layers at room temperature with a saturation magnetic field of ∼11,000 Oe, a saturation magnetization of ∼710 emu/cm3 and a coercivity of ∼2.0 Oe. Moreover, the DSyAF has a good thermal stability up to 400 °C, at which CFA films show B2-ordered structure. Therefore, the CFA-based DSyAFs are favorable for applications in future spintronic devices.
Schmitz, F. H.
1991-01-01
The physical characteristics and sources of rotorcraft noise as they exist today are presented. Emphasis is on helicopter-like vehicles, that is, on rotorcraft in nonaxial flight. The mechanisms of rotor noise are reviewed in a simple physical manner for the most dominant sources of rotorcraft noise. With simple models, the characteristic time- and frequency-domain features of these noise sources are presented for idealized cases. Full-scale data on several rotorcraft are then reviewed to allow for the easy identification of the type and extent of the radiating noise. Methods and limitations of using scaled models to test for several noise sources are subsequently presented. Theoretical prediction methods are then discussed and compared with experimental data taken under very controlled conditions. Finally, some promising noise reduction technology is reviewed.
Probing the evolution of antiferromagnetism in multiferroics
Energy Technology Data Exchange (ETDEWEB)
Holcomb, M.; Martin, L.; Scholl, A.; He, Q.; Yu, P.; Yang, C.-H.; Yang, S.; Glans, P.-A.; Valvidares, M.; Huijben, M.; Kortright, J.; Guo,, J.; Chu, Y.-H.; Ramesh, R.
2010-06-09
This study delineates the evolution of magnetic order in epitaxial films of the room-temperature multiferroic BiFeO3 system. Using angle- and temperature-dependent dichroic measurements and spectromicroscopy, we have observed that the antiferromagnetic order in the model multiferroic BiFeO3 evolves systematically as a function of thickness and strain. Lattice-mismatch-induced strain is found to break the easy-plane magnetic symmetry of the bulk and leads to an easy axis of magnetization which can be controlled through strain. Understanding the evolution of magnetic structure and how to manipulate the magnetism in this model multiferroic has significant implications for utilization of such magnetoelectric materials in future applications.
Dynamic rotor mode in antiferromagnetic nanoparticles
DEFF Research Database (Denmark)
Lefmann, Kim; Jacobsen, H.; Garde, J.;
2015-01-01
We present experimental, numerical, and theoretical evidence for an unusual mode of antiferromagnetic dynamics in nanoparticles. Elastic neutron scattering experiments on 8-nm particles of hematite display a loss of diffraction intensity with temperature, the intensity vanishing around 150 K....... However, the signal from inelastic neutron scattering remains above that temperature, indicating a magnetic system in constant motion. In addition, the precession frequency of the inelastic magnetic signal shows an increase above 100 K. Numerical Langevin simulations of spin dynamics reproduce all...... measured neutron data and reveal that thermally activated spin canting gives rise to an unusual type of coherent magnetic precession mode. This "rotor" mode can be seen as a high-temperature version of superparamagnetism and is driven by exchange interactions between the two magnetic sublattices. The...
Ising antiferromagnet on the Archimedean lattices
Yu, Unjong
2015-06-01
Geometric frustration effects were studied systematically with the Ising antiferromagnet on the 11 Archimedean lattices using the Monte Carlo methods. The Wang-Landau algorithm for static properties (specific heat and residual entropy) and the Metropolis algorithm for a freezing order parameter were adopted. The exact residual entropy was also found. Based on the degree of frustration and dynamic properties, ground states of them were determined. The Shastry-Sutherland lattice and the trellis lattice are weakly frustrated and have two- and one-dimensional long-range-ordered ground states, respectively. The bounce, maple-leaf, and star lattices have the spin ice phase. The spin liquid phase appears in the triangular and kagome lattices.
Quantum Phase Transitions in Antiferromagnets and Superfluids
Sachdev, Subir
2000-03-01
A general introduction to the non-zero temperature dynamic and transport properties of low-dimensional systems near a quantum phase transition shall be presented. Basic results will be reviewed in the context of experiments on the spin-ladder compounds. Recent large N computations (M. Vojta and S. Sachdev, Phys. Rev. Lett. 83), 3916 (1999) on an extended t-J model motivate a global scenario of the quantum phases and transitions in the high temperature superconductors, and connections will be made to numerous experiments. A universal theory (S. Sachdev, C. Buragohain, and M. Vojta, Science, in press M. Vojta, C. Buragohain, and S. Sachdev, cond- mat/9912020) of quantum impurities in spin-gap antiferromagnets near a magnetic ordering transition will be compared quantitatively to experiments on Zn doped Y Ba2 Cu3 O7 (Fong et al.), Phys. Rev. Lett. 82, 1939 (1999)
Order and disorder in two geometrically frustrated antiferromagnets
International Nuclear Information System (INIS)
2Ti2O7, by N. P. Raju, M. Dion, M. J. P. Gingras, T. E. Mason, and J. E. Greedan, Phys. Rev. B 59, 14489 (1999). Our second study, the results of which appear in Chapter 4, addresses the question of whether the ground state for the spin-1/2 nearest- neighbor antiferromagnetic Heisenberg model on a version of the pyrochlore lattice in 2D is ordered or disordered. We perform exact diagonalization calculations on small clusters of spins on this lattice. From an analysis of the low-lying energy levels in these systems, we find a large gap to spin excitations which does not appear to close in the thermodynamic limit. We see no order, as evidenced by measurements of ground state correlation functions and the structure of the low energy excitation spectrum. We find that spin-spin and spin-Peierls correlations decay rapidly with distance and that a large number of non-magnetic states fill the spin gap. Comparing our results to other exact diagonalization studies of the same model on the triangular and kagome lattices, we conclude that there is no Neel order in the ground state for this system. (author)
Directory of Open Access Journals (Sweden)
Alain Destexhe
2010-03-01
Full Text Available Cortical neurons in vivo may operate in high-conductance states, in which the major part of the neuron's input conductance is due to synaptic activity, sometimes several-fold larger than the resting conductance. We examine here the contribution of inhibition in such high-conductance states. At the level of the absolute conductance values, several studies have shown that cortical neurons in vivo are characterized by strong inhibitory conductances. However, conductances are balanced and spiking activity is mostly determined by fluctuations, but not much is known about excitatory and inhibitory contributions to these fluctuations. Models and dynamic-clamp experiments show that, during high-conductance states, spikes are mainly determined by fluctuations of inhibition, or by inhibitory noise. This stands in contrast to low-conductance states, in which excitatory conductances determine spiking activity. To determine these contributions from experimental data, maximum likelihood methods can be designed and applied to intracellular recordings in vivo. Such methods indicate that action potentials are indeed mostly correlated with inhibitory fluctuations in awake animals. These results argue for a determinant role for inhibitory fluctuations in evoking spikes, and do not support feed-forward modes of processing, for which opposite patterns are predicted.
Bose-Einstein condensation in antiferromagnets at low temperatures
International Nuclear Information System (INIS)
The Bose-Einstein condensation (BEC) was predicted by Einstein in 1925 and this effect is characterized by the formation of a collective quantum state, when macroscopic number of particles is governed by a single wave function. The BEC of magnons was discovered experimentally in superfluid phase of 3He. In the present work we report our progress on the BEC of magnons investigations in solid antiferromagnets at low temperatures by magnetic resonance methods. The duration of the FID signal in two samples of easy-plane antiferromagnets CsMnF3 has been studied. Obtained data confirm the formation of magnon BEC in antiferromagnet CsMnF3
Electron spin resonance study of NiO antiferromagnetic nanoparticles
International Nuclear Information System (INIS)
The electron spin resonance (ESR) spectra of antiferromagnetic nanoparticle NiO specimens have been investigated as a function of temperature at x-band (microwave) frequencies. Below the nominal Neel temperature, the x-band resonances arising from the bulk antiferromagnets, including NiO particles with diameters greater than 100 A, all vanish due to the emergence of large molecular exchange fields. The ESR resonance signals of 60 A antiferromagnetic nanoparticles, however, persist to the lowest temperatures. These nanoparticle resonance lines shift to lower fields rapidly as the temperature is decreased, while the lineshapes broaden and distort
Horio, M; Adachi, T; Mori, Y; Takahashi, A; Yoshida, T; Suzuki, H; Ambolode, L C C; Okazaki, K; Ono, K; Kumigashira, H; Anzai, H; Arita, M; Namatame, H; Taniguchi, M; Ootsuki, D; Sawada, K; Takahashi, M; Mizokawa, T; Koike, Y; Fujimori, A
2016-01-01
In the hole-doped cuprates, a small number of carriers suppresses antiferromagnetism and induces superconductivity. In the electron-doped cuprates, on the other hand, superconductivity appears only in a narrow window of high-doped Ce concentration after reduction annealing, and strong antiferromagnetic correlation persists in the superconducting phase. Recently, Pr1.3-xLa0.7CexCuO4 (PLCCO) bulk single crystals annealed by a protect annealing method showed a high critical temperature of around 27 K for small Ce content down to 0.05. Here, by angle-resolved photoemission spectroscopy measurements of PLCCO crystals, we observed a sharp quasi-particle peak on the entire Fermi surface without signature of an antiferromagnetic pseudogap unlike all the previous work, indicating a dramatic reduction of antiferromagnetic correlation length and/or of magnetic moments. The superconducting state was found to extend over a wide electron concentration range. The present results fundamentally challenge the long-standing picture on the electronic structure in the electron-doped regime. PMID:26843063
Quantum critical response function in quasi-two-dimensional itinerant antiferromagnets
Varma, C. M.; Zhu, Lijun; Schröder, Almut
2015-10-01
We reexamine the experimental results for the magnetic response function χ''(q ,E ,T ) for q around the antiferromagnetic vectors Q , in the quantum-critical region, obtained by inelastic neutron scattering, on an Fe-based superconductor and on a heavy-fermion compound. The motivation is to compare the results with a recent theory, which shows that the fluctuations in a generic antiferromagnetic model for itinerant fermions map to those in the universality class of the dissipative quantum-XY model. The quantum-critical fluctuations in this model, in a range of parameters, are given by the correlations of spatial and temporal topological defects. The theory predicts a χ''(q ,E ,T ) (i) which is a separable function of (q -Q ) and of (E ,T ) , (ii) at criticality, the energy-dependent part is ∝tanh(E /2 T ) below a cutoff energy, (iii) the correlation time departs from its infinite value at criticality on the disordered side by an essential singularity, and (iv) the correlation length depends logarithmically on the correlation time, so that the dynamical critical exponent z is ∞ . The limited existing experimental results are found to be consistent with the first two unusual predictions from which the linear dependence of the resistivity on T and the T lnT dependence of the entropy also follow. More experiments are suggested, especially to test the theory of variations on the correlation time and length on the departure from criticality.
Thompson, Marie
2014-01-01
Marie will explore the relationship between constructions of femininity and noise, which is understood here as an affective transformative force, rather than simply as unwanted sound. She will suggest that ‘feminine’ noises are often deemed negative; not because of what they mean, but as a result of the transformations they threaten to induce. Marie will raise questions around essentialism – does talking of a feminine or feminized noise require us to adopt an essentialist position, or can an ...
Cristina Voican; Constantin Stanescu
2012-01-01
Noise regulation includes statutes or guidelines relating to sound transmission established by national, state or provincial and municipal levels of government. After the watershed passage of the United States Noise Control Act of 1972, other local and state governments passed further regulations. Although the UK and Japan enacted national laws in 1960 and 1967 respectively, these laws were not at all comprehensive or fully enforceable as to address generally rising ambient noise, enforceable...
Ultrafast Band Engineering and Transient Spin Currents in Antiferromagnetic Oxides
Gu, Mingqiang; Rondinelli, James M.
2016-01-01
We report a dynamic structure and band engineering strategy with experimental protocols to induce indirect-to-direct band gap transitions and coherently oscillating pure spin-currents in three-dimensional antiferromagnets (AFM) using selective phononic excitations. In the Mott insulator LaTiO3, we show that a photo-induced nonequilibrium phonon mode amplitude destroys the spin and orbitally degenerate ground state, reduces the band gap by 160 meV and renormalizes the carrier masses. The time scale of this process is a few hundreds of femtoseconds. Then in the hole-doped correlated metallic titanate, we show how pure spin-currents can be achieved to yield spin-polarizations exceeding those observed in classic semiconductors. Last, we demonstrate the generality of the approach by applying it to the non-orbitally degenerate AFM CaMnO3. These results advance our understanding of electron-lattice interactions in structures out-of-equilibrium and establish a rational framework for designing dynamic phases that may be exploited in ultrafast optoelectronic and optospintronic devices. PMID:27126354
Jamming Behavior of Domain Walls in an Antiferromagnetic Film
Sinha, Sunil
2014-03-01
Over the last few years, attempts have been made to unify many aspects of the freezing behavior of glasses, granular materials, gels, supercooled liquids, etc. into a general conceptual framework of what is called jamming behavior. This occurs when particles reach packing densities high enough that their motions become highly restricted. A general phase diagram has been proposed onto which various materials systems, e.g glasses or granular materials, can be mapped. We will discuss some recent applications of resonant and non-resonant soft X-ray Grazing Incidence Scattering to mesoscopic science, for example the study of magnetic domain wall fluctuations in thin films. For these studies, we use resonant magnetic x-ray scattering with a coherent photon beam and the technique of X-ray Photon Correlation Spectroscopy. find that at the ordering temperature the domains of an antiferromagnetic system, namely Dysprosium metal, behave very much also like a jammed system and their associated fluctuations exhibit behavior which exhibit some of the universal characteristics of jammed systems, such as non-exponential relaxation and Vogel-Fulcher type freezing. Work supported by Basic Energy Sciences, U.S. Dept. of Energy under Grant Number: DE-SC0003678.
A nonmagnetic impurity in a 2D quantum critical antiferromagnet
Troyer, Matthias
2003-03-01
We compute the properties of a mobile hole and a static impurity injected into a two-dimensional antiferromagnet or superconductor in the vicinity of a magnetic quantum critical point. A static S=1/2 impurity doped into a quantum-disordered spin gap system induces a local moment with spin S=1/2 and a corresponding Curie-like impurity susceptibility, while the same impurity in a Néel ordered state only gives a finite impurity susceptibility. For the quantum critical system however an interesting field-theoretical prediction has been made that there the impurity spin susceptibility still has a Curie-like divergence, but with a universal effective spin that is neither an integer nor a half-odd integer [1]. In large-scale quantum Monte Carlo (QMC) simulations using the loop algorithm we calculate the impurity susceptibility and find that, unfortunately, this effect is not observable since the renormalization of the effective spin away from S=1/2 is minimal. Other predictions of the field theory, such as a new critical exponent η' describing the time-dependent impurity spin correlations can however be confirmed [2]. Next we compute the spectral function of a hole injected into a 2D antiferromagnet or superconductor in the vicinity of a magnetic quantum critical point [3]. We show that, near van Hove singularities, the problem maps onto that of a static vacancy. This allows the calculation of the spectral function in a QMC simulation without encountering the negative sign problem. We find a vanishing quasiparticle residue at the critical point, a new exponent η_h0.080.04 describing the frequency dependence of the spectral function G_h(ω)(ɛ_0-ω)-1+ηh and discuss possible relevance to photoemission spectra of cuprate superconductors near the antinodal points. ^1 S. Sachdev, C. Buragohain and M. Vojta, Science 286, 2479 (1999). ^2 M. Troyer, in Prog. Theor. Phys. Suppl. 145 (2002); M. Körner and M. Troyer, ibid. ^3 S. Sachdev, M. Troyer, and M. Vojta, Phys. Rev
Characterization of the Dilute Ising Antiferromagnet
Energy Technology Data Exchange (ETDEWEB)
Wiener, T.
2000-09-12
A spin glass is a magnetic ground state in which ferromagnetic and antiferromagnetic exchange interactions compete, thereby creating frustration and a multidegenerate state with no long range order. An Ising system is a system where the spins are constrained to lie parallel or antiparallel to a primary axis. There has been much theoretical interest in the past ten years in the effects of applying a magnetic field transverse to the primary axis in an Ising spin glass at low temperatures and thus study phase transitions at the T=0 limit. The focus of this study is to search for and characterize a new Ising spin glass system. This is accomplished by site diluting yttrium for terbium in the crystalline material TbNi{sub 2}Ge{sub 2}. The first part of this work gives a brief overview of the physics of rare earth magnetism and an overview of experimental characteristics of spin glasses. This is followed by the methodology used to manufacture the large single crystals used in this study, as well as the measurement techniques used. Next, a summary of the results of magnetic measurements on across the dilution series from pure terbium to pure yttrium is presented. This is followed by detailed measurements on particular dilutions which demonstrate spin glass behavior. Pure TbNi{sub 2}Ge{sub 2} is an Ising antiferromagnet with a several distinct metamagnetic states below 17 K. As the terbium is alloyed with yttrium, these magnetic states are weakened in a consistent manner, as is seen in measurements of the transition temperatures and analysis of Curie-Weiss behavior at high temperature. At low concentrations of terbium, below 35%, long range order is no longer present and a spin-glass-like state emerges. This state is studied through various measurements, dc and ac susceptibility, resistivity, and specific heat. This magnetic behavior was then compared to that of other well characterized spin glasses. It is concluded that there is a region of concentration s for which a spin
Space-Time Parity Violation and Magnetoelectric Interactions in Antiferromagnets
Kadomtseva, A.M.; Zvezdin, A. K.; Popov, Yu. F.; Pyatakov, A. P.; Vorob'ev, G. P.
2004-01-01
The properties of antiferromagnetic materials with violated space-time parity are considered. Particular attention is given to the bismuth ferrite BiFeO3 ferroelectric magnet. This material is distinguished from other antiferromagnets in that the inversion center is absent in its crystal and magnetic structures. This circumstance gives rise to the diversified and unusual properties, namely, to the appearance of a spatially modulated spin structure and to the unique possibility of the linear m...
Quantum fluctuations of the antiferro-antiferromagnetic double-layer
Institute of Scientific and Technical Information of China (English)
Jiang Wei; Zhu Cheng-Bo; Yu Gui-Hong; Lo Veng-Cheong
2009-01-01
This paper stuides the magnetization and quantum fluctuations of an antiferro-antiferromagnetic (AF-AF) doublelayer at zero temperature.It is found that the exchanges and anisotropy constants affect the quantum fluctuations of spins. If the anisotropy exists,there will be no acoustic energy branch in the system. The anisotropy constant,antiferromagnetic intralayer and interlayer coupling have important roles in a balance of the quantum competition.
Nonlinear Absorption of Radio Waves in a Noncollinear Antiferromagnet
Tikhonov, Aleksey M.; Pavlov, Nikolay G.
2015-01-01
The nonlinear absorption of radio waves (200 - 800 MHz) in a noncollinear cubic antiferromagnet Mn3Al2Ge3O12 in an external magnetic field H || [001] has been studied in the temperature range of 1.2 - 4.2 K. We attribute the observed dissipation of the electromagnetic energy to the parametric excitation of inhomogeneous surface waves at the boundaries of antiferromagnetic domains.
Michel, Ulf; Dobrzynski, Werner; Splettstoesser, Wolf; Delfs, Jan; Isermann, Ullrich; Obermeier, Frank
Aircraft industry is exposed to increasing public pressure aiming at a continuing reduction of aircraft noise levels. This is necessary to both compensate for the detrimental effect on noise of the expected increase in air traffic and improve the quality of living in residential areas around airports.
James Dow; Gary Gorton
2006-01-01
Noise traders are agents whose theoretical existence has been hypothesized as a way of solving certain fundamental problems in Financial Economics. We briefly review the literature on noise traders. The is an entry for The New Palgrave: A Dictionary of Economics, 2nd Edition (Palgrave Macmillan: New York), edited by Steven N. Durlauf and Lawrence E. Blume, forthcoming in 2008.
Ambient noise near the sea-route
Institute of Scientific and Technical Information of China (English)
HE Li; LI ZhengLin; PENG ZhaoHui
2009-01-01
Ambient noise data measured in an experiment conducted in shallow water near a sea-route were analyzed. It was observed that, at low frequency, the horizontal correlation has an obvious difference from that predicted by the classical ambient noise model. The theoretical analyses show that this phenomenon is caused by wind noise together with the discrete shipping noise nearby. An ambient noise model was proposed to include the effects caused by both the noise sources. Data measured at different times verify that the proposed model can be used to forecast the ambient noise field in shal-low water near the sea-route.
Ambient noise near the sea-route
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
Ambient noise data measured in an experiment conducted in shallow water near a sea-route were analyzed. It was observed that, at low frequency, the horizontal correlation has an obvious difference from that predicted by the classical ambient noise model. The theoretical analyses show that this phenomenon is caused by wind noise together with the discrete shipping noise nearby. An ambient noise model was proposed to include the effects caused by both the noise sources. Data measured at different times verify that the proposed model can be used to forecast the ambient noise field in shallow water near the sea-route.
Room-temperature antiferromagnetic memory resistor
Marti, X.; Fina, I.; Frontera, C.; Liu, Jian; Wadley, P.; He, Q.; Paull, R. J.; Clarkson, J. D.; Kudrnovský, J.; Turek, I.; Kuneš, J.; Yi, D.; Chu, J.-H.; Nelson, C. T.; You, L.; Arenholz, E.; Salahuddin, S.; Fontcuberta, J.; Jungwirth, T.; Ramesh, R.
2014-04-01
The bistability of ordered spin states in ferromagnets provides the basis for magnetic memory functionality. The latest generation of magnetic random access memories rely on an efficient approach in which magnetic fields are replaced by electrical means for writing and reading the information in ferromagnets. This concept may eventually reduce the sensitivity of ferromagnets to magnetic field perturbations to being a weakness for data retention and the ferromagnetic stray fields to an obstacle for high-density memory integration. Here we report a room-temperature bistable antiferromagnetic (AFM) memory that produces negligible stray fields and is insensitive to strong magnetic fields. We use a resistor made of a FeRh AFM, which orders ferromagnetically roughly 100 K above room temperature, and therefore allows us to set different collective directions for the Fe moments by applied magnetic field. On cooling to room temperature, AFM order sets in with the direction of the AFM moments predetermined by the field and moment direction in the high-temperature ferromagnetic state. For electrical reading, we use an AFM analogue of the anisotropic magnetoresistance. Our microscopic theory modelling confirms that this archetypical spintronic effect, discovered more than 150 years ago in ferromagnets, is also present in AFMs. Our work demonstrates the feasibility of fabricating room-temperature spintronic memories with AFMs, which in turn expands the base of available magnetic materials for devices with properties that cannot be achieved with ferromagnets.
Antiferromagnetic semiconductor LiMnAs
Energy Technology Data Exchange (ETDEWEB)
Novak, Vit; Jungwirth, Tomas; Cukr, Miroslav [Institute of Physics AS CR, Cukrovarnicka 10, Praha (Czech Republic); Svoboda, Stepan [Institute of Physics AS CR, Cukrovarnicka 10, Praha (Czech Republic); Charles University, Ke Karlovu 5, Praha (Czech Republic); Soban, Zbynek [Institute of Physics AS CR, Cukrovarnicka 10, Praha (Czech Republic); Czech Technical University, Technicka 2, Praha (Czech Republic); Marti, Xavier; Holy, Vaclav; Horodyska, Petra; Nemec, Petr [Charles University, Ke Karlovu 5, Praha (Czech Republic)
2011-07-01
LiMnAs belongs to the theoretically predicted class of I-Mn-V semiconductors with the antiferromagnetic ordering of Mn atoms. We report its first successful preparation in form of a thin film by molecular beam epitaxy. Structural properties of the material were examined in-situ by RHEED, and ex-situ by XPS and XRD, confirming the tetragonal crystal structure with its [100] direction oriented along the [110] direction of the InAs substrate. Transparency of LiMnAs in the spectral range of 870 to 1400 nm confirms the existence of an optical gap and indicates the band-gap energy above 1.4 eV. Magnetic properties measured by SQUID magnetometry show nearly compensated net magnetic moment in temperatures up to 400 K and magnetic fields up to 7 T, in a clear contrast to the ferromagnetic character of MnAs or to the paramagnetic behavior of the same amount of uncoupled Mn atoms.
Antiferromagnetic Skyrmion: Stability, Creation and Manipulation
Zhang, Xichao; Zhou, Yan; Ezawa, Motohiko
2016-04-01
Magnetic skyrmions are particle-like topological excitations in ferromagnets, which have the topo-logical number Q = ± 1, and hence show the skyrmion Hall effect (SkHE) due to the Magnus force effect originating from the topology. Here, we propose the counterpart of the magnetic skyrmion in the antiferromagnetic (AFM) system, that is, the AFM skyrmion, which is topologically protected but without showing the SkHE. Two approaches for creating the AFM skyrmion have been described based on micromagnetic lattice simulations: (i) by injecting a vertical spin-polarized current to a nanodisk with the AFM ground state; (ii) by converting an AFM domain-wall pair in a nanowire junction. It is demonstrated that the AFM skyrmion, driven by the spin-polarized current, can move straightly over long distance, benefiting from the absence of the SkHE. Our results will open a new strategy on designing the novel spintronic devices based on AFM materials.
Noise and mental performance: personality attributes and noise sensitivity.
Belojevic, G; Jakovljevic, B; Slepcevic, V
2003-01-01
The contradictory and confusing results in noise research on humans may partly be due to individual differences between the subjects participating in different studies. This review is based on a twelve year research on the role of neuroticism, extroversion and subjective noise sensitivity during mental work in noisy environment. Neurotic persons might show enhanced "arousability" i.e. their arousal level increases more in stress. Additional unfavorable factors for neurotics are worrying and anxiety, which might prevent them coping successfully with noise, or some other stressors during mental performance. In numerous experiments introverts have showed higher sensitivity to noise during mental performance compared to extroverts, while extroverts often cope with a boring task even by requesting short periods of noise during performance. Correlation analyses have regularly revealed a highly significant negative relation between extroversion and noise annoyance during mental processing. Numerous studies have shown that people with high noise sensitivity may be prevented from achieving the same work results as other people in noisy environment, thus leading to psychosomatic, neurotic or other difficulties. Positive relation between noise annoyance and subjective noise sensitivity might be very strong. Our results have shown, after matching with the results of other relevant studies, that more stable personality, with extroversive tendencies and with a relatively lower subjective noise sensitivity measured with standard questionnaires, may be expected to better adapt to noise during mental performance, compared to people with opposite personality traits. PMID:14965455
Yin, Xinmao; Zeng, Shengwei; Das, Tanmoy; Baskaran, G.; Asmara, Teguh Citra; Santoso, Iman; Yu, Xiaojiang; Diao, Caozheng; Yang, Ping; Breese, Mark B. H.; Venkatesan, T.; Lin, Hsin; Ariando; Rusydi, Andrivo
2016-05-01
We report the first observation of the coexistence of a distinct midgap state and a Mott state in undoped and their evolution in electron and hole-doped ambipolar Y0.38 La0.62 (Ba0.82 La0.18 )2Cu3 Oy films using spectroscopic ellipsometry and x-ray absorption spectroscopies at the O K and Cu L3 ,2 edges. Supported by theoretical calculations, the midgap state is shown to originate from antiferromagnetic correlation. Surprisingly, while the magnetic state collapses and its correlation strength weakens with dopings, the Mott state in contrast moves toward a higher energy and its correlation strength increases. Our result provides important clues to the mechanism of electronic correlation strengths and superconductivity in cuprates.
Chain reconfiguration in active noise
Samanta, Nairhita; Chakrabarti, Rajarshi
2016-05-01
In a typical single molecule experiment, the dynamics of an unfolded protein is studied by determining the reconfiguration time using long-range Förster resonance energy transfer, where the reconfiguration time is the characteristic decay time of the position correlation between two residues of the protein. In this paper we theoretically calculate the reconfiguration time for a single flexible polymer in the presence of active noise. The study suggests that though the mean square displacement grows faster, the chain reconfiguration is always slower in the presence of long-lived active noise with exponential temporal correlation. Similar behavior is observed for a worm-like semi-flexible chain and a Zimm chain. However it is primarily the characteristic correlation time of the active noise and not the strength that controls the increase in the reconfiguration time. In brief, such active noise makes the polymer move faster but the correlation loss between the monomers becomes slow.
Chain reconfiguration in active noise
International Nuclear Information System (INIS)
In a typical single molecule experiment, the dynamics of an unfolded protein is studied by determining the reconfiguration time using long-range Förster resonance energy transfer, where the reconfiguration time is the characteristic decay time of the position correlation between two residues of the protein. In this paper we theoretically calculate the reconfiguration time for a single flexible polymer in the presence of active noise. The study suggests that though the mean square displacement grows faster, the chain reconfiguration is always slower in the presence of long-lived active noise with exponential temporal correlation. Similar behavior is observed for a worm-like semi-flexible chain and a Zimm chain. However it is primarily the characteristic correlation time of the active noise and not the strength that controls the increase in the reconfiguration time. In brief, such active noise makes the polymer move faster but the correlation loss between the monomers becomes slow. (paper)
Quantum entanglement in trimer spin-1/2 Heisenberg chains with antiferromagnetic coupling
Del Cima, O M; da Silva, S L L
2015-01-01
The quantum entanglement measure is determined, for the first time, for antiferromagnetic trimer spin-1/2 Heisenberg chains. The physical quantity proposed to measure the entanglement is the distance between states by adopting the Hilbert-Schmidt norm. The method is applied to the new magnetic Cu(II) trimer system, 2b.3CuCl_2.2H_2O, and to the trinuclear Cu(II) halide salt, (3MAP)_2Cu_2Cl_8. The decoherence temperature, above which the entanglement is suppressed, is determined for the both systems. A correlation among their decoherence temperatures and their respective exchange coupling constants is established.
Transverse Ising antiferromagnetic in a longitudinal magnetic field: study of the ground state
International Nuclear Information System (INIS)
The two-dimensional antiferromagnetic Ising model in a transverse magnetic field (Ω) and uniform longitudinal field is studied for the first time (H). Using the effective-field theory (EFT) with correlation in one-site cluster calculation the ground-state phase diagram in the Ω-H plane is determined for the honeycomb (z=3) and square (z=4) lattices. It is shown that there is an order-disordered transition line (second-order phase transition) qualitatively in agreement with rigorous results of renormalization group in d=1. The critical curve in the classical approach is also obtained and the results are compared
Tricritical behaviour of the frustrated Ising antiferromagnet on the honeycomb lattice
Bobák, A.; Lučivjanský, T.; Žukovič, M.; Borovský, M.; Balcerzak, T.
2016-08-01
We use the effective-field theory with correlations based on different cluster sizes to investigate phase diagrams of the frustrated Ising antiferromagnet on the honeycomb lattice with isotropic interactions of the strength J1 present results for the ground-state energy as a function of the frustration parameter R =J2 / |J1 |. We find that the cluster-size has a considerable effect on the existence and location of a tricritical point in the phase diagram at which the phase transition changes from the second order to the first one.
Mechanisms for spin supersolidity in S=(1/2) spin-dimer antiferromagnets
International Nuclear Information System (INIS)
Using perturbative expansions and the contractor renormalization (CORE) algorithm, we obtain effective hard-core bosonic Hamiltonians describing the low-energy physics of S=1/2 spin-dimer antiferromagnets known to display supersolid phases under an applied magnetic field. The resulting effective models are investigated by means of mean-field analysis and quantum Monte Carlo simulations. A ''leapfrog mechanism,'' through means of which extra singlets delocalize in a checkerboard-solid environment via correlated hoppings, is unveiled that accounts for the supersolid behavior
Topological Aspects of Symmetry Breaking in Triangular-Lattice Ising Antiferromagnets
Smerald, Andrew; Korshunov, Sergey; Mila, Frédéric
2016-05-01
Using a specially designed Monte Carlo algorithm with directed loops, we investigate the triangular lattice Ising antiferromagnet with coupling beyond the nearest neighbors. We show that the first-order transition from the stripe state to the paramagnet can be split, giving rise to an intermediate nematic phase in which algebraic correlations coexist with a broken symmetry. Furthermore, we demonstrate the emergence of several properties of a more topological nature such as fractional edge excitations in the stripe state, the proliferation of double domain walls in the nematic phase, and the Kasteleyn transition between them. Experimental implications are briefly discussed.
Stochastic resonance of bias signal-modulated noise in a single-mode laser
Institute of Scientific and Technical Information of China (English)
Wang Jun; Cao Li; Wu Da-Jin
2004-01-01
Stochastic resonance (SR) for bias signal modulation is studied in a single-mode laser system. By investigating a gain-noise model driven by correlated pump noise and quantum noir, we find that, whether the correlation coefficient between both the noises is positive or negative, SR always appears in the dependence of signal-to-noise ratio (SNR) upon the noise correlation time and the frequency of the modulation signal. However, only when the correlation coefficient between both noises is negative can SR occur in the dependence of SNR upon the quantum noise intensity and pump noise intensity, while when the correlation coefficient between both noises is positive, it shows monotonically.
Mendel, Brock; Shleifer, Andrei
2012-01-01
We present a simple model in which rational but uninformed traders occasionally chase noise as if it were information, thereby amplifying sentiment shocks and moving prices away from fundamental values. We fill a theoretical gap in the literature by showing conditions under which noise traders can have an impact on market equilibrium disproportionate to their size in the market. The model offers a partial explanation for the surprisingly low market price of financial risk in the Spring of 2007.
Sethna, James P.; Dahmen, Karin A.; Christopher R Myers
2001-01-01
Crackling noise arises when a system responds to changing external conditions through discrete, impulsive events spanning a broad range of sizes. A wide variety of physical systems exhibiting crackling noise have been studied, from earthquakes on faults to paper crumpling. Because these systems exhibit regular behavior over many decades of sizes, their behavior is likely independent of microscopic and macroscopic details, and progress can be made by the use of very simple models. The fact tha...
Mario Forni; Luca Gambetti; Marco Lippi; Luca Sala
2014-01-01
We introduce noisy information into a standard present value stock price model. Agents receive a noisy signal about the structural shock driving future dividend variations. The resulting equilibrium stock price includes a transitory component — the "noise bubble" — which can be responsible for boom and bust episodes unrelated to economic fundamentals. We propose a non-standard VAR procedure to estimate the structural shock and the "noise" shock, their impulse response functions and the bubble...
Analysis and Optimization of Noise Response for Low-Noise CMOS Image Sensors
Martin-Gonthier, Philippe; Molina, Romain; Cervantes, Paola; Magnan, Pierre
2012-01-01
CMOS image sensors are nowadays widely used in imaging applications and particularly in low light flux applications. This is really possible thanks to a reduction of noise obtained, among others, by the use of pinned photodiode associated with a Correlated Double Sampling readout. It reveals new noise sources which become the major contributors. This paper presents noise measurements on low-noise CMOS image sensor. Image sensor noise is analyzed and optimization is done in order to reach an i...
Universal Exchange-Driven Phonon Splitting in Antiferromagnets
Kant, Ch.; Schmidt, M.; Wang, Zhe; Mayr, F.; Tsurkan, V.; Deisenhofer, J.; Loidl, A.
2012-04-01
We report a linear dependence of the phonon splitting Δω on the nondominant exchange coupling constant Jnd in the antiferromagnetic transition-metal monoxides MnO, FeO, CoO, NiO, and in the frustrated antiferromagnetic oxide spinels CdCr2O4, MgCr2O4, and ZnCr2O4. It directly confirms the theoretical prediction of an exchange-induced splitting of the zone-center optical phonon for the monoxides and explains the magnitude and the change of sign of the phonon splitting on changing the sign of the nondominant exchange also in the frustrated oxide spinels. The experimentally found linear relation ℏΔω=βJndS2 with slope β=3.7 describes the splitting for both systems and agrees with the observations in the antiferromagnets KCoF3 and KNiF3 with perovskite structure and negligible next-nearest neighbor coupling. The common behavior found for very different classes of cubic antiferromagnets suggests a universal dependence of the exchange-induced phonon splitting at the antiferromagnetic transition on the nondominant exchange coupling.
Nematic antiferromagnetic states in bulk FeSe
Liu, Kai; Lu, Zhong-Yi; Xiang, Tao
2016-05-01
The existence of nematic order, which breaks the lattice rotational symmetry with nonequivalent a and b axes in iron-based superconductors, is a well-established experimental fact. An antiferromagnetic (AFM) transition is accompanying this order, observed in nearly all parent compounds, except bulk FeSe. The absence of the AFM order in FeSe casts doubt on the magnetic mechanism of iron-based superconductivity, since the nematic order is believed to be driven by the same interaction that is responsible for the superconducting pairing in these materials. Here we show, through systematic first-principles electronic structure calculations, that the ground state of FeSe is in fact strongly AFM correlated but without developing a magnetic long-range order. Actually, there are a series of staggered n -mer AFM states with corresponding energies below that of the single stripe AFM state, which is the ground state for the parent compounds of most iron-based superconductors. Here, the staggered n -mer (n any integer >1 ) means a set of n adjacent parallel spins on a line along the b axis with antiparallel spins between n -mers along both a and b axes. Moreover, different n -mers can antiparallelly mix with each other to coexist. Among all the states, we find that the lowest energy states formed by the staggered dimer, staggered trimer, and their random antiparallel aligned spin states along the b axis are quasidegenerate. The thermal average of these states does not show any magnetic long-range order, but it does possess a hidden one-dimensional AFM order along the a axis, which can be detected by elastic neutron scattering measurements. Our finding gives a natural account for the absence of long-range magnetic order and suggests that the nematicity is driven predominantly by spin fluctuations even in bulk FeSe, providing a unified description on the phase diagram of iron-based superconductors.
Antiferromagnetic coupling across silicon regulated by tunneling currents
Gareev, Rashid; Schmid, Maximilian; Vancea, Johann; Back, Christian; Schreiber, Reinert; Buergler, Daniel; Stromberg, Frank; Wende, Heiko
2012-02-01
We present the room temperature enhancement of antiferromagnetic coupling in epitaxial Fe(3 nm)/Si(2.4 nm)/Fe(3 nm) structures by voltage-driven spin-polarized tunneling currents. Using the ballistic electron magnetic microscopy we established that the saturation field for the collector current corresponding to parallel alignment of magnetizations rises up with the tunneling current, thus demonstrating stabilization of the antiparallel alignment and increase of antiferromagnetic coupling. We connect the enhancement of antiferromagnetic coupling with local dynamic spin torques mediated by spin-polarized tunneling electrons. Finally, in the antiparallel state the spin-polarized majority (minority) electrons exert dynamic torques in the bottom (upper) iron layer and, thus, additionally stabilize magnetization alignment.
Vertex functions at finite momentum: Application to antiferromagnetic quantum criticality
Wölfle, Peter; Abrahams, Elihu
2016-02-01
We analyze the three-point vertex function that describes the coupling of fermionic particle-hole pairs in a metal to spin or charge fluctuations at nonzero momentum. We consider Ward identities, which connect two-particle vertex functions to the self-energy, in the framework of a Hubbard model. These are derived using conservation laws following from local symmetries. The generators considered are the spin density and particle density. It is shown that at certain antiferromagnetic critical points, where the quasiparticle effective mass is diverging, the vertex function describing the coupling of particle-hole pairs to the spin density Fourier component at the antiferromagnetic wave vector is also divergent. Then we give an explicit calculation of the irreducible vertex function for the case of three-dimensional antiferromagnetic fluctuations, and show that it is proportional to the diverging quasiparticle effective mass.
Functional renormalization for antiferromagnetism and superconductivity in the Hubbard model
International Nuclear Information System (INIS)
Results of a renormalization group study for the 2-dimensional Hubbard model close to half-filling at finite temperature are presented. Bosonic degrees of freedom corresponding to antiferromagnetic and d-wave superconducting order are introduced, and flow equations for the corresponding coupling constants are deduced from an exact flow equation for the effective average action. The influence of bosonic fluctuations on the onset of local antiferromagnetic order is discussed. At low enough temperatures and close to half-filling the discrete symmetry of the lattice is broken and incommensurate antiferromagnetic fluctuations dominate. The phase diagram is shown for the parameter regime close to half-filling in the presence of vanishing as well as non-vanishing next-to-nearest-neighbor hopping t'. Finally, the potential emergence of d-wave superconducting order at larger distances from half-filling is discussed.
Experimental and theoretical studies of nanoparticles of antiferromagnetic materials
DEFF Research Database (Denmark)
Mørup, Steen; Madsen, Daniel Esmarch; Frandsen, Cathrine;
2007-01-01
nanoparticles, but it depends crucially on the size of the uncompensated moment. Excitation of the uniform mode results in a so-called thermoinduced moment, because the two sublattices are not strictly antiparallel when this mode is excited. The magnetic dipole interaction between antiferromagnetic......The magnetic properties of nanoparticles of antiferromagnetic materials are reviewed. The magnetic structure is often similar to the bulk structure, but there are several examples of size-dependent magnetic structures. Owing to the small magnetic moments of antiferromagnetic nanoparticles, the...... commonly used analysis of magnetization curves above the superparamagnetic blocking temperature may give erroneous results, because the distribution in magnetic moments and the magnetic anisotropy are not taken into account. We discuss how the magnetic dynamics can be studied by use of magnetization...
How Colored Environmental Noise Affects Population Extinction
Kamenev, Alex; Meerson, Baruch; Shklovskii, Boris
2008-12-01
Environmental noise can cause an exponential reduction in the mean time to extinction (MTE) of an isolated population. We study this effect on an example of a stochastic birth-death process with rates modulated by a colored (that is, correlated) Gaussian noise. A path integral formulation yields a transparent way of evaluating the MTE and finding the optimal realization of the environmental noise that determines the most probable path to extinction. The population-size dependence of the MTE changes from exponential in the absence of the environmental noise to a power law for a short-correlated noise and to no dependence for long-correlated noise. We also establish the validity domains of the white-noise limit and adiabatic limit.
The subjective importance of noise spectral content
Baxter, Donald; Phillips, Jonathan; Denman, Hugh
2014-01-01
This paper presents secondary Standard Quality Scale (SQS2) rankings in overall quality JNDs for a subjective analysis of the 3 axes of noise, amplitude, spectral content, and noise type, based on the ISO 20462 softcopy ruler protocol. For the initial pilot study, a Python noise simulation model was created to generate the matrix of noise masks for the softcopy ruler base images with different levels of noise, different low pass filter noise bandwidths and different band pass filter center frequencies, and 3 different types of noise: luma only, chroma only, and luma and chroma combined. Based on the lessons learned, the full subjective experiment, involving 27 observers from Google, NVIDIA and STMicroelectronics was modified to incorporate a wider set of base image scenes, and the removal of band pass filtered noise masks to ease observer fatigue. Good correlation was observed with the Aptina subjective noise study. The absence of tone mapping in the noise simulation model visibly reduced the contrast at high levels of noise, due to the clipping of the high levels of noise near black and white. Under the 34-inch viewing distance, no significant difference was found between the luma only noise masks and the combined luma and chroma noise masks. This was not the intuitive expectation. Two of the base images with large uniform areas, `restaurant' and `no parking', were found to be consistently more sensitive to noise than the texture rich scenes. Two key conclusions are (1) there are fundamentally different sensitivities to noise on a flat patch versus noise in real images and (2) magnification of an image accentuates visual noise in a way that is non-representative of typical noise reduction algorithms generating the same output frequency. Analysis of our experimental noise masks applied to a synthetic Macbeth ColorChecker Chart confirmed the color-dependent nature of the visibility of luma and chroma noise.
Noise Effects on Synchronized Globally Coupled Oscillators
Moro, Esteban; Sánchez, Angel
1998-01-01
The synchronized phase of globally coupled identical nonlinear oscillators subject to noise fluctuations is studied by means of a new analytical approach able to tackle general couplings, nonlinearities, and noise temporal correlations. Our results show that the interplay between coupling and noise modi es the e ective frequency of the system in a nontrivial way. Whereas for linear couplings the e ect of noise is always to increase the e ective frequency, for nonlinear coupling...
Holes in a two-dimensional quantum antiferromagnet
International Nuclear Information System (INIS)
A brief review is presented on the studies of the hole motion in a two-dimensional quantum antiferromagnetic. An extended introduction is given to cover the background of the problem. The quantum Bogoliubov-de Gennes formalism which treats the local distortion of the spin configuration and the quantum renormalization process on an equal footing, is outlined. The latest development on the central issue, whether a hole can freely propagate on an antiferromagnetic background, is overviewed. (author). 108 refs, 11 figs, 1 tab
Bond-Dilution-Induced Quantum Phase Transitions in Heisenberg Antiferromagnets
Yasuda, Chitoshi; Todo, Synge; Takayama, Hajime
2006-01-01
Bond-dilution effects on the ground state of the square-lattice antiferromagnetic Heisenberg model, consisting of coupled bond-alternating chains, are investigated by means of the quantum Monte Carlo simulation. It is found that, when the ground state of the non-diluted system is a non-magnetic state with a finite spin gap, a sufficiently weak bond dilution induces a disordered state with a mid gap in the original spin gap, and under a further stronger bond dilution an antiferromagnetic long-...
On the interpretation of magnetization data for antiferromagnetic nanoparticles
DEFF Research Database (Denmark)
Madsen, Daniel Esmarch; Mørup, Steen; Hansen, Mikkel Fougt
2006-01-01
We have investigated the influence of anisotropy on the magnetization curves of antiferromagnetic nanoparticles. We show that if such curves are analyzed in a conventional way, i.e. using a Langevin function in combination with a linear term, this usually results in good quality fits, but with an...... apparent temperature dependence of parameters such as the magnetic moment per particle and the antiferromagnetic susceptibility. In order to avoid the problems associated with anisotropy as well as volume/moment distributions we propose that the initial susceptibility is used when analyzing the temperature...... dependence of the magnetic moment....
Estimation of particle magnetic moment distribution for antiferromagnetic ferrihydrite nanoparticles
International Nuclear Information System (INIS)
Magnetization as a function of applied magnetic field at different temperatures for antiferromagnetic nanoparticles of ferrihydrite is measured and analyzed considering a distribution in particle magnetic moment. We find that the magnetization of this nanoparticle system is affected by the presence of particle magnetic moment distribution. This particle magnetic moment distribution is estimated at different temperatures. - Highlights: • Magnetic behavior of a nanoparticle system is affected by the presence of particle magnetic moment distribution. • One can not get correct and physically meaningful fit parameters if the particle magnetic moment distribution is ignored. • This particle magnetic moment distribution using the magnetization data is estimated for 2 nm antiferromagnetic ferrihydrite particles
Spin waves in antiferromagnetic FeF2
DEFF Research Database (Denmark)
Hutchings, M T; Rainford, B.D.; Guggenheim, H J
1970-01-01
Spin-wave dispersion in antiferromagnetic FeF2 has been investigated by inelastic neutron scattering using a chopper time-of-flight spectrometer. The single mode observed has a relatively flat dispersion curve rising from 53 cm-1 at the zone centre to 79 cm-1 at the zone boundary. A spin Hamilton......Spin-wave dispersion in antiferromagnetic FeF2 has been investigated by inelastic neutron scattering using a chopper time-of-flight spectrometer. The single mode observed has a relatively flat dispersion curve rising from 53 cm-1 at the zone centre to 79 cm-1 at the zone boundary. A spin...
Ferro- and antiferro-magnetism in (Np, Pu)BC
International Nuclear Information System (INIS)
Two new transuranium metal boron carbides, NpBC and PuBC, have been synthesized. Rietveld refinements of powder XRD patterns of (Np,Pu)BC confirmed in both cases isotypism with the structure type of UBC. Temperature dependent magnetic susceptibility data reveal antiferromagnetic ordering for PuBC below TN = 44 K, whereas ferromagnetic ordering was found for NpBC below TC = 61 K. Heat capacity measurements prove the bulk character of the observed magnetic transition for both compounds. The total energy electronic band structure calculations support formation of the ferromagnetic ground state for NpBC and the antiferromagnetic ground state for PuBC
Raman scattering in a two-layer antiferromagnet
Morr, Dirk K.; Chubukov, Andrey V.; Kampf, Arno P.; Blumberg, G.
1995-01-01
Two--magnon Raman scattering is a useful tool to verify recent suggestions concerning the value of the interplanar exchange constant in antiferromagnetic two--layer systems, such as $YBa_2Cu_3O_{6+x}$. We present a theory for Raman scattering in a two--layer antiferromagnet. We study the spectra for the electronic and magnetic excitations across the charge transfer gap within the one--band Hubbard model and derive the matrix elements for the Raman scattering cross section in a diagrammatic fo...
Thermal Generation of Spin Current in an Antiferromagnet.
Seki, S; Ideue, T; Kubota, M; Kozuka, Y; Takagi, R; Nakamura, M; Kaneko, Y; Kawasaki, M; Tokura, Y
2015-12-31
The longitudinal spin Seebeck effect has been investigated for a uniaxial antiferromagnetic insulator Cr(2)O(3), characterized by a spin-flop transition under magnetic field along the c axis. We have found that a temperature gradient applied normal to the Cr(2)O(3)/Pt interface induces inverse spin Hall voltage of spin-current origin in Pt, whose magnitude turns out to be always proportional to magnetization in Cr(2)O(3). The possible contribution of the anomalous Nernst effect is confirmed to be negligibly small. The above results establish that an antiferromagnetic spin wave can be an effective carrier of spin current. PMID:26765011
Fridman, P A
2010-01-01
Radio frequency interference (RFI) already limits the sensitivity of existing radio telescopes in several frequency bands and may prove to be an even greater obstacle for future generation instruments to overcome. I aim to create a structure of radio astronomy correlators which will be statistically stable (robust) in the presence of interference. A statistical analysis of the mixture of system noise + signal noise + RFI is proposed here which could be incorporated into the block diagram of a correlator. Order and rank statistics are especially useful when calculated in both temporal and frequency domains. Several new algorithms of robust correlators are proposed and investigated here. Computer simulations and processing of real data demonstrate the efficacy of the proposed algorithms.
Institute of Scientific and Technical Information of China (English)
李娜; 杨晓丽
2015-01-01
In this paper, by using the Terman-Wang small-world neuronal network with electrical synapse coupling, we inves-tigate the synchronous dynamics of neuronal network system subjected to spatially correlated white noise. First, the dynamical mean-field approximation theory is extended to the small-world network system under spatially correlated white noise, through which the original 2N-dimensional stochastic differential equations of the network system are trans-formed to 11-dimensional deterministic moment differential equations. Then, based on this set of moment differential equations, the key effects of spatially correlated noise and network structure on the synchronous firing property are dis-cussed in the Terman-Wang neuronal network system. The results show that the synchronization ratio of this considered neuronal network system becomes higher not only as the noise correlation coeﬃcient is increased but also as the coupling strength and the average vertex degree are added. Those results imply that the noise spatial correlation coeﬃcient, the coupling strength, and the average vertex degree can play a positive role in inducing synchronous neuronal behaviors. Furthermore, the synchronous dynamics of the original neuronal network system, obtained by direct numerical simula-tions, is compared with those obtained by the dynamical mean-field approximation theory, and good consistence between them is revealed.
Li, Zixiang; Yao, Hong; Wang, Fa; Lee, Dung-Hai
Superconductivity is an emergent phenomena in the sense that the energy scale at which Cooper pairs form is generically much lower than the bare energy scale, namely the electron kinetic energy bandwidth. Addressing the mechanism of Cooper pairing amounts to finding out the effective interaction (or the renormalized interaction) that operates at the low energies. Finding such interaction from the bare microscopic Hamiltonian has not been possible for strong correlated superconductors such as the copper-oxide high temperature superconductor. In fact even one is given the effective interaction, determining its implied electronic instabilities without making any approximation has been a formidable task. Here, we perform sign-free quantum Monte-Carlo simulations to study the antiferromagnetic, superconducting, and the charge density wave instabilities which are ubiquitous in both electron and hole doped cuprates. Our result suggests only after including both the nematic and antiferromagnetic fluctuation, are the observed properties associated with these instabilities reproduced by the theory.
Disorder-induced phases in the S=1 antiferromagnetic Heisenberg chain
Lajkó, Péter; Carlon, Enrico; Rieger, Heiko; Iglói, Ferenc
2005-09-01
We use extensive density matrix renormalization group (DMRG) calculations to explore the phase diagram of the random S=1 antiferromagnetic Heisenberg chain with a power-law distribution of the exchange couplings. We use open chains and monitor the lowest gaps, the end-to-end correlation function and the string order parameter. For this distribution at weak disorder, the system is in the gapless Haldane phase with a disorder dependent dynamical exponent, z , and z=1 signals the border between the nonsingular and singular regions of the local susceptibility. For strong enough disorder, which approximately corresponds to a uniform distribution, a transition into the random singlet phase is detected, at which the string order parameter as well as the average end-to-end correlation function are vanishing and at the same time the dynamical exponent is divergent. Singularities of physical quantities are found to be somewhat different in the random singlet phase and in the critical point.
Macrospin dynamics in antiferromagnets triggered by sub-20 femtosecond injection of nanomagnons
Bossini, D.; Dal Conte, S.; Hashimoto, Y.; Secchi, A.; Pisarev, R. V.; Rasing, Th.; Cerullo, G.; Kimel, A. V.
2016-02-01
The understanding of how the sub-nanoscale exchange interaction evolves in macroscale correlations and ordered phases of matter, such as magnetism and superconductivity, requires to bridging the quantum and classical worlds. This monumental challenge has so far only been achieved for systems close to their thermodynamical equilibrium. Here we follow in real time the ultrafast dynamics of the macroscale magnetic order parameter in the Heisenberg antiferromagnet KNiF3 triggered by the impulsive optical generation of spin excitations with the shortest possible nanometre wavelength and femtosecond period. Our magneto-optical pump-probe experiments also demonstrate the coherent manipulation of the phase and amplitude of these femtosecond nanomagnons, whose frequencies are defined by the exchange energy. These findings open up opportunities for fundamental research on the role of short-wavelength spin excitations in magnetism and strongly correlated materials; they also suggest that nanospintronics and nanomagnonics can employ coherently controllable spin waves with frequencies in the 20 THz domain.
International Nuclear Information System (INIS)
Full text: In some low-dimensional quantum antiferromagnets a transition can occur between a Neel ordered ground state, characterised by gapless excitations and long range correlations, and a disordered ground state with a gap and short range correlations. The disordered phase is characterised by strong singlet formation on pairs of neighbouring spins. We have used a new analytic many body approach together with numerical series and exact diagonalisation methods to study such transitions in 1. a bilayer Heisenberg system 2. a spin analogue of the Kondo lattice model at half filling. A Letter on this work has been published. The analytic method is based on a 'bond operator' representation for spins which is used to transform the problem to an interacting Bose gas with a hardcore repulsion which is treated exactly. The results are in excellent agreement with numerical estimates, and represent a significant improvement on previous calculations
Phase transitions in n=4 type II antiferromagnets
International Nuclear Information System (INIS)
The Landau-Ginzburg-Wilson (LGW) Hamiltonian associated with n=4 type II fcc antiferromagnets is discussed. It is shown that the model is expected to exhibit a first order transition in d=3 dimensions. Recent experimental results on CeS, CeSe and CeTe are discussed. (author)
Upper critical fields of superconductor-antiferromagnet superlattices
International Nuclear Information System (INIS)
Nucleation of the superconducting phase in proximity coupled superconductor-antiferromagnetic (SC/AF) multilayers is studied theoretically. Assuming that both superconducting and antiferromagnetic metals are dirty the superconducting transition temperature, Tc, and upper critical fields, Hc2parallel(T) and Hc2perpendicular(T), as functions from the system parameters have been calculated. Comparison of the results for the SC/AF structures and for the SC/ferromagnetic multilayers shows that the values of the Tc, Hc2parallel(T) and Hc2perpendicular(T) are more sensitive to the ferromagnetic exchange field than to the antiferromagnetic one. The main difference in the values of the critical fields is obtained for the structures formed by thin superconducting layers. The finite effect on the superconducting properties of the multilayers does not depend on the strength of the magnetism only, but on the scattering mechanism of the electrons at the interfaces too. The advantage of the antiferromagnetic interaction for nucleation of the SC phase will be lost if nearly all Cooper pairs are destroyed due to the interface scattering
Oscillating Solitons Pinned to a Nonmagnetic Impurity in Layered Antiferromagnets
Mól, L. A. S.; Pereira, A. R.; Moura-Melo, W. A.
2002-01-01
We argue that an oscillatory motion of impurity-pinned solitons may occur in layered antiferromagnetic compounds. The characteristic frequencies of these modes, that may be detected by resonance or inelastic neutron scattering, are estimated analytically and depend on the soliton sizes and types .
Superconductivity and Antiferromagnetism in Quasi-one-dimensional Organic Conductors
Dupuis, N.; Bourbonnais, C.; Nickel, J. C.
2005-01-01
We review the current understanding of superconductivity in the quasi-one-dimensional organic conductors of the Bechgaard and Fabre salt families. We discuss the interplay between superconductivity, antiferromagnetism, and charge-density-wave fluctuations. The connection to recent experimental observations supporting unconventional pairing and the possibility of a triplet-spin order parameter for the superconducting phase is also presented.
On the magnetism of Heisenberg double-layer antiferromagnets
International Nuclear Information System (INIS)
The author investigates the sublattice magnetization and the susceptibility of the double-layer Heisenberg antiferromagnet K3M2F7 by employing the techniques of elastic and quasi-elastic critical magnetic scattering of neutrons. (G.T.H.)
Observation of Antiferromagnetic Resonance in an Organic Superconductor
DEFF Research Database (Denmark)
Torrance, J. B.; Pedersen, H. J.; Bechgaard, K.
1982-01-01
Anomalous microwave absorption has been observed in the organic superconductor TMTSF2AsF6 (TMTSF: tetramethyltetraselenafulvalene) below its metal-nonmetal transition near 12 K. This absorption is unambiguously identified as antiferromagnetic resonance by the excellent agreement between a spin...
Antiferromagnetism in Pr3In: Singlet/triplet physics withfrustration
Energy Technology Data Exchange (ETDEWEB)
Christianson, A.D.; Lawrence, J.M.; Zarestky, J.L.; Suzuki, H.; Thompson, J.D.; Hundley, M.F.; Sarrao, J.L.; Booth, C.H.; Antonio, D.; Cornelius, A.L.
2004-11-18
We present neutron diffraction, magnetic susceptibility and specific heat data for a single-crystal sample of the cubic (Cu{sub 3}Au structure) compound Pr{sub 3}In. This compound is believed to have a singlet ({Lambda}{sub 1}) groundstate and a low-lying triplet ({Lambda}{sub 4}) excited state. In addition, nearest-neighbor antiferromagnetic interactions are frustrated in this structure. Antiferromagnetic order occurs below T{sub N} = 12K with propagation vector (0, 0, 0.5 {center_dot}{delta}) where {delta} {approx} 1/12. The neutron diffraction results can be approximated with the following model: ferromagnetic sheets from each of the three Pr sites alternate in sign along the propagation direction with a twelve-unit-cell square-wave modulation. The three moments of the unit cell of 1 {micro}{sub B} magnitude are aligned so as to sum to zero as expected for nearest-neighbor antiferromagnetic interactions on a triangle. The magnetic susceptibility indicates that in addition to the antiferromagnetic transition at 12K, there is a transition near 70K below which there is a small (0.005 {micro}{sub B}) ferromagnetic moment. There is considerable field and sample dependence to these transitions. The specific heat data show almost no anomaly at T{sub N} = 12K. This may be a consequence of the induced moment in the {Lambda}{sub 1} singlet, but may also be a sample-dependent effect.
Antiferromagnetic order in tetragonal bismuth ferrite-lead titanate
International Nuclear Information System (INIS)
Neutron powder diffraction of particulates of 0.7BiFeO3-0.3PbTiO3 in the tetragonal P4mm phase has been used to determine the type of antiferromagnetic order that occurs below 220 K. It is shown that G-type antiferromagnetic ordering occurs, with magnetic propagation along the 1/2 1/2 1/2 direction. Unlike the rhombohedral R3c phase the direction of antiferromagnetic propagation and the ferroelectric order parameter are not parallel in the tetragonal phase, but at an angle of 49.9o. The ground state (at 4 K) magnetic moment is 4.1 μB. - Highlights: → G-type antiferromagnetic ordering below 220 K in 0.7BiFeO3-0.3PbTiO3. → Ground state magnetic moment=4.1 μB. → Magnetic propagation vector k=(1/2 1/2 1/2 ). → Ferroelectric ordering (0 0 1) at 49.9o to magnetic propagation vector.
Antiferromagnetic ground state in NpCoGe
Czech Academy of Sciences Publication Activity Database
Colineau, E.; Griveau, J.C.; Eloirdi, R.; Gaczyński, P.; Khmelevskyi, S.; Shick, Alexander; Caciuffo, R.
2014-01-01
Roč. 89, č. 11 (2014), "115135-1"-"115135-11". ISSN 1098-0121 R&D Projects: GA ČR(CZ) GAP204/10/0330 Institutional support: RVO:68378271 Keywords : neptunium * anti-ferromagnetism * quantum critical phenomena Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.736, year: 2014
Antiferromagnetic structure in tetragonal CuMnAs thin films
Czech Academy of Sciences Publication Activity Database
Wadley, P.; Hills, V.; Shahedkhah, M.R.; Edmonds, K. W.; Campion, R. P.; Novák, Vít; Ouladdiaf, B.; Khalyavin, D.; Langridge, S.; Saidl, V.; Němec, P.; Rushforth, A.W.; Gallagher, B. L.; Dhesi, S.S.; Maccherozzi, F.; Železný, Jakub; Jungwirth, Tomáš
2015-01-01
Roč. 5, Nov (2015), s. 17079. ISSN 2045-2322 R&D Projects: GA MŠk(CZ) LM2011026; GA ČR GB14-37427G EU Projects: European Commission(XE) 268066 - 0MSPIN Institutional support: RVO:68378271 Keywords : spintronics * antiferromagnets Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 5.578, year: 2014
Institute of Scientific and Technical Information of China (English)
谢崇伟; 梅冬成
2003-01-01
We study the transient properties of a bistable kinetic system driven by correlated noises for the cases of multiplicative coloured noise and additive white noise. The mean first-passage time (MFPT) of the system is calculated.From numerical computations we find that: (i) The MFPT of the bistable system are affected by the correlation time of multiplicative coloured noise τ and the cross-correlation strength between noises λ and, τ and λ play the same roles in the MFPT. (ii) The MFPT corresponding to weakly correlated noises and strongly correlated noises exhibits the very different behaviour and there is a one-peak structure in the MFPT for strongly correlated noises. The peak grows highly as τ increases, which means that the noisy colour causes the suppression effect of the escape rate to become more pronounced.
Lagae, Ares; Lefebvre, Sylvain; Dutré, Philip
2011-01-01
We have recently proposed a new procedural noise function, Gabor noise, which offers a combination of properties not found in existing noise functions. In this paper, we present three significant improvements to Gabor noise: (1) an isotropic kernel for Gabor noise, which speeds up isotropic Gabor noise with a factor of roughly two, (2) an error analysis of Gabor noise, which relates the kernel truncation radius to the relative error of the noise, and (3) spatially varying Gabor noise, which e...
Idris, Ibrahim Mu'awiyya; Bakar, Mohd. Rizam Abu
2016-06-01
The steady state properties for the effect of non-immunogenic microenvironmental factors on tumor growth dynamics in the presence of immune response is investigated. The corresponding Fokker-Planck equation to the Langevin model equation interpreted in the sense of Stratonovich is used to derive the steady state distribution ρst (x) and the mean st of the tumor growth system. We find that the correlation strength ϕ stimulates the effect of the non-immunogenic microenvironmental factors σ on the tumor growth dynamics, and the tumor response M to the non-immunogenic microenvironmental factors within the tumor site may inhibits tumor growth, but not sufficient enough to cause extinction. Moreover, the result also indicates that the stronger the immune response λ the more the tumor population disappears.
Noise-assisted estimation of attractor invariants
Restrepo, Juan F.; Schlotthauer, Gastón
2016-07-01
In this article, the noise-assisted correlation integral (NCI) is proposed. The purpose of the NCI is to estimate the invariants of a dynamical system, namely the correlation dimension (D ), the correlation entropy (K2), and the noise level (σ ). This correlation integral is induced by using random noise in a modified version of the correlation algorithm, i.e., the noise-assisted correlation algorithm. We demonstrate how the correlation integral by Grassberger et al. and the Gaussian kernel correlation integral (GCI) by Diks can be thought of as special cases of the NCI. A third particular case is the U -correlation integral proposed herein, from which we derived coarse-grained estimators of the correlation dimension (DmU), the correlation entropy (KmU), and the noise level (σmU). Using time series from the Henon map and the Mackey-Glass system, we analyze the behavior of these estimators under different noise conditions and data lengths. The results show that the estimators DmU and σmU behave in a similar manner to those based on the GCI. However, for the calculation of K2, the estimator KmU outperforms its GCI-based counterpart. On the basis of the behavior of these estimators, we have proposed an automatic algorithm to find D ,K2, and σ from a given time series. The results show that by using this approach, we are able to achieve statistically reliable estimations of those invariants.
David Dillenberger; Uzi Segal
2013-01-01
Experimental evidence suggests that individuals who face an asymmetric distribution over the likelihood of a specific event might actually prefer not to know the exact value of this probability. We address these findings by studying a decision maker who has recursive, non-expected utility preferences over two-stage lotteries. For a binary lottery that yields the better outcome with probability p, we identify noise around p with a compound lottery that induces a probability distribution over t...
Hydrodynamical noise and Gubser flow
Yan, Li
2015-01-01
Hydrodynamical noise is introduced on top of Gubser's analytical solution to viscous hydrodynamics. With respect to the ultra-central collision events of Pb-Pb, p-Pb and p-p at the LHC energies, we solve the evolution of noisy fluid systems and calculate the radial flow velocity correlations. We show that the absolute amplitude of the hydrodynamical noise is determined by the multiplicity of the collision event. The evolution of azimuthal anisotropies, which is related to the generation of harmonic flow, receives finite enhancements from hydrodynamical noise. Although it is strongest in the p-p systems, the effect of hydrodynamical noise on flow harmonics is found to be negligible, especially in the ultra-central Pb-Pb collisions. For the short-range correlations, hydrodynamical noise contributes to the formation of a near-side peak on top of the correlation structure originated from initial state fluctuations. The shape of the peak is affected by the strength of hydrodynamical noise, whose height and width g...
Critical space-time networks and geometric phase transitions from frustrated edge antiferromagnetism
Trugenberger, Carlo A.
2015-12-01
Recently I proposed a simple dynamical network model for discrete space-time that self-organizes as a graph with Hausdorff dimension dH=4 . The model has a geometric quantum phase transition with disorder parameter (dH-ds) , where ds is the spectral dimension of the dynamical graph. Self-organization in this network model is based on a competition between a ferromagnetic Ising model for vertices and an antiferromagnetic Ising model for edges. In this paper I solve a toy version of this model defined on a bipartite graph in the mean-field approximation. I show that the geometric phase transition corresponds exactly to the antiferromagnetic transition for edges, the dimensional disorder parameter of the former being mapped to the staggered magnetization order parameter of the latter. The model has a critical point with long-range correlations between edges, where a continuum random geometry can be defined, exactly as in Kazakov's famed 2D random lattice Ising model but now in any number of dimensions.
Temperature-driven growth of antiferromagnetic domains in thin-film FeRh
International Nuclear Information System (INIS)
The evolution of the antiferromagnetic phase across the temperature-driven ferromagnetic (FM) to antiferromagnetic (AF) phase transition in epitaxial FeRh thin films was studied by x-ray magnetic linear and circular dichroism (XMLD and XMCD) and photoemission electron microscopy. By comparing XMLD and XMCD images recorded at the same temperature, the AF phase was identified, its structure directly imaged, and its evolution studied across the transition. A quantitative analysis of the correlation length of the images shows differences between the characteristic length scale of the two phases with the AF phase having a finer feature size. The asymmetry of the transition from FM to AF upon cooling and AF–FM upon heating is evidenced: upon cooling the formation of AF phase is dominated by nucleation at defects, with little subsequent growth, resulting in a small and non-random final AF domain structure, while upon heating, heterogeneous nucleation at different sites followed by significant domain size growth of the FM phase is observed, resulting in a non-reproducible final FM large domain structure. (paper)
Critical Space-Time Networks and Geometric Phase Transitions from Frustrated Edge Antiferromagnetism
Trugenberger, Carlo A
2015-01-01
Recently I proposed a simple dynamical network model for discrete space-time which self-organizes as a graph with Hausdorff dimension d_H=4. The model has a geometric quantum phase transition with disorder parameter (d_H-d_s) where d_s is the spectral dimension of the dynamical graph. Self-organization in this network model is based on a competition between a ferromagnetic Ising model for vertices and an antiferromagnetic Ising model for edges. In this paper I solve a toy version of this model defined on a bipartite graph in the mean field approximation. I show that the geometric phase transition corresponds exactly to the antiferromagnetic transition for edges, the dimensional disorder parameter of the former being mapped to the staggered magnetization order parameter of the latter. The model has a critical point with long-range correlations between edges, where a continuum random geometry can be defined, exactly as in Kazakov's famed 2D random lattice Ising model but now in any number of dimensions.
Temperature-driven growth of antiferromagnetic domains in thin-film FeRh
Baldasseroni, C.; Bordel, C.; Antonakos, C.; Scholl, A.; Stone, K. H.; Kortright, J. B.; Hellman, F.
2015-06-01
The evolution of the antiferromagnetic phase across the temperature-driven ferromagnetic (FM) to antiferromagnetic (AF) phase transition in epitaxial FeRh thin films was studied by x-ray magnetic linear and circular dichroism (XMLD and XMCD) and photoemission electron microscopy. By comparing XMLD and XMCD images recorded at the same temperature, the AF phase was identified, its structure directly imaged, and its evolution studied across the transition. A quantitative analysis of the correlation length of the images shows differences between the characteristic length scale of the two phases with the AF phase having a finer feature size. The asymmetry of the transition from FM to AF upon cooling and AF-FM upon heating is evidenced: upon cooling the formation of AF phase is dominated by nucleation at defects, with little subsequent growth, resulting in a small and non-random final AF domain structure, while upon heating, heterogeneous nucleation at different sites followed by significant domain size growth of the FM phase is observed, resulting in a non-reproducible final FM large domain structure.
Sequential write-read operations in FeRh antiferromagnetic memory
Moriyama, Takahiro; Matsuzaki, Noriko; Kim, Kab-Jin; Suzuki, Ippei; Taniyama, Tomoyasu; Ono, Teruo
2015-09-01
B2-ordered FeRh has been known to exhibit antiferromagnetic-ferromagnetic (AF-F) phase transitions in the vicinity of room temperature. Manipulation of the Néel order via AF-F phase transition and recent experimental observation of the anisotropic magnetoresistance in antiferromagnetic FeRh has proven that FeRh is a promising candidate for antiferromagnetic memory material. In this work, we demonstrate sequential write and read operations in antiferromagnetic memory resistors made of B2-orderd FeRh thin films by a magnetic field and electric current only, which open a realistic pathway towards operational antiferromagnetic memory devices.
Causes of EIT Intensity Correlation Power Broadening
Zheng, Aojie; Crescimanno, Michael; O'Leary, Shannon
2015-01-01
EIT noise correlation spectroscopy holds promise as a simple, robust method for performing high resolution spectroscopy used in optical magnetometry and clocks. Of relevance to these applications, we report here on a measurement of and a theory model for power broadening of EIT noise correlation resonances. Taken together they identify physical antecedents of noise correlation power broadening.
Entropic stochastic resonance in a confined structure driven by dichotomous noise and white noises
International Nuclear Information System (INIS)
The entropic stochastic resonance (ESR) in a confined system subjected to dichotomous noise and white noise and driven by a periodic sinusoidal force along the x axis of the structure and a time-dependent force in the declining direction, is investigated. Under the adiabatic approximation condition and based on the two-state theory, the expression of the output signal-to-noise ratio (SNR) is obtained. The results show that the SNR is a non-monotonic function of the strengths of dichotomous noise, white noise, and correlated strength of correlated noise. In addition, the SNR varies non-monotonically with the increase of the shape parameters of the confined structure, and also with the increase of the constant force along the y axis of the structure. The influence of the correlation rate of the dichotomous noise, and that of the frequency of the periodic force on the SNR are discussed. (general)
Noise annoyance from wind turbines a review
International Nuclear Information System (INIS)
This study summarises present knowledge on noise perception and annoyances from wind turbines in areas were people live or spend recreation time. There are two main types of noise from a wind turbine: mechanical noise and aerodynamic noise. The aerodynamic noise emits from the rotor blades passing the air. It has a swishing character with a modulation that makes it noticeable from the background noise. This part of the wind turbine noise was found to be the most annoying. Field studies performed among people living in the vicinity of wind turbines showed that there was a correlation between sound pressure level and noise annoyance, but annoyance was also influenced by visual factors such as the attitude to wind turbines' impact on the landscape. Noise annoyance was found at lower sound pressure levels than in studies of annoyance from traffic noise. There is no scientific evidence that noise at levels created by wind turbines could cause health problems other than annoyance. No studies on noise from wind turbines in wilderness areas have been found, but the reaction to other noise sources such as aircraft have been studied. In recreational areas, the expectation of quietness is high among visitors, but wind turbines are, in contrary to aircraft, stationary and could be avoided by recreationists. The visual impact of wind turbines might though be the dominant source of annoyance. Regulations on noise from wind turbines are based on different principles. Some states, e.g. Denmark, have a special legislation concerning wind turbines, while others, like Sweden, have used recommendations originally developed for a different noise source. The noise level could either be absolute, as in Germany, or related to the background noise level as in France. This background noise level could be standardised, measured or related to wind speed
Control of antiferromagnetic domain distribution via polarization-dependent optical annealing.
Higuchi, Takuya; Kuwata-Gonokami, Makoto
2016-01-01
The absence of net magnetization inside antiferromagnetic domains has made the control of their spatial distribution quite challenging. Here we experimentally demonstrate an optical method for controlling antiferromagnetic domain distributions in MnF2. Reduced crystalline symmetry can couple an order parameter with non-conjugate external stimuli. In the case of MnF2, time-reversal symmetry is macroscopically broken reflecting the different orientations of the two magnetic sublattices. Thus, it exhibits different absorption coefficients between two orthogonal linear polarizations below its antiferromagnetic transition temperature under an external magnetic field. Illumination with linearly polarized laser light under this condition selectively destructs the formation of a particular antiferromagnetic order via heating. As a result, the other antiferromagnetic order is favoured inside the laser spot, achieving spatially localized selection of an antiferromagnetic order. Applications to control of interface states at antiferromagnetic domain boundaries, exchange bias and control of spin currents are expected. PMID:26911337
Harmonic Retrieval in Colored ARMA Noise
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
We propose a new approach to harmonic retrieval in colored ARMA noise. A suitable filter is first used to remove all the sharp power spectrum peaks of the noisy observed process, then some kinds of cross correlation is employed to identify the noise characteristics. After filtering the noisy observed process with the identified noise characteristics again, SVD-TLS method can be applied to retrieve the harmonics. The proposed approach can be used to retrieve real-valued harmonic signals in colored ARMA noise with no restrictions on the phase coupling of harmonics and the distribution of the noise. Simulation examples show its effectiveness.
Random fields and ordering in antiferromagnetic insulators
International Nuclear Information System (INIS)
Neutron scattering measurements of the effect on the long range order and phase transitions of random magnetic fields are reviewed. The results at low temperatures in Rb2Co/sub x/Zn/sub 1-x/F4 and Co/sub x/Zn/sub 1-x/F2 show that the long range order is not established when samples are cooled in a magnetic field, but they form a state with unusually long magnetic correlations. In Mn/sub x/Zn/sub 1-x/F2 a similar state is formed but only very close in temperature to T/sub N/
Bolčina, Matjaž
2014-01-01
Noise is everywhere. Noise is a sound that makes people stressful and irritate. It often couses sleep disorders and also health problems like different cardiovascular disorders, hearing loss…In most cases traffic noise is the most disturbing. There are different ways to prevent people from traffic noise like building noise barriers and insulation of facades. However noise barriers and insulation of facades do not prevent noise formation, but are lowering existing noise. Another disadvantage i...