From Loschmidt daemons to time-reversed waves.
Fink, Mathias
2016-06-13
Time-reversal invariance can be exploited in wave physics to control wave propagation in complex media. Because time and space play a similar role in wave propagation, time-reversed waves can be obtained by manipulating spatial boundaries or by manipulating time boundaries. The two dual approaches will be discussed in this paper. The first approach uses 'time-reversal mirrors' with a wave manipulation along a spatial boundary sampled by a finite number of antennas. Related to this method, the role of the spatio-temporal degrees of freedom of the wavefield will be emphasized. In a second approach, waves are manipulated from a time boundary and we show that 'instantaneous time mirrors', mimicking the Loschmidt point of view, simultaneously acting in the entire space at once can also radiate time-reversed waves. PMID:27140968
Loschmidt echo and time reversal in complex systems.
Goussev, Arseni; Jalabert, Rodolfo A; Pastawski, Horacio M; Wisniacki, Diego A
2016-06-13
Echoes are ubiquitous phenomena in several branches of physics, ranging from acoustics, optics, condensed matter and cold atoms to geophysics. They are at the base of a number of very useful experimental techniques, such as nuclear magnetic resonance, photon echo and time-reversal mirrors. Particularly interesting physical effects are obtained when the echo studies are performed on complex systems, either classically chaotic, disordered or many-body. Consequently, the term Loschmidt echo has been coined to designate and quantify the revival occurring when an imperfect time-reversal procedure is applied to a complex quantum system, or equivalently to characterize the stability of quantum evolution in the presence of perturbations. Here, we present the articles which discuss the work that has shaped the field in the past few years. PMID:27140977
Loschmidt echo and time reversal in complex systems
Goussev, Arseni; Jalabert, Rodolfo A.; Pastawski, Horacio M.; Wisniacki, Diego A.
2016-01-01
Echoes are ubiquitous phenomena in several branches of physics, ranging from acoustics, optics, condensed matter and cold atoms to geophysics. They are at the base of a number of very useful experimental techniques, such as nuclear magnetic resonance, photon echo and time-reversal mirrors. Particularly interesting physical effects are obtained when the echo studies are performed on complex systems, either classically chaotic, disordered or many-body. Consequently, the term Loschmidt echo has been coined to designate and quantify the revival occurring when an imperfect time-reversal procedure is applied to a complex quantum system, or equivalently to characterize the stability of quantum evolution in the presence of perturbations. Here, we present the articles which discuss the work that has shaped the field in the past few years. PMID:27140977
Loschmidt echo in many-spin systems: contrasting time scales of local and global measurements.
Zangara, Pablo R; Bendersky, Denise; Levstein, Patricia R; Pastawski, Horacio M
2016-06-13
A local excitation in a quantum many-spin system evolves deterministically. A time-reversal procedure, involving the inversion of the signs of every energy and interaction, should produce the excitation revival. This idea, experimentally coined in nuclear magnetic resonance, embodies the concept of the Loschmidt echo (LE). While such an implementation involves a single spin autocorrelation M(1,1), i.e. a local LE, theoretical efforts have focused on the study of the recovery probability of a complete many-body state, referred to here as global or many-body LE MMB Here, we analyse the relation between these magnitudes, with regard to their characteristic time scales and their dependence on the number of spins N We show that the global LE can be understood, to some extent, as the simultaneous occurrence of N independent local LEs, i.e. MMB∼(M(1,1))(N/4) This extensive hypothesis is exact for very short times and confirmed numerically beyond such a regime. Furthermore, we discuss a general picture of the decay of M1,1 as a consequence of the interplay between the time scale that characterizes the reversible interactions (T(2)) and that of the perturbation (τ(Σ)). Our analysis suggests that the short-time decay, characterized by the time scale τ(Σ), is greatly enhanced by the complex processes that occur beyond T(2) This would ultimately lead to the experimentally observed T(3), which was found to be roughly independent of τ(Σ) but closely tied to T(2). PMID:27140970
Towards a time reversal mirror for quantum systems
NASA Astrophysics Data System (ADS)
Pastawski, H. M.; Danieli, E. P.; Calvo, H. L.; Foa Torres, L. E. F.
2007-02-01
The reversion of the time evolution of a quantum state can be achieved by changing the sign of the Hamiltonian as in the Loschmidt echo and polarization echo experiment in NMR. In this work we describe an alternative mechanism inspired by the acoustic time reversal mirror. By solving the inverse time problem in a discrete space we develop a new procedure, the perfect inverse filter. It achieves the exact time reversion in a given region by reinjecting a prescribed wave function at the region's boundary.
Microscopic time-reversibility and macroscopic irreversibility: Still a paradox
Posch, H.A.; Dellago, Ch.; Hoover, W.G.; Kum, O. |
1995-09-13
Microscopic time reversibility and macroscopic irreversibility are a paradoxical combination. This was first observed by J. Loschmidt in 1876 and was explained, for conservative systems, by L. Boltzmann the following year. Both these features are also present in modern simulations of classic many-body systems in steady nonequilibrium states. We illustrate them here for the simplest possible models, a continuous one-dimensional model of field-driven diffusion, the so-called driven Lorentz gas or Galton Board, and an ergodic time reversible dissipative map.
Time reversal mirror and perfect inverse filter in a microscopic model for sound propagation
NASA Astrophysics Data System (ADS)
Calvo, Hernán L.; Danieli, Ernesto P.; Pastawski, Horacio M.
2007-09-01
Time reversal of quantum dynamics can be achieved by a global change of the Hamiltonian sign (a hasty Loschmidt daemon), as in the Loschmidt Echo experiments in NMR, or by a local but persistent procedure (a stubborn daemon) as in the time reversal mirror (TRM) used in ultrasound acoustics. While the first is limited by chaos and disorder, the last procedure seems to benefit from it. As a first step to quantify such stability we develop a procedure, the perfect inverse filter (PIF), that accounts for memory effects, and we apply it to a system of coupled oscillators. In order to ensure a numerical many-body dynamics intrinsically reversible, we develop an algorithm, the pair partitioning, based on the Trotter strategy used for quantum dynamics. We analyze situations where the PIF gives substantial improvements over the TRM.
The two Loschmidt daemons and the origin of infidelity
NASA Astrophysics Data System (ADS)
Pastawski, Horacio M.; Danieli, Ernesto P.; Foa Torres, Luis F. F.
2004-03-01
In an open quantum system a local excitation spreads away. Producing a Loschmidt Echo (LE) requires the action of a mechanism called a Loschmidt daemon. An actual realization of one of such creatures, which we dubbed the hasty daemon, is an instantaneous action with global effect: the change in the sign of the Hamiltonian. The chaotic nature of a many-body dynamics produces a fragility to perturbations that degrades the fidelity of the evolution and limits the LE formation [1]. An alternative, the stubborn daemon, is inspired in the acoustic time reversal mirror [2] which through a persistent local action of reinjection of wave function amplitude can produce a backward propagation. Although its theoretical description is not yet fully developed, the procedure is known to be quite robust. We use the Keldysh formalism to prescribe the injection required for a perfect LE. We also use a semiclassical approximation to discuss why chaos in the underlying classical system favors the action of this stubborn daemon.[1] P. R. Levstein, et al. J. Chem. Phys.108, 2718 (1998);[2] A. Tourin, et al. Phys. Rev. Lett. 87, 274301 (2001)
Loschmidt echo in one-dimensional interacting Bose gases
Lelas, K.; Seva, T.; Buljan, H.
2011-12-15
We explore Loschmidt echo in two regimes of one-dimensional interacting Bose gases: the strongly interacting Tonks-Girardeau (TG) regime, and the weakly interacting mean-field regime. We find that the Loschmidt echo of a TG gas decays as a Gaussian when small (random and time independent) perturbations are added to the Hamiltonian. The exponent is proportional to the number of particles and the magnitude of a small perturbation squared. In the mean-field regime the Loschmidt echo shows richer behavior: it decays faster for larger nonlinearity, and the decay becomes more abrupt as the nonlinearity increases; it can be very sensitive to the particular realization of the noise potential, especially for relatively small nonlinearities.
Quantum Operation Time Reversal
Crooks, Gavin E.
2008-03-25
The dynamics of an open quantum system can be described by a quantum operation: A linear, complete positive map of operators. Here, I exhibit a compact expression for the time reversal of a quantum operation, which is closely analogous to the time reversal of a classical Markov transition matrix. Since open quantum dynamics are stochastic, and not, in general, deterministic, the time reversal is not, in general, an inversion of the dynamics. Rather, the system relaxes toward equilibrium in both the forward and reverse time directions. The probability of a quantum trajectory and the conjugate, time reversed trajectory are related by the heat exchanged with the environment.
Ultrasonic Time Reversal Mirrors
NASA Astrophysics Data System (ADS)
Fink, Mathias; Montaldo, Gabriel; Tanter, Mickael
2004-11-01
For more than ten years, time reversal techniques have been developed in many different fields of applications including detection of defects in solids, underwater acoustics, room acoustics and also ultrasound medical imaging and therapy. The essential property that makes time reversed acoustics possible is that the underlying physical process of wave propagation would be unchanged if time were reversed. In a non dissipative medium, the equations governing the waves guarantee that for every burst of sound that diverges from a source there exists in theory a set of waves that would precisely retrace the path of the sound back to the source. If the source is pointlike, this allows focusing back on the source whatever the medium complexity. For this reason, time reversal represents a very powerful adaptive focusing technique for complex media. The generation of this reconverging wave can be achieved by using Time Reversal Mirrors (TRM). It is made of arrays of ultrasonic reversible piezoelectric transducers that can record the wavefield coming from the sources and send back its time-reversed version in the medium. It relies on the use of fully programmable multi-channel electronics. In this paper we present some applications of iterative time reversal mirrors to target detection in medical applications.
Transient Loschmidt echo in quenched Ising chains
NASA Astrophysics Data System (ADS)
Lupo, Carla; Schiró, Marco
2016-07-01
We study the response to sudden local perturbations of highly excited quantum Ising spin chains. The key quantity encoding this response is the overlap between time-dependent wave functions, which we write as a transient Loschmidt Echo. Its asymptotics at long time differences contain crucial information about the structure of the highly excited nonequilibrium environment induced by the quench. We compute the echo perturbatively for a weak local quench but for arbitrarily large global quench, using a cumulant expansion. Our perturbative results suggest that the echo decays exponentially, rather than power law as in the low-energy orthogonality catastrophe, a further example of quench-induced decoherence already found in the case of quenched Luttinger liquids. The emerging decoherence scale is set by the strength of the local potential and the bulk excitation energy.
Loschmidt echo for quantum metrology
NASA Astrophysics Data System (ADS)
Macrı, Tommaso; Smerzi, Augusto; Pezzè, Luca
2016-07-01
We propose a versatile Loschmidt echo protocol to detect and quantify multiparticle entanglement. It allows us to extract the quantum Fisher information for arbitrary pure states, and finds direct application in quantum metrology. In particular, the protocol applies to states that are generally difficult to characterize, as non-Gaussian states, and states that are not symmetric under particle exchange. We focus on atomic systems, including trapped ions, polar molecules, and Rydberg atoms, where entanglement is generated dynamically via long-range interaction, and show that the protocol is stable against experimental detection errors.
Discrepancies between decoherence and the Loschmidt echo
NASA Astrophysics Data System (ADS)
Casabone, B.; García-Mata, I.; Wisniacki, D. A.
2010-03-01
The Loschmidt echo and the purity are two quantities that can provide invaluable information about the evolution of a quantum system. While the Loschmidt echo characterizes instability and sensitivity to perturbations, purity measures the loss of coherence produced by an environment coupled to the system. For classically chaotic systems both quantities display a number of —supposedly universal— regimes that can lead to think of them as equivalent quantities. We study the decay of the Loschmidt echo and the purity for systems with finite-dimensional Hilbert space and present numerical evidence of some fundamental differences between them.
Loschmidt Echo in a System of Interacting Electrons
Manfredi, G.; Hervieux, P.-A.
2006-11-10
We study the Loschmidt echo for a system of electrons interacting through mean-field Coulomb forces. The electron gas is modeled by a self-consistent set of hydrodynamic equations. It is observed that the quantum fidelity drops abruptly after a time that is proportional to the logarithm of the perturbation amplitude. The fidelity drop is related to the breakdown of the symmetry properties of the wave function.
Time reversal communication system
Candy, James V.; Meyer, Alan W.
2008-12-02
A system of transmitting a signal through a channel medium comprises digitizing the signal, time-reversing the digitized signal, and transmitting the signal through the channel medium. The channel medium may be air, earth, water, tissue, metal, and/or non-metal.
Buljubasich, Lisandro; Dente, Axel D.; Levstein, Patricia R.; Chattah, Ana K.; Pastawski, Horacio M.; Sánchez, Claudia M.
2015-10-28
We performed Loschmidt echo nuclear magnetic resonance experiments to study decoherence under a scaled dipolar Hamiltonian by means of a symmetrical time-reversal pulse sequence denominated Proportionally Refocused Loschmidt (PRL) echo. The many-spin system represented by the protons in polycrystalline adamantane evolves through two steps of evolution characterized by the secular part of the dipolar Hamiltonian, scaled down with a factor |k| and opposite signs. The scaling factor can be varied continuously from 0 to 1/2, giving access to a range of complexity in the dynamics. The experimental results for the Loschmidt echoes showed a spreading of the decay rates that correlate directly to the scaling factors |k|, giving evidence that the decoherence is partially governed by the coherent dynamics. The average Hamiltonian theory was applied to give an insight into the spin dynamics during the pulse sequence. The calculations were performed for every single radio frequency block in contrast to the most widely used form. The first order of the average Hamiltonian numerically computed for an 8-spin system showed decay rates that progressively decrease as the secular dipolar Hamiltonian becomes weaker. Notably, the first order Hamiltonian term neglected by conventional calculations yielded an explanation for the ordering of the experimental decoherence rates. However, there is a strong overall decoherence observed in the experiments which is not reflected by the theoretical results. The fact that the non-inverted terms do not account for this effect is a challenging topic. A number of experiments to further explore the relation of the complete Hamiltonian with this dominant decoherence rate are proposed.
NASA Astrophysics Data System (ADS)
Buljubasich, Lisandro; Sánchez, Claudia M.; Dente, Axel D.; Levstein, Patricia R.; Chattah, Ana K.; Pastawski, Horacio M.
2015-10-01
We performed Loschmidt echo nuclear magnetic resonance experiments to study decoherence under a scaled dipolar Hamiltonian by means of a symmetrical time-reversal pulse sequence denominated Proportionally Refocused Loschmidt (PRL) echo. The many-spin system represented by the protons in polycrystalline adamantane evolves through two steps of evolution characterized by the secular part of the dipolar Hamiltonian, scaled down with a factor |k| and opposite signs. The scaling factor can be varied continuously from 0 to 1/2, giving access to a range of complexity in the dynamics. The experimental results for the Loschmidt echoes showed a spreading of the decay rates that correlate directly to the scaling factors |k|, giving evidence that the decoherence is partially governed by the coherent dynamics. The average Hamiltonian theory was applied to give an insight into the spin dynamics during the pulse sequence. The calculations were performed for every single radio frequency block in contrast to the most widely used form. The first order of the average Hamiltonian numerically computed for an 8-spin system showed decay rates that progressively decrease as the secular dipolar Hamiltonian becomes weaker. Notably, the first order Hamiltonian term neglected by conventional calculations yielded an explanation for the ordering of the experimental decoherence rates. However, there is a strong overall decoherence observed in the experiments which is not reflected by the theoretical results. The fact that the non-inverted terms do not account for this effect is a challenging topic. A number of experiments to further explore the relation of the complete Hamiltonian with this dominant decoherence rate are proposed.
Dynamical phase transitions and Loschmidt echo in the infinite-range XY model.
Žunkovič, Bojan; Silva, Alessandro; Fabrizio, Michele
2016-06-13
We compare two different notions of dynamical phase transitions in closed quantum systems. The first is identified through the time-averaged value of the equilibrium-order parameter, whereas the second corresponds to non-analyticities in the time behaviour of the Loschmidt echo. By exactly solving the dynamics of the infinite-range XY model, we show that in this model non-analyticities of the Loschmidt echo are not connected to standard dynamical phase transitions and are not robust against quantum fluctuations. Furthermore, we show that the existence of either of the two dynamical transitions is not necessarily connected to the equilibrium quantum phase transition. PMID:27140975
NASA Astrophysics Data System (ADS)
Fannjiang, Albert C.
2009-09-01
The concept of time reversal (TR) of a scalar wave is reexamined from basic principles. Five different time-reversal mirrors (TRMs) are introduced and their relations are analyzed. For the boundary behavior, it is shown that for a paraxial wave only the monopole TR scheme satisfies the exact boundary condition while for the spherical wave only the MD-mode TR scheme satisfies the exact boundary condition. The asymptotic analysis of the near-field focusing property is presented for two dimensions and three dimensions. It is shown that to have a subwavelength focal spot, the TRM should consist of dipole transducers. The transverse resolution of the dipole TRM is linearly proportional to the distance between the point source and the TRM. The mixed mode TRM has the similar (linear) behavior in three dimensions, but in two dimensions the transverse resolution behaves as the square root of the distance between the point source and the TRM. The monopole TRM is ineffective in focusing below the wavelength. Contrary to the matched field processing and the phase processor, both of which resemble TR, TR in a weak- or non-scattering medium is usually biased in the longitudinal direction, especially when TR is carried out on a single plane with a finite aperture. This is true for all five TR schemes. On the other hand, the TR focal spot has been shown repeatedly in the literature, both theoretically and experimentally, to be centered at the source point when the medium is multiple scattering. A reconciliation of the two seemingly conflicting results is found in the random fluctuations in the intensity of the Green function for a multiple scattering medium and the notion of scattering-enlarged effective aperture.
Quinn, H; /SLAC
2009-01-27
This talk briefly reviews three types of time-asymmetry in physics, which I classify as universal, macroscopic and microscopic. Most of the talk is focused on the latter, namely the violation of T-reversal invariance in particle physics theories. In sum tests of microscopic T-invariance, or observations of its violation, are limited by the fact that, while we can measure many processes, only in very few cases can we construct a matched pair of process and inverse process and observe it with sufficient sensitivity to make a test. In both the cases discussed here we can achieve an observable T violation making use of flavor tagging, and in the second case also using the quantum properties of an antisymmetric coherent state of two B mesons to construct a CP-tag. Both these tagging properties depend only on very general properties of the flavor and/or CP quantum numbers and so provide model independent tests for T-invariance violations. The microscopic laws of physics are very close to T-symmetric. There are small effects that give CP- and T-violating processes in three-generation-probing weak decays. Where a T-violating observable can be constructed we see the relationships between T-violation and CP-violation expected in a CPT conserving theory. These microscopic effects are unrelated to the 'arrow of time' that is defined by increasing entropy, or in the time direction defined by the expansion of our Universe.
Loschmidt echo and the many-body orthogonality catastrophe in a qubit-coupled Luttinger liquid.
Dóra, Balázs; Pollmann, Frank; Fortágh, József; Zaránd, Gergely
2013-07-26
We investigate the many-body generalization of the orthogonality catastrophe by studying the generalized Loschmidt echo of Luttinger liquids (LLs) after a global change of interaction. It decays exponentially with system size and exhibits universal behavior: the steady state exponent after quenching back and forth n times between 2 LLs (bang-bang protocol) is 2n times bigger than that of the adiabatic overlap and depends only on the initial and final LL parameters. These are corroborated numerically by matrix-product state based methods of the XXZ Heisenberg model. An experimental setup consisting of a hybrid system containing cold atoms and a flux qubit coupled to a Feshbach resonance is proposed to measure the Loschmidt echo using rf spectroscopy or Ramsey interferometry. PMID:23931387
Remote Whispering Applying Time Reversal
Anderson, Brian Eric
2015-07-16
The purpose of this project was to explore the use of time reversal technologies as a means for communication to a targeted individual or location. The idea is to have the privacy of whispering in one’s ear, but to do this remotely from loudspeakers not located near the target. Applications of this work include communicating with hostages and survivors in rescue operations, communicating imaging and operational conditions in deep drilling operations, monitoring storage of spent nuclear fuel in storage casks without wires, or clandestine activities requiring signaling between specific points. This technology provides a solution in any application where wires and radio communications are not possible or not desired. It also may be configured to self calibrate on a regular basis to adjust for changing conditions. These communications allow two people to converse with one another in real time, converse in an inaudible frequency range or medium (i.e. using ultrasonic frequencies and/or sending vibrations through a structure), or send information for a system to interpret (even allowing remote control of a system using sound). The time reversal process allows one to focus energy to a specific location in space and to send a clean transmission of a selected signal only to that location. In order for the time reversal process to work, a calibration signal must be obtained. This signal may be obtained experimentally using an impulsive sound, a known chirp signal, or other known signals. It may also be determined from a numerical model of a known environment in which the focusing is desired or from passive listening over time to ambient noise.
Three component vibrational time reversal communication
Anderson, Brian E.; Ulrich, Timothy J.; Ten Cate, James A.
2015-01-01
Time reversal provides an optimal prefilter matched signal to apply to a communication signal before signal transmission. Time reversal allows compensation for wave speed dispersion and can function well in reverberant environments. Time reversal can be used to focus elastic energy to each of the three components of motion independently. A pipe encased in concrete was used to demonstrate the ability to conduct communications of information using three component time reversal. Furthermore, the ability of time reversal to compensate for multi-path distortion (overcoming reverberation) will be demonstrated and the rate of signal communication will be presented. [The U.S. Department ofmore » Energy, through the LANL/LDRD Program, is gratefully acknowledged for supporting this work.]« less
Three component vibrational time reversal communication
Anderson, Brian E.; Ulrich, Timothy J.; Ten Cate, James A.
2015-01-01
Time reversal provides an optimal prefilter matched signal to apply to a communication signal before signal transmission. Time reversal allows compensation for wave speed dispersion and can function well in reverberant environments. Time reversal can be used to focus elastic energy to each of the three components of motion independently. A pipe encased in concrete was used to demonstrate the ability to conduct communications of information using three component time reversal. Furthermore, the ability of time reversal to compensate for multi-path distortion (overcoming reverberation) will be demonstrated and the rate of signal communication will be presented. [The U.S. Department of Energy, through the LANL/LDRD Program, is gratefully acknowledged for supporting this work.
Time-reversed, flow-reversed ballistics simulations
Zernow, L.; Chapyak, E. J.; Scheffler, D. R.
2001-01-01
Two-dimensional simulations of planar sheet jet formation are studied to examine the hydrodynamic issues involved when simulations are carried out in the inverse direction, that is, with reversed time and flow. Both a realistic copper equation of state and a shockless equation of state were used. These studies are an initial step in evaluating this technique as a ballistics design tool.
Time reversibility in the quantum frame
Masot-Conde, Fátima
2014-12-04
Classic Mechanics and Electromagnetism, conventionally taken as time-reversible, share the same concept of motion (either of mass or charge) as the basis of the time reversibility in their own fields. This paper focuses on the relationship between mobile geometry and motion reversibility. The goal is to extrapolate the conclusions to the quantum frame, where matter and radiation behave just as elementary mobiles. The possibility that the asymmetry of Time (Time’s arrow) is an effect of a fundamental quantum asymmetry of elementary particles, turns out to be a consequence of the discussion.
Probing localization in absorbing systems via Loschmidt echos.
Bodyfelt, Joshua D; Zheng, Mei C; Kottos, Tsampikos; Kuhl, Ulrich; Stöckmann, Hans-Jürgen
2009-06-26
We measure Anderson localization in quasi-one-dimensional waveguides in the presence of absorption by analyzing the echo dynamics due to small perturbations. We specifically show that the inverse participation number of localized modes dictates the decay of the Loschmidt echo, differing from the Gaussian decay expected for diffusive or chaotic systems. Our theory, based on a random matrix modeling, agrees perfectly with scattering echo measurements on a quasi-one-dimensional microwave cavity filled with randomly distributed scatterers. PMID:19659075
Time reversals of irreversible quantum maps
NASA Astrophysics Data System (ADS)
Aurell, Erik; Zakrzewski, Jakub; Życzkowski, Karol
2015-09-01
We propose an alternative notion of time reversal in open quantum systems as represented by linear quantum operations, and a related generalization of classical entropy production in the environment. This functional is the ratio of the probability to observe a transition between two states under the forward and the time reversed dynamics, and leads, as in the classical case, to fluctuation relations as tautological identities. As in classical dynamics in contact with a heat bath, time reversal is not unique, and we discuss several possibilities. For any bistochastic map its dual map preserves the trace and describes a legitimate dynamics reversed in time, in that case the entropy production in the environment vanishes. For a generic stochastic map we construct a simple quantum operation which can be interpreted as a time reversal. For instance, the decaying channel, which sends the excited state into the ground state with a certain probability, can be reversed into the channel transforming the ground state into the excited state with the same probability.
Time reversal signal processing for communication.
Young, Derek P.; Jacklin, Neil; Punnoose, Ratish J.; Counsil, David T.
2011-09-01
Time-reversal is a wave focusing technique that makes use of the reciprocity of wireless propagation channels. It works particularly well in a cluttered environment with associated multipath reflection. This technique uses the multipath in the environment to increase focusing ability. Time-reversal can also be used to null signals, either to reduce unintentional interference or to prevent eavesdropping. It does not require controlled geometric placement of the transmit antennas. Unlike existing techniques it can work without line-of-sight. We have explored the performance of time-reversal focusing in a variety of simulated environments. We have also developed new algorithms to simultaneously focus at a location while nulling at an eavesdropper location. We have experimentally verified these techniques in a realistic cluttered environment.
Time reversal communication with a mobile source.
Song, H C
2013-10-01
Broadband underwater acoustic communication signals undergo either a compression or dilation in the presence of relative motion between a source and a receiver. Consequently, underwater acoustic communications with a mobile source/receiver require Doppler compensation through resampling. However, resampling may not be necessary when a channel-estimate-based time reversal approach is applied with frequent channel updates. Using experimental data (20-30 kHz), it is demonstrated that the performance of time reversal communication without resampling is similar to the case with resampling, along with the benefit of a modest computational saving. PMID:24116398
Time-forward speech intelligibility in time-reversed rooms
Longworth-Reed, Laricia; Brandewie, Eugene; Zahorik, Pavel
2009-01-01
The effects of time-reversed room acoustics on word recognition abilities were examined using virtual auditory space techniques, which allowed for temporal manipulation of the room acoustics independent of the speech source signals. Two acoustical conditions were tested: one in which room acoustics were simulated in a realistic time-forward fashion and one in which the room acoustics were reversed in time, causing reverberation and acoustic reflections to precede the direct-path energy. Significant decreases in speech intelligibility—from 89% on average to less than 25%—were observed between the time-forward and time-reversed rooms. This result is not predictable using standard methods for estimating speech intelligibility based on the modulation transfer function of the room. It may instead be due to increased degradation of onset information in the speech signals when room acoustics are time-reversed. PMID:19173377
Time reversal technique for gas leakage detection.
Maksimov, A O; Polovinka, Yu A
2015-04-01
The acoustic remote sensing of subsea gas leakage traditionally uses sonars as active acoustic sensors and hydrophones picking up the sound generated by a leak as passive sensors. When gas leaks occur underwater, bubbles are produced and emit sound at frequencies intimately related to their sizes. The experimental implementation of an acoustic time-reversal mirror (TRM) is now well established in underwater acoustics. In the basic TRM experiment, a probe source emits a pulse that is received on an array of sensors, time reversed, and re-emitted. After time reversal, the resulting field focuses back at the probe position. In this study, a method for enhancing operation of the passive receiving system has been proposed by using it in the regime of TRM. Two factors, the local character of the acoustic emission signal caused by the leakage and a resonant nature of the bubble radiation at their birth, make particularly effective scattering with the conjugate wave (CW). Analytical calculations are performed for the scattering of CW wave on a single bubble when CW is formed by bubble birthing wail received on an array, time reversed, and re-emitted. The quality of leakage detection depends on the spatio-temporal distribution of ambient noise. PMID:25920866
Listing all sorting reversals in quadratic time
2011-01-01
We describe an average-case O(n2) algorithm to list all reversals on a signed permutation π that, when applied to π, produce a permutation that is closer to the identity. This algorithm is optimal in the sense that, the time it takes to write the list is Ω(n2) in the worst case. PMID:21504604
Momentum-Space Entanglement and Loschmidt Echo in Luttinger Liquids after a Quantum Quench
NASA Astrophysics Data System (ADS)
Dóra, Balázs; Lundgren, Rex; Selover, Mark; Pollmann, Frank
2016-07-01
Luttinger liquids (LLs) arise by coupling left- and right-moving particles through interactions in one dimension. This most natural partitioning of LLs is investigated by the momentum-space entanglement after a quantum quench using analytical and numerical methods. We show that the momentum-space entanglement spectrum of a LL possesses many universal features both in equilibrium and after a quantum quench. The largest entanglement eigenvalue is identical to the Loschmidt echo, i.e., the overlap of the disentangled and final wave functions of the system. The second largest eigenvalue is the overlap of the first excited state of the disentangled system with zero total momentum and the final wave function. The entanglement gap is universal both in equilibrium and after a quantum quench. The momentum-space entanglement entropy is always extensive and saturates fast to a time independent value after the quench, in sharp contrast to a spatial bipartitioning.
Momentum-Space Entanglement and Loschmidt Echo in Luttinger Liquids after a Quantum Quench.
Dóra, Balázs; Lundgren, Rex; Selover, Mark; Pollmann, Frank
2016-07-01
Luttinger liquids (LLs) arise by coupling left- and right-moving particles through interactions in one dimension. This most natural partitioning of LLs is investigated by the momentum-space entanglement after a quantum quench using analytical and numerical methods. We show that the momentum-space entanglement spectrum of a LL possesses many universal features both in equilibrium and after a quantum quench. The largest entanglement eigenvalue is identical to the Loschmidt echo, i.e., the overlap of the disentangled and final wave functions of the system. The second largest eigenvalue is the overlap of the first excited state of the disentangled system with zero total momentum and the final wave function. The entanglement gap is universal both in equilibrium and after a quantum quench. The momentum-space entanglement entropy is always extensive and saturates fast to a time independent value after the quench, in sharp contrast to a spatial bipartitioning. PMID:27419554
Time-reversal generation of rogue waves.
Chabchoub, Amin; Fink, Mathias
2014-03-28
The formation of extreme localizations in nonlinear dispersive media can be explained and described within the framework of nonlinear evolution equations, such as the nonlinear Schrödinger equation (NLS). Within the class of exact NLS breather solutions on a finite background, which describe the modulational instability of monochromatic wave trains, the hierarchy of rational solutions localized in both time and space is considered to provide appropriate prototypes to model rogue wave dynamics. Here, we use the time-reversal invariance of the NLS to propose and experimentally demonstrate a new approach to constructing strongly nonlinear localized waves focused in both time and space. The potential applications of this time-reversal approach include remote sensing and motivated analogous experimental analysis in other nonlinear dispersive media, such as optics, Bose-Einstein condensates, and plasma, where the wave motion dynamics is governed by the NLS. PMID:24724652
Time-Reversal Generation of Rogue Waves
NASA Astrophysics Data System (ADS)
Chabchoub, Amin; Fink, Mathias
2014-03-01
The formation of extreme localizations in nonlinear dispersive media can be explained and described within the framework of nonlinear evolution equations, such as the nonlinear Schrödinger equation (NLS). Within the class of exact NLS breather solutions on a finite background, which describe the modulational instability of monochromatic wave trains, the hierarchy of rational solutions localized in both time and space is considered to provide appropriate prototypes to model rogue wave dynamics. Here, we use the time-reversal invariance of the NLS to propose and experimentally demonstrate a new approach to constructing strongly nonlinear localized waves focused in both time and space. The potential applications of this time-reversal approach include remote sensing and motivated analogous experimental analysis in other nonlinear dispersive media, such as optics, Bose-Einstein condensates, and plasma, where the wave motion dynamics is governed by the NLS.
Time-reversal asymmetry in financial systems
NASA Astrophysics Data System (ADS)
Jiang, X. F.; Chen, T. T.; Zheng, B.
2013-11-01
We investigate the large-fluctuation dynamics in financial markets, based on the minute-to-minute and daily data of the Chinese Indices and the German DAX. The dynamic relaxation both before and after the large fluctuations is characterized by a power law, and the exponents p± usually vary with the strength of the large fluctuations. The large-fluctuation dynamics is time-reversal symmetric at the time scale in minutes, while asymmetric at the daily time scale. Careful analysis reveals that the time-reversal asymmetry is mainly induced by external forces. It is also the external forces which drive the financial system to a non-stationary state. Different characteristics of the Chinese and German stock markets are uncovered.
Sánchez, C M; Levstein, P R; Buljubasich, L; Pastawski, H M; Chattah, A K
2016-06-13
In this work, we overview time-reversal nuclear magnetic resonance (NMR) experiments in many-spin systems evolving under the dipolar Hamiltonian. The Loschmidt echo (LE) in NMR is the signal of excitations which, after evolving with a forward Hamiltonian, is recovered by means of a backward evolution. The presence of non-diagonal terms in the non-equilibrium density matrix of the many-body state is directly monitored experimentally by encoding the multiple quantum coherences. This enables a spin counting procedure, giving information on the spreading of an excitation through the Hilbert space and the formation of clusters of correlated spins. Two samples representing different spin systems with coupled networks were used in the experiments. Protons in polycrystalline ferrocene correspond to an 'infinite' network. By contrast, the liquid crystal N-(4-methoxybenzylidene)-4-butylaniline in the nematic mesophase represents a finite proton system with a hierarchical set of couplings. A close connection was established between the LE decay and the spin counting measurements, confirming the hypothesis that the complexity of the system is driven by the coherent dynamics. PMID:27140972
Time reversal invariance in polarized neutron decay
Wasserman, E.G.
1994-03-01
An experiment to measure the time reversal invariance violating (T-violating) triple correlation (D) in the decay of free polarized neutrons has been developed. The detector design incorporates a detector geometry that provides a significant improvement in the sensitivity over that used in the most sensitive of previous experiments. A prototype detector was tested in measurements with a cold neutron beam. Data resulting from the tests are presented. A detailed calculation of systematic effects has been performed and new diagnostic techniques that allow these effects to be measured have been developed. As the result of this work, a new experiment is under way that will improve the sensitivity to D to 3 {times} 10{sup {minus}4} or better. With higher neutron flux a statistical sensitivity of the order 3 {times} 10{sup {minus}5} is ultimately expected. The decay of free polarized neutrons (n {yields} p + e + {bar v}{sub e}) is used to search for T-violation by measuring the triple correlation of the neutron spin polarization, and the electron and proton momenta ({sigma}{sub n} {center_dot} p{sub p} {times} p{sub e}). This correlation changes sign under reversal of the motion. Since final state effects in neutron decay are small, a nonzero coefficient, D, of this correlation indicates the violation of time reversal invariance. D is measured by comparing the numbers of coincidences in electron and proton detectors arranged symmetrically about a longitudinally polarized neutron beam. Particular care must be taken to eliminate residual asymmetries in the detectors or beam as these can lead to significant false effects. The Standard Model predicts negligible T-violating effects in neutron decay. Extensions to the Standard Model include new interactions some of which include CP-violating components. Some of these make first order contributions to D.
Real time inverse filter focusing through iterative time reversal.
Montaldo, Gabriel; Tanter, Mickaël; Fink, Mathias
2004-02-01
In order to achieve an optimal focusing through heterogeneous media we need to build the inverse filter of the propagation operator. Time reversal is an easy and robust way to achieve such an inverse filter in nondissipative media. However, as soon as losses appear in the medium, time reversal is not equivalent to the inverse filter anymore. Consequently, it does not produce the optimal focusing and beam degradations may appear. In such cases, we showed in previous works that the optimal focusing can be recovered by using the so-called spatiotemporal inverse filter technique. This process requires the presence of a complete set of receivers inside the medium. It allows one to reach the optimal focusing even in extreme situations such as ultrasonic focusing through human skull or audible sound focusing in strongly reverberant rooms. But, this technique is time consuming and implied fastidious numerical calculations. In this paper we propose a new way to process this inverse filter focusing technique in real time and without any calculation. The new process is based on iterative time reversal process. Contrary to the classical inverse filter technique, this iteration does not require any computation and achieves the inverse filter in an experimental way using wave propagation instead of computational power. The convergence from time reversal to inverse filter during the iterative process is theoretically explained. Finally, the feasibility of this iterative technique is experimentally demonstrated for ultrasound applications. PMID:15000188
Time Reversal in Solids (Linear and Nonlinear Elasticity): Multimedia Resources in Time Reversal
Dynamic nonlinear elastic behavior, nonequilibrium dynamics, first observed as a curiosity in earth materials has now been observed in a great variety of solids. The primary manifestations of the behavior are characteristic wave distortion, and slow dynamics, a recovery process to equilibrium that takes place linearly with the logarithm of time, over hours to days after a wave disturbance. The link between the diverse materials that exhibit nonequilibrium dynamics appears to be the presence of soft regions, thought to be 'damage' at many scales, ranging from order 10-9 m to 10-1 m at least. The regions of soft matter may be distributed as in a rock sample, or isolated, as in a sample with a single crack [LANLhttp://www.lanl.gov/orgs/ees/ees11/geophysics/nonlinear/nonlinear.shtml]. The Geophysics Group (EES-11) at Los Alamos National Laboratory has posted two or more multimedia items under each of the titles below to demonstrate aspects of their work: 1) Source Reconstruction Using Time Reversal; 2) Robustness and Efficiency of Time Reversal Acoustics in Solid Media; 3) Audio Example of Time Reversal - Speech Privacy; 4) Crack Imagining with Time Reversal - Experimental Results; 5) Time Reversal of the 2004 (M9.0) Sumatra Earthquake.
Time-reversal violation in beta decay
Herczeg, P.
2003-01-01
At present there is no unambigous direct evidence for time-reversal (T) violation in the fundamental interactions. But T-violation is intimately connected with CP-violation by the CPT theorem. A stringent bound on possible violation of CPT invariance comes from the properties of K{sup 0} - {bar K}{sup 0} mixing [I]. In the following we shall assume that CPT violating interactions, if present, can be neglected, and use the terms 'T-violation' and 'CP-violation' interchangably.
Time-reversal and the Bessel equation
NASA Astrophysics Data System (ADS)
Alfinito, Eleonora; Vitiello, Giuseppe
2015-07-01
The system of two damped/amplified oscillator equations is of widespread interest in the study of many physical problems and phenomena, from inflationary models of the Universe to thermal field theories, in condensed matter physics as well in high energy physics, and also in neuroscience. In this report we review the equivalence, in a suitable parametrization, between such a system of equations and the Bessel equations. In this connection, we discuss the breakdown of loop-antiloop symmetry, its relation with time-reversal symmetry and the mechanism of group contraction. Euclidean algebras such as e(2) and e(3) are also discussed in relation with Virasoro-like algebra.
Reverse-Time Migration Based Optical Imaging.
Wang, Zhiyong; Ding, Hao; Lu, Guijin; Bi, Xiaohong
2016-01-01
We theoretically demonstrated a new optical imaging technique based on reverse-time migration (RTM) for reconstructing optical structures in homogeneous media for the first time. RTM is a powerful wave-equation-based method to reconstruct the image of the structure by modeling the wave propagation inside the media with both forward modeling and reverse-time extrapolation. While RTM is commonly used with acoustic seismic waves, this paper represents the first effort to develop optical RTM imaging method for biomedical research. To refine the image quality, we further developed new methods to suppress the low-wavenumber artifact (LWA). When compared with the conventional means for LWA suppression such as Laplacian filtering, illumination normalization, and the ratio method, our new derivative-based and power-image methods are able to significantly reduce LWA, resulting in high-quality reconstructed images with sufficient contrasts and spatial resolutions for structure identification. The optical RTM imaging technique may provide a new platform for non-invasive optical imaging of structures in deep layers of tissues for biomedical applications. PMID:26292337
Time-reversal-symmetry breaking in turbulence
NASA Astrophysics Data System (ADS)
Jucha, Jennifer; Xu, Haitao; Pumir, Alain; Bodenschatz, Eberhard
2014-11-01
In three-dimensional turbulent flows, the flux of energy from large to small scales breaks time symmetry. We show here that this irreversibility can be quantified by following the relative motion of several Lagrangian tracers. We find by analytical calculation, numerical analysis and experimental observation that the existence of the energy flux implies that, at short times, two particles separate temporally slower forwards than backwards, and the difference between forward and backward dispersion grows as t3. We also find the geometric deformation of material volumes, surrogated by four points spanning an initially regular tetrahedron, to show sensitivity to the time-reversal with an effect growing linearly in t. We associate this with the structure of the strain rate in the flow. We thank the support from Max Planck Society, the Humboldt Foundation, ANR, and PSMN at ENS-Lyon.
Nematic electroconvection under time-reversed excitation
NASA Astrophysics Data System (ADS)
Pietschmann, Dirk; John, Thomas; Stannarius, Ralf
2010-10-01
We study nematic electrohydrodynamic convection (EHC) under excitation with superimposed harmonic wave forms. Within the standard model for EHC, a time reversal of the excitation does not affect threshold voltages and pattern wavelengths obtained in a linear stability analysis. This was confirmed in experiments with superimposed square waves [Heuer , Phys. Rev. E 78, 036218 (2008)10.1103/PhysRevE.78.036218]. We show here that this symmetry with respect to time reversal of the excitation breaks down close to the transition from the conduction regime to the dielectric regime. The EHC standard model without flexoelectric terms fails to predict quantitatively correct threshold curves and wavelengths in a certain parameter range below the transition. This is an indication that a more elaborate description of the EHC mechanism is necessary in this range. We suggest that the weak electrolyte model has to be employed for a correct description. This is in accordance with observations of traveling rolls and of localized structures at onset of the convection in earlier experiments described in literature.
Time reversal violation for entangled neutral mesons
NASA Astrophysics Data System (ADS)
Bernabéu, J.
2013-07-01
A direct evidence for Time Reversal Violation (TRV) means an experiment that, considered by itself, clearly shows TRV independent of, and unconnected to, the results for CP Violation. No existing result before the recent BABAR experiment with entangled neutral B mesons had demonstrated TRV in this sense. There is a unique opportunity for a search of TRV with unstable particles thanks to the Einstein-Podolsky-Rosen (EPR) Entanglement between the two neutral mesons in B, and PHI, Factories. The two quantum effects of the first decay as a filtering measurement and the transfer of information to the still living partner allow performing a genuine TRV asymmetry with the exchange of "in" and "out" states. With four independent TRV asymmetries, BABAR observes a large deviation of T-invariance with a statistical significance of 14 standard deviations, far more than needed to declare the result as a discovery. This is the first direct observation of TRV in the time evolution of any system.
Direct observation of time reversal violation
NASA Astrophysics Data System (ADS)
Bernabéu, J.
2013-06-01
A direct evidence for Time Reversal Violation (TRV) means an experiment that, considered by itself, clearly shows TRV independent of, and unconnected to, the results for CP Violation. No existing result before the recent BABAR experiment with entangled neutral B mesons had demonstrated TRV in this sense. There is a unique opportunity for a search of TRV with unstable particles thanks to the Einstein-Podolsky-Rosen (EPR) Entanglement between the two neutral mesons in B, and PHI, Factories. The two quantum effects of the first decay as a filtering measurement and the transfer of information to the still living partner allow performing a genuine TRV asymmetry with the exchange of "in" and "out" states. With four independent TRV asymmetries, BABAR observes a large deviation of T-invariance with a statistical significance of 14 standard deviations, far more than needed to declare the result as a discovery. This is the first direct observation of TRV in the time evolution of any system.
Time-reversibility and particle sedimentation
NASA Technical Reports Server (NTRS)
Golubitsky, Martin; Krupa, Martin; Lim, Chjan
1991-01-01
This paper studies an ODE model, called the Stokeslet model, and describes sedimentation of small clusters of particles in a highly viscous fluid. This model has a trivial solution in which the n particles arrange themselves at the vertices of a regular n-sided polygon. When n = 3, Hocking and Caflisch et al. (1988) proved the existence of periodic motion (in the frame moving with the center of gravity in the cluster) in which the particles form an isosceles triangle. Here, the study of periodic and quasi-periodic solutions of the Stokeslet model is continued, with emphasis on the spatial and time-reversal symmetry of the model. For three particles, the existence of a second family of periodic solutions and a family of quasi-periodic solutions is proved. It is also indicated how the methods generalize to the case of n particles.
Time reversal acoustic communication for multiband transmission.
Song, Aijun; Badiey, Mohsen
2012-04-01
In this letter, multiband acoustic communication is proposed to access a relatively wide frequency band. The entire frequency band is divided into multiple separated sub-bands, each of which is several kilohertz in width. Time reversal decision feedback equalizers are used to compensate for inter-symbol interference at each sub-band. The communication scheme was demonstrated in a shallow water acoustic experiment conducted in Kauai, Hawaii during the summer of 2011. Using quadrature phase-shift keying signaling at four sub-bands over the frequency band of 10-32 kHz, a data rate of 32 k bits/s was achieved over a 3 km communication range. PMID:22502482
Time reversal violation for entangled neutral mesons
Bernabeu, J.
2014-07-23
A direct evidence for Time Reversal Violation (TRV) means an experiment that, considered by itself, clearly shows TRV independent of, and unconnected to, the results for CP Violation. No existing result before the recent BABAR experiment with entangled neutral B mesons had demonstrated TRV in this sense. There is a unique solution for the test of TRV with unstable particles thanks to the Einstein-Podolsky-Rosen (EPR) Entanglement between the two neutral mesons in B, and φ, Factories. The two quantum effects of the decays as filtering measurements of the meson states and the transfer of information of the first decay to the still living partner allow performing a genuine TRV asymmetry with the exchange of “in” and “out” states. With four independent TRV asymmetries, BABAR observes a large deviation of T-invariance with a statistical significance of 14 standard deviations, far more than needed to declare the result as a discovery. This is the first direct observation of TRV in the time evolution of any system. The perspectives for future additional studies of TRV are discussed.
Time reversal violation for entangled neutral mesons
NASA Astrophysics Data System (ADS)
Bernabeu, J.
2014-07-01
A direct evidence for Time Reversal Violation (TRV) means an experiment that, considered by itself, clearly shows TRV independent of, and unconnected to, the results for CP Violation. No existing result before the recent BABAR experiment with entangled neutral B mesons had demonstrated TRV in this sense. There is a unique solution for the test of TRV with unstable particles thanks to the Einstein-Podolsky-Rosen (EPR) Entanglement between the two neutral mesons in B, and φ, Factories. The two quantum effects of the decays as filtering measurements of the meson states and the transfer of information of the first decay to the still living partner allow performing a genuine TRV asymmetry with the exchange of "in" and "out" states. With four independent TRV asymmetries, BABAR observes a large deviation of T-invariance with a statistical significance of 14 standard deviations, far more than needed to declare the result as a discovery. This is the first direct observation of TRV in the time evolution of any system. The perspectives for future additional studies of TRV are discussed.
Breast cancer detection using time reversal
NASA Astrophysics Data System (ADS)
Sheikh Sajjadieh, Mohammad Hossein
Breast cancer is the second leading cause of cancer death after lung cancer among women. Mammography and magnetic resonance imaging (MRI) have certain limitations in detecting breast cancer, especially during its early stage of development. A number of studies have shown that microwave breast cancer detection has potential to become a successful clinical complement to the conventional X-ray mammography. Microwave breast imaging is performed by illuminating the breast tissues with an electromagnetic waveform and recording its reflections (backscatters) emanating from variations in the normal breast tissues and tumour cells, if present, using an antenna array. These backscatters, referred to as the overall (tumour and clutter) response, are processed to estimate the tumour response, which is applied as input to array imaging algorithms used to estimate the location of the tumour. Due to changes in the breast profile over time, the commonly utilized background subtraction procedures used to estimate the target (tumour) response in array processing are impractical for breast cancer detection. The thesis proposes a new tumour estimation algorithm based on a combination of the data adaptive filter with the envelope detection filter (DAF/EDF), which collectively do not require a training step. After establishing the superiority of the DAF/EDF based approach, the thesis shows that the time reversal (TR) array imaging algorithms outperform their conventional conterparts in detecting and localizing tumour cells in breast tissues at SNRs ranging from 15 to 30dB.
Three dimensional time reversal optical tomography
NASA Astrophysics Data System (ADS)
Wu, Binlin; Cai, W.; Alrubaiee, M.; Xu, M.; Gayen, S. K.
2011-03-01
Time reversal optical tomography (TROT) approach is used to detect and locate absorptive targets embedded in a highly scattering turbid medium to assess its potential in breast cancer detection. TROT experimental arrangement uses multi-source probing and multi-detector signal acquisition and Multiple-Signal-Classification (MUSIC) algorithm for target location retrieval. Light transport from multiple sources through the intervening medium with embedded targets to the detectors is represented by a response matrix constructed using experimental data. A TR matrix is formed by multiplying the response matrix by its transpose. The eigenvectors with leading non-zero eigenvalues of the TR matrix correspond to embedded objects. The approach was used to: (a) obtain the location and spatial resolution of an absorptive target as a function of its axial position between the source and detector planes; and (b) study variation in spatial resolution of two targets at the same axial position but different lateral positions. The target(s) were glass sphere(s) of diameter ~9 mm filled with ink (absorber) embedded in a 60 mm-thick slab of Intralipid-20% suspension in water with an absorption coefficient μa ~ 0.003 mm-1 and a transport mean free path lt ~ 1 mm at 790 nm, which emulate the average values of those parameters for human breast tissue. The spatial resolution and accuracy of target location depended on axial position, and target contrast relative to the background. Both the targets could be resolved and located even when they were only 4-mm apart. The TROT approach is fast, accurate, and has the potential to be useful in breast cancer detection and localization.
Method for distinguishing multiple targets using time-reversal acoustics
Berryman, James G.
2004-06-29
A method for distinguishing multiple targets using time-reversal acoustics. Time-reversal acoustics uses an iterative process to determine the optimum signal for locating a strongly reflecting target in a cluttered environment. An acoustic array sends a signal into a medium, and then receives the returned/reflected signal. This returned/reflected signal is then time-reversed and sent back into the medium again, and again, until the signal being sent and received is no longer changing. At that point, the array has isolated the largest eigenvalue/eigenvector combination and has effectively determined the location of a single target in the medium (the one that is most strongly reflecting). After the largest eigenvalue/eigenvector combination has been determined, to determine the location of other targets, instead of sending back the same signals, the method sends back these time reversed signals, but half of them will also be reversed in sign. There are various possibilities for choosing which half to do sign reversal. The most obvious choice is to reverse every other one in a linear array, or as in a checkerboard pattern in 2D. Then, a new send/receive, send-time reversed/receive iteration can proceed. Often, the first iteration in this sequence will be close to the desired signal from a second target. In some cases, orthogonalization procedures must be implemented to assure the returned signals are in fact orthogonal to the first eigenvector found.
Reducing current reversal time in electric motor control
Bredemann, Michael V
2014-11-04
The time required to reverse current flow in an electric motor is reduced by exploiting inductive current that persists in the motor when power is temporarily removed. Energy associated with this inductive current is used to initiate reverse current flow in the motor.
Echo-to-reverberation enhancement using a time reversal mirror
NASA Astrophysics Data System (ADS)
Kim, S.; Kuperman, W. A.; Hodgkiss, W. S.; Song, H. C.; Edelmann, G.; Akal, T.
2004-04-01
Reverberation from rough ocean boundaries often degrades the performance of active sonar systems in the ocean. The focusing capability of the time-reversal method provides a new approach to this problem. A time-reversal mirror (TRM) focuses acoustic energy on a target enhancing the target echo while shadowing the boundaries below and above the focus in a waveguide, thereby reducing reverberation. The resulting echo-to-reverberation enhancement has been demonstrated experimentally using a time-reversal mirror in the 3-4 kHz band in shallow water.
Three-dimensional time reversal communications in elastic media.
Anderson, Brian E; Ulrich, Timothy J; Le Bas, Pierre-Yves; Ten Cate, James A
2016-02-01
This letter presents a series of vibrational communication experiments, using time reversal, conducted on a set of cast iron pipes. Time reversal has been used to provide robust, private, and clean communications in many underwater acoustic applications. Here the use of time reversal to communicate along sections of pipes and through a wall is demonstrated to overcome the complications of dispersion and multiple scattering. These demonstrations utilize a single source transducer and a single sensor, a triaxial accelerometer, enabling multiple channels of simultaneous communication streams to a single location. PMID:26936580
Three-dimensional time reversal communications in elastic media
Anderson, Brian E.; Ulrich, Timothy J.; Le Bas, Pierre-Yves; Ten Cate, James A.
2016-02-23
Our letter presents a series of vibrational communication experiments, using time reversal, conducted on a set of cast iron pipes. Time reversal has been used to provide robust, private, and clean communications in many underwater acoustic applications. Also, the use of time reversal to communicate along sections of pipes and through a wall is demonstrated here in order to overcome the complications of dispersion and multiple scattering. These demonstrations utilize a single source transducer and a single sensor, a triaxial accelerometer, enabling multiple channels of simultaneous communication streams to a single location.
Faraday Waves under Time-Reversed Excitation
NASA Astrophysics Data System (ADS)
Pietschmann, Dirk; Stannarius, Ralf; Wagner, Christian; John, Thomas
2013-03-01
Do parametrically driven systems distinguish periodic excitations that are time mirrors of each other? Faraday waves in a Newtonian fluid are studied under excitation with superimposed harmonic wave forms. We demonstrate that the threshold parameters for the stability of the ground state are insensitive to a time inversion of the driving function. This is a peculiarity of some dynamic systems. The Faraday system shares this property with standard electroconvection in nematic liquid crystals [J. Heuer , Phys. Rev. E 78, 036218 (2008)PLEEE81539-3755]. In general, time inversion of the excitation affects the asymptotic stability of a parametrically driven system, even when it is described by linear ordinary differential equations. Obviously, the observed symmetry has to be attributed to the particular structure of the underlying differential equation system. The pattern selection of the Faraday waves above threshold, on the other hand, discriminates between time-mirrored excitation functions.
Faraday waves under time-reversed excitation.
Pietschmann, Dirk; Stannarius, Ralf; Wagner, Christian; John, Thomas
2013-03-01
Do parametrically driven systems distinguish periodic excitations that are time mirrors of each other? Faraday waves in a Newtonian fluid are studied under excitation with superimposed harmonic wave forms. We demonstrate that the threshold parameters for the stability of the ground state are insensitive to a time inversion of the driving function. This is a peculiarity of some dynamic systems. The Faraday system shares this property with standard electroconvection in nematic liquid crystals [J. Heuer et al., Phys. Rev. E 78, 036218 (2008)]. In general, time inversion of the excitation affects the asymptotic stability of a parametrically driven system, even when it is described by linear ordinary differential equations. Obviously, the observed symmetry has to be attributed to the particular structure of the underlying differential equation system. The pattern selection of the Faraday waves above threshold, on the other hand, discriminates between time-mirrored excitation functions. PMID:23496716
Transmission mode time-reversal super-resolution imaging.
Lehman, Sean K; Devaney, Anthony J
2003-05-01
The theory of time-reversal super-resolution imaging of point targets embedded in a reciprocal background medium [A. J. Devaney, "Super-resolution imaging using time-reversal and MUSIC," J. Acoust. Soc. Am. (to be published)] is generalized to the case where the transmitter and receiver sensor arrays need not be coincident and for cases where the background medium can be nonreciprocal. The new theory developed herein is based on the singular value decomposition of the generalized multistatic data matrix of the sensor system rather than the standard eigenvector/eigenvalue decomposition of the time-reversal matrix as was employed in the above-mentioned work and other treatments of time-reversal imaging [Prada, Thomas, and Fink, "The iterative time reversal process: Analysis of the convergence," J. Acoust. Soc. Am. 97, 62 (1995); Prada et al., "Decomposition of the time reversal operator: Detection and selective focusing on two scatterers," J. Acoust. Soc. Am. 99, 2067 (1996)]. A generalized multiple signal classification (MUSIC) algorithm is derived that allows super-resolution imaging of both well-resolved and non-well-resolved point targets from arbitrary sensor array geometries. MUSIC exploits the orthogonal nature of the scatterer and noise subspaces defined by the singular vectors of the multistatic data matrix to form scatterer images. The time-reversal/MUSIC algorithm is tested and validated in two computer simulations of offset vertical seismic profiling where the sensor sources are aligned along the earth's surface and the receiver array is aligned along a subsurface borehole. All results demonstrate the high contrast, high resolution imaging capabilities of this new algorithm combination when compared with "classical" backpropagation or field focusing. Above and beyond the application of seismo-acoustic imaging, the time-reversal super-resolution theory has applications in ocean acoustics for target location, and ultrasonic nondestructive evaluation of
Time Reversal Method for Pipe Inspection with Guided Wave
NASA Astrophysics Data System (ADS)
Deng, Fei; He, Cunfu; Wu, Bin
2008-02-01
The temporal-spatial focusing effect of the time reversal method on the guided wave inspection in pipes is investigated. A steel pipe model with outer diameter of 70 mm and wall thickness of 3.5 mm is numerically built to analyse the reflection coefficient of L(0,2) mode when the time reversal method is applied in the model. According to the calculated results, it is shown that a synthetic time reversal array method is effective to improve the signal-to-noise ratio of a guided wave inspection system. As an intercepting window is widened, more energy can be included in a re-emitted signal, which leads to a large reflection coefficient of L(0,2) mode. It is also shown that when a time reversed signal is reapplied in the pipe model, by analysing the motion of the time reversed wave propagating along the pipe model, a defect can be identified. Therefore, it is demonstrated that the time reversal method can be used to locate the circumferential position of a defect in a pipe. Finally, through an experiment corresponding with the pipe model, the experimental result shows that the above-mentioned method can be valid in the inspection of a pipe.
All-linear time reversal by a dynamic artificial crystal
Chumak, Andrii V.; Tiberkevich, Vasil S.; Karenowska, Alexy D.; Serga, Alexander A.; Gregg, John F.; Slavin, Andrei N.; Hillebrands, Burkard
2010-01-01
The time reversal of pulsed signals or propagating wave packets has long been recognized to have profound scientific and technological significance. Until now, all experimentally verified time-reversal mechanisms have been reliant upon nonlinear phenomena such as four-wave mixing. In this paper, we report the experimental realization of all-linear time reversal. The time-reversal mechanism we propose is based on the dynamic control of an artificial crystal structure, and is demonstrated in a spin-wave system using a dynamic magnonic crystal. The crystal is switched from an homogeneous state to one in which its properties vary with spatial period a, while a propagating wave packet is inside. As a result, a linear coupling between wave components with wave vectors k≈π/a and k′=k−2ππ/a≈−π/a is produced, which leads to spectral inversion, and thus to the formation of a time-reversed wave packet. The reversal mechanism is entirely general and so applicable to artificial crystal systems of any physical nature. PMID:21266991
Photonic topological insulator with broken time-reversal symmetry
He, Cheng; Sun, Xiao-Chen; Liu, Xiao-Ping; Lu, Ming-Hui; Chen, Yulin; Feng, Liang; Chen, Yan-Feng
2016-01-01
A topological insulator is a material with an insulating interior but time-reversal symmetry-protected conducting edge states. Since its prediction and discovery almost a decade ago, such a symmetry-protected topological phase has been explored beyond electronic systems in the realm of photonics. Electrons are spin-1/2 particles, whereas photons are spin-1 particles. The distinct spin difference between these two kinds of particles means that their corresponding symmetry is fundamentally different. It is well understood that an electronic topological insulator is protected by the electron’s spin-1/2 (fermionic) time-reversal symmetry Tf2=−1. However, the same protection does not exist under normal circumstances for a photonic topological insulator, due to photon’s spin-1 (bosonic) time-reversal symmetry Tb2=1. In this work, we report a design of photonic topological insulator using the Tellegen magnetoelectric coupling as the photonic pseudospin orbit interaction for left and right circularly polarized helical spin states. The Tellegen magnetoelectric coupling breaks bosonic time-reversal symmetry but instead gives rise to a conserved artificial fermionic-like-pseudo time-reversal symmetry, Tp (Tp2=−1), due to the electromagnetic duality. Surprisingly, we find that, in this system, the helical edge states are, in fact, protected by this fermionic-like pseudo time-reversal symmetry Tp rather than by the bosonic time-reversal symmetry Tb. This remarkable finding is expected to pave a new path to understanding the symmetry protection mechanism for topological phases of other fundamental particles and to searching for novel implementations for topological insulators. PMID:27092005
Photonic topological insulator with broken time-reversal symmetry.
He, Cheng; Sun, Xiao-Chen; Liu, Xiao-Ping; Lu, Ming-Hui; Chen, Yulin; Feng, Liang; Chen, Yan-Feng
2016-05-01
A topological insulator is a material with an insulating interior but time-reversal symmetry-protected conducting edge states. Since its prediction and discovery almost a decade ago, such a symmetry-protected topological phase has been explored beyond electronic systems in the realm of photonics. Electrons are spin-1/2 particles, whereas photons are spin-1 particles. The distinct spin difference between these two kinds of particles means that their corresponding symmetry is fundamentally different. It is well understood that an electronic topological insulator is protected by the electron's spin-1/2 (fermionic) time-reversal symmetry [Formula: see text] However, the same protection does not exist under normal circumstances for a photonic topological insulator, due to photon's spin-1 (bosonic) time-reversal symmetry [Formula: see text] In this work, we report a design of photonic topological insulator using the Tellegen magnetoelectric coupling as the photonic pseudospin orbit interaction for left and right circularly polarized helical spin states. The Tellegen magnetoelectric coupling breaks bosonic time-reversal symmetry but instead gives rise to a conserved artificial fermionic-like-pseudo time-reversal symmetry, Tp ([Formula: see text]), due to the electromagnetic duality. Surprisingly, we find that, in this system, the helical edge states are, in fact, protected by this fermionic-like pseudo time-reversal symmetry Tp rather than by the bosonic time-reversal symmetry Tb This remarkable finding is expected to pave a new path to understanding the symmetry protection mechanism for topological phases of other fundamental particles and to searching for novel implementations for topological insulators. PMID:27092005
Sound focusing in rooms: the time-reversal approach.
Yon, Sylvain; Tanter, Mickael; Fink, Mathias
2003-03-01
New perspectives in audible range acoustics, such as virtual sound space creation and active noise control, rely on the ability of the rendering system to recreate precisely a desired sound field. This ability to control sound in a given volume of a room is directly linked to the capacity to focus acoustical energy both in space and time. However, sound focusing in rooms remains a complicated problem, essentially because of the multiple reflections on obstacles and walls occurring during propagation. In this paper, the technique of time-reversal focusing, well known in ultrasound, is experimentally applied to audible range acoustics. Compared to classical focusing techniques such as delay law focusing, time reversal appears to considerably improve quality of both temporal and spatial focusing. This so-called super-resolution phenomenon is due to the ability of time reversal to take into account all of the different sound paths between the emitting antenna and the focal point, thus creating an adaptive spatial and temporal matched filter for the considered propagation medium. Experiments emphasize the strong robustness of time-reversal focusing towards small modifications in the medium, such as people in motion or temperature variations. Sound focusing through walls using the time-reversal approach is also experimentally demonstrated. PMID:12656388
Quantum Transport Enhancement by Time-Reversal Symmetry Breaking
Zimborás, Zoltán; Faccin, Mauro; Kádár, Zoltán; Whitfield, James D.; Lanyon, Ben P.; Biamonte, Jacob
2013-01-01
Quantum mechanics still provides new unexpected effects when considering the transport of energy and information. Models of continuous time quantum walks, which implicitly use time-reversal symmetric Hamiltonians, have been intensely used to investigate the effectiveness of transport. Here we show how breaking time-reversal symmetry of the unitary dynamics in this model can enable directional control, enhancement, and suppression of quantum transport. Examples ranging from exciton transport to complex networks are presented. This opens new prospects for more efficient methods to transport energy and information. PMID:23917452
Majorana mass, time reversal symmetry, and the dimension of space
NASA Astrophysics Data System (ADS)
Herbut, Igor F.
2013-04-01
The Weyl fermions with a well defined chirality are known to demand that the dimension of space which they inhabit must be odd. It is shown here, however, that not all odd dimensional spaces are equally good hosts: in particular, an arbitrary number of chiral Weyl fermions can acquire a Majorana type of mass only in three (modulo eight) dimensions. The argument utilizes (a) the precise analogy between the Majorana mass term and the coupling of time-reversed Weyl fermions, and (b) the conditions on the requisite time reversal operator, which are implied by the real representations of Clifford algebras. In particular, it is shown that the latter allows only an even number of Majorana-massive Weyl fermions in seven (modulo eight) spatial dimensions. The theorem connects the observed odd number of neutrino flavors, the time reversal symmetry, and the dimension of our space and strengthens the argument for the possible violation of the lepton number conservation law.
Time-Reversal Test for Stochastic Quantum Dynamics
NASA Astrophysics Data System (ADS)
Dowling, Mark R.; Drummond, Peter D.; Davis, Matthew J.; Deuar, Piotr
2005-04-01
The calculation of quantum dynamics is currently a central issue in theoretical physics, with diverse applications ranging from ultracold atomic Bose-Einstein condensates to condensed matter, biology, and even astrophysics. Here we demonstrate a conceptually simple method of determining the regime of validity of stochastic simulations of unitary quantum dynamics by employing a time-reversal test. We apply this test to a simulation of the evolution of a quantum anharmonic oscillator with up to 6.022×1023 (Avogadro’s number) of particles. This system is realizable as a Bose-Einstein condensate in an optical lattice, for which the time-reversal procedure could be implemented experimentally.
Wavefield separation and polarity reversal correction in elastic reverse time migration
NASA Astrophysics Data System (ADS)
Li, Zhiyuan; Ma, Xiaona; Fu, Chao; Liang, Guanghe
2016-04-01
In elastic reverse time migration (RTM), one of the problems that are often encountered is the cross-talk between P- and S-wavefields. A useful processing technique to reduce the cross-talk is separating the P- and S-wavefields by using divergence and curl operators before applying an elastic imaging condition. However, the separated wavefields lose their physical meaning because their phase and amplitude are changed. In this paper, we modify the divergence and curl operators to give the separated wavefields a clear physical meaning: the separated wavefield is the first derivative of the input wavefield with respect to time. Another problem often encountered is polarity reversals in PS and SP images, which can cause destructive interference in the final stacked image and thus destroy the migrated events. In this paper we also develop a procedure for polarity reversal correction based on the polarization vectors of the P- and S-wavefields in the common-shot domain. The correction factor is first calculated at every imaging point during the wavefield reconstruction and is then multiplied by the PS and SP images at each time step when an elastic imaging condition is applied. Numerical examples with synthetic data have shown that the modified wavefield separation method is correct, and the procedure of polarity reversal correction is effective for a complex model.
Time reversal invariance violation in neutron-deuteron scattering
Song, Young-Ho; Gudkov, Vladimir; Lazauskas, Rimantas
2011-06-15
Time reversal invariance-violating (TRIV) effects in low-energy elastic neutron-deuteron scattering are calculated using meson exchange and EFT-type TRIV potentials in a distorted-wave Born approximation with realistic hadronic strong interaction wave functions, obtained by solving the three-body Faddeev equations in configuration space. The relation between TRIV and parity-violating observables is discussed.
Acoustic imaging with time reversal methods: From medicine to NDT
NASA Astrophysics Data System (ADS)
Fink, Mathias
2015-03-01
This talk will present an overview of the research conducted on ultrasonic time-reversal methods applied to biomedical imaging and to non-destructive testing. We will first describe iterative time-reversal techniques that allow both focusing ultrasonic waves on reflectors in tissues (kidney stones, micro-calcifications, contrast agents) or on flaws in solid materials. We will also show that time-reversal focusing does not need the presence of bright reflectors but it can be achieved only from the speckle noise generated by random distributions of non-resolved scatterers. We will describe the applications of this concept to correct distortions and aberrations in ultrasonic imaging and in NDT. In the second part of the talk we will describe the concept of time-reversal processors to get ultrafast ultrasonic images with typical frame rates of order of 10.000 F/s. It is the field of ultrafast ultrasonic imaging that has plenty medical applications and can be of great interest in NDT. We will describe some applications in the biomedical domain: Quantitative Elasticity imaging of tissues by following shear wave propagation to improve cancer detection and Ultrafast Doppler imaging that allows ultrasonic functional imaging.
NDE of composite structures using microwave time reversal imaging
NASA Astrophysics Data System (ADS)
Mukherjee, Saptarshi; Tamburrino, Antonello; Udpa, Lalita; Udpa, Satish
2016-02-01
Composite materials are being increasingly used to replace metals, partially or completely, in aerospace, shipping and automotive industries because of their light weight, corrosion resistance, and mechanical strength. Integrity of these materials may be compromised during manufacturing or due to impact damage during usage, resulting in defects such as porosity, delamination, cracks and disbonds. Microwave NDE techniques have the ability to propagate through composite materials, without suffering much attenuation. The scattered fields depend on the dielectric properties of the medium, and hence provide information about the structural integrity of these materials. Time Reversal focusing is based on the fact that when a wave solution is reversed in time and back propagated it refocuses back at the source. This paper presents a model based parametric study of time reversal principles with microwave data in composite materials. A two dimensional FDTD model is developed to implement the forward and time reversed electromagnetic wave propagation in a test geometry comprising metal-composite structures. Simulation results demonstrate the feasibility of this approach to detect and characterize different defects.
Adaptive spatial combining for passive time-reversed communications.
Gomes, João; Silva, António; Jesus, Sérgio
2008-08-01
Passive time reversal has aroused considerable interest in underwater communications as a computationally inexpensive means of mitigating the intersymbol interference introduced by the channel using a receiver array. In this paper the basic technique is extended by adaptively weighting sensor contributions to partially compensate for degraded focusing due to mismatch between the assumed and actual medium impulse responses. Two algorithms are proposed, one of which restores constructive interference between sensors, and the other one minimizes the output residual as in widely used equalization schemes. These are compared with plain time reversal and variants that employ postequalization and channel tracking. They are shown to improve the residual error and temporal stability of basic time reversal with very little added complexity. Results are presented for data collected in a passive time-reversal experiment that was conducted during the MREA'04 sea trial. In that experiment a single acoustic projector generated a 24-PSK (phase-shift keyed) stream at 200400 baud, modulated at 3.6 kHz, and received at a range of about 2 km on a sparse vertical array with eight hydrophones. The data were found to exhibit significant Doppler scaling, and a resampling-based preprocessing method is also proposed here to compensate for that scaling. PMID:18681595
Wave-Based Turing Machine: Time Reversal and Information Erasing.
Perrard, S; Fort, E; Couder, Y
2016-08-26
The investigation of dynamical systems has revealed a deep-rooted difference between waves and objects regarding temporal reversibility and particlelike objects. In nondissipative chaos, the dynamic of waves always remains time reversible, unlike that of particles. Here, we explore the dynamics of a wave-particle entity. It consists in a drop bouncing on a vibrated liquid bath, self-propelled and piloted by the surface waves it generates. This walker, in which there is an information exchange between the particle and the wave, can be analyzed in terms of a Turing machine with waves as the information repository. The experiments reveal that in this system, the drop can read information backwards while erasing it. The drop can thus backtrack on its previous trajectory. A transient temporal reversibility, restricted to the drop motion, is obtained in spite of the system being both dissipative and chaotic. PMID:27610859
Time-reversal imaging of Earthquake and Seismic hum
NASA Astrophysics Data System (ADS)
Phung, T.; Montagner, J.; Fink, M.; Capdeville, Y.; Larmat, C.
2008-12-01
The time-reversal technique is based upon spatial reciprocity and time invariance. This method was successfully applied in the past to acoustic waves in many fields such as sound waves in water or air, ultrasonic waves in human bodies, and electromagnetic waves in free space and recently to seismic waves in seismology. We present here, applications of time-reversal method in Seismology to synthetic and real tests, by using normal mode theory in the PREM model (Dziewonski and Anderson, 1981). We back-propagate 3 components of seismic data at very long period (T > 120s) (complete seismogram and one-bit seismogram). We show that the focusing is primarily dependent on the phase rather than the amplitude of seismogram. An excellent focusing at location and time of earthquake is usually obtained. Ten years ago a few groups reported existence of Earth's background free oscillations even on seismically quiet days (the "Hum")(Suda et al.,1998; Kobayashi and Nishida, 1998; Tanimoto, 1998). We started a systematic investigation of station located worldwide (FDSN) data during quiet periods of time. In this work we show that the excited modes are almost exclusively fundamental spheroidal modes and time-reversal experiment of seismic hum data (2-6 mHz) is attempted for the first time (only the vertical component of seismic data).
Quantum state transfer by time reversal in the continuum
NASA Astrophysics Data System (ADS)
Longhi, S.
2016-03-01
A method for high-fidelity quantum state transfer in a quantum network coupled to a continuum, based on time reversal in the continuum after decay, is theoretically suggested. Provided that the energy spectrum of the network is symmetric around a reference energy and symmetric energy states are coupled the same way to the common continuum, ideal perfect state transfer can be obtained after time reversal. In particular, it is shown that in a linear tight-binding chain a quantum state can be transformed into its mirror image with respect to the center of the chain after a controllable time. As compared to a quantum mirror image based on coherent transport in a static chain with properly tailored inhomogeneous hopping rates, our method does not require hopping rate engineering and is less sensitive to disorder for long transfer times.
Time reversal and the spatio-temporal matched filter
Lehman, S K; Poggio, A J; Kallman, J S; Meyer, A W; Candy, J V
2004-03-08
It is known that focusing of an acoustic field by a time-reversal mirror (TRM) is equivalent to a spatio-temporal matched filter under conditions where the Green's function of the field satisfies reciprocity and is time invariant, i.e. the Green's function is independent of the choice of time origin. In this letter, it is shown that both reciprocity and time invariance can be replaced by a more general constraint on the Green's function that allows a TRM to implement the spatio-temporal matched filter even when conditions are time varying.
NASA Astrophysics Data System (ADS)
Rajak, Atanu; Divakaran, Uma
2016-04-01
We study the effect of two simultaneous local quenches on the evolution of the Loschmidt echo (LE) and entanglement entropy (EE) of a one dimensional transverse Ising model. In this work, one of the local quenches involves the connection of two spin-1/2 chains at a certain time and the other corresponds to a sudden change in the magnitude of the transverse field at a given site in one of the spin chains. We numerically calculate the dynamics associated with the LE and the EE as a result of such double quenches, and discuss the various timescales involved in this problem using the picture of quasiparticles (QPs) generated as a result of such quenches. We perform a detailed analysis of the probability of QPs produced at the two sites and the nature of the QPs in various phases, and obtain interesting results. More specifically, we find partial reflection of these QPs at the defect center or the site of h-quench, resulting in new timescales which have never been reported before.
Time-reversible molecular dynamics algorithms with bond constraints
NASA Astrophysics Data System (ADS)
Toxvaerd, Søren; Heilmann, Ole J.; Ingebrigtsen, Trond; Schrøder, Thomas B.; Dyre, Jeppe C.
2009-08-01
Time-reversible molecular dynamics algorithms with bond constraints are derived. The algorithms are stable with and without a thermostat and in double precision as well as in single-precision arithmetic. Time reversibility is achieved by applying a central-difference expression for the velocities in the expression for Gauss' principle of least constraint. The imposed time symmetry results in a quadratic expression for the Lagrange multiplier. For a system of complex molecules with connected constraints the corresponding set of coupled quadratic equations is easily solved by a consecutive iteration scheme. The algorithms were tested on two models. One is a dumbbell model of Toluene, the other system consists of molecules with four connected constraints forming a triangle and a branch point of constraints. The equilibrium particle distributions and the mean-square particle displacements for the dumbbell model were compared to the corresponding functions obtained by GROMACS. The agreement is perfect within statistical error.
Broadband performance of time-reversing arrays in shallow water
NASA Astrophysics Data System (ADS)
Sabra, Karim Ghazi
Active acoustic time reversal is the process of recording the signal from a remote source with a transducer array, and then replaying the signal in a time-reversed fashion to retro-direct the replayed sound back to the remote source to form a retrofocus, in an unknown environment. Time-Reversing Arrays (TRAs) perform well in the absence of acoustic absorption losses and temporal changes in the environment when there is sufficient array aperture and high signal-to-noise ratio. Future active sonar and underwater communication systems for use in unknown shallow ocean waters may be developed from the automatic spatial and temporal focusing properties of TRAs. The performance of TRAs can be determined by four criteria: the size, the longevity and the field amplitude of the array's retrofocus, as well as the correlation of the retrofocus signal with a time-reversed version of the original signal. Four issues related to TRAs performance are investigated in this thesis: (i) the impact of noise, (ii) the influence of array and source motion, (iii) the effects of oceanic currents, and (iv) the effectiveness of blind deconvolution of the original signal via artificial time-reversal. Noise influences TRA performance twice because the array both listens and transmits. Degradation of TRA's performance caused by noise in the acoustic environment is investigated through an analytical formulation that can be reduced to an algebraic relationship for a simple noise model. Numerical experiments that illustrate this effort are also shown. Another limitation of TRA performance is the Doppler effect induced by the dynamic source-array configuration or the moving medium. Normal modes and parabolic equation simulations illustrate these influences for various oceanic waveguides and array geometry. Finally a novel blind deconvolution technique, artificial time-reversal (ATR), is developed for providing an estimate of an unknown source signal propagating in an unknown shallow oceanic
Broadband performance of a moving time reversing array
NASA Astrophysics Data System (ADS)
Sabra, Karim G.; Dowling, David R.
2003-09-01
Acoustic time reversal exploits reciprocity between sources and receivers to generate backward propagating waves that automatically focus at their point of origin. In underwater acoustics, an array of transducers that can both transmit and receive, referred to as a time reversing array (TRA) or time reversal mirror (TRM), generates the back-propagating waves. Such arrays have been shown to spatially and temporally focus sound in unknown complicated multipath environments, and are therefore of interest for active sonar and underwater communication applications. Although stationary vertical linear TRAs have been favored in prior studies, practical applications of acoustic time reversal in underwater environments are likely to involve towed, tilted, horizontal, or bottom-mounted arrays. In particular, array motion introduces Doppler effects and eliminates source-receiver reciprocity, two factors that potentially impact the automatic focusing capability of TRAs. This paper presents the results from a theoretical and computational investigation into how array motion and orientation influence TRA retrofocusing in the shallow ocean. Here, the TRA tow speed is assumed constant, and the array is assumed to be straight and linear (vertical, horizontal, or tilted). And, for simplicity, the TRA is assumed to respond to a stationary point source emitting a broadband pulse. When a TRA moves, the retrofocus is predicted to shift in the direction of array motion due to the translation of the array between its reception and broadcast times. In addition, the performance of a towed horizontal TRA is predicted to degrade more rapidly with towing speed than that of an equivalent (but clearly idealized) towed vertical array because of range-dependent Doppler phase differences that do not influence the vertical array. However, short tilted arrays may approach vertical array performance and appear to be a potentially versatile compromise for implementing TRA concepts in active sonar or
Broadband performance of a moving time reversing array.
Sabra, Karim G; Dowling, David R
2003-09-01
Acoustic time reversal exploits reciprocity between sources and receivers to generate backward propagating waves that automatically focus at their point of origin. In underwater acoustics, an array of transducers that can both transmit and receive, referred to as a time reversing array (TRA) or time reversal mirror (TRM), generates the back-propagating waves. Such arrays have been shown to spatially and temporally focus sound in unknown complicated multipath environments, and are therefore of interest for active sonar and underwater communication applications. Although stationary vertical linear TRAs have been favored in prior studies, practical applications of acoustic time reversal in underwater environments are likely to involve towed, tilted, horizontal, or bottom-mounted arrays. In particular, array motion introduces Doppler effects and eliminates source-receiver reciprocity, two factors that potentially impact the automatic focusing capability of TRAs. This paper presents the results from a theoretical and computational investigation into how array motion and orientation influence TRA retrofocusing in the shallow ocean. Here, the TRA tow speed is assumed constant, and the array is assumed to be straight and linear (vertical, horizontal, or tilted). And, for simplicity, the TRA is assumed to respond to a stationary point source emitting a broadband pulse. When a TRA moves, the retrofocus is predicted to shift in the direction of array motion due to the translation of the array between its reception and broadcast times. In addition, the performance of a towed horizontal TRA is predicted to degrade more rapidly with towing speed than that of an equivalent (but clearly idealized) towed vertical array because of range-dependent Doppler phase differences that do not influence the vertical array. However, short tilted arrays may approach vertical array performance and appear to be a potentially versatile compromise for implementing TRA concepts in active sonar or
A digital matched filter for reverse time chaos.
Bailey, J Phillip; Beal, Aubrey N; Dean, Robert N; Hamilton, Michael C
2016-07-01
The use of reverse time chaos allows the realization of hardware chaotic systems that can operate at speeds equivalent to existing state of the art while requiring significantly less complex circuitry. Matched filter decoding is possible for the reverse time system since it exhibits a closed form solution formed partially by a linear basis pulse. Coefficients have been calculated and are used to realize the matched filter digitally as a finite impulse response filter. Numerical simulations confirm that this correctly implements a matched filter that can be used for detection of the chaotic signal. In addition, the direct form of the filter has been implemented in hardware description language and demonstrates performance in agreement with numerical results. PMID:27475068
A digital matched filter for reverse time chaos
NASA Astrophysics Data System (ADS)
Bailey, J. Phillip; Beal, Aubrey N.; Dean, Robert N.; Hamilton, Michael C.
2016-07-01
The use of reverse time chaos allows the realization of hardware chaotic systems that can operate at speeds equivalent to existing state of the art while requiring significantly less complex circuitry. Matched filter decoding is possible for the reverse time system since it exhibits a closed form solution formed partially by a linear basis pulse. Coefficients have been calculated and are used to realize the matched filter digitally as a finite impulse response filter. Numerical simulations confirm that this correctly implements a matched filter that can be used for detection of the chaotic signal. In addition, the direct form of the filter has been implemented in hardware description language and demonstrates performance in agreement with numerical results.
Search for time reversal invariance violation in neutron transmission
Bowman, J. David; Gudkov, Vladimir
2014-12-29
Time reversal invariance violating (TRIV) effects in neutron transmission through a nuclear target are discussed. Here, we demonstrate the existence of a class of experiments that are free from false asymmetries. We discuss the enhancement of TRIV effects for neutron energies corresponding to p-wave resonances in the compound nuclear system. Finaly, we analyze a model experiment and show that such tests can have a discovery potential of 10^{2}-10^{4} compared to current limits.
Search for time reversal invariance violation in neutron transmission
Bowman, J. David; Gudkov, Vladimir
2014-12-29
Time reversal invariance violating (TRIV) effects in neutron transmission through a nuclear target are discussed. Here, we demonstrate the existence of a class of experiments that are free from false asymmetries. We discuss the enhancement of TRIV effects for neutron energies corresponding to p-wave resonances in the compound nuclear system. Finaly, we analyze a model experiment and show that such tests can have a discovery potential of 102-104 compared to current limits.
Broadband time-reversing array retrofocusing in noisy environments
NASA Astrophysics Data System (ADS)
Sabra, Karim G.; Khosla, Sunny R.; Dowling, David R.
2002-02-01
Acoustic time reversal is a promising technique for spatial and temporal focusing of sound in unknown environments. Acoustic time reversal can be implemented with an array of transducers that listens to a remote sound source and then transmits a time-reversed version of what was heard. In a noisy environment, the performance of such a time-reversing array (TRA) will be degraded because the array will receive and transmit noise, and the intended signal may be masked by ambient noise at the retrofocus location. This article presents formal results for the signal-to-noise ratio at the intended focus (SNRf) for TRAs that receive and send finite-duration broadband signals in noisy environments. When the noise is homogeneous and uncorrelated, and a broadcast power limitation sets the TRA's electronic amplification, the formal results can be simplified to an algebraic formula that includes the characteristics of the signal, the remote source, the TRA, and the noisy environment. Here, SNRf is found to be proportional to the product of the signal bandwidth and the duration of the signal pulse after propagation through the environment. Using parabolic-equation propagation simulations, the formal results for SNRf are illustrated for a shallow water environment at source-array ranges of 1 to 40 km and bandwidths from several tens of Hz to more than 500 Hz for a signal center frequency of 500 Hz. Shallow-water TRA noise rejection is predicted to be superior to that possible in free space because TRAs successfully exploit multipath-propagation.
Time reversal in photoacoustic tomography and levitation in a cavity
NASA Astrophysics Data System (ADS)
Palamodov, V. P.
2014-12-01
A class of photoacoustic acquisition geometries in {{{R}}n} is considered such that the spherical mean transform admits an exact filtered back projection reconstruction formula. The reconstruction is interpreted as a time reversion mirror that reproduces exactly an arbitrary source distribution in the cavity. A series of examples of non-uniqueness of the inverse potential problem is constructed based on the same geometrical technique.
Prolonged and tunable residence time using reversible covalent kinase inhibitors
Bradshaw, J. Michael; McFarland, Jesse M.; Paavilainen, Ville O.; Bisconte, Angelina; Tam, Danny; Phan, Vernon T.; Romanov, Sergei; Finkle, David; Shu, Jin; Patel, Vaishali; Ton, Tony; Li, Xiaoyan; Loughhead, David G.; Nunn, Philip A.; Karr, Dane E.; Gerritsen, Mary E.; Funk, Jens Oliver; Owens, Timothy D.; Verner, Erik; Brameld, Ken A.; Hill, Ronald J.; Goldstein, David M.; Taunton, Jack
2015-01-01
Drugs with prolonged, on-target residence time often show superior efficacy, yet general strategies for optimizing drug-target residence time are lacking. Here, we demonstrate progress toward this elusive goal by targeting a noncatalytic cysteine in Bruton's tyrosine kinase (BTK) with reversible covalent inhibitors. Utilizing an inverted orientation of the cysteine-reactive cyanoacrylamide electrophile, we identified potent and selective BTK inhibitors that demonstrate biochemical residence times spanning from minutes to 7 days. An inverted cyanoacrylamide with prolonged residence time in vivo remained bound to BTK more than 18 hours after clearance from the circulation. The inverted cyanoacrylamide strategy was further utilized to discover fibroblast growth factor receptor (FGFR) kinase inhibitors with residence times of several days, demonstrating generalizability of the approach. Targeting noncatalytic cysteines with inverted cyanoacrylamides may serve as a broadly applicable platform that facilitates “residence time by design”, the ability to modulate and improve the duration of target engagement in vivo. PMID:26006010
Ultrafast relaxation rates and reversal time in disordered ferrimagnets
NASA Astrophysics Data System (ADS)
Suarez, O. J.; Nieves, P.; Laroze, D.; Altbir, D.; Chubykalo-Fesenko, O.
2015-10-01
In response to ultrafast laser pulses, single-phase metals have been classified as "fast" (with magnetization quenching on the time scale of the order of 100 fs and recovery in the time scale of several picoseconds and below) and "slow" (with longer characteristic time scales). Disordered ferrimagnetic alloys consisting of a combination of "fast" transition (TM) and "slow" rare-earth (RE) metals have been shown to exhibit an ultrafast all-optical switching mediated by the heat mechanism. The behavior of the characteristic time scales of coupled alloys is more complicated and is influenced by many parameters such as the intersublattice exchange, doping (RE) concentration, and the temperature. Here, the longitudinal relaxation times of each sublattice are analyzed within the Landau-Lifshitz-Bloch framework. We show that for moderate intersublattice coupling strength both materials slow down as a function of slow (RE) material concentration. For larger coupling, the fast (TM) material may become faster, while the slow (RE) one is still slower. These conclusions may have important implications in the switching time of disordered ferrimagnets such as GdFeCo with partial clustering. Using atomistic modeling, we show that in the moderately coupled case, the reversal would start in the Gd-rich region, while the situation may be reversed if the coupling strength is larger.
Focusing properties of near-field time reversal
NASA Astrophysics Data System (ADS)
de Rosny, Julien; Fink, Mathias
2007-12-01
A time-reversal mirror (TRM) is a plane apparatus that generates the time symmetric of a wave produced by an initial source. Here we look for the conditions to obtain subwavelength focusing when the initial source is in the near field of the TRM and the propagating medium is homogeneous and isotropic. Three variants of TRM are studied: TRM made of monopoles, dipoles, or both of them. The analysis is performed in terms of evanescent and propagative waves. We conclude that only the dipole-TRM leads to subwavelength focusing.
Focusing properties of near-field time reversal
Rosny, Julien de; Fink, Mathias
2007-12-15
A time-reversal mirror (TRM) is a plane apparatus that generates the time symmetric of a wave produced by an initial source. Here we look for the conditions to obtain subwavelength focusing when the initial source is in the near field of the TRM and the propagating medium is homogeneous and isotropic. Three variants of TRM are studied: TRM made of monopoles, dipoles, or both of them. The analysis is performed in terms of evanescent and propagative waves. We conclude that only the dipole-TRM leads to subwavelength focusing.
Statistical Stability and Time-Reversal Imgaing in Random Media
Berryman, J; Borcea, L; Papanicolaou, G; Tsogka, C
2002-02-05
Localization of targets imbedded in a heterogeneous background medium is a common problem in seismic, ultrasonic, and electromagnetic imaging problems. The best imaging techniques make direct use of the eigenfunctions and eigenvalues of the array response matrix, as recent work on time-reversal acoustics has shown. Of the various imaging functionals studied, one that is representative of a preferred class is a time-domain generalization of MUSIC (MUltiple Signal Classification), which is a well-known linear subspace method normally applied only in the frequency domain. Since statistical stability is not characteristic of the frequency domain, a transform back to the time domain after first diagonalizing the array data in the frequency domain takes optimum advantage of both the time-domain stability and the frequency-domain orthogonality of the relevant eigenfunctions.
New Limit on Time-Reversal Violation in Beta Decay
Mumm, H. P.; Chupp, T. E.; Cooper, R. L.; Coulter, K. P.; Freedman, S. J.; Fujikawa, B. K.; Garcia, A.; Jones, G. L.; Nico, J. S.; Thompson, A. K.; Trull, C. A.; Wietfeldt, F. E.; Wilkerson, J. F.
2011-09-02
We report the results of an improved determination of the triple correlation DP{center_dot}(p{sub e}xp{sub v}) that can be used to limit possible time-reversal invariance in the beta decay of polarized neutrons and constrain extensions to the standard model. Our result is D=[-0.96{+-}1.89(stat){+-}1.01(sys)]x10{sup -4}. The corresponding phase between g{sub A} and g{sub V} is {phi}{sub AV}=180.013 deg. {+-}0.028 deg. (68% confidence level). This result represents the most sensitive measurement of D in nuclear {beta} decay.
Ergodic time-reversible chaos for Gibbs' canonical oscillator
NASA Astrophysics Data System (ADS)
Hoover, William Graham; Sprott, Julien Clinton; Patra, Puneet Kumar
2015-12-01
Nosé's pioneering 1984 work inspired a variety of time-reversible deterministic thermostats. Though several groups have developed successful doubly-thermostated models, single-thermostat models have failed to generate Gibbs' canonical distribution for the one-dimensional harmonic oscillator. A 2001 doubly-thermostated model, claimed to be ergodic, has a singly-thermostated version. Though neither of these models is ergodic this work has suggested a successful route toward singly-thermostated ergodicity. We illustrate both ergodicity and its lack for these models using phase-space cross sections and Lyapunov instability as diagnostic tools.
Ergodicity, mixing, and time reversibility for atomistic nonequilibrium steady states
Hoover, W.G.; Kum, O.
1997-11-01
Ergodic mixing is prerequisite to any statistical-mechanical calculation of properties derived from atomistic dynamical simulations. Thus the time-reversible thermostats and ergostats used in simulating Gibbsian equilibrium dynamics or nonequilibrium steady-state dynamics should impose ergodicity and mixing. Though it is hard to visualize many-dimensional phase-space distributions, recent developments provide several practical numerical approaches to the problem of ergodic mixing. Here we apply three of these approaches to a useful nonequilibrium test problem, an oscillator in a temperature gradient. {copyright} {ital 1997} {ital The American Physical Society}
Electric Dipole States and Time Reversal Violation in Nuclei.
NASA Astrophysics Data System (ADS)
Auerbach, N.
2016-06-01
The nuclear Schiff moment is essential in the mechanism that induces a parity and time reversal violation in the atom. In this presentation we explore theoretically the properties and systematics of the isoscalar dipole in nuclei with the emphasis on the low-energy strength and the inverse energy weighted sum which determines the Schiff moment. We also study the influence of the isovector dipole strength distribution on the Schiff moment. The influence of a large neutron excess in nuclei is examined. The centroid energies of the isoscalar giant resonance (ISGDR) and the overtone of the isovector giant dipole resonance (OIVGDR) are given for a range of nuclei.
Experimental implementation of reverse time migration for nondestructive evaluation applications.
Anderson, Brian E; Griffa, Michele; Bas, Pierre-Yves Le; Ulrich, Timothy J; Johnson, Paul A
2011-01-01
Reverse time migration (RTM) is a commonly employed imaging technique in seismic applications (e.g., to image reservoirs of oil). Its standard implementation cannot account for multiple scattering/reverberation. For this reason it has not yet found application in nondestructive evaluation (NDE). This paper applies RTM imaging to NDE applications in bounded samples, where reverberation is always present. This paper presents a fully experimental implementation of RTM, whereas in seismic applications, only part of the procedure is done experimentally. A modified RTM imaging condition is able to localize scatterers and locations of disbonding. Experiments are conducted on aluminum samples with controlled scatterers. PMID:21302980
Time-Reversal Acoustics and Maximum-Entropy Imaging
Berryman, J G
2001-08-22
Target location is a common problem in acoustical imaging using either passive or active data inversion. Time-reversal methods in acoustics have the important characteristic that they provide a means of determining the eigenfunctions and eigenvalues of the scattering operator for either of these problems. Each eigenfunction may often be approximately associated with an individual scatterer. The resulting decoupling of the scattered field from a collection of targets is a very useful aid to localizing the targets, and suggests a number of imaging and localization algorithms. Two of these are linear subspace methods and maximum-entropy imaging.
Topological aspects of systems with broken time-reversal symmetry
NASA Astrophysics Data System (ADS)
Raghu, Srinivas
This thesis deals with two topics involving topological "vortex-like" defects arising due to the breaking of time-reversal symmetry. A recurring theme shall be the interplay between the bulk properties and the physics at the boundaries of such systems. In the first part of the thesis, we construct direct analogs of quantum Hall effect edge modes in photonic systems with broken time-reversal symmetry. We will show how "photonic crystals" built out of time-reversal breaking Faraday effect media can exhibit "chiral" edge modes in which light propagates unidirectionally along boundaries across which the Faraday axis reverses. The crucial feature underlying this idea is that the photon bands of interest have non-zero Chern numbers (topological integers, which in the case at hand, represent the winding number of the Berry gauge connection of the bands). Using both numerical diagonalization and simple analytical models, we show how to construct photon bands with non-zero Chern invariants, and we use them to realize the precise classical counterpart of the electronic edge modes of the quantum Hall effect. To study these modes numerically, we have designed and implemented novel real-space treatments of the source-free Maxwell normal mode problem on a discrete network. In the second part of the thesis, we focus on extreme type II superconductors in externally applied magnetic fields. Motivated by experiments of Ong and collaborators on the Nernst effect in the cuprate superconductors, we consider a model of a superconductor which permits fluctuations only in the phase of the order parameter. In the presence of the magnetic field, a net vorticity is induced in the system, and we consider the various static and thermoelectric signatures of these superconducting vortices. Using numerical simulations, analytical calculations, and arguments from duality, we study thermoelectric transport and boundary diamagnetic currents. We conclude that such simple models of superconductors
Topological Field Theory of Time-Reversal Invariant Insulators
Qi, Xiao-Liang; Hughes, Taylor; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.
2010-03-19
We show that the fundamental time reversal invariant (TRI) insulator exists in 4 + 1 dimensions, where the effective field theory is described by the 4 + 1 dimensional Chern-Simons theory and the topological properties of the electronic structure is classified by the second Chern number. These topological properties are the natural generalizations of the time reversal breaking (TRB) quantum Hall insulator in 2 + 1 dimensions. The TRI quantum spin Hall insulator in 2 + 1 dimensions and the topological insulator in 3 + 1 dimension can be obtained as descendants from the fundamental TRI insulator in 4 + 1 dimensions through a dimensional reduction procedure. The effective topological field theory, and the Z{sub 2} topological classification for the TRI insulators in 2+1 and 3+1 dimensions are naturally obtained from this procedure. All physically measurable topological response functions of the TRI insulators are completely described by the effective topological field theory. Our effective topological field theory predicts a number of novel and measurable phenomena, the most striking of which is the topological magneto-electric effect, where an electric field generates a magnetic field in the same direction, with an universal constant of proportionality quantized in odd multiples of the fine structure constant {alpha} = e{sup 2}/hc. Finally, we present a general classification of all topological insulators in various dimensions, and describe them in terms of a unified topological Chern-Simons field theory in phase space.
Ultrasound breast imaging using frequency domain reverse time migration
NASA Astrophysics Data System (ADS)
Roy, O.; Zuberi, M. A. H.; Pratt, R. G.; Duric, N.
2016-04-01
Conventional ultrasonography reconstruction techniques, such as B-mode, are based on a simple wave propagation model derived from a high frequency approximation. Therefore, to minimize model mismatch, the central frequency of the input pulse is typically chosen between 3 and 15 megahertz. Despite the increase in theoretical resolution, operating at higher frequencies comes at the cost of lower signal-to-noise ratio. This ultimately degrades the image contrast and overall quality at higher imaging depths. To address this issue, we investigate a reflection imaging technique, known as reverse time migration, which uses a more accurate propagation model for reconstruction. We present preliminary simulation results as well as physical phantom image reconstructions obtained using data acquired with a breast imaging ultrasound tomography prototype. The original reconstructions are filtered to remove low-wavenumber artifacts that arise due to the inclusion of the direct arrivals. We demonstrate the advantage of using an accurate sound speed model in the reverse time migration process. We also explain how the increase in computational complexity can be mitigated using a frequency domain approach and a parallel computing platform.
Time reversal invariance - a test in free neutron decay
Lising, Laura J.
1999-05-18
Time reversal invariance violation plays only a small role in the Standard Model, and the existence of a T-violating effect above the predicted level would be an indication of new physics. A sensitive probe of this symmetry in the weak interaction is the measurement of the T-violating ''D''-correlation in the decay of free neutrons. The triple-correlation D{sigma}{sub n}{center_dot}p{sub e} x p{sub v} involves three kinematic variables, the neutron spin, electron momentu, and neutrino (or proton) momentum, and changes sign under time reversal. This experiment detects the decay products of a polarized cold neutron beam with an octagonal array of scintillation and solid-state detectors. Data from first run at NIST's Cold Neutron Research Facility give a D-coefficient of -0.1 {+-} 1.3(stat.) {+-} 0.7(syst) x 10{sup -3}. This measurement has the greatest bearing on extensions to the Standard model that incorporate leptoquarks, although exotic fermion and lift-right symmetric models also allow a D as large as the present limit.
Time reversal in heterogeneous solid half-spaces
NASA Astrophysics Data System (ADS)
Ying, Yingzi; Bean, Chris; Lokmer, Ivan
2013-04-01
The heterogeneities of elastic properties in the Earth's interior exist over all scales. Seismic waves propagating through heterogeneous media are scattered thus the waveforms are distorted. Consequently, our ability to image the source is compromised. Time reversal technique can utilize the reciprocity of linear elastodynamics and can be applied effectively in heterogeneous media. In this work, the refocusing properties of time reversal wave fields in heterogeneous solid half-spaces are investigated numerically. Here the 3D numerical simulations are performed with a spectral-element method by using open-source software package SPECFEM3D. The simulation results indicate that in the regime where the heterogeneous scale is of the order of the dominant seismic wavelength, the refocusing fields become statistical stable that they are independent of the particular realizations of random fields. Furthermore, the super-resolution phenomenon is also observed as the width of focal spot can transcend the diffraction limit, i.e., the effective array aperture is increased due to the multi-pathing and multi-scattering effects caused by heterogeneities.
Applications of Time-Reversal Processing for Planetary Surface Communications
NASA Technical Reports Server (NTRS)
Barton, Richard J.
2007-01-01
Due to the power constraints imposed on wireless sensor and communication networks deployed on a planetary surface during exploration, energy efficient transfer of data becomes a critical issue. In situations where groups of nodes within a network are located in relatively close proximity, cooperative communication techniques can be utilized to improve the range, data rate, power efficiency, and lifetime of the network. In particular, if the point-to-point communication channels on the network are well modeled as frequency non-selective, distributed or cooperative beamforming can employed. For frequency-selective channels, beamforming itself is not generally appropriate, but a natural generalization of it, time-reversal communication (TRC), can still be effective. Time-reversal processing has been proposed and studied previously for other applications, including acoustical imaging, electromagnetic imaging, underwater acoustic communication, and wireless communication channels. In this paper, we study both the theoretical advantages and the experimental performance of cooperative TRC for wireless communication on planetary surfaces. We give a brief introduction to TRC and present several scenarios where TRC could be profitably employed during planetary exploration. We also present simulation results illustrating the performance of cooperative TRC employed in a complex multipath environment and discuss the optimality of cooperative TRC for data aggregation in wireless sensor networks
Strain-induced time-reversal odd superconductivity in graphene
NASA Astrophysics Data System (ADS)
Juricic, Vladimir; Roy, Bitan
2014-03-01
I will discuss the possibility of realizing a time-reversal-symmetry breaking superconducting state that exhibits an f + is pairing symmetry in strained graphene. Although the underlying attractive interactions need to be sufficiently strong and comparable in pristine graphene to support such pairing state, I will argue that strain can be conducive for its formation even for weak interactions. I will show that quantum-critical behavior near the transition is controlled by a fermionic multicritical point, characterized by various critical exponents computed in the framework of an ɛ-expansion near four spacetime dimensions. I will then discuss the scaling of the superconducting gap with the strain-induced axial pseudo-magnetic field. Furthermore, a vortex in this mixed superconducting state hosts a pair of Majorana fermions supporting a quartet of insulating and superconducting orders, among which quantum spin Hall topological insulator. Finally, I will mention some experimental signatures of this f + is time-reversal odd superconductor. These findings suggest that strained graphene could provide a platform for the realization of exotic superconducting states of Dirac fermions. VJ is supported by the Netherlands Organization for Scientific Research (NWO).
Frequency-swept time-reversed ultrasonically encoded optical focusing
Suzuki, Yuta; Wang, Lihong V.
2014-01-01
A technique to rapidly scan an optical focus inside a turbid medium is attractive for various biomedical applications. Time-reversed ultrasonically encoded (TRUE) optical focusing has previously demonstrated light focusing into a turbid medium, using both analog and digital devices. Although the digital implementation can generate a focus with high energy, it has been time consuming to scan the TRUE focus inside a sample. Here, by sweeping the frequencies of both ultrasound and light, we demonstrate a multiplex recording of ultrasonically encoded wavefronts, accelerating the generation of multiple TRUE foci. Using this technique, we obtained a 2-D image of a fluorescent target centered inside a turbid sample having a thickness of 2.4 transport mean free paths. PMID:25425744
Angle-domain imaging condition for elastic reverse time migration
NASA Astrophysics Data System (ADS)
Yan, R.; Xie, X.; Wu, R.
2010-12-01
In exploration seismology, elastic reverse time migration (RTM) has spurred much interest in recent years because of the increased imaging challenges posed by complex subsurface targets and affordable computer resources such as Linux clusters. Elastic RTM reconstructs the source wavefields forward in time and receiver wavefields backward in time by finite difference method. It then applies an imaging condition that evaluates the match between source and receiver wavefields. To construct the image which describes the physical property of the medium, we prefer to separate the wavefields into P and S modes, and implement the imaging condition as cross-correlation of pure wave mode rather than of Cartesian component of the displacement wavefields. However, simple cross-correlation can cause some image problems which impede the further seismic interpretation. For example, PP image is contaminated by strong artifacts resulted from unwanted cross-correlation between diving wave, turning wave or back-scattered wave and their time-reversed counterpart; PS image suffers from polarization problem due to the polarity reversal of converted S-wave. We found it necessary to apply certain intrinsic properties (e.g., the wave propagation directions and particle motion information) in reconstructed wavefields in order to solve the problems exhibited in elastic RTM image. This paper presents a procedure to decompose the source and receiver wavefields into local plane waves in pure P and S modes. We generate the partial PP and PS images in angle domain by cross-correlating any combination of decomposed plane wave component, and then formulate an imaging condition as a product of an angle-domain operator and the partial images. The new angle-domain imaging condition substantially reduces the artifacts in the PP image and produces the PS image with correct polarizations. Synthetic examples demonstrate that the imaging condition works very well on producing clean and consistent image
An excitation potential imaging condition for elastic reverse time migration
NASA Astrophysics Data System (ADS)
Gu, Bingluo; Liu, Youshan; Li, Zhiyuan; Ma, Xiaona; Liang, Guanghe
2014-09-01
Elastic reverse time migration (ERTM) has been demonstrated to be more accurate than scalar RTM. However, low efficiency (large storage and heavy calculated amount) and strong artifacts caused by the crosstalk between different wave modes are the two primary barriers to the application of the ERTM during the processing of real data. The scalar (P) and vector (S) potentials of the elastic wavefield and the arrival times corresponding to the first energy extremum of the wavefield are saved at each grid point during the forward modeling of the source wavefield. The angle-dependent reflection coefficient images are subsequently obtained by dividing the scalar and vector potentials of the backward extrapolated receiver wavefield by the saved scalar and vector potentials at the grid points that satisfy the image time at each time step, respectively. The proposed imaging condition does not need to store the snapshots of the source wavefield, while it can considerably improve the computational efficiency and decrease the amount of storage and Input/Output manipulation (compared with the cross-correlation imaging condition) in addition to suppressing the crosstalk between compressive and shear wave modes. Compared with the excitation time imaging condition, the proposed imaging condition reduces the energy loss caused by the opposite polarity of the horizontal component at opposite sides of the source in stacked images. Numerical tests with synthetic data of the Sigsbee2a model have demonstrated that this imaging condition is a cost-effective and practical imaging condition for use in prestack ERTM.
NMR Loschmidt echoes as quantifiers of decoherence in interacting spin systems
NASA Astrophysics Data System (ADS)
Sánchez, C. M.; Levstein, P. R.; Acosta, R. H.; Chattah, A. K.
2009-07-01
In this work we present solid-state nuclear magnetic-resonance experiments to study decoherence in the dynamics of many-spin systems. We characterize the global Loschmidt echo and the distribution of multiple-quantum coherence orders during the evolution under dipolar and double-quantum Hamiltonians. To study an infinite H1 system and a closed cluster of nuclear spins we use polycrystalline adamantane and the liquid crystal 5CB in the nematic mesophase, respectively, as model systems. The infinite or finite nature of the system is clearly manifested through spin counting measurements. Comparison between experimental and numerical results gives insights on the decoherence mechanisms in these systems. Contrastingly, the dominating mechanism in 5CB affects all coherence orders in the same way, while in adamantane higher orders of coherence decay faster than the lower ones.
NMR Loschmidt echoes as quantifiers of decoherence in interacting spin systems
Sanchez, C. M.; Levstein, P. R.; Acosta, R. H.; Chattah, A. K.
2009-07-15
In this work we present solid-state nuclear magnetic-resonance experiments to study decoherence in the dynamics of many-spin systems. We characterize the global Loschmidt echo and the distribution of multiple-quantum coherence orders during the evolution under dipolar and double-quantum Hamiltonians. To study an infinite {sup 1}H system and a closed cluster of nuclear spins we use polycrystalline adamantane and the liquid crystal 5CB in the nematic mesophase, respectively, as model systems. The infinite or finite nature of the system is clearly manifested through spin counting measurements. Comparison between experimental and numerical results gives insights on the decoherence mechanisms in these systems. Contrastingly, the dominating mechanism in 5CB affects all coherence orders in the same way, while in adamantane higher orders of coherence decay faster than the lower ones.
Reverse time migration in tilted transversely isotropic media
Zhang, Linbing; Rector III, James W.; Hoversten, G. Michael
2004-07-01
This paper presents a reverse time migration (RTM) method for the migration of shot records in tilted transversely isotropic (TTI) media. It is based on the tilted TI acoustic wave equation that was derived from the dispersion relation. The RTM is a full depth migration allowing for velocity to vary laterally as well as vertically and has no dip limitations. The wave equation is solved by a tenth-order finite difference scheme. Using 2D numerical models, we demonstrate that ignoring the tilt angle will introduce both lateral and vertical shifts in imaging. The shifts can be larger than 0.5 wavelength in the vertical direction and 1.5 wavelength in the lateral direction.
Single-molecule stochastic times in a reversible bimolecular reaction.
Keller, Peter; Valleriani, Angelo
2012-08-28
In this work, we consider the reversible reaction between reactants of species A and B to form the product C. We consider this reaction as a prototype of many pseudobiomolecular reactions in biology, such as for instance molecular motors. We derive the exact probability density for the stochastic waiting time that a molecule of species A needs until the reaction with a molecule of species B takes place. We perform this computation taking fully into account the stochastic fluctuations in the number of molecules of species B. We show that at low numbers of participating molecules, the exact probability density differs from the exponential density derived by assuming the law of mass action. Finally, we discuss the condition of detailed balance in the exact stochastic and in the approximate treatment. PMID:22938217
Topological Anderson insulators in systems without time-reversal symmetry
NASA Astrophysics Data System (ADS)
Su, Ying; Avishai, Y.; Wang, X. R.
2016-06-01
Occurrence of the topological Anderson insulator (TAI) in a HgTe quantum well suggests that when time-reversal symmetry (TRS) is maintained, the pertinent topological phase transition, marked by re-entrant 2 e2/h quantized conductance contributed by helical edge states, is driven by disorder. Here we show that when TRS is broken, the physics of the TAI becomes even richer. The pattern of longitudinal conductance and nonequilibrium local current distribution displays novel TAI phases characterized by nonzero Chern numbers, indicating the occurrence of multiple chiral edge modes. Tuning either disorder or Fermi energy (in both topologically trivial and nontrivial phases), drives transitions between these distinct TAI phases, characterized by jumps of the quantized conductance from 0 to e2/h and from e2/h to 2 e2/h . An effective medium theory based on the Born approximation yields an accurate description of different TAI phases in parameter space.
Magnetotelluric inversion via reverse time migration algorithm of seismic data
Ha, Taeyoung . E-mail: tyha@math.snu.ac.kr; Shin, Changsoo . E-mail: css@model.snu.ac.kr
2007-07-01
We propose a new algorithm for two-dimensional magnetotelluric (MT) inversion. Our algorithm is an MT inversion based on the steepest descent method, borrowed from the backpropagation technique of seismic inversion or reverse time migration, introduced in the middle 1980s by Lailly and Tarantola. The steepest descent direction can be calculated efficiently by using the symmetry of numerical Green's function derived from a mixed finite element method proposed by Nedelec for Maxwell's equation, without calculating the Jacobian matrix explicitly. We construct three different objective functions by taking the logarithm of the complex apparent resistivity as introduced in the recent waveform inversion algorithm by Shin and Min. These objective functions can be naturally separated into amplitude inversion, phase inversion and simultaneous inversion. We demonstrate our algorithm by showing three inversion results for synthetic data.
Time reversed photonic beamforming of arbitrary waveform ladar arrays
NASA Astrophysics Data System (ADS)
Cox, Joseph L.; Zmuda, Henry; Bussjaeger, Rebecca J.; Erdmann, Reinhard K.; Fanto, Michael L.; Hayduk, Michael J.; Malowicki, John E.
2007-04-01
Herein is described a novel approach of performing adaptive photonic beam forming of an array of optical fibers with the expressed purpose of performing laser ranging. The beam forming technique leverages the concepts of time reversal, previously implemented in the sonar community, and wherein photonic implementation has recently been described for use by beamforming of ultra-wideband radar arrays. Photonic beam forming is also capable of combining the optical output of several fiber lasers into a coherent source, exactly phase matched on a pre-determined target. By implementing electro-optically modulated pulses from frequency chirped femtosecond-scale laser pulses, ladar waveforms can be generated with arbitrary spectral and temporal characteristics within the limitations of the wide-band system. Also described is a means of generating angle/angle/range measurements of illuminated targets.
Time reversal and charge conjugation in an embedding quantum simulator
Zhang, Xiang; Shen, Yangchao; Zhang, Junhua; Casanova, Jorge; Lamata, Lucas; Solano, Enrique; Yung, Man-Hong; Zhang, Jing-Ning; Kim, Kihwan
2015-01-01
A quantum simulator is an important device that may soon outperform current classical computations. A basic arithmetic operation, the complex conjugate, however, is considered to be impossible to be implemented in such a quantum system due to the linear character of quantum mechanics. Here, we present the experimental quantum simulation of such an unphysical operation beyond the regime of unitary and dissipative evolutions through the embedding of a quantum dynamics in the electronic multilevels of a 171Yb+ ion. We perform time reversal and charge conjugation, which are paradigmatic examples of antiunitary symmetry operators, in the evolution of a Majorana equation without the tomographic knowledge of the evolving state. Thus, these operations can be applied regardless of the system size. Our approach offers the possibility to add unphysical operations to the toolbox of quantum simulation, and provides a route to efficiently compute otherwise intractable quantities, such as entanglement monotones. PMID:26239028
Time reversal and charge conjugation in an embedding quantum simulator.
Zhang, Xiang; Shen, Yangchao; Zhang, Junhua; Casanova, Jorge; Lamata, Lucas; Solano, Enrique; Yung, Man-Hong; Zhang, Jing-Ning; Kim, Kihwan
2015-01-01
A quantum simulator is an important device that may soon outperform current classical computations. A basic arithmetic operation, the complex conjugate, however, is considered to be impossible to be implemented in such a quantum system due to the linear character of quantum mechanics. Here, we present the experimental quantum simulation of such an unphysical operation beyond the regime of unitary and dissipative evolutions through the embedding of a quantum dynamics in the electronic multilevels of a (171)Yb(+) ion. We perform time reversal and charge conjugation, which are paradigmatic examples of antiunitary symmetry operators, in the evolution of a Majorana equation without the tomographic knowledge of the evolving state. Thus, these operations can be applied regardless of the system size. Our approach offers the possibility to add unphysical operations to the toolbox of quantum simulation, and provides a route to efficiently compute otherwise intractable quantities, such as entanglement monotones. PMID:26239028
Time-Reversal Study of the Hemet (CA) Tremor Source
NASA Astrophysics Data System (ADS)
Larmat, C. S.; Johnson, P. A.; Guyer, R. A.
2010-12-01
Since its first observation by Nadeau & Dolenc (2005) and Gomberg et al. (2008), tremor along the San Andreas fault system is thought to be a probe into the frictional state of the deep part of the fault (e.g. Shelly et al., 2007). Tremor is associated with slow, otherwise deep, aseismic slip events that may be triggered by faint signals such as passing waves from remote earthquakes or solid Earth tides.Well resolved tremor source location is key to constrain frictional models of the fault. However, tremor source location is challenging because of the high-frequency and highly-scattered nature of tremor signal characterized by the lack of isolated phase arrivals. Time Reversal (TR) methods are emerging as a useful tool for location. The unique requirement is a good velocity model for the different time-reversed phases to arrive coherently onto the source point. We present results of location for a tremor source near the town of Hemet, CA, which was triggered by the 2002 M 7.9 Denali Fault earthquake (Gomberg et al., 2008) and by the 2009 M 6.9 Gulf of California earthquake. We performed TR in a volume model of 88 (N-S) x 70 (W-E) x 60 km (Z) using the full-wave 3D wave-propagation package SPECFEM3D (Komatitsch et al., 2002). The results for the 2009 episode indicate a deep source (at about 22km) which is about 4km SW the fault surface scarp. We perform STA/SLA and correlation analysis in order to have independent confirmation of the Hemet tremor source. We gratefully acknowledge the support of the U. S. Department of Energy through the LANL/LDRD Program for this work.
Phase reversal technique decreases cortical stimulation time during motor mapping.
Simon, Mirela V; Sheth, Sameer A; Eckhardt, Christine A; Kilbride, Ronan D; Braver, Diana; Williams, Ziv; Curry, William; Cahill, Dan; Eskandar, Emad N
2014-06-01
Neurophysiologic mapping of the primary motor cortex (PMC) is commonly used in supratentorial surgery. Electrical cortical stimulation is guided by anatomic landmarks towards the precentral gyrus, with recording of the triggered primary motor responses (TPMR) in the contralateral hemibody. Thus, factors such as distortion of the pericentral anatomy, small surgical fields, brain shifts and miscalibrated neuronavigational systems may lengthen the process and result in unnecessary stimulations, increasing the probability of triggering seizures. We hypothesized that central sulcus localization via the median somatosensory evoked potentials phase reversal technique (MSSEP PRT) accurately guides the surgeon, resulting in prompt identification of the PMC with minimal electrical stimulation. Multivariate Cox regression was used to study the impact of MSSEP PRT on time spent performing electrical cortical stimulation to TPMR. The analysis was adjusted for presence of increased cortical excitability, high motor thresholds, lesions close to PMC and fMRI data, in 100 consecutive standardized motor mapping procedures for brain tumor resection and epilepsy surgery. Phase reversal and change morphology of the recorded somatosensory evoked potentials quadrupled (hazard ratio [HR] 4.13, p<0.0001) and doubled (HR 2.14, p=0.02) the rate of obtaining TPMR, respectively. A 1mA increase in motor threshold decreased the rate by 9% (HR 0.91, p=0.0002). Afterdischarges triggered before TPMR and lesions in close proximity to PMC decreased the rate of TPMR by 76% (HR 0.23, p<0.0001) and 48% (HR 0.52, p=0.04), respectively. Informative PRT decreases stimulation time. Afterdischarges triggered before TPMR, high motor thresholds and lesions close to the PMC increase it. PMID:24679940
Object detection and imaging with acoustic time reversal mirrors
NASA Astrophysics Data System (ADS)
Fink, Mathias
1993-11-01
Focusing an acoustic wave on an object of unknown shape through an inhomogeneous medium of any geometrical shape is a challenge in underground detection. Optimal detection and imaging of objects needs the development of such focusing techniques. The use of a time reversal mirror (TRM) represents an original solution to this problem. It realizes in real time a focusing process matched to the object shape, to the geometries of the acoustic interfaces and to the geometries of the mirror. It is a self adaptative technique which compensates for any geometrical distortions of the mirror structure as well as for diffraction and refraction effects through the interfaces. Two real time 64 and 128 channel prototypes have been built in our laboratory and TRM experiments demonstrating the TRM performance through inhomogeneous solid and liquid media are presented. Applications to medical therapy (kidney stone detection and destruction) and to nondestructive testing of metallurgical samples of different geometries are described. Extension of this study to underground detection and imaging will be discussed.
3D seismic reverse time migration on GPGPU
NASA Astrophysics Data System (ADS)
Liu, Guofeng; Liu, Yaning; Ren, Li; Meng, Xiaohong
2013-09-01
Reverse time migration (RTM) is a powerful seismic imaging method for the interpretation of steep-dips and subsalt regions; however, implementation of the RTM method is computationally expensive. In this paper, we present a fast and computationally inexpensive implementation of RTM using a NVIDIA general purpose graphic processing unit (GPGPU) powered with Compute Unified Device Architecture (CUDA). To accomplish this, we introduced a random velocity boundary in the source propagation kernel. By creating a random velocity layer at the left, right, and bottom boundaries, the wave fields that encounter the boundary regions are pseudo-randomized. Reflections off the random layers have minimal coherent correlation in the reverse direction. This process eliminates the need to write the wave fields to a disk, which is important when using a GPU because of the limited bandwidth of the PCI-E that is connected to the CPU and GPU. There are four GPU kernels in the code: shot, receiver, modeling, and imaging. The shot and receiver insertion kernels are simple and are computed using a GPU because the wave fields reside in GPU's memory. The modeling kernel is computed using Micikevicius's tiling method, which uses shared memory to improve bandwidth usage in 2D and 3D finite difference problems. In the imaging kernel, we also use this tiling method. A Tesla C2050 GPU with 4 GB memory and 480 stream processing units was used to test the code. The shot and receiver modeling kernel occupancy achieved 85%, and the imaging kernel occupancy was 100%. This means that the code achieved a good level of optimization. A salt model test verified the correct and effective implementation of the GPU RTM code.
The time dependence of reversed archeomagnetic flux patches
NASA Astrophysics Data System (ADS)
Terra-Nova, Filipe; Amit, Hagay; Hartmann, Gelvam A.; Trindade, Ricardo I. F.
2015-02-01
Archeomagnetic field models may provide important insights to the geodynamo. Here we investigate the existence and mobility of reversed flux patches (RFPs) in an archeomagnetic field model. We introduce topological algorithms to define, identify, and track RFPs. In addition, we explore the relations between RFPs and dipole changes and apply robustness tests to the RFPs. In contrast to previous definitions, patches that reside on the geographic equator are adequately identified based on our RFPs definition. Most RFPs exhibit a westward drift and migrate toward higher latitudes. Undulations of the magnetic equator and RFPs oppose the axial dipole moment (ADM). Filtered models show a tracking behavior similar to the nonfiltered model, and surprisingly new RFPs occasionally emerge. The advection and diffusion of RFPs have worked in unison to yield the decrease of the ADM at recent times. The absence of RFPs in the period 550-1440 A.D. is related to a low in intermediate degrees of the geomagnetic power spectrum. We thus hypothesize that the RFPs are strongly dependent on intermediate spherical harmonic degrees 4 and above.
Time-Reversal Symmetric U (1 ) Quantum Spin Liquids
NASA Astrophysics Data System (ADS)
Wang, Chong; Senthil, T.
2016-01-01
We study possible quantum U (1 ) spin liquids in three dimensions with time-reversal symmetry. We find a total of seven families of such U (1 ) spin liquids, distinguished by the properties of their emergent electric or magnetic charges. We show how these spin liquids are related to each other. Two of these classes admit nontrivial protected surface states which we describe. We show how to access all of the seven spin liquids through slave particle (parton) constructions. We also provide intuitive loop gas descriptions of their ground-state wave functions. One of these phases is the "topological Mott insulator," conventionally described as a topological insulator of an emergent fermionic "spinon." We show that this phase admits a remarkable dual description as a topological insulator of emergent fermionic magnetic monopoles. This results in a new (possibly natural) surface phase for the topological Mott insulator and a new slave particle construction. We describe some of the continuous quantum phase transitions between the different U (1 ) spin liquids. Each of these seven families of states admits a finer distinction in terms of their surface properties, which we determine by combining these spin liquids with symmetry-protected topological phases. We discuss lessons for materials such as pyrochlore quantum spin ices which may harbor a U (1 ) spin liquid. We suggest the topological Mott insulator as a possible ground state in some range of parameters for the quantum spin ice Hamiltonian.
Application of time reversal acoustics focusing for nonlinear imaging ms
NASA Astrophysics Data System (ADS)
Sarvazyan, Armen; Sutin, Alexander
2001-05-01
Time reversal acoustic (TRA) focusing of ultrasound appears to be an effective tool for nonlinear imaging in industrial and medical applications because of its ability to efficiently concentrate ultrasonic energy (close to diffraction limit) in heterogeneous media. In this study, we used two TRA systems to focus ultrasonic beams with different frequencies in coinciding focal points, thus causing the generation of ultrasonic waves with combination frequencies. Measurements of the intensity of these combination frequency waves provide information on the nonlinear parameter of medium in the focal region. Synchronized stirring of two TRA focused beams enables obtaining 3-D acoustic nonlinearity images of the object. Each of the TRA systems employed an aluminum resonator with piezotransducers glued to its facet. One of the free facets of each resonator was submerged into a water tank and served as a virtual phased array capable of ultrasound focusing and beam steering. To mimic a medium with spatially varying acoustical nonlinearity a simplest model such as a microbubble column in water was used. Microbubbles were generated by electrolysis of water using a needle electrode. An order of magnitude increase of the sum frequency component was observed when the ultrasound beams were focused in the area with bubbles.
Broadband time reversed acoustic focusing and steering system
NASA Astrophysics Data System (ADS)
Sutin, Alexander; Sarvazyan, Armen; Montaldo, Gabriel; Palacio, Delphine; Bercoff, Jeremy; Tanter, Mickael; Fink, Mathias
2001-05-01
We present results of experimental testing and theoretical modeling of a time reversal acoustic (TRA) focusing system based on a multifaceted aluminum resonator with 15 piezoceramic transducers glued to the resonator facets. One of the facets of the resonator, a pentagon with characteristic dimension of about 30 mm, was submerged into a water tank and served as a virtual phased array which provided ultrasound focusing and beam steering in a wide frequency band (0.7-3 MHz). Ultrasonic pulses with different carrier frequencies and various complex waveforms were focused; the focal length was varied in the range of 10-55 mm and the focused beam was steered in a range of angles of +/-60 deg. The amplitude of the signal in the focal region reached 40 MPa. A theoretical model was based on an assumption that the radiating part of the resonator works as a phase conjugation screen for a spherical wave radiated from the focal point. Theoretical dependencies of the field structure on the position of the focus point and ultrasound frequency are in a good agreement with experimental results. TRA based focusing of ultrasound has numerous applications in medical diagnostics, surgery and therapy. [Work supported by NIH grant.
Multiple time-reversed guide-sources in shallow water
NASA Astrophysics Data System (ADS)
Gaumond, Charles F.; Fromm, David M.; Lingevitch, Joseph F.; Gauss, Roger C.; Menis, Richard
2003-10-01
Detection in a monostatic, broadband, active sonar system in shallow water is degraded by propagation-induced spreading. The detection improvement from multiple spatially separated guide sources (GSs) is presented as a method to mitigate this degradation. The improvement of detection by using information in a set of one-way transmissions from a variety of positions is shown using sea data. The experimental area is south of the Hudson Canyon off the coast of New Jersey. The data were taken using five elements of a time-reversing VLA. The five elements were contiguous and at midwater depth. The target and guide source was an echo repeater positioned at various ranges and at middepth. The transmitted signals were 3.0- to 3.5-kHz LFMs. The data are analyzed to show the amount of information present in the collection, a baseline probability of detection (PD) not using the collection of GS signals, the improvement in PD from the use of various sets of GS signals. The dependence of the improvement as a function of range is also shown. [The authors acknowledge support from Dr. Jeffrey Simmen, ONR321OS, and the chief scientist Dr. Charles Holland. Work supported by ONR.
The time dependence of reversed archeomagnetic flux patches
NASA Astrophysics Data System (ADS)
Terra-Nova, Filipe; Amit, Hagay; Hartmann, Gelvam A.; Trindade, Ricardo I. F.
2016-04-01
Archeomagnetic field models may provide important insights to the geodynamo. Here we investigate the existence and mobility of reversed flux patches (RFPs) in archeomagnetic field model CALS3k.4b of Korte and Constable (2011; PEPI, 188, 247-259). We introduce topological algorithms to define, identify and track RPFs. In addition, we explore the relations between RFPs and dipole changes, and apply robustness tests to the RFPs. In contrast to previous definitions, patches that reside on the geographic equator are adequately identified based on our RFPs definition that takes the magnetic equator as a reference. Most RFPs exhibit a westward drift and migrate towards higher latitudes. Undulations of the magnetic equator and RFPs oppose the axial dipole moment (ADM). Filtered models show a tracking behaviour similar to the non-filtered model, and surprisingly new RFPs occasionally emerge. The advection and diffusion of RFPs have worked in unison to yield the decrease of the ADM at recent times. The absence of RFPs in the period 550-1440 AD is related to a low in intermediate degrees of the geomagnetic power spectrum. We thus hypothesize that the RFPs are strongly dependent on intermediate spherical harmonic degrees 4 and above. Comparison of tracking of RFPs among various archeomagnetic field models was also performed and gives more complex results.
Nanowire antenna absorption probed with time-reversed fourier microscopy.
Grzela, Grzegorz; Paniagua-Domínguez, Ramón; Barten, Tommy; van Dam, Dick; Sánchez-Gil, José A; Rivas, Jaime Gómez
2014-06-11
Understanding light absorption in individual nanostructures is crucial for optimizing the light-matter interaction at the nanoscale. Here, we introduce a technique named time-reversed Fourier microscopy that enables the measurement of the angle-dependent light absorption in dilute arrays of uncoupled semiconductor nanowires. Because of their large separation, the nanowires have a response that can be described in terms of individual nanostructures. The geometry of individual nanowires makes them behave as nanoantennas that show a strong interaction with the incident light. The angle-dependent absorption measurements, which are compared to numerical simulations and Mie scattering calculations, show the transition from guided-mode to Mie-resonance absorption in individual nanowires and the relative efficiency of these two absorption mechanisms in the same nanostructures. Mie theory fails to describe the absorption in finite-length vertical nanowires illuminated at small angles with respect to their axis. At these angles, the incident light is efficiently absorbed after being coupled to guided modes. Our findings are relevant for the design of nanowire-based photodetectors and solar cells with an optimum efficiency. PMID:24810791
Time Reversal Acoustic Communication Using Filtered Multitone Modulation
Sun, Lin; Chen, Baowei; Li, Haisen; Zhou, Tian; Li, Ruo
2015-01-01
The multipath spread in underwater acoustic channels is severe and, therefore, when the symbol rate of the time reversal (TR) acoustic communication using single-carrier (SC) modulation is high, the large intersymbol interference (ISI) span caused by multipath reduces the performance of the TR process and needs to be removed using the long adaptive equalizer as the post-processor. In this paper, a TR acoustic communication method using filtered multitone (FMT) modulation is proposed in order to reduce the residual ISI in the processed signal using TR. In the proposed method, FMT modulation is exploited to modulate information symbols onto separate subcarriers with high spectral containment and TR technique, as well as adaptive equalization is adopted at the receiver to suppress ISI and noise. The performance of the proposed method is assessed through simulation and real data from a trial in an experimental pool. The proposed method was compared with the TR acoustic communication using SC modulation with the same spectral efficiency. Results demonstrate that the proposed method can improve the performance of the TR process and reduce the computational complexity of adaptive equalization for post-process. PMID:26393586
Improving the gradient in least-squares reverse time migration
NASA Astrophysics Data System (ADS)
Liu, Qiancheng
2016-04-01
Least-squares reverse time migration (LSRTM) is a linearized inversion technique used for estimating high-wavenumber reflectivity. However, due to the redundant overlay of the band-limited source wavelet, the gradient based on the cross-correlated imaging principle suffers from a loss of wavenumber information. We first prepare the residuals between observed and demigrated data by deconvolving with the amplitude spectrum of the source wavelet, and then migrate the preprocessed residuals by using the cross-correlation imaging principle. In this way, a gradient that preserves the spectral signature of data residuals is obtained. The computational cost of source-wavelet removal is negligible compared to that of wavefield simulation. The two-dimensional Marmousi model containing complex geology structures is considered to test our scheme. Numerical examples show that our improved gradient in LSRTM has a better convergence behavior and promises inverted results of higher resolution. Finally, we attempt to update the background velocity with our inverted velocity perturbations to approach the true velocity.
Time Reversal Signal Processing in Communications - A Feasibility Study
Meyer, A W; Candy, J V; Poggio, A J
2002-01-30
A typical communications channel is subjected to a variety of signal distortions, including multipath, that corrupt the information being transmitted and reduce the effective channel capacity. The mitigation of the multipath interference component is an ongoing concern for communication systems operating in complex environments such as might be experienced inside buildings, urban environments, and hilly or heavily wooded areas. Communications between mobile units and distributed sensors, so important to national security, are dependent upon flawless conveyance of information in complex environments. The reduction of this multipath corruption necessitates better channel equalization, i.e., the removal of channel distortion to extract the transmitted information. But, the current state of the art in channel equalization either requires a priori knowledge of the channel or the use of a known training sequence and adaptive filtering. If the ''assumed'' model within the equalization processor does not at least capture the dominant characteristics of the channel, then the received information may still be highly distorted and possibly useless. Also, the processing required for classical equalization is demanding in computational resources. To remedy this situation, many techniques have been investigated to replace classical equalization. Such a technique, the subject of this feasibility study, is Time Reversal Signal Processing (TRSP). Multipath is particularly insidious and a major factor in the deterioration of communication channels. Unlike most other characteristics that corrupt a communications channel, the detrimental effects of multipath cannot be overcome by merely increasing the transmitted power. Although the power in a signal diminishes as a function of the distance between the transmitter and receiver, multipath further degrades a signal by creating destructive interference that results in a loss of received power in a very localized area, a loss often
Time Reversal Beam Focusing of Ultrasonic Array Transducer on a Defect in a Two Layer Medium
NASA Astrophysics Data System (ADS)
Jeong, Hyunjo; Lee, Jeong-Sik; Lee, Chung-Hoon
2010-02-01
The ability of time reversal techniques to focus ultrasonic beams on the source location is important in many aspects of ultrasonic nondestructive evaluation. In this paper, we investigate the time reversal beam focusing of ultrasonic array sensors on a defect in layered media. Numerical modeling is performed using the commercially available software which employs a time domain finite difference method. Two different time reversal approaches are considered—the through transmission and the pulse-echo. Linear array sensors composed of N elements of line sources are used for signal reception/excitation, time reversal, and reemission in time reversal processes associated with the scattering source of a side-drilled hole located in the second layer of two layer structure. The simulation results demonstrate the time reversal focusing even with multiple reflections from the interface of layered structure. We examine the focusing resolution that is related to the propagation distance, the size of array sensor and the wavelength.
Prestack reverse time migration for tilted transversely isotropic media
NASA Astrophysics Data System (ADS)
Jang, Seonghyung; Hien, Doan Huy
2013-04-01
According to having interest in unconventional resource plays, anisotropy problem is naturally considered as an important step for improving the seismic image quality. Although it is well known prestack depth migration for the seismic reflection data is currently one of the powerful tools for imaging complex geological structures, it may lead to migration error without considering anisotropy. Asymptotic analysis of wave propagation in transversely isotropic (TI) media yields a dispersion relation of couple P- and SV wave modes that can be converted to a fourth order scalar partial differential equation (PDE). By setting the shear wave velocity equal zero, the fourth order PDE, called an acoustic wave equation for TI media, can be reduced to couple of second order PDE systems and we try to solve the second order PDE by the finite difference method (FDM). The result of this P wavefield simulation is kinematically similar to elastic and anisotropic wavefield simulation. We develop prestack depth migration algorithm for tilted transversely isotropic media using reverse time migration method (RTM). RTM is a method for imaging the subsurface using inner product of source wavefield extrapolation in forward and receiver wavefield extrapolation in backward. We show the subsurface image in TTI media using the inner product of partial derivative wavefield with respect to physical parameters and observation data. Since the partial derivative wavefields with respect to the physical parameters require extremely huge computing time, so we implemented the imaging condition by zero lag crosscorrelation of virtual source and back propagating wavefield instead of partial derivative wavefields. The virtual source is calculated directly by solving anisotropic acoustic wave equation, the back propagating wavefield on the other hand is calculated by the shot gather used as the source function in the anisotropic acoustic wave equation. According to the numerical model test for a simple
Impulse source localization in an urban environment: Time reversal versus time matching.
Cheinet, Sylvain; Ehrhardt, Loïc; Broglin, Thierry
2016-01-01
This study investigates two approaches for localizing an impulse sound source with distributed sensors in an urban environment under controlled processing time. In both approaches, the numerical model used for calculating the sound propagation is a finite-difference time-domain (FDTD) model. The simulations are drastically accelerated by restricting to the lower frequencies of the impulse signals and are evaluated against in situ measurements. The first tested localization technique relies on the time reversal of the measurements with the model. In the second technique, the source is localized by matching the observed differences in the first times of arrival of the signals to those obtained from a pre-defined database of simulations with known source positions. The localization performance is physically investigated on the basis of the measurements, considering two source positions and all possible combinations from 5 to 15 microphones. The time matching localization attains an accuracy of 10 m, which is targeted in this study, in the vast majority of the configurations. In comparison, the time reversal localization is affected by the weakness of contributions from sensors masked and distant from the source. Practical requirements are also discussed, such as real-time constraints, hardware and description of the urban environment. PMID:26827011
The effects of non-uniform loss on time reversal mirrors
NASA Astrophysics Data System (ADS)
Taddese, Biniyam Tesfaye; Antonsen, Thomas M.; Ott, Edward; Anlage, Steven M.
2014-08-01
Time reversal mirrors work perfectly only for lossless wave propagation; dissipation destroys time-reversal invariance and limits the performance of time-reversal mirrors. Here, a new measure of time-reversal mirror performance is introduced and the adverse effect of dissipation on this performance measure is investigated. The technique of exponential amplification is employed to partially overcome the effect of non-uniform loss distributions, and its success is tested quantitatively using the new performance measure. A numerical model of a star graph is employed to test the applicability of this technique on realizations with various random spatial distributions of loss. A subset of the numerical results are also verified by experimental results from an electromagnetic time-reversal mirror. The exponential amplification technique is a simple way to improve the performance of emerging technologies based on time-reversed wave propagation such as directed communication and wireless power transfer.
Least-squares reverse-time migration of Cranfield VSP data for monitoring CO2 injection
NASA Astrophysics Data System (ADS)
TAN, S.; Huang, L.
2012-12-01
Cost-effective monitoring for carbon utilization and sequestration requires high-resolution imaging with a minimal amount of data. Least-squares reverse-time migration is a promising imaging method for this purpose. We apply least-squares reverse-time migration to a portion of the 3D vertical seismic profile data acquired at the Cranfield enhanced oil recovery field in Mississippi for monitoring CO2 injection. Conventional reverse-time migration of limited data suffers from significant image artifacts and a poor image resolution. Lease-squares reverse-time migration can reduce image artifacts and improves the image resolution. We demonstrate the significant improvements of least-squares reverse-time migration by comparing its migration images of the Cranfield VSP data with that obtained using the conventional reverse-time migration.
NASA Astrophysics Data System (ADS)
Kugler, T.; Rausch, M. H.; Fröba, A. P.
2015-11-01
The paper reports on binary diffusion coefficient data for the gaseous systems argon-neon, krypton-helium, ammonia-helium, nitrous oxide-nitrogen, and propane-helium measured using a Loschmidt cell combined with holographic interferometry between (293.15 and 353.15) K as well as between (1 and 10) bar. The investigations on the noble gas systems aimed to validate the measurement apparatus by comparing the binary diffusion coefficients measured as a function of temperature and pressure with theoretical data. In previous studies, it was already shown that the raw concentration-dependent data measured with the applied setup are affected by systematic effects if pure gases are used prior to the diffusion process. Hence, the concentration-dependent measurement data were processed to obtain averaged binary diffusion coefficients at a mean mole fraction of 0.5. The data for the molecular gas systems complete literature data on little investigated systems of technical interest and point out the capabilities of the applied measurement apparatus. Further experimental data are reported for the systems argon-helium, krypton-argon, krypton-neon, xenon-helium, xenon-krypton, nitrous oxide-carbon dioxide, and propane-carbon dioxide at 293.15 K, 2 bar, and a mean mole fraction of 0.5.
Time-Reversal MUSIC Imaging with Time-Domain Gating Technique
NASA Astrophysics Data System (ADS)
Choi, Heedong; Ogawa, Yasutaka; Nishimura, Toshihiko; Ohgane, Takeo
A time-reversal (TR) approach with multiple signal classification (MUSIC) provides super-resolution for detection and localization using multistatic data collected from an array antenna system. The theory of TR-MUSIC assumes that the number of antenna elements is greater than that of scatterers (targets). Furthermore, it requires many sets of frequency-domain data (snapshots) in seriously noisy environments. Unfortunately, these conditions are not practical for real environments due to the restriction of a reasonable antenna structure as well as limited measurement time. We propose an approach that treats both noise reduction and relaxation of the transceiver restriction by using a time-domain gating technique accompanied with the Fourier transform before applying the TR-MUSIC imaging algorithm. Instead of utilizing the conventional multistatic data matrix (MDM), we employ a modified MDM obtained from the gating technique. The resulting imaging functions yield more reliable images with only a few snapshots regardless of the limitation of the antenna arrays.
Entropy of seismic electric signals: Analysis in natural time under time reversal
Varotsos, P.A.; Skordas, E.S.; Sarlis, N.V.; Lazaridou, M.S.; Tanaka, H.K.
2006-03-15
Electric signals have been recently recorded at the Earth's surface with amplitudes appreciably larger than those hitherto reported. Their entropy in natural time is smaller than that of a 'uniform' distribution. The same holds for their entropy upon time reversal. Such a behavior, which is also found by numerical simulations in fractional Brownian motion time series and in an on-off intermittency model, stems from infinitely ranged long range temporal correlations and hence these signals are probably seismic electric signal activities (critical dynamics). This classification is strikingly confirmed since three strong nearby earthquakes occurred (which is an extremely unusual fact) after the original submission of the present paper. The entropy fluctuations are found to increase upon approaching bursting, which is reminiscent of the behavior identifying sudden cardiac death individuals when analyzing their electrocardiograms.
Electric Dipole Moments in Radioactive Nuclei, Tests of Time Reversal Symmetry
Auerbach, N.
2010-11-24
The research of radioactive nuclei opens new possibilities to study fundamental symmetries, such as time reversal and reflection symmetry. Such nuclei often provide conditions to check in an optimal way certain symmetries and the violation of such symmetries. We will discuss the possibility of obtaining improved limits on violation of time reversal symmetry using pear shaped radioactive nuclei. An effective method to test time reversal invariance in the non-strange sector is to measure parity and time reversal violating (T-P-odd) electromagnetic moments, (such as the static electric dipole moment). Parity and time reversal violating components in the nuclear force may produce P-T-odd moments in nuclei which in turn induce such moments in atoms. We will discuss the possibility that in some reflection asymmetric, heavy nuclei (which are radioactive) these moments are enhanced by several orders of magnitude. Present and future experiments, which will test this idea, will be mentioned.
Fast time-reversible algorithms for molecular dynamics of rigid-body systems.
Kajima, Yasuhiro; Hiyama, Miyabi; Ogata, Shuji; Kobayashi, Ryo; Tamura, Tomoyuki
2012-06-21
In this paper, we present time-reversible simulation algorithms for rigid bodies in the quaternion representation. By advancing a time-reversible algorithm [Y. Kajima, M. Hiyama, S. Ogata, and T. Tamura, J. Phys. Soc. Jpn. 80, 114002 (2011)] that requires iterations in calculating the angular velocity at each time step, we propose two kinds of iteration-free fast time-reversible algorithms. They are easily implemented in codes. The codes are compared with that of existing algorithms through demonstrative simulation of a nanometer-sized water droplet to find their stability of the total energy and computation speeds. PMID:22779579
Health monitoring of bolted joints using the time reversal method and piezoelectric transducers
NASA Astrophysics Data System (ADS)
Tao, Wang; Shaopeng, Liu; Junhua, Shao; Yourong, Li
2016-02-01
In this paper, the time reversal method based on piezoelectric active sensing is investigated for health monitoring of bolted joints. Experiments are conducted on bolted joints to study the relationship between the time reversal focused signal peak amplitudes and the bolt preload. Two piezoelectric patches are bonded on two different sides of a bolted joint. Any one of the piezoelectric patches can be used as an actuator to generate an ultrasonic wave, and the other one can be used as a sensor to detect the propagated wave. With the time reversal method, the received response signal is reversed in the time domain and then is re-emitted as an excitation signal to acquire the time reversal focused signals. The experimental results show that the time reversal focused signal peak amplitudes increase with the increasing bolt preload until reaching saturation, and when the bolt preload increases to a certain value, the focused signal peak amplitudes will remain unchanged. Experiments show that the surface roughness of the bolted joint impacts the saturation value. A higher surface roughness value corresponds to a higher saturation value. In addition, the proposed method has a high signal to noise ratio benefiting from the time reversal method time and space focusing ability.
Directed Current Without Dissipation: Reincarnation of a Maxwell-Loschmidt Demon
NASA Astrophysics Data System (ADS)
Goychuk, Igor; Haenggi, Peter
We investigate whether for initially localized particles a directed current in rocked periodic structures is possible in absence of a dissipative mechanism. With a pure Hamiltonian dynamics the breaking of Time-Reversal-Invariante presents anecessary condition to find nonzero current values. Numerical studies are presented for the classical Hamiltonian dynamical case. These support the fact that indeed a finite current does occur when a time-reversal symmetry-breaking signal, such as a harmonic mixing signal, is acting. To gain analytical insight we consider the coherent driven quantum transport in a one-dimensional tight-binding lattice. Here, a finite coherent current is absent for initially localized preparations; it emerges, however, when the initial preparation (with zero initial current) possesses finite coherence. The presence of phase fluctuations will eventually kill any finite current, thereby rendering the nondissipative currents a transient phenomenon.
Overcoming of the Diffraction Limit for the Discrete Case in Time Reversed Acoustics
NASA Astrophysics Data System (ADS)
Velázquez-Arcos, J. M.; Vargas, C. A.; Fernández-Chapou, L.; Granados-Samaniego, J.
2008-04-01
The time reversal phenomenon in sound waves for the discrete case is revisited. Our purpose is to improve a previous explanation of this problem in which there was a more limited scope. We develop a formulation which includes sink terms in the time reversed process, which allow going beyond the diffraction limit. By employing a reversed signal it is possible to reach a definition of a fourteenth of the wavelength. In the present work we discuss a matrix formulation for the discrete case in terms of the Fourier transforms of the input and output signals and the Green function. With this function it is possible to characterize the propagation of signals emitted by an array of devices. We are able to express the time reversed signal and precisely select the destination site, among other useful objectives. Finally we show an experimental arrangement using a Michelson interferometer in order to observe this phenomenon. Time Reversal originates from the second order time derivative in the wave equation. This is different from the case of nonlinear behavior in media known as acoustic or electromagnetic inverse scattering. Some of the fields which Time Reversal opens for investigation are the time reversal of a signal by a sound mirror (Time Reversal Mirror or TRM) or by a Time Reversal Cavity (TRC), and the possibility of sending a message to a precise physical location. Recently a new and powerful application has been reported in the literature, namely the abovementioned overcoming of the diffraction limit in wave physics. Although our experimental proposal is based on reports from others authors, the experimental arrangement used here, the specific way of operation and the image construction are original.
Time reversibility of intracranial human EEG recordings in mesial temporal lobe epilepsy
NASA Astrophysics Data System (ADS)
van der Heyden, M. J.; Diks, C.; Pijn, J. P. M.; Velis, D. N.
1996-02-01
Intracranial electroencephalograms from patients suffering from mesial temporal lobe epilepsy were tested for time reversibility. If the recorded time series is irreversible, the input of the recording system cannot be a realisation of a linear Gaussian random process. We confirmed experimentally that the measurement equipment did not introduce irreversibility in the recorded output when the input was a realisation of a linear Gaussian random process. In general, the non-seizure recordings are reversible, whereas the seizure recordings are irreversible. These results suggest that time reversibility is a useful property for the characterisation of human intracranial EEG recordings in mesial temporal lobe epilepsy.
Use of the FDTD method for time reversal: application to microwave breast cancer detection
NASA Astrophysics Data System (ADS)
Kosmas, Panagiotis; Rappaport, Carey
2004-05-01
The feasibility of microwave breast cancer detection with a time reversal algorithm is examined. This time reversal algorithm, based on the finite difference time domain method (FDTD), time reverses not only the recorded field, but also the medium. It compensates for the wave decay and therefore is suitable for lossy media. We present two-dimensional (2D) breast models and geometries, and assume knowledge of the system's response in the absence of tumor (distorted wave Born approximation). Our results illustrate the system's detection and localization abilities, and its robustness to dispersion and measurement noise. Good performance using a simple time reversal mirror shows that this method is a promising technique for microwave imaging, and encourages us to further examine its applicability to microwave breast cancer detection.
Time reversibility from visibility graphs of nonstationary processes
NASA Astrophysics Data System (ADS)
Lacasa, Lucas; Flanagan, Ryan
2015-08-01
Visibility algorithms are a family of methods to map time series into networks, with the aim of describing the structure of time series and their underlying dynamical properties in graph-theoretical terms. Here we explore some properties of both natural and horizontal visibility graphs associated to several nonstationary processes, and we pay particular attention to their capacity to assess time irreversibility. Nonstationary signals are (infinitely) irreversible by definition (independently of whether the process is Markovian or producing entropy at a positive rate), and thus the link between entropy production and time series irreversibility has only been explored in nonequilibrium stationary states. Here we show that the visibility formalism naturally induces a new working definition of time irreversibility, which allows us to quantify several degrees of irreversibility for stationary and nonstationary series, yielding finite values that can be used to efficiently assess the presence of memory and off-equilibrium dynamics in nonstationary processes without the need to differentiate or detrend them. We provide rigorous results complemented by extensive numerical simulations on several classes of stochastic processes.
Dynamics-independent null experiment for testing time-reversal invariance
NASA Astrophysics Data System (ADS)
Arash, Firooz; Moravcsik, Michael J.; Goldstein, Gary R.
1985-06-01
It is shown that it is impossible to construct, in any reaction in atomic, nuclear, or particle physics, a null experiment that would unambiguously test the validity of time-reversal invariance independently of dynamical assumptions.
A study of perfectly matched layers for joint multicomponent reverse-time migration
NASA Astrophysics Data System (ADS)
Du, Qi-Zhen; Sun, Rui-Yan; Qin, Tong; Zhu, Yi-Tong; Bi, Li-Fei
2010-06-01
Reverse-time migration in finite space requires effective boundary processing technology to eliminate the artificial truncation boundary effect in the migration result. On the basis of the elastic velocity-stress equations in vertical transversely isotropic media and the idea of the conventional split perfectly matched layer (PML), the PML wave equations in reverse-time migration are derived in this paper and then the high order staggered grid discrete schemes are subsequently given. Aiming at the “reflections” from the boundary to the computational domain, as well as the effect of seismic event’s abrupt changes at the two ends of the seismic array, the PML arrangement in reverse-time migration is given. The synthetic and real elastic, prestack, multi-component, reverse-time depth migration results demonstrate that this method has much better absorbing effects than other methods and the joint migration produces good imaging results.
Time Reversed Electromagnetics as a Novel Method for Wireless Power Transfer
NASA Astrophysics Data System (ADS)
Challa, Anu; Anlage, Steven M.; Tesla Team
Taking advantage of ray-chaotic enclosures, time reversal has been shown to securely transmit information via short-wavelength waves between two points, yielding noise at all other sites. In this presentation, we propose a method to adapt the signal-focusing technique to electromagnetic signals in order to transmit energy to portable devices. Relying only on the time-reversal invariance properties of waves, the technique is unencumbered by the inversely-proportional-to-distance path loss or precise orientation requirements of its predecessors, making it attractive for power transfer applications. We inject a short microwave pulse into a complex, wave-chaotic chamber and collect the resulting long time-domain signal at a designated transceiver. The signal is then time reversed and emitted from the collection site, collapsing as a time-reversed replica of the initial pulse at the injection site. When amplified, this reconstruction is robust, as measured through metrics of peak-to-peak voltage and energy transfer ratio. We experimentally demonstrate that time reversed collapse can be made on a moving target, and propose a way to selectively target devices through nonlinear time-reversal. University of Maryland Gemstone Team TESLA: Frank Cangialosi, Anu Challa, Tim Furman, Tyler Grover, Patrick Healey, Ben Philip, Brett Potter, Scott Roman, Andrew Simon, Liangcheng Tao, Alex Tabatabai.
NASA Astrophysics Data System (ADS)
Hossain, Md. Delwar; Mohan, Ananda Sanagavarapu
2015-02-01
This paper deals with the coherent processing of time-reversal operator for microwave imaging in the frequency domain. In frequency domain time-reversal imaging approach, images obtained for different frequency bins over ultrawideband are incoherently processed. In highly dense and cluttered medium, the signal subspace over each narrow frequency bin varies from that obtained using the complete ultrawideband. As a result, the detection and localization from noncoherent imaging approach is often inconclusive. In order to improve the stability of time-reversal microwave imaging, we propose coherent processing using novel focusing matrix approach. The proposed focusing matrix makes possible the time-reversal imaging technique to coherently process each frequency bin to yield a consistent signal subspace. The performance of coherent focusing is investigated when combined with time-reversal robust Capon beamformer (TR-RCB). We have used numerical experiments on breast cancer detection using finite difference time domain employing anatomically realistic numerical breast phantoms that contain varying amounts of dense fibroglandular tissue content. The imaging results indicate that the proposed coherent-TR-RCB could overcome the limitations of time-reversal imaging in a highly heterogeneous and cluttered medium.
Mapping the three-body system - decay time and reversibility
NASA Astrophysics Data System (ADS)
Lehto, H. J.; Kotiranta, S.; Valtonen, M. J.; Heinämäki, P.; Mikkola, S.; Chernin, A. D.
2008-08-01
In this paper we carry out a quantitative analysis of the three-body systems and map them as a function of decaying time and initial configuration, look at this problem as an example of a simple deterministic system and ask to what extent the orbits are really predictable. We have investigated the behaviour of about 200000 general Newtonian three-body systems using the simplest initial conditions. Within our resolution these cover all the possible states where the objects are initially at rest and have no angular momentum. We have determined the decay time-scales of the triple systems and show that the distribution of this parameter is fractal in appearance. Some areas that appear stable on large scales exhibit very narrow strips of instability and the overall pattern, dominated by resonances, reminds us of a traditional Maasai warrior shield. Also an attempt is made to recover the original starting configuration of the three bodies by backward integration. We find there are instances where the evolution to the future and to the past lead to different orbits, in spite of time symmetric initial conditions. This implies that even in simple deterministic systems there exists an arrow of time.
Reverse time migration: A seismic processing application on the connection machine
NASA Technical Reports Server (NTRS)
Fiebrich, Rolf-Dieter
1987-01-01
The implementation of a reverse time migration algorithm on the Connection Machine, a massively parallel computer is described. Essential architectural features of this machine as well as programming concepts are presented. The data structures and parallel operations for the implementation of the reverse time migration algorithm are described. The algorithm matches the Connection Machine architecture closely and executes almost at the peak performance of this machine.
Fuchs, M E; Anderson, R E; Ostrowski, K A; Brant, W O; Fuchs, E F
2016-01-01
The absence of sperm in the ejaculate after vasectomy reversal is commonly caused by failure to recognize and subsequently bypass epididymal or proximal vasal obstruction at the time of vasectomy reversal. If intra-operative proximal obstruction is suspected, vasoepididymostomy (VE) is recommended rather than vasovasostomy (VV). We sought to calculate the associated risk of needing VE, rather than VV with time from original vasectomy (obstructive interval) using a large cohort of vasectomy reversal patients. We reviewed the electronic and paper vasectomy reversal database by a single surgeon from 1978 through 2012. We performed univariate analysis to identify variables that predicted the need for VE rather than VV, and then combined only significant univariates into our multi-variable analysis. 2697 total men underwent vasectomy reversal, and 239 were repeat procedures. Of the 5296 individual testes operated on, 1029 were VE. Significant variables that predicted the need for VE on univariate analysis included: age, obstructive time interval, vasectomy reversal after previous VV (repeat vasectomy reversal), and year the procedure was performed. On multi-variable analysis significant risk factors for VE were age above 50 (OR 1.36), repeat vasectomy reversal (OR 5.78), and greater obstructive time interval (OR 1.56). For every 3 years since original vasectomy, the risk of needing VE increases by 56%. There is a linear relationship between obstructive interval and need for VE. Men undergoing repeat vasectomy reversal have five times greater risk of requiring VE and men greater than 50 years of age are also at higher risk. Using these pre-operative predictors is helpful in identifying patients who will benefit from referral to an experienced surgeon who can perform VE. PMID:26663812
Mechanism, time-reversal symmetry, and topology of superconductivity in noncentrosymmetric systems
NASA Astrophysics Data System (ADS)
Scheurer, M. S.
2016-05-01
We analyze the possible interaction-induced superconducting instabilities in noncentrosymmetric systems based on symmetries of the normal state. It is proven that pure electron-phonon coupling will always lead to a fully gapped superconductor that does not break time-reversal symmetry and is topologically trivial. We show that topologically nontrivial behavior can be induced by magnetic doping without gapping out the resulting Kramers pair of Majorana edge modes. In the case of superconductivity arising from the particle-hole fluctuations associated with a competing instability, the properties of the condensate crucially depend on the time-reversal behavior of the order parameter of the competing instability. When the order parameter preserves time-reversal symmetry, we obtain exactly the same properties as in the case of phonons. If it is odd under time reversal, the Cooper channel of the interaction will be fully repulsive leading to sign changes of the gap and making spontaneous time-reversal-symmetry breaking possible. To discuss topological properties, we focus on fully gapped time-reversal-symmetric superconductors and derive constraints on possible pairing states that yield necessary conditions for the emergence of topologically nontrivial superconductivity. These conditions might serve as a tool in the search for topological superconductors. We also discuss implications for oxide heterostructures and single-layer FeSe.
NASA Astrophysics Data System (ADS)
Du, Guofeng; Kong, Qingzhao; Wu, Fanghong; Ruan, Jiabiao; Song, Gangbing
2016-03-01
Corrosion pits on pipelines lead to the formation of small holes, which cause further pipeline damage and even catastrophic consequences. Since many pipelines are located underground, the detection of corrosion pits on pipelines in real time is still an engineering challenge. In this paper, an experimental feasibility study on pipeline corrosion pit detection using the time reversal technique with a piezoceramic transducer as a time reversal mirror was investigated. A specimen of steel pipeline section was fabricated with an artificially drilled hole, which was to mimic a corrosion pit. By gradually increasing the depth of the hole, the evolution of the corrosion pit on the pipeline was simulated and studied. Two piezoceramic transducers were employed to generate a stress wave to propagate along the pipeline and to detect the propagated stress wave. With both the properties of sensing and actuating functions, a piezoceramic transducer was used as a time reversal mirror, which first detected the propagated stress wave signal and then sent ‘back’ the time-reversed signal as a propagating stress wave. With the inherent auto-focusing property of the time reversal technique, the detected time-reversed stress wave had a distinct focused peak. A corrosion pit on a pipeline, as a structural defect, reduces the energy of the focused signal received by the piezoceramic sensor and the attenuation ratio of the focused signal depends strongly on the degree of corrosion depth. Experimental results show that the amplitudes of the focused signal peak decrease with the increase of corrosion pit depth and we can use the peak amplitude of the focused signal to determine the state of pipeline corrosion. The time reversal based method proposed in this paper shows the potential to quantitatively monitor the damage degree of corrosion pits on pipelines in real time.
Retrieving the Green's function of attenuating heterogeneous media by time-reversal modeling
NASA Astrophysics Data System (ADS)
Zhu, T.
2014-12-01
The Green's function between two locations within which seismograms that were not physically recorded, are retrieved by cross-correlation, convolution or deconvolution and summation of other recorded wavefields (also known as seismic interferometry). More recently seismic interferometry was applied in exploration seismology by Bakulin and Calvert (2006) and Schuster et al. (2004), in ultrasound by Weaver and Lobkis (2001), in crustal seismology by Campillo and Paul (2003), Sabra et al. (2005a, b), Roux et al. (2005) and Shapiro et al. (2005), and in helioseismology by Rickett and Claerbout (1999). Theory of the retrieval of Green's function can also be represented by time-reversal propagation because of time invariance of wave equations in the lossless media. In the presence of intrinsic attenuation in the media, however, the time invariance of wave equations is invalid. My previous work present methods of using novel viscoacoustic and viscoelastic wave equations to recover the time invariance property of such wave equations for viscoacoustic and viscoelastic time-reversal modeling. More importantly, attenuation effects are compensated for during time-reversal wave propagation. In this paper, I investigate the possibility of retrieving the Green's function through time-reversal modeling techniques in attenuating media. I consider two different models to illustrate the feasibility of Green's function retrieval in attenuating media. I consider the viscoacoustic as well as the viscoelastic situation. Numerical results show that the Green's function can be retrieved in the correct amplitude and phase by time-reversal modeling with compensating both amplitude loss and dispersion effects.
Reversal of age-related neural timing delays with training.
Anderson, Samira; White-Schwoch, Travis; Parbery-Clark, Alexandra; Kraus, Nina
2013-03-12
Neural slowing is commonly noted in older adults, with consequences for sensory, motor, and cognitive domains. One of the deleterious effects of neural slowing is impairment of temporal resolution; older adults, therefore, have reduced ability to process the rapid events that characterize speech, especially in noisy environments. Although hearing aids provide increased audibility, they cannot compensate for deficits in auditory temporal processing. Auditory training may provide a strategy to address these deficits. To that end, we evaluated the effects of auditory-based cognitive training on the temporal precision of subcortical processing of speech in noise. After training, older adults exhibited faster neural timing and experienced gains in memory, speed of processing, and speech-in-noise perception, whereas a matched control group showed no changes. Training was also associated with decreased variability of brainstem response peaks, suggesting a decrease in temporal jitter in response to a speech signal. These results demonstrate that auditory-based cognitive training can partially restore age-related deficits in temporal processing in the brain; this plasticity in turn promotes better cognitive and perceptual skills. PMID:23401541
Reversal of age-related neural timing delays with training
Anderson, Samira; White-Schwoch, Travis; Parbery-Clark, Alexandra; Kraus, Nina
2013-01-01
Neural slowing is commonly noted in older adults, with consequences for sensory, motor, and cognitive domains. One of the deleterious effects of neural slowing is impairment of temporal resolution; older adults, therefore, have reduced ability to process the rapid events that characterize speech, especially in noisy environments. Although hearing aids provide increased audibility, they cannot compensate for deficits in auditory temporal processing. Auditory training may provide a strategy to address these deficits. To that end, we evaluated the effects of auditory-based cognitive training on the temporal precision of subcortical processing of speech in noise. After training, older adults exhibited faster neural timing and experienced gains in memory, speed of processing, and speech-in-noise perception, whereas a matched control group showed no changes. Training was also associated with decreased variability of brainstem response peaks, suggesting a decrease in temporal jitter in response to a speech signal. These results demonstrate that auditory-based cognitive training can partially restore age-related deficits in temporal processing in the brain; this plasticity in turn promotes better cognitive and perceptual skills. PMID:23401541
Time Reversal Imaging of Seismic Sources by the Spectral Element Method.
NASA Astrophysics Data System (ADS)
Larmat, C.; Montagner, J.; Fink, M.; Capdeville, Y.; Clevede, E.; Tourin, A.
2005-12-01
The increasing power of computers and numerical methods (such as spectral elements methods) makes it possible to simulate more and more accurately the propagation of seismic waves in heterogeneous media and even to conceive new applications such as time reversal experiments within the three--dimensional Earth. These latter use the time reversal invariance and the spatial reciprocity of the wave equation. The idea is to construct a reverse movie of the propagation by sending the time--reversed recorded signals back from the receivers. The energy refocuses back at the location and the time of the original source. The concept of time-reversal has previously been successfully applied for acoustic waves in many fields such as medical imaging, oceanography and non destructive testing. For simulating the propagation of waves in the Earth as well as their time-reversed propagation, we used 2 different techniques, the normal mode summation technique (Gilbert and Dziewonski, 1975) and the spectral element method coupled with the modal solution (Capdeville et al., 2003). The first method is very accurate for 1D-earth models such as PREM whereas the second method is required for general heterogeneous 3D-models. For the first time, we have performed several synthetic and real data time-reversal experiments for seismic waves until the time of focalisation at the source. These tests show that sources are successfully localized in time and in space (though less accurately at depth), especially at very long period (> 200s) where the seismic properties of the Earth are well constrained. The corresponding movies are visible at the following address: http://www.gps.caltech.edu/~carene. We collect and send back the seismograms of the Global network of broadband seismic stations of the Federation of Digital Seismic Network (FDSN). We first consider a moderately large earthquake which can be considered as a point source in both time and space (Peru, June 23, 2001, Mw = 8.4). The
Time-resolved reversal of spin-transfer switching in a nanomagnet.
Koch, R H; Katine, J A; Sun, J Z
2004-02-27
Time-resolved measurements of spin-transfer-induced (STI) magnetization reversal were made in current-perpendicular spin-valve nanomagnetic junctions subject to a pulsed current bias. These results can be understood within the framework of a Landau-Lifshitz-Gilbert equation that includes STI corrections and a Langevin random field for finite temperature. Comparison of these measurements with model calculations demonstrates that spin-transfer induced excitation is responsible for the observed magnetic reversal in these samples. PMID:14995820
NASA Astrophysics Data System (ADS)
Sabra, Karim G.; Roux, Philippe; Song, Hee-Chun; Hodgkiss, William; Kuperman, William A.; Akal, Tuncay; Stevenson, Mark R.
2005-09-01
For most shallow-water waveguides, the backscattered energy measured in a monostatic configuration is dominated by ocean bottom reverberation. A selected time-gated portion of the measured reverberation signals is used to provide a transfer function between a time-reversing array and a corresponding range interval on the bottom. Ultrasonic and at-sea experiments demonstrate focusing capabilities along the rough bottom interface of a time-reversing array using these reverberation signals only. The iterative time-reversal technique facilitates robust focusing along the ocean bottom, with little signal-processing effort involved and a priori information on the environment, and the enhancement of detection and localization of proud or buried targets in complex shallow-water environments. A passive implementation of the iterative time-reversal processing is used to construct reflectivity maps, similar to a sonar map, but with an enhanced contrast for the strongest reflectors (or scatterers), at the water-bottom interface. Ultrasonic and at-sea experiments show that targets lying on the seafloor located up to 400 wavelengths from the time-reversing array were detected over the bottom reverberation.
Time reversal imaging and cross-correlations techniques by normal mode theory
NASA Astrophysics Data System (ADS)
Montagner, J.; Fink, M.; Capdeville, Y.; Phung, H.; Larmat, C.
2007-12-01
Time-reversal methods were successfully applied in the past to acoustic waves in many fields such as medical imaging, underwater acoustics, non destructive testing and recently to seismic waves in seismology for earthquake imaging. The increasing power of computers and numerical methods (such as spectral element methods) enables one to simulate more and more accurately the propagation of seismic waves in heterogeneous media and to develop new applications, in particular time reversal in the three-dimensional Earth. Generalizing the scalar approach of Draeger and Fink (1999), the theoretical understanding of time-reversal method can be addressed for the 3D- elastic Earth by using normal mode theory. It is shown how to relate time- reversal methods on one hand, with auto-correlation of seismograms for source imaging and on the other hand, with cross-correlation between receivers for structural imaging and retrieving Green function. The loss of information will be discussed. In the case of source imaging, automatic location in time and space of earthquakes and unknown sources is obtained by time reversal technique. In the case of big earthquakes such as the Sumatra-Andaman earthquake of december 2004, we were able to reconstruct the spatio-temporal history of the rupture. We present here some new applications at the global scale of these techniques on synthetic tests and on real data.
Determination of time-reversal symmetry breaking lengths in an InGaAs interferometer array.
Ren, S L; Heremans, J J; Vijeyaragunathan, S; Mishima, T D; Santos, M B
2015-05-13
Quantum interference oscillations due to the Aharonov-Bohm phase were measured in a ring interferometer array fabricated on a two-dimensional electron system in an InGaAs/InAlAs heterostructure. Coexisting oscillations with magnetic flux periodicity h/e and h/2e were observed and their amplitudes compared as function of applied magnetic field. The h/2e oscillations originate in time-reversed trajectories with the ring interferometers operating in Sagnac-type mode, while the h/e oscillations result from Mach-Zehnder operation. The h/2e oscillations require time-reversal symmetry and hence can be used to quantify time-reversal symmetry breaking, more particularly the fundamental mesoscopic dephasing length associated with time-reversal symmetry breaking under applied magnetic field, an effective magnetic length. The oscillation amplitudes were investigated over magnetic fields spanning 2.2 T, using Fourier transforms over short segments of 40 mT. As the magnetic field increased, the h/2e oscillation amplitude decreased due to time-reversal symmetry breaking by the local magnetic flux in the interferometer arms. A dephasing model for quantum-coherent arrays was used to experimentally quantify effective magnetic lengths. The data was then compared with analytical expressions for diffusive, ballistic and confined systems. PMID:25880699
Finneran, James J; Wu, Teri; Borror, Nancy; Tormey, Megan; Brewer, Arial; Black, Amy; Bakhtiari, Kimberly
2013-12-01
In matched filter processing, a stored template of the emitted sonar pulse is compared to echoes to locate individual replicas of the emitted pulse embedded in the echo stream. A number of experiments with bats have suggested that bats utilize matched filter processing for target ranging, but not for target detection. For dolphins, the few available data suggest that dolphins do not utilize matched filter processing. In this study, the effect of time-reversing a dolphin's emitted click was investigated. If the dolphin relied upon matched filter processing, time-reversal of the click would be expected to reduce the correlation between the (unaltered) click and the echoes and therefore lower detection performance. Two bottlenose dolphins were trained to perform a phantom echo detection task. On a small percentage of trials ("probe trials"), a dolphin's emitted click was time-reversed before interacting with the phantom echo system. Data from the normal and time-reversed trials were then analyzed and compared. There were no significant differences in detection performance or click emissions between the normal and time-reversed conditions for either subject, suggesting that the dolphins did not utilize matched filter processing for this echo detection task. PMID:25669264
Effects of nonlinearities in power ultrasonic transducers using time reversal focalization
NASA Astrophysics Data System (ADS)
Pérez Alvarez, N.; Noris Franceschetti, N.; Adamowski, J. C.
2010-01-01
This paper presents the characterization of nonlinearities in a Langevin-type ultrasonic power transducer using pulse excitations and a time reversal focalization technique. The nonlinear behavior of this power transducer is evaluated analyzing the signal obtained after focalization in time reversal process. In a linear regime, time reversal produces a focused pulse which amplitude and width depends only on the transducer's transfer function. When the supplied power is increased, three non-linear effects appear in the systems response. First, the focus shape loss symmetry respect to center; second, the focus amplitude increases without proportionality to input voltage, and finally, in the frequency spectrum appears harmonics of the thickness mode resonance frequency. The displacement at the end transducer surface was measured by an optical fiber vibrometer. Traditional frequency domain methods are also used to show phase variations close to each resonance frequency. The time reversal is implemented using the Frequency Domain Time Reversal (FDTR), that technique ensures the linear regime in the first step of the process.
Imaging in the presence of grain noise using the decomposition of the time reversal operator
NASA Astrophysics Data System (ADS)
Kerbrat, E.; Prada, C.; Cassereau, D.; Fink, M.
2003-03-01
In this paper, we are interested in detecting and imaging defects in samples of cylindrical geometry with large speckle noise due to the microstructure. The time reversal process is an appropriate technique for detecting flaws in such heterogeneous media as titanium billets. Furthermore, time reversal can be iterated to select the defect with the strongest reflectivity and to reduce the contribution of speckle noise. The DORT (the French acronym for Decomposition of the Time Reversal Operator) method derives from the mathematical analysis of the time reversal process. This detection technique allows the determination of a set of signals to be applied to the transducers in order to focus on each defect separately. In this paper, we compare three immersion techniques on a titanium sample, standard transmit/receive focusing, the time reversal mirror (TRM), and the DORT method. We compare the sensitivity of these three techniques, especially the sensitivity to a poor alignment of the array with the front face of the sample. Then we show how images of the sample can be obtained with the TRM and the DORT method using backpropagation algorithm.
Effects of time-reversing array deformation in an ocean wave guide
NASA Astrophysics Data System (ADS)
Sabra, Karim G.; Dowling, David R.
2004-06-01
Active acoustic time reversal is a technique for focusing sounds recorded in complex unknown environments back to their remote point(s) of origin. It can be accomplished with a transducer array-a time-reversing array (TRA)-that sends and receives sound. Nearly all prior work on TRA performance has involved stationary arrays. This letter describes how random array deformation influences TRA retrofocusing in shallow ocean environments. For harmonic signals, randomly drifting array elements degrade TRA performance by ~20% when the average horizontal wavenumber times the root-mean-square horizontal element displacement approaches 0.5. TRA focusing should be less sensitive to vertical element drift.
Efficiency Statistics and Bounds for Systems with Broken Time-Reversal Symmetry
NASA Astrophysics Data System (ADS)
Jiang, Jian-Hua; Agarwalla, Bijay Kumar; Segal, Dvira
2015-07-01
Universal properties of the statistics of stochastic efficiency for mesoscopic time-reversal symmetry broken energy transducers are revealed in the Gaussian approximation. We also discuss how the second law of thermodynamics restricts the statistics of stochastic efficiency. The tight-coupling limit becomes unfavorable, characterized by an infinitely broad distribution of efficiency at all times, when time-reversal symmetry breaking leads to an asymmetric Onsager response matrix. The underlying physics is demonstrated through the quantum Hall effect and further elaborated in a triple-quantum-dot three-terminal thermoelectric engine.
Efficiency Statistics and Bounds for Systems with Broken Time-Reversal Symmetry.
Jiang, Jian-Hua; Agarwalla, Bijay Kumar; Segal, Dvira
2015-07-24
Universal properties of the statistics of stochastic efficiency for mesoscopic time-reversal symmetry broken energy transducers are revealed in the Gaussian approximation. We also discuss how the second law of thermodynamics restricts the statistics of stochastic efficiency. The tight-coupling limit becomes unfavorable, characterized by an infinitely broad distribution of efficiency at all times, when time-reversal symmetry breaking leads to an asymmetric Onsager response matrix. The underlying physics is demonstrated through the quantum Hall effect and further elaborated in a triple-quantum-dot three-terminal thermoelectric engine. PMID:26252673
NASA Astrophysics Data System (ADS)
Armitage, N. P.
2014-07-01
Optical spectroscopies are most often used to probe dynamical correlations in materials, but they are also a probe of symmetry. Polarization anisotropies are of course sensitive to structural anisotropies, but have been much less used as a probe of more exotic symmetry breakings in ordered states. In this paper, a Jones transfer matrix formalism is discussed to infer the existence of exotic broken symmetry states of matter from their electrodynamic response for a full complement of possible broken symmetries including reflection, rotation, rotation reflection, inversion, and time reversal. A specific condition to distinguish the case of macroscopic time-reversal symmetry breaking is particularly important as in a dynamical experiment like optics, one must distinguish reciprocity from time-reversal symmetry as dissipation violates strict time-reversal symmetry of an experiment. Different forms of reciprocity can be distinguished, but only one is a sufficient (but not necessary) condition for macroscopic time-reversal symmetry breaking. I show the constraints that a Jones matrix develops under the presence or absence of such symmetries. These constraints typically appear in the form of an algebra relating matrix elements or overall constraints (transposition, unitarity, hermiticity, normality, etc.) on the form of the Jones matrix. I work out a number of examples including the trivial case of a ferromagnet and the less trivial cases of magnetoelectrics and vector and scalar spin "chiral" states. I show that the formalism can be used to demonstrate that Kerr rotation must be absent in time-reversal symmetric chiral materials. The formalism here is discussed with an eye towards its use in time-domain terahetrz spectroscopy in transmission, but with small modifications it is more generally applicable.
Experimental demonstration of the utility of pressure sensitivity kernels in time-reversal.
Raghukumar, Kaustubha; Cornuelle, Bruce D; Hodgkiss, William S; Kuperman, William A
2010-09-01
Pressure sensitivity kernels were recently applied to time-reversal acoustics in an attempt to explain the enhanced stability of the time-reversal focal spot [Raghukumar et al., J. Acoust. Soc. Am. 124, 98-112 (2008)]. The theoretical framework developed was also used to derive optimized source functions, closely related to the inverse filter. The use of these optimized source functions results in an inverse filter-like focal spot which is more robust to medium sound speed fluctuations than both time-reversal and the inverse filter. In this paper the theory is applied to experimental data gathered during the Focused Acoustic Fields experiment, conducted in 2005, north of Elba Island in Italy. Sensitivity kernels are calculated using a range-independent sound-speed profile, for a geometry identical to that used in the experiment, and path sensitivities are identified with observed arrivals. The validity of the kernels in tracking time-evolving Green's functions is studied, along with limitations that result from a linearized analysis. An internal wave model is used to generate an ensemble of sound speed profiles, which are then used along with the calculated sensitivity kernels to derive optimized source functions. Focal spots obtained using the observed Green's functions with these optimized source functions are then compared to those obtained using time-reversal and the inverse-filter. It is shown that these functions are able to provide a focal spot superior to time-reversal while being more robust to sound speed fluctuations than the inverse filter or time-reversal. PMID:20815436
Time-reversal asymmetry without local moments via directional scalar spin chirality
NASA Astrophysics Data System (ADS)
Hosur, Pavan
Quantum phases of matter that violate time-reversal symmetry invariably develop local spin or orbital moments in the ground state. Here, a directional scalar spin chiral order (DSSCO) phase is introduced, that disrespects time-reversal symmetry but has no static moments. It can be obtained by melting the spin moments in a magnetically ordered phase but retaining residual broken time-reversal symmetry. Orbital moments are then precluded by the spatial symmetries of the spin rotation symmetric state. Interestingly, polar Kerr effect in the 3D DSSCO has the same symmetries as those observed experimentally in the pseudogap phase of several underdoped cuprates. Finally, it is shown that the DSSCO provides a phenomenological route for reconciling the results of Kerr effect and nuclear magnetic resonance experiments in the cuprates, with charge ordering tendencies - observed in X-ray diffraction studies - playing a crucial role. The so-called ''memory effect'' in the cuprates can be incorporated into this picture as well.
Suppression of tissue harmonics for pulse-inversion contrast imaging using time reversal
NASA Astrophysics Data System (ADS)
Couture, Olivier; Aubry, Jean-François; Montaldo, Gabriel; Tanter, Mickael; Fink, Mathias
2008-10-01
Pulse-inversion (PI) sequences are sensitive to the nonlinear echoes from microbubbles allowing an improvement in the blood-to-tissue contrast. However, at larger mechanical indices, this contrast is reduced by harmonics produced during nonlinear propagation. A method for tissue harmonics cancellation exploiting time reversal is experimentally implemented using a 128-channel 12-bit emitter receiver. The probe calibration is performed by acquiring the nonlinear echo of a wire in water. These distorted pulses are time-reversed, optimized and used for the PI imaging of a tissue phantom. Compared to normal (straight) pulses, the time-reversed distorted pulses reduced the tissue signal in PI by 11 dB. The second harmonic signals from microbubbles flowing in a wall-less vessel were unaffected by the correction. This technique can thus increase the blood-to-tissue contrast ratio while keeping the pressure and the number of pulses constant.
Suppression of tissue harmonics for pulse-inversion contrast imaging using time reversal.
Couture, Olivier; Aubry, Jean-François; Montaldo, Gabriel; Tanter, Mickael; Fink, Mathias
2008-10-01
Pulse-inversion (PI) sequences are sensitive to the nonlinear echoes from microbubbles allowing an improvement in the blood-to-tissue contrast. However, at larger mechanical indices, this contrast is reduced by harmonics produced during nonlinear propagation. A method for tissue harmonics cancellation exploiting time reversal is experimentally implemented using a 128-channel 12-bit emitter receiver. The probe calibration is performed by acquiring the nonlinear echo of a wire in water. These distorted pulses are time-reversed, optimized and used for the PI imaging of a tissue phantom. Compared to normal (straight) pulses, the time-reversed distorted pulses reduced the tissue signal in PI by 11 dB. The second harmonic signals from microbubbles flowing in a wall-less vessel were unaffected by the correction. This technique can thus increase the blood-to-tissue contrast ratio while keeping the pressure and the number of pulses constant. PMID:18765888
Multi-channel time-reversal receivers for multi and 1-bit implementations
Candy, James V.; Chambers, David H.; Guidry, Brian L.; Poggio, Andrew J.; Robbins, Christopher L.
2008-12-09
A communication system for transmitting a signal through a channel medium comprising digitizing the signal, time-reversing the digitized signal, and transmitting the signal through the channel medium. In one embodiment a transmitter is adapted to transmit the signal, a multiplicity of receivers are adapted to receive the signal, a digitizer digitizes the signal, and a time-reversal signal processor is adapted to time-reverse the digitized signal. An embodiment of the present invention includes multi bit implementations. Another embodiment of the present invention includes 1-bit implementations. Another embodiment of the present invention includes a multiplicity of receivers used in the step of transmitting the signal through the channel medium.
Enhanced focal-resolution of dipole sources using aeroacoustic time-reversal in a wind tunnel
NASA Astrophysics Data System (ADS)
Mimani, A.; Moreau, D. J.; Prime, Z.; Doolan, C. J.
2016-05-01
This paper presents the first application of the Point-Time-Reversal-Sponge-Layer (PTRSL) damping technique to enhance the focal-resolution of experimental flow-induced dipole sources obtained using the Time-Reversal (TR) source localization method. Experiments were conducted in an Anechoic Wind Tunnel for the case of a full-span cylinder located in a low Mach number cross-flow. The far-field acoustic pressure sampled using two line arrays of microphones located above and below the cylinder exhibited a dominant Aeolian tone. The aeroacoustic TR simulations were implemented using the time-reversed signals whereby the source map revealed the lift-dipole nature at the Aeolian tone frequency. A PTRSL (centred at the predicted dipole location) was shown to reduce the size of dipole focal spots to 7/20th of a wavelength as compared to one wavelength without its use, thereby dramatically enhancing the focal-resolution of the TR technique.
Quantum-Enhanced Sensing Based on Time Reversal of Nonlinear Dynamics.
Linnemann, D; Strobel, H; Muessel, W; Schulz, J; Lewis-Swan, R J; Kheruntsyan, K V; Oberthaler, M K
2016-07-01
We experimentally demonstrate a nonlinear detection scheme exploiting time-reversal dynamics that disentangles continuous variable entangled states for feasible readout. Spin-exchange dynamics of Bose-Einstein condensates is used as the nonlinear mechanism which not only generates entangled states but can also be time reversed by controlled phase imprinting. For demonstration of a quantum-enhanced measurement we construct an active atom SU(1,1) interferometer, where entangled state preparation and nonlinear readout both consist of parametric amplification. This scheme is capable of exhausting the quantum resource by detecting solely mean atom numbers. Controlled nonlinear transformations widen the spectrum of useful entangled states for applied quantum technologies. PMID:27419565
Comparison study of time reversal OFDM acoustic communication with vector and scalar sensors
NASA Astrophysics Data System (ADS)
Wang, Zhongkang; Zhang, Hongtao; Xie, Zhe
2012-11-01
To compare the performance of time reversal orthogonal frequency division multiplexing (OFDM) acoustic communication on vector and scalar sensors, the vector and scalar acoustic fields were modeled. Time reversal OFDM acoustic communication was then simulated for each sensor type. These results are compared with data from the CAPEx'09 experiment. The abilityof particle velocity channels to achieve reliable acoustic communication, as predicted by the model, is confirmed with the experiment data. Experimental results show that vector receivers can reduce the required array size, in comparisonto hydrophone arrays, whileproviding comparable communication performance.
The Born Rule and Time-Reversal Symmetry of Quantum Equations of Motion
NASA Astrophysics Data System (ADS)
Ilyin, Aleksey V.
2016-07-01
It was repeatedly underlined in literature that quantum mechanics cannot be considered a closed theory if the Born Rule is postulated rather than derived from the first principles. In this work the Born Rule is derived from the time-reversal symmetry of quantum equations of motion. The derivation is based on a simple functional equation that takes into account properties of probability, as well as the linearity and time-reversal symmetry of quantum equations of motion. The derivation presented in this work also allows to determine certain limits to applicability of the Born Rule.
Time reverse modeling of acoustic emissions in a reinforced concrete beam.
Kocur, Georg Karl; Saenger, Erik H; Grosse, Christian U; Vogel, Thomas
2016-02-01
The time reverse modeling (TRM) is applied for signal-based acoustic emission (AE) analysis of reinforced concrete (RC) specimens. TRM uses signals obtained from physical experiments as input. The signals are re-emitted numerically into a structure in a time-reversed manner, where the wavefronts interfere and appear as dominant concentrations of energy at the origin of the AE. The experimental and numerical results presented for selected AE signals confirm that TRM is capable of localizing AE activity in RC caused by concrete cracking. The accuracy of the TRM results is corroborated by three-dimensional crack distributions obtained from X-ray computed tomography images. PMID:26518525
Quantum-Enhanced Sensing Based on Time Reversal of Nonlinear Dynamics
NASA Astrophysics Data System (ADS)
Linnemann, D.; Strobel, H.; Muessel, W.; Schulz, J.; Lewis-Swan, R. J.; Kheruntsyan, K. V.; Oberthaler, M. K.
2016-07-01
We experimentally demonstrate a nonlinear detection scheme exploiting time-reversal dynamics that disentangles continuous variable entangled states for feasible readout. Spin-exchange dynamics of Bose-Einstein condensates is used as the nonlinear mechanism which not only generates entangled states but can also be time reversed by controlled phase imprinting. For demonstration of a quantum-enhanced measurement we construct an active atom SU(1,1) interferometer, where entangled state preparation and nonlinear readout both consist of parametric amplification. This scheme is capable of exhausting the quantum resource by detecting solely mean atom numbers. Controlled nonlinear transformations widen the spectrum of useful entangled states for applied quantum technologies.
NASA Astrophysics Data System (ADS)
Van Damme, Bart; Van Den Abeele, Koen; Bou Matar, Olivier
2012-02-01
A combination of time reversed acoustics and nonlinear elastic wave spectroscopy techniques is introduced to localize surface breaking defects in a non-destructive manner. Reciprocal time reversal is applied at two neighbouring positions in order to create a vibration dipole with high amplitudes. At surface breaking cracks, nonlinear elastic effects are triggered by the shear forces due to induced friction of the crack interfaces. By mapping the nonlinearity generated by the vibration dipole over the sample surface, the position of a surface breaking crack can be visualized. The technique is tested on an industrial steel sample containing a closed crack.
Multiple line arrays for the characterization of aeroacoustic sources using a time-reversal method.
Mimani, A; Doolan, C J; Medwell, P R
2013-10-01
This letter investigates the use of multiple line arrays (LAs) in a Time-Reversal Mirror for localizing and characterizing multipole aeroacoustic sources in a uniform subsonic mean flow using a numerical Time-Reversal (TR) method. Regardless of the original source characteristics, accuracy of predicting the source location can be significantly improved using at least two LAs. Furthermore, it is impossible to determine the source characteristics using a single LA, rather a minimum of two are required to establish either the monopole or dipole source nature, while four LAs (fully surrounding the source) are required for characterizing a lateral quadrupole source. PMID:24116538
The Born Rule and Time-Reversal Symmetry of Quantum Equations of Motion
NASA Astrophysics Data System (ADS)
Ilyin, Aleksey V.
2016-04-01
It was repeatedly underlined in literature that quantum mechanics cannot be considered a closed theory if the Born Rule is postulated rather than derived from the first principles. In this work the Born Rule is derived from the time-reversal symmetry of quantum equations of motion. The derivation is based on a simple functional equation that takes into account properties of probability, as well as the linearity and time-reversal symmetry of quantum equations of motion. The derivation presented in this work also allows to determine certain limits to applicability of the Born Rule.
Reconstructed imaging of acoustic cloak using time-lapse reversal method
NASA Astrophysics Data System (ADS)
Zhou, Chen; Cheng, Ying; Xu, Jian-yi; Li, Bo; Liu, Xiao-jun
2014-08-01
We proposed and investigated a solution to the inverse acoustic cloak problem, an anti-stealth technology to make cloaks visible, using the time-lapse reversal (TLR) method. The TLR method reconstructs the image of an unknown acoustic cloak by utilizing scattered acoustic waves. Compared to previous anti-stealth methods, the TLR method can determine not only the existence of a cloak but also its exact geometric information like definite shape, size, and position. Here, we present the process for TLR reconstruction based on time reversal invariance. This technology may have potential applications in detecting various types of cloaks with different geometric parameters.
Finite-element implementation of reverse-time migration for anisotropic media
NASA Astrophysics Data System (ADS)
Zhang, Meigen; Li, Xiaofan; Wang, Miaoyue
2004-06-01
Reverse-time migration for post-stack seismic data in anisotropic media is implemented using the finite-element method. As an accurate digital method, the finite-element method is flexible for dealing with complicated geological structures, inner and man-made boundaries despite its intensive computation. Applying it in reverse-time migration may produce accurate images for anisotropic media. To eliminate man-made boundary reflections, the absorbing boundary condition for anisotropic elastic waves is also studied. An efficient and stable absorbing boundary scheme is presented combining a discrete transparent boundary condition with an attenuation boundary condition.
Colloquium: Time-reversal violation with quantum-entangled B mesons
NASA Astrophysics Data System (ADS)
Bernabéu, J.; Martínez-Vidal, F.
2015-01-01
Symmetry transformations have been proven a bedrock tool for understanding the nature of particle interactions, formulating, and testing fundamental theories. Based on the up to now unbroken C P T symmetry, the violation of the C P symmetry between matter and antimatter by weak interactions, discovered in the decay of kaons in 1964 and observed more recently in 2001 in B mesons, strongly suggests that the behavior of these particles under weak interactions must also be asymmetric under time reversal T . However, until recent years there has not been a direct detection of the expected time-reversal violation in the time evolution of any system. This Colloquium examines the field of time-reversal symmetry breaking in the fundamental laws of physics. For transitions, its observation requires an asymmetry with exchange of initial and final states. A discussion is given of the conceptual basis for such an exchange with unstable particles, using the quantum properties of Einstein-Podolsky-Rosen entanglement available at B meson factories combined with the decay as a filtering measurement. The method allows a clear-cut separation of different transitions between flavor and C P eigenstates in the decay of neutral B mesons. These ideas have been implemented for the experiment by the BABAR Collaboration at SLAC's B factory. The results, presented in 2012, prove beyond any doubt the violation of time-reversal invariance in the time evolution between these two states of the neutral B meson.
Time-reversal symmetry and universal conductance fluctuations in a driven two-level system.
Gustavsson, Simon; Bylander, Jonas; Oliver, William D
2013-01-01
In the presence of time-reversal symmetry, quantum interference gives strong corrections to the electric conductivity of disordered systems. The self-interference of an electron wave function traveling time-reversed paths leads to effects such as weak localization and universal conductance fluctuations. Here, we investigate the effects of broken time-reversal symmetry in a driven artificial two-level system. Using a superconducting flux qubit, we implement scattering events as multiple Landau-Zener transitions by driving the qubit periodically back and forth through an avoided crossing. Interference between different qubit trajectories gives rise to a speckle pattern in the qubit transition rate, similar to the interference patterns created when coherent light is scattered off a disordered potential. Since the scattering events are imposed by the driving protocol, we can control the time-reversal symmetry of the system by making the drive waveform symmetric or asymmetric in time. We find that the fluctuations of the transition rate exhibit a sharp peak when the drive is time symmetric, similar to universal conductance fluctuations in electronic transport through mesoscopic systems. PMID:23383819
Polarity Reversal Time of the Magnetic Dipole Component of the Sun in Solar Cycle 24
NASA Astrophysics Data System (ADS)
Hakamada, Kazuyuki
2013-04-01
The Sun's general magnetic field has shown polarity reversal three times during the last three solar cycles. We attempt to estimate the upcoming polarity reversal time of the solar magnetic dipole by using the coronal field model and synoptic data of the photospheric magnetic field. The scalar magnetic potential of the coronal magnetic field is expanded into a spherical harmonic series. The long-term variations of the dipole component (g01) calculated from the data of National Solar Observatory/Kitt Peak and Wilcox Solar Observatory are compared with each other. It is found that the two g01 values show a similar tendency and an approximately linear increase between the Carrington rotation periods CR 2070 and CR 2118. The next polarity reversal is estimated by linear extrapolation to be between CR 2132.2 (December 2012) and CR2134.8 (March 2013).
Two-dimensional pre-stack reverse time imaging based on tunnel space
NASA Astrophysics Data System (ADS)
Cheng, Fei; Liu, Jiangping; Qu, Niannian; Mao, Mao; Zhou, Liming
2014-05-01
In order to increase the safety and efficiency in tunnel constructions, there is a need to carry out an effective and precise tunnel prediction method to detect unexpected lithological and structural heterogeneities ahead of tunnel face. Seismic prediction is considered as one correct and efficient method. The assumption, which differs from the reality, taken in most of the current tunnel seismic imaging methods is that the tunnel space is a homogeneous medium with surrounded layers with the same elastic characters. In this paper, taking into account the actual situation of tunnel space, we propose some new tunnel geological models that are closer to the reality using the first-order coupled elastic equations of particle velocity and stress, and high order staggered grid finite-difference algorithm to fulfill numerical simulation of seismic full-wave fields in tunnel space. Then for these synthetic simulated records, we utilize reverse time migration operator based on non-conversion wave equation with decoupled P- and S-waves, and excitation time imaging condition to achieve reliable two dimensional (2D) reverse time migration imaging (RTM) based on tunnel space effectively. Results demonstrate that (1) it is able to achieve synthetic simulation and reverse time migration imaging correctly by using a staggered grid finite-difference (FD) algorithm with second-order accuracy in time and fourth-order accuracy in space, and reverse time operator based on non-conversion wave equation with decoupled P- and S-waves; (2) tunnel-based reverse time migration imaging can effectively suppress mirror artifact occurring in conventional imaging approaches; and (3) as the dip angle of lithological interface decreases, the energy of P wave imaging increases while the energy of S wave imaging decreases when shooting and receiving at the same side of interface, while when the dip angle of interface is 90°, common-source gather with shots near the tunnel face is beneficial to the
Time reversal invariance violating and parity conserving effects in neutron-deuteron scattering
Song, Young-Ho; Gudkov, Vladimir; Lazauskas, Rimantas
2011-08-15
Time reversal invariance violating and parity conserving effects for low-energy elastic neutron-deuteron scattering are calculated for meson exchange and effective field theory type potentials in a distorted wave-born approximation using realistic hadronic wave functions, obtained by solving three-body Faddeev equations in configuration space.
Time reversal invariance violating and parity conserving effects in proton-deuteron scattering
NASA Astrophysics Data System (ADS)
Song, Young-Ho; Lazauskas, Rimantas; Gudkov, Vladimir
2016-06-01
Time reversal invariance violating parity conserving (TVPC) effects are calculated for elastic proton-deuteron scattering with proton energies up to 2 MeV. The distorted-wave Born approximation is employed to estimate TVPC matrix elements, based on hadronic wave functions, obtained by solving three-body Faddeev-Merkuriev equations in configuration space with realistic potentials.
NASA Technical Reports Server (NTRS)
Norbury, John W.
1989-01-01
The invariance of classical electromagnetism under charge-conjugation, parity, and time-reversal (CPT) is studied by considering the motion of a charged particle in electric and magnetic fields. Upon applying CPT transformations to various physical quantities and noting that the motion still behaves physically demonstrates invariance.
Robust time reversal focusing based on Maximin criterion in a waveguide with uncertain water depth
NASA Astrophysics Data System (ADS)
Pan, Xiang; Wang, Nan; Zhang, JiangFan; Xu, Wen; Gong, XianYi
2013-10-01
Time reversal processing (TRP) might be regarded as matched field processing with known environmental knowledge. However, the performance of TRP is degraded in an uncertain environment. A technique based on the Maximin criterion is proposed for enhancing the robustness of TRP in a waveguide with uncertain water depth. The relationship between the water depth and the focal spot translation is examined based on the waveguide-invariant theory. Then the time reversal transmission scheme with the Maximin criterion is performed to maximize the minimum transmission power on a target of interest. At the receiving end, coherent summation operation is carried out over the received data by a reception focusing bank. If it is necessary to enhance the target echo further, the iterative time reversal can be considered where the target echo corresponding to the first time reversal transmission is regarded as a secondary source. Numerical simulations and experimental results of the target localization in a waveguide tank have verified the effectiveness of robust TRP.
Analysis of the time reversal operator for a scatterer undergoing small displacements.
Philippe, Franck D; Prada, Claire; Fink, Mathias; Garnier, Josselin; de Rosny, Julien
2013-01-01
The method of the time reversal operator decomposition is usually employed to detect and characterize static targets using the invariants of the time reversal operator. This paper presents a theoretical and experimental investigation into the impact of small displacements of the target on these invariants. To find these invariants, the time reversal operator is built from the multistatic response matrix and then diagonalized. Two methods of recording the multistatic response matrix while the target is moving are studied: Acquisition either element by element or column by column. It is demonstrated that the target displacement generates new significant eigenvalues. Using a perturbation theory, the analytical expressions of the eigenvalues of the time-reversal operator for both acquisition methods are derived. We show that the distribution of the new eigenvalues strongly depends on these two methods. It is also found that for the column by column acquisition, the second eigenvector is simply linked to the scatterer displacements. At last, the implications on the Maximum Likelihood and Multiple Signal Classification detection are also discussed. The theoretical results are in good agreement with numerical and 3.4 MHz ultrasonic experiments. PMID:23297886
Agrahari, J K; Kapuria, S
2016-08-01
To develop an effective baseline-free damage detection strategy using the time-reversal process (TRP) of Lamb waves in thin walled structures, it is essential to develop a good understanding of the parameters that affect the amplitude dispersion and consequently the time reversibility of the Lamb wave signal. In this paper, the effects of adhesive layer between the transducers and the host plate, the tone burst count of the excitation signal, the plate thickness, and the piezoelectric transducer thickness on the time reversibility of Lamb waves in metallic plates are studied using experiments and finite element simulations. The effect of adhesive layer on the forward propagation response and frequency tuning has been also studied. The results show that contrary to the general expectation, the quality of the reconstruction of the input signal after the TRP may increase with the increase in the adhesive layer thickness at certain frequency ranges. Similarly, an increase in the tone burst count resulting in a narrowband signal does not necessarily enhance the time reversibility at all frequencies, contrary to what has been reported earlier. For a given plate thickness, a thinner transducer yields a better reconstruction, but for a given transducer thickness, the similarity of the reconstructed signal may not be always higher for a thicker plate. It is important to study these effects to achieve the best quality of reconstruction in undamaged plates, for effective damage detection. PMID:27176646
Cowie, Sarah; Elliffe, Douglas; Davison, Michael
2013-09-01
Six pigeons worked on concurrent exponential variable-interval schedules in which the relative frequency of food deliveries for responding on the two alternatives reversed at a fixed time after each food delivery. Across conditions, the point of food-ratio reversal was varied from 10 s to 30 s, and the overall reinforcer rate was varied from 1.33 to 4 per minute. The effect of rate of food delivery and food-ratio-reversal time on choice and response rates was small. In all conditions, postfood choice was toward the locally richer key, regardless of the last-food location. Unlike the local food ratio which changed in a stepwise fashion, local choice changed according to a decelerating monotonic function, becoming substantially less extreme than the local food ratio soon after food delivery. This deviation in choice appeared to result from the birds' inaccurate discrimination of the time of food deliveries; local choice was described well by a model that assumed that log response ratios matched food ratios that were redistributed across surrounding time bins with mean time t and a constant coefficient of variation. We suggest that local choice is controlled by the likely availability of food in time, and that choice matches the discriminated log of the ratio of food rates across time since the last food delivery. PMID:23943395
Fast damage imaging using the time-reversal technique in the frequency-wavenumber domain
NASA Astrophysics Data System (ADS)
Zhu, R.; Huang, G. L.; Yuan, F. G.
2013-07-01
The time-reversal technique has been successfully used in structural health monitoring (SHM) for quantitative imaging of damage. However, the technique is very time-consuming when it is implemented in the time domain. In this paper, we study the technique in the frequency-wavenumber (f-k) domain for fast real-time imaging of multiple damage sites in plates using scattered flexural plate waves. Based on Mindlin plate theory, the time reversibility of dispersive flexural waves in an isotropic plate is theoretically investigated in the f-k domain. A fast damage imaging technique is developed by using the cross-correlation between the back-propagated scattered wavefield and the incident wavefield in the frequency domain. Numerical simulations demonstrate that the proposed technique cannot only localize multiple damage sites but also potentially identify their sizes. Moreover, the time-reversal technique in the f-k domain is about two orders of magnitude faster than the method in the time domain. Finally, experimental testing of an on-line SHM system with a sparse piezoelectric sensor array is conducted for fast multiple damage identification using the proposed technique.
Vogt, Katrin; Yarali, Ayse; Tanimoto, Hiromu
2015-01-01
Animals need to associate different environmental stimuli with each other regardless of whether they temporally overlap or not. Drosophila melanogaster displays olfactory trace conditioning, where an odor is followed by electric shock reinforcement after a temporal gap, leading to conditioned odor avoidance. Reversing the stimulus timing in olfactory conditioning results in the reversal of memory valence such that an odor that follows shock is later on approached (i.e. relief conditioning). Here, we explored the effects of stimulus timing on memory in another sensory modality, using a visual conditioning paradigm. We found that flies form visual memories of opposite valence depending on stimulus timing and can associate a visual stimulus with reinforcement despite being presented with a temporal gap. These results suggest that associative memories with non-overlapping stimuli and the effect of stimulus timing on memory valence are shared across sensory modalities. PMID:26430885
Vogt, Katrin; Yarali, Ayse; Tanimoto, Hiromu
2015-01-01
Animals need to associate different environmental stimuli with each other regardless of whether they temporally overlap or not. Drosophila melanogaster displays olfactory trace conditioning, where an odor is followed by electric shock reinforcement after a temporal gap, leading to conditioned odor avoidance. Reversing the stimulus timing in olfactory conditioning results in the reversal of memory valence such that an odor that follows shock is later on approached (i.e. relief conditioning). Here, we explored the effects of stimulus timing on memory in another sensory modality, using a visual conditioning paradigm. We found that flies form visual memories of opposite valence depending on stimulus timing and can associate a visual stimulus with reinforcement despite being presented with a temporal gap. These results suggest that associative memories with non-overlapping stimuli and the effect of stimulus timing on memory valence are shared across sensory modalities. PMID:26430885
Laforest, M.; Baugh, J.; Laflamme, R.
2006-03-15
Within the context of quantum teleportation, a proposed interpretation of bipartite entanglement describes teleportation as consisting of a qubit of information evolving along and against the flow of time of an external observer. We investigate the physicality of such a model by applying time reversal to the Schroedinger equation in the teleportation context. To do so, we first present the theory of time reversal applied to the circuit model. We then show that the outcome of a teleportationlike circuit is consistent with the usual tensor product treatment and is therefore independent of the physical quantum system used to encode the information. Finally, we illustrate these concepts with a proof-of-principle experiment on a liquid-state NMR quantum-information processor. The experimental results are consistent with the interpretation that information can be seen as flowing backward in time through entanglement.
Germano Filho, P A; Cavalcanti, I L; Barrucand, L; Verçosa, N
2015-08-01
Magnesium potentiates neuromuscular blockade. Sugammadex reverses rocuronium-induced blockade. The aim of this study was to determine the effect of pre-treatment with magnesium sulphate on sugammadex reversal time for neuromuscular blockade. Seventy-three patients were randomly assigned to receive magnesium sulphate (40 mg.kg(-1) ) or saline intravenously. After anaesthetic induction, continuous train-of-four monitoring was performed and rocuronium was administered (0.6 mg.kg(-1) ). When a second twitch appeared, the patients received sugammadex (2 mg.kg(-1) ). The median (IQR [range]) reversal time of moderate neuromuscular blockade to a train-of-four ratio of 0.9 facilitated by sugammadex was 115 (93-177.5 [68-315]) s in the magnesium group and 120 (105-140 [70-298]) s in the saline group (p = 0.79). The median (IQR [range]) clinical duration was 45 (35.5-53 [22-102]) min in the magnesium group and 37 (31-43 [19-73]) min in the saline group (p = 0.031). Pre-treatment with magnesium did not significantly affect sugammadex reversal time of moderate neuromuscular blockade induced by rocuronium. PMID:25829048
NASA Technical Reports Server (NTRS)
Castelli, Michael G.; Arnold, Steven M.
2000-01-01
Structural materials for the design of advanced aeropropulsion components are usually subject to loading under elevated temperatures, where a material's viscosity (resistance to flow) is greatly reduced in comparison to its viscosity under low-temperature conditions. As a result, the propensity for the material to exhibit time-dependent deformation is significantly enhanced, even when loading is limited to a quasi-linear stress-strain regime as an effort to avoid permanent (irreversible) nonlinear deformation. An understanding and assessment of such time-dependent effects in the context of combined reversible and irreversible deformation is critical to the development of constitutive models that can accurately predict the general hereditary behavior of material deformation. To this end, researchers at the NASA Glenn Research Center at Lewis Field developed a unique experimental technique that identifies the existence of and explicitly determines a threshold stress k, below which the time-dependent material deformation is wholly reversible, and above which irreversible deformation is incurred. This technique is unique in the sense that it allows, for the first time, an objective, explicit, experimental measurement of k. The underlying concept for the experiment is based on the assumption that the material s time-dependent reversible response is invariable, even in the presence of irreversible deformation.
NASA Astrophysics Data System (ADS)
Heinemann, M.; Larraza, A.; Smith, K. B.
2003-06-01
The most difficult problem in shallow underwater acoustic communications is considered to be the time-varying multipath propagation because it impacts negatively on data rates. At high data rates the intersymbol interference requires adaptive algorithms on the receiver side that lead to computationally intensive and complex signal processing. A novel technique called time-reversal acoustics (TRA) can environmentally adapt the acoustic propagation effects of a complex medium in order to focus energy at a particular target range and depth. Using TRA, the multipath structure is reduced because all the propagation paths add coherently at the intended target location. This property of time-reversal acoustics suggests a potential application in the field of noncoherent acoustic communications. This work presents results of a tank scale experiment using an algorithm for rapid transmission of binary data in a complex underwater environment with the TRA approach. A simple 15-symbol code provides an example of the simplicity and feasibility of the approach. Covert coding due to the inherent scrambling induced by the environment at points other than the intended receiver is also investigated. The experiments described suggest a high potential in data rate for the time-reversal approach in underwater acoustic communications while keeping the computational complexity low.
NASA Astrophysics Data System (ADS)
Hou, Fengzhen; Huang, Xiaolin; Chen, Ying; Huo, Chengyu; Liu, Hongxing; Ning, Xinbao
2013-01-01
Symbolic dynamics method and time reversal asymmetry analysis are both important approaches in the study of heartbeat interval series. However, there is limited research work reported on combining these two methods. We provide a method of time reversal asymmetry analysis which focuses on the differences between the forward and backward embedding “m words” after the operation of equiprobable symbolization. To investigate the total amplitude as well as the distribution features of the difference, four indices are proposed. Based on the application to simulation series, we found that these measures can successfully detect time reversal asymmetry in chaos series. With application to human heartbeat interval series (RR series), it is suggested that the distribution features of the forward-backward difference can sensitively capture the dynamical changes caused by diseases or aging. In particular, the index ED, which reflects the random degree of the forward-backward difference distribution, can significantly discriminate healthy subjects from diseased ones. We conclude that RR series from healthy subjects show more asymmetry in temporal structure on the original time scale from the perspective of equiprobable symbolization, whereas diseases account for loss of this asymmetry.
Yang, Qiang; Xu, Xiao; Lai, Puxiang; Xu, Daxiong
2013-01-01
Abstract. Focusing light inside highly scattering media is a challenging task in biomedical optical imaging, manipulation, and therapy. A recent invention has overcome this challenge by time reversing ultrasonically encoded diffuse light to an ultrasound-modulated volume inside a turbid medium. In this technique, a photorefractive (PR) crystal or polymer can be used as the phase conjugate mirror for optical time reversal. Accordingly, a relatively long ultrasound burst, whose duration matches the PR response time of the PR material, is usually used to encode the diffuse light. This long burst results in poor focusing resolution along the acoustic axis. In this work, we propose to use two intersecting ultrasound beams, emitted from two ultrasonic transducers at different frequencies, to modulate the diffuse light at the beat frequency within the intersection volume. We show that the time reversal of the light encoded at the beat frequency can converge back to the intersection volume. Experimentally, an acoustic axial resolution of ∼1.1 mm was demonstrated inside turbid media, agreeing with theoretical estimation. PMID:24194060
NASA Astrophysics Data System (ADS)
Shen, Jun; Zhou, Jianqin; Astrath, Nelson G. C.; Navessin, Titichai; Liu, Zhong-Sheng (Simon); Lei, Chao; Rohling, Jurandir H.; Bessarabov, Dmitri; Knights, Shanna; Ye, Siyu
In this work, using an in-house made Loschmidt diffusion cell, we measure the effective coefficient of dry gas (O 2-N 2) diffusion in cathode catalyst layers of PEM fuel cells at 25 °C and 1 atmosphere. The thicknesses of the catalyst layers under investigation are from 6 to 29 μm. Each catalyst layer is deposited on an Al 2O 3 membrane substrate by an automated spray coater. Diffusion signal processing procedure is developed to deduce the effective diffusion coefficient, which is found to be (1.47 ± 0.05) × 10 -7 m 2 s -1 for the catalyst layers. Porosity and pore size distribution of the catalyst layers are also measured using Hg porosimetry. The diffusion resistance of the interface between the catalyst layer and the substrate is found to be negligible. The experimental results show that the O 2-N 2 diffusion in the catalyst layers is dominated by the Knudsen effect.
Time reversal odd fragmentation functions in semi-inclusive deep inelastic lepton-hadron scattering
Mulders, P.J.; Levelt, J.
1994-04-01
In semi-inclusive scattering of polarized leptons from unpolarized hadrons, one can measure a time reversal odd structure function. It shows up as a sin({phi}) asymmetry of the produced hadrons. This asymmetry can be expressed as the product of a twist-three {open_quotes}hadron {r_arrow} quark{close_quotes} profile function and a time reversal odd twist-two {open_quotes}quark {r_arrow} hadron{close_quotes} fragmentation function. This fragmentation function can only be measured for nonzero transverse momenta of the produced hadron. Its appearance is a consequence of final state interactions between the produced hadron and the rest of the final state.
NASA Astrophysics Data System (ADS)
Shang, Xuefeng; de Hoop, Maarten V.; van der Hilst, Robert D.
2012-08-01
We present a wave equation prestack depth migration to image crust and mantle structures using multi-component earthquake data recorded at dense seismograph arrays. Transmitted P and S waves recorded on the surface are back propagated using an elastic wave equation solver. The wave modes are separated after the reverse-time continuation of the wavefield from the surface, and subjected to a (cross-correlation type) imaging condition forming an inverse scattering transform. Reverse time migration (RTM) does not make assumptions about the presence or properties of interfaces - notably, it does not assume that interfaces are (locally) horizontal. With synthetic experiments, and different background models, we show that passive source RTM can reconstruct dipping and vertically offset interfaces even in the presence of complex wave phenomena (such as caustics and point diffraction) and that its performance is superior to traditional receiver function analysis, e.g., common conversion point (CCP) stacking, in complex geological environments.
Berry curvature induced nonlinear Hall effect in time-reversal invariant materials
NASA Astrophysics Data System (ADS)
Sodemann, Inti; Fu, Liang
2015-03-01
It is well-known that a non-vanishing Hall conductivity requires time-reversal symmetry breaking. However, in this work, we demonstrate that a Hall-like transverse current can occur in second-order response to an external electric field in a wide class of time-reversal invariant and inversion breaking materials. This nonlinear Hall effect arises from the dipole moment of the Berry curvature in momentum space, which generates a net anomalous velocity when the system is in a current-carrying state. We show that the nonlinear Hall coefficient is a rank-two pseudo-tensor, whose form is determined by point group symmetry. We will describe the optimal conditions and candidate materials to observe this effect. IS is supported by the Pappalardo Fellowship in Physics. LF is supported by DOE Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award DE-SC0010526.
NASA Astrophysics Data System (ADS)
Differt, Dominik; Hensen, Matthias; Pfeiffer, Walter
2016-05-01
Spatiotemporal nanolocalization of ultrashort pulses in a random scattering nanostructure via time reversal and adaptive optimization employing a genetic algorithm and a suitably defined fitness function is studied for two embedded nanoparticles that are separated by only a tenth of the free space wavelength. The nanostructure is composed of resonant core-shell nanoparticles (TiO2 core and Ag shell) placed randomly surrounding these two nanoparticles acting as targets. The time reversal scheme achieves selective nanolocalization only by chance if the incident radiation can couple efficiently to dipolar local modes interacting with the target/emitter particle. Even embedding the structure in a reverberation chamber fails improving the nanolocalization. In contrast, the adaptive optimization strategy reliably yields nanolocalization of the radiation and allows a highly selective excitation of either target position. This demonstrates that random scattering structures are interesting multi-purpose optical nanoantennas to realize highly flexible spatiotemporal optical near-field control.
Real-time Assessment of Flow Reversal in an Eccentric Arterial Stenotic Model
Ai, Lisong; Zhang, Lequan; Dai, Wangde; Hu, Changhong; Shung, K. Kirk; Hsiai, Tzung K.
2010-01-01
Plaque rupture is the leading cause of acute coronary syndromes and stroke. Plaque formation, or otherwise known as stenosis, preferentially occurs in the regions of arterial bifurcation or curvatures. To date, real-time assessment of stenosis-induced flow reversal remains a clinical challenge. By interfacing Micro-electro-mechanical Systems (MEMS) thermal sensors with the high frequency Pulsed Wave (PW) Doppler ultrasound, we proposed to assess flow reversal in the presence of an eccentric stenosis. We developed a 3-D stenotic model (inner diameter of 6 mm, an eccentric stenosis with a height of 2.75mm and width of 21 mm) simulating a superficial arterial vessel. We demonstrated that heat transfer from the sensing element (2 × 80 μm) to the flow field peaked as a function of flow rates at the throat of the stenosis alone the center/midline of arterial model, and dropped downstream from the stenosis where flow reversal was detected by the high frequency ultrasound device at 45 MHz. Computational fluid dynamics (CFD) codes were in agreement with the ultrasound-acquired flow profiles upstream, downstream, and at the throat of the stenosis. Hence, we characterized regions of eccentric stenosis in terms of changes in heat transfer alone the midline of vessel and identified points of flow reversal with high spatial and temporal resolution. PMID:20655537
Study on the time difference of solar polar field reversal between the north and south hemisphere
NASA Astrophysics Data System (ADS)
Shukuya, D.; Kusano, K.
2013-12-01
Dynamo is a mechanism whereby the kinetic energy of plasma is converted to the magnetic energy. This mechanism works to generate and maintain the solar and stellar magnetic field. Since the sun is only a star whose magnetic field can be directly observed, the understanding of solar dynamo can provide clues to clarify dynamo mechanisms. On the other hand, because solar activities, which are caused by solar dynamo, can influence the Earth's climate, solar variability is an important issue also to understand long-term evolution of the Earth's climate. It is widely known that the polarity of the solar magnetic fields on the north and south poles periodically reverses at every sunspot maxima. It is also known that the reversal at one pole is followed by that on the other pole. The time difference of magnetic field reversal between the poles was first noted by Babcock (1959) from the very first observation of polar field. Recently, it was confirmed by detailed observations with the HINODE satellite (Shiota et al. 2012). Svalgaard and Kamide (2013) indicated that there is a relationship between the time difference of the polarity reversal and the hemispheric asymmetry of the sunspot activity. However, the mechanisms for the hemispheric asymmetry are still open to be revealed. In this paper, we study the asymmetric feature of the solar dynamo based on the flux transport dynamo model (Chatterjee et al. 2004) to explain the time difference of magnetic polarity reversal between the north and south poles. In order to calculate long-term variations of solar activities, we use the mean field kinematic dynamo model, which is derived from magnetohydrodynamics (MHD) equation through the mean field and other approximations. We carried out the mean field dynamo simulations using the updated SURYA code which was developed originally by Choudhuri and his collaborators (2004). We decomposed the symmetric and asymmetric components of magnetic field, which correspond respectively to the
Reverse time migration for reconstructing extended obstacles in planar acoustic waveguides
NASA Astrophysics Data System (ADS)
Chen, ZhiMing; Huang, GuangHui
2015-09-01
We propose a new reverse time migration method for reconstructing extended obstacles in the planar waveguide using acoustic waves at a fixed frequency. We prove the resolution of the reconstruction method in terms of the aperture and the thickness of the waveguide. The resolution analysis implies that the imaginary part of the cross-correlation imaging function is always positive and thus may have better stability properties. Numerical experiments are included to illustrate the powerful imaging quality and to confirm our resolution results.
Test of Time-Reversal Invariance Violation in Neutron Scattering At Spallation Neutron Sources
NASA Astrophysics Data System (ADS)
Gudkov, Vladimir
2015-10-01
Time Reversal Invariant Violating effects in neutron transmission through a nuclear target are discussed. A class of free from false asymmetries experiments is presented, and a comparison of a sensitivity of these transmission experiments and electric dipole moment measurements to different mechanisms of CP-violation is discussed. This material is based upon work supported by the U.S. Department of Energy Office of Science, Office of Nuclear Physics program under Award Number DE-FG02-09ER41621.
Time-reversal duality of high-efficiency RF power amplifiers
Reveyrand, T; Ramos, I; Popovic, Z
2012-12-06
The similarity between RF power amplifiers and rectifiers is discussed. It is shown that the same high-efficiency harmonically-terminated power amplifier can be operated in a dual rectifier mode. Nonlinear simulations with a GaN HEMT transistor model show the time-reversal intrinsic voltage and current waveform relationship between a class-F amplifier and rectifier. Measurements on a class-F-1 amplifier and rectifier at 2.14 GHz demonstrate over 80% efficiency in both cases.
The Θ-KMS adjoint and time reversed quantum Markov semigroups
NASA Astrophysics Data System (ADS)
Bolaños-Servin, Jorge R.; Quezada, Roberto
2015-08-01
We introduce the notion of Θ-KMS adjoint of a quantum Markov semigroup, which is identified with the time reversed semigroup. The break of Θ-KMS symmetry, or Θ-standard quantum detailed balance in the sense of Fagnola-Umanità,11 is measured by means of the von Neumann relative entropy of states associated with the semigroup and its Θ-KMS adjoint.
Semiclassical matrix model for quantum chaotic transport with time-reversal symmetry
Novaes, Marcel
2015-10-15
We show that the semiclassical approach to chaotic quantum transport in the presence of time-reversal symmetry can be described by a matrix model. In other words, we construct a matrix integral whose perturbative expansion satisfies the semiclassical diagrammatic rules for the calculation of transport statistics. One of the virtues of this approach is that it leads very naturally to the semiclassical derivation of universal predictions from random matrix theory.
Transmission fluctuations in chaotic microwave billiards with and without time-reversal symmetry.
Schanze, H; Alves, E R; Lewenkopf, C H; Stöckmann, H J
2001-12-01
Transmission fluctuations have been studied in a microwave billiard in dependence to the number of attached wave guides on its entrance and exit. To investigate the influence of breaking time-reversal symmetry, ferrite cylinders were introduced into the billiard. The obtained transmission intensity distributions are compared with predictions from the random matrix theory. Because of the strong absorption caused by the ferrites, the existing statistical scattering theories had to be modified, by incorporating a number of additional absorbing scattering channels. PMID:11736225
Breast cancer detection based on time reversal and the optical theorem
NASA Astrophysics Data System (ADS)
Marengo, Edwin A.; Tu, Jing
2015-03-01
We report a wave physics-based approach to change detection which can be used to detect anomalies in biological tissues such as cancer lesions from active sensing data. Of particular interest are nonionizing radiation methods such as microwave breast imaging, ultrasound imaging, and diffuse optical tomography. The biological medium surrounding the target of interest, e.g., a tumor, is assumed to be highly nonhomogeneous and reverberating. This implies that there are in general multiple paths for the propagation of wave signals from an interior domain where the target of interest is located to the sensing aperture where the scattered fields are measured. Two physical concepts are used to exploit this rich multipath environment so as to enhance change detection performance: wave time reversal, and the optical theorem which describes energy conservation in scattering phenomena. Previous related work has reported the use of time reversal for breast cancer detection. We use not only time reversal, but also the optical theorem, and propose novel algorithms based on both.
NASA Astrophysics Data System (ADS)
Dupré, Matthieu; Lemoult, Fabrice; Fink, Mathias; Lerosey, Geoffroy
2016-05-01
Materials which possess a high local density of states varying at a subwavelength scale theoretically permit the focusing of waves onto focal spots much smaller than the free space wavelength. To do so, metamaterials—manmade composite media exhibiting properties not available in nature—are usually considered. However, this approach is limited to narrow bandwidths due to their resonant nature. Here, we prove that it is possible to use a fractal resonator alongside time reversal to focus microwaves onto λ /15 subwavelength focal spots from the far field, on extremely wide bandwidths. We first numerically prove that this approach can be realized using a multiple-channel time reversal mirror that utilizes all the degrees of freedom offered by the fractal resonator. Then, we experimentally demonstrate that this approach can be drastically simplified by coupling the fractal resonator to a complex medium, here a cavity, that efficiently converts its spatial degrees of freedom into temporal ones. This makes it possible to achieve deep subwavelength focusing of microwave radiation by time reversing a single channel. Our method can be generalized to other systems coupling complex media and fractal resonators.
NASA Astrophysics Data System (ADS)
Johnson, Jami L.; Shragge, Jeffrey; van Wijk, Kasper
2015-03-01
We propose a new reconstruction algorithm for photoacoustic and laser-ultrasound imaging based on reverse time migration (RTM), a time reversal imaging algorithm originally developed for exploration seismology. RTM inherently handles strong velocity heterogeneity and complex propagation paths. A successful RTM analysis with appropriate handling of boundary conditions results in enhanced signal-to-noise, accurately located structures, and minimal artifacts. A laser-ultrasound experiment begins with a source wave field generated at the surface that propagates through the sample. Acoustic scatterers in the propagation path give rise to a scattered wave field, which travels to the surface and is recorded by acoustic detectors. To reconstruct the laser-ultrasound image, a synthetic source function is forward propagated and cross-correlated with the time-reversed and back-propagated recorded (scattered) wave field to image the scatterers at the correct location. Conversely, photoacoustic waves are generated by chromophores within the sample and propagate "one-way" to the detection surface. We utilize the velocity model validated by the laser-ultrasound reconstruction to accurately reconstruct the photoacoustic image with RTM. This approach is first validated with simulations, where inclusions behave both as a photoacoustic source and an acoustic scatterer. Subsequently, we demonstrate the capabilities of RTM with tissue phantom experiments using an all-optical, multi-channel acquisition geometry.
NASA Astrophysics Data System (ADS)
Ishida, H.; Wortmann, D.
2016-03-01
The embedding potential defined on the boundary surface of a semi-infinite crystal relates the value and normal derivative of generalized Bloch states propagating or decaying toward the interior of the crystal. It becomes Hermitian when the electron energy ɛ is located in a projected bulk band gap at a given wave vector k in the surface Brillouin zone (SBZ). If one plots the real eigenvalues of the embedding potential for a time-reversal invariant insulator in the projected bulk band gap along a path ɛ =ɛ0(k ) passing between two time-reversal invariant momentum (TRIM) points in the SBZ, then, they form Kramers doublets at both end points. We will demonstrate that the Z2 topological invariant, ν , which is either 0 or 1, depending on the product of time-reversal polarizations at the two TRIM points, can be determined from the two different ways these eigenvalues are connected between the two TRIM points. Furthermore, we will reveal a relation, ν =P mod 2, where P denotes the number of poles that the embedding potential exhibits along the path. We also discuss why gapless surface states crossing the bulk band gap inevitably occur on the surface of topological band insulators from the view point of the embedding theory.
Momentum-independent reflectionless transmission in the non-Hermitian time-reversal symmetric system
Zhang, X.Z.; Song, Z.
2013-12-15
We theoretically study the non-Hermitian systems, the non-Hermiticity of which arises from the unequal hopping amplitude (UHA) dimers. The distinguishing features of these models are that they have full real spectra if all of the eigenvectors are time-reversal (T) symmetric rather than parity-time-reversal (PT) symmetric, and that their Hermitian counterparts are shown to be an experimentally accessible system, which have the same topological structures as that of the original ones but modulated hopping amplitudes within the unbroken region. Under the reflectionless transmission condition, the scattering behavior of momentum-independent reflectionless transmission (RT) can be achieved in the concerned non-Hermitian system. This peculiar feature indicates that, for a certain class of non-Hermitian systems with a balanced combination of the RT dimers, the defects can appear fully invisible to an outside observer. -- Highlights: •We investigate the non-Hermitian system with time reversal symmetry. •The Hermitian counterpart is experimentally accessible system. •The behavior of momentum-independent reflectionless transmission can be achieved. •A balanced combination of reflectionless transmission dimers leads to invisibility. •It paves an alternative way for the design of invisible cloaking devices.
Using time-reversal to generate generalized transversely localized transient waves (X-waves).
Walker, S C
2009-03-01
In the traditional approach to X-waves, the X-wave field is synthesized from a superposition of solutions to the homogenous wave equation (in three-dimensions) without regard to boundary conditions. As a consequence the synthesized solution is acausal. Here, it is shown that the solution to the inhomogenous scalar wave equation for the acoustic field from a supersonic source distribution consistent with the radiation condition, i.e., a Mach front, defines a causal X-wave. Using the connection between X-waves and a physical source, it is shown that an X-wave can be generated from a planar aperture using time-reversal. By appealing to the demonstrated self-adaptivity of time-reversal processes, the method should allow for the generation of X-waves in arbitrary (inhomogenous) media. Typically, the generation of approximate acoustic X-waves from a planar aperture is achieved using a complicated annular transducer arrangement. Here, the time-reversal method for the generation of approximate acoustic X-waves is experimentally proven using a line transducer array in two-dimensional geometry in free space. PMID:19275313
Damage imaging in a laminated composite plate using an air-coupled time reversal mirror
Le Bas, P. -Y.; Remillieux, M. C.; Pieczonka, L.; Ten Cate, J. A.; Anderson, B. E.; Ulrich, T. J.
2015-11-03
We demonstrate the possibility of selectively imaging the features of a barely visible impact damage in a laminated composite plate by using an air-coupled time reversal mirror. The mirror consists of a number of piezoelectric transducers affixed to wedges of power law profiles, which act as unconventional matching layers. The transducers are enclosed in a hollow reverberant cavity with an opening to allow progressive emission of the ultrasonic wave field towards the composite plate. The principle of time reversal is used to focus elastic waves at each point of a scanning grid spanning the surface of the plate, thus allowingmore » localized inspection at each of these points. The proposed device and signal processing removes the need to be in direct contact with the plate and reveals the same features as vibrothermography and more features than a C-scan. More importantly, this device can decouple the features of the defect according to their orientation, by selectively focusing vector components of motion into the object, through air. For instance, a delamination can be imaged in one experiment using out-of-plane focusing, whereas a crack can be imaged in a separate experiment using in-plane focusing. As a result, this capability, inherited from the principle of time reversal, cannot be found in conventional air-coupled transducers.« less
Damage imaging in a laminated composite plate using an air-coupled time reversal mirror
Le Bas, P. -Y.; Remillieux, M. C.; Pieczonka, L.; Ten Cate, J. A.; Anderson, B. E.; Ulrich, T. J.
2015-11-03
We demonstrate the possibility of selectively imaging the features of a barely visible impact damage in a laminated composite plate by using an air-coupled time reversal mirror. The mirror consists of a number of piezoelectric transducers affixed to wedges of power law profiles, which act as unconventional matching layers. The transducers are enclosed in a hollow reverberant cavity with an opening to allow progressive emission of the ultrasonic wave field towards the composite plate. The principle of time reversal is used to focus elastic waves at each point of a scanning grid spanning the surface of the plate, thus allowing localized inspection at each of these points. The proposed device and signal processing removes the need to be in direct contact with the plate and reveals the same features as vibrothermography and more features than a C-scan. More importantly, this device can decouple the features of the defect according to their orientation, by selectively focusing vector components of motion into the object, through air. For instance, a delamination can be imaged in one experiment using out-of-plane focusing, whereas a crack can be imaged in a separate experiment using in-plane focusing. As a result, this capability, inherited from the principle of time reversal, cannot be found in conventional air-coupled transducers.
Automatic determination of the number of targets present when using the time reversal operator.
Quinlan, Angela; Barbot, Jean-Pierre; Larzabal, Pascal
2006-04-01
Acoustical time reversal mirrors have been shown to provide a highly accurate means of studying and focusing on acoustical sources. The DORT method is a derivation of the time reversal process, which allows for focusing on multiple targets. An important step in this process is the determination of the number of targets or sources present. This is achieved by examining the eigenvalues of the time reversal operator (TRO). The number of significant eigenvalues is then chosen as the number of sources present. However, as mentioned in [N. Mordant, C. Prada, and M. Fink, J. Acoust. Soc. Am. 105, 2634-2642 (1999) and C. Prada, M. Tanter, and M. Fink, in Proceedings of the IEEE Symposium, 1997, pp. 679-683], factors such as low signal to noise ratio (SNR), small data sample, array configuration and the target location may result in the eigenvalues corresponding to the targets no longer being distinguishable from the background noise eigenvalues. This paper proposes a robust method of automatically determining the number of targets even in the presence of a small number of snapshots. For white Gaussian noise, the profile of the ordered eigenvalues is seen to fit an exponential law. The observed eigenvalues are then compared to this model and a mismatch is detected between the observed profile and the noise-only model. The index of the mismatch gives the number of scatterers present. PMID:16642836
NASA Astrophysics Data System (ADS)
Patacchini, L.; Hutchinson, I. H.
2009-04-01
A new explicit time-reversible orbit integrator for the equations of motion in a static homogeneous magnetic field - called Cyclotronic integrator - is presented. Like Spreiter and Walter's Taylor expansion algorithm, for sufficiently weak electric field gradients this second order method does not require a fine resolution of the Larmor motion; it has however the essential advantage of being symplectic, hence time-reversible. The Cyclotronic integrator is only subject to a linear stability constraint ( ΩΔ t < π, Ω being the Larmor angular frequency), and is therefore particularly suitable to electrostatic Particle In Cell codes with uniform magnetic field where Ω is larger than any other characteristic frequency, yet a resolution of the particles' gyromotion is required. Application examples and a detailed comparison with the well-known (time-reversible) Boris algorithm are presented; it is in particular shown that implementation of the Cyclotronic integrator in the kinetic codes SCEPTIC and Democritus can reduce the cost of orbit integration by up to a factor of ten.
Damage imaging in a laminated composite plate using an air-coupled time reversal mirror
NASA Astrophysics Data System (ADS)
Le Bas, P.-Y.; Remillieux, M. C.; Pieczonka, L.; Ten Cate, J. A.; Anderson, B. E.; Ulrich, T. J.
2015-11-01
We demonstrate the possibility of selectively imaging the features of a barely visible impact damage in a laminated composite plate by using an air-coupled time reversal mirror. The mirror consists of a number of piezoelectric transducers affixed to wedges of power law profiles, which act as unconventional matching layers. The transducers are enclosed in a hollow reverberant cavity with an opening to allow progressive emission of the ultrasonic wave field towards the composite plate. The principle of time reversal is used to focus elastic waves at each point of a scanning grid spanning the surface of the plate, thus allowing localized inspection at each of these points. The proposed device and signal processing removes the need to be in direct contact with the plate and reveals the same features as vibrothermography and more features than a C-scan. More importantly, this device can decouple the features of the defect according to their orientation, by selectively focusing vector components of motion into the object, through air. For instance, a delamination can be imaged in one experiment using out-of-plane focusing, whereas a crack can be imaged in a separate experiment using in-plane focusing. This capability, inherited from the principle of time reversal, cannot be found in conventional air-coupled transducers.
Gunji, Y; Nakamura, T
1991-01-01
In the present paper the self-consistency or operational closure of autopoiesis is described by introducing time explicitly. It is an extension of Spencer-Brown's idea of time, however. The definition of time is segregated into two parts, corresponding to the syntax and semantics of language, respectively. In this context, time reversibility is defined by the formalization of the relationship between time and self-consistency. This idea has also been discussed in the context of designation and/or naming. Here we will discuss it in the context of cellular automata and explain the structure of one-to-many type mappings. Our approach is the first attempt to extend autopoietic systems in terms of dynamics. It illustrates how to introduce an autopoietic time which looks irreversible, but without the concept of entropy. PMID:1912385
Application of Carbonate Reservoir using waveform inversion and reverse-time migration methods
NASA Astrophysics Data System (ADS)
Kim, W.; Kim, H.; Min, D.; Keehm, Y.
2011-12-01
Recent exploration targets of oil and gas resources are deeper and more complicated subsurface structures, and carbonate reservoirs have become one of the attractive and challenging targets in seismic exploration. To increase the rate of success in oil and gas exploration, it is required to delineate detailed subsurface structures. Accordingly, migration method is more important factor in seismic data processing for the delineation. Seismic migration method has a long history, and there have been developed lots of migration techniques. Among them, reverse-time migration is promising, because it can provide reliable images for the complicated model even in the case of significant velocity contrasts in the model. The reliability of seismic migration images is dependent on the subsurface velocity models, which can be extracted in several ways. These days, geophysicists try to obtain velocity models through seismic full waveform inversion. Since Lailly (1983) and Tarantola (1984) proposed that the adjoint state of wave equations can be used in waveform inversion, the back-propagation techniques used in reverse-time migration have been used in waveform inversion, which accelerated the development of waveform inversion. In this study, we applied acoustic waveform inversion and reverse-time migration methods to carbonate reservoir models with various reservoir thicknesses to examine the feasibility of the methods in delineating carbonate reservoir models. We first extracted subsurface material properties from acoustic waveform inversion, and then applied reverse-time migration using the inverted velocities as a background model. The waveform inversion in this study used back-propagation technique, and conjugate gradient method was used in optimization. The inversion was performed using the frequency-selection strategy. Finally waveform inversion results showed that carbonate reservoir models are clearly inverted by waveform inversion and migration images based on the
Two effective approaches to reduce data storage in reverse time migration
NASA Astrophysics Data System (ADS)
Sun, Weijia; Fu, Li-Yun
2013-07-01
Prestack reverse time migration (RTM) requires extensive data storage since it computes wavefields in forward time and accesses wavefields in reverse order. We first review several successful schemes that have been proposed to reduce data storage, but require more computational redundancies. We propose two effective strategies to reduce data storage during RTM. The first strategy is based on the Nyquist sampling theorem, which involves no extra computational cost. The fact is that the time sampling intervals required by numerical algorithms or given by field records is generally several times smaller than that satisfied by the Nyquist sampling theorem. Therefore, we can correlate the source wavefields with the receiver wavefields at the Nyquist time step, which helps decrease storage of time history. The second strategy is based on a lossless compression algorithm, which is widely used in computer science and information theory. The compression approach reduces storage significantly at a little computational cost. Numerical examples show that the two proposed strategies are effective and efficient.
Bounds on Time Reversal Violation From Polarized Neutron Capture With Unpolarized Targets
Davis, E. D.; Gould, C. R.; Mitchell, G. E.; Sharapov, E. I.
2005-01-01
We have analyzed constraints on parity-odd time-reversal noninvariant interactions derived from measurements of the energy dependence of parity-violating polarized neutron capture on unpolarized targets. As previous authors found, a perturbation in energy dependence due to a parity (P)-odd time (T)-odd interaction is present. However, the perturbation competes with T-even terms which can obscure the T-odd signature. We estimate the magnitudes of these competing terms and suggest strategies for a practicable experiment. PMID:27308172
Maes, Michaël; Willebrords, Joost; Crespo Yanguas, Sara; Cogliati, Bruno; Vinken, Mathieu
2016-01-01
Summary Although connexin production is mainly regulated at the protein level, altered connexin gene expression has been identified as the underlying mechanism of several pathologies. When studying the latter, appropriate methods to quantify connexin mRNA levels are required. The present chapter describes a well-established reverse transcription quantitative real-time polymerase chain reaction procedure optimized for analysis of hepatic connexins. The method includes RNA extraction and subsequent quantification, generation of complementary DNA, quantitative real-time polymerase chain reaction and data analysis. PMID:27207283
Maes, Michaël; Willebrords, Joost; Crespo Yanguas, Sara; Cogliati, Bruno; Vinken, Mathieu
2016-01-01
Although connexin production is mainly regulated at the protein level, altered connexin gene expression has been identified as the underlying mechanism of several pathologies. When studying the latter, appropriate methods to quantify connexin RNA levels are required. The present chapter describes a well-established reverse transcription quantitative real-time polymerase chain reaction procedure optimized for analysis of hepatic connexins. The method includes RNA extraction and subsequent quantification, generation of complementary DNA, quantitative real-time polymerase chain reaction, and data analysis. PMID:27207283
Least-squares reverse-time migration with cost-effective computation and memory storage
NASA Astrophysics Data System (ADS)
Liu, Xuejian; Liu, Yike; Huang, Xiaogang; Li, Peng
2016-06-01
Least-squares reverse-time migration (LSRTM), which involves several iterations of reverse-time migration (RTM) and Born modeling procedures, can provide subsurface images with better balanced amplitudes, higher resolution and fewer artifacts than standard migration. However, the same source wavefield is repetitively computed during the Born modeling and RTM procedures of different iterations. We developed a new LSRTM method with modified excitation-amplitude imaging conditions, where the source wavefield for RTM is forward propagated only once while the maximum amplitude and its excitation-time at each grid are stored. Then, the RTM procedure of different iterations only involves: (1) backward propagation of the residual between Born modeled and acquired data, and (2) implementation of the modified excitation-amplitude imaging condition by multiplying the maximum amplitude by the back propagated data residuals only at the grids that satisfy the imaging time at each time-step. For a complex model, 2 or 3 local peak-amplitudes and corresponding traveltimes should be confirmed and stored for all the grids so that multiarrival information of the source wavefield can be utilized for imaging. Numerical experiments on a three-layer and the Marmousi2 model demonstrate that the proposed LSRTM method saves huge computation and memory cost.
A New Characteristic Function for Fast Time-Reverse Seismic Event Location
NASA Astrophysics Data System (ADS)
Hendriyana, Andri; Bauer, Klaus; Weber, Michael; Jaya, Makky; Muksin, Muksin
2015-04-01
Microseismicity produced by natural activities is usually characterized by low signal-to-noise ratio and huge amount of data as recording is conducted for a long period of time. Locating microseismic events is preferably carried out using migration-based methods such as time-reverse modeling (TRM). The original TRM is based on backpropagating the wavefield from the receiver down to the source location. Alternatively, we are using a characteristic function (CF) derived from the measured wavefield as input for the TRM. The motivation for such a strategy is to avoid undesired contributions from secondary arrivals which may generate artifacts in the final images. In this presentation, we introduce a new CF as input for TRM method. To obtain this CF, initially we apply kurtosis-based automatic onset detection and convolution with a given wavelet. The convolution with low frequency wavelets allows us to conduct time-reverse modeling using coarser sampling hence it will reduce computing time. We apply the method to locate seismic events measured along an active part of the Sumatra Fault around the Tarutung pull-apart basin (North Sumatra, Indonesia). The results show that seismic events are well-determined since they are concentrated along the Sumatran fault. Internal details of the Tarutung basin structure could be derived. Our results are consistent with those obtained from inversion of manually picked travel time data.
Time-reversal symmetric resolution of unity without background integrals in open quantum systems
Hatano, Naomichi; Ordonez, Gonzalo
2014-12-15
We present a new complete set of states for a class of open quantum systems, to be used in expansion of the Green’s function and the time-evolution operator. A remarkable feature of the complete set is that it observes time-reversal symmetry in the sense that it contains decaying states (resonant states) and growing states (anti-resonant states) parallelly. We can thereby pinpoint the occurrence of the breaking of time-reversal symmetry at the choice of whether we solve Schrödinger equation as an initial-condition problem or a terminal-condition problem. Another feature of the complete set is that in the subspace of the central scattering area of the system, it consists of contributions of all states with point spectra but does not contain any background integrals. In computing the time evolution, we can clearly see contribution of which point spectrum produces which time dependence. In the whole infinite state space, the complete set does contain an integral but it is over unperturbed eigenstates of the environmental area of the system and hence can be calculated analytically. We demonstrate the usefulness of the complete set by computing explicitly the survival probability and the escaping probability as well as the dynamics of wave packets. The origin of each term of matrix elements is clear in our formulation, particularly, the exponential decays due to the resonance poles.
NASA Astrophysics Data System (ADS)
Wang, Yue
A new variable grid-size and time-step finite-difference (FD) method is developed and applied to three different geophysical problems: simulation of tube waves in boreholes, three-dimensional (3-D) ground-motion simulation in sedimentary basin models, and reverse-time migration of multicomponent data. Unlike the conventional FD method, which uses a fixed grid-size and time-step for the entire model region, spatially variable grid-sizes and time-steps are used to achieve the optimal computational efficiency. For tube wave simulations, a fine grid-spacing is used for simulation inside the borehole region, while a coarse grid is used in the exterior region. While the stability condition requires a very fine time step for the fine grid, a variable time-step method provides coarse time steps for simulation in the coarse grid. Variable grid-size and time-step changes are used to achieve both accuracy and efficiency in the simulations. Numerical tests are performed for the Bayou Choctaw salt-flank model with different borehole models. The results show the important borehole effects on the seismic wavefield for a realistic source bandwidth. The combination of variable grid-size and time-step methods reduces computational costs by several orders of magnitude for the borehole models. Viscoelastic 3-D simulations are performed for a three-layer Salt Lake basin model. The near-surface unconsolidated layer is modeled with a fine grid, and the deep part of the model is modeled by a coarse grid. Simulation results show that the 3-D basin features and the shallow layer significantly affect the amplitude and duration time of the ground motion. In the elastic case, the approximation by 2-D modeling is insufficient to simulate the 3-D ground motion response. A basin model without a shallow low-velocity layer underestimates the ground motion duration and cumulative kinetic energy by 50% or more. The simulation of a Bingham Mine blast suggests that a lower S-velocity should be used to
Unconventional vortex dynamics in superconducting states with broken time-reversal symmetry
NASA Astrophysics Data System (ADS)
Dumont, Elisabeth; Mota, Ana Celia
2002-04-01
We report vortex dynamics in the unconventional superconductors Sr2RuO4, thoriated UBe13 and compare it with previous data on UPt3 [A. Amann, A. C. Mota, M. B. Maple, and H.v. Löhneysen, Phys. Rev. B 57, 3640 (1998)]. In all three systems, a pinning mechanism, which is very distinct from the standard pinning by defects, can be associated with the appearance of broken time-reversal symmetry in the superconducting state. The pinning mechanism is so strong that no vortex creep is observed in a time scale of several hours. Our observations could be explained by the presence of domain walls, separating different degenerate superconducting states, as proposed by Sigrist and Agterberg [Prog. Theor. Phys. 102, 965 (1999)]. A conventional vortex approaching such a domain wall can decay into vortices with fractional flux quanta. Domain walls occupied with strongly pinned fractional vortices, represent efficient barriers for vortex motion and thus prevent relaxation towards equilibrium. In the case of UPt3 and U0.9725Th0.0275Be13, two consecutive phase transitions are known to occur at H=0, of which the low temperature one leads to a superconducting phase with broken time-reversal symmetry. In both systems, one observes a sharp drop of initial creep rates by more than three orders of magnitude to undetectabely low levels at their second superconducting transition. In Sr2RuO4 time-reversal symmetry is reported to occur right below Tc. However, we do not observe unconventional pinning immediately below the superconducting transition, but zero creep sets in only much below Tc. While in U0.9725Th0.0275Be13 and UPt3, the drop in creep rates at the lower superconducting transition temperature is very sudden and strong, in Sr2RuO4 it looks more like a crossover.
Geomagnetic Field Reversals and Life on the Earth in Phanerozoic Time
NASA Astrophysics Data System (ADS)
Pechersky, D. M.
2014-10-01
Global paleomagnetic and biostratigraphic data are generalized. As a result it is found out that the direct connection between geomagnetic reversals, biozones and maxima of mass extinction of a biota is absent. At the same time it is noted close to a synchronous total picture of consistent changes of biozones and geomagnetic polarity. It is explained by the general source - the Earth's diurnal rotation. The reversal polarity of a geomagnetic field prevailed during the Phanerozoic that is agreed with the Earth's counterclockwise rotation. Change of polarity of a field, most likely, is connected with acceleration or deceleration of rotation speed of the internal core relative to the Earth's mantle. Lack of direct interrelation between changes in the biosphere and geomagnetic field indicate a lack of influence of a field on life evolution on Earth. It follows also from the fact that life on Earth developed from primitive unicellular forms to mammals and the man and diversity of biota was grew against a close condition of a geomagnetic field during ~2,5 billion years and irrespective of numerous geomagnetic reversals. Main conclusion: evolutionary development of life on Earth doesn't depend both on large changes of a geomagnetic field, and on the extreme catastrophic events conducting to mass extinction of a biota.
A sponge-layer damping technique for aeroacoustic Time-Reversal
NASA Astrophysics Data System (ADS)
Mimani, A.; Prime, Z.; Doolan, C. J.; Medwell, P. R.
2015-04-01
This paper presents the underlying theory, associated mathematical modelling and analysis of a sponge-layer damping technique, termed the Time-Reversal-Sponge-Layer (TRSL), that significantly improves the performance of aeroacoustic Time-Reversal (TR). The TR technique requires the use of multiple Line Arrays (LAs) in a Time-Reversal Mirror (TRM) to accurately predict the source location and its characteristics. However, it is shown that when using multiple LAs, the interference between the opposite propagating fluxes near the LA boundaries results in the formation of spurious local maxima regions throughout the computational domain, thereby reducing the capacity of TR to resolve acoustic sources. The novel TRSL technique proposed in this work minimises this unwanted interference by damping the flux normally incident on a LA boundary and is implemented using the Pseudo-Characteristic Formulation (PCF) of the two-dimensional Linearised Euler Equations (LEE). The performance of TRSL is assessed by simulating a number of test cases such as an idealised time-harmonic monopole, dipole and lateral quadrupole sources as well as multiple (two) dipole sources of different strengths located in a nonuniform mean shear flow. The use of TRSL suppresses the formation of spurious maxima and significantly improves the source map, thereby demonstrating the effectiveness of this damping technique. The performance of TRSL is compared with two other methods: a TR superposition technique and Conventional Beamforming (CB). The TR superposition technique prevents the flux interference problem near the LA boundaries by superposing the instantaneous time-reversed acoustic pressure fields computed from individual LAs. The source map obtained using the superposition technique was found to be identical to that obtained using the TRSL damping technique, however, the computational cost was much higher. A comparison with CB indicated that although CB accurately predicts the aeroacoustic source
Song, L; Magleby, K L
1994-01-01
An assumption usually made when developing kinetic models for the gating of ion channels is that the transitions among the various states involved in the gating obey microscopic reversibility. If this assumption is incorrect, then the models and estimated rate constants made with the assumption would be in error. This paper examines whether the gating of a large conductance Ca-activated K+ channel in skeletal muscle is consistent with microscopic reversibility. If microscopic reversibility is obeyed, then the number of forward and backward transitions per unit time for each individual reaction step will, on average, be identical and, consequently, the gating must show time reversibility. To look for time reversibility, two-dimensional dwell-time distributions of the durations of open and closed intervals were obtained from single-channel current records analyzed in the forward and in the backward directions. Two-dimensional dwell-time distributions of pairs of open intervals and of pairs of closed intervals were also analyzed to extend the resolution of the method to special circumstances in which intervals from different closed (or open) states might have similar durations. No significant differences were observed between the forward and backward analysis of the two-dimensional dwell-time distributions, suggesting time reversibility. Thus, we find no evidence to indicate that the gating of the maxi K+ channel violates microscopic reversibility. PMID:7919030
Results of the Baikal Experiment on Observations of oscopic Nonlocal Correlations in Reverse Time
NASA Astrophysics Data System (ADS)
Korotaev, S. M.; Serdyuk, V. O.; Kiktenko, E. O.; Budnev, N. M.; Gorohov, J. V.
Although the general theory oscopic quantum entanglement of is still in its infancy, consideration of the matter in the framework of action-at-a distance electrodynamics predicts for the random dissipative processes observability of the advanced nonlocal correlations (time reversal causality). These correlations were really revealed in our previous experiments with some large-scale heliogeophysical processes as the source ones and the lab detectors as the probe ones. Recently a new experiment has been performing on the base of Baikal Deep Water Neutrino Observatory. The thick water layer is an excellent shield against any local impacts on the detectors. The first annual series 2012/2013 has demonstrated that detector signals respond to the heliogeophysical (external) processes and causal connection of the signals directed downwards: from the Earth surface to the Baikal floor. But this nonlocal connection proved to be in reverse time. In addition advanced nonlocal correlation of the detector signal with the regional source-process: the random component of hydrological activity in the upper layer was revealed and the possibility of its forecast on nonlocal correlations was demonstrated. But the strongest oscopic nonlocal correlations are observed at extremely low frequencies, that is at periods of several months. Therefore the above results should be verified in a longer experiment. We verify them by data of the second annual series 2013/2014 of the Baikal experiment. All the results have been confirmed, although some quantitative parameters of correlations and time reversal causal links turned out different due to nonstationarity of the source-processes. A new result is displaying of the advanced response of nonlocal correlation detector to the earthquake. This opens up the prospect of the earthquake forecast on the new physical principle, although further confirmation in the next events is certainly needed. The continuation of the Baikal experiment with expanded
NASA Astrophysics Data System (ADS)
Korotaev, S. M.; Serdyuk, V. O.; Kiktenko, E. O.; Budnev, N. M.; Gorohov, J. V.
Although the general theory macroscopic quantum entanglement of is still in its infancy, consideration of the matter in the framework of action-at-a distance electrodynamics predicts for the random dissipative processes observability of the advanced nonlocal correlations (time reversal causality). These correlations were really revealed in our previous experiments with some large-scale heliogeophysical processes as the source ones and the lab detectors as the probe ones. Recently a new experiment has been performing on the base of Baikal Deep Water Neutrino Observatory. The thick water layer is an excellent shield against any local impacts on the detectors. The first annual series 2012/2013 has demonstrated that detector signals respond to the heliogeophysical (external) processes and causal connection of the signals directed downwards: from the Earth surface to the Baikal floor. But this nonlocal connection proved to be in reverse time. In addition advanced nonlocal correlation of the detector signal with the regional source-process: the random component of hydrological activity in the upper layer was revealed and the possibility of its forecast on nonlocal correlations was demonstrated. But the strongest macroscopic nonlocal correlations are observed at extremely low frequencies, that is at periods of several months. Therefore the above results should be verified in a longer experiment. We verify them by data of the second annual series 2013/2014 of the Baikal experiment. All the results have been confirmed, although some quantitative parameters of correlations and time reversal causal links turned out different due to nonstationarity of the source-processes. A new result is displaying of the advanced response of nonlocal correlation detector to the earthquake. This opens up the prospect of the earthquake forecast on the new physical principle, although further confirmation in the next events is certainly needed. The continuation of the Baikal experiment with
Polarity-consistent excitation amplitude imaging condition for elastic reverse time migration
NASA Astrophysics Data System (ADS)
Du, Qizhen; Zhang, Mingqiang; Gong, Xufei; Chen, Xiaoran
2015-02-01
Imaging conditions can not only affect the computational efficiency and storage cost of reverse time migration (RTM) but determine the quality of the final migrated images. This paper extends the idea of the well amplitude-preserved and highly-efficient excitation amplitude imaging condition from acoustic RTM to elastic RTM. For elastic RTM, the maximum amplitude of the separated P-wave and the corresponding image time of each grid point are saved during the forward modeling of the source wavefield and then PP and PS images are obtained by dividing the separated P- and S-waves of the backward-propagated receiver wavefield by the precomputed P-waves at each grid point that satisfies the image time. However, polarity reversals of the PS image will cause destructive interference when the stacked image is needed. In order to solve this problem, we propose the polarity-consistent excitation amplitude imaging condition by combining the excitation amplitude imaging condition with a shot-domain polarity reversal correction method. Then we provide the detailed realization process of this imaging condition in elastic RTM. By utilizing the relatively stable and well amplitude-preserved source-normalized cross-correlation imaging condition as a comparison, we testify to the feasibility and validity of the proposed imaging condition in the aspects of amplitude preservation property, imaging capability of complex structures, storage cost and computational efficiency. Considering the balance between the efficiency and image quality, the polarity-consistent excitation amplitude imaging condition can be a good choice for elastic RTM.
Observation of coherence in the time-reversed relativistic photoelectric effect.
Tashenov, S; Banaś, D; Beyer, H; Brandau, C; Fritzsche, S; Gumberidze, A; Hagmann, S; Hillenbrand, P-M; Jörg, H; Kojouharov, I; Kozhuharov, Ch; Lestinsky, M; Litvinov, Yu A; Maiorova, A V; Schaffner, H; Shabaev, V M; Spillmann, U; Stöhlker, Th; Surzhykov, A; Trotsenko, S
2014-09-12
The photoelectric effect has been studied in the regime of hard x rays and strong Coulomb fields via its time-reversed process of radiative recombination (RR). In the experiment, the relativistic electrons recombined into the 2p_{3/2} excited state of hydrogenlike uranium ions, and both the RR x rays and the subsequently emitted characteristic x rays were detected in coincidence. This allowed us to observe the coherence between the magnetic substates in a highly charged ion and to identify the contribution of the spin-orbit interaction to the RR process. PMID:25259973
Boltzmann Gibbs distribution of fortune and broken time reversible symmetry in econodynamics
NASA Astrophysics Data System (ADS)
Ao, P.
2007-08-01
Within the framework of stochastic differential equations it is demonstrated that the existence of Boltzmann-Gibbs type distribution in economy is independent of the time reversal symmetry in econodynamics. Both power law and exponential distributions can be accommodated naturally. The demonstration is based on a mathematical structure discovered during a study in gene regulatory network dynamics. Further possible analogy between equilibrium economy and thermodynamics is explored, suggesting that statistical physics methods can indeed play an important role in the study of complex systems.
NASA Astrophysics Data System (ADS)
Ying, Ying-Zi; Ma, Li; Guo, Sheng-Ming
2011-05-01
In active sonar operation, the presence of background reverberation and the low signal-to-noise ratio hinder the detection of targets. This paper investigates the application of single-channel monostatic iterative time reversal to mitigate the difficulties by exploiting the resonances of the target. Theoretical analysis indicates that the iterative process will adaptively lead echoes to converge to a narrowband signal corresponding to a scattering object's dominant resonance mode, thus optimising the return level. The experiments in detection of targets in free field and near a planar interface have been performed. The results illustrate the feasibility of the method.
Polycentric spatial focus of time-reversal electromagnetic field in rectangular conductor cavity.
Chen, Yingming; Wang, Bing-Zhong
2013-11-01
Polycentric focus effect of time-reversal (TR) electromagnetic field is found in a rectangular resonant cavity. Theoretical deduction shows that the effect is due to the mirror symmetry of the cavity and the maximum number of focus points is 27 including 1 main focus point and 26 secondary focus points. A case of 6 focus points is calculated, in which the numerical results are consistent with the theoretical predictions, and particularly the 5 secondary focus points have directly resulted in inaccurate imaging and pulse signal interception. PMID:24216886
Search for Time Reversal Violating Effects: R-Correlation Measurement in Neutron Decay
Bodek, K.; Ban, G.; Beck, M.; Bialek, A.; Bryś, T.; Czarnecki, A.; Fetscher, W.; Gorel, P.; Kirch, K.; Kistryn, St.; Kozela, A.; Kuźniak, M.; Lindroth, A.; Naviliat-Cuncic, O.; Pulut, J.; Serebrov, A.; Severijns, N.; Stephan, E.; Zejma, J.
2005-01-01
An experiment aiming at the simultaneous determination of both transversal polarization components of electrons emitted in the decay of free neutrons begins data taking using the polarized cold neutron beam (FUNSPIN) from the Swiss Neutron Spallation Source (SINQ) at the Paul-Scherrer Institute, Villigen. A non-zero value of R due to the e− polarization component, which is perpendicular to the plane spanned by the spin of the decaying neutron and the electron momentum, would signal a violation of time reversal symmetry and thus physics beyond the Standard Model. Present status of the project and the results from analysis of the first data sample will be discussed. PMID:27308168
Locating the Origin of Scattered Waves By Simulating Time Reversal of the Seismic Wavefield
NASA Astrophysics Data System (ADS)
Myers, S. C.; Pitarka, A.; Sjogreen, B.; Petersson, A.; Simmons, N. A.; Johannesson, G.
2014-12-01
The Source Physics Experiment (SPE) is a series of underground chemical explosions at the Nevada National Security Site (NNSS) that are improving our physical understanding how explosion sources generate seismic waves. Better understanding the origin of S-waves from explosions is a primary goal of the SPE. Even at distances of a few kilometers from the SPE sources, seismic recordings include arrivals of unknown origin that could originate as S-waves at the explosive source or from topographic and subsurface scatterers. Back propagation of time reversed seismograms has been used to determine the location of seismic events (e.g. Tromp et al., 2005; Larmat et al., 2006), and Myers et al. (2007) demonstrated that the time-reversal method can be used to determine the origin of direct and scattered waves in seismic simulations. In this study we identify the origin of distinct features in synthetic seismograms that are generated by elastic, finite-difference simulation of seismic propagation from SPE explosions through a model that has been developed specifically for the SPE. The SPE model includes 3-dimensional velocity discontinuities at geologic boundaries, as well as free-surface topography. Although the largest arrivals in the synthetic seismograms are expected to originate at the explosion source, other prominent features are likely to originate as scattered energy from model discontinuities. Scattering sources in the SPE model that are needed in order to match synthetic seismograms to field recordings of SPE shots will be identified. Conversely, model structures may be removed if they result in disagreement between synthetic seismograms and field recordings. Ultimately, we plan to constrain the origin of prominent features in field recordings of SPE shots by directly using the field recordings as inputs to time reversal simulations. Direct use of field recordings will require development of methods that account for the uncertainty of the seismic model through which
Effective Field Theory and Time-Reversal Violation in Light Nuclei
NASA Astrophysics Data System (ADS)
Mereghetti, E.; van Kolck, U.
2015-10-01
Thanks to the unnaturally small value of the QCD vacuum angle [Formula: see text], time-reversal violation ([Formula: see text]) offers a window into physics beyond the Standard Model (SM) of particle physics. We review the effective field theory framework that establishes a clean connection between (a) [Formula: see text] mechanisms, which can be represented by higher-dimensional operators involving SM fields and symmetries, and (b) hadronic interactions, which allow for controlled calculations of low-energy observables involving strong interactions. The chiral properties of [Formula: see text] mechanisms lead to a pattern that should be identifiable in measurements of the electric dipole moments of the nucleon and light nuclei.
High-frequency reverse-time chaos generation using an optical matched filter.
Jiang, Xingxing; Liu, Deming; Cheng, Mengfan; Deng, Lei; Fu, Songnian; Zhang, Minming; Tang, Ming; Shum, Ping
2016-03-15
The optical reverse-time chaos is realized by modulating a binary pseudo-random bit sequence onto an optical carrier, and then driving an optical matched filter. The filter is demonstrated experimentally by using two fiber Bragg gratings and a Fourier-domain programmable optical processor. The complexity relationship between the binary input sequence and the output chaos signal is studied. This approach could be a novel way to generate a high speed repeatable and controllable optical chaos signal, which has the potential to be used in optical secure communication systems. PMID:26977658
Depth profile of a time-reversal focus in an elastic solid
Remillieux, Marcel C.; Anderson, Brian E.; Ulrich, T. J.; Le Bas, Pierre -Yves; Payan, Cedric
2015-04-01
The out-of-plane velocity component is focused on the flat surface of an isotropic solid sample using the principle of time reversal. This experiment is often reproduced in the context of nondestructive testing for imaging features near the surface of the sample. However, it is not clear how deep the focus extends into the bulk of the sample and what its profile is. In this paper, this question is answered using both numerical simulations and experimental data. The profiles of the foci are expressed in terms of the wavelengths of the dominant waves, based on the interpretation of the Lamb’s problem and the use of the diffraction limit.
Thermoelectric Signatures of Time-Reversal Symmetry Breaking States in Multiband Superconductors
NASA Astrophysics Data System (ADS)
Garaud, Julien; Silaev, Mihail; Babaev, Egor
2016-03-01
We show that superconductors with broken time-reversal symmetry have very specific magnetic and electric responses to inhomogeneous heating. A local heating of such superconductors induces a magnetic field with a profile that is sensitive to the presence of domain walls and crystalline anisotropy of superconducting states. A nonstationary heating process produces an electric field and a charge imbalance in different bands. These effects can be measured and used to distinguish s +i s and s +i d superconducting states in the candidate materials such as Ba1 -xKx Fe2 As2 .
Thermoelectric Signatures of Time-Reversal Symmetry Breaking States in Multiband Superconductors.
Garaud, Julien; Silaev, Mihail; Babaev, Egor
2016-03-01
We show that superconductors with broken time-reversal symmetry have very specific magnetic and electric responses to inhomogeneous heating. A local heating of such superconductors induces a magnetic field with a profile that is sensitive to the presence of domain walls and crystalline anisotropy of superconducting states. A nonstationary heating process produces an electric field and a charge imbalance in different bands. These effects can be measured and used to distinguish s+is and s+id superconducting states in the candidate materials such as Ba_{1-x}K_{x}Fe_{2}As_{2}. PMID:26991194
Time-reversal-symmetric single-photon wave packets for free-space quantum communication.
Trautmann, N; Alber, G; Agarwal, G S; Leuchs, G
2015-05-01
Readout and retrieval processes are proposed for efficient, high-fidelity quantum state transfer between a matter qubit, encoded in the level structure of a single atom or ion, and a photonic qubit, encoded in a time-reversal-symmetric single-photon wave packet. They are based on controlling spontaneous photon emission and absorption of a matter qubit on demand in free space by stimulated Raman adiabatic passage. As these processes do not involve mode selection by high-finesse cavities or photon transport through optical fibers, they offer interesting perspectives as basic building blocks for free-space quantum-communication protocols. PMID:25978231
Universal transport properties of open microwave cavities with and without time-reversal symmetry.
Schanze, H; Stöckmann, H-J; Martínez-Mares, M; Lewenkopf, C H
2005-01-01
We measure the transmission through asymmetric and reflection-symmetric chaotic microwave cavities in dependence on the number of attached waveguides. Ferrite cylinders are placed inside the cavities to break time-reversal symmetry. The phase-breaking properties of the ferrite and its range of applicability are discussed in detail. We use the random matrix theory accounting for absorption effects to calculate the universal distribution of transmission coefficients T and their energy derivatives dT/depsilon. Using the absorption strength as a fitting parameter, we find good agreement between universal transmission fluctuations predicted by the theory and the experimental data. PMID:15697714
Time reversal of continuous-wave, monochromatic signals in elastic media
Anderson, Brian E; Guyer, Robert A; Ulrich, Timothy J; Johnson, Paul A
2009-01-01
Experimental observations of spatial focusing of continuous-wave, steady-state elastic waves in a reverberant elastic cavity using time reversal are reported here. Spatially localized focusing is achieved when multiple channels are employed, while a single channel does not yield such focusing. The amplitude of the energy at the focal location increases as the square of the number of channels used, while the amplitude elsewhere in the medium increases proportionally with the number of channels used. The observation is important in the context of imaging in solid laboratory samples as well as problems involving continuous-wave signals in Earth.
Pairing state with a time-reversal symmetry breaking in FeAs-based superconductors
Lee, Wei-Sheng
2010-05-26
We investigate the competition between the extended s{+-} wave and dx2-y2 -wave pairing order parameters in the iron-based superconductors. Because of the frustrating pairing interactions among the electron and the hole fermi pockets, a time-reversal symmetry breaking s + id pairing state could be favored. We analyze this pairing state within the Ginzburg-Landau theory, and explore the experimental consequences. In such a state, spatial inhomogeneity induces supercurrent near a non-magnetic impurity and the corners of a square sample. The resonance mode between the s{+-} and dx2?y2 -wave order parameters can be detected through the B1g-Raman spectroscopy.
Time-Reversal-Symmetric Single-Photon Wave Packets for Free-Space Quantum Communication
NASA Astrophysics Data System (ADS)
Trautmann, N.; Alber, G.; Agarwal, G. S.; Leuchs, G.
2015-05-01
Readout and retrieval processes are proposed for efficient, high-fidelity quantum state transfer between a matter qubit, encoded in the level structure of a single atom or ion, and a photonic qubit, encoded in a time-reversal-symmetric single-photon wave packet. They are based on controlling spontaneous photon emission and absorption of a matter qubit on demand in free space by stimulated Raman adiabatic passage. As these processes do not involve mode selection by high-finesse cavities or photon transport through optical fibers, they offer interesting perspectives as basic building blocks for free-space quantum-communication protocols.
NASA Astrophysics Data System (ADS)
Hoover, Wm. G.; Hoover, Carol G.; Grond, Florian
2008-08-01
We investigate and discuss the time-reversible nature of phase-space instabilities for several flows, x˙=f(x). The flows describe thermostated oscillator systems in from two through eight phase-space dimensions. We determine the local extremal phase-space growth rates, which bound the instantaneous comoving Lyapunov exponents. The extremal rates are point functions which vary continuously in phase space. The extremal rates can best be determined with a "singular-value decomposition" algorithm. In contrast to these precisely time-reversible local "point function" values, a time-reversibility analysis of the comoving Lyapunov spectra is more complex. The latter analysis is nonlocal and requires the additional storing and playback of relatively long (billion-step) trajectories. All the oscillator models studied here show the same time reversibility symmetry linking their time-reversed and time-averaged "global" Lyapunov spectra. Averaged over a long-time-reversed trajectory, each of the long-time-averaged Lyapunov exponents simply changes signs. The negative/positive sign of the summed-up and long-time-averaged spectra in the forward/backward time directions is the microscopic analog of the Second Law of Thermodynamics. This sign changing of the individual global exponents contrasts with typical more-complex instantaneous "local" behavior, where there is no simple relation between the forward and backward exponents other than the local (instantaneous) dissipative constraint on their sum. As the extremal rates are point functions, they too always satisfy the sum rule.
Adaptive instant record signals applied to detection with time reversal operator decomposition.
Folegot, Thomas; de Rosny, Julien; Prada, Claire; Fink, Mathias
2005-06-01
Time reversal arrays are becoming common tools whether for detection or tomography. These applications require the measurement of the response from the array to one or several receivers. The most natural way to record the impulse responses for several sources is to generate pulses successively from each emitting point and record simultaneously the signals from the receivers. However, this method is very time consuming or inefficient in terms of signal-to-noise ratio. To overcome this limitation quasi-orthogonal pseudonoise signals like Kasami sequences can be used. For guided wave propagation, a very high degree of orthogonality between the signal is necessary to allow an accurate measure of the whole multipath structure of the transfer function. Hence, in this work, we propose a new family of pseudo-orthogonal signals that is adapted to the environment and more specifically, to highly dispersive media. These adaptive instant records signals are used experimentally to detect targets using the time reversal operator decomposition method. The accuracy of the 15 x 15 transfer functions acquired simultaneously, and therefore the detection capability, are demonstrated in an experimental ultrasonic waveguide as a small-scale model of shallow water propagation including bottom absorption and reverberation. PMID:16018479
Topological crystalline semimetals in non-symmorphic lattices without time-reversal symmetry
NASA Astrophysics Data System (ADS)
Chen, Yige; Kim, Heung-Sik; Kee, Hae-Young
Numerous efforts have been devoted to reveal exotic semimetallic phases with topologically non-trivial bulk and surface states in materials with strong spin-orbit coupling. Recent theoretical works on orthorhombic perovskite iridates SrIrO3 have indicated that non-symmorphic symmetry is crucial to protect a nodal line Fermi surface (FS) in addition to space-time inversion symmetry [C. Fang et.al, PRB 92, 081201(R) (2015), Y. Chen et.al, Nat. Commu. 6, (2015)]. In this work, we investigate possible topological semimetals in the absence of time-reversal symmetry. In principle, an anti-unitary operator, defined as a product of time-reversal and glide operators, can protect a four-fold or two-fold degenerate nodal FS. Indeed this happens in SrIrO3 with the magnetic field along a particular direction. A trivial gapped insulator can also occur due to a lack of such anti-unitary operation. This study shows that non-symmorphic crystals with multiple fractional lattice translations exhibit rich topological properties.
Jin, Yuanwei; Ying, Yujie; Zhao, Deshuang
2013-01-01
In this paper, we present and demonstrate a low complexity elastic wave signaling and reception method to achieve high data rate communication on dispersive solid elastic media, such as metal pipes, using piezoelectric transducers of PZT (lead zirconate titanate). Data communication is realized using pulse position modulation (PPM) as the signaling method and the elastic medium as the communication channel. The communication system first transmits a small number of training pulses to probe the dispersive medium. The time-reversed probe signals are then utilized as the information carrying waveforms. Rapid timing acquisition of transmitted waveforms for demodulation over elastic medium is made possible by exploring the reciprocity property of guided elastic waves. The experimental tests were conducted using a National Instrument PXI system for waveform excitation and data acquisition. Data telemetry bit rates of 10 kbps, 20 kbps, 50 kbps and 100 kbps with the average bit error rates of 0, 5.75 x 10-4, 1.09 x 10-2 and 5.01 x 10-2, respectively, out of a total of 40, 000 transmitted bits were obtained when transmitting at the center frequency of 250 kHz and a 500 kHz bandwidth on steel pipe specimens. To emphasize the influence of time reversal, no complex processing techniques, such as adaptive channel equalization or error correction coding, were employed. PMID:23881122
Rivière, Jacques; Haupert, Sylvain; Laugier, Pascal; Ulrich, T J; Le Bas, Pierre-Yves; Johnson, Paul A
2012-03-01
This study broadens vibration-like techniques developed for osseointegration monitoring to the nonlinear field. The time reversed elastic nonlinearity diagnostic is applied to two mock models. The first one consists of tightening a dental implant at different torques in a mock cortical bone; the second one allows one to follow glue curing at the interface between a dental implant and a mock jaw. Energy is focused near the implant interface using the time reversal technique. Two nonlinear procedures termed pulse inversion and the scaling subtraction method, already used successfully in other fields such as contrast agents and material characterization, are employed. These two procedures are compared for both models. The results suggest that nonlinear elasticity can provide new information regarding the interface, complementary to the linear wave velocity and attenuation. The curing experiment exhibits an overall low nonlinear level due to the fact that the glue significantly damps elastic nonlinearity at the interface. In contrast, the torque experiment shows strong nonlinearities at the focus time. Consequently, a parallel analysis of these models, both only partially reflecting a real case, enables one to envisage future in vivo experiments. PMID:22423689
Song, Aijun; Badiey, Mohsen
2012-01-01
Multiple-input/multiple-output (MIMO) techniques can lead to significant improvements of underwater acoustic communication capabilities. In this paper, receivers based on time reversal processing are developed for high frequency underwater MIMO channels. Time reversal followed by a single channel decision feedback equalizer, aided by frequent channel updates, is used to compensate for the time-varying inter-symbol interference. A parallel interference cancellation method is incorporated to suppress the co-channel interference in the MIMO system. The receiver performance is demonstrated by a 2008 shallow water experiment in Kauai, Hawaii. In the experiment, high frequency MIMO signals centered at 16 kHz were transmitted every hour during a 35 h period from an 8-element source array to a wide aperture 16-element vertical receiving array at 4 km range. The interference cancellation method is shown to generate significant performance enhancement, on average 2-4 dB in the output signal-to-noise ratio per data stream, throughout the 35 h MIMO transmissions. Further, communication performance and achieved data rates exhibit significant changes over the 35 h period as a result of stratification of the water column. PMID:22280591
Time-Resolved AMR measurements of current induced magnetization reversal in ferromagnetic nanowires
NASA Astrophysics Data System (ADS)
Guittienne, Ph.; Wegrowe, J.-E.; Kelly, D.; Ansermet, J.-Ph.
2001-03-01
Time-resolved detection of the magnetization switching in static magnetic fields was achieved by pulsing current densities of about 107 A/cm2 in single isolated Nickel nanowires (80nm in diameter, 6000 nm in length, electrodeposited in porous membranes), using a Weathstone bridge of a 1GHz bandwidth. This irreversible transition is found to occur in a time of about 10 ns. The time of switching within the pulse, tsw, is measured as a function of applied field and current. The temperature rise due to Joule heating is deduced from the change in resistance. The entire set of data tsw(H,T) are fitted with a simple activation law, with the energy barrier height as the unique fitting parameter. The results show a strong departure from pure thermal activation indicating a current-induced magnetization reversal.
Parity and time-reversal symmetry nonconservation in neutron-nucleus interactions
Bowman, J.D.; Bowman, C.D.; Knudson, J.; Penttilae, S.; Seestrom, S.J.; Szymanski, J.J.; Yuan, V.W. ); Bush, J.E.; Frankle, C.M.; Gould, C.R.; Haase, D.G.; Mitchell, G.E Triangle Universities Nuclear Lab., Durham, NC ); Delheij, P.P.J. ); Postma, H. (Technische Hogeschool Delft (Netherlands
1990-01-01
Parity non-conversation was studied for seventeen states in the compound nucleus {sup 239}U by measuring the helicity dependence of the p-wave resonance cross section for epithermal neutrons scattered from {sup 238}U. The root-mean-squared parity-violating matrix element for the mixing of p-wave and s-wave states was determined to be M = 0.58{sub -0.25}{sup +0.50} meV. This corresponds to a parity-violating spreading width of {Gamma}{sup PV} = 1.0 {times} 10{sup {minus}7} eV. This gives a value of 4 {times} 10{sup {minus}7} for {alpha}{sub p}, the ratio of strengths of the P-odd and P-even effective nucleon-nucleon interactions in {sup 239}U. The implications of these results for studies of Time Reversal Symmetry in the compound nucleus is discussed.
NASA Astrophysics Data System (ADS)
Nguyen, Bao D.
Imaging with prestack reverse-time migration (RTM) is typically approached via a zero-lag crosscorrelation between source and receiver wavefields, which imposes unnecessarily stringent requirements for computational resources and disk storage. The imaging principle for reflectivity is analyzed and we demonstrate that a single maximal energy arrival event is often sufficient for migration imaging. Methods to alleviate the cost of crosscorrelation imaging are proposed and categorized into reconstructive and non-reconstructive schemes. Source wavefield reconstruction treats the source extrapolation as a method of providing the auxiliary conditions for an initial-boundary value problem. A first-pass (forward-time) extrapolation for the source wavefield identifies the boundary and/or initial values necessary to uniquely reconstruct it using a second (reverse-time) backward propagation. Mixed value, or hybrid, reconstruction is proposed as the most accurate alternative to storing the source wavefield time history. Reconstructing the source wavefield reduces storage costs by up to two orders of magnitude without an appreciable loss of image quality. Boundary value and initial value reconstruction methods are extended from acoustic to elastic RTM. Non-reconstructive approaches deviate from the conventional imaging paradigm, as only the most salient information required for imaging is kept. A maximal energy arrival event (termed the `excitation amplitude') imaging condition is explored as the direct analog for the theoretical reflection coefficient for acoustic isotropic media, and extended for elastic RTM. Sparse crosscorrelation is proposed as an equivalent method to standard crosscorrelation where the migrated image is now represented with a minimized data set. Time-binning is dynamic sorting algorithm with linear time complexity proposed for use with both excitation amplitude and sparse crosscorrelation approches to further expedite imaging. These parsimonious imaging
Bittner, S; Dietz, B; Harney, H L; Miski-Oglu, M; Richter, A; Schäfer, F
2014-03-01
Scattering experiments with microwave cavities were performed and the effects of broken time-reversal invariance (TRI), induced by means of a magnetized ferrite placed inside the cavity, on an isolated doublet of nearly degenerate resonances were investigated. All elements of the effective Hamiltonian of this two-level system were extracted. As a function of two experimental parameters, the doublet and the associated eigenvectors could be tuned to coalesce at a so-called exceptional point (EP). The behavior of the eigenvalues and eigenvectors when encircling the EP in parameter space was studied, including the geometric amplitude that builds up in the case of broken TRI. A one-dimensional subspace of parameters was found where the differences of the eigenvalues are either real or purely imaginary. There, the Hamiltonians were found to be PT invariant under the combined operation of parity (P) and time reversal (T) in a generalized sense. The EP is the point of transition between both regions. There a spontaneous breaking of PT occurs. PMID:24730915
The effective chiral Lagrangian from dimension-six parity and time-reversal violation
Vries, J. de; Mereghetti, E.; Timmermans, R.G.E.; Kolck, U. van
2013-11-15
We classify the parity- and time-reversal-violating operators involving quark and gluon fields that have effective dimension six: the quark electric dipole moment, the quark and gluon chromo-electric dipole moments, and four four-quark operators. We construct the effective chiral Lagrangian with hadronic and electromagnetic interactions that originate from them, which serves as the basis for calculations of low-energy observables. The form of the effective interactions depends on the chiral properties of these operators. We develop a power-counting scheme and calculate within this scheme, as an example, the parity- and time-reversal-violating pion–nucleon form factor. We also discuss the electric dipole moments of the nucleon and light nuclei. -- Highlights: •Classification of T-odd dimension-six sources based on impact on observables. •Building of the chiral Lagrangian for each dimension-six source. •Calculation of the PT-odd pion–nucleon form factor for each source. •Discussion of hadronic EDMs for each source and comparison with the theta term.
Optical focusing inside scattering media with time-reversed ultrasound microbubble encoded light
Ruan, Haowen; Jang, Mooseok; Yang, Changhuei
2015-01-01
Focusing light inside scattering media in a freely addressable fashion is challenging, as the wavefront of the scattered light is highly disordered. Recently developed ultrasound-guided wavefront shaping methods are addressing this challenge, albeit with relatively low modulation efficiency and resolution limitations. In this paper, we present a new technique, time-reversed ultrasound microbubble encoded (TRUME) optical focusing, which can focus light with improved efficiency and sub-ultrasound wavelength resolution. This method ultrasonically destroys microbubbles, and measures the wavefront change to compute and render a suitable time-reversed wavefront solution for focusing. We demonstrate that the TRUME technique can create an optical focus at the site of bubble destruction with a size of ∼2 μm. We further demonstrate a twofold enhancement in addressable focus resolution in a microbubble aggregate target by exploiting the nonlinear pressure-to-destruction response of the microbubbles. The reported technique provides a deep tissue-focusing solution with high efficiency, resolution, and specificity. PMID:26597439
Analysis of the time-reversal operator for planar dipole arrays
Chambers, D H; Berryman, J G
2004-01-16
The problem of imaging of targets in random media or cluttered environments is found in a wide variety of different applications, including ocean acoustics, medical ultrasound, geophysics, and radar. The solution often requires separating targets of interest from other scatterers, and compensating for wave speed variations in the medium. The problem is not usually the lack of data, but too much data, specifically the lack of a useful organizing principle for the data. The difficult part is separating the meaningful data from the remainder. It would therefore be most helpful if there were some means for skipping over those parts of the data that we do not really want to image very much, and looking at those parts (targets) that do interest us. This sounds challenging (maybe even impossible), but recent developments in acoustics make it clear that certain very limited imaging goals are achievable with much smaller data sets than are traditionally needed in, for example, seismic array processing. Early versions of this new method have been given the names of ''time-reversal acoustics'' or ''time-reversal mirrors,'' and have been developed most extensively by the French ultrasonics group led by Fink.
Unexpected edge conduction in mercury telluride quantum wells under broken time-reversal symmetry
Ma, Eric Yue; Calvo, M. Reyes; Wang, Jing; Lian, Biao; Mühlbauer, Mathias; Brüne, Christoph; Cui, Yong-Tao; Lai, Keji; Kundhikanjana, Worasom; Yang, Yongliang; Baenninger, Matthias; König, Markus; Ames, Christopher; Buhmann, Hartmut; Leubner, Philipp; Molenkamp, Laurens W.; Zhang, Shou-Cheng; Goldhaber-Gordon, David; Kelly, Michael A.; Shen, Zhi-Xun
2015-01-01
The realization of quantum spin Hall effect in HgTe quantum wells is considered a milestone in the discovery of topological insulators. Quantum spin Hall states are predicted to allow current flow at the edges of an insulating bulk, as demonstrated in various experiments. A key prediction yet to be experimentally verified is the breakdown of the edge conduction under broken time-reversal symmetry. Here we first establish a systematic framework for the magnetic field dependence of electrostatically gated quantum spin Hall devices. We then study edge conduction of an inverted quantum well device under broken time-reversal symmetry using microwave impedance microscopy, and compare our findings to a non-inverted device. At zero magnetic field, only the inverted device shows clear edge conduction in its local conductivity profile, consistent with theory. Surprisingly, the edge conduction persists up to 9 T with little change. This indicates physics beyond simple quantum spin Hall model, including material-specific properties and possibly many-body effects. PMID:26006728
Iterative Time-Reversed Ultrasonically Encoded Light Focusing in Backscattering Mode
NASA Astrophysics Data System (ADS)
Ruan, Haowen; Jang, Mooseok; Judkewitz, Benjamin; Yang, Changhuei
2014-11-01
The Time-Reversed Ultrasound-Encoded (TRUE) light technique enables noninvasive focusing deep inside scattering media. However, the time-reversal procedure usually has a low signal-to-noise ratio because the intensity of ultrasound-encoded light is intrinsically low. Consequently, the contrast and resolution of TRUE focus is far from ideal, especially in the backscattering geometry, which is more practical in many biomedical applications. To improve the light intensity and resolution of TRUE focus, we developed an iterative TRUE (iTRUE) light focusing technique that employs the TRUE focus itself as a signal source (rather than diffused light) for subsequent TRUE procedures. Importantly, this iTRUE technique enables light focusing in backscattering mode. Here, we demonstrate the concept by focusing light in between scattering layers in a backscattering configuration and show that the light intensity at the focus is progressively enhanced by a factor of ~20. By scanning across a fluorescent bead between these two scattering layers, the focusing resolution in the ultrasound axial and lateral directions was improved ~2-fold and ~3-fold, respectively. We further explored the application of iTRUE in biological samples by focusing light between 1 mm thick chicken tissue and cartilage, and light intensity enhancements of the same order were also observed.
Imaging Faults with Reverse-Time Migration for Geothermal Exploration at Jemez Pueblo in New Mexico
Huang, Lianjie; Albrecht, Michael; Kaufman, Greg; Kelley, Shari; Rehfeldt, Kenneth; Zhang, Zhifu
2011-01-01
The fault zones at Jemez Pueblo may dominate the flow paths of hot water, or confine the boundaries of the geothermal reservoir. Therefore, it is crucial to image the geometry of these fault zones for geothermal exploration in the area. We use reverse-time migration with a separation imaging condition to image the faults at Jemez Pueblo. A finite-difference full-wave equation method with a perfectly-matching-layer absorbing boundary condition is used for backward propagation of seismic reflection data from receivers and forward propagation of wavefields from sources. In the imaging region, the wavefields are separated into the upgoing and downgoing waves, and leftgoing and rightgoing waves. The upgoing and downgoing waves are used to obtain the downward-looking image, and the leftgoing and rightgoing waves are used to form the left-looking image and right-looking image from sources. The left-looking and right-looking images are normally weaker than the downward-looking image because the reflections from the fault zones are much weaker than those from sedimentary layers, but these migration results contain the images of the faults. We apply our reverse-time migration with a wavefield separation imaging condition to seismic data acquired at Jemez Pueblo, and our preliminary results reveal many faults in the area.
Unexpected edge conduction in mercury telluride quantum wells under broken time-reversal symmetry
Ma, Eric Yue; Calvo, M. Reyes; Wang, Jing; Lian, Biao; Muhlbauer, Mathias; Brune, Christoph; Cui, Yong -Tao; Lai, Keji; Kundhikanjana, Worasom; Yang, Yongliang; et al
2015-05-26
The realization of quantum spin Hall effect in HgTe quantum wells is considered a milestone in the discovery of topological insulators. Quantum spin Hall states are predicted to allow current flow at the edges of an insulating bulk, as demonstrated in various experiments. A key prediction yet to be experimentally verified is the breakdown of the edge conduction under broken time-reversal symmetry. Here we first establish a systematic framework for the magnetic field dependence of electrostatically gated quantum spin Hall devices. We then study edge conduction of an inverted quantum well device under broken time-reversal symmetry using microwave impedance microscopy,more » and compare our findings to a non-inverted device. At zero magnetic field, only the inverted device shows clear edge conduction in its local conductivity profile, consistent with theory. Surprisingly, the edge conduction persists up to 9 T with little change. Finally, this indicates physics beyond simple quantum spin Hall model, including material-specific properties and possibly many-body effects.« less
Unexpected edge conduction in mercury telluride quantum wells under broken time-reversal symmetry
Ma, Eric Yue; Calvo, M. Reyes; Wang, Jing; Lian, Biao; Muhlbauer, Mathias; Brune, Christoph; Cui, Yong -Tao; Lai, Keji; Kundhikanjana, Worasom; Yang, Yongliang; Baenninger, Matthias; Konig, Markus; Ames, Christopher; Buhmann, Hartmut; Leubner, Philipp; Molenkamp, Laurens W.; Zhang, Shou -Cheng; Goldhaber-Gordon, David; Kelly, Michael A.; Shen, Zhi -Xun
2015-05-26
The realization of quantum spin Hall effect in HgTe quantum wells is considered a milestone in the discovery of topological insulators. Quantum spin Hall states are predicted to allow current flow at the edges of an insulating bulk, as demonstrated in various experiments. A key prediction yet to be experimentally verified is the breakdown of the edge conduction under broken time-reversal symmetry. Here we first establish a systematic framework for the magnetic field dependence of electrostatically gated quantum spin Hall devices. We then study edge conduction of an inverted quantum well device under broken time-reversal symmetry using microwave impedance microscopy, and compare our findings to a non-inverted device. At zero magnetic field, only the inverted device shows clear edge conduction in its local conductivity profile, consistent with theory. Surprisingly, the edge conduction persists up to 9 T with little change. Finally, this indicates physics beyond simple quantum spin Hall model, including material-specific properties and possibly many-body effects.
Gâteau, Jérôme; Marsac, Laurent; Pernot, Mathieu; Aubry, Jean-Francois; Tanter, Mickaël; Fink, Mathias
2010-01-01
Brain treatment through the skull with High Intensity Focused Ultrasound (HIFU) can be achieved with multichannel arrays and adaptive focusing techniques such as time-reversal. This method requires a reference signal to be either emitted by a real source embedded in brain tissues or computed from a virtual source, using the acoustic properties of the skull derived from CT images. This non-invasive computational method focuses with precision, but suffers from modeling and repositioning errors that reduce the accessible acoustic pressure at the focus in comparison with fully experimental time-reversal using an implanted hydrophone. In this paper, this simulation-based targeting has been used experimentally as a first step for focusing through an ex vivo human skull at a single location. It has enabled the creation of a cavitation bubble at focus that spontaneously emitted an ultrasonic wave received by the array. This active source signal has allowed 97%±1.1% of the reference pressure (hydrophone-based) to be restored at the geometrical focus. To target points around the focus with an optimal pressure level, conventional electronic steering from the initial focus has been combined with bubble generation. Thanks to step by step bubble generation, the electronic steering capabilities of the array through the skull were improved. PMID:19770084
NASA Astrophysics Data System (ADS)
Queiroz, Raquel; Schnyder, Andreas P.
2015-01-01
Noncentrosymmetric superconductors with strong spin-orbit coupling and the B phase of 3He are possible realizations of topological superconductors with time-reversal symmetry. The nontrivial topology of these time-reversal invariant superconductors manifests itself at the material surface in the form of helical Majorana modes. In this paper, using extensive numerical simulations, we investigate the stability and properties of these Majorana states under strong surface disorder, which influences both bulk and surface states. To characterize the effects of strong disorder, we compute the level spacing statistics and the local density of states of both two- and three-dimensional topological superconductors. The Majorana surface states, which are located in the outermost layers of the superconductor, are protected against weak disorder due to their topological characteristic. Sufficiently strong disorder, on the other hand, partially localizes the surface layers, with a more pronounced effect on states with energies close to the gap than on those with energies close to zero. In particular, we observe that for all disorder strengths and configurations there always exist two extended states at zero energy that can carry thermal current. At the crossover from weak to strong disorder the surface state wave functions and the local density of states show signs of critical delocalization. We find that at this crossover the edge density of states of two-dimensional topological superconductors exhibits a zero-energy divergence, reminiscent of the Dyson singularity of quasi-one-dimensional dirty superconductors.
Unexpected edge conduction in mercury telluride quantum wells under broken time-reversal symmetry
NASA Astrophysics Data System (ADS)
Ma, Eric Yue; Calvo, M. Reyes; Wang, Jing; Lian, Biao; Mühlbauer, Mathias; Brüne, Christoph; Cui, Yong-Tao; Lai, Keji; Kundhikanjana, Worasom; Yang, Yongliang; Baenninger, Matthias; König, Markus; Ames, Christopher; Buhmann, Hartmut; Leubner, Philipp; Molenkamp, Laurens W.; Zhang, Shou-Cheng; Goldhaber-Gordon, David; Kelly, Michael A.; Shen, Zhi-Xun
2015-05-01
The realization of quantum spin Hall effect in HgTe quantum wells is considered a milestone in the discovery of topological insulators. Quantum spin Hall states are predicted to allow current flow at the edges of an insulating bulk, as demonstrated in various experiments. A key prediction yet to be experimentally verified is the breakdown of the edge conduction under broken time-reversal symmetry. Here we first establish a systematic framework for the magnetic field dependence of electrostatically gated quantum spin Hall devices. We then study edge conduction of an inverted quantum well device under broken time-reversal symmetry using microwave impedance microscopy, and compare our findings to a non-inverted device. At zero magnetic field, only the inverted device shows clear edge conduction in its local conductivity profile, consistent with theory. Surprisingly, the edge conduction persists up to 9 T with little change. This indicates physics beyond simple quantum spin Hall model, including material-specific properties and possibly many-body effects.
Optical focusing inside scattering media with time-reversed ultrasound microbubble encoded light
NASA Astrophysics Data System (ADS)
Ruan, Haowen; Jang, Mooseok; Yang, Changhuei
2015-11-01
Focusing light inside scattering media in a freely addressable fashion is challenging, as the wavefront of the scattered light is highly disordered. Recently developed ultrasound-guided wavefront shaping methods are addressing this challenge, albeit with relatively low modulation efficiency and resolution limitations. In this paper, we present a new technique, time-reversed ultrasound microbubble encoded (TRUME) optical focusing, which can focus light with improved efficiency and sub-ultrasound wavelength resolution. This method ultrasonically destroys microbubbles, and measures the wavefront change to compute and render a suitable time-reversed wavefront solution for focusing. We demonstrate that the TRUME technique can create an optical focus at the site of bubble destruction with a size of ~2 μm. We further demonstrate a twofold enhancement in addressable focus resolution in a microbubble aggregate target by exploiting the nonlinear pressure-to-destruction response of the microbubbles. The reported technique provides a deep tissue-focusing solution with high efficiency, resolution, and specificity.
Seismic modeling and reverse-time depth migration by flux-corrected transport
Fei, Tong
1993-01-01
Where the Earth`s subsurface is generally inhomogeneous, lateral and vertical variation in velocity and density should be considered when doing seismic modeling and migration. Finite-difference modeling and reverse-time depth migration based on the full wave equation are approaches that take such variation into account. Here, through a change of dependent variables, the second-order acoustic wave equation is replaced by four first-order partial differential equations. The flux-corrected transport (FCT) method, commonly used in hydrodynamics for shockwave simulation, can then be used in solving these equations. The FCT method offers the opportunity to preserve a broader range of frequencies at lower computational cost than in conventional finite-difference modeling and reverse-time wave extrapolation. Moreover, it is also applicable in circumstances involving discontinuities in the wavefield, where other conventional finite-difference approaches fail. Computed two-dimensional impulse responses and synthetic data indicate that this method can accurately image positions of reflectors with greater than 90-degree dip for variable-velocity media.
Seismic modeling and reverse-time depth migration by flux-corrected transport
Fei, Tong.
1993-01-01
Where the Earth's subsurface is generally inhomogeneous, lateral and vertical variation in velocity and density should be considered when doing seismic modeling and migration. Finite-difference modeling and reverse-time depth migration based on the full wave equation are approaches that take such variation into account. Here, through a change of dependent variables, the second-order acoustic wave equation is replaced by four first-order partial differential equations. The flux-corrected transport (FCT) method, commonly used in hydrodynamics for shockwave simulation, can then be used in solving these equations. The FCT method offers the opportunity to preserve a broader range of frequencies at lower computational cost than in conventional finite-difference modeling and reverse-time wave extrapolation. Moreover, it is also applicable in circumstances involving discontinuities in the wavefield, where other conventional finite-difference approaches fail. Computed two-dimensional impulse responses and synthetic data indicate that this method can accurately image positions of reflectors with greater than 90-degree dip for variable-velocity media.
Iterative Time-Reversed Ultrasonically Encoded Light Focusing in Backscattering Mode
Ruan, Haowen; Jang, Mooseok; Judkewitz, Benjamin; Yang, Changhuei
2014-01-01
The Time-Reversed Ultrasound-Encoded (TRUE) light technique enables noninvasive focusing deep inside scattering media. However, the time-reversal procedure usually has a low signal-to-noise ratio because the intensity of ultrasound-encoded light is intrinsically low. Consequently, the contrast and resolution of TRUE focus is far from ideal, especially in the backscattering geometry, which is more practical in many biomedical applications. To improve the light intensity and resolution of TRUE focus, we developed an iterative TRUE (iTRUE) light focusing technique that employs the TRUE focus itself as a signal source (rather than diffused light) for subsequent TRUE procedures. Importantly, this iTRUE technique enables light focusing in backscattering mode. Here, we demonstrate the concept by focusing light in between scattering layers in a backscattering configuration and show that the light intensity at the focus is progressively enhanced by a factor of ~20. By scanning across a fluorescent bead between these two scattering layers, the focusing resolution in the ultrasound axial and lateral directions was improved ~2-fold and ~3-fold, respectively. We further explored the application of iTRUE in biological samples by focusing light between 1 mm thick chicken tissue and cartilage, and light intensity enhancements of the same order were also observed. PMID:25412687
Precise discussion of time-reversal asymmetries in B-meson decays
Morozumi, Takuya; Okane, Hideaki; Umeeda, Hiroyuki
2015-02-26
BaBar collaboration announced that they observed time reversal (T) asymmetry through B meson system. In the experiment, time dependencies of two distinctive processes, B_ →B¯0 and B¯0 → B_ (– expresses CP value) are compared with each other. In our study, we examine event number difference of these two processes. In contrast to the BaBar asymmetry, the asymmetry of events number includes the overall normalization difference for rates. Time dependence of the asymmetry is more general and it includes terms absent in one used by BaBar collaboration. Both of the BaBar asymmetry and ours are naively thought to be T-oddmore » since two processes compared are related with flipping time direction. We investigate the time reversal transformation property of our asymmetry. Using our notation, one can see that the asymmetry is not precisely a T-odd quantity, taking into account indirect CP and CPT violation of K meson systems. The effect of ϵK is extracted and gives rise to O(10–3) contribution. The introduced parameters are invariant under rephasing of quarks so that the coefficients of our asymmetry are expressed as phase convention independent quantities. Some combinations of the asymmetry enable us to extract parameters for wrong sign decays of Bd meson, CPT violation, etc. As a result, we also study the reason why the T-even terms are allowed to contribute to the asymmetry, and find that several conditions are needed for the asymmetry to be a T-odd quantity.« less
Precise discussion of time-reversal asymmetries in B-meson decays
Morozumi, Takuya; Okane, Hideaki; Umeeda, Hiroyuki
2015-02-26
BaBar collaboration announced that they observed time reversal (T) asymmetry through B meson system. In the experiment, time dependencies of two distinctive processes, B_ →B¯^{0} and B¯^{0} → B_ (– expresses CP value) are compared with each other. In our study, we examine event number difference of these two processes. In contrast to the BaBar asymmetry, the asymmetry of events number includes the overall normalization difference for rates. Time dependence of the asymmetry is more general and it includes terms absent in one used by BaBar collaboration. Both of the BaBar asymmetry and ours are naively thought to be T-odd since two processes compared are related with flipping time direction. We investigate the time reversal transformation property of our asymmetry. Using our notation, one can see that the asymmetry is not precisely a T-odd quantity, taking into account indirect CP and CPT violation of K meson systems. The effect of ^{ ϵ}K is extracted and gives rise to O(10^{–3}) contribution. The introduced parameters are invariant under rephasing of quarks so that the coefficients of our asymmetry are expressed as phase convention independent quantities. Some combinations of the asymmetry enable us to extract parameters for wrong sign decays of B_{d} meson, CPT violation, etc. As a result, we also study the reason why the T-even terms are allowed to contribute to the asymmetry, and find that several conditions are needed for the asymmetry to be a T-odd quantity.
NASA Astrophysics Data System (ADS)
Aspect, Alain
In the early 1980's, observation of a magneto-resistance anomaly in metallic thin films was attributed to the phenomenon of weak localization of electrons and to time-reversal symmetry breaking due to a magnetic field acting upon charged particles. We have observed weak localization of ultra-cold atoms in a 2D configuration, placed in a disordered potential created by a laser speckle. In order to manipulate time-reversal symmetry with our neutral atoms, we take advantage of the slow evolution of our system, and we observe the suppression and revival of weak localization when time reversal symmetry is cancelled and reestablished. References: K. Muller, J. Richard, V. V. Volchkov, V. Denechaud, P. Bouyer, A. Aspect, and V. Josse, ''Suppression and Revival of Weak Localization through Control of Time-Reversal Symmetry,'' Physical Review Letters 114 (20) (2015) and references in. Work supported by the ERC Avanced Grant Quantatop.
Real-Time Reverse Transcription–Polymerase Chain Reaction Assay for SARS-associated Coronavirus
Emery, Shannon L.; Bowen, Michael D.; Newton, Bruce R.; Winchell, Jonas M.; Meyer, Richard F.; Tong, Suxiang; Cook, Byron T.; Holloway, Brian P.; McCaustland, Karen A.; Rota, Paul A.; Bankamp, Bettina; Lowe, Luis E.; Ksiazek, Tom G.; Bellini, William J.; Anderson, Larry J.
2004-01-01
A real-time reverse transcription–polymerase chain reaction (RT-PCR) assay was developed to rapidly detect the severe acute respiratory syndrome–associated coronavirus (SARS-CoV). The assay, based on multiple primer and probe sets located in different regions of the SARS-CoV genome, could discriminate SARS-CoV from other human and animal coronaviruses with a potential detection limit of <10 genomic copies per reaction. The real-time RT-PCR assay was more sensitive than a conventional RT-PCR assay or culture isolation and proved suitable to detect SARS-CoV in clinical specimens. Application of this assay will aid in diagnosing SARS-CoV infection. PMID:15030703
Ma, Cheng; Xu, Xiao; Liu, Yan; Wang, Lihong V.
2014-01-01
The ability to steer and focus light inside scattering media has long been sought for a multitude of applications. To form optical foci inside scattering media, the only feasible strategy at present is to guide photons by using either implanted1 or virtual2–4 guide stars, which can be inconvenient and limits potential applications. Here, we report a scheme for focusing light inside scattering media by employing intrinsic dynamics as guide stars. By time-reversing the perturbed component of the scattered light adaptively, we show that it is possible to focus light to the origin of the perturbation. Using the approach, we demonstrate non-invasive dynamic light focusing onto moving targets and imaging of a time-variant object obscured by highly scattering media. Anticipated applications include imaging and photoablation of angiogenic vessels in tumours as well as other biomedical uses. PMID:25530797
NASA Astrophysics Data System (ADS)
Steinhauer, Loren C.; Milroy, Richard D.; Slough, John T.
1985-03-01
A one-dimensional transport model is developed to simulate the confinement of plasma and magnetic flux in a field-reversed configuration. Given the resistivity, the confinement times can be calculated. Approximate expressions are found which yield the magnitude and gross profile of the resistivity if the confinement times are known. These results are applied to experimental data from experiments, primarily TRX-1, to uncover trends in the transport properties. Several important conclusions emerge. The transport depends profoundly, and inexplicably, on the plasma formation mode. The inferred transport differs in several ways from the predictions of local lower-hybrid-drift turbulence theory. Finally, the gross resistivity exhibits an unusual trend with xs (separatrix radius rs divided by the conducting wall radius rc ), and is peaked near the magnetic axis for certain predictable conditions.
NASA Astrophysics Data System (ADS)
Ha, Jiho; Shin, Sungryul; Shin, Changsoo; Chung, Wookeen
2015-05-01
Because complex mixed waves are typically generated in elastic media, wavefield decomposition is required for such media to obtain migration images accurately. In isotropic media, this is achieved according to the Helmholtz decomposition theorem; in particular, the divergence operator is commonly applied to P-wavefield decomposition. In this study, two types of elastic reverse-time migration algorithms are proposed for decomposition of the P-wavefield without requiring the divergence operator. The first algorithm involves formulation of the stress tensor by spatially differentiated displacement according to the stress-strain relationship and is utilized to construct an imaging condition for the decomposed P-wavefield. We demonstrate this approach through numerical testing. The second algorithm allows us to obtain emphasized interfaces through the application of the absolute value function to decomposed wavefield in imaging condition. Because reverse-time migration can be defined by a zero-lag cross-correlation relationship between the partial-derivative wavefield and the observed wavefield data, we derive the virtual source to construct the partial-derivative wavefield based on a 2D staggered-grid finite-difference modeling method in the time domain. The explicitly computed partial-derivative wavefield from virtual sources with the stress tensor is in agreement with the partial-derivative wavefield directly computed from residual by between with and without a perturbation point in the subsurface. Moreover, the back-propagation technique is used to enhance the computational efficiency. To validate our two types of imaging conditions, numerical tests are conducted. The migration images created according to our imaging conditions can represent the subsurface structure accurately. Thus, we can confirm the feasibility of obtaining migration images of the decomposed P-wavefield without requiring the application of the divergence operator.
Digital Sequences and a Time Reversal-Based Impact Region Imaging and Localization Method
Qiu, Lei; Yuan, Shenfang; Mei, Hanfei; Qian, Weifeng
2013-01-01
To reduce time and cost of damage inspection, on-line impact monitoring of aircraft composite structures is needed. A digital monitor based on an array of piezoelectric transducers (PZTs) is developed to record the impact region of impacts on-line. It is small in size, lightweight and has low power consumption, but there are two problems with the impact alarm region localization method of the digital monitor at the current stage. The first one is that the accuracy rate of the impact alarm region localization is low, especially on complex composite structures. The second problem is that the area of impact alarm region is large when a large scale structure is monitored and the number of PZTs is limited which increases the time and cost of damage inspections. To solve the two problems, an impact alarm region imaging and localization method based on digital sequences and time reversal is proposed. In this method, the frequency band of impact response signals is estimated based on the digital sequences first. Then, characteristic signals of impact response signals are constructed by sinusoidal modulation signals. Finally, the phase synthesis time reversal impact imaging method is adopted to obtain the impact region image. Depending on the image, an error ellipse is generated to give out the final impact alarm region. A validation experiment is implemented on a complex composite wing box of a real aircraft. The validation results show that the accuracy rate of impact alarm region localization is approximately 100%. The area of impact alarm region can be reduced and the number of PZTs needed to cover the same impact monitoring region is reduced by more than a half. PMID:24084123
Digital sequences and a time reversal-based impact region imaging and localization method.
Qiu, Lei; Yuan, Shenfang; Mei, Hanfei; Qian, Weifeng
2013-01-01
To reduce time and cost of damage inspection, on-line impact monitoring of aircraft composite structures is needed. A digital monitor based on an array of piezoelectric transducers (PZTs) is developed to record the impact region of impacts on-line. It is small in size, lightweight and has low power consumption, but there are two problems with the impact alarm region localization method of the digital monitor at the current stage. The first one is that the accuracy rate of the impact alarm region localization is low, especially on complex composite structures. The second problem is that the area of impact alarm region is large when a large scale structure is monitored and the number of PZTs is limited which increases the time and cost of damage inspections. To solve the two problems, an impact alarm region imaging and localization method based on digital sequences and time reversal is proposed. In this method, the frequency band of impact response signals is estimated based on the digital sequences first. Then, characteristic signals of impact response signals are constructed by sinusoidal modulation signals. Finally, the phase synthesis time reversal impact imaging method is adopted to obtain the impact region image. Depending on the image, an error ellipse is generated to give out the final impact alarm region. A validation experiment is implemented on a complex composite wing box of a real aircraft. The validation results show that the accuracy rate of impact alarm region localization is approximately 100%. The area of impact alarm region can be reduced and the number of PZTs needed to cover the same impact monitoring region is reduced by more than a half. PMID:24084123
NASA Astrophysics Data System (ADS)
Sarlis, N. V.; Christopoulos, S.-R. G.; Bemplidaki, M. M.
2015-01-01
The entropy S in natural time as well as the entropy in natural time under time reversal S- have already found useful applications in the physics of complex systems, e.g., in the analysis of electrocardiograms (ECGs). Here, we focus on the complexity measures Λl which result upon considering how the statistics of the time series Δ S≤ft[\\equiv S- S-\\right] changes upon varying the scale l. These scale-specific measures are ratios of the standard deviations σ(Δ S_l) and hence independent of the mean value and the standard deviation of the data. They focus on the different dynamics that appear on different scales. For this reason, they can be considered complementary to other standard measures of heart rate variability in ECG, like SDNN, as well as other complexity measures already defined in natural time. An application to the analysis of ECG —when solely using NN intervals— is presented: We show how Λl can be used to separate ECG of healthy individuals from those suffering from congestive heart failure and sudden cardiac death.
Rakotoarisoa, Ifanila; Fischer, Jeoffrey; Valeau, Vincent; Marx, David; Prax, Christian; Brizzi, Laurent-Emmanuel
2014-11-01
This study focuses on the identification of intermittent aeroacoustic sources in flows by using the time-domain beamforming technique. It is first shown that this technique can be seen as a time-reversal (TR) technique, working with approximate Green functions in the case of a shear flow. Some numerical experiments investigate the case of an array measurement of a generic acoustic pulse emitted in a wind-tunnel flow, with a realistic multi-arm spiral array. The results of the time-domain beamforming successfully match those given by a numerical TR technique over a wide range of flow speeds (reaching the transonic regime). It is shown how the results should be analyzed in a focusing plane parallel to the microphone array in order to estimate the location and emission time of the pulse source. An experimental application dealing with the aeroacoustic radiation of a bluff body in a wind-tunnel flow is also considered, and shows that some intermittent events can be clearly identified in the noise radiation. Time-domain beamforming is then an efficient tool for analyzing intermittent acoustic sources in flows, and is a computationally cheaper alternative to the numerical TR technique, which should be used for complex configurations where the Green function is not available. PMID:25373968
Structure-guided residence time optimization of a dabigatran reversal agent.
Schiele, Felix; van Ryn, Joanne; Litzenburger, Tobias; Ritter, Michael; Seeliger, Daniel; Nar, Herbert
2015-01-01
Novel oral anticoagulants are effective and safe alternatives to vitamin-K antagonists for anticoagulation therapy. However, anticoagulation therapy in general is associated with an elevated risk of bleeding. Idarucizumab is a reversal agent for the direct thrombin inhibitor, dabigatran etexilate (Pradaxa®) and is currently in Phase 3 studies. Here, we report data on the antibody fragment aDabi-Fab2, a putative backup molecule for idarucizumab. Although aDabi-Fab2 completely reversed effects of dabigatran in a rat model in vivo, we observed significantly reduced duration of action compared to idarucizumab. Rational protein engineering, based on the X-ray structure of aDabi-Fab2, led to the identification of mutant Y103W. The mutant had optimized shape complementarity to dabigatran while maintaining an energetically favored hydrogen bond. It displayed increased affinity for dabigatran, mainly driven by a slower off-rate. Interestingly, the increased residence time translated into longer duration of action in vivo. It was thus possible to further enhance the efficacy of aDabi-Fab2 based on rational design, giving it the potential to serve as a back-up candidate for idarucizumab. PMID:26047352
Rethinking fast and slow based on a critique of reaction-time reverse inference
Krajbich, Ian; Bartling, Björn; Hare, Todd; Fehr, Ernst
2015-01-01
Do people intuitively favour certain actions over others? In some dual-process research, reaction-time (RT) data have been used to infer that certain choices are intuitive. However, the use of behavioural or biological measures to infer mental function, popularly known as ‘reverse inference', is problematic because it does not take into account other sources of variability in the data, such as discriminability of the choice options. Here we use two example data sets obtained from value-based choice experiments to demonstrate that, after controlling for discriminability (that is, strength-of-preference), there is no evidence that one type of choice is systematically faster than the other. Moreover, using specific variations of a prominent value-based choice experiment, we are able to predictably replicate, eliminate or reverse previously reported correlations between RT and selfishness. Thus, our findings shed crucial light on the use of RT in inferring mental processes and strongly caution against using RT differences as evidence favouring dual-process accounts. PMID:26135809
Structure-guided residence time optimization of a dabigatran reversal agent
Schiele, Felix; van Ryn, Joanne; Litzenburger, Tobias; Ritter, Michael; Seeliger, Daniel; Nar, Herbert
2015-01-01
Novel oral anticoagulants are effective and safe alternatives to vitamin-K antagonists for anticoagulation therapy. However, anticoagulation therapy in general is associated with an elevated risk of bleeding. Idarucizumab is a reversal agent for the direct thrombin inhibitor, dabigatran etexilate (Pradaxa®) and is currently in Phase 3 studies. Here, we report data on the antibody fragment aDabi-Fab2, a putative backup molecule for idarucizumab. Although aDabi-Fab2 completely reversed effects of dabigatran in a rat model in vivo, we observed significantly reduced duration of action compared to idarucizumab. Rational protein engineering, based on the X-ray structure of aDabi-Fab2, led to the identification of mutant Y103W. The mutant had optimized shape complementarity to dabigatran while maintaining an energetically favored hydrogen bond. It displayed increased affinity for dabigatran, mainly driven by a slower off-rate. Interestingly, the increased residence time translated into longer duration of action in vivo. It was thus possible to further enhance the efficacy of aDabi-Fab2 based on rational design, giving it the potential to serve as a back-up candidate for idarucizumab. PMID:26047352
Candy, J V; Chambers, D H; Robbins, C L; Guidry, B L; Poggio, A J; Dowla, F; Hertzog, C A
2006-01-12
The development of multichannel time-reversal (T/R) processing techniques continues to progress rapidly especially when the need to communicate in a highly reverberative environment becomes critical. The underlying T/R concept is based on time-reversing the Green's function characterizing the uncertain communications channel investigating the deleterious dispersion and multipath effects. In this paper, attention is focused on two major objectives: (1) wideband communications leading to a time reference modulation technique; and (2) multichannel acoustic communications in a tunnel (or cave or pipe) with many obstructions, multipath returns, severe background noise, disturbances, long propagation paths ({approx}180) with disruptions (bends). For this extremely hostile environment, it is shown that multichannel T/R receivers can easily be extended to the wideband designs while demonstrating their performance in both the ''canonical'' stairwell of our previous work as well as a tunnel-like structure. Acoustic information signals are transmitted with an 8-element host or base station array to two client receivers with a significant loss in signal levels due to the propagation environment. In this paper, the results of the new wideband T/R processor and modulation scheme are discussed to demonstrate the overall performance for both high (24-bit) and low (1-bit) bit level analog-to-digital (A/D) converter designs. These results are validated by performing proof-of-principle acoustic communications experiments in air. It is shown that the resulting T/R receivers are capable of extracting the transmitted coded sequence from noisy microphone array measurements with zero-bit error.
NASA Astrophysics Data System (ADS)
Nojima, Kazuhisa; Ge, Sheng; Katayama, Yoshinori; Ueno, Shoogo; Iramina, Keiji
2010-05-01
The aim of this study is to investigate the effect of the stimulus frequency and pulses number of repetitive transcranial magnetic stimulation (rTMS) on the inter-reversal time (IRT) of perceptual reversal on the right superior parietal lobule (SPL). The spinning wheel illusion was used as the ambiguous figures stimulation in this study. To investigate the rTMS effect over the right SPL during perceptual reversal, 0.25 Hz 60 pulse, 1 Hz 60 pulse, 0.5 Hz 120 pulse, 1 Hz 120 pulse, and 1 Hz 240 pulse biphasic rTMS at 90% of resting motor threshold was applied over the right SPL and the right posterior temporal lobe (PTL), respectively. As a control, a no TMS was also conducted. It was found that rTMS on 0.25 Hz 60 pulse and 1 Hz 60 pulse applied over the right SPL caused shorter IRT. In contrast, it was found that rTMS on 1 Hz 240-pulse applied over the right SPL caused longer IRT. On the other hand, there is no significant difference between IRTs when the rTMS on 0.5 Hz 120 pulse and 1 Hz 120 pulse were applied over the right SPL. Therefore, the applying of rTMS over the right SPL suggests that the IRT of perceptual reversal is effected by the rTMS conditions such as the stimulus frequency and the number of pulses.
NASA Astrophysics Data System (ADS)
Horstmann, T.; Harrington, R. M.; Cochran, E. S.
2012-12-01
Frequently, the lack of distinctive phase arrivals makes locating tectonic tremor more challenging than locating earthquakes. Classic location algorithms based on travel times cannot be directly applied because impulsive phase arrivals are often difficult to recognize. Traditional location algorithms are often modified to use phase arrivals identified from stacks of recurring low-frequency events (LFEs) observed within tremor episodes, rather than single events. Stacking the LFE waveforms improves the signal-to-noise ratio for the otherwise non-distinct phase arrivals. In this study, we apply a different method to locate tectonic tremor: a modified time-reversal imaging approach that potentially exploits the information from the entire tremor waveform instead of phase arrivals from individual LFEs. Time reversal imaging uses the waveforms of a given seismic source recorded by multiple seismometers at discrete points on the surface and a 3D velocity model to rebroadcast the waveforms back into the medium to identify the seismic source location. In practice, the method works by reversing the seismograms recorded at each of the stations in time, and back-propagating them from the receiver location individually into the sub-surface as a new source time function. We use a staggered-grid, finite-difference code with 2.5 ms time steps and a grid node spacing of 50 m to compute the rebroadcast wavefield. We calculate the time-dependent curl field at each grid point of the model volume for each back-propagated seismogram. To locate the tremor, we assume that the source time function back-propagated from each individual station produces a similar curl field at the source position. We then cross-correlate the time dependent curl field functions and calculate a median cross-correlation coefficient at each grid point. The highest median cross-correlation coefficient in the model volume is expected to represent the source location. For our analysis, we use the velocity model of
Multipathing Via Three Parameter Common Image Gathers (CIGs) From Reverse Time Migration
NASA Astrophysics Data System (ADS)
Ostadhassan, M.; Zhang, X.
2015-12-01
A noteworthy problem for seismic exploration is effects of multipathing (both wanted or unwanted) caused by subsurface complex structures. We show that reverse time migration (RTM) combined with a unified, systematic three parameter framework that flexibly handles multipathing can be accomplished by adding one more dimension (image time) to the angle domain common image gather (ADCIG) data. RTM is widely used to generate prestack depth migration images. When using the cross-correlation image condition in 2D prestack migration in RTM, the usual practice is to sum over all the migration time steps. Thus all possible wave types and paths automatically contribute to the resulting image, including destructive wave interferences, phase shifts, and other distortions. One reason is that multipath (prismatic wave) contributions are not properly sorted and mapped in the ADCIGs. Also, multipath arrivals usually have different instantaneous attributes (amplitude, phase and frequency), and if not separated, the amplitudes and phases in the final prestack image will not stack coherently across sources. A prismatic path satisfies an image time for it's unique path; Cavalca and Lailly (2005) show that RTM images with multipaths can provide more complete target information in complex geology, as multipaths usually have different incident angles and amplitudes compared to primary reflections. If the image time slices within a cross-correlation common-source migration are saved for each image time, this three-parameter (incident angle, depth, image time) volume can be post-processed to generate separate, or composite, images of any desired subset of the migrated data. Images can by displayed for primary contributions, any combination of primary and multipath contributions (with or without artifacts), or various projections, including the conventional ADCIG (angle vs depth) plane. Examples show that signal from the true structure can be separated from artifacts caused by multiple
Test for time reversal symmetry breaking in superconducting Sr_2RuO_4
NASA Astrophysics Data System (ADS)
Agterberg, Daniel F.; Sigrist, Manfred
1998-03-01
We examine the consequences of different orientations of the magnetic field on the superconductivity in Sr_2RuO4 under the assumption of a doubly degenerate odd-parity pairing state. In particular we show that for the field along one of the crystallographic directions in the basal plane there must exist two superconducting transitions as the field is decreased if the zero-field phase breaks time reversal symmetry. The second transition provides a possible explanation for the second dissipation peak observed in AC susceptibility measurements (K. Yoshida, Y. Maeno, S. Nishizaki, and T. Fujita, J. Phys. Soc. Jpn. 65), 2220 (1996). We also examine under which conditions a square vortex lattice will arise for this pairing state when the field is along the c-axis.
NASA Astrophysics Data System (ADS)
Wu, Binlin; Alrubaiee, Mohammad; Gayen, S. K.
2016-03-01
Time reversal optical tomography (TROT), a recently introduced diffuse optical imaging approach, is used to detect, locate, and obtain cross-section images of tumors inside a "model human breast." The model cancerous breast is assembled as a semi-cylindrical slab of uniform thickness using ex vivo human breast tissues with two pieces of tumors embedded in it. The experimental arrangement used a 750-nm light beam from a Ti:sapphire laser to illuminate an end face (source plane) of the sample in a multi-source probing scheme. A multi-detector signal acquisition scheme measured transmitted light intensity distribution on the other end face (detector plane). The perturbations in light intensity distribution in the detector plane were analyzed using TROT to obtain locations of the tumor pieces in three dimensions and estimate their cross sections. The estimated locations and dimensions of targets are in good agreement with the results of a corroborating magnetic resonance imaging experiment.
Time-reversal-invariance-violating nucleon-nucleon potential in the 1 /Nc expansion
NASA Astrophysics Data System (ADS)
Samart, Daris; Schat, Carlos; Schindler, Matthias R.; Phillips, Daniel R.
2016-08-01
We apply the large-Nc expansion to the time-reversal-invariance-violating (TV) nucleon-nucleon potential. The operator structures contributing to next-to-next-to-leading order in the large-Nc counting are constructed. For the TV and parity-violating case we find a single operator structure at leading order. The TV but parity-conserving potential contains two leading-order terms, which, however, are suppressed by 1 /Nc compared to the parity-violating potential. Comparison with phenomenological potentials, including the chiral effective field theory potential in the TV parity-violating case, leads to large-Nc scaling relations for TV meson-nucleon and nucleon-nucleon couplings.
Spin-Orbit-Free Topological Insulators without Time-Reversal Symmetry
NASA Astrophysics Data System (ADS)
Alexandradinata, A.; Fang, Chen; Gilbert, Matthew J.; Bernevig, B. Andrei
2014-09-01
We explore the 32 crystallographic point groups and identify topological phases of matter with robust surface modes. For n=3,4, and 6 of the Cnv groups, we find the first-known 3D topological insulators without spin-orbit coupling, and with surface modes that are protected only by point groups; i.e., the relevant symmetries are purely crystalline and do not include time reversal. To describe these Cnv systems, we introduce the notions of (a) a halved mirror chirality, an integer invariant which characterizes half-mirror-planes in the 3D Brillouin zone, and (b) a bent Chern number, the traditional Thouless-Kohmoto-Nightingale-den Nijs invariant generalized to bent 2D manifolds. We find that a Weyl semimetallic phase intermediates two gapped phases with distinct halved chiralities. In addition to electronic systems without spin-orbit coupling, our findings also apply to intrinsically spinless systems such as photonic crystals and ultracold atoms.
Thermodynamic glass transition in a spin glass without time-reversal symmetry
Baños, Raquel Alvarez; Cruz, Andres; Fernandez, Luis Antonio; Gil-Narvion, Jose Miguel; Gordillo-Guerrero, Antonio; Guidetti, Marco; Iñiguez, David; Maiorano, Andrea; Marinari, Enzo; Martin-Mayor, Victor; Monforte-Garcia, Jorge; Muñoz Sudupe, Antonio; Navarro, Denis; Parisi, Giorgio; Perez-Gaviro, Sergio; Ruiz-Lorenzo, Juan Jesus; Schifano, Sebastiano Fabio; Seoane, Beatriz; Tarancon, Alfonso; Tellez, Pedro; Tripiccione, Raffaele; Yllanes, David
2012-01-01
Spin glasses are a longstanding model for the sluggish dynamics that appear at the glass transition. However, spin glasses differ from structural glasses in a crucial feature: they enjoy a time reversal symmetry. This symmetry can be broken by applying an external magnetic field, but embarrassingly little is known about the critical behavior of a spin glass in a field. In this context, the space dimension is crucial. Simulations are easier to interpret in a large number of dimensions, but one must work below the upper critical dimension (i.e., in d < 6) in order for results to have relevance for experiments. Here we show conclusive evidence for the presence of a phase transition in a four-dimensional spin glass in a field. Two ingredients were crucial for this achievement: massive numerical simulations were carried out on the Janus special-purpose computer, and a new and powerful finite-size scaling method. PMID:22493229
Modified time reversal imaging of a closed crack based on nonlinear scattering
NASA Astrophysics Data System (ADS)
Blanloeuil, Philippe; Rose, L. R. Francis; Guinto, Jed A.; Veidt, Martin; Wang, Chun H.
2016-04-01
A recent variant of time reversal imaging is used to detect and characterize a closed crack based on both the fundamental and the second harmonic components of the scattered waves in the presence of Contact Acoustic Nonlinearity at the crack interface. A Finite Element model, which includes unilateral contact with Coulomb friction to account for contact between the crack faces, is used to compute the scattered field resulting from the interaction between incident longitudinal plane waves and the crack. The knowledge of the scattering for multiple incident angles constitutes the input for the imaging algorithm. Good reconstruction of the crack is obtained from both harmonic sources, and second harmonic based images also enables one to identify the location of the second harmonic sources along the crack. This first imaging based on the second harmonic also offers potential baseline free detection of closed cracks.
Four-port photonic structures with mirror-time reversal symmetries
NASA Astrophysics Data System (ADS)
Li, Huanan; Thomas, Roney; Ellis, F. M.; Kottos, Tsampikos
2016-07-01
We investigate the transport characteristics of a four-port gyrotropic photonic structure with mirror-time reversal symmetry. The structure consists of two coupled cavities with balanced amplification and attenuation. The cavities are placed on top of a gyrotropic substrate and are coupled to two bus waveguides. Using detail simulations in the microwave domain we demonstrate a strong non-reciprocal intra-guide port transport and an enhanced inter-guide port transmittance. The non-reciprocal features are dramatically amplified in the gain–loss parameter domain where an exceptional point degeneracy, for the associated isolated set-up, occurs. These results are explained theoretically in terms of an equivalent lumped circuit.
NASA Astrophysics Data System (ADS)
Koch, Jens; Houck, A. A.; Girvin, S. M.; Le Hur, Karyn
2010-03-01
Recently, theoretical studies have advertised EM resonator arrays, coherently coupled to artificial atoms (e.g., superconducting qubits) as a new venue for constructing quantum simulators for strongly correlated states of matter [1]. Here, we explore the possibilities of breaking time-reversal symmetry in such interacting photon systems by coupling transmission line resonators via a superconducting circuit. We demonstrate that, given an external magnetic field and a mechanism for breaking particle-hole symmetry, such a circuit can produce complex phases in the hopping amplitudes for photons. Finally, we address the prospects of this scheme for studying new quantum phase transitions in interacting photon systems, and the realization of novel 2D lattices for photons, such as the Kagome lattice. [4pt] [1] M. J. Hartmann, F. G. S. L. Brandão, and M. B. Plenio, Laser & Photonics Review 2, 527 (2008), and references therein.
Acoustic Longitudinal Field NIF Optic Feature Detection Map Using Time-Reversal & MUSIC
Lehman, S K
2006-02-09
We developed an ultrasonic longitudinal field time-reversal and MUltiple SIgnal Classification (MUSIC) based detection algorithm for identifying and mapping flaws in fused silica NIF optics. The algorithm requires a fully multistatic data set, that is one with multiple, independently operated, spatially diverse transducers, each transmitter of which, in succession, launches a pulse into the optic and the scattered signal measured and recorded at every receiver. We have successfully localized engineered ''defects'' larger than 1 mm in an optic. We confirmed detection and localization of 3 mm and 5 mm features in experimental data, and a 0.5 mm in simulated data with sufficiently high signal-to-noise ratio. We present the theory, experimental results, and simulated results.
Depth profile of a time-reversal focus in an elastic solid
Remillieux, Marcel C.; Anderson, Brian E.; Ulrich, T. J.; Le Bas, Pierre -Yves; Payan, Cedric
2015-04-01
The out-of-plane velocity component is focused on the flat surface of an isotropic solid sample using the principle of time reversal. This experiment is often reproduced in the context of nondestructive testing for imaging features near the surface of the sample. However, it is not clear how deep the focus extends into the bulk of the sample and what its profile is. In this paper, this question is answered using both numerical simulations and experimental data. The profiles of the foci are expressed in terms of the wavelengths of the dominant waves, based on the interpretation of the Lamb’s problemmore » and the use of the diffraction limit.« less
Frustration and time-reversal symmetry breaking for Fermi and Bose-Fermi systems
NASA Astrophysics Data System (ADS)
Sacha, Krzysztof; Targońska, Katarzyna; Zakrzewski, Jakub
2012-05-01
The modulation of an optical lattice potential that breaks time-reversal symmetry enables the realization of complex tunneling amplitudes in the corresponding tight-binding model. For a superfluid Fermi gas in a triangular lattice potential with complex tunnelings, the pairing function acquires a complex phase, so the frustrated magnetism of fermions can be realized. Bose-Fermi mixtures of bosonic molecules and unbound fermions in the lattice also show interesting behavior. Due to boson-fermion coupling, the fermions become enslaved by the bosons and the corresponding pairing function takes the complex phase determined by the bosons. In the presence of bosons the Fermi system can reveal both gapped and gapless superfluidity.
Double-Polarized pd Scattering and Test of Time-reversal Invariance
NASA Astrophysics Data System (ADS)
Uzikov, Yuriy
2016-02-01
The integrated proton-deuteron cross section σ˜ for the case of transversal polarization ppy of the proton and tensor polarization Pxz of the deuteron provides a null test signal for time-reversal invariance violating but P-parity conserving effects. The corresponding experiment is planned at COSY to measure the observable σ˜. Here we consider in general case the status of the null-test observable in pd scattering, calculate σ˜ within the Glauber theory of the double-polarized pd scattering at 100 - 1000 MeV and study the contribution of the deuteron S- and D-waves for several type of the T-odd NN interactions.
Iterative Time Reversal Simulation for Selective Focusing in Multi-target Nonlinear Media
NASA Astrophysics Data System (ADS)
Su, Chang; Peng, Zhefan; Lin, Weijun
In High Intensity Focused Ultrasound (HIFU), when multiple targets are present in a linear medium, ultrasound can focus on the strongest target by using an iterative time-reversal(TR) method. However, the validation of iterative TR in nonlinear human tissue still needs to be investigated. In the study, the TR and iterative TR processes are numerically simulated with a finite difference method in two dimension, considering the nonlinear effects. Results show that TR is valid in nonlinear human tissues with some difference in focus accuracy and intensity gain comparing to that in linear media. The nonlinearity of the media increases the intensity gain at the focal point, while the absorption decreases the focal gain and changes the position of the focal spot. Iterative TR works well in nonlinear media and the lobe on the weaker target attenuates more rapidly than in linear media.
NASA Astrophysics Data System (ADS)
Grusdt, Fabian; Abanin, Dmitry; Demler, Eugene
2013-05-01
Recently experiments with ultracold atoms started to explore topological phases in 1D optical lattices. While transport measurements are challenging in these systems, ways to directly measure topological quantum numbers using a combination of Bloch oscillations and Ramsey interferometry have been explored (Atala et al., arXiv:1212.0572). In this talk I will present ways to measure the Z2 topological quantum numbers of two and three dimensional time-reversal invariant (TR) topological insulators. In this case non-Abelian Bloch oscillations can be combined with Ramsey interferometry to map out the topological properties of a given band-structure. Our method is very general and works even in the presence of accidental degeneracies. The applicability of the scheme is discussed for different theoretically proposed implementations of TR topological insulators using ultracold atoms. F. G. is grateful to Harvard University for hospitality and acknowledges financial support from Graduate School Materials Science in Mainz (MAINZ).
Evidence for broken time-reversal symmetry in the superconducting phase of URu2Si2
NASA Astrophysics Data System (ADS)
Schemm, E. R.; Baumbach, R. E.; Tobash, P. H.; Ronning, F.; Bauer, E. D.; Kapitulnik, A.
2015-04-01
Recent experimental and theoretical interest in the superconducting phase of the heavy-fermion material URu2Si2 has led to a number of proposals in which the superconducting order parameter breaks time-reversal symmetry (TRS). In this study we measure the polar Kerr effect (PKE) as a function of temperature for several high-quality single crystals of URu2Si2 . We find an onset of PKE below the superconducting transition that is consistent with a TRS-breaking order parameter. This effect appears to be independent of an additional, possibly extrinsic, PKE generated above the hidden order transition at THO=17.5 K, and contains a structure below Tc suggestive of additional physics within the superconducting state.
Electromagnetic response of time-reversal breaking metallic phases in two dimensions
NASA Astrophysics Data System (ADS)
Chua, Victor; Assawasunthonnet, Wathid; Fradkin, Eduardo
The electromagnetic response of models of nematic non Fermi-liquids previously proposed in Ref. are re-examined using conventional many-body methods. Nematic phases of this model are described by two 2-component real vectors which express the isotropy breaking nematicity in two Fermi-surfaces. Of interest is the time-reversal symmetry breaking nematic phase with a non-vanishing unquantized spontaneous anomalous Hall effect at zero external magnetic fields, and has a geometrical description as a Berry phase. We compare and contrast our results with conventional response calculations with those predicted with the higher-dimensional bosonization method. Finally we present preliminary results on an RG analysis of this system. This work was supported by the Gordon and Betty Moore Foundation.
Observation of broken time-reversal symmetry with Andreev bound state tunneling spectroscopy
NASA Astrophysics Data System (ADS)
Greene, L. H.; Covington, M.; Aprili, M.; Badica, E.; Pugel, D. E.
2000-05-01
Quasiparticle (QP) planar tunneling spectroscopy is used to investigate the density of states (DoS) of YBa 2Cu 3O 7 (YBCO). Temperature, crystallographic orientation, doping, damage and magnetic field dependencies confirm that the observed zero-bias conductance peak (ZBCP) is an Andreev bound state (ABS), an intrinsic property of a d-wave superconducting order parameter (OP) at an interface. In zero applied field, the splitting of the ZBCP below ∼8 K confirms a near-surface phase transition into a superconducting state with spontaneously broken time-reversal symmetry (BTRS). Tunneling into the ABS provides a phase-sensitive spectroscopy that can be used to measure a variety of DoS properties in an unconventional superconductor.
Polar Kerr Effect as Probe for Time-Reversal Symmetry Breaking in Unconventional Superconductors
Kapitulnik, A.
2010-05-26
The search for broken time reversal symmetry (TRSB) in unconventional superconductors intensified in the past year as more systems have been predicted to possess such a state. Following our pioneering study of TRSB states in Sr{sub 2}RuO{sub 4} using magneto-optic probes, we embarked on a systematic study of several other of these candidate systems. The primary instrument for our studies is the Sagnac magneto-optic interferometer, which we recently developed. This instrument can measure magneto-optic Faraday or Kerr effects with an unprecedented sensitivity of 10 nanoradians at temperatures as low as 100 mK. In this paper we review our recent studies of TRSB in several systems, emphasizing the study of the pseudogap state of high temperature superconductors and the inverse proximity effect in superconductor/ferromagnet proximity structures.
Wideband nonlinear time reversal seismo-acoustic method for landmine detection.
Sutin, Alexander; Libbey, Brad; Fillinger, Laurent; Sarvazyan, Armen
2009-04-01
Acoustic and seismic waves provide a method to localize compliant mines by vibrating the top plate and a thin soil layer above the mine. This vibration is mostly linear, but also includes a small nonlinear deviation. The main goal of this paper is to introduce a method of processing that uses phase-inversion to observe nonlinear effects in a wide frequency band. The method extracts a nonlinear part of surface velocity from two similar broadcast signals of opposite sign by summing and cancelling the linear components and leaving the nonlinear components. This phase-inversion method is combined with time reversal focusing to provide increased seismic vibration and enhance the nonlinear effect. The experiments used six loudspeakers in a wood box placed over sand in which inert landmines were buried. The nonlinear surface velocity of the sand with a mine compared to the sand without a mine was greater as compared to a linear technique. PMID:19354365
Studies of parity and time reversal symmetries in neutron scattering from165Ho
NASA Astrophysics Data System (ADS)
Haase, D. G.; Gould, C. R.; Koster, J. E.; Roberson, N. R.; Seagondollar, L. W.; Soderstrum, J. P.; Schneider, M. B.; Zhu, X.
1988-12-01
We describe searches for parity and time reversal violations in the scattering of polarized neutrons from polarized and aligned165Ho targets. We have completed a search with 7.1 and 11.0 MeV neutrons for PoddTodd terms in the elastic scattering forward amplitude of the form s. ( I×K), where s is the neutron spin, I is the target spin and k is the neutron momentum vector. The target was a single crystal of holmium, polarized horizontally along its b axis by a 1 Tesla magnetic field. The neutrons were polarized vertically. Differences in the neutron transmission were measured for neutrons with spins parallel (antiparallel) to I×k. The P,T violating analyzing powers were found to be consistent with zero at the few 10-3 level: ρP,T(7.1 MeV)=-0.88 (±2.02) x 10-3, ρP,T(11.0 MeV)=-0.4 (±2.88) x 10-3. We have also attempted to find enhancements with MeV neutrons in P-violation due to the term s k. We are preparing an aligned target cryostat for investigations of PevenTodd terms {bd(Ik)(I×k)s} in neutron scattering. The target will be a single crystal cylinder of165Ho cooled to 100 mK in a bath of liquid helium and rotated by a shaft from a room temperature stepping motor. The cylinder will be oriented vertically and the alignment ( c) axis oriented horizontally. Warming or rotation of the sample allows one to separate effects that mimic the sought-after time reversal violating term.
NASA Astrophysics Data System (ADS)
Lucia, Umberto
2016-02-01
The balance of forces and processes between the system and the environment and the processes inside the system are the result of the flows of the quanta. Moreover, the transition between two thermodynamic states is the consequence of absorption or emission of quanta, but, during the transition, the entropy variation due to the irreversibility occurs and it breaks any symmetry of time. Consequently, the irreversibility is the result of a transition, a process, an interaction between the system and its environment. This interaction results completely time-irreversible for any real process because of irreversibility. As a consequence, a proof of the third law is obtained proving that the zero temperature state can be achieved only for an infinite work lost for dissipation or in an infinite time. The fundamental role of time both in equilibrium and in non equilibrium analysis is pointed out. Moreover, the non equilibrium temperature is related to the entropy generation and its fluctuation rate; indeed, non-stationary temperature means that the system has not yet attained free energy minimum state, i.e., the maximum entropy state; the consequence is that the zero temperature state can be achieved only for an infinite work lost for dissipation or in an infinite time. In engineering thermodynamics the efficiency is always obtained without any consideration on time, while, here, just the time is introduced as a fundamental quantity of the analysis of non equilibrium states.
Estimation of contributions to population growth: a reverse-time capture-recapture approach
Nichols, J.D.; Hines, J.E.; Lebreton, J.D.; Pradel, R.
2000-01-01
We consider methods for estimating the relative contributions of different demographic components, and their associated vital rates, to population growth. We identify components of the population at time i (including a component for animals not in the population at i). For each such component we ask the following question: 'What is the probability that an individual randomly selected from the population at time i + 1 was a member of this component at i?' The estimation methods for these probabilities ((i) are based on capture-recapture studies of marked animal populations and use reverse-time modeling. We consider several different sampling situations and present example analyses for meadow voles, Microtus pennsylvanicus. The relationship between these (i parameters and elasticities (and other parameters based on projection matrix asymptotics) is noted and discussed. We conclude by suggesting that model-based asymptotics be viewed as demographic theory and that direct estimation approaches be used to test this theory with data from sampled populations with marked animals.
A nodal discontinuous Galerkin method for reverse-time migration on GPU clusters
NASA Astrophysics Data System (ADS)
Modave, A.; St-Cyr, A.; Mulder, W. A.; Warburton, T.
2015-11-01
Improving both accuracy and computational performance of numerical tools is a major challenge for seismic imaging and generally requires specialized implementations to make full use of modern parallel architectures. We present a computational strategy for reverse-time migration (RTM) with accelerator-aided clusters. A new imaging condition computed from the pressure and velocity fields is introduced. The model solver is based on a high-order discontinuous Galerkin time-domain (DGTD) method for the pressure-velocity system with unstructured meshes and multirate local time stepping. We adopted the MPI+X approach for distributed programming where X is a threaded programming model. In this work we chose OCCA, a unified framework that makes use of major multithreading languages (e.g. CUDA and OpenCL) and offers the flexibility to run on several hardware architectures. DGTD schemes are suitable for efficient computations with accelerators thanks to localized element-to-element coupling and the dense algebraic operations required for each element. Moreover, compared to high-order finite-difference schemes, the thin halo inherent to DGTD method reduces the amount of data to be exchanged between MPI processes and storage requirements for RTM procedures. The amount of data to be recorded during simulation is reduced by storing only boundary values in memory rather than on disk and recreating the forward wavefields. Computational results are presented that indicate that these methods are strong scalable up to at least 32 GPUs for a three-dimensional RTM case.
An efficient higher-order PML in WLP-FDTD method for time reversed wave simulation
NASA Astrophysics Data System (ADS)
Wei, Xiao-Kun; Shao, Wei; Ou, Haiyan; Wang, Bing-Zhong
2016-09-01
Derived from a stretched coordinate formulation, a higher-order complex frequency shifted (CFS) perfectly matched layer (PML) is proposed for the unconditionally stable finite-difference time-domain (FDTD) method based on weighted Laguerre polynomials (WLPs). The higher-order PML is implemented with an auxiliary differential equation (ADE) approach. In order to further improve absorbing performance, the parameter values of stretching functions in the higher-order PML are optimized by the multi-objective genetic algorithm (MOGA). The optimal solutions can be chosen from the Pareto front for trading-off between two independent objectives. It is shown in a numerical test that the higher-order PML is efficient in terms of attenuating propagating waves and reducing late time reflections. Moreover, the higher-order PML can be placed very close to the wall when analyzing the channel characteristics of time reversal (TR) waves in a multipath indoor environment. Numerical examples of TR wave propagation demonstrate the availability of the proposed method.
Rapid expansion and pseudo spectral implementation for reverse time migration in VTI media
NASA Astrophysics Data System (ADS)
Pestana, Reynam C.; Ursin, Bjørn; Stoffa, Paul L.
2012-06-01
In isotropic media, we use the scalar acoustic wave equation to perform reverse time migration (RTM) of the recorded pressure wavefield data. In anisotropic media, P- and SV-waves are coupled, and the elastic wave equation should be used for RTM. For computational efficiency, a pseudo-acoustic wave equation is often used. This may be solved using a coupled system of second-order partial differential equations. We solve these using a pseudo spectral method and the rapid expansion method (REM) for the explicit time marching. This method generates a degenerate SV-wave in addition to the P-wave arrivals of interest. To avoid this problem, the elastic wave equation for vertical transversely isotropic (VTI) media can be split into separate wave equations for P- and SV-waves. These separate wave equations are stable, and they can be effectively used to model and migrate seismic data in VTI media where |ɛ - δ| is small. The artifact for the SV-wave has also been removed. The independent pseudo-differential wave equations can be solved one for each mode using the pseudo spectral method for the spatial derivatives and the REM for the explicit time advance of the wavefield. We show numerically stable and high-resolution modeling and RTM results for the pure P-wave mode in VTI media.
A Time-Reversed Reciprocal Method for Detecting High-frequency events in Civil Structures
NASA Astrophysics Data System (ADS)
Kohler, M. D.; Heaton, T. H.
2007-12-01
A new method that uses the properties of wave propagation reciprocity and time-reversed reciprocal Green's functions is presented for identifying high-frequency events that occur within engineered structures. Wave propagation properties of a seismic source in an elastic medium are directly applicable to structural waveform data. The number of structures with dense seismic networks embedded in them is increasing, making it possible to develop new approaches to identifying failure events such as fracturing welds that take advantage of the large number of recordings. The event identification method is based on the hypothesis that a database can be compiled of pre-event, source-receiver Green's functions using experimental sources. For buildings it is assumed that the source-time excitation is a delta function, proportional to the displacement produced at the receiver site. In theory, if all the Green's functions for a structure are known for a complete set of potential failure event locations, forward modeling can be used to compute a range of displacements to identify the correct Green's functions, locations, and source times from the suite of displacements that recorded actual events. The method is applied to a 17-story, steel, moment-frame building using experimentally applied impulse-force hammer sources. The building has an embedded, 72-channel, accelerometer array that is continuously recorded by 24-bit data loggers at 100 and 500 sps. The focus of this particular application is the identification of brittle- fractured welds of beam-column connections.
McPhee, Jeffrey T; Scott, Eric; Levinger, Nancy E; Van Orden, Alan
2011-08-11
Cyanine-3 (Cy3) fluorescent dye molecules confined in sodium di-2-ethylhexyl sulfosuccinate (AOT) reverse micelles were examined using steady-state absorption and emission as well as time-resolved fluorescence spectroscopy to understand the effect of confinement on the spectroscopic properties of the dye. This study explored a wide range of reverse micelle sizes, with hydrodynamic radii ranging from ∼1.7 to ∼5 nm. The relative concentrations of Cy3 and AOT reverse micelles were such that, on average, one dye molecule was present for every 2 × 10(4) to 9 × 10(5) reverse micelles. In the smallest reverse micelles examined, observed changes in the absorption and emission spectra and fluorescence lifetime of the dye molecules indicated H-aggregation of Cy3 into side-by-side dimers. It is hypothesized that this dimerization is governed by the high local concentrations that result from the confinement of the Cy3 in the reverse micelles. What is notable about this study is that this dimer occurs even at overall dye concentrations in the nanomolar range. Such concentrations are too low for aggregation to occur in bulk solution. Hence, the reverse micelles serve as nanocatalysts for this aggregation process. PMID:21761942
Imaging Fracking Zones by Microseismic Reverse Time Migration for Downhole Microseismic Monitoring
NASA Astrophysics Data System (ADS)
Lin, Y.; Zhang, H.
2015-12-01
Hydraulic fracturing is an engineering tool to create fractures in order to better recover oil and gas from low permeability reservoirs. Because microseismic events are generally associated with fracturing development, microseismic monitoring has been used to evaluate the fracking process. Microseismic monitoring generally relies on locating microseismic events to understand the spatial distribution of fractures. For the multi-stage fracturing treatment, fractures created in former stages are strong scatterers in the medium and can induce strong scattering waves on the waveforms for microseismic events induced during later stages. In this study, we propose to take advantage of microseismic scattering waves to image fracking zones by using seismic reverse time migration method. For downhole microseismic monitoring that involves installing a string of seismic sensors in a borehole near the injection well, the observation geometry is actually similar to the VSP (vertical seismic profile) system. For this reason, we adapt the VSP migration method for the common shot gather to the common event gather. Microseismic reverse-time migration method involves solving wave equation both forward and backward in time for each microseismic event. At current stage, the microseismic RTM is based on 2D acoustic wave equation (Zhang and Sun, 2008), solved by the finite-difference method with PML absorbing boundary condition applied to suppress the reflections of artificial boundaries. Additionally, we use local wavefield decomposition instead of cross-correlation imaging condition to suppress the imaging noise. For testing the method, we create a synthetic dataset for a downhole microseismic monitoring system with multiple fracking stages. It shows that microseismic migration using individual event is able to clearly reveal the fracture zone. The shorter distance between fractures and the microseismic event the clearer the migration image is. By summing migration images for many
The detection of flaws in austenitic welds using the decomposition of the time-reversal operator
Cunningham, Laura J.; Mulholland, Anthony J.; Gachagan, Anthony; Harvey, Gerry; Bird, Colin
2016-01-01
The non-destructive testing of austenitic welds using ultrasound plays an important role in the assessment of the structural integrity of safety critical structures. The internal microstructure of these welds is highly scattering and can lead to the obscuration of defects when investigated by traditional imaging algorithms. This paper proposes an alternative objective method for the detection of flaws embedded in austenitic welds based on the singular value decomposition of the time-frequency domain response matrices. The distribution of the singular values is examined in the cases where a flaw exists and where there is no flaw present. A lower threshold on the singular values, specific to austenitic welds, is derived which, when exceeded, indicates the presence of a flaw. The detection criterion is successfully implemented on both synthetic and experimental data. The datasets arising from welds containing a flaw are further interrogated using the decomposition of the time-reversal operator (DORT) method and the total focusing method (TFM), and it is shown that images constructed via the DORT algorithm typically exhibit a higher signal-to-noise ratio than those constructed by the TFM algorithm. PMID:27274683
Tolardo, Aline Lavado; Souza, William Marciel de; Romeiro, Marilia Farignoli; Vieira, Luiz Carlos; Luna, Luciano Kleber de Souza; Henriques, Dyana Alves; Araujo, Jansen de; Siqueira, Carlos Eduardo Hassegawa; Colombo, Tatiana Elias; Aquino, Victor Hugo; Fonseca, Benedito Antonio Lopes da; Bronzoni, Roberta Vieira de Morais; Nogueira, Maurício Lacerda; Durigon, Edison Luiz; Figueiredo, Luiz Tadeu Moraes
2016-06-01
Vesiculoviruses (VSV) are zoonotic viruses that cause vesicular stomatitis disease in cattle, horses and pigs, as well as sporadic human cases of acute febrile illness. Therefore, diagnosis of VSV infections by reliable laboratory techniques is important to allow a proper case management and implementation of strategies for the containment of virus spread. We show here a sensitive and reproducible real-time reverse transcriptase polymerase chain reaction (RT-PCR) for detection and quantification of VSV. The assay was evaluated with arthropods and serum samples obtained from horses, cattle and patients with acute febrile disease. The real-time RT-PCR amplified the Piry, Carajas, Alagoas and Indiana Vesiculovirus at a melting temperature 81.02 ± 0.8ºC, and the sensitivity of assay was estimated in 10 RNA copies/mL to the Piry Vesiculovirus. The viral genome has been detected in samples of horses and cattle, but not detected in human sera or arthropods. Thus, this assay allows a preliminary differential diagnosis of VSV infections. PMID:27276185
NASA Astrophysics Data System (ADS)
Santos, Serge Dos; Farova, Zuzana; Kus, Vaclav; Prevorovsky, Zdenek
2012-05-01
This paper examines possibilities of using Nonlinear Elastic Wave Spectroscopy (NEWS) methods in dental investigations. Themain task consisted in imaging cracks or other degradation signatures located in dentin close to the Enamel-Dentine Junction (EDJ). NEWS approach was investigated experimentally with a new bi-modal acousto-optic set-up based on the chirp-coded nonlinear ultrasonic time reversal (TR) concepts. Complex internal structure of the tooth is analyzed by the TR-NEWS procedure adapted to tomography-like imaging of the tooth damages. Ultrasonic instrumentation with 10 MHz bandwidth has been set together including laser vibrometer used to detect responses of the tooth on its excitation carried out by a contact piezoelectric transducer. Bi-modal TR-NEWS images of the tooth were created before and after focusing, which resulted from the time compression. The polar B-scan of the tooth realized with TR-NEWS procedure is suggested to be applied as a new echodentography imaging.
Implementation of elastic reverse-time migration using wavefield separation in the frequency domain
NASA Astrophysics Data System (ADS)
Chung, Wookeen; Pyun, Sukjoon; Bae, Ho Seuk; Shin, Changsoo; Marfurt, Kurt J.
2012-06-01
Considerable effort has been devoted to the migration of multicomponent data in elastic media with wavefield separation techniques being the most successful. Most of this work has been carried out in the time domain. In this paper, we formulate a multicomponent migration technique in the frequency domain. Reverse-time migration can be viewed as the zero-lag cross-correlation between virtual source and back-propagated wavefields. Cross-correlating the Helmholtz decomposed wavefields rather than directly correlating the vector displacement fields results in sharper, more interpretable images, contaminated by fewer crosstalk artefacts. The end products are separate P and S wave (and if desired, PS and SP) migration images. We test our migration algorithm on synthetic seismic data generated using the SEG/EAGE salt-dome, Overthrust and Marmousi-2 models. We correctly image the location and shape of the target zone for oil exploration using these data sets. Furthermore, we demonstrate that our new migration technique provides good images even when the initial velocity model is only approximate.
Tolardo, Aline Lavado; de Souza, William Marciel; Romeiro, Marilia Farignoli; Vieira, Luiz Carlos; Luna, Luciano Kleber de Souza; Henriques, Dyana Alves; de Araujo, Jansen; Siqueira, Carlos Eduardo Hassegawa; Colombo, Tatiana Elias; Aquino, Victor Hugo; da Fonseca, Benedito Antonio Lopes; Bronzoni, Roberta Vieira de Morais; Nogueira, Maurício Lacerda; Durigon, Edison Luiz; Figueiredo, Luiz Tadeu Moraes
2016-01-01
Vesiculoviruses (VSV) are zoonotic viruses that cause vesicular stomatitis disease in cattle, horses and pigs, as well as sporadic human cases of acute febrile illness. Therefore, diagnosis of VSV infections by reliable laboratory techniques is important to allow a proper case management and implementation of strategies for the containment of virus spread. We show here a sensitive and reproducible real-time reverse transcriptase polymerase chain reaction (RT-PCR) for detection and quantification of VSV. The assay was evaluated with arthropods and serum samples obtained from horses, cattle and patients with acute febrile disease. The real-time RT-PCR amplified the Piry, Carajas, Alagoas and Indiana Vesiculovirus at a melting temperature 81.02 ± 0.8ºC, and the sensitivity of assay was estimated in 10 RNA copies/mL to the Piry Vesiculovirus. The viral genome has been detected in samples of horses and cattle, but not detected in human sera or arthropods. Thus, this assay allows a preliminary differential diagnosis of VSV infections. PMID:27276185
NASA Astrophysics Data System (ADS)
Scaringi, S.; Maccarone, T. J.; Middleton, M.
2014-11-01
We explore the non-linear, high-frequency, aperiodic variability properties in the three cataclysmic variables MV Lyr, KIC 8751494 and V1504 Cyg observed with Kepler, as well as the X-ray binary Cyg X-1 observed with RXTE. This is done through the use of a high-order Fourier statistic called the bispectrum and its related biphase and bicoherence, as well as the time-skewness statistic. We show how all objects display qualitatively similar biphase trends. In particular, all biphase amplitudes are found to be smaller than π/2, suggesting that the flux distributions for all sources are positively skewed on all observed time-scales, consistent with the lognormal distributions expected from the fluctuating accretion disc model. We also find that for all objects, the biphases are positive at frequencies where the corresponding power spectral densities display their high-frequency break. This suggests that the noise-like flaring observed is rising more slowly than it is falling, and thus not time-reversible. This observation is also consistent with the fluctuating accretion disc model. Furthermore, we observe the same qualitative biphase trends in all four objects, where the biphases display a distinct decrease at frequencies below the high-frequency break in their respective power spectral densities. This behaviour can also be observed in the time skewness of all four objects. As far as we are aware, there is no immediate explanation for the observed biphase decreases. The biphase decreases may thus suggest that the fluctuating accretion disc model begins to break down at frequencies below the high-frequency break.
Double plane wave reverse time migration with plane wave Green's function
NASA Astrophysics Data System (ADS)
Zhao, Z.; Sen, M. K.; Stoffa, P. L.
2015-12-01
Reverse time migration (RTM) is effective in obtaining complex subsurface structures from seismic data. By solving the two-way wave equation, RTM can use entire wavefield for imaging. Although powerful computer are becoming available, the conventional pre-stack shot gather RTM is still computationally expensive. Solving forward and backward wavefield propagation for each source location and shot gather is extremely time consuming, especially for large seismic datasets. We present an efficient, accurate and flexible plane wave RTM in the frequency domain where we utilize a compressed plane wave dataset, known as the double plane wave (DPW) dataset. Provided with densely sampled seismic dataset, shot gathers can be decomposed into source and receiver plane wave components with minimal artifacts. The DPW RTM is derived under the Born approximation and utilizes frequency domain plane wave Green's function for imaging. Time dips in the shot profiles can help to estimate the range of plane wave components present in shot gathers. Therefore, a limited number of plane wave Green's functions are needed for imaging. Plane wave Green's functions can be used for imaging both source and receiver plane waves. Source and receiver reciprocity can be used for imaging plane wave components at no cost and save half of the computation time. As a result, the computational burden for migration is substantially reduced. Plane wave components can be migrated independently to recover specific targets with given dips, and ray parameter common image gathers (CIGs) can be generated after migration directly. The ray parameter CIGs can be used to justify the correctness of velocity models. Subsurface anisotropy effects can also be included in our imaging condition, provided with plane wave Green's functions in the anisotropic media.
ERIC Educational Resources Information Center
Mucientes, A. E.; de la Pena, M. A.
2009-01-01
The concentration-time integrals method has been used to solve kinetic equations of parallel-consecutive first-order reactions with a reversible step. This method involves the determination of the area under the curve for the concentration of a given species against time. Computer techniques are used to integrate experimental curves and the method…
Detecting a subsurface cylinder by a Time Reversal MUSIC like method
NASA Astrophysics Data System (ADS)
Solimene, Raffaele; Dell'Aversano, Angela; Leone, Giovanni
2014-05-01
In this contribution the problem of imaging a buried homogeneous circular cylinder is dealt with for a two-dimensional scalar geometry. Though the addressed geometry is extremely simple as compared to real world scenarios, it can be considered of interest for a classical GPR civil engineering applicative context: that is the subsurface prospecting of urban area in order to detect and locate buried utilities. A large body of methods for subsurface imaging have been presented in literature [1], ranging from migration algorithms to non-linear inverse scattering approaches. More recently, also spectral estimation methods, which benefit from sub-array data arrangement, have been proposed and compared in [2].Here a Time Reversal MUSIC (TRM) like method is employed. TRM has been initially conceived to detect point-like scatterers and then generalized to the case of extended scatterers [3]. In the latter case, no a priori information about the scatterers is exploited. However, utilities often can be schematized as circular cylinders. Here, we develop a TRM variant which use this information to properly tailor the steering vector while implementing TRM. Accordingly, instead of a spatial map [3], the imaging procedure returns the scatterer's parameters such as its center position, radius and dielectric permittivity. The study is developed by numerical simulations. First the free-space case is considered in order to more easily introduce the idea and the problem mathematical structure. Then the analysis is extended to the half-space case. In both situations a FDTD forward solver is used to generate the synthetic data. As usual in TRM, a multi-view/multi-static single-frequency configuration is considered and emphasis is put on the role played by the number of available sensors. Acknowledgement This work benefited from networking activities carried out within the EU funded COST Action TU1208 "Civil Engineering Applications of Ground Penetrating Radar." [1] A. Randazzo and R
Jacobs, J.P.
1991-01-01
Optically pumped atomic oscillators driven with a modulated light source have been used to measure the Permanent Electric Dipole Moment (PEDM) of the {sup 199}Hg atom. A nonzero PEDM on the ground state of {sup 199}Hg would by a direct violation of time reversal symmetry. The measurement was obtained by searching for a relative shift in the resonance frequency of the processing nuclear magnetic moments when an externally applied electric field was reversed relative to an externally applied magnetic field. The null result, d({sup 199}Hg) = (.3 {plus minus} 5.7 {plus minus}5.0) {times} 10{sup {minus}28} e{center dot}cm, represents nearly a factor of 15 improvement over previous {sup 199}Hg measurements, and a factor of 25 improvement in statistical uncertainty. When combined with theoretical calculations, the result sets stringent limits on possible sources of time reversal symmetry violation in atomic systems.
Real-Time Reverse Transcription-PCR Assay for Comprehensive Detection of Human Rhinoviruses▿
Lu, Xiaoyan; Holloway, Brian; Dare, Ryan K.; Kuypers, Jane; Yagi, Shigeo; Williams, John V.; Hall, Caroline B.; Erdman, Dean D.
2008-01-01
Human rhinoviruses (HRVs) are important contributors to respiratory disease, but their healthcare burden remains unclear, primarily because of the lack of sensitive, accurate, and convenient means of determining their causal role. To address this, we developed and clinically validated the sensitivity and specificity of a real-time reverse transcription-PCR (RT-PCR) assay targeting the viral 5′ noncoding region defined by sequences obtained from all 100 currently recognized HRV prototype strains and 85 recently circulating field isolates. The assay successfully amplified all HRVs tested and could reproducibly detect 50 HRV RNA transcript copies, with a dynamic range of over 7 logs. In contrast, a quantified RNA transcript of human enterovirus 68 (HEV68) that showed the greatest sequence homology to the HRV primers and probe set was not detected below a concentration of 5 × 105 copies per reaction. Nucleic acid extracts of 111 coded respiratory specimens that were culture positive for HRV or HEV were tested with the HRV real-time RT-PCR assay and by two independent laboratories that used different in-house HRV/HEV RT-PCR assays. Eighty-seven HRV-culture-positive specimens were correctly identified by the real-time RT-PCR assay, and 4 of the 24 HEV-positive samples were positive for HRV. HRV-specific sequences subsequently were identified in these four specimens, suggesting HRV/HEV coinfection in these patients. The assay was successfully applied in an investigation of a coincidental outbreak of HRV respiratory illness among laboratory staff. PMID:18057136
NASA Astrophysics Data System (ADS)
Huang, L.; Huang, H.
2012-12-01
Time-lapse walkaway vertical seismic profiling (VSP) surveys can reveal important reservoir changes caused by CO2 injection. We study the capability of time-lapse walkaway VSP imaging using reverse-time migration in the angle-domain for monitoring CO2 injection. During the Phase II project of the Southwest Regional Partnership on Carbon Sequestration, one baseline and one repeat walkaway VSP surveys were conducted in 2008 and 2009, respectively, at the SACROC enhanced oil recovery (EOR) field for monitoring CO2 injection. The datasets were acquired by Baker Atlas in collaboration with Kinder Morgan. In this study, we apply reverse-time migration in the angle domain to the time-lapse walkaway VSP datasets from the SACROC EOR field, and conduct detailed analyses of common-image gathers. Our migration results demonstrate that reverse-time migration in the angle domain produces images of time-lapse walkaway VSP data with a better image quality compared to those obtained using conventional reverse-time migration. The time-lapse image difference along the bottom of the reservoir where CO2 is injected is much more significant than that along the top of the reservoir. This is partially because we use the same baseline velocity model for migrations of both datasets. The reservoir velocity decreases during CO2 injection, leading to slightly change in the migration image location along the bottom of the reservoir for the repeat VSP data.
Time-reversal acoustic focusing system as a virtual random phased array.
Sarvazyan, Armen; Fillinger, Laurent; Gavrilov, Leonid
2010-04-01
This paper compares the performance of two different systems for dynamic focusing of ultrasonic waves: conventional 2-D phased arrays (PA) and a focusing system based on the principles of time-reversed acoustics (TRA). Focused ultrasound fields obtained in the experiments with the TRA focusing system (TRA FS), which employs a liquid-filled reverberator with 4 piezotransducers attached to its wall, are compared with the focused fields obtained by mathematical simulation of PAs comprised from several tens to several hundreds of elements distributed randomly on the array surface. The experimental and simulated focusing systems had the same aperture and operated at a frequency centered about 600 kHz. Experimental results demonstrated that the TRA FS with a small number of channels can produce complex focused patterns and can steer them with efficiency comparable to that of a PA with hundreds of elements. It is shown that the TRA FS can be realized using an extremely simple means, such as a reverberator made of a water-filled plastic bottle with just a few piezotransducers attached to its walls. PMID:20378444
NASA Astrophysics Data System (ADS)
Budich, Jan Carl; Ardonne, Eddy
2013-10-01
A one-dimensional time-reversal-symmetric topological superconductor (symmetry class DIII) features a single Kramers pair of Majorana bound states at each of its ends. These holographic quasiparticles are non-Abelian anyons that obey Ising-type braiding statistics. In the special case where an additional U(1) spin rotation symmetry is present, this state can be understood as two copies of a Majorana wire in symmetry class D, one copy for each spin block. We present a manifestly gauge invariant construction of the topological invariant for the generic case, i.e., in the absence of any additional symmetries like spin rotation symmetry. Furthermore, we show how the presence of inversion symmetry simplifies the calculation of the topological invariant. The proposed scheme is suitable for the classification of both interacting and disordered systems and allows for a straightforward numerical evaluation of the invariant since it does not rely on fixing a continuous phase relation between Bloch functions. Finally, we apply our method to compute the topological phase diagram of a Rashba wire with competing s-wave and p-wave superconducting pairing terms.
Ultrasound imaging of extended targets using a windowed time-reversal MUSIC method
NASA Astrophysics Data System (ADS)
Labyed, Yassin; Huang, Lianjie
2012-03-01
Time-reversal with Multiple Signal Classification (TR-MUSIC) is an ultrasound imaging algorithm for detecting small targets embedded in a medium. This technique can produce images with subwavelength resolution when the targets are pointlike, and when the number of targets is fewer than the number of transducer elements used to image the medium. In this experimental study, we evaluate the performance of the TR-MUSIC algorithm when the interrogated medium contains extended targets that cannot be considered as point scatterers. We construct tissue-mimicking phantoms embedded with distributed glass spheres. We show that the quality of the phantom images obtained using the TR-MUSIC algorithm decreases with increasing sphere size. However, significant improvement is achieved when the image plane is divided into sub-regions, where each sub-region is imaged separately. The windowed TR-MUSIC algorithm accurately locates the spheres (extended targets), but the images do not provide quantitative information about the shape and reflectivity of the spheres.
Sanderlin, Jamie S; Waser, Peter M; Hines, James E; Nichols, James D
2012-02-01
Metapopulation ecology has historically been rich in theory, yet analytical approaches for inferring demographic relationships among local populations have been few. We show how reverse-time multi-state capture-recapture models can be used to estimate the importance of local recruitment and interpopulation dispersal to metapopulation growth. We use 'contribution metrics' to infer demographic connectedness among eight local populations of banner-tailed kangaroo rats, to assess their demographic closure, and to investigate sources of variation in these contributions. Using a 7 year dataset, we show that: (i) local populations are relatively independent demographically, and contributions to local population growth via dispersal within the system decline with distance; (ii) growth contributions via local survival and recruitment are greater for adults than juveniles, while contributions involving dispersal are greater for juveniles; (iii) central populations rely more on local recruitment and survival than peripheral populations; (iv) contributions involving dispersal are not clearly related to overall metapopulation density; and (v) estimated contributions from outside the system are unexpectedly large. Our analytical framework can classify metapopulations on a continuum between demographic independence and panmixia, detect hidden population growth contributions, and make inference about other population linkage forms, including rescue effects and source-sink structures. Finally, we discuss differences between demographic and genetic population linkage patterns for our system. PMID:21697173
Performance analysis of spatial multiplexing MIMO system with time reversal technology
NASA Astrophysics Data System (ADS)
Shrestha, Sanjeeb; Dou, Zheng; Khan, Zayed
2013-03-01
This paper deals with the performance analysis of Spatial Multiplexing(SM) multiple input multiple output (MIMO) system with time reversal (TR) technology. Focus is given on the spatial multiplexing gain of MIMO than the diversity gain aspect with the notion that the idea of diversity is inseparably associated with the uncertainty of the channel. If transmitter knows Channel State Information (CSI) before transmission, potential benefits can be harvested. TR is used here, to provide Channel State Information (CSI) at the transmitter before transmission. With the features of temporal and spatial focusing, TR not only can provide immunity against fading for spatially multiplexed data stream but also help boost its Multi Stream Interference (MSI) limited performance by mitigating it. The performance analysis of SM-MIMOTR is carried out with the aim of average minimum error probability for quantity of interest data rate. The interest date rate is 19.07 Mbps, where as the average minimum error probably is set to be that of Single Input Multi Output (SIMO) maximum ratio combining system (MRC). BER of Single Input Single Output (SISO) system is also simulated for making comparison tangible. Simulation study shows that Bit Error Rate (BER) performance of the system with the data rate of interest nearly coincides with that of SIMO system at the range of 10-15db and is better than SISO in all simulated Eb/No points. Additionally, from the standpoint of tread off curve, between diversity gain and spatial multiplexing gain, the non linearity nature still holds.
Laser ultrasound and simulated time reversal on bulk waves for non destructive control
NASA Astrophysics Data System (ADS)
Diot, G.; Walaszek, H.; Kouadri-David, A.; Guégan, S.; Flifla, J.
2014-06-01
Laser welding of aluminium generally creates embedded welding defects, such as porosities or cracks. Non Destructive Inspection (NDI) after processing may ensure an acceptable weld quality by defect detection. Nowadays, NDI techniques used to control the inside of a weld are mainly limited to X-Rays or ultrasonics. The current paper describes the use of a Laser Ultrasound (LU) technique to inspect porosities in 2 and 4-mm thick sheet lap welds. First experimentations resulted in the detection of 0.5-mm drilled holes in bulk aluminium sheets. The measurement of the depth of these defects is demonstrated too. Further experimentations shows the applicability of the LU technique to detect porosities in aluminium laser welds. However, as the interpretation of raw measures is limiting the detection capacity of this technique, we developed a signal processing using Time-Reversal capabilities to enhance detection capacities. Furthermore, the signal processing output is a geometrical image of the material's inner state, increasing the ease of interpretation. It is based on a mass-spring simulation which enables the back-propagation of the acquired ultrasound signal. The spring-mass simulation allows the natural generation of all the different sound waves and thus enables the back-propagation of a raw signal without any need of filtering or wave identification and extraction. Therefore the signal processing uses the information contained in the compression wave as well as in the shear wave.
Pseudo-time-reversal symmetry and topological edge states in two-dimensional acoustic crystals.
Mei, Jun; Chen, Zeguo; Wu, Ying
2016-01-01
We propose a simple two-dimensional acoustic crystal to realize topologically protected edge states for acoustic waves. The acoustic crystal is composed of a triangular array of core-shell cylinders embedded in a water host. By utilizing the point group symmetry of two doubly degenerate eigenstates at the Γ point, we can construct pseudo-time-reversal symmetry as well as pseudo-spin states in this classical system. We develop an effective Hamiltonian for the associated dispersion bands around the Brillouin zone center, and find the inherent link between the band inversion and the topological phase transition. With numerical simulations, we unambiguously demonstrate the unidirectional propagation of acoustic edge states along the interface between a topologically nontrivial acoustic crystal and a trivial one, and the robustness of the edge states against defects with sharp bends. Our work provides a new design paradigm for manipulating and transporting acoustic waves in a topologically protected manner. Technological applications and devices based on our design are expected in various frequency ranges of interest, spanning from infrasound to ultrasound. PMID:27587311
An experimental application of aeroacoustic time-reversal to the Aeolian tone.
Mimani, A; Prime, Z; Moreau, D J; Doolan, C J
2016-02-01
This paper presents an experimental application of the aeroacoustic time-reversal (TR) source localization technique for studying flow-induced noise problems and compares the TR results with those obtained using conventional beamforming (CB). Experiments were conducted in an anechoic wind tunnel for the benchmark test-case of a full-span circular cylinder located in subsonic cross-flow wherein the far-field acoustic pressure was sampled using two line arrays (LAs) of microphones located above and below the cylinder. The source map obtained using the signals recorded at the two LAs without modeling the reflective surfaces of the contraction-outlet and cylinder during TR simulations revealed the lift-dipole nature of aeroacoustic source generated at the Aeolian tone; however, it indicates an error of 3/20 of Aeolian tone wavelength in the predicted location. Modeling the reflective contraction-outlet during TR was shown to improve the focal-resolution of the source and reduce side-lobe levels, especially in the low-frequency range. The experimental TR results were shown to be comparable to (a) the simulation results of an idealized dipole at the cylinder location in wind-tunnel flow and (b) that obtained by monopole and dipole CB, thereby demonstrating the suitability of TR method as a diagnostic tool to analyze flow-induced noise generation mechanism. PMID:26936557
Time-reversal constraint limits unidirectional photon emission in slow-light photonic crystals.
Lang, Ben; Beggs, Daryl M; Oulton, Ruth
2016-08-28
Photonic crystal waveguides are known to support C-points-point-like polarization singularities with local chirality. Such points can couple with dipole-like emitters to produce highly directional emission, from which spin-photon entanglers can be built. Much is made of the promise of using slow-light modes to enhance this light-matter coupling. Here we explore the transition from travelling to standing waves for two different photonic crystal waveguide designs. We find that time-reversal symmetry and the reciprocal nature of light places constraints on using C-points in the slow-light regime. We observe two distinctly different mechanisms through which this condition is satisfied in the two waveguides. In the waveguide designs, we consider a modest group velocity of vg≈c/10 is found to be the optimum for slow-light coupling to the C-points.This article is part of the themed issue 'Unifying physics and technology in light of Maxwell's equations'. PMID:27458258
Sanderlin, J.S.; Waser, P.M.; Hines, J.E.; Nichols, J.D.
2012-01-01
Metapopulation ecology has historically been rich in theory, yet analytical approaches for inferring demographic relationships among local populations have been few. We show how reverse-time multi-state capture-recapture models can be used to estimate the importance of local recruitment and interpopulation dispersal to metapopulation growth. We use 'contribution metrics' to infer demographic connectedness among eight local populations of banner-tailed kangaroo rats, to assess their demographic closure, and to investigate sources of variation in these contributions. Using a 7 year dataset, we show that: (i) local populations are relatively independent demographically, and contributions to local population growth via dispersal within the system decline with distance; (ii) growth contributions via local survival and recruitment are greater for adults than juveniles, while contributions involving dispersal are greater for juveniles; (iii) central populations rely more on local recruitment and survival than peripheral populations; (iv) contributions involving dispersal are not clearly related to overall metapopulation density; and (v) estimated contributions from outside the system are unexpectedly large. Our analytical framework can classify metapopulations on a continuum between demographic independence and panmixia, detect hidden population growth contributions, and make inference about other population linkage forms, including rescue effects and source-sink structures. Finally, we discuss differences between demographic and genetic population linkage patterns for our system. ?? 2011 The Royal Society.
Development and Evaluation of an Enterovirus D68 Real-Time Reverse Transcriptase PCR Assay
Wylie, Todd N.; Wylie, Kristine M.; Buller, Richard S.; Cannella, Maria
2015-01-01
We have developed and evaluated a real-time reverse transcriptase PCR (RT-PCR) assay for the detection of human enterovirus D68 (EV-D68) in clinical specimens. This assay was developed in response to the unprecedented 2014 nationwide EV-D68 outbreak in the United States associated with severe respiratory illness. As part of our evaluation of the outbreak, we sequenced and published the genome sequence of the EV-D68 virus circulating in St. Louis, MO. This sequence, along with other GenBank sequences from past EV-D68 occurrences, was used to computationally select a region of EV-D68 appropriate for targeting in a strain-specific RT-PCR assay. The RT-PCR assay amplifies a segment of the VP1 gene, with an analytic limit of detection of 4 copies per reaction, and it was more sensitive than commercially available assays that detect enteroviruses and rhinoviruses without distinguishing between the two, including three multiplex respiratory panels approved for clinical use by the FDA. The assay did not detect any other enteroviruses or rhinoviruses tested and did detect divergent strains of EV-D68, including the first EV-D68 strain (Fermon) identified in California in 1962. This assay should be useful for identifying and studying current and future outbreaks of EV-D68 viruses. PMID:26063859
Time reversed test particle calculations at Titan, based on CAPS-IMS measurements
NASA Astrophysics Data System (ADS)
Bebesi, Zsofia; Erdos, Geza; Szego, Karoly; Young, David T.
2013-04-01
We used the theoretical approach of Kobel and Flückiger (1994) to construct a magnetic environment model in the vicinity of Titan - with the exception of placing the bow shock (which is not present at Titan) into infinity. The model has 4 free parameters to calibrate the shape and orientation of the field. We investigate the CAPS-IMS Singles data to calculate/estimate the location of origin of the detected cold ions at Titan, and we also use the measurements of the onboard Magnetometer to set the parameters of the model magnetic field. A 4th order Runge-Kutta method is applied to calculate the test particle trajectories in a time reversed scenario, in the curved magnetic environment. Several different ion species can be tracked by the model along their possible trajectories, as a first approach we considered three particle groups (1, 2 and 16 amu ions). In this initial study we show the results for some thoroughly discussed flybys like TA, TB and T5, but we consider more recent tailside encounters as well. Reference: Kobel, E. and E.O. Flückiger, A model of the steady state magnetic field in the magnetosheath, JGR 99, Issue A12, 23617, 1994
NASA Astrophysics Data System (ADS)
Yan, Zhongbo; Wan, Shaolong
2016-02-01
Tunneling magnetoresistance between two ferrromagnets is an issue of fundamental importance in spintronics. In this work, we show that tunneling magnetoresistance can also emerge in junctions composed of ferromagnets and time-reversal invariant topological superconductors without spin-rotation symmetry. Here the physical origin is that when the spin-polarization direction of an injected electron from the ferromagnet lies in the same plane of the spin-polarization direction of Majorana zero modes, the electron will undergo a perfect spin-equal Andreev reflection, while injected electrons with other spin-polarization directions will be partially Andreev reflected and partially normal reflected, which consequently has a lower conductance, and therefore, the magnetoresistance effect emerges. Compared to conventional magnetic tunnel junctions, an unprecedented advantage of the junctions studied here is that arbitrary high tunneling magnetoresistance can be obtained even when the magnetization of the ferromagnets are weak and the insulating tunneling barriers are featureless. Our findings provide a new fascinating mechanism to obtain high tunneling magnetoresistance.
Time reversal optical tomography locates fluorescent targets in a turbid medium
NASA Astrophysics Data System (ADS)
Wu, Binlin; Cai, W.; Gayen, S. K.
2013-03-01
A fluorescence optical tomography approach that extends time reversal optical tomography (TROT) to locate fluorescent targets embedded in a turbid medium is introduced. It uses a multi-source illumination and multi-detector signal acquisition scheme, along with TR matrix formalism, and multiple signal classification (MUSIC) to construct pseudo-image of the targets. The samples consisted of a single or two small tubes filled with water solution of Indocyanine Green (ICG) dye as targets embedded in a 250 mm × 250 mm × 60 mm rectangular cell filled with Intralipid-20% suspension as the scattering medium. The ICG concentration was 1μM, and the Intralipid-20% concentration was adjusted to provide ~ 1-mm transport length for both excitation wavelength of 790 nm and fluorescence wavelength around 825 nm. The data matrix was constructed using the diffusely transmitted fluorescence signals for all scan positions, and the TR matrix was constructed by multiplying data matrix with its transpose. A pseudo spectrum was calculated using the signal subspace of the TR matrix. Tomographic images were generated using the pseudo spectrum. The peaks in the pseudo images provided locations of the target(s) with sub-millimeter accuracy. Concurrent transmission TROT measurements corroborated fluorescence-TROT findings. The results demonstrate that TROT is a fast approach that can be used to obtain accurate three-dimensional position information of fluorescence targets embedded deep inside a highly scattering medium, such as, a contrast-enhanced tumor in a human breast.
Locating the source of diffusion in complex networks by time-reversal backward spreading
NASA Astrophysics Data System (ADS)
Shen, Zhesi; Cao, Shinan; Wang, Wen-Xu; Di, Zengru; Stanley, H. Eugene
2016-03-01
Locating the source that triggers a dynamical process is a fundamental but challenging problem in complex networks, ranging from epidemic spreading in society and on the Internet to cancer metastasis in the human body. An accurate localization of the source is inherently limited by our ability to simultaneously access the information of all nodes in a large-scale complex network. This thus raises two critical questions: how do we locate the source from incomplete information and can we achieve full localization of sources at any possible location from a given set of observable nodes. Here we develop a time-reversal backward spreading algorithm to locate the source of a diffusion-like process efficiently and propose a general locatability condition. We test the algorithm by employing epidemic spreading and consensus dynamics as typical dynamical processes and apply it to the H1N1 pandemic in China. We find that the sources can be precisely located in arbitrary networks insofar as the locatability condition is assured. Our tools greatly improve our ability to locate the source of diffusion in complex networks based on limited accessibility of nodal information. Moreover, they have implications for controlling a variety of dynamical processes taking place on complex networks, such as inhibiting epidemics, slowing the spread of rumors, pollution control, and environmental protection.
Development and Evaluation of an Enterovirus D68 Real-Time Reverse Transcriptase PCR Assay.
Wylie, Todd N; Wylie, Kristine M; Buller, Richard S; Cannella, Maria; Storch, Gregory A
2015-08-01
We have developed and evaluated a real-time reverse transcriptase PCR (RT-PCR) assay for the detection of human enterovirus D68 (EV-D68) in clinical specimens. This assay was developed in response to the unprecedented 2014 nationwide EV-D68 outbreak in the United States associated with severe respiratory illness. As part of our evaluation of the outbreak, we sequenced and published the genome sequence of the EV-D68 virus circulating in St. Louis, MO. This sequence, along with other GenBank sequences from past EV-D68 occurrences, was used to computationally select a region of EV-D68 appropriate for targeting in a strain-specific RT-PCR assay. The RT-PCR assay amplifies a segment of the VP1 gene, with an analytic limit of detection of 4 copies per reaction, and it was more sensitive than commercially available assays that detect enteroviruses and rhinoviruses without distinguishing between the two, including three multiplex respiratory panels approved for clinical use by the FDA. The assay did not detect any other enteroviruses or rhinoviruses tested and did detect divergent strains of EV-D68, including the first EV-D68 strain (Fermon) identified in California in 1962. This assay should be useful for identifying and studying current and future outbreaks of EV-D68 viruses. PMID:26063859
NASA Astrophysics Data System (ADS)
Lamberti, Alfredo; Semperlotti, Fabio
2013-12-01
Closing delaminations in composite laminated structures exhibit a nonlinear dynamic response when excited by high frequency elastic waves. The contact acoustic nonlinear effects taking place at the damage interface act as a mechanism of energy redistribution from the driving frequency to the nonlinear harmonic frequencies. In this paper, we extend the concept of nonlinear structural intensity (NSI) to the analysis of closing delaminations in composite laminated plates. NSI is calculated using a method based on a combination of finite element and finite difference techniques, which is suitable for processing both numerical and experimental data. NSI is proven to be an effective metric to identify the presence and location of closing delaminations. The highly directional nature of orthotropic composites results in vibrational energy propagating in a different direction from that of the initial elastic wave. This aspect reduces the ability to effectively interrogate the damage and, therefore, the sensitivity to the damage. The time reversal mirror technique is explored as a possible approach to overcome the effect of the material directionality and increase the ability to interrogate the damage. Numerical simulations show that this technique is able to overcome the material directionality and to drastically enhance the ability to interrogate the damage.
Time reversal ultrasound focusing to a point away from the beacon location
NASA Astrophysics Data System (ADS)
Sinelnikov, Yegor; Sutin, Alexander; Gandhi, Gaurav; Sarvazyan, Armen
2012-10-01
In percutaneous procedures there is often a need to focus therapeutic ultrasound to a predefined area without affecting surrounding tissues. Focusing based on Time Reversal Acoustics (TRA) principles constitutes a promising approach for generating high intensity ultrasound field tailored to the shape of the predefined area. Conventional TRA technique enables ultrasound focusing only at a site, where there is an ultrasound beacon, e.g. piezo-transducer mounted at the tip of a catheter. We developed a method of steering the focus away from the beacon location. The method is based on the measurements of impulse response (IR) in several reference points and calculating virtual IRs for the points outside the reference beacon location. The IR for the point away from the beacon is constructed based on mathematical extrapolation of the measured reference IRs frequency spectra, particularly phases. The effectiveness of extrapolated TRA focusing is explored experimentally and by computer simulation. Potential applications include ultrasounda-ssisted drug delivery, artery recanalization and tumor ablation.
Locating the source of diffusion in complex networks by time-reversal backward spreading.
Shen, Zhesi; Cao, Shinan; Wang, Wen-Xu; Di, Zengru; Stanley, H Eugene
2016-03-01
Locating the source that triggers a dynamical process is a fundamental but challenging problem in complex networks, ranging from epidemic spreading in society and on the Internet to cancer metastasis in the human body. An accurate localization of the source is inherently limited by our ability to simultaneously access the information of all nodes in a large-scale complex network. This thus raises two critical questions: how do we locate the source from incomplete information and can we achieve full localization of sources at any possible location from a given set of observable nodes. Here we develop a time-reversal backward spreading algorithm to locate the source of a diffusion-like process efficiently and propose a general locatability condition. We test the algorithm by employing epidemic spreading and consensus dynamics as typical dynamical processes and apply it to the H1N1 pandemic in China. We find that the sources can be precisely located in arbitrary networks insofar as the locatability condition is assured. Our tools greatly improve our ability to locate the source of diffusion in complex networks based on limited accessibility of nodal information. Moreover, they have implications for controlling a variety of dynamical processes taking place on complex networks, such as inhibiting epidemics, slowing the spread of rumors, pollution control, and environmental protection. PMID:27078360
Prestack reverse time migration for 3D marine reflection seismic data
Jang, Seonghyung; Kim, Taeyoun
2015-03-10
Prestack reverse time migration (RTM) is a method for imaging the subsurface using the inner product of wavefield extrapolation in shot domain and in receiver domain. It is well known that RTM is better for preserving amplitudes and phases than other prestack migrations. Since 3D seismic data is huge data volume and it needs heavy computing works, it requires parallel computing in order to have a meaningful depth image of the 3D subsurface. We implemented a parallelized version of 3D RTM for prestack depth migration. The results of numerical example for 3D SEG/EAGE salt model showed good agreement with the original geological model. We applied RTM to offshore 3D seismic reflection data. The study area is 12 × 25 km with 120 survey lines. Shot and receiver spacing is 25 m and 12.5 m. The line spacing is 100 m. Shot gathers were preprocessed to enhance signal to noise ratio and velocity model was calculated from conventional stack velocity. Both of them were used to obtain 3D image using RTM. The results show reasonable subsurface image.
Quantum anomalous Hall effect in time-reversal-symmetry breaking topological insulators.
Chang, Cui-Zu; Li, Mingda
2016-03-31
The quantum anomalous Hall effect (QAHE), the last member of Hall family, was predicted to exhibit quantized Hall conductivity σ(yx) = e2/h without any external magnetic field. The QAHE shares a similar physical phenomenon with the integer quantum Hall effect (QHE), whereas its physical origin relies on the intrinsic topological inverted band structure and ferromagnetism. Since the QAHE does not require external energy input in the form of magnetic field, it is believed that this effect has unique potential for applications in future electronic devices with low-power consumption. More recently, the QAHE has been experimentally observed in thin films of the time-reversal symmetry breaking ferromagnetic (FM) topological insulators (TI), Cr- and V- doped (Bi,Sb)2Te3. In this topical review, we review the history of TI based QAHE, the route to the experimental observation of the QAHE in the above two systems, the current status of the research of the QAHE, and finally the prospects for future studies. PMID:26934535
NASA Astrophysics Data System (ADS)
Tafti, Fazel; Gibson, Quinn; Kushwaha, Satya; Haldolaarachchige, Neel; Cava, Robert; Cava Lab Team
Time reversal symmetry protects the metallic surface modes of topological insulators (TIs). The transport signature of robust metallic surface modes of TIs is a plateau that arrests the exponential divergence of the insulating bulk with decreasing temperature. This universal behavior is observed in all TI candidates ranging from Bi2Te2Se to SmB6. Recently, several topological semimetals (TSMs) have been found that exhibit extreme magnetoresistance (XMR) and TI universal resistivity behavior revealed only when breaking TRS, a regime where TIs theoretically cease to exist. Amongst these new materials, TaAs and NbP are nominated for Weyl semimetal due to their lack of inversion symmetry, Cd3As2 is nominated for Dirac semimetal due to linear band crossing, and WTe2 is nominated for resonant compensated semimetal due to perfect electron-hole symmetry. Here we introduce LaSb, a simple rock-salt structure material without broken inversion symmetry, without perfect linear band crossing, and without perfect electron-hole symmetry. Yet LaSb portrays all the exotic field induced behaviors of the aforementioned semimetals. It shows the universal TI resistivity with a plateau at 15 K, revealed by a magnetic field, ultrahigh mobility of carriers, quantum oscillations with 2D Fermi surface, and XMR of about one million percent. Due to its dramatic simplicity, LaSb is the ideal model system to formulate a theoretical understanding of the exotic consequences of breaking TRS in TSMs.
Pseudo-time-reversal symmetry and topological edge states in two-dimensional acoustic crystals
Mei, Jun; Chen, Zeguo; Wu, Ying
2016-01-01
We propose a simple two-dimensional acoustic crystal to realize topologically protected edge states for acoustic waves. The acoustic crystal is composed of a triangular array of core-shell cylinders embedded in a water host. By utilizing the point group symmetry of two doubly degenerate eigenstates at the Γ point, we can construct pseudo-time-reversal symmetry as well as pseudo-spin states in this classical system. We develop an effective Hamiltonian for the associated dispersion bands around the Brillouin zone center, and find the inherent link between the band inversion and the topological phase transition. With numerical simulations, we unambiguously demonstrate the unidirectional propagation of acoustic edge states along the interface between a topologically nontrivial acoustic crystal and a trivial one, and the robustness of the edge states against defects with sharp bends. Our work provides a new design paradigm for manipulating and transporting acoustic waves in a topologically protected manner. Technological applications and devices based on our design are expected in various frequency ranges of interest, spanning from infrasound to ultrasound. PMID:27587311
Time reversal for localization of sources of infrasound signals in a windy stratified atmosphere.
Lonzaga, Joel B
2016-06-01
Time reversal is used for localizing sources of recorded infrasound signals propagating in a windy, stratified atmosphere. Due to the convective effect of the background flow, the back-azimuths of the recorded signals can be substantially different from the source back-azimuth, posing a significant difficulty in source localization. The back-propagated signals are characterized by negative group velocities from which the source back-azimuth and source-to-receiver (STR) distance can be estimated using the apparent back-azimuths and trace velocities of the signals. The method is applied to several distinct infrasound arrivals recorded by two arrays in the Netherlands. The infrasound signals were generated by the Buncefield oil depot explosion in the U.K. in December 2005. Analyses show that the method can be used to substantially enhance estimates of the source back-azimuth and the STR distance. In one of the arrays, for instance, the deviations between the measured back-azimuths of the signals and the known source back-azimuth are quite large (-1° to -7°), whereas the deviations between the predicted and known source back-azimuths are small with an absolute mean value of <1°. Furthermore, the predicted STR distance is off only by <5% of the known STR distance. PMID:27369127
Discrimination of time-reversed harmonic complexes by normal-hearing and hearing-impaired listeners.
Lauer, Amanda M; Molis, Michelle; Leek, Marjorie R
2009-12-01
Normal-hearing (NH) listeners and hearing-impaired (HI) listeners detected and discriminated time-reversed harmonic complexes constructed of equal-amplitude harmonic components with fundamental frequencies (F0s) ranging from 50 to 800 Hz. Component starting phases were selected according to the positive and negative Schroeder-phase algorithms to produce within-period frequency sweeps with relatively flat temporal envelopes. Detection thresholds were not affected by component starting phases for either group of listeners. At presentation levels of 80 dB SPL, NH listeners could discriminate the two waveforms nearly perfectly when the F0s were less than 300-400 Hz but fell to chance performance for higher F0s. HI listeners performed significantly poorer, with reduced discrimination at several of the F0s. In contrast, at a lower presentation level meant to nearly equate sensation levels for the two groups, NH listeners' discrimination was poorer than HI listeners at most F0s. Roving presentation levels had little effect on performance by NH listeners but reduced performance by HI listeners. The differential impact of roving level suggests a weaker perception of timbre differences and a greater susceptibility to the detrimental effects of experimental uncertainty in HI listeners. PMID:19705203
Quantum anomalous Hall effect in time-reversal-symmetry breaking topological insulators
NASA Astrophysics Data System (ADS)
Chang, Cui-Zu; Li, Mingda
2016-03-01
The quantum anomalous Hall effect (QAHE), the last member of Hall family, was predicted to exhibit quantized Hall conductivity {σyx}=\\frac{{{e}2}}{h} without any external magnetic field. The QAHE shares a similar physical phenomenon with the integer quantum Hall effect (QHE), whereas its physical origin relies on the intrinsic topological inverted band structure and ferromagnetism. Since the QAHE does not require external energy input in the form of magnetic field, it is believed that this effect has unique potential for applications in future electronic devices with low-power consumption. More recently, the QAHE has been experimentally observed in thin films of the time-reversal symmetry breaking ferromagnetic (FM) topological insulators (TI), Cr- and V- doped (Bi,Sb)2Te3. In this topical review, we review the history of TI based QAHE, the route to the experimental observation of the QAHE in the above two systems, the current status of the research of the QAHE, and finally the prospects for future studies.
Time-reversal symmetry violation in molecules induced by nuclear magnetic quadrupole moments.
Flambaum, V V; DeMille, D; Kozlov, M G
2014-09-01
Recent measurements in paramagnetic molecules improved the limit on the electron electric dipole moment (EDM) by an order of magnitude. Time-reversal (T) and parity (P) symmetry violation in molecules may also come from their nuclei. We point out that nuclear T, P-odd effects are amplified in paramagnetic molecules containing deformed nuclei, where the primary effects arise from the T, P-odd nuclear magnetic quadrupole moment (MQM). We perform calculations of T, P-odd effects in the molecules TaN, ThO, ThF+, HfF+, YbF, HgF, and BaF induced by MQMs. We compare our results with those for the diamagnetic TlF molecule, where the T, P-odd effects are produced by the nuclear Schiff moment. We argue that measurements in molecules with MQMs may provide improved limits on the strength of T, P-odd nuclear forces, on the proton, neutron, and quark EDMs, on quark chromo-EDMs, and on the QCD θ term and CP-violating quark interactions. PMID:25238355
Universal reverse-transcriptase real-time PCR for infectious hematopoietic necrosis virus (IHNV)
Purcell, Maureen K.; Thompson, Rachel L.; Garver, Kyle A.; Hawley, Laura M.; Batts, William N.; Sprague, Laura; Sampson, Corie; Winton, James R.
2013-01-01
Infectious hematopoietic necrosis virus (IHNV) is an acute pathogen of salmonid fishes in North America, Europe and Asia and is reportable to the World Organization for Animal Health (OIE). Phylogenetic analysis has identified 5 major virus genogroups of IHNV worldwide, designated U, M, L, E and J; multiple subtypes also exist within those genogroups. Here, we report the development and validation of a universal IHNV reverse-transcriptase real-time PCR (RT-rPCR) assay targeting the IHNV nucleocapsid (N) gene. Properties of diagnostic sensitivity (DSe) and specificity (DSp) were defined using laboratory-challenged steelhead trout Oncorhynchus mykiss, and the new assay was compared to the OIE-accepted conventional PCR test and virus isolation in cell culture. The IHNV N gene RT-rPCR had 100% DSp and DSe and a higher estimated diagnostic odds ratio (DOR) than virus culture or conventional PCR. The RT-rPCR assay was highly repeatable within a laboratory and highly reproducible between laboratories. Field testing of the assay was conducted on a random sample of juvenile steelhead collected from a hatchery raceway experiencing an IHN epizootic. The RT-rPCR detected a greater number of positive samples than cell culture and there was 40% agreement between the 2 tests. Overall, the RT-rPCR assay was highly sensitive, specific, repeatable and reproducible and is suitable for use in a diagnostic setting.
NASA Astrophysics Data System (ADS)
Lai, Puxiang; Suzuki, Yuta; Xu, Xiao; Wang, Lihong V.
2013-07-01
Scattering dominates light propagation in biological tissue, and therefore restricts both resolution and penetration depth in optical imaging within thick tissue. As photons travel into the diffusive regime, typically 1 mm beneath human skin, their trajectories transition from ballistic to diffusive due to the increased number of scattering events, which makes it impossible to focus, much less track, photon paths. Consequently, imaging methods that rely on controlled light illumination are ineffective in deep tissue. This problem has recently been addressed by a novel method capable of dynamically focusing light in thick scattering media via time reversal of ultrasonically encoded (TRUE) diffused light. Here, using photorefractive materials as phase conjugate mirrors, we show a direct visualization and dynamic control of optical focusing with this light delivery method, and demonstrate its application for focused fluorescence excitation and imaging in thick turbid media. These abilities are increasingly critical for understanding the dynamic interactions of light with biological matter and processes at different system levels, as well as their applications for biomedical diagnosis and therapy.
Reversing the hands of time: changing the mapping from seeing to saying.
Kuchinsky, Stefanie E; Bock, Kathryn; Irwin, David E
2011-05-01
To describe a scene, speakers must map visual information to a linguistic plan. Eye movements capture features of this linkage in a tendency for speakers to fixate referents just before they are mentioned. The current experiment examined whether and how this pattern changes when speakers create atypical mappings. Eye movements were monitored as participants told the time from analog clocks. Half of the participants did this in the usual manner. For the other participants, the denotations of the clock hands were reversed, making the big hand the hour and the little hand the minute. Eye movements revealed that it was not the visual features or configuration of the hands that determined gaze patterns, but rather top-down control from upcoming referring expressions. Differences in eye-voice spans further suggested a process in which scene elements are relationally structured before a linguistic plan is executed. This provides evidence for structural rather than lexical incrementality in planning and supports a "seeing-for-saying" hypothesis in which the visual system is harnessed to the linguistic demands of an upcoming utterance. PMID:21534707
Two applications of time reversal mirrors: seismic radio and seismic radar.
Hanafy, Sherif M; Schuster, Gerard T
2011-10-01
Two seismic applications of time reversal mirrors (TRMs) are introduced and tested with field experiments. The first one is sending, receiving, and decoding coded messages similar to a radio except seismic waves are used. The second one is, similar to radar surveillance, detecting and tracking a moving object(s) in a remote area, including the determination of the objects speed of movement. Both applications require the prior recording of calibration Green's functions in the area of interest. This reference Green's function will be used as a codebook to decrypt the coded message in the first application and as a moving sensor for the second application. Field tests show that seismic radar can detect the moving coordinates (x(t), y(t), z(t)) of a person running through a calibration site. This information also allows for a calculation of his velocity as a function of location. Results with the seismic radio are successful in seismically detecting and decoding coded pulses produced by a hammer. Both seismic radio and radar are highly robust to signals in high noise environments due to the super-stacking property of TRMs. PMID:21973353
Switching times of nanoscale FePt: Finite size effects on the linear reversal mechanism
Ellis, M. O. A.; Chantrell, R. W.
2015-04-20
The linear reversal mechanism in FePt grains ranging from 2.316 nm to 5.404 nm has been simulated using atomistic spin dynamics, parametrized from ab-initio calculations. The Curie temperature and the critical temperature (T{sup *}), at which the linear reversal mechanism occurs, are observed to decrease with system size whilst the temperature window T{sup *}
On-chip single-copy real-time reverse-transcription PCR in isolated picoliter droplets
Beer, N R; Wheeler, E; Lee-Houghton, L; Watkins, N; Nasarabadi, S; Hebert, N; Leung, P; Arnold, D; Bailey, C; Colston, B
2007-12-19
The first lab-on-chip system for picoliter droplet generation and RNA isolation, followed by reverse transcription, and PCR amplification with real-time fluorescence detection in the trapped droplets has been developed. The system utilized a shearing T-junction in a fused silica device to generate a stream of monodisperse picoliter-scale droplets that were isolated from the microfluidic channel walls and each other by the oil phase carrier. An off-chip valving system stopped the droplets on-chip, allowing thermal cycling for reverse transcription and subsequent PCR amplification without droplet motion. This combination of the established real-time reverse transcription-PCR assay with digital microfluidics is ideal for isolating single-copy RNA and virions from a complex environment, and will be useful in viral discovery and gene-profiling applications.
NASA Astrophysics Data System (ADS)
Parvasi, Seyed Mohammad; Ho, Siu Chun Michael; Kong, Qingzhao; Mousavi, Reza; Song, Gangbing
2016-08-01
Bolted joints are ubiquitous structural elements, and form critical connections in mechanical and civil structures. As such, loosened bolted joints may lead to catastrophic failures of these structures, thus inspiring a growing interest in monitoring of bolted joints. A novel energy based wave method is proposed in this study to monitor the axial load of bolted joint connections. In this method, the time reversal technique was used to focus the energy of a piezoelectric (PZT)-generated ultrasound wave from one side of the interface to be measured as a signal peak by another PZT transducer on the other side of the interface. A tightness index (TI) was defined and used to correlate the peak amplitude to the bolt axial load. The TI bypasses the need for more complex signal processing required in other energy-based methods. A coupled, electro-mechanical analysis with elasto-plastic finite element method was used to simulate and analyze the PZT based ultrasonic wave propagation through the interface of two steel plates connected by a single nut and bolt connection. Numerical results, backed by experimental results from testing on a bolted connection between two steel plates, revealed that the peak amplitude of the focused signal increases as the bolt preload (torque level) increases due to the enlarging true contact area of the steel plates. The amplitude of the focused peak saturates and the TI reaches unity as the bolt axial load reaches a threshold value. These conditions are associated with the maximum possible true contact area between the surfaces of the bolted connection.
Bai, Mingsian R; Tsai, Yao Kun
2011-03-01
In this paper, a combined impact localization and haptic feedback system based on time-reversal signal processing is presented for touch panel applications. Theoretical impulse responses are derived from a propagation model of bending waves in a thin elastic plate. On the basis of the impulse responses, the time-reversal technique is exploited to spot the impact location as well as to generate haptic feedback. The chief advantage of the time-reversal technique lies in its robustness of tackling broadband sources in a reverberant environment. Piezoelectric ceramic plates and voice-coil motors are used as sensors for localization, whereas only voice-coil motors are used as the actuator for haptic feedback. Experimental results demonstrated that the proposed system was effective in precise impact localization for a thin panel, while haptic feedback also implemented using time-reversal principle can generate an impulse at the previously touched position. The combined impact localization and haptic feedback system is capable of enhancing the sensation of man-machine interaction in real time fashion. PMID:21428493
NASA Astrophysics Data System (ADS)
Michal, Carl A.; Tycko, Robert
2001-01-01
Time-reversal of the evolution of a dipole-coupled, many-spin system under continuous resonant excitation with a radio-frequency (rf) field of arbitrary amplitude is demonstrated in solid-state 1H nuclear magnetic resonance (NMR) experiments on polycrystalline adamantane. Time-reversed evolution is accomplished with an rf pulse sequence that generates an effective nuclear spin Hamiltonian that includes both dipole-dipole coupling and rf interaction terms, with signs opposite to those in forward evolution. The amplitude of the effective continuous rf field is varied by varying the phases of rf pulses in the sequence. Experiments show echo-like NMR signals under time-reversed evolution after forward evolution to an apparent quasiequilibrium state under continuous rf excitation. Such echolike signals are inconsistent with the hypothesis of spin temperature in the rotating frame, according to which the approach to quasiequilibrium under continuous rf excitation is an irreversible process. The use of this time-reversed evolution in multiple quantum (MQ) NMR spectroscopy is also demonstrated. MQ NMR spectra obtained with increasing excitation times exhibit a partial confinement of nuclear spin order to zero- and one-quantum operators. This novel behavior is shown to be a consequence of energy conservation.
Closeout Report - Search for Time Reversal Symmetry Violation with TREK at J-PARC
Kohl, Michael
2015-04-15
positions. Two former graduate students of the group have graduated and received their PhD degrees in nuclear physics (Dr. Anusha Liyanage and Dr. Ozgur Ates). In particular, this award has enabled Dr. Kohl to pursue the TREK project (Time Reversal Experiment with Kaons) at J-PARC, which he has been leading and advancing as International Spokesperson. Originally proposed as a search for time reversal symmetry violation [6], the project has evolved into a precision test of lepton flavor universality in the Standard Model along with sensitive searches for physics beyond the Standard Model through a possible discovery of new particles such as a sterile neutrino or a neutral gauge boson from the hidden sector in the mass region up to 300 MeV/c2 [7]. Experiment TREK/E36, first proposed in 2010, has been mounted between November 2014 and April 2015, and commissioning with beam has been started in April 2015, with production running anticipated in early summer and late fall 2015. It uses the apparatus from the previous KEK/E-246 experiment with partial upgrades to measure the ratio of decay widths of leptonic two-body decays of the charged kaon to µν and eν, respectively, which is highly sensitive to the ratio of electromagnetic charged lepton couplings and possible new physics processes that could differentiate between μ and e, hence breaking lepton flavor universality of the Standard Model. Through the searches for neutral massive particles, TREK/E36 can severely constrain any new physics scenarios designed to explain the proton radius puzzle [12, 13].
Short Gamma-Ray Bursts in the "Time-reversal" Scenario
NASA Astrophysics Data System (ADS)
Ciolfi, Riccardo; Siegel, Daniel M.
2015-01-01
Short gamma-ray bursts (SGRBs) are among the most luminous explosions in the universe and their origin still remains uncertain. Observational evidence favors the association with binary neutron star or neutron star-black hole (NS-BH) binary mergers. Leading models relate SGRBs to a relativistic jet launched by the BH-torus system resulting from the merger. However, recent observations have revealed a large fraction of SGRB events accompanied by X-ray afterglows with durations ~102-105 s, suggesting continuous energy injection from a long-lived central engine, which is incompatible with the short (lsim 1 s) accretion timescale of a BH-torus system. The formation of a supramassive NS, resisting the collapse on much longer spin-down timescales, can explain these afterglow durations, but leaves serious doubts on whether a relativistic jet can be launched at the merger. Here we present a novel scenario accommodating both aspects, where the SGRB is produced after the collapse of a supramassive NS. Early differential rotation and subsequent spin-down emission generate an optically thick environment around the NS consisting of a photon-pair nebula and an outer shell of baryon-loaded ejecta. While the jet easily drills through this environment, spin-down radiation diffuses outward on much longer timescales and accumulates a delay that allows the SGRB to be observed before (part of) the long-lasting X-ray signal. By analyzing diffusion timescales for a wide range of physical parameters, we find delays that can generally reach ~105 s, compatible with observations. The success of this fundamental test makes this "time-reversal" scenario an attractive alternative to current SGRB models.
NASA Astrophysics Data System (ADS)
Moodera, Jagadeesh
Breaking time reversal symmetry (TRS) in a topological insulator (TI) with ferromagnetic perturbation can lead to many exotic quantum phenomena exhibited by Dirac surface states including the quantum anomalous Hall (QAH) effect and dissipationless quantized Hall transport. The realization of the QAH effect in realistic materials requires ferromagnetic insulating materials and topologically non-trivial electronic band structures. In a TI, the ferromagnetic order and TRS breaking is achievable by conventional way, through doping with a magnetic element, or by ferromagnetic proximity coupling. Our experimental studies by both approaches will be discussed. In doped TI van Vleck ferromagnetism was observed. The proximity induced magnetism at the interface was stable, beyond the expected temperature range. We shall describe in a hard ferromagnetic TI system a robust QAH state and dissipationless edge current flow is achieved,1,2 a major step towards dissipationless electronic applications with no external fields, making such devices more amenable for metrology and spintronics applications. Our study of the gate and temperature dependences of local and nonlocal magnetoresistance, may elucidate the causes of the dissipative edge channels and the need for very low temperature to observe QAH. In close collaboration with: CuiZu Chang,2,3 Ferhat Katmis, 1 . 2 , 3 Peng Wei. 1 , 2 , 3 ; From Nuclear Eng. Dept. MIT, M. Li, J. Li; From Penn State U, W-W. Zhao, D. Y. Kim, C-x. Liu, J. K. Jain, M. H. W. Chan; From Oakridge National Lab, V. Lauter; From Northeastern U., B. A. Assaf, M. E. Jamer, D. Heiman; From Argonne Lab, J. W. Freeland; From Ruhr-Universitaet Bochum (Germany), F. S. Nogueira, I. Eremin; From Saha Institute of Nuclear Physics (India), B. Satpati. Work supported by NSF Grant DMR-1207469, the ONR Grant N00014-13-1-0301, and the STC Center for Integrated Quantum Materials under NSF Grant DMR-1231319.
SHORT GAMMA-RAY BURSTS IN THE ''TIME-REVERSAL'' SCENARIO
Ciolfi, Riccardo; Siegel, Daniel M. E-mail: daniel.siegel@aei.mpg.de
2015-01-10
Short gamma-ray bursts (SGRBs) are among the most luminous explosions in the universe and their origin still remains uncertain. Observational evidence favors the association with binary neutron star or neutron star-black hole (NS-BH) binary mergers. Leading models relate SGRBs to a relativistic jet launched by the BH-torus system resulting from the merger. However, recent observations have revealed a large fraction of SGRB events accompanied by X-ray afterglows with durations ∼10{sup 2}-10{sup 5} s, suggesting continuous energy injection from a long-lived central engine, which is incompatible with the short (≲ 1 s) accretion timescale of a BH-torus system. The formation of a supramassive NS, resisting the collapse on much longer spin-down timescales, can explain these afterglow durations, but leaves serious doubts on whether a relativistic jet can be launched at the merger. Here we present a novel scenario accommodating both aspects, where the SGRB is produced after the collapse of a supramassive NS. Early differential rotation and subsequent spin-down emission generate an optically thick environment around the NS consisting of a photon-pair nebula and an outer shell of baryon-loaded ejecta. While the jet easily drills through this environment, spin-down radiation diffuses outward on much longer timescales and accumulates a delay that allows the SGRB to be observed before (part of) the long-lasting X-ray signal. By analyzing diffusion timescales for a wide range of physical parameters, we find delays that can generally reach ∼10{sup 5} s, compatible with observations. The success of this fundamental test makes this ''time-reversal'' scenario an attractive alternative to current SGRB models.
NASA Astrophysics Data System (ADS)
Zhang, Liuyu; Wang, Chenyu; Huo, Linsheng; Song, Gangbing
2016-03-01
Cuplok scaffolds are widely used to form temporary supporting structures when constructing bridges and other structures all over the world. The safety and stability of cuplok scaffolds are important issues during construction. Cuplok scaffolds are subjected to various types of vibrations, which may loosen the cuplok connection, negatively impacting the stability of the structure and even leading to severe accidents. In this paper, the authors propose a time reversal (TR) method to monitor the looseness status of the cuplok connection by using stress wave-based active sensing. Lead zirconate titanate (PZT), a commonly used piezoceramic material with a strong piezoelectric effect, is employed. In the proposed approach, PZT patches are used as sensors and actuators to monitor the cuplok joint looseness. One PZT patch is bonded to the vertical bar and two PZT patches are bonded to the cross bars of the cuplok scaffold. The PZT patch on the vertical bar is used as an actuator to generate a stress wave and the other two PZT patches are used as sensors to detect the propagated waves through the cuplok connection, the looseness of which will directly impact the stress wave propagation. The TR method is used to analyse the transmitted signal between the PZT patches through the cuplok connection. By comparing the peak values of the TR focused signal, it can be found that the peak value increases as the tightness of the cuplok connection increases. Therefore, the peak value of the TR focused signal can be used to monitor the tightness of the cuplok connection. In addition, the experimental results demonstrated that the TR method is superior to the energy method in consistency, sensitivity and anti-noise properties.
Three-dimensional time optimal double angular momentum reversal trajectory using solar sails
NASA Astrophysics Data System (ADS)
Zeng, Xiangyuan; Baoyin, Hexi; Li, Junfeng; Gong, Shengping
2011-12-01
A new concept of three dimensional non-Keplerian trajectories with double angular momentum reversal is investigated with high performance solar sails. The main discussion of this paper is about such 3D solar inverse orbits with inner constraints. The problem is addressed in a time optimal control framework solved by an indirect method. Two typical solar inverse orbits have been achieved and presented in a 3D non-dimensional dynamic model in the Heliocentric Inertial Frame. Starting from the Earth orbit ecliptic plane, a sailcraft in the inverse orbit exhibits a butterfly shape trajectory. As such, the new orbits are symmetrical with respect to a plane which contains the Sun-perihelion line. The relation of the sail attitude angles between the two symmetrical parts of the orbits are used to reduce the simulation effort. The quasi-heliostationary property at its aphelia is demonstrated with variation of the orbital radius. Evolutions of the orbital velocity and optimal sail orientations are also outlined and discussed to benefit future design work. As is suited for space observation guaranteed by its butterfly shape, the inverse orbits are thoroughly studied in terms of the concerned parameters. The discussion of the parametric influence is ranked in order as perihelion distance r E , required maximum position z max, perihelion position z f and the sail lightness number β. Suitable ranges of each parameter are adopted to illustrate the orbital variation trend. Through numerical simulations the features of such inverse orbits are further emphasized to provide an initial reference for future researchers.
Reverse time migration imaging of ground-penetrating radar data in complex environments
NASA Astrophysics Data System (ADS)
Bradford, J. H.
2014-12-01
Because reverse-time migration (RTM) honors the physics of wave propagation more closely than other migration algorithms, it has become the preferred imaging tool in seismic exploration over the past 10-15 years. This shift has been facilitated by advances in computational power which have made it feasible to routinely migrate large datasets. Despite this evolution in exploration seismology, the use of RTM has remained relatively limited in ground-penetrating radar (GPR) applications even though the advantages in GPR imaging are comparable. For example, within the RTM framework it is possible to include antenna radiation directly in the imaging algorithm. Additionally complications such as irregular surface topography and highly heterogeneous subsurface electrical properties can be incorporated naturally into an RTM algorithm. I have implemented both pre- and post-stack RTM algorithms for GPR imaging. The post-stack algorithm utilizes the exploding reflector concept and an approximate formulation of the EM wave equation to account for propagation through lossy media. The pre-stack algorithm utilizes the full two way solution to Maxwell's equations, and includes radiation patterns directly in the imaging routine. Here, I investigate amplitude reconstruction using RTM in complex environments with a focus on complex topography and the interplay between radar radiation patterns and topography. Complex topography alters wavefield kinematics making for a challenging imaging problem; topographic variation can substantially distort radiation patterns, produce irregular spreading, and alter amplitudes by focusing and defocusing effects at the surface. The effects are magnified when the topographic variations are on the same order as the depth of investigation - a situation that is often encountered in GPR investigations. I consider both pre- and post-stack GPR imaging in the presence of large topographic and subsurface variability. Using both synthetic and field examples I
Acceleration of stable TTI P-wave reverse-time migration with GPUs
NASA Astrophysics Data System (ADS)
Kim, Youngseo; Cho, Yongchae; Jang, Ugeun; Shin, Changsoo
2013-03-01
When a pseudo-acoustic TTI (tilted transversely isotropic) coupled wave equation is used to implement reverse-time migration (RTM), shear wave energy is significantly included in the migration image. Because anisotropy has intrinsic elastic characteristics, coupling P-wave and S-wave modes in the pseudo-acoustic wave equation is inevitable. In RTM with only primary energy or the P-wave mode in seismic data, the S-wave energy is regarded as noise for the migration image. To solve this problem, we derive a pure P-wave equation for TTI media that excludes the S-wave energy. Additionally, we apply the rapid expansion method (REM) based on a Chebyshev expansion and a pseudo-spectral method (PSM) to calculate spatial derivatives in the wave equation. When REM is incorporated with the PSM for the spatial derivatives, wavefields with high numerical accuracy can be obtained without grid dispersion when performing numerical wave modeling. Another problem in the implementation of TTI RTM is that wavefields in an area with high gradients of dip or azimuth angles can be blown up in the progression of the forward and backward algorithms of the RTM. We stabilize the wavefields by applying a spatial-frequency domain high-cut filter when calculating the spatial derivatives using the PSM. In addition, to increase performance speed, the graphic processing unit (GPU) architecture is used instead of traditional CPU architecture. To confirm the degree of acceleration compared to the CPU version on our RTM, we then analyze the performance measurements according to the number of GPUs employed.
Technology Transfer Automated Retrieval System (TEKTRAN)
A subtype specific H7 real-time reverse transcriptase polymerase chain reaction (RT-PCR) assay developed by the Southeast Poultry Research Laboratory (SEPRL) for the detection of H7 in North and South American wild aquatic birds and poultry was validated as a collaborative effort by the SEPRL and Na...
NASA Astrophysics Data System (ADS)
Zmuda, Henry; Fanto, Michael; McEwen, Thomas
2008-04-01
This paper describes a new concept for a photonic implementation of a time reversed RF antenna array beamforming system. The process does not require analog to digital conversion to implement and is therefore particularly suited for high bandwidth applications. Significantly, propagation distortion due to atmospheric effects, clutter, etc. is automatically accounted for with the time reversal process. The approach utilizes the reflection of an initial interrogation signal from off an extended target to precisely time match the radiating elements of the array so as to re-radiate signals precisely back to the target's location. The backscattered signal(s) from the desired location is captured by each antenna and used to modulate a pulsed laser. An electrooptic switch acts as a time gate to eliminate any unwanted signals such as those reflected from other targets whose range is different from that of the desired location resulting in a spatial null at that location. A chromatic dispersion processor is used to extract the exact array parameters of the received signal location. Hence, other than an approximate knowledge of the steering direction needed only to approximately establish the time gating, no knowledge of the target position is required, and hence no knowledge of the array element time delay is required. Target motion and/or array element jitter is automatically accounted for. Presented here are experimental results that demonstrate the ability of a photonic processor to perform the time-reversal operation on ultra-short electronic pulses.
Ma, Cheng; Xu, Xiao; Wang, Lihong V.
2015-01-01
Recent breakthrough in wavefront engineering shows great promises in controlling light propagation inside scattering media. At present, the digital approaches enjoy high gain, while their speeds are slow because of high data throughputs. In contrast, the analog approaches are intrinsically fast but suffer from poor efficiencies and small gains. Further improvements in both speed and gain are necessary to advance the existing technologies toward real-world applications. Here, we report analog time-reversal of acousto-optically tagged photons with a flux amplification of over 33,000 times (45 dB) at a target location inside scattering media. Such a substantial power gain enhancement is achieved when the temporal width of the time-reversed photon packet is squeezed below the carrier-recombination-limited hologram decay time in a photorefractive crystal. Despite a focusing energy gain below unity, the unprecedented power gain is expected to enable new optical imaging, sensing, manipulation and treatment applications. PMID:25753905
NASA Astrophysics Data System (ADS)
Ma, Cheng; Xu, Xiao; Wang, Lihong V.
2015-03-01
Recent breakthrough in wavefront engineering shows great promises in controlling light propagation inside scattering media. At present, the digital approaches enjoy high gain, while their speeds are slow because of high data throughputs. In contrast, the analog approaches are intrinsically fast but suffer from poor efficiencies and small gains. Further improvements in both speed and gain are necessary to advance the existing technologies toward real-world applications. Here, we report analog time-reversal of acousto-optically tagged photons with a flux amplification of over 33,000 times (45 dB) at a target location inside scattering media. Such a substantial power gain enhancement is achieved when the temporal width of the time-reversed photon packet is squeezed below the carrier-recombination-limited hologram decay time in a photorefractive crystal. Despite a focusing energy gain below unity, the unprecedented power gain is expected to enable new optical imaging, sensing, manipulation and treatment applications.
Mellow, Tim; Kärkkäinen, Leo
2014-03-01
An acoustic curtain is an array of microphones used for recording sound which is subsequently reproduced through an array of loudspeakers in which each loudspeaker reproduces the signal from its corresponding microphone. Here the sound originates from a point source on the axis of symmetry of the circular array. The Kirchhoff-Helmholtz integral for a plane circular curtain is solved analytically as fast-converging expansions, assuming an ideal continuous array, to speed up computations and provide insight. By reversing the time sequence of the recording (or reversing the direction of propagation of the incident wave so that the point source becomes an "ideal" point sink), the curtain becomes a time reversal mirror and the analytical solution for this is given simultaneously. In the case of an infinite planar array, it is demonstrated that either a monopole or dipole curtain will reproduce the diverging sound field of the point source on the far side. However, although the real part of the sound field of the infinite time-reversal mirror is reproduced, the imaginary part is an approximation due to the missing singularity. It is shown that the approximation may be improved by using the appropriate combination of monopole and dipole sources in the mirror. PMID:24606267
NASA Astrophysics Data System (ADS)
Larmat, C. S.; Johnson, P.; Huang, L.; Randall, G.; Patton, H.; Montagner, J.
2007-12-01
In this work we describe Time Reversal experiments applying seismic waves recorded from the 2004 M6.0 Parkfield Earthquake. The reverse seismic wavefield is created by time-reversing recorded seismograms and then injecting them from the seismograph locations into a whole entire Earth velocity model. The concept is identical to acoustic Time-Reversal Mirror laboratory experiments except the seismic data are numerically backpropagated through a velocity model (Fink, 1996; Ulrich et al, 2007). Data are backpropagated using the finite element code SPECFEM3D (Komatitsch et al, 2002), employing the velocity model s20rts (Ritsema et al, 2000). In this paper, we backpropagate only the vertical component of seismic data from about 100 broadband surface stations located worldwide (FDSN), using the period band of 23-120s. We use those only waveforms that are highly correlated with forward-propagated synthetics. The focusing quality depends upon the type of waves back- propagated; for the vertical displacement component the possible types include body waves, Rayleigh waves, or their combination. We show that Rayleigh waves, both real and artifact, dominate the reverse movie in all cases. They are created during rebroadcast of the time reverse signals, including body wave phases, because we use point-like-force sources for injection. The artifact waves, termed "ghosts" manifest as surface waves, do not correspond to real wave phases during the forward propagation. The surface ghost waves can significantly blur the focusing at the source. We find that the ghosts cannot be easily eliminated in the manner described by Tsogka&Papanicolaou (2002). It is necessary to understand how they are created in order to remove them during TRM studies, particularly when using only the body waves. For this moderate magnitude of earthquake we demonstrate the robustness of the TRM as an alternative location method despite the restriction to vertical component phases. One advantage of TRM location
An Introductory-Geology Exercise on the Polar-Reversal Time Scale.
ERIC Educational Resources Information Center
Shea, James Herbert
1986-01-01
Presents a three-part exercise which provides undergraduates with opportunities to work with data related to the earth's magnetic field. Includes student materials for activities in determining the history of the earth's magnetic field, in finding the general pattern of declination, and for looking for a polar reversal history. (ML)
Reverse-time migration-based reflection tomography using teleseismic free surface multiples
NASA Astrophysics Data System (ADS)
Burdick, S.; de Hoop, M. V.; Wang, S.; van der Hilst, R. D.
2014-02-01
Converted and multiply reflected phases from teleseismic events are routinely used to create structural images of the crust-mantle boundary (Moho) and the elasticity contrasts within the crust and upper mantle. The accuracy of these images is to a large extent determined by the background velocity model used to propagate these phases to depth. In order to improve estimates of 3-D velocity variations and, hence, improve imaging, we develop a method of reverse-time migration-based reflection tomography for use with wavefields from teleseismic earthquakes recorded at broad-band seismograph arrays. Reflection tomography makes use of data redundancy-that is, the ability to generate numerous structural images of the subsurface with different parts of the wavefield. In exploration seismology (where it is known as migration velocity analysis) reflection tomography typically involves the generation of an extended image (e.g. offset- or angle-gathers), and the fitness of the background model is evaluated through the application of image-domain annihilators. In regional-scale passive source seismology, however, annihilation-based methods are inadequate because the sparse and irregular distribution of teleseismic sources is not likely to produce illumination over a sufficient range of angles. To overcome this problem we turn towards a source-indexed moveout scheme. Instead of extended image annihilation, we determine the success of the tomographic velocity model by cross correlating images produced with multiply scattered waves from different teleseismic sources. The optimal velocity model is the one that minimizes correlation power between windowed images away from zero depth shift. We base our inversion scheme on the seismic adjoint method and a conjugate gradient solver. For each image pair, the update direction is determined by correlations between downgoing wavefields with upgoing adjoint wavefields for both images. The sensitivity kernels used in this method is similar
NASA Astrophysics Data System (ADS)
Wang, K.; Davenport, K. K.; Hole, J. A.; Chapman, M. C.; Quiros, D. A.; Brown, L. D.
2013-12-01
Reverse time migration has previously been used to back-project energy recorded by dense arrays to the source region of large subduction-zone earthquakes. The results have illuminated energy release as a function of time and space on the fault surface, improving our understanding of rupture processes. We apply reverse time migration to data from a dense local aftershock array to image magnitude <0 to 3.7 events. AIDA (Aftershock Imaging with Dense Arrays) recorded aftershocks of the August 23, 2011, magnitude 5.8 earthquake in Louisa County, Virginia. AIDA deployed 201 stations in three phases to record wavefields at 200-400 m spacing to reduce spatial aliasing and to lower the event detection threshold. Aftershocks recorded by AIDA were reverse-time migrated in a velocity model created by aftershock travel-time tomography. An aftershock with a magnitude less than 0 was successfully imaged as a point source with a resolution of <200 m. Slip propagation was successfully imaged for a magnitude 3.7 aftershock, propagating 200-300 m shallower and southward. Both P and S-wave data were independently migrated, with similar results. The method is being applied to automatically detect and locate tiny events with low signal-to-noise ratio. Tests show that the images are limited by insufficient temporal sampling and predictable migration artifacts caused by the station geometry. Future aftershock deployments can improve these conditions.
Haworth, Kevin J.; Fowlkes, J. Brian; Carson, Paul L.; Kripfgans, Oliver D.
2009-01-01
A theoretical shot noise model to describe the output of a time-reversal experiment in a multiple-scattering medium is developed. This (non-wave equation based) model describes the following process. An arbitrary waveform is transmitted through a high-order multiple-scattering environment and recorded. The recorded signal is arbitrarily windowed and then time-reversed. The processed signal is retransmitted into the environment and the resulting signal recorded. The temporal and spatial signal and noise of this process is predicted statistically. It is found that the time when the noise is largest depends on the arbitrary windowing and this noise peak can occur at times outside the main lobe. To determine further trends, a common set of parameters is applied to the general result. It is seen that as the duration of the input function increases, the signal-to-noise ratio (SNR) decreases (independent of signal bandwidth). It is also seen that longer persisting impulse responses result in increased main lobe amplitudes and SNR. Assumptions underpinning the generalized shot noise model are compared to an experimental realization of a multiple-scattering medium (a time-reversal chaotic cavity). Results from the model are compared to random number numerical simulation. PMID:19425655
NASA Astrophysics Data System (ADS)
Kim, W.; Kim, Y.; Min, D.; Oh, J.; Huh, C.; Kang, S.
2012-12-01
During last two decades, CO2 sequestration in the subsurface has been extensively studied and progressed as a direct tool to reduce CO2 emission. Commercial projects such as Sleipner, In Salah and Weyburn that inject more than one million tons of CO2 per year are operated actively as well as test projects such as Ketzin to study the behavior of CO2 and the monitoring techniques. Korea also began the CCS (CO2 capture and storage) project. One of the prospects for CO2 sequestration in Korea is the southwestern continental margin of Ulleung basin. To monitor the behavior of CO2 underground for the evaluation of stability and safety, several geophysical monitoring techniques should be applied. Among various geophysical monitoring techniques, seismic survey is considered as the most effective tool. To verify CO2 migration in the subsurface more effectively, seismic numerical simulation is an essential process. Furthermore, the efficiency of the seismic migration techniques should be investigated for various cases because numerical seismic simulation and migration test help us accurately interpret CO2 migration. In this study, we apply the reverse-time migration and Kirchhoff migration to synthetic seismic monitoring data generated for the simplified model based on the geological structures of Ulleung basin in Korea. Synthetic seismic monitoring data are generated for various cases of CO2 migration in the subsurface. From the seismic migration images, we can investigate CO2 diffusion patterns indirectly. From seismic monitoring simulation, it is noted that while the reverse-time migration generates clear subsurface images when subsurface structures are steeply dipping, Kirchhoff migration has an advantage in imaging horizontal-layered structures such as depositional sediments appearing in the continental shelf. The reverse-time migration and Kirchhoff migration present reliable subsurface images for the potential site characterized by stratigraphical traps. In case of
NASA Astrophysics Data System (ADS)
Ma, Cheng; Xu, Xiao; Wang, Lihong V.
2016-03-01
Focusing light deep inside scattering media plays a key role in such biomedical applications as high resolution optical imaging, control, and therapy. In recent years, wavefront shaping technologies have come a long way in controlling light propagation in complex media. A prominent example is time-reversed ultrasonically encoded (TRUE) focusing, which allows noninvasive introduction of "guide stars" inside biological tissue to guide light focusing. By measuring the optical wavefront emanating from an ultrasound focus created at the target location, TRUE determines the desired wavefront non-iteratively, and achieves focusing at the target position via a subsequent optical time reversal. Compared to digital counterparts that employ slow electronic spatial light modulators and cameras, analog TRUE focusing relies on nonlinear photorefractive crystals that inherently accommodate more spatial modes and eliminate the troublesome alignment and data transfer required by digital approaches. However, analog TRUE focusing suffers from its small gain, defined as the energy or power ratio between the focusing and probing beams in the focal volume. Here, by implementing a modified analog TRUE focusing scheme that squeezes the duration of the time-reversed photon packet below the carrier-recombination-limited hologram decay time of the crystal, we demonstrated a photon flux amplification much greater than unity at a preset focal voxel in between two scattering layers. Although the energy gain was still below unity, the unprecedented power gain will nevertheless benefit new biomedical applications.
NASA Astrophysics Data System (ADS)
Yang, Qiang; Xu, Xiao; Lai, Puxiang; Sang, Xinzhu; Wang, Lihong V.
2014-03-01
Focusing light inside highly scattering media beyond the ballistic regime is a challenging task in biomedical optical imaging, manipulation, and therapy. This challenge can be overcome by time reversing ultrasonically encoded (TRUE) diffuse light to the ultrasonic focus inside a turbid medium. In TRUE optical focusing, a photorefractive crystal or polymer is used as the phase conjugate mirror for optical time reversal. Accordingly, a relatively long ultrasound burst, whose duration matches the response time of the photorefractive material, is used to encode the diffuse light. With this long ultrasound burst, the resolution of the TRUE focus along the acoustic axis is poor. In this work, we used two transducers, emitting two intersecting ultrasound beams at 3.4 MHz and 3.6 MHz respectively, to modulate the diffuse light within their intersection volume at the beat frequency. We show that light encoded at the beat frequency can be time-reversed and converge to the intersection volume. Experimentally, TRUE focusing with an acoustic axial resolution of ~1.1 mm was demonstrated inside turbid media, agreeing with the theoretical estimation.
Enhanced charge detection: Amplification factor, phase reversal and measurement time dependence
Thorgrimson, J.; Sachrajda, A. S.; Studenikin, S. A.; Bogan, A.; Aers, G. C.; Kam, A.; Zawadzki, P.; Wasilewski, Z. R.
2013-12-04
Studenikin et al. recently demonstrated a significant enhancement of the fringe contrast of coherent Landau-Zener-Stückelberg (LZS) oscillations between singlet S and triplet T+ two-spin states using a modified charge detection technique called enhanced charge detection (ECD). In this paper we explain the amplitude phase reversal and confirm the magnitude of the effect is consistent with our calibrations. We also show that the enhancement cannot be explained by a T{sub 1} effect.
NASA Astrophysics Data System (ADS)
Higemoto, Wataru; Aoki, Yuji; MacLaughlin, Douglas E.
2016-09-01
Unconventional superconductivity based on the strong correlation of electrons is one of the central issues of solid-state physics. Although many experimental techniques are appropriate for investigating unconventional superconductivity, a complete perspective has not been established yet. The symmetries of electron pairs are crucial properties for understanding the essential state of unconventional superconductivity. In this review, we discuss the investigation of the time-reversal and spin symmetries of superconducting electron pairs using the muon spin rotation and relaxation technique. By detecting a spontaneous magnetic field under zero field and/or the temperature dependence of the muon Knight shift in the superconducting phase, the time-reversal symmetry and spin parity of electron pairs have been determined for several unconventional superconductors.
Mimani, A; Doolan, C J; Medwell, P R
2014-09-01
This letter presents the Point-Time-Reversal-Sponge-Layer (PTRSL) technique to enhance the focal-resolution of aeroacoustic Time-Reversal (TR). A PTRSL is implemented on a square domain centered at the predicted source location and is based on damping the radial components of the incoming and outgoing fluxes propagating toward and away from the source, respectively. A PTRSL is shown to overcome the conventional half-wavelength diffraction-limit; its implementation significantly reduces the focal spot size to one-fifth of a wavelength for a monopole source. Furthermore, PTRSL reduces the focal spots of a dipole source to three-tenths of a wavelength, as compared to three-fifths without its implementation. PMID:25190421
Speckle-scale focusing in the diffusive regime with time reversal of variance-encoded light (TROVE)
NASA Astrophysics Data System (ADS)
Judkewitz, Benjamin; Wang, Ying Min; Horstmeyer, Roarke; Mathy, Alexandre; Yang, Changhuei
2013-04-01
Focusing of light in the diffusive regime inside scattering media has long been considered impossible. Recently, this limitation has been overcome with time reversal of ultrasound-encoded light (TRUE), but the resolution of this approach is fundamentally limited by the large number of optical modes within the ultrasound focus. Here, we introduce a new approach, time reversal of variance-encoded light (TROVE), which demixes these spatial modes by variance encoding to break the resolution barrier imposed by the ultrasound. By encoding individual spatial modes inside the scattering sample with unique variances, we effectively uncouple the system resolution from the size of the ultrasound focus. This enables us to demonstrate optical focusing and imaging with diffuse light at an unprecedented, speckle-scale lateral resolution of ~5 µm.
Waters, Zachary J; Dzikowicz, Benjamin R; Simpson, Harry J
2012-01-01
Iterative, single-channel time reversal is employed to isolate backscattering resonances of an air-filled spherical shell in a frequency range of 0.5-20 kHz. Numerical simulations of free-field target scattering suggest improved isolation of the dominant target response frequency in the presence of varying levels of stochastic noise, compared to processing returns from a single transmission and also coherent averaging. To test the efficacy of the technique in a realistic littoral environment, monostatic scattering experiments are conducted in the Gulf of Mexico near Panama City, Florida. The time reversal technique is applied to returns from a hollow spherical shell target sitting proud on a sandy bottom in 14 m deep water. Distinct resonances in the scattering response of the target are isolated, depending upon the bandwidth of the sonar system utilized. PMID:22280594
And the first one now will later be last: Time-reversal in cormack-jolly-seber models
Nichols, James
2016-01-01
The models of Cormack, Jolly and Seber (CJS) are remarkable in providing a rich set of inferences about population survival, recruitment, abundance and even sampling probabilities from a seemingly limited data source: a matrix of 1's and 0's reflecting animal captures and recaptures at multiple sampling occasions. Survival and sampling probabilities are estimated directly in CJS models, whereas estimators for recruitment and abundance were initially obtained as derived quantities. Various investigators have noted that just as standard modeling provides direct inferences about survival, reversing the time order of capture history data permits direct modeling and inference about recruitment. Here we review the development of reverse-time modeling efforts, emphasizing the kinds of inferences and questions to which they seem well suited.
Hwang, Ji-Hyeon; Shin, Yong-Keol; Park, So-Yeon; Kim, Jeesoo; Kim, Su-Mi; Kim, Byounghan; Park, Jong-Hyeon; Lee, Jong-Soo
2015-01-01
During an outbreak of foot-and-mouth disease (FMD), real-time reverse transcription-PCR (rRT-PCR) is the most commonly used diagnostic method to detect viral RNA. However, while this assay is often conducted during the outbreak period, there is an inevitable risk of carryover contamination. This study shows that the carryover contamination can be prevented by the use of target-specific restriction endonuclease in that assay. PMID:26560537
Finn, John M.
2015-03-01
Properties of integration schemes for solenoidal fields in three dimensions are studied, with a focus on integrating magnetic field lines in a plasma using adaptive time stepping. It is shown that implicit midpoint (IM) and a scheme we call three-dimensional leapfrog (LF) can do a good job (in the sense of preserving KAM tori) of integrating fields that are reversible, or (for LF) have a 'special divergence-free' property. We review the notion of a self-adjoint scheme, showing that such schemes are at least second order accurate and can always be formed by composing an arbitrary scheme with its adjoint. We also review the concept of reversibility, showing that a reversible but not exactly volume-preserving scheme can lead to a fractal invariant measure in a chaotic region, although this property may not often be observable. We also show numerical results indicating that the IM and LF schemes can fail to preserve KAM tori when the reversibility property (and the SDF property for LF) of the field is broken. We discuss extensions to measure preserving flows, the integration of magnetic field lines in a plasma and the integration of rays for several plasma waves. The main new result of this paper relates to non-uniform time stepping for volume-preserving flows. We investigate two potential schemes, both based on the general method of Ref. [11], in which the flow is integrated in split time steps, each Hamiltonian in two dimensions. The first scheme is an extension of the method of extended phase space, a well-proven method of symplectic integration with non-uniform time steps. This method is found not to work, and an explanation is given. The second method investigated is a method based on transformation to canonical variables for the two split-step Hamiltonian systems. This method, which is related to the method of non-canonical generating functions of Ref. [35], appears to work very well.
Focusing waves at arbitrary locations in a ray-chaotic enclosure using time-reversed synthetic sonas
NASA Astrophysics Data System (ADS)
Xiao, Bo; Antonsen, Thomas M.; Ott, Edward; Anlage, Steven M.
2016-05-01
Time-reversal methods are widely used to achieve wave focusing in acoustics and electromagnetics. Past time-reversal experiments typically require that a transmitter be initially present at the target focusing point, which limits the application of this technique. In this paper, we propose a method to focus waves at an arbitrary location inside a complex enclosure using a numerically calculated wave excitation signal. We use a semiclassical ray algorithm to calculate the signal that would be received at a transceiver port resulting from the injection of a short pulse at the desired target location. The time-reversed version of this signal is then injected into the transceiver port, and an approximate reconstruction of the short pulse is created at the target. The quality of the pulse reconstruction is quantified in three different ways, and the values of these metrics are shown to be predicted by the statistics of the scattering parameter | S21|2 between the transceiver and target points in the enclosure over the bandwidth of the pulse. We demonstrate the method experimentally using a flat microwave billiard, and we quantify the reconstruction quality as a function of enclosure loss, port coupling, and other considerations.
NASA Astrophysics Data System (ADS)
Gu, Bingluo; Li, Zhiyuan; Ma, Xiaona; Liang, Guanghe
2015-01-01
The vector P- and S-seismograms in an elastic common-shot gather generated with a P-wave source in a two-dimensional model using a finite difference solution of the P- and S-wave separated velocity-stress equations can be imaged by two independent ERTMs based on the same equations. The inputs as boundary conditions for reverse-time extrapolation are the pure vector P- and S-waves, respectively. The vector P-wave image components can be obtained by the normalized correlation operation between the vector P-source wavefields and receiver wavefields, which are obtained by extrapolating the vector P-seismograms in reverse-time using the same equations as the forward modeling. The vector S-wave image components can be obtained by a similar method. Compared with the conventional ERTM, this method can minimize the artifacts caused by the crosstalk between different wave modes and can preserve the phase and amplitude attributes of migration images very well. Furthermore, the polarity-reversal of the vector S-wave data can be corrected automatically during the imaging process, so destructive interferences between data from adjacent sources do not exist. Numerical examples with synthetic data have demonstrated the feasibility and effectiveness of this method for complex structures.
NASA Astrophysics Data System (ADS)
McGrann, John V.; Shaw, Gordon L.; Shenoy, Krishna V.; Leng, Xiaodan; Mathews, Robert B.
1994-06-01
Symmetries have long been recognized as a vital component of physical and biological systems. What we propose here is that symmetry operations are an important feature of higher brain function and result from the spatial and temporal modularity of the cortex. These symmetry operations arise naturally in the trion model of the cortex. The trion model is a highly structured mathematical realization of the Mountcastle organizational principle [Mountcastle, in The Mindful Brain (MIT, Cambridge, 1978)] in which the cortical column is the basic neural network of the cortex and is comprised of subunit minicolumns, which are idealized as trions with three levels of firing. A columnar network of a small number of trions has a large repertoire of quasistable, periodic spatial-temporal firing magic patterns (MP's), which can be excited. The MP's are related by specific symmetries: Spatial rotation, parity, ``spin'' reversal, and time reversal as well as other ``global'' symmetry operations in this abstract internal language of the brain. These MP's can be readily enhanced (as well as inherent categories of MP's) by only a small change in connection strengths via a Hebb learning rule. Learning introduces small breaking of the symmetries in the connectivities which enables a symmetry in the patterns to be recognized in the Monte Carlo evolution of the MP's. Examples of the recognition of rotational invariance and of a time-reversed pattern are presented. We propose the possibility of building a logic device from the hardware implementation of a higher level architecture of trion cortical columns.
Time-reversal and nonlocal effects in PT-symmetric nonlinear lattices with balanced gain and loss
NASA Astrophysics Data System (ADS)
Sukhorukov, Andrey A.; Xu, Zhiyong; Dmitriev, Sergey V.; Suchkov, Sergey V.; Kivshar, Yuri S.
2011-09-01
We reveal a number of fundamentally important effects which underpin the key aspects of light propagation in photonic structures composed of coupled waveguides with loss and gain regions, which are designed as optical analogues of complex parity-time (or PT) symmetric potentials. We identify a generic nature of time-reversals in PT-symmetric optical couplers, which enables flexible control of all-optical switching and a realization of logic operations. We also show that light propagation in PT-symmetric structures can exhibit strongly nonlocal sensitivity to topology of a photonic structure. These results suggest new possibilities for shaping optical beams and pulses compared to conservative structures.
2-D PSTD Simulation of the time-reversed ultrasound-encoded deep-tissue imaging technique
Tseng, Snow H.; Ting, Wei-Lun; Wang, Shiang-Jiu
2014-01-01
We present a robust simulation technique to model the time-reversed ultrasonically encoded (TRUE) technique for deep-tissue imaging. The pseudospectral time-domain (PSTD) algorithm is employed to rigorously model the electromagnetic wave interaction of light propagating through a macroscopic scattering medium. Based upon numerical solutions of Maxwell’s equations, the amplitude and phase are accurately accounted for to analyze factors that affect the TRUE propagation of light through scattering media. More generally, we demonstrate the feasibility of modeling light propagation through a virtual tissue model of macroscopic dimensions with numerical solutions of Maxwell’s equations. PMID:24688821
NASA Astrophysics Data System (ADS)
Reiser, Andreas; Schubert, Klaus R.; Stiewe, Jürgen
2012-08-01
Weak interactions break time-reversal (T) symmetry in the two-state system of neutral K-mesons. We present and discuss a two-state mechanical system, i.e. a Foucault-type pendulum on a rotating table, for a full representation of {K^0}{{\\overlineK}{}^0} transitions by the pendulum motions including T violation. The pendulum moves with two different oscillation frequencies and two different magnetic dampings. Its equation of motion is identical to the differential equation for the real part of the CPT-symmetric K-meson wavefunction. The pendulum is able to represent microscopic CP and T violation with CPT symmetry owing to the macroscopic Coriolis force, which breaks the symmetry under reversal-of-motion. Video clips of the pendulum motions are given as supplementary material.
Rodríguez, E M; Jaque, D; Cantelar, E; Cussó, F; Lifante, G; Busacca, A C; Cino, A; Sanseverino, S R
2007-07-01
In this work we report on the time and spatial resolved fluorescence of Neodymium ions in LiNbO(3) channel waveguides fabricated by Reverse Proton Exchange. The analysis of the fluorescence decay curves obtained with a sub-micrometric resolution has evidenced the presence of a relevant fluorescence quenching inside the channel waveguide. From the comparison between diffusion simulations and the spatial dependence of the (4)F(3/2) fluorescence decay rate we have concluded that the observed fluorescence quenching can be unequivocally related to the presence of H+ ions in the LiNbO(3) lattice. Nevertheless, it turns out that Reverse Proton Exchange guarantees a fluorescence quenching level significantly lower than in similar configurations based on Proton Exchange waveguides. This fluorescence quenching has been found to be accompanied by a relevant red-shift of the (4)F(3/2)?(4)I(9/2) fluorescence band. PMID:19547216
NASA Astrophysics Data System (ADS)
Rodríguez, E. M.; Jaque, D.; Cantelar, E.; Cussó, F.; Lifante, G.; Busacca, A. C.; Cino, A.; Sanseverino, S. R.
2007-07-01
In this work we report on the time and spatial resolved fluorescence of Neodymium ions in LiNbO3 channel waveguides fabricated by Reverse Proton Exchange. The analysis of the fluorescence decay curves obtained with a sub-micrometric resolution has evidenced the presence of a relevant fluorescence quenching inside the channel waveguide. From the comparison between diffusion simulations and the spatial dependence of the 4F3/2 fluorescence decay rate we have concluded that the observed fluorescence quenching can be unequivocally related to the presence of H+ ions in the LiNbO3 lattice. Nevertheless, it turns out that Reverse Proton Exchange guarantees a fluorescence quenching level significantly lower than in similar configurations based on Proton Exchange waveguides. This fluorescence quenching has been found to be accompanied by a relevant red-shift of the 4F3/2→4I9/2 fluorescence band.
Iba, Toshiaki; Emmi, Mari; Hiki, Makoto; Nagayama, Masataka; Aihara, Koichiro; Tabe, Yoko; Yuri, Maiko; Ohsaka, Akimichi
2016-06-01
Clinical demand for the prompt assessment of the activity of direct-acting factor Xa inhibitors in the emergency care setting is increasing. In the present study, we examined whether prothrombin time (PT) tests can serve as a clinically useful indicator of anti-factor Xa activity. In the first series, the in vitro effect of edoxaban on PT was evaluated by spiking human plasma with edoxaban and measuring PT using three different commercial PT tests. In the second series, the reversal effect of prothrombin complex concentrates (PCC) and activated PCC (aPCC) in edoxaban-spiked plasma was evaluated. In the third series, PT of plasma samples from patients administered either 15 or 30 mg/day of edoxaban was assessed, and the results were compared with edoxaban concentrations determined by a calibrated anti-factor Xa activity assay. The spike test revealed that all PT reagents positively correlated with edoxaban. The sensitivity to edoxaban varied among the three reagents and Triniclot(®) Excel S showed the best performance. Prolonged PT by edoxaban was reversed by PCC and aPCC in a dose-dependent manner; however, complete reversal was not achieved. Positive correlation between anti-factor Xa activity and PT was shown in the clinical samples at the edoxaban range from 0 to >300 ng/mL. PMID:26984594
Xu, Limin; Xie, Mengqi; Huang, Jianbin; Yan, Yun
2016-06-14
In situ characterization of the structure of reversible coordination polymers remains a challenge because of their dynamic and concentration-responsive nature. It is especially difficult to determine these structures in their self-assemblies where their degree of polymerization responds to the local concentration. In this paper, we report on the structure of reversible lanthanide coordination polymers in electrostatic assemblies using time-resolved luminescence (TRL) measurement. The reversible coordinating system is composed of the bifunctional ligand 1,11-bis(2,6-dicarboxypyridin-4-yloxy)-3,6,9-trioxaundecane (L2EO4) and europium ion Eu(3+). Upon mixing with the positively charged diblock copolymer poly(2-vinylpyridine)-b-poly(ethylene oxide) (P2VP41-b-PEO205), electrostatic polyion micelles are formed and the negatively charged L2EO4-Eu coordination complex simultaneously transforms into coordination "polymers" in the micellar core. By virtue of the water-sensitive luminescence of Eu(3+), we are able to obtain the structural information of the L2EO4-Eu coordination polymers before and after the formation of polyion micelles. Upon analyzing the fluorescence decay curves of Eu(3+) before and after micellization, the fraction of Eu(3+) fully coordinated with L2EO4 is found to increase from 32 to 83%, which verifies the occurrence of chain extension of the L2EO4-Eu coordination polymers in the micellar core. Our work provides a qualitative picture for the structure change of reversible coordination polymers, which allows us to look into these "invisible" structures. PMID:27228142
Veblen in Reverse: Evidence from the Multinational Time-Use Archive
ERIC Educational Resources Information Center
Gershuny, Jonathan
2009-01-01
This paper explores the historical change in the work-leisure balance using time-diary evidence. Much of the recent discussion of this balance in the developed world has focused on paid work alone. What follows takes a different approach, considering the balance of "all" work time (paid plus unpaid) against leisure time and observes a tendency…
Finn, John M.
2015-03-15
Properties of integration schemes for solenoidal fields in three dimensions are studied, with a focus on integrating magnetic field lines in a plasma using adaptive time stepping. It is shown that implicit midpoint (IM) and a scheme we call three-dimensional leapfrog (LF) can do a good job (in the sense of preserving KAM tori) of integrating fields that are reversible, or (for LF) have a “special divergence-free” (SDF) property. We review the notion of a self-adjoint scheme, showing that such schemes are at least second order accurate and can always be formed by composing an arbitrary scheme with its adjoint. We also review the concept of reversibility, showing that a reversible but not exactly volume-preserving scheme can lead to a fractal invariant measure in a chaotic region, although this property may not often be observable. We also show numerical results indicating that the IM and LF schemes can fail to preserve KAM tori when the reversibility property (and the SDF property for LF) of the field is broken. We discuss extensions to measure preserving flows, the integration of magnetic field lines in a plasma and the integration of rays for several plasma waves. The main new result of this paper relates to non-uniform time stepping for volume-preserving flows. We investigate two potential schemes, both based on the general method of Feng and Shang [Numer. Math. 71, 451 (1995)], in which the flow is integrated in split time steps, each Hamiltonian in two dimensions. The first scheme is an extension of the method of extended phase space, a well-proven method of symplectic integration with non-uniform time steps. This method is found not to work, and an explanation is given. The second method investigated is a method based on transformation to canonical variables for the two split-step Hamiltonian systems. This method, which is related to the method of non-canonical generating functions of Richardson and Finn [Plasma Phys. Controlled Fusion 54, 014004 (2012
NASA Astrophysics Data System (ADS)
Sowiński, Tomasz; Łaçki, Mateusz; Dutta, Omjyoti; Pietraszewicz, Joanna; Sierant, Piotr; Gajda, Mariusz; Zakrzewski, Jakub; Lewenstein, Maciej
2013-11-01
We study the ground-state properties of bosons loaded into the p band of a one-dimensional optical lattice. We show that the phase diagram of the system is substantially affected by the anharmonicity of the lattice potential. In particular, for a certain range of tunneling strength, the full many-body ground state of the system becomes degenerate. In this region, an additional symmetry of the system, namely, the parity of the occupation number of the chosen orbital, is spontaneously broken. The state with a nonvanishing staggered angular momentum, which breaks the time-reversal symmetry, becomes the true ground state of the system.
Sowiński, Tomasz; Łącki, Mateusz; Dutta, Omjyoti; Pietraszewicz, Joanna; Sierant, Piotr; Gajda, Mariusz; Zakrzewski, Jakub; Lewenstein, Maciej
2013-11-22
We study the ground-state properties of bosons loaded into the p band of a one-dimensional optical lattice. We show that the phase diagram of the system is substantially affected by the anharmonicity of the lattice potential. In particular, for a certain range of tunneling strength, the full many-body ground state of the system becomes degenerate. In this region, an additional symmetry of the system, namely, the parity of the occupation number of the chosen orbital, is spontaneously broken. The state with a nonvanishing staggered angular momentum, which breaks the time-reversal symmetry, becomes the true ground state of the system. PMID:24313497
Stöhlker, T; Ma, X; Ludziejewski, T; Beyer, H F; Bosch, F; Brinzanescu, O; Dunford, R W; Eichler, J; Hagmann, S; Ichihara, A; Kozhuharov, C; Krämer, A; Liesen, D; Mokler, P H; Stachura, Z; Swiat, P; Warczak, A
2001-02-01
Radiative electron capture, the time-reversed photoionization process occurring in ion-atom collisions, provides presently the only access to photoionization studies for very highly charged ions. By applying the deceleration mode of the ESR storage ring, we studied this process in low-energy collisions of bare uranium ions with low- Z target atoms. This technique allows us to extend the current information about photoionization to much lower energies than those accessible for neutral heavy elements in the direct reaction channel. The results prove that for high- Z systems, higher-order multipole contributions and magnetic corrections persist even at energies close to the threshold. PMID:11177990
Finn, John M.
2015-03-01
Properties of integration schemes for solenoidal fields in three dimensions are studied, with a focus on integrating magnetic field lines in a plasma using adaptive time stepping. It is shown that implicit midpoint (IM) and a scheme we call three-dimensional leapfrog (LF) can do a good job (in the sense of preserving KAM tori) of integrating fields that are reversible, or (for LF) have a 'special divergence-free' property. We review the notion of a self-adjoint scheme, showing that such schemes are at least second order accurate and can always be formed by composing an arbitrary scheme with its adjoint. Wemore » also review the concept of reversibility, showing that a reversible but not exactly volume-preserving scheme can lead to a fractal invariant measure in a chaotic region, although this property may not often be observable. We also show numerical results indicating that the IM and LF schemes can fail to preserve KAM tori when the reversibility property (and the SDF property for LF) of the field is broken. We discuss extensions to measure preserving flows, the integration of magnetic field lines in a plasma and the integration of rays for several plasma waves. The main new result of this paper relates to non-uniform time stepping for volume-preserving flows. We investigate two potential schemes, both based on the general method of Ref. [11], in which the flow is integrated in split time steps, each Hamiltonian in two dimensions. The first scheme is an extension of the method of extended phase space, a well-proven method of symplectic integration with non-uniform time steps. This method is found not to work, and an explanation is given. The second method investigated is a method based on transformation to canonical variables for the two split-step Hamiltonian systems. This method, which is related to the method of non-canonical generating functions of Ref. [35], appears to work very well.« less
Mean-field studies of time reversal breaking states in super-heavy nuclei with the Gogny force
Robledo, L. M.
2015-10-15
Recent progress on the description of time reversal breaking (odd mass and multi-quasiparticle excitation) states in super-heavy nuclei within a mean field framework and using several flavors of the Gogny interaction is reported. The study includes ground and excited states in selected odd mass isotopes of nobelium and mendelevium as well as high K isomeric states in {sup 254}No. These are two and four-quasiparticle excitations that are treated in the same self-consistent HFB plus blocking framework as the odd mass states.
Jang, Mooseok; Ruan, Haowen; Judkewitz, Benjamin; Yang, Changhuei
2014-01-01
The time-reversed ultrasonically encoded (TRUE) optical focusing technique is a method that is capable of focusing light deep within a scattering medium. This theoretical study aims to explore the depth limits of the TRUE technique for biological tissues in the context of two primary constraints – the safety limit of the incident light fluence and a limited TRUE’s recording time (assumed to be 1 ms), as dynamic scatterer movements in a living sample can break the time-reversal scattering symmetry. Our numerical simulation indicates that TRUE has the potential to render an optical focus with a peak-to-background ratio of ~2 at a depth of ~103 mm at wavelength of 800 nm in a phantom with tissue scattering characteristics. This study sheds light on the allocation of photon budget in each step of the TRUE technique, the impact of low signal on the phase measurement error, and the eventual impact of the phase measurement error on the strength of the TRUE optical focus. PMID:24663917
NASA Astrophysics Data System (ADS)
Ordway, Stephen; King, Dawn; Bahar, Sonya
Reaction-diffusion processes, such as branching-coalescing random walks, can be used to describe the underlying dynamics of nonequilibrium phase transitions. In an agent-based, neutral model of evolutionary dynamics, we have previously shown that our system undergoes a continuous, nonequilibrium phase transition, from extinction to survival, as various system parameters were tuned. This model was shown to belong to the directed percolation (DP) universality class, by measuring the critical exponents corresponding to correlation length ξ⊥, correlation time ξ| |, and particle density β. The fourth critical exponent that defines the DP universality class is β', which measures the survival probability of growth from a single seed organism. Since DP universality is theorized to have time-reversal symmetry, it is assumed that β = β '. In order to confirm the existence of time-reversal symmetry in our model, we evaluate the system growth from a single asexually reproducing organism. Importantly, the critical exponent β' could be useful for comparison to experimental studies of phase transitions in biological systems, since observing growth of microbial populations is significantly easier than observing death. This research was supported by funding from the James S. McDonnell Foundation.
Suzuki, Yuta; Tay, Jian Wei; Yang, Qiang; Wang, Lihong V.
2014-01-01
Time-reversed ultrasonically encoded (TRUE) optical focusing in turbid media was previously implemented using both analog and digital phase conjugation. The digital approach, in addition to its large energy gain, can improve the focal intensity and resolution by iterative focusing. However, performing iterative focusing at each focal position can be time-consuming. Here, we show that by gradually moving the focal position, the TRUE focal intensity is improved, as in iterative focusing at a fixed position, and can be continuously scanned to image fluorescent targets in a shorter time. Also, our setup is the first demonstration of TRUE focusing using a digital phase conjugate mirror in reflection mode, which is more suitable for practical applications. PMID:24978506
Line Nodes and Time Reversal Symmetry Breaking in p-wave Sr2RuO4
NASA Astrophysics Data System (ADS)
Annett, Jf; Gyorffy, Bl; Litak, G.; Wysokinski, Ki
2001-03-01
The superconductor Sr_2RuO4 exhibits broken time reversal symmetry and has a contant Knight shift below Tc. These experiments suggest a pairing state of the ^3He-A type, d(k) = (k_x+ik_y)hatz. On the other hand specific heat measurements of Nishizaki Maeno and Mao (J. Phys. Soc. Japan 69, 572 (2000)) imply that the gap has line nodes. To resolve this contradiction we calculate the energy gap and heat capacity in several alternative scenarios for the pairing interaction. We find that on-site Hunds rule exchange cannot produce the observed T_c. Nearest neighbour spin independent attraction leads to d-wave pairing, while nearest neighbour parallel spin interaction leads to a p-wave state with no line nodes. However we can also obtain a state with line nodes on the alpha-beta Fermi surface sheets, and time reversal symmetry breaking on the gamma sheet. We discuss the possible physical origin of this state and the comparison with available experimental data.
NASA Astrophysics Data System (ADS)
Anversa, Jonas; Piquini, Paulo; Fazzio, Adalberto; Schmidt, Tome M.
2014-11-01
The observation of the quantum spin Hall effect without the need of an external magnetic field in HgTe/CdTe heterostructures triggered the study of materials exhibiting persistent spin-polarized electronic currents at their interfaces. These Dirac-like spin states are predicted to be topologically protected against perturbations preserving time-reversal symmetry. However, nonmagnetic (time-reversal preserving) perturbations will certainly affect these interface states. In this work, the density functional theory is used to characterize the topologically protected states of the (001) HgTe/CdTe heterostructure as well as to understand the influence of external adiabatic parameters as pressure and electric fields on these states. The intrasite Hubbard U term is seen to be important to correctly describe the HgTe bulk band structure. It is shown that, differently from the three-dimensional topological insulators, the HgTe/CdTe interface states present fully in-plane Rashba-like spin texture. Further, biaxial external pressures and electric fields perpendicular to the interfaces are seen to change the energetics and dispersion of the protected states, modifying the energy ordering of the crossing of the polarized interface states inside the band structure, and altering their Fermi velocities while not changing the topological quantum phase. These adiabatic variables can then be used to tune the topologically protected states with respect to the Fermi level.
Effects of time reversal symmetry on phonons in sapphire substrate for ZnO and GaN
NASA Astrophysics Data System (ADS)
Kunert, H. W.; Hoffmann, A.; Machatine, A. G. J.; Malherbe, J.; Barnas, J.; Kaczmarczyk, G.; Haboeck, U.; Seguin, R.
2007-07-01
Vibrational states in a crystal are classified according to the irreducible representations (irreps) of the corresponding factor group G0k/T. The wave vector k runs over the entire Brillouin zone (BZ). For trigonal BZs, the factor groups are determined by the symmetry points Γ, F, L, T, and the symmetry lines Λ, Σ, Y. When the irreps are complex, the time reversal symmetry has to be taken into account. Using the Frobenuis-Schur criterion adapted to space groups with real and complex irreps, we have investigated high symmetry points and lines of the phonons in trigonal crystals: Cr 2O 3,Fe 2O 3,Ti 2O 3,V 2O 3,FeCO 3,CaCO 3,CdCO 3,MgCO 3,MnCO 3,NaCO 3 and ZnCO 3, with the common space group D3d6( R3¯c). We have found several phonons which are influenced by the time reversal symmetry. Therefore, an extra degeneracy of phonons arises. The theoretical results are also compared with available experimental data.
Dynamical invariants in systems with and without broken time-reversal symmetry
Schuch, Dieter
2011-03-21
In the first part of the lectures dynamical invariants in classical mechanics and conventional quantum mechanics will be considered. In particular, we will begin with some remarks on classical mechanics and on quantization in order to establish the theory in the form that will be used later on. Starting from the time-dependent Schroedinger equation, the dynamics of Gaussian wave packets and Ermakov invariants, the time-dependent Green function/Feynman kernel, quantum-classical connections, energetics and Lagrange-Hamilton formalism for quantum uncertainties, momentum space representation and the relation between the Wigner function and the Ermakov invariant will be discussed. The representation of canonical transformations in time-independent and time-dependent quantum mechanics, factorization of the Ermakov invariant and generalized creation/annihilation operators will be studied. Subsequently, the time-independent Schroedinger equation, leading to nonlinear quantum mechanics related to Riccati/Ermakov systems as well as the occurrence of Riccati/Ermakov systems in the treatment of Bose-Einstein condensates via the so-called moment method will be analyzed.In part two, irreversible dynamics of dissipative systems, classical and quantum mechanical descriptions and corresponding invariants will be treated. After some general remarks on classical and quantum mechanics with unitary time-evolution and energy conservation, phenomenological Langevin and Fokker--Planck equations, master equations in classical and quantum mechanics and the system-plus-reservoir approach will be mentioned briefly. Then follows a more detailed discussion of modified Schroedinger equations and, particularly, of a nonlinear Schroedinger equation with complex logarithmic nonlinearity; its properties, solutions, invariants and energetics will be studied. Finally, a comparison with a classical description in expanding coordinates will lead to a non-unitary connection between the logarithmic
NASA Astrophysics Data System (ADS)
Frank, Anna
Magnetic reconnection is a basis for many impulsive phenomena in space and laboratory plasmas accompanied by effective transformation of magnetic energy. Reconnection processes usually occur in relatively thin current sheets (CSs), which separate magnetic fields of different or opposite directions. We report on recent observations of time dependent bending of CSs, which results from plasma dynamics inside the sheet. The experiments are carried out with the CS-3D laboratory device (Institute of General Physics RAS, Moscow) [1]. The CS magnetic structure with an X line provides excitation of the Hall currents and plasma acceleration from the X line to both side edges [2]. In the presence of the guide field By the Hall currents give rise to bending of the sheet: the peripheral regions located away from the X line are deflected from CS middle plane (z=0) in the opposite directions ±z [3]. We have revealed generation of reverse currents jy near the CS edges, i.e. the currents flowing in the opposite direction to the main current in the sheet [4]. There are strong grounds to believe that reverse currents are generated by the outflow plasma jets [5], accelerated inside the sheet and penetrated into the regions with strong normal magnetic field component Bz [4]. An impressive effect of sudden change in the sign of the CS bend has been disclosed recently, when analyzing distributions of plasma density [6] and current away from the X line, in the presence of the guide field By. The CS configuration suddenly becomes opposite from that observed at the initial stage, and this effect correlates well with generation of reverse currents. Consequently this effect can be related to excitation of the reverse Hall currents owing to generation of reverse currents jy in the CS. Hence it may be concluded that CSs may exhibit time dependent vertical z-displacements, and the sheet geometry depends on excitation of the Hall currents, acceleration of plasma jets and generation of reverse
This project involves development, validation testing and application of a fast, efficient method of quantitatively measuring occurrence and concentration of common human viral pathogens, enterovirus and hepatitis A virus, in ground water samples using real-time reverse transcrip...
Liu, Yan; Lai, Puxiang; Ma, Cheng; Xu, Xiao; Grabar, Alexander A.; Wang, Lihong V.
2015-01-01
Focusing light deep inside living tissue has not been achieved despite its promise to play a central role in biomedical imaging, optical manipulation and therapy. To address this challenge, internal-guide-star-based wavefront engineering techniques—for example, time-reversed ultrasonically encoded (TRUE) optical focusing—were developed. The speeds of these techniques, however, were limited to no greater than 1 Hz, preventing them from in vivo applications. Here we improve the speed of optical focusing deep inside scattering media by two orders of magnitude, and focus diffuse light inside a dynamic scattering medium having a speckle correlation time as short as 5.6 ms, typical of living tissue. By imaging a target, we demonstrate the first focusing of diffuse light inside a dynamic scattering medium containing living tissue. Since the achieved focusing speed approaches the tissue decorrelation rate, this work is an important step towards in vivo deep tissue noninvasive optical imaging, optogenetics and photodynamic therapy. PMID:25556918
GPU-accelerated Modeling and Element-free Reverse-time Migration with Gauss Points Partition
NASA Astrophysics Data System (ADS)
Zhen, Z.; Jia, X.
2014-12-01
Element-free method (EFM) has been applied to seismic modeling and migration. Compared with finite element method (FEM) and finite difference method (FDM), it is much cheaper and more flexible because only the information of the nodes and the boundary of the study area are required in computation. In the EFM, the number of Gauss points should be consistent with the number of model nodes; otherwise the accuracy of the intermediate coefficient matrices would be harmed. Thus when we increase the nodes of velocity model in order to obtain higher resolution, we find that the size of the computer's memory will be a bottleneck. The original EFM can deal with at most 81×81 nodes in the case of 2G memory, as tested by Jia and Hu (2006). In order to solve the problem of storage and computation efficiency, we propose a concept of Gauss points partition (GPP), and utilize the GPUs to improve the computation efficiency. Considering the characteristics of the Gaussian points, the GPP method doesn't influence the propagation of seismic wave in the velocity model. To overcome the time-consuming computation of the stiffness matrix (K) and the mass matrix (M), we also use the GPUs in our computation program. We employ the compressed sparse row (CSR) format to compress the intermediate sparse matrices and try to simplify the operations by solving the linear equations with the CULA Sparse's Conjugate Gradient (CG) solver instead of the linear sparse solver 'PARDISO'. It is observed that our strategy can significantly reduce the computational time of K and Mcompared with the algorithm based on CPU. The model tested is Marmousi model. The length of the model is 7425m and the depth is 2990m. We discretize the model with 595x298 nodes, 300x300 Gauss cells and 3x3 Gauss points in each cell. In contrast to the computational time of the conventional EFM, the GPUs-GPP approach can substantially improve the efficiency. The speedup ratio of time consumption of computing K, M is 120 and the
On the Way to Experimental Test of the Time Reversal Invariance in the Nuclear Reactions
Skoy, Vadim R.; Ino, Takashi; Masuda, Yasuhiro; Muto, Suguru; Kim, Guinyun
2005-01-01
Time (T) violation can be related with charge-parity (CP) violation through the CPT theorem. The CP violation was discovered experimentally in the K0-meson decays about 35 years ago. The T violating interaction related with the CP violation violates parity as well. However, an extension of the theory beyond the locality of the interactions might violate the CPT theorem. The result of the CPLEAR experiment [1], which has given direct evidence of T violation in the elementary-particle phenomena, could be considered under assumption of the CPT invariance. PMID:27308170
NASA Astrophysics Data System (ADS)
Liu, Yan; Lai, Puxiang; Ma, Cheng; Xu, Xiao; Suzuki, Yuta; Grabar, Alexander A.; Wang, Lihong V.
2014-03-01
Time-reversed ultrasonically encoded (TRUE) optical focusing is an emerging technique that focuses light deep into scattering media by phase-conjugating ultrasonically encoded diffuse light. In previous work, the speed of TRUE focusing was limited to no faster than 1 Hz by the response time of the photorefractive phase conjugate mirror, or the data acquisition and streaming speed of the digital camera; photorefractive-crystal-based TRUE focusing was also limited to the visible spectral range. These time-consuming schemes prevent this technique from being applied in vivo, since living biological tissue has a speckle decorrelation time on the order of a millisecond. In this work, using a Tedoped Sn2P2S6 photorefractive crystal at a near-infrared wavelength of 793 nm, we achieved TRUE focusing inside dynamic scattering media having a speckle decorrelation time as short as 7.7 ms. As the achieved speed approaches the tissue decorrelation rate, this work is an important step forward toward in vivo applications of TRUE focusing in deep tissue imaging, photodynamic therapy, and optical manipulation.
Space Time Reversal Experiment by Use of Pulsed Neutron Ramsey Resonance
Masuda, Y.; Jeong, S. C.; Watanabe, Y.; Skoy, V.; Ino, T.
2007-06-13
We have developed a pulsed neutron Ramsey resonance for a T-violation experiment on polarized neutron transmission through a polarized nuclear target. Two separated oscillatory fields were placed in a pulsed neutron beam line, which were synchronized with a neutron pulse for precision neutron spin manipulation. We observed neutron Larmor precession between the two oscillatory fields as a function of a neutron time of flight (TOF). We modulated the phase of the second oscillatory field with respect to the first oscillatory field. The effect of the phase modulation was found in a neutron intensity modulation as a function of the TOF. From the neutron intensity modulation, the neutron spin direction as well as the neutron velocity between the two oscillatory fields was precisely obtained.
NASA Astrophysics Data System (ADS)
Gill, Wonpyong
2013-01-01
The probability of additional offspring with a beneficial reversal allele for growing to a size NC for a range of population sizes N, sequence lengths L, selective advantages s, and measuring parameters C was calculated for a haploid, asexual population in the coupled discrete-time mutation-selection model in an asymmetric sharply-peaked landscape with a positive selective advantage of the reversal allele over the optimal allele. The growing probability in the stochastic region was inversely proportional to the measuring parameter when C < 1 /Ns, bent when C ≈ 1/ Ns and saturated when C > 1/ Ns. The crossing time and the time dependence of the increase in relative density of the reversal allele in the coupled discrete-time mutation-selection model was approximated using the Wright-Fisher two-allele model with the same selective advantage and corresponding effective mutation rate. The growth behavior of additional offspring with the reversal allele in the asymmetric sharply-peaked landscape in the coupled discrete-time mutation-selection model was controlled by the selective advantage of the reversal allele compared to the optimal allele and could be described by using the Wright-Fisher two-allele model, in spite of there being many other alleles with lower fitness, and in spite of there being two alleles, the optimal and reversal allele, separated by a low-fitness valley with a tunable depth and width.
Manipulating one-way space wave and its refraction by time-reversal and parity symmetry breaking
Poo, Yin; He, Cheng; Xiao, Chao; Lu, Ming-Hui; Wu, Rui-Xin; Chen, Yan-Feng
2016-01-01
One-way transmission and negative refraction are the exotic wave properties founded in photonic crystals which attract a great attention due to their promising applications in photonic devices. How to integrate such two phenomena in one material or device is interesting and valuable. In this work, we theoretically and experimentally demonstrate that one-way electromagnetic space wave can be realized by means of two-dimensional magnetic photonic crystals. Simultaneously breaking the time-reversal and parity symmetries of the magnetic photonic crystals designed, we observe oblique incident space wave propagating one-way in the magnetic photonic crystals with positive or negative refraction occurring at interfaces, which can be manipulated upon the incident angle and operating frequency. Our work may offer a potential platform to realize some exotic photoelectronic and microwave devices such as one-way imaging and one-way cloaking. PMID:27387438
Manipulating one-way space wave and its refraction by time-reversal and parity symmetry breaking
NASA Astrophysics Data System (ADS)
Poo, Yin; He, Cheng; Xiao, Chao; Lu, Ming-Hui; Wu, Rui-Xin; Chen, Yan-Feng
2016-07-01
One-way transmission and negative refraction are the exotic wave properties founded in photonic crystals which attract a great attention due to their promising applications in photonic devices. How to integrate such two phenomena in one material or device is interesting and valuable. In this work, we theoretically and experimentally demonstrate that one-way electromagnetic space wave can be realized by means of two-dimensional magnetic photonic crystals. Simultaneously breaking the time-reversal and parity symmetries of the magnetic photonic crystals designed, we observe oblique incident space wave propagating one-way in the magnetic photonic crystals with positive or negative refraction occurring at interfaces, which can be manipulated upon the incident angle and operating frequency. Our work may offer a potential platform to realize some exotic photoelectronic and microwave devices such as one-way imaging and one-way cloaking.
Manipulating one-way space wave and its refraction by time-reversal and parity symmetry breaking.
Poo, Yin; He, Cheng; Xiao, Chao; Lu, Ming-Hui; Wu, Rui-Xin; Chen, Yan-Feng
2016-01-01
One-way transmission and negative refraction are the exotic wave properties founded in photonic crystals which attract a great attention due to their promising applications in photonic devices. How to integrate such two phenomena in one material or device is interesting and valuable. In this work, we theoretically and experimentally demonstrate that one-way electromagnetic space wave can be realized by means of two-dimensional magnetic photonic crystals. Simultaneously breaking the time-reversal and parity symmetries of the magnetic photonic crystals designed, we observe oblique incident space wave propagating one-way in the magnetic photonic crystals with positive or negative refraction occurring at interfaces, which can be manipulated upon the incident angle and operating frequency. Our work may offer a potential platform to realize some exotic photoelectronic and microwave devices such as one-way imaging and one-way cloaking. PMID:27387438
NASA Astrophysics Data System (ADS)
Lee, Kang Il; Choi, Bok Kyoung
2014-10-01
A new method for measuring the speed of sound (SOS) in trabecular bone by using a time reversal acoustics (TRA) focusing system was proposed and validated with measurements obtained by using the conventional pulse-transmission technique. The SOS measured in 14 bovine femoral trabecular bone samples by using the two methods was highly correlated each other, although the SOS measured by using the TRA focusing system was slightly lower by an average of 2.2 m/s. The SOS measured by using the two methods showed high correlation coefficients of r = 0.92 with the apparent bone density, consistent with the behavior in human trabecular bone in vitro. These results prove the efficacy of the new method based on the principle of TRA to measure the SOS in trabecular bone.
It's Only A Matter of Time (Reversal): A New Search For The Electric Dipole Moment Of The Neutron
Cooper, M. D.
2007-10-26
An international collaboration has undertaken a project to search for the electric dipole moment (EDM) of the neutron with a sensitivity of 10{sup -28} e{center_dot}cm. The search should span a region of sensitivity where effects are expected from supersysmmetric models and from models of time reversal violation that might explain electroweak baryogenesis. The technique utilizes the special properties for producing and storing ultra-cold neutrons in a bottle filled with liquid {sup 4}He and doped with a small amount of {sup 3}He. The technique will be discussed and compared to that of competing experiments. The extensive R and D program undertaken by the collaboration will be reviewed. The status of the DOE project will be explained.
NASA Astrophysics Data System (ADS)
Martin, Brett D.; Fontana, Jake; Wang, Zheng; Trammell, Scott A.
2015-04-01
Reverse micelles (RMs) containing aqueous solutions of Ag+ ions in their core produce fluorescent Ag nanoclusters (NCs), upon exposure to gamma irradiation. The fluorescence spectra of the NCs evolve over days to weeks after the exposure, and usually show large increases in intensity. Responses of as high as 2.8 × 104 CPS/Gy were reached. A dosage as low as 0.5 Gy (10 % of the lethal dosage for humans) produces NCs having fluorescence intensities higher than background. The RMs can be employed in novel gamma radiation detectors with appearance of fluorescence indicating that radiation was once present. In applications involving detection and tracking of fissile materials, the evolution of the fluorescence spectra over time may provide additional information about the radiation source. A two-phase liquid system is used for RM formation in a simple procedure. It is likely that this synthesis method may be adapted to produce NCs from other metal ions.
Alternative stable qP wave equations in TTI media with their applications for reverse time migration
NASA Astrophysics Data System (ADS)
Zhou, Yang; Wang, Huazhong; Liu, Wenqing
2015-10-01
Numerical instabilities may arise if the spatial variation of symmetry axis is handled improperly when implementing P-wave modeling and reverse time migration in heterogeneous tilted transversely isotropic (TTI) media, especially in the cases where fast changes exist in TTI symmetry axis’ directions. Based on the pseudo-acoustic approximation to anisotropic elastic wave equations in Cartesian coordinates, alternative second order qP (quasi-P) wave equations in TTI media are derived in this paper. Compared with conventional stable qP wave equations, the proposed equations written in stress components contain only spatial derivatives of wavefield variables (stress components) and are free from spatial derivatives involving media parameters. These lead to an easy and efficient implementation for stable P-wave modeling and imaging. Numerical experiments demonstrate the stability and computational efficiency of the presented equations in complex TTI media.
Pérez-Carro, G; Fernández-Alonso, R; González-Diéguez, M L; Rodríguez-García, M; Junceda-Moreno, J
2014-04-01
Clinical case A patient with chronic, painless, bilateral loss of vision, after significant intake of interferon (IFNα) and ribavirina due to liver transplant. Ocular fundus is normal. A suspected retrobulbar optic neuropathy is confirmed by a prolongation of the latency of the patient's visual evoked potential. There being no prior record of risk factors and with the patient's systemic analysis giving normal results, the clinical improvement and the electro-physiological tests conducted after the drug was withdrawn point to interferon as negatively affecting the bilateral optic nerve. Discussion Interferon-α is used in the treatment of viral and neoplastic illnesses. Currently the drug is formulated as Interferon alfa pegilado (IFNα-p) in order to reduce toxicity and increase tolerance. The most common secondary effects are flu symptoms, asthenia and weigh loss. Affected ocular tissue is rare and optic neuropathy is also an infrequent complication: retinopathy at the beginning of treatment is, however, more frequent. The most widely accepted hypothesis as to the cause of toxicity is the presence of circulating immune complexes. It is, therefore, essential for ophthalmologists to be aware of the toxicity of this drug in order to be able to withdraw it in good time, thus preventing potentially irreversible sight loss. PMID:24269470
Spin-photon interaction in a cavity with time-reversal symmetry breaking
NASA Astrophysics Data System (ADS)
Goryachev, Maxim; Farr, Warrick G.; Creedon, Daniel L.; Tobar, Michael E.
2014-06-01
Employing a sapphire whispering gallery mode resonator, we demonstrate features of the spin-photon interaction in cavities with broken time-reflection symmetry. The broken symmetry leads to a lifting of the degeneracy between left-handed and right-handed polarized cavity photons, which results in an observable gyrotropic effect. In the high-Q cavity limit, such a situation requires a modification of the Tavis-Cummings Hamiltonian to take into account conservation of spin angular momentum and the corresponding selection rules. As a result, the system is represented by a system of two linearly coupled bosonic modes, with each one coupled to its own subensemble of two-level systems with different energy splittings. In the experimental example, these subensembles originate from Fe3+ impurity ions effectively seen as a two-level system at the interaction frequency. The temperature dependence of the population of each subensemble (in terms of effective susceptibility of the medium) is determined experimentally in accordance with the theoretical predictions revealing various paramagnetic impurity types in the solid. The regimes of backscatterer and spin ensemble domination are discussed and compared.
Mekata, Tohru; Sudhakaran, Raja; Kono, Tomoya; U-taynapun, Kittichon; Supamattaya, Kidchakan; Suzuki, Yoshihiro; Sakai, Masahiro; Itami, Toshiaki
2009-12-01
A real-time reverse transcription loop-mediated isothermal amplification (real-time RT-LAMP) method was applied for detecting the replicase polyprotein-encoding gene of yellow head virus (YHV) in shrimp, Penaeus monodon. It is a novel, gene-specific assay that amplifies nucleic acid with high specificity, sensitivity and rapidity under isothermal conditions using a set of six specially designed primers that recognize eight distinct sequences of the target gene. This method works with even low copies of DNA and is based on magnesium pyrophosphate turbidity detection by an inexpensive photometer for quantitative analysis. A user-friendly protocol was developed with optimal conditions standardized at 63 degrees C for 60 min. With this protocol, the assay sensitivity was 10 times higher than the widely used YHV nested RT-PCR system. Cross-reactivity analysis using other shrimp virus DNA/cDNA and YHV-negative shrimp demonstrated high specificity of the assay. The real-time RT-LAMP method was performed also for an internal control gene, EF-1alpha, to compare with the expressions of the YHV gene in different organs of infected shrimp, and the resulting standard curves showed high correlation coefficient values. These results suggest that this assay is applicable widely as a new quantitative detection method in the pursuit of YHV-free shrimp culture. PMID:19646483
NASA Astrophysics Data System (ADS)
Gupta, Niraj K.; Hwang, Yongsoon; Cameron, Brent D.
2016-03-01
Recent developments in the identification of biomarkers offer a potential means to facilitate early disease detection, gauge treatment in drug therapy clinical trials, and to assess the impact of fatigue and/or stress as related to human physical and cognitive performance. For practical implementation, however, real-time sensing and quantification of such physiological biomarkers is preferred. Some key aspects in this process are continuous sample collection and real time detection. Traditionally, blood is considered the gold standard for samples but frequent phlebotomy is painful and inconvenient. Other sources like saliva and passive sweat cannot be precisely controlled and are affected by other limitations. Some of these can be addressed by reverse iontophoresis which is a noninvasive technique capable of facilitating controlled transport of biomolecules up to 20kDa in size across the skin barrier by passing a low level current between two dermal electrodes. The samples collected at the electrode site can then be monitored at site or transported via a microfluidic channel towards a sensor. In the case reported here, the sensor is based on surface plasmon resonance (SPR), which is a label free, real time, and highly sensitive optical sensing technique. The real time SPR detection of targeted biomarkers is then achieved through the use of aptamer surface modification. In this experiment, extraction and detection of orexin A, a stress related biomarker, is used for demonstration purposes.
Delnatte, Pauline; Mak, Matthew; Ojkic, Davor; Raghav, Raj; DeLay, Josepha; Smith, Dale A
2014-03-01
Avian bornavirus (ABV), the cause of proventricular dilation disease in psittacine birds, has been detected in multiple tissues of infected birds using immunohistochemical staining (IHC) and reverse transcription polymerase chain reaction (RT-PCR). In the current study, real-time RT-PCR, using primers targeting the ABV matrix gene, was used to detect ABV in 146 tissues from 7 ABV-infected psittacine birds. Eighty-six percent of the samples tested positive, with crossing point values ranging from 13.82 to 37.82 and a mean of 22.3. These results were compared to the findings of a previous study using gel-based RT-PCR and IHC on the same samples. The agreement between the 2 RT-PCR techniques was 91%; when tests disagreed it was because samples were negative using gel-based RT-PCR but positive on real-time RT-PCR. Agreement with IHC was 77%; 16 out of 74 samples were negative using IHC but positive on real-time RT-PCR. The results suggest that real-time RT-PCR is a more sensitive technique than gel-based RT-PCR and IHC to detect ABV in tissues. The tissues that were ranked most frequently as having a high amount of viral RNA were proventriculus, kidney, colon, cerebrum, and cerebellum. Skeletal muscle, on the other hand, was found to have a consistently low amount of viral RNA. PMID:24518276
Nordgård, Oddmund; Kvaløy, Jan Terje; Farmen, Ragne Kristin; Heikkilä, Reino
2006-09-15
Real-time reverse transcription polymerase chain reaction (RT-PCR) has gained wide popularity as a sensitive and reliable technique for mRNA quantification. The development of new mathematical models for such quantifications has generally paid little attention to the aspect of error propagation. In this study we evaluate, both theoretically and experimentally, several recent models for relative real-time RT-PCR quantification of mRNA with respect to random error accumulation. We present error propagation expressions for the most common quantification models and discuss the influence of the various components on the total random error. Normalization against a calibrator sample to improve comparability between different runs is shown to increase the overall random error in our system. On the other hand, normalization against multiple reference genes, introduced to improve accuracy, does not increase error propagation compared to normalization against a single reference gene. Finally, we present evidence that sample-specific amplification efficiencies determined from individual amplification curves primarily increase the random error of real-time RT-PCR quantifications and should be avoided. Our data emphasize that the gain of accuracy associated with new quantification models should be validated against the corresponding loss of precision. PMID:16899212
NASA Astrophysics Data System (ADS)
Kisielowski, Christian; Wang, Lin-Wang; Specht, Petra; Calderon, Hector A.; Barton, Bastian; Jiang, Bin; Kang, Joo H.; Cieslinski, Robert
2013-07-01
The dynamic responses of a rhodium catalyst and a graphene sheet are investigated upon random excitation with 80 kV electrons. An extraordinary electron microscope stability and resolution allow studying temporary atom displacements from their equilibrium lattice sites into metastable sites across projected distances as short as 60 pm. In the rhodium catalyst, directed and reversible atom displacements emerge from excitations into metastable interstitial sites and surface states that can be explained by single atom trajectories. Calculated energy barriers of 0.13 eV and 1.05 eV allow capturing single atom trapping events at video rates that are stabilized by the Rh [110] surface corrugation. Molecular dynamics simulations reveal that randomly delivered electrons can also reversibly enhance the sp3 and the sp1 characters of the sp2-bonded carbon atoms in graphene. The underlying collective atom motion can dynamically stabilize characteristic atom displacements that are unpredictable by single atom trajectories. We detect three specific displacements and use two of them to propose a path for the irreversible phase transformation of a graphene nanoribbon into carbene. Collectively stabilized atom displacements greatly exceed the thermal vibration amplitudes described by Debye-Waller factors and their measured dose rate dependence is attributed to tunable phonon contributions to the internal energy of the systems. Our experiments suggest operating electron microscopes with beam currents as small as zepto-amperes/nm2 in a weak-excitation approach to improve on sample integrity and allow for time-resolved studies of conformational object changes that probe for functional behavior of catalytic surfaces or molecules.
Real-Time Reverse Transcription-PCR Assay for Detection of Mumps Virus RNA in Clinical Specimens▿
Boddicker, Jennifer D.; Rota, Paul A.; Kreman, Trisha; Wangeman, Andrea; Lowe, Louis; Hummel, Kimberly B.; Thompson, Robert; Bellini, William J.; Pentella, Michael; DesJardin, Lucy E.
2007-01-01
The mumps virus is a negative-strand RNA virus in the family Paramyxoviridae. Mumps infection results in an acute illness with symptoms including fever, headache, and myalgia, followed by swelling of the salivary glands. Complications of mumps can include meningitis, deafness, pancreatitis, orchitis, and first-trimester abortion. Laboratory confirmation of mumps infection can be made by the detection of immunoglobulin M-specific antibodies to mumps virus in acute-phase serum samples, the isolation of mumps virus in cell culture, or by detection of the RNA of the mumps virus by reverse transcription (RT)-PCR. We developed and validated a multiplex real-time RT-PCR assay for rapid mumps diagnosis in a clinical setting. This assay used oligonucleotide primers and a TaqMan probe targeting the mumps SH gene, as well as primers and a probe that targeted the human RNase P gene to assess the presence of PCR inhibitors and as a measure of specimen quality. The test was specific, since it did not amplify a product from near-neighbor viruses, as well as sensitive and accurate. Real-time RT-PCR results showed 100% correlation with results from viral culture, the gold standard for mumps diagnostic testing. Assay efficiency was over 90% and displayed good precision after performing inter- and intraassay replicates. Thus, we have developed and validated a molecular method for rapidly diagnosing mumps infection that may be used to complement existing techniques. PMID:17652480
Petritis, Konstantinos; Kangas, Lars J.; Yan, Bo; Monroe, Matthew E.; Strittmatter, Eric F.; Qian, Weijun; Adkins, Joshua N.; Moore, Ronald J.; Xu, Ying; Lipton, Mary S.; Camp, David G.; Smith, Richard D.
2006-07-15
We describe an improved artificial neural network (ANN)-based method for predicting peptide retention times in reversed phase liquid chromatography. In addition to the peptide amino acid composition, this study investigated several other peptide descriptors to improve the predictive capability, such as peptide length, sequence, hydrophobicity and hydrophobic moment, and nearest neighbor amino acid, as well as peptide predicted structural configurations (i.e., helix, sheet, coil). An ANN architecture that consisted of 1052 input nodes, 24 hidden nodes, and 1 output node was used to fully consider the amino acid residue sequence in each peptide. The network was trained using {approx}345,000 non-redundant peptides identified from a total of 12,059 LC-MS/MS analyses of more than 20 different organisms, and the predictive capability of the model was tested using 1303 confidently identified peptides that were not included in the training set. The model demonstrated an average elution time precision of {approx}1.5% and was able to distinguish among isomeric peptides based upon the inclusion of peptide sequence information. The prediction power represents a significant improvement over our earlier report (Petritis et al., Anal. Chem. 2003, 75, 1039-1048) and other previously reported models.
Robert, Jean-Luc; Fink, Mathias
2009-01-01
The decomposition of the time reversal operator, known by the French acronym DORT, is widely used to detect, locate, and focus on scatterers in various domains such as underwater acoustics, medical ultrasound, and nondestructive evaluation. In the case of point-scatterers, the theory is well understood: The number of nonzero eigenvalues is equal to the number of scatterers, and the eigenvectors correspond to the scatterers Green's function. In the case of extended objects, however, the formalism is not as simple. It is shown here that, in the Fraunhofer approximation, analytical solutions can be found and that the solutions are functions called prolate spheroidal wave-functions. These functions have been studied in information theory as a basis of band-limited and time-limited signals. They also arise in optics. The theoretical solutions are compared to simulation results. Most importantly, the intuition that for an extended objects, the number of nonzero eigenvalues is proportional to the number of resolution cell in the object is justified. The case of three-dimensional objects imaged by a two-dimensional array is also dealt with. Comparison with previous solutions is made, and an application to super-resolution of scatterers is presented. PMID:19173409
Qian, Zhaosheng; Chai, Lujing; Zhou, Qian; Huang, Yuanyuan; Tang, Cong; Chen, Jianrong; Feng, Hui
2015-07-21
A reversible fluorescence nanoswitch by integrating carbon quantum dots nanoassembly and pyrophosphate ion is developed, and a reliable real-time fluorescent assay for acid phosphatase (ACP) activity is established on the basis of the fluorescence nanoswitch. Carbon quantum dots (CQDs) abundant in carboxyl groups on the surface, nickel(II) ion and pyrophosphate ion comprise the fluorescent nanoswitch, which operates in the following way: the nanoassembly consisting of CQDs and nickel ions can be triggered by pyrophosphate ion serving as an external stimulus. At the same time, the fluorescence nanoswitch switches between two fluorescence states (OFF and ON) accompanying shifts in their physical states aggregation and disaggregation. Based on the nanoswitch, the introduction of ACP leads to breakdown of pyrophosphate ions into phosphate ions and resultant fluorescence quenching due to catalytic hydrolysis of ACP toward pyrophosphate ions (PPi). Quantitative evaluation of ACP activity in a broad range from 18.2 U/L to 1300 U/L, with a detection limit of 5.5 U/L, can be achieved in this way, which endows the assay with sufficiently high sensitivity for practical detection in human serum and seminal plasma. PMID:26115095
Hierro, Núria; Esteve-Zarzoso, Braulio; González, Ángel; Mas, Albert; Guillamón, Jose M.
2006-01-01
Real-time PCR, or quantitative PCR (QPCR), has been developed to rapidly detect and quantify the total number of yeasts in wine without culturing. Universal yeast primers were designed from the variable D1/D2 domains of the 26S rRNA gene. These primers showed good specificity with all the wine yeasts tested, and they did not amplify the most representative wine species of acetic acid bacteria and lactic acid bacteria. Numerous standard curves were constructed with different strains and species grown in yeast extract-peptone-dextrose medium or incubated in wine. The small standard errors with these replicas proved that the assay is reproducible and highly robust. This technique was validated with artificially contaminated and natural wine samples. We also performed a reverse transcription-QPCR (RT-QPCR) assay from rRNA for total viable yeast quantification. This technique had a low detection limit and was more accurate than QPCR because the dead cells were not quantified. As far as we know, this is the first time that RT-QPCR has been performed to quantify viable yeasts from rRNA. RT-QPCR is a rapid and accurate technique for enumerating yeasts during industrial wine fermentation and controlling the risk of wine spoilage. PMID:17088381
NASA Astrophysics Data System (ADS)
Sun, Dong; Jiao, Kun; Cheng, Xin; Vigh, Denes
2015-06-01
In conventional marine seismic surveys, due to the time-delayed reflections from the sea surface on both source and receiver sides, ghosts present in recorded seismograms and lead to both phase and spectrum distortions (especially near certain frequency notches). To achieve a high-quality broad-band image/velocity model with conventional reverse time migration (RTM)/full waveform inversion (FWI) that adopts a synthetic zero-phase source wavelet and absorbing surface condition during wavefield modelling, marine seismic data have to be pre-processed to remove ghost effects. However, seismic deghosting is not a trivial task. Instead of employing an external deghosting process, we propose a strategy to compensate for ghost effects during FWI and RTM, which consists of two parts: first, to address phase distortions due to ghost effects by means of obtaining an accurate source wavelet estimation and adopting an appropriate surface boundary condition in both forward and backward wave propagation to appropriately generate ghosts; secondly, to build a compensation operator in the adjoint state computation to mitigate spectrum distortions caused by dominant ghost effects. To demonstrate the success and robustness of the proposed strategy, we present both synthetic experiments and field examples, which suggest that this strategy can lead to successful applications of FWI/RTM directly on marine seismic data without an extra deghosting process.
Buitrago, Dolores; Rocha, Ana; Tena-Tomás, Cristina; Vigo, Marta; Agüero, Montserrat; Jiménez-Clavero, Miguel Angel
2012-09-01
In September 2010, an outbreak of disease in 2 wild bird species (red-legged partridge, Alectoris rufa; ring-necked pheasant, Phasianus colchicus) occurred in southern Spain. Bagaza virus (BAGV) was identified as the etiological agent of the outbreak. BAGV had only been reported before in Western Africa (Central African Republic, Senegal) and in India. The first occurrence of BAGV in Spain stimulated a demand for rapid, reliable, and efficacious diagnostic methods to facilitate the surveillance of this disease in the field. This report describes a real-time reverse transcription polymerase chain reaction (RT-PCR) method based on a commercial 5'-Taq nuclease-3' minor groove binder DNA probe and primers targeting the Bagaza NS5 gene. The method allowed the detection of BAGV with a high sensitivity, whereas other closely related flaviviruses (Usutu virus, West Nile virus, and Japanese encephalitis virus) were not detected. The assay was evaluated using field samples of red-legged partridges dead during the outbreak (n = 11), as well as samples collected from partridges during surveillance programs (n = 81). The results were compared to those obtained with a pan-flaviviral hemi-nested RT-PCR followed by nucleotide sequencing, which was employed originally to identify the virus involved in the outbreak. The results obtained with both techniques were 100% matching, indicating that the newly developed real-time RT-PCR is a valid technique for BAGV genome detection, useful in both diagnosis and surveillance studies. PMID:22807508
Real-Time Reverse Transcription-PCR Quantitation of Substance P Receptor (NK-1R) mRNA
Lai, Jian-Ping; Douglas, Steven D.; Wang, Yan-Jian; Ho, Wen-Zhe
2005-01-01
The substance P (SP)-preferring receptor, neurokinin-1 receptor (NK-1R), has an important role in inflammation, immune regulation, and viral infection. We applied a newly developed real-time reverse transcription (RT)-PCR assay to quantify NK-1R mRNA in human neuronal cell line (NT-2N), a human B-cell line (IM9), monocyte-derived macrophages (MDM), peripheral blood lymphocytes (PBL), and human astroglioma cells (U87 MG). The NK-1R real-time RT-PCR assay has a sensitivity of 100 mRNA copies, with a dynamic range of detection between 102 and 107 copies of NK-1R gene transcripts per reaction. This assay is highly reproducible, with an intraassay coefficient variation of threshold cycle (Ct) of less than 1.9%. The NK-1R real-time RT-PCR is highly sensitive for quantitative determination of NK-1R mRNA in human immune cells (MDM and PBL) that express low levels of NK-1R mRNA. In addition, the assay has the ability to accurately quantitate the dynamic changes in NK-1R mRNA expression in interleukin-1β-stimulated U87 MG. These data indicate that the NK-1R real-time RT-PCR has potential for a wide application in investigation of NK-1R expression at the mRNA level under physiological and pathological conditions in both the central nervous system and the immune system. PMID:15817763
NASA Astrophysics Data System (ADS)
Wu, Binlin
New near-infrared (NIR) diffuse optical tomography (DOT) approaches were developed to detect, locate, and image small targets embedded in highly scattering turbid media. The first approach, referred to as time reversal optical tomography (TROT), is based on time reversal (TR) imaging and multiple signal classification (MUSIC). The second approach uses decomposition methods of non-negative matrix factorization (NMF) and principal component analysis (PCA) commonly used in blind source separation (BSS) problems, and compare the outcomes with that of optical imaging using independent component analysis (OPTICA). The goal is to develop a safe, affordable, noninvasive imaging modality for detection and characterization of breast tumors in early growth stages when those are more amenable to treatment. The efficacy of the approaches was tested using simulated data, and experiments involving model media and absorptive, scattering, and fluorescent targets, as well as, "realistic human breast model" composed of ex vivo breast tissues with embedded tumors. The experimental arrangements realized continuous wave (CW) multi-source probing of samples and multi-detector acquisition of diffusely transmitted signal in rectangular slab geometry. A data matrix was generated using the perturbation in the transmitted light intensity distribution due to the presence of absorptive or scattering targets. For fluorescent targets the data matrix was generated using the diffusely transmitted fluorescence signal distribution from the targets. The data matrix was analyzed using different approaches to detect and characterize the targets. The salient features of the approaches include ability to: (a) detect small targets; (b) provide three-dimensional location of the targets with high accuracy (~within a millimeter or 2); and (c) assess optical strength of the targets. The approaches are less computation intensive and consequently are faster than other inverse image reconstruction methods that
NASA Astrophysics Data System (ADS)
Ghosh, Arindam
Three-dimensional bulk-doped semiconductors, in particular phosphorus (P)-doped silicon (Si) and germanium (Ge), are among the best studied systems for many fundamental concepts in solid state physics, ranging from the Anderson metal-insulator transition to the many-body Coulomb interaction effects on quantum transport. Recent advances in material engineering have led to vertically confined doping of phosphorus (P) atoms inside bulk crystalline silicon and germanium, where the electron transport occurs through one or very few atomic layers, constituting a new and unique platform to investigate many of these phenomena at reduced dimensions. In this talk I shall present results of extensive quantum transport experiments in delta-doped silicon and germanium epilayers, over a wide range of doping density that allow independent tuning of the on-site Coulomb interaction and hopping energy scales. We find that low-frequency flicker noise, or the 1 / f noise, in the electrical conductance of these systems is exceptionally low, and in fact among the lowest when compared with other low-dimensional materials. This is attributed to the physical separation of the conduction electrons, embedded inside the crystalline semiconductor matrix, from the charged fluctuators at the surface. Most importantly, we find a remarkable suppression of weak localization effects, including the quantum correction to conductivity and universal conductance fluctuations, with decreasing doping density or, equivalently, increasing effective on-site Coulomb interaction. In-plane magneto-transport measurements indicate the presence of intrinsic local spin fluctuations at low doping although no signatures of long range magnetic order could be identified. We argue that these results indicate a spontaneous breakdown of time reversal symmetry, which is one of the most fundamental and robust symmetries of nonmagnetic quantum systems. While the microscopic origin of this spontaneous time reversal symmetry
NASA Astrophysics Data System (ADS)
Ławniczak, Michał; Bauch, Szymon; Hul, Oleh; Sirko, Leszek
2010-04-01
We present the results of the experimental study of the two-port scattering matrix Ŝ elastic enhancement factor WS,β for microwave irregular networks simulating quantum graphs with preserved and broken time reversal symmetry in the presence of moderate and strong absorption. In the experiment, quantum graphs with preserved time reversal symmetry were simulated by microwave networks which were built of coaxial cables and attenuators connected by joints. Absorption in the networks was controlled by the length of microwave cables and the use of microwave attenuators. In order to simulate quantum graphs with broken time reversal symmetry we used the microwave networks with microwave circulators. We show that the experimental results obtained for networks with moderate and strong absorption are in good agreement with the ones obtained within the framework of random matrix theory.
Ławniczak, Michał; Bauch, Szymon; Hul, Oleh; Sirko, Leszek
2010-04-01
We present the results of the experimental study of the two-port scattering matrix S[over ] elastic enhancement factor W{S,beta} for microwave irregular networks simulating quantum graphs with preserved and broken time reversal symmetry in the presence of moderate and strong absorption. In the experiment, quantum graphs with preserved time reversal symmetry were simulated by microwave networks which were built of coaxial cables and attenuators connected by joints. Absorption in the networks was controlled by the length of microwave cables and the use of microwave attenuators. In order to simulate quantum graphs with broken time reversal symmetry we used the microwave networks with microwave circulators. We show that the experimental results obtained for networks with moderate and strong absorption are in good agreement with the ones obtained within the framework of random matrix theory. PMID:20481804
NASA Astrophysics Data System (ADS)
Liu, Sixin; Lei, Linlin; Fu, Lei; Wu, Junjun
2014-08-01
Reverse-time migration (RTM) is used for subsurface imaging to handle complex velocity models including steeply dipping interfaces and dramatic lateral variations and promises better imaging results compared to traditional migration method such as Kirchhoff migration algorithm. RTM has been increasingly used in seismic surveys for hydrocarbon resource explorations. Based on the similarity of kinematics and dynamics between electromagnetic wave and elastic wave, we develop pre-stack RTM method and apply it to process ground penetrating radar (GPR) data. Finite-difference time domain (FDTD) numerical method is used to simulate the electromagnetic wave propagation including forward and backward extrapolations, the cross-correlation imaging condition is used to obtain the final image. In order to provide a velocity model with relatively higher accuracy as the initial velocity model for RTM, we apply a full waveform inversion (FWI) in time domain to estimate the subsurface velocity structure based on reflection radar data. For testing the effectiveness of the algorithm, we have constructed a complex geological model, common-offset radar data and common-shot profile (CSP) radar reflection data are synthesized. All data are migrated with traditional Kirchhoff migration method and pre-stack RTM method separately, the migration results from pre-stack RTM show better coincidence with the true model. Furthermore, we have performed a physical experiment in a sandbox where a polyvinyl chloride (PVC) box is buried in the sand, the obtained common-offset radar data and common-shot radar data are migrated by using Kirchhoff migration method and pre-stack RTM algorithm separately, the pre-stack RTM result shows that RTM algorithm could get better imaging results.
Time-dependent reversal of long-term potentiation by brief cooling shocks in rat hippocampal slices.
Bittar, P; Muller, D
1993-08-27
Using a recording chamber built with peltier elements, we studied the effects of fast and brief reductions in temperature on synaptic transmission and plasticity in area CA1 of rat hippocampal slices. Cooling shocks consisted of a drop in temperature from 33 degrees C to 30 degrees C, 27 degrees C or 24 degrees C for 2-5 min. Equilibrium to the new temperature was reached in about 30 s. During these cooling episodes, marked modifications of the size and time course of synaptic responses were observed. Changing the temperature for 4-5 min from 33 degrees C to 24 degrees C resulted in a 75% reduction in amplitude and 158% prolongation of the rise time of excitatory postsynaptic potentials (EPSPs). These changes were followed by a complete recovery of synaptic transmission. This recovery was very fast for the EPSP rise time (about 30 s), but much slower for the amplitude or initial slope (20-30 min). This slow recovery was correlated with changes in size of the presynaptic fiber volley, thereby indicating transient modifications of cell excitability. Application of cooling episodes of 4-5 min from 33 degrees C to 24 degrees C during the first 20 min that followed induction of long-term potentiation resulted in a complete reversal of synaptic potentiation. The LTP abolished by a cooling shock could be reinstated by re-applying high frequency trains. Several sequential induction/abolition effects could thus be obtained. In contrast, cooling episodes applied later than 25 min after LTP induction did not affect synaptic potentiation.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:8396492
Pedersen, J.; Killian, M.L.; Hines, N.; Senne, D.; Panigrahy, B.; Ip, H.S.; Spackman, Erica
2010-01-01
This report describes the validation of an avian influenza virus (AIV) H7 subtype-specific real-time reverse transcriptasePCR (rRT-PCR) assay developed at the Southeast Poultry Research Laboratory (SEPRL) for the detection of H7 AI in North and South American wild aquatic birds and poultry. The validation was a collaborative effort by the SEPRL and the National Veterinary Services Laboratories. The 2008 H7 rRT-PCR assay detects 101 50% embryo infectious doses per reaction, or 103104 copies of transcribed H7 RNA. Diagnostic sensitivity and specificity were estimated to be 97.5% and 82.4%, respectively; the assay was shown to be specific for H7 AI when tested with >270 wild birds and poultry viruses. Following validation, the 2008 H7 rRT-PCR procedure was adopted as an official U.S. Department of Agriculture procedure for the detection of H7 AIV. The 2008 H7 assay replaced the previously used (2002) assay, which does not detect H7 viruses currently circulating in wild birds in North and South America. ?? 2010 American Association of Avian Pathologists.
NASA Astrophysics Data System (ADS)
Derakhshan, V.; Ketabi, S. A.; Moghaddam, A. G.
2016-09-01
We employed the formalism of bond currents, expressed in terms of non-equilibrium Green’s function to obtain the local currents and transport features of zigzag silicene ribbon in the presence of magnetic impurity. When only intrinsic and Rashba spin–orbit interactions are present, silicene behaves as a two-dimensional topological insulator with gapless edge states. But in the presence of finite intrinsic spin–orbit interaction, the edge states start to penetrate into the bulk of the sample by increasing Rashba interaction strength. The exchange interaction induced by local impurities breaks the time-reversal symmetry of the gapless edge states and influences the topological properties strongly. Subsequently, the singularity of partial Berry curvature disappears and the silicene nanoribbon becomes a trivial insulator. On the other hand, when the concentration of the magnetic impurities is low, the edge currents are not affected significantly. In this case, when the exchange field lies in the x–y plane, the spin mixing around magnetic impurity is more profound rather than the case in which the exchange field is directed along the z-axis. Nevertheless, when the exchange field of magnetic impurities is placed in the x–y plane, a spin-polarized conductance is observed. The resulting conductance polarization can be tuned by the concentration of the impurities and even completely polarized spin transport is achievable.
NASA Astrophysics Data System (ADS)
Liu, Qiancheng; Zhang, Jianfeng; Zhang, Hao
2016-07-01
Cross-correlation reverse-time migration is the kernel of two-way wave-equation migration and inversion. However, it more or less tapers the spectrum of receiver data due to a redundant overlay of the source wavelet, whose amplitude spectrum is usually bandlimited and non-flat. To circumvent this issue, there are two optional strategies: whitening the source directly, or preconditioning the seismic traces by division with the amplitude spectrum of the source in the frequency domain. In this paper, we choose the latter one because the source signature is crucial to illumination compensation and seismic inversion. To avoid division by zero, a modified stabilized division algorithm based on the Taylor-expansion is developed. The modified division is easy to complete with computers and can be extend to any order. Moreover, when simulating 2-D source wavefield, the half-integral effect is also considered. We will demonstrate our proposed scheme using the Sigsbee2b synthetic data and a real field data.
NASA Astrophysics Data System (ADS)
Hajati, Yaser
2015-04-01
We investigate the charge transport through a graphene-based ferromagnetic-insulator-superconductor junction with a broken time reversal symmetry (BTRS) of dx2-y2 + is and dx2-y2 + idxy superconductor using the extended Blonder-Tinkham-Klapwijk formalism. Our analysis have shown several charateristics in this junction, providing a useful probe to understand the role of the order parameter symmetry in the superconductivity. We find that the presence of the BTRS (X) state in the superconductor region has a strong effect on the tunneling conductance curves which leads to a decrease in the height of the zero-bias conductance peak (ZBCP). In particular, we show that the magnitude of the superconducting proximity effect depends to a great extent on X and by increasing X, the zero-bias charge conductance oscillations with respect to the rotation angle β are suppressed. In addition, we find that at the maximum rotation angle β = π/4, introducing BTRS in the FIS junction causes oscillatory behavior of the zero-bias charge conductance with the barrier strength (χG) by a period of π and by approaching the X to 1, the amplitude of charge conductance oscillations increases. This behavior is drastically different from none BTRS similar graphene junctions. At last, we suggest an experimental setup for verifying our predicted effects.
NASA Astrophysics Data System (ADS)
Yu, Yang; Bing-Zhong, Wang; Shuai, Ding
2016-05-01
Utilizing channel reciprocity, time reversal (TR) technique increases the signal-to-noise ratio (SNR) at the receiver with very low transmitter complexity in complex multipath environment. Present research works about TR multiple-input multiple-output (MIMO) communication all focus on the system implementation and network building. The aim of this work is to analyze the influence of antenna coupling on the capacity of wideband TR MIMO system, which is a realistic question in designing a practical communication system. It turns out that antenna coupling stabilizes the capacity in a small variation range with statistical wideband channel response. Meanwhile, antenna coupling only causes a slight detriment to the channel capacity in a wideband TR MIMO system. Comparatively, uncorrelated stochastic channels without coupling exhibit a wider range of random capacity distribution which greatly depends on the statistical channel. The conclusions drawn from information difference entropy theory provide a guideline for designing better high-performance wideband TR MIMO communication systems. Project supported by the National Natural Science Foundation of China (Grant Nos. 61331007, 61361166008, and 61401065) and the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20120185130001).
NASA Astrophysics Data System (ADS)
Tu, Hui-Lin; Xiao, Shao-Qiu
2016-05-01
The resonant metalens consisting of metal-wire resonators with equally finite length can break the diffraction barrier well suited for super-resolution imaging. In this study, a basic combination constructed by two metal-wire resonators with different lengths is proposed, and its resonant characteristics is analyzed using the method of moments (MoM). Based on the time reversal (TR) technique, this kind of combination can be applied to a sub-wavelength two-element antenna array with a 1/40-wavelength interval to make the elements work simultaneously with little interference in the frequency band of 1.0-1.5 GHz and 1.5-2.0 GHz, respectively. The simulations and experiments show that analysis of MoM and the application of the resonators can be used to design multi-frequency sub-wavelength antenna arrays efficiently. This general design method is convenient and can be used for many applications, such as weakening jamming effectiveness in communication systems, and sub-wavelength imaging in a broad frequency band.
NASA Astrophysics Data System (ADS)
Weinberg, Seth H.
2015-10-01
Alternans, a beat-to-beat alternation in the cardiac action potential duration (APD), is a dynamical instability linked with the initiation of arrhythmias and sudden cardiac death, and arises via a period-doubling bifurcation when myocytes are stimulated at fast rates. In this study, we analyze the stability of a propagating electrical wave in a one-dimensional cardiac myocyte model in response to an arrhythmogenic rhythm known as alternate pacing. Using a discrete-time kinematic model and complex frequency (Z) domain analysis, we derive analytical expressions to predict phase reversals and spatial discordance in the interbeat interval (IBI) and APD, which, importantly, cannot be predicted with a model that neglects the influence of cell coupling on repolarization. We identify key dimensionless parameters that determine the transition from spatial concordance to discordance. Finally, we show that the theoretical predictions agree closely with numerical simulations of an ionic myocyte model, over a wide range of parameters, including variable IBI, altered ionic current gating, and reduced cell coupling. We demonstrate a novel approach to predict instability in cardiac tissue during alternate pacing and further illustrate how this approach can be generalized to more detail models of myocyte dynamics.
Zhang, Jing.
1992-01-01
The authors investigate the effects of temperature, salt concentration, and water loading on the internal dynamics of AOT Aerosol-OT, sodium bis (2-ethylhexyl sulfosuccinate) micelles in liquid heptane, using ANS-like (anilino-naphthalene sulfate) fluorescent probes. The important results from these experiments are that: (1) the molecular geometry of the probe is the predominant factor controlling partitioning even at high water loadings; (2) the photophysics of ANS is strongly dependent on the water content and temperature and corresponds to changes in local polarity and viscosity; (3) addition of electrolytes changes the dynamic fluorescence which is in turn related to the changes in internal microenvironments; and (4) a nanosecond solvent relaxation process occurs within reverse micelles. It was wondered if the continuous phase (alkane) density could be used to control the internal dynamics within a reverse micelle. To answer this question, research focused on: (1) the effects of water loading, temperature, and fluid density on solute partitioning and determination of the density effects on micellar aggregates; (2) the effects of solute structure on the distribution of probe molecules within reverse micelles; and (3) the effects of fluid density, water concentration, and temperature on the reorganizational dynamics within AOT reverse micelles. Simple thermodynamic measurements and nanosecond solvent relaxation experiments are used to account for this partitioning and water reorganization in AOT reverse micelles, respectively. Results on excited-state deprotonation reactions in AOT reverse micelles maintained in sub-critical propane, provides a useful model for density-controlled deprotonation reactions within reverse micelles. Preliminary work shows that the continuous phase density can be used to control reactions within reverse micelles formed in near- and supercritical alkanes.
Chao, Day-Yu; Davis, Brent S; Chang, Gwong-Jen J
2007-02-01
A multiplex real-time reverse transcriptase PCR has been developed for the rapid detection and identification of eight medically important flaviviruses from laboratory-reared, virus-infected mosquito pools. The method used involves the gene-specific amplification of yellow fever virus (YFV), Japanese encephalitis virus (JEV), West Nile virus (WNV), St. Louis encephalitis virus (SLEV), and dengue virus (DENV) serotypes 1 to 4 (DENV-1 to DENV-4, respectively) by use of the flavivirus consensus amplimers located at the RNA-dependent RNA polymerase domain of nonstructural protein 5. Virus-specific amplicons were detected by four newly characterized TaqMan fluorogenic probes (probes specific for YFV, JEV, WNV, and SLEV) and four previously published probes specific for DENV-1 to -4 (L. J. Chien, T. L. Liao, P. Y. Shu, J. H. Huang, D. J. Gubler, and G. J. Chang, J. Clin. Microbiol. 44:1295-1304, 2006). This assay had a specificity of 100% and various sensitivities of at least 3.5 PFU/ml for YFV, 2.0 PFU/ml for JEV, 10.0 PFU/ml for WNV, and 10.0 PFU/ml for SLEV. Additionally, we have developed an in vitro transcription system to generate RNase-resistant RNA templates for each of these eight viruses. These templates can be incorporated into the assay as RNA copy number controls and/or as external controls for RNA-spiked mosquito pools for quality assurance purposes. Although further study with mosquitoes collected in the field is needed, the incorporation of this assay into mosquito surveillance could be used as an early-warning system for the detection of medically important flaviviruses, particularly when the cocirculation of multiple viruses in the same region is suspected. PMID:17108075
Lavenir, Rachel; Lepelletier, Anthony; Faouzi, Abdellah; Troupin, Cécile; Nourlil, Jalal; Buchy, Philippe; Bourhy, Herve
2016-01-01
The definitive diagnosis of lyssavirus infection (including rabies) in animals and humans is based on laboratory confirmation. The reference techniques for post-mortem rabies diagnosis are still based on direct immunofluorescence and virus isolation, but molecular techniques, such as polymerase chain reaction (PCR) based methods, are increasingly being used and now constitute the principal tools for diagnosing rabies in humans and for epidemiological analyses. However, it remains a key challenge to obtain relevant specificity and sensitivity with these techniques while ensuring that the genetic diversity of lyssaviruses does not compromise detection. We developed a dual combined real-time reverse transcription polymerase chain reaction (combo RT-qPCR) method for pan-lyssavirus detection. This method is based on two complementary technologies: a probe-based (TaqMan) RT-qPCR for detecting the RABV species (pan-RABV RT-qPCR) and a second reaction using an intercalating dye (SYBR Green) to detect other lyssavirus species (pan-lyssa RT-qPCR). The performance parameters of this combined assay were evaluated with a large panel of primary animal samples covering almost all the genetic variability encountered at the viral species level, and they extended to almost all lyssavirus species characterized to date. This method was also evaluated for the diagnosis of human rabies on 211 biological samples (positive n = 76 and negative n = 135) including saliva, skin and brain biopsies. It detected all 41 human cases of rabies tested and confirmed the sensitivity and the interest of skin biopsy (91.5%) and saliva (54%) samples for intra-vitam diagnosis of human rabies. Finally, this method was successfully implemented in two rabies reference laboratories in enzootic countries (Cambodia and Morocco). This combined RT-qPCR method constitutes a relevant, useful, validated tool for the diagnosis of rabies in both humans and animals, and represents a promising tool for lyssavirus
Fuhrman, Jed A; Liang, Xiaolin; Noble, Rachel T
2005-08-01
Despite viral contamination of recreational waters, only bacterial, not viral, indicators are monitored routinely, due to a lack of rapid and cost-effective assays. We used negatively charged filters to capture enteroviruses from seawater and freshwater. Viral RNA was extracted using a commercial kit, and the viruses were quantified by real-time quantitative reverse transcriptase PCR (qRT-PCR). Poliovirus (6.6 to 330,000 virus particles/ml) was added to samples from watersheds in Los Angeles, California, and analysis showed that with 50-ml samples, a cellulose acetate/nitrate (HA) filter yielded final recovery of 51% (r2= 0.99) in fresh water and 23% (r2= 0.90) in seawater. However, for additions of low levels of virus (more likely to represent field samples; <10(4) enterovirus particles/ml), the recovery was lower and more variable, with HA being best in freshwater (17%, r2= 0.97) and the type GF/F glass filter having higher average recovery in seawater (GF/F, 17%; r2= 0.93; HA 12%, r2= 0.87). The optimized method was used with 1-liter field samples from two very different freshwater "creeks" that drain into Santa Monica Bay, California: Topanga Creek (TC), a relatively pristine mountain creek, and Ballona Creek (BC), a concrete-lined urban storm drain. One TC site out of 10 and 2 BC sites out of 7 tested significantly positive for enteroviruses, with higher enterovirus concentrations in BC than in TC (ca. 10 to 25 versus 1 equivalent enterovirus particle/ml). The presented filtration-qRT-PCR approach is fast (<8 h from sampling to results), sensitive, and cost efficient and is promising for monitoring viral contamination in environmental water samples. PMID:16085845
Dacheux, Laurent; Larrous, Florence; Lavenir, Rachel; Lepelletier, Anthony; Faouzi, Abdellah; Troupin, Cécile; Nourlil, Jalal; Buchy, Philippe; Bourhy, Herve
2016-07-01
The definitive diagnosis of lyssavirus infection (including rabies) in animals and humans is based on laboratory confirmation. The reference techniques for post-mortem rabies diagnosis are still based on direct immunofluorescence and virus isolation, but molecular techniques, such as polymerase chain reaction (PCR) based methods, are increasingly being used and now constitute the principal tools for diagnosing rabies in humans and for epidemiological analyses. However, it remains a key challenge to obtain relevant specificity and sensitivity with these techniques while ensuring that the genetic diversity of lyssaviruses does not compromise detection. We developed a dual combined real-time reverse transcription polymerase chain reaction (combo RT-qPCR) method for pan-lyssavirus detection. This method is based on two complementary technologies: a probe-based (TaqMan) RT-qPCR for detecting the RABV species (pan-RABV RT-qPCR) and a second reaction using an intercalating dye (SYBR Green) to detect other lyssavirus species (pan-lyssa RT-qPCR). The performance parameters of this combined assay were evaluated with a large panel of primary animal samples covering almost all the genetic variability encountered at the viral species level, and they extended to almost all lyssavirus species characterized to date. This method was also evaluated for the diagnosis of human rabies on 211 biological samples (positive n = 76 and negative n = 135) including saliva, skin and brain biopsies. It detected all 41 human cases of rabies tested and confirmed the sensitivity and the interest of skin biopsy (91.5%) and saliva (54%) samples for intra-vitam diagnosis of human rabies. Finally, this method was successfully implemented in two rabies reference laboratories in enzootic countries (Cambodia and Morocco). This combined RT-qPCR method constitutes a relevant, useful, validated tool for the diagnosis of rabies in both humans and animals, and represents a promising tool for lyssavirus
Technology Transfer Automated Retrieval System (TEKTRAN)
A SYBR® Green-based real-time quantitative reverse transcription PCR (qRT-PCR) assay in combination with melt curve analysis (MCA) was developed for the detection of nine grapevine viruses. The detection limits for singleplex qRT-PCR for all nine grapevine viruses were determined to be in the range ...
Technology Transfer Automated Retrieval System (TEKTRAN)
A multiplex Taqman®-based real-time reverse transcription (RT) polymerase chain reaction (PCR) assay was developed to detect all strains of Citrus tristeza virus (CTV) and to identify potentially severe strains of the virus. A CTV TaqMan probe (CTV-CY5) based on the coat protein (CP) gene sequences...
Technology Transfer Automated Retrieval System (TEKTRAN)
Efforts to analyze the replicative RNA produced by Maize fine streak virus (MFSV) within maize tissue was complicated by the lack of specificity during cDNA generation using standard reverse transcriptase protocols. Real-time qRT-PCR using cDNA generated by priming with random hexamers does not dist...
Technology Transfer Automated Retrieval System (TEKTRAN)
The effect of pooling five or 11 orophyarngeal (O/P) swabbings on detecting avian influenza virus (AIV) by real-time reverse transcription-polymerase chain reaction (RRT-PCR) was evaluated. The model used for the evaluation was designed to minimize viral load and thus assess the effect of the pooli...
Technology Transfer Automated Retrieval System (TEKTRAN)
A highly sensitive detection test for Rinderpest virus (RPV), based on a real-time reverse transcription-PCR (RT-PR) system, was developed. Five different RPV genomic targets were examined, and one was selected and optimized to detect viral RNA in infected tissue culture fluid with a level of detec...
Technology Transfer Automated Retrieval System (TEKTRAN)
Efforts to analyze the replicative RNA produced by Maize fine streak virus (MVSF) within maize tissue was complicated by the lack of specificity during cDNA generation using standard reverse transcriptase protocols. Real-time qRT-PCR using cDNA generated by priming with random hexamers does not dist...
A real-time, reverse transcription-PCR (RT-qPCR) assay was developed to differentiate the four genogroups of male-specific ssRNA coliphages (FRNA) (family Leviviridae). As FRNA display a trend of source-specificity (human sewage or animal waste) at the genogroup level, this assa...
Technology Transfer Automated Retrieval System (TEKTRAN)
A real-time reverse transcription polymerase chain reaction (rtRT-PCR) assay was developed for the identification of marine vesiviruses. The primers were designed to target a 176-nucleotide fragment within a highly conserved region of the San Miguel sea lion viruses (SMSVs) capsid gene. The assay de...
NASA Astrophysics Data System (ADS)
Tourin, A.; Fink, M.
2010-12-01
The concept of time-reversal (TR) focusing was introduced in acoustics by Mathias Fink in the early nineties: a pulsed wave is sent from a source, propagates in an unknown media and is captured at a transducer array termed a “Time Reversal Mirror (TRM)”. Then the waveforms received at each transducer are flipped in time and sent back resulting in a wave converging at the original source regardless of the complexity of the propagation medium. TRMs have now been implemented in a variety of physical scenarios from GHz microwaves to MHz ultrasonics and to hundreds of Hz in ocean acoustics. Common to this broad range of scales is a remarkable robustness exemplified by observations that the more complex the medium (random or chaotic), the sharper the focus. A TRM acts as an antenna that uses complex environments to appear wider than it is, resulting for a broadband pulse, in a refocusing quality that does not depend on the TRM aperture. We show that the time-reversal concept is also at the heart of very active research fields in seismology and applied geophysics: imaging of seismic sources, passive imaging based on noise correlations, seismic interferometry, monitoring of CO2 storage using the virtual source method. All these methods can indeed be viewed in a unified framework as an application of the so-called time-reversal cavity approach. That approach uses the fact that a wave field can be predicted at any location inside a volume (without source) from the knowledge of both the field and its normal derivative on the surrounding surface S, which for acoustic scalar waves is mathematically expressed in the Helmholtz Kirchhoff (HK) integral. Thus in the first step of an ideal TR process, the field coming from a point-like source as well as its normal derivative should be measured on S. In a second step, the initial source is removed and monopole and dipole sources reemit the time reversal of the components measured in the first step. Instead of directly computing
Belker, A M
1987-02-01
A vasovasostomy may be performed on an outpatient basis with local anesthesia, but also may be performed on an outpatient basis with epidural or general anesthesia. Local anesthesia is preferred by most of my patients, the majority of whom choose this technique. With proper preoperative and intraoperative sedation, patients sleep lightly through most of the procedure. Because of the length of time often required for bilateral microsurgical vasoepididymostomy, epidural or general anesthesia and overnight hospitalization are usually necessary. Factors influencing the preoperative choice for vasovasostomy or vasoepididymostomy in patients undergoing vasectomy reversal are considered. The preoperative planned choice of vasovasostomy or vasoepididymostomy for patients having vasectomy reversal described herein does not have the support of all urologists who regularly perform these procedures. My present approach has evolved as the data reported in Tables 1 and 2 have become available, but it may change as new information is evaluated. However, it offers a logical method for planning choices of anesthesia and inpatient or outpatient status for patients undergoing vasectomy reversal procedures. PMID:3811050
On thermodynamic and microscopic reversibility
Crooks, Gavin E.
2011-07-12
The word 'reversible' has two (apparently) distinct applications in statistical thermodynamics. A thermodynamically reversible process indicates an experimental protocol for which the entropy change is zero, whereas the principle of microscopic reversibility asserts that the probability of any trajectory of a system through phase space equals that of the time reversed trajectory. However, these two terms are actually synonymous: a thermodynamically reversible process is microscopically reversible, and vice versa.