165 results on '"time reversal"'
Search Results
2. A Review of the Concept of Time Reversal and the Direction of Time
- Author
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Cristian López and Olimpia Lombardi
- Subjects
time reversal ,motion reversal ,time asymmetry ,symmetry ,the arrow of time ,Science ,Astrophysics ,QB460-466 ,Physics ,QC1-999 - Abstract
Abstract: In the debate about the direction of time in physics, the concept of time reversal has been central. Tradition has it that time-reversal invariant laws are sufficient to state that the direction of time is non-fundamental or emergent. In this paper, we review some of the debates that have gravitated around the concept of time reversal and its relation to the direction of time. We also clarify some of the central concepts involved, showing that the very concept of time reversal is more complex than frequently thought.
- Published
- 2024
- Full Text
- View/download PDF
3. Research on Time-Reversal Focusing Imaging Method to Evaluate a Multi-Layer Armor Composite Structure
- Author
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Jian Jiang, Linfang Qian, and Yadong Xu
- Subjects
time reversal ,imaging method ,armor composite structure ,structure health monitoring ,Technology ,Engineering (General). Civil engineering (General) ,TA1-2040 ,Biology (General) ,QH301-705.5 ,Physics ,QC1-999 ,Chemistry ,QD1-999 - Abstract
Armor composite structures have attracted interest in structural health monitoring (SHM) for their applications in damage localization. The signal propagation and the frequency dispersion features of the Lamb wave signal on thick armor composite structures are more complicated than their counterparts on other composite plates. In this research, a time-reversal localization and imaging method for impact localization of armor composite structures is proposed. First, composite sandwich structures were designed that are typically composed of ballistic-resistant ceramic materials as the face panel and a composite material as the core layer, sandwiched between metal materials serving as the backplate. The results show that the proposed method can validate the position of impact efficiently, and radial error is within 4.12 mm and 5.39 mm in single-damage and multi-damage imaging localization, respectively.
- Published
- 2024
- Full Text
- View/download PDF
4. Simultaneity and Time Reversal in Quantum Mechanics in Relation to Proper Time
- Author
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Salim Yasmineh
- Subjects
proper time ,time reversal ,simultaneity ,wavefunction ,Physics ,QC1-999 - Abstract
In Newtonian physics, the equation of motion is invariant when the direction of time (t→−t) is flipped. However, in quantum physics, flipping the direction of time changes the sign of the Schrödinger equation. An anti-unitary operator is needed to restore time reversal in quantum physics, but this is at the cost of not having a consistent definition of time reversal applicable to all fundamental theories. On the other hand, a quantum system composed of a pair of entangled particles behaves in such a manner that when the state of one particle is measured, the second particle ‘simultaneously’ acquires a determinate state. A notion of absolute simultaneity seems to be inferred by quantum mechanics, even though it is forbidden by the postulates of relativity. We aim to point out that the above two problems can be overcome if the wavefunction is defined with respect to proper time, which in fact is the real physical time instead of ordinary time.
- Published
- 2022
- Full Text
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5. Why Physics is not Wrong on Temporal Directionality, and Why This is not Necessarily Good News for Physicalism.
- Author
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Dolev, Yuval
- Subjects
- *
MATERIALISM , *TIME reversal , *PHYSICS , *SCIENTIFIC language , *SECOND law of thermodynamics - Abstract
This paper claims that, to the extent that temporal direction figures in physics at all, it is found there as part of the extra-scientific language science employs. The asymmetry between "before" and "after" is not captured by the mathematics of any theory, nor can it be derived from the laws of any theory. This, I argue, is true even of theories whose laws are not time reversal invariant. Recognizing that physics does not yield temporal direction but receives it from the background in which physics develops and operates does not, however, expose any hitherto unknown limitations or deficiencies of physics. The claim is not about physics, but about metaphysical stances regarding physics, specifically, physicalism, which requires from physics to deliver more than it does, or should. Once the place of temporal direction in physics is understood, infamous difficulties can be addressed in a novel way. Issues emerging from the 2nd law of thermodynamics, such as the minimum problem, and the worry that the law generates outlandish predictions, are removed. A side benefit is the recognition that the past hypothesis is superfluous. A final conclusion of the paper is that the relationship between physics and everyday language, far from being a source of difficulties, is healthy and beneficial to both. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
6. On the sensitivity of the D parameter to new physics.
- Author
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Falkowski, Adam and Rodríguez-Sánchez, Antonio
- Subjects
- *
ELECTRIC dipole moments , *CONSTRAINTS (Physics) , *TIME reversal , *PHYSICS , *STANDARD model (Nuclear physics) , *BETA decay - Abstract
Measurements of angular correlations in nuclear beta decay are important tests of the Standard Model (SM). Among those, the so-called D correlation parameter occupies a particular place because it is odd under time reversal, and because the experimental sensitivity is at the 10 - 4 level, with plans of further improvement in the near future. Using effective field theory (EFT) techniques, we reassess its potential to discover or constrain new physics beyond the SM. We provide a comprehensive classification of CP-violating EFT scenarios which generate a shift of the D parameter away from the SM prediction. We show that, in each scenario, a shift larger than 10 - 5 is in serious tension with the existing experimental data, where bounds coming from electric dipole moments and LHC observables play a decisive role. The tension can only be avoided by fine tuning of the parameters in the UV completion of the EFT. We illustrate this using examples of leptoquark UV completions. Finally, we comment on the possibility to probe CP-conserving new physics via the D parameter. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
7. PATLAB: A graphical computational software package for photoacoustic computed tomography research
- Author
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P. Omidi, L.C.M. Yip, E. Rascevska, M. Diop, and J.J.L. Carson
- Subjects
Photoacoustic tomography ,Image reconstruction ,Back projection ,Filtered back projection ,Universal back projection ,Time reversal ,Physics ,QC1-999 ,Acoustics. Sound ,QC221-246 ,Optics. Light ,QC350-467 - Abstract
Photoacoustic tomography (PAT) provides high resolution optical images of tissue at depths of up to several centimetres. This modality has been of interest to researchers for at least 30 years and is still the subject of intensive research. However, PAT researchers lack access to a comprehensive open-source graphical simulation and reconstruction software package. In this article, we introduce PATLAB, an open-source MATLAB-based graphical software package that can perform both PAT simulation and image reconstruction. PATLAB is simple to use yet is capable of complex PAT data processing tasks and offers advanced users a framework to build and test new methods.
- Published
- 2022
- Full Text
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8. Commentary: "Physical time within human time" and "Bridging the neuroscience and physics of time".
- Author
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Deng, Natalja
- Subjects
PHYSICS ,PHYSICAL laws ,NEUROSCIENCES ,TIME reversal - Published
- 2023
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9. INSTANTANEOUS TIME MIRRORS AND WAVE EQUATIONS WITH TIME-SINGULAR COEFFICIENTS.
- Author
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PINAUD, OLIVIER
- Subjects
- *
TIME reversal , *MIRRORS , *PHYSICS , *WAVE equation - Abstract
In this work we study the concept of instantaneous time mirrors that were recently introduced in the physics literature in [V. Bacot et al., Nature Phys., 12 (2016), pp. 972-977). They offer a new method for time reversal with a simplified experimental setup compared to classical techniques. At the mathematical level, these time mirrors are modeled by singularities in the time variable in the coefficients of a wave equation, and a prototype of such singularity is a Dirac delta. Our main goal in this work is to obtain refocusing estimates for the wavefield that quantify the quality of time reversal. This amounts to analyzing the wave equation with Dirac-type singularities and developing a proper regularity theory as well as deriving uniform estimates. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
10. Causality in Reversed Time Series: Reversed or Conserved?
- Author
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Jakub Kořenek and Jaroslav Hlinka
- Subjects
causality ,time reversal ,temporal symmetry ,reversed time series ,vector autoregressive process ,random networks ,Science ,Astrophysics ,QB460-466 ,Physics ,QC1-999 - Abstract
The inference of causal relations between observable phenomena is paramount across scientific disciplines; however, the means for such enterprise without experimental manipulation are limited. A commonly applied principle is that of the cause preceding and predicting the effect, taking into account other circumstances. Intuitively, when the temporal order of events is reverted, one would expect the cause and effect to apparently switch roles. This was previously demonstrated in bivariate linear systems and used in design of improved causal inference scores, while such behaviour in linear systems has been put in contrast with nonlinear chaotic systems where the inferred causal direction appears unchanged under time reversal. The presented work explores the conditions under which the causal reversal happens—either perfectly, approximately, or not at all—using theoretical analysis, low-dimensional examples, and network simulations, focusing on the simplified yet illustrative linear vector autoregressive process of order one. We start with a theoretical analysis that demonstrates that a perfect coupling reversal under time reversal occurs only under very specific conditions, followed up by constructing low-dimensional examples where indeed the dominant causal direction is even conserved rather than reversed. Finally, simulations of random as well as realistically motivated network coupling patterns from brain and climate show that level of coupling reversal and conservation can be well predicted by asymmetry and anormality indices introduced based on the theoretical analysis of the problem. The consequences for causal inference are discussed.
- Published
- 2021
- Full Text
- View/download PDF
11. Causality and Information Transfer Between the Solar Wind and the Magnetosphere–Ionosphere System
- Author
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Pouya Manshour, Georgios Balasis, Giuseppe Consolini, Constantinos Papadimitriou, and Milan Paluš
- Subjects
time series ,causality ,information transfer ,time reversal ,solar wind-magnetosphere–ionosphere system ,space weather ,Science ,Astrophysics ,QB460-466 ,Physics ,QC1-999 - Abstract
An information-theoretic approach for detecting causality and information transfer is used to identify interactions of solar activity and interplanetary medium conditions with the Earth’s magnetosphere–ionosphere systems. A causal information transfer from the solar wind parameters to geomagnetic indices is detected. The vertical component of the interplanetary magnetic field (Bz) influences the auroral electrojet (AE) index with an information transfer delay of 10 min and the geomagnetic disturbances at mid-latitudes measured by the symmetric field in the H component (SYM-H) index with a delay of about 30 min. Using a properly conditioned causality measure, no causal link between AE and SYM-H, or between magnetospheric substorms and magnetic storms can be detected. The observed causal relations can be described as linear time-delayed information transfer.
- Published
- 2021
- Full Text
- View/download PDF
12. Granger Causality on forward and Reversed Time Series
- Author
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Martina Chvosteková, Jozef Jakubík, and Anna Krakovská
- Subjects
time reversal ,Granger causality ,predictive error ,endogeneity ,Science ,Astrophysics ,QB460-466 ,Physics ,QC1-999 - Abstract
In this study, the information flow time arrow is investigated for stochastic data defined by vector autoregressive models. The time series are analyzed forward and backward by different Granger causality detection methods. Besides the normal distribution, which is usually required for the validity of Granger causality analysis, several other distributions of predictive errors are considered. A clear effect of a change in the order of cause and effect on the time-reversed series of unidirectionally connected variables was detected with standard Granger causality test (GC), when the product of the connection strength and the ratio of the predictive errors of the driver and the recipient was below a certain level, otherwise bidirectional causal connection was detected. On the other hand, opposite causal link was detected unconditionally by the methods based on the time reversal testing, but they were not able to detect correct bidirectional connection. The usefulness of the backward analysis is manifested in cases where falsely detected unidirectional connections can be rejected by applying the result obtained after the time reversal, and in cases of uncorrelated causally independent variables, where the absence of a causal link detected by GC on the original series should be confirmed on the time-reversed series.
- Published
- 2021
- Full Text
- View/download PDF
13. Study on Time Reversal Maximum Ratio Combining in Underwater Acoustic Communications
- Author
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Anbang Zhao, Caigao Zeng, Juan Hui, Keren Wang, and Kaiyu Tang
- Subjects
time reversal ,underwater acoustic communications ,maximum ratio combining ,weight coefficient ,focusing gain ,Technology ,Engineering (General). Civil engineering (General) ,TA1-2040 ,Biology (General) ,QH301-705.5 ,Physics ,QC1-999 ,Chemistry ,QD1-999 - Abstract
Time reversal (TR) can achieve temporal and spatial focusing by exploiting spatial diversity in complex underwater environments with significant multipath. This property makes TR useful for underwater acoustic (UWA) communications. Conventional TR is realized by performing equal gain combining (EGC) on the single element TR output signals of each element of the vertical receive array (VRA). However, in the actual environment, the signal-to-noise ratio (SNR) and the received noise power of each element are different, which leads to the reduction of the focusing gain. This paper proposes a time reversal maximum ratio combining (TR-MRC) method to process the received signals of the VRA, so that a higher output SNR can be obtained. The theoretical derivation of the TR-MRC weight coefficients indicates that the weight coefficients are only related to the input noise power of each element, and are not affected by the multipath structure. The correctness of the derivation is demonstrated with the experimental data of the long-range UWA communications conducted in the South China Sea. In addition, the experimental results illustrate that compared to the conventional TR, TR-MRC can provide better performance in terms of output SNR and bit error rate (BER) in UWA communications.
- Published
- 2021
- Full Text
- View/download PDF
14. Some Aspects of Time-Reversal in Chemical Kinetics
- Author
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Ulrich Maas
- Subjects
chemical kinetics ,time reversal ,time scales ,low-dimensional manifolds ,Science ,Astrophysics ,QB460-466 ,Physics ,QC1-999 - Abstract
Chemical kinetics govern the dynamics of chemical systems leading towards chemical equilibrium. There are several general properties of the dynamics of chemical reactions such as the existence of disparate time scales and the fact that most time scales are dissipative. This causes a transient relaxation to lower dimensional attracting manifolds in composition space. In this work, we discuss this behavior and investigate how a time reversal effects this behavior. For this, both macroscopic chemical systems as well as microscopic chemical systems (elementary reactions) are considered.
- Published
- 2020
- Full Text
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15. Implementation of an Off-Axis Digital Optical Phase Conjugation System for Turbidity Suppression on Scattering Medium
- Author
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Kai Zhang, Zhiyang Wang, Haihan Zhao, Chao Liu, Haoyun Zhang, and Bin Xue
- Subjects
off-axis holography ,time reversal ,digital phase conjugation ,scattering medium ,Technology ,Engineering (General). Civil engineering (General) ,TA1-2040 ,Biology (General) ,QH301-705.5 ,Physics ,QC1-999 ,Chemistry ,QD1-999 - Abstract
Due to the light scattering effect, it is difficult to directly achieve optical focusing and imaging in turbid media, such as milk and biological tissue. The turbidity suppression of a scattering medium and control of light through the scattering medium are important for imaging on biological tissue or biophotonics. Optical phase conjugation is a novel technology on turbidity suppression by directly creating phase conjugation light waves to form time-reversed light. In this work, we report a digital optical phase conjugation system based on off-axis holography. Compared with traditional digital optical phase conjugation methods, the off-axis holography acquires the conjugation phase using only one interference image, obviously saving photo acquisition time. Furthermore, we tested the optical phase conjugate reduction performance of this system and also achieved optical focusing through the diffuser. We also proved that the reversing of random scattering in turbid media is achievable by phase conjugation.
- Published
- 2020
- Full Text
- View/download PDF
16. Accelerated Correction of Reflection Artifacts by Deep Neural Networks in Photo-Acoustic Tomography
- Author
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Hongming Shan, Ge Wang, and Yang Yang
- Subjects
photo-acoustic tomography ,reflection artifacts ,deep learning ,convolutional neural network ,time reversal ,Landweber algorithm ,U-net ,Technology ,Engineering (General). Civil engineering (General) ,TA1-2040 ,Biology (General) ,QH301-705.5 ,Physics ,QC1-999 ,Chemistry ,QD1-999 - Abstract
Photo-Acoustic Tomography (PAT) is an emerging non-invasive hybrid modality driven by a constant yearning for superior imaging performance. The image quality, however, hinges on the acoustic reflection, which may compromise the diagnostic performance. To address this challenge, we propose to incorporate a deep neural network into conventional iterative algorithms to accelerate and improve the correction of reflection artifacts. Based on the simulated PAT dataset from computed tomography (CT) scans, this network-accelerated reconstruction approach is shown to outperform two state-of-the-art iterative algorithms in terms of the peak signal-to-noise ratio (PSNR) and the structural similarity (SSIM) in the presence of noise. The proposed network also demonstrates considerably higher computational efficiency than conventional iterative algorithms, which are time-consuming and cumbersome.
- Published
- 2019
- Full Text
- View/download PDF
17. An Efficient Time Reversal Method for Lamb Wave-Based Baseline-Free Damage Detection in Composite Laminates
- Author
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Liping Huang, Junmin Du, Feiyu Chen, and Liang Zeng
- Subjects
Lamb waves ,time reversal ,baseline-free ,composite laminates ,Technology ,Engineering (General). Civil engineering (General) ,TA1-2040 ,Biology (General) ,QH301-705.5 ,Physics ,QC1-999 ,Chemistry ,QD1-999 - Abstract
Time reversal (TR) concept is widely used for Lamb wave-based damage detection. However, the time reversal process (TRP) faces the challenge that it requires two actuating-sensing steps and requires the extraction of re-emitted and reconstructed waveforms. In this study, the effects of the two extracted components on the performance of TRP are studied experimentally. The results show that the two time intervals, in which the waveforms are extracted, have great influence on the accuracy of damage detection of the time reversal method (TRM). What is more, it requires a large number of experiments to determine these two time intervals. Therefore, this paper proposed an efficient time reversal method (ETRM). Firstly, a broadband excitation is applied to obtain response at a wide range of frequencies, and ridge reconstruction based on inverse short-time Fourier transform is applied to extract desired mode components from the broadband response. Subsequently, deconvolution is used to extract narrow-band reconstructed signal. In this method, the reconstructed signal can be easily obtained without determining the two time intervals. Besides, the reconstructed signals related to a series of different excitations could be obtained through only one actuating-sensing step. Finally, the effectiveness of the ETRM for damage detection in composite laminates is verified through experiments.
- Published
- 2018
- Full Text
- View/download PDF
18. Making Space for Time.
- Author
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Dodd, Scott
- Subjects
- *
TIME , *TIME reversal , *PHYSICS , *PHYSICAL cosmology , *ASTROPHYSICS , *METAPHYSICAL cosmology - Abstract
The article discusses the unsuccessful attempts of physicists to answer the question of why time is not reversible. The other basic physical properties of the universe are more symmetrical and the mystery of why time does not follow the same pattern has been called 'time's arrow.' The hope that improved cosmological observations will illuminate the question is discussed.
- Published
- 2008
- Full Text
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19. Microcanonical Entropy, Partitions of a Natural Number into Squares and the Bose–Einstein Gas in a Box
- Author
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Paolo De Gregorio and Lamberto Rondoni
- Subjects
time correlation functions ,time reversal ,parity ,quantum symmetry transformations ,Science ,Astrophysics ,QB460-466 ,Physics ,QC1-999 - Abstract
From basic principles, we review some fundamentals of entropy calculations, some of which are implicit in the literature. We mainly deal with microcanonical ensembles to effectively compare the counting of states in continuous and discrete settings. When dealing with non-interacting elements, this effectively reduces the calculation of the microcanonical entropy to counting the number of certain partitions, or compositions of a number. This is true in the literal sense, when quantization is assumed, even in the classical limit. Thus, we build on a moderately dated, ingenuous mathematical work of Haselgrove and Temperley on counting the partitions of an arbitrarily large positive integer into a fixed (but still large) number of summands, and show that it allows us to exactly calculate the low energy/temperature entropy of a one-dimensional Bose–Einstein gas in a box. Next, aided by the asymptotic analysis of the number of compositions of an integer as the sum of three squares, we estimate the entropy of the three-dimensional problem. For each selection of the total energy, there is a very sharp optimal number of particles to realize that energy. Therefore, the entropy is ‘large’ and almost independent of the particles, when the particles exceed that number. This number scales as the energy to the power of ( 2 / 3 ) -rds in one dimension, and ( 3 / 5 ) -ths in three dimensions. In the one-dimensional case, the threshold approaches zero temperature in the thermodynamic limit, but it is finite for mesoscopic systems. Below that value, we studied the intermediate stage, before the number of particles becomes a strong limiting factor for entropy optimization. We apply the results of moments of partitions of Coons and Kirsten to calculate the relative fluctuations of the ground state and excited states occupation numbers. At much lower temperatures than threshold, they vanish in all dimensions. We briefly review some of the same results in the grand canonical ensemble to show to what extents they differ.
- Published
- 2018
- Full Text
- View/download PDF
20. Time reversal of arbitrary photonic temporal modes via nonlinear optical frequency conversion
- Author
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Michael G Raymer, Dileep V Reddy, Steven J van Enk, and Colin J McKinstrie
- Subjects
time reversal ,frequency conversion ,temporal modes ,photon ,Science ,Physics ,QC1-999 - Abstract
Single-photon wave packets can carry quantum information between nodes of a quantum network. An important general operation in photon-based quantum information systems is ‘blind’ reversal of a photon’s temporal wave packet envelope, that is, the ability to reverse an envelope without knowing the temporal state of the photon. We present an all-optical means for doing so, using nonlinear-optical frequency conversion driven by a short pump pulse. The process used may be sum-frequency generation or four-wave Bragg scattering. This scheme allows for quantum operations such as a temporal-mode parity sorter. We also verify that the scheme works for arbitrary states (not only single-photon ones) of an unknown wave packet.
- Published
- 2018
- Full Text
- View/download PDF
21. Performance of Time Reversal Based Underwater Target Detection in Shallow Water
- Author
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Baeksan On, Sungbin Im, and Iksu Seo
- Subjects
underwater target detection ,time reversal ,active sonar ,shallow water ,Technology ,Engineering (General). Civil engineering (General) ,TA1-2040 ,Biology (General) ,QH301-705.5 ,Physics ,QC1-999 ,Chemistry ,QD1-999 - Abstract
In this paper, a scheme based on the time reversal technique is proposed to improve the detection performance for detecting a cylindrical object bottoming at the seafloor in shallow water. When the time reversal technique is applied to the response of the clutter with the strong time-varying characteristic of shallow water, it is difficult to obtain a high peak response. However, in the case where a cylindrical object is placed on the seafloor because the time-invariant property of the target response is stronger than the time-varying property of the reverberation by the clutters, the time reversal technique can be applied to enhance the target signal. In this paper, it is demonstrated that the peak due to the target that is contacted at the seabed becomes higher when applying the time reversal technique. The performance is investigated by using numerical computation of the probability of detection for various probabilities of false alarm and computer simulation.
- Published
- 2017
- Full Text
- View/download PDF
22. Causality in Reversed Time Series: Reversed or Conserved?
- Author
-
Jaroslav Hlinka and Jakub Kořenek
- Subjects
reversed time series ,causality ,Science ,QC1-999 ,media_common.quotation_subject ,time reversal ,General Physics and Astronomy ,Inference ,Bivariate analysis ,Astrophysics ,Asymmetry ,Article ,Causality (physics) ,Statistical physics ,Mathematics ,media_common ,brain network ,Physics ,vector autoregressive process ,Linear system ,Contrast (statistics) ,QB460-466 ,Nonlinear system ,Causal inference ,climate network ,temporal symmetry ,random networks - Abstract
The inference of causal relations between observable phenomena is paramount across scientific disciplines, however, the means for such enterprise without experimental manipulation are limited. A commonly applied principle is that of the cause preceding and predicting the effect, taking into account other circumstances. Intuitively, when the temporal order of events is reverted, one would expect the cause and effect to apparently switch roles. This was previously demonstrated in bivariate linear systems and used in design of improved causal inference scores, while such behaviour in linear systems has been put in contrast with nonlinear chaotic systems where the inferred causal direction appears unchanged under time reversal. The presented work explores the conditions under which the causal reversal happens—either perfectly, approximately, or not at all—using theoretical analysis, low-dimensional examples, and network simulations, focusing on the simplified yet illustrative linear vector autoregressive process of order one. We start with a theoretical analysis that demonstrates that a perfect coupling reversal under time reversal occurs only under very specific conditions, followed up by constructing low-dimensional examples where indeed the dominant causal direction is even conserved rather than reversed. Finally, simulations of random as well as realistically motivated network coupling patterns from brain and climate show that level of coupling reversal and conservation can be well predicted by asymmetry and anormality indices introduced based on the theoretical analysis of the problem. The consequences for causal inference are discussed.
- Published
- 2021
- Full Text
- View/download PDF
23. The Black Hole Firewall Transformation and Realism in Quantum Mechanics
- Author
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Gerard 't Hooft
- Subjects
High Energy Physics - Theory ,antipodal mapping ,gr-qc ,time reversal ,standard model ,General Physics and Astronomy ,FOS: Physical sciences ,Penrose diagram ,General Relativity and Quantum Cosmology (gr-qc) ,QC793-793.5 ,General Relativity and Quantum Cosmology ,horizon ,symbols.namesake ,quant-ph ,Quantum mechanics ,black hole ,Firewall (physics) ,Quantum ,Planck scale ,Physics ,Quantum Physics ,Spacetime ,hep-th ,Hilbert space ,Elementary particle physics ,Interpretations of quantum mechanics ,firewall ,Black hole ,Cauchy surface ,Schwarzschild metric ,High Energy Physics - Theory (hep-th) ,Metric (mathematics) ,symbols ,fast variables ,cellular automaton ,Quantum Physics (quant-ph) ,determinism, ontology - Abstract
A procedure to derive a unitary evolution law for a quantised black hole, has been proposed by the author. The proposal requires that one starts off with the entire Penrose diagram for the eternal black hole as the background metric, after which a procedure was proposed to identify the two asymptotic domains of this metric, such that they both refer to the same outside world. In this paper we focus on the need to include time reversal in applying this identification. This forces us to postulate the existence of an 'anti-vacuum' state in our world, which is the state where energy density reaches a maximal value. We find that this squares well with the deterministic interpretation of quantum mechanics, according to which quantum Hilbert space is to be regarded as the 'vector representation' of a real world. One has to understand how to deal with gravity in such considerations. The non-perturbative component of the gravitational force seems to involve cut-and-paste procedures as dynamical features of space and time, of which the re-arrangement of space-time into two connected domains in the Penrose diagram is a primary example. Thus we attempt to obtain new insights in the nature of particle interactions at the Planck scale, as well as quantum mechanics itself. In this newer version of the paper an important correction is made concerning the antipodal transformation: applying more insight in the situation, as explained in newer publications by the author, we now regard region II of the Penrose diagram as an exact quantum copy of region I , still with time being reversed, but interchanging a region of spacetime with its antipodes is now seen to be incorrect., Comment: 20 pages (incl. title page), 2 figures
- Published
- 2021
24. Evaluation of barely visible indentation damage (BVID) in CF/EP sandwich composites using guided wave signals.
- Author
-
Mustapha, Samir, Ye, Lin, Dong, Xingjian, and Alamdari, Mehrisadat Makki
- Subjects
- *
SANDWICH construction (Materials) , *QUANTUM theory , *LAMINATED materials , *LIGHTWEIGHT construction , *PHYSICS - Abstract
Barely visible indentation damage after quasi-static indentation in sandwich CF/EP composites was assessed using ultrasonic guided wave signals. Finite element analyses were conducted to investigate the interaction between guided waves and damage, further to assist in the selection process of the Lamb wave sensitive modes for debonding identification. Composite sandwich beams and panels structures were investigated. Using the beam structure, a damage index was defined based on the change in the peak magnitude of the captured wave signals before and after the indentation, and the damage index was correlated with the residual deformation (defined as the depth of the dent), that was further correlated with the amount of crushing within the core. Both A 0 and S 0 Lamb wave modes showed high sensitivity to the presence of barely visible indentation damage with residual deformation of 0.2 mm. Furthermore, barely visible indentation damage was assessed in composite sandwich panels after indenting to 3 and 5 mm, and the damage index was defined, based on (a) the peak magnitude of the wave signals before and after indentation or (b) the mismatch between the original and reconstructed wave signals based on a time-reversal algorithm, and was subsequently applied to locate the position of indentation. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
25. Damage localization method for plates based on the time reversal of the mode-converted Lamb waves
- Author
-
Takayuki Kusaka, Naoki Mori, and Shiro Biwa
- Subjects
Physics ,Damage localization ,Acoustics and Ultrasonics ,business.industry ,Antisymmetric relation ,Time reversal ,Mode (statistics) ,Magnitude (mathematics) ,Wavelength ,Optics ,Transducer ,Lamb waves ,Lamb wave ,Wave mode ,Mode conversion ,business ,Finite integration - Abstract
A damage localization method based on the time reversal focusing of the mode-converted scattered Lamb wave is proposed for plate structures with a non-symmetric defect in the thickness direction. Dual transducers are attached symmetrically on the upper and lower surfaces of the plate to selectively emit and receive the lowest-order symmetric (S0) and antisymmetric (A0) modes. The localization of damage is achieved by the numerical time-reversed (TR) simulation of the mode-converted Lamb wave generated at the defect. To investigate the validity of the proposed method, the signals of the Lamb waves in a plate with a partial-thickness notch are numerically simulated by the three-dimensional elastodynamic finite integration technique (EFIT). When the S0 mode is emitted in the damaged plate, not only the S0 mode is scattered but also the A0 mode is generated due to mode conversion at the notch. Similar mode conversion behavior is confirmed when the A0 mode is emitted. The time reversal of the mode-converted scattered Lamb waves creates focused spots at the damage location without using baseline data for the undamaged plate. The proposed method reduces the magnitude of the artifacts compared to the time reversal of the non-mode-converted Lamb wave, and yields the focused spot whose size is associated with the size of the notch and the half wavelength of the time-reversed wave mode. Furthermore, the proposed method is applied to a plate with a notch-type defect adjacent to an a priori known through-thickness hole, demonstrating the damage localization in a relatively complicated structure.
- Published
- 2019
26. Subwavelength Field Shaping Approach Based on Time Reversal Technique and Defective Metasurfaces
- Author
-
Shuai Ding, Zhipeng Wang, Sheng Liu, Bing-Zhong Wang, Jin-Pin Liu, Mo-Ran Zhang, Yan-He Lv, and Ren Wang
- Subjects
Physics ,0303 health sciences ,General Computer Science ,Field (physics) ,business.industry ,time reversal ,Resolution (electron density) ,General Engineering ,Defective metasurfaces ,020206 networking & telecommunications ,02 engineering and technology ,03 medical and health sciences ,Optics ,Dimension (vector space) ,Field shaping ,0202 electrical engineering, electronic engineering, information engineering ,Wireless ,General Materials Science ,Wireless power transfer ,lcsh:Electrical engineering. Electronics. Nuclear engineering ,business ,lcsh:TK1-9971 ,subwavelength field shaping ,030304 developmental biology ,Metamaterial antenna - Abstract
The resolution limitation is a main problem in the time-reversed field shaping system. In this paper, a subwavelength field shaping approach is proposed by combining time reversal (TR) technique and defective resonant metasurfaces. The subwavelength 2D and 3D field patterns can be effectively realized in both single-target and multi-target field-shaping systems. The resolution in both single-target and multi-target field-shaping systems aided with defective metasurfaces is approximately $0.1~\lambda $ , which is corresponding to the dimension of the applied metasurface cell. The proposed technique can be used for wireless power transfer, industrial heating, and localized wireless communications.
- Published
- 2019
27. Time Reversal Invariance Test at the COSY Ring
- Author
-
P. Lenisa and G. Ciullo
- Subjects
Physics ,Economica ,PE2_2 ,PE2_1 ,Quantum mechanics ,Polarization ,Socio-culturale ,Ambientale ,Time Reversal ,Storage Ring ,Ring (chemistry) ,PE2_3 - Published
- 2021
28. Gravitational quantum states as finite representations of the Lorentz group
- Author
-
Francesco Cianfrani, Physique des interactions ioniques et moléculaires (PIIM), Centre National de la Recherche Scientifique (CNRS)-Aix Marseille Université (AMU), and Aix Marseille Université (AMU)-Centre National de la Recherche Scientifique (CNRS)
- Subjects
constraint: scalar ,Physics and Astronomy (miscellaneous) ,Representation theory of the Lorentz group ,time reversal ,symmetry: discrete ,group theory ,FOS: Physical sciences ,General Relativity and Quantum Cosmology (gr-qc) ,Loop quantum gravity ,Wigner ,Euclidean ,Lorentz invariance ,01 natural sciences ,General Relativity and Quantum Cosmology ,Quantum state ,representation: Lorentz ,0103 physical sciences ,group: Lorentz ,010306 general physics ,quantum field theory ,Mathematical physics ,Physics ,010308 nuclear & particles physics ,Group (mathematics) ,Computer Science::Information Retrieval ,Immirzi parameter ,Scalar (physics) ,Parity (physics) ,SU(2) ,parity ,quantum gravity ,covariance ,Homogeneous space ,[PHYS.GRQC]Physics [physics]/General Relativity and Quantum Cosmology [gr-qc] ,quantum gravity: loop space - Abstract
A manifestly Lorentz-covariant formulation of Loop Quantum Gravity (LQG) is given in terms of finite-dimensional representations of the Lorentz group. The formulation accounts for discrete symmetries, such as parity and time-reversal, and it establishes a link with Wigner classification of particles. The resulting quantum model can be seen as LQG with the internal $SU(2)\otimes SU(2)$ group and it is free of the Immirzi parameter, while the scalar constraint is just the Euclidean part., 5 pages, to appear in Classical and Quantum Gravity
- Published
- 2021
29. Symmetry Breaking and Harmonic Generation in Metasurfaces and 2-Dimensional Materials
- Author
-
Ginsberg, Jared Scott
- Subjects
Boron nitride ,Particles (Nuclear physics)--Chirality ,Mirror symmetry ,Physics ,Time reversal ,Physics::Optics ,Optics ,Graphene - Abstract
A strong argument can be made that physics is, at its core, the study of symmetries. Nonlinear optics is certainly no exception, with an enormous number of distinct processes each depending in its own way on the underlying symmetries of the physical system, the light, or of nature itself. Restricting ourselves to optical harmonic generation, we will explore three unique physical systems as well as three symmetries. In each case, the controlled breaking of that symmetry will lead to optical enhancements, novel nonlinearities, or deep physical insights. Beginning with silicon metasurfaces, we will explore the effects of even and odd spatial symmetries in optical systems. The periodic breaking of this symmetry will lead us to the highly engineerable physics of bound states in the continuum. By studying the harmonic emission from an atomic gas in the volume surrounding the metasurface, we will come to understand that significant nonlinear optical enhancements can be engineered with any linewidth and at any wavelength. In the context of the two-dimensional material hexagonal boron nitride, we will investigate and break crystal inversion symmetries. Using an intense laser tuned to the phonon resonance of hexagonal boron nitride, large amplitude anharmonic ionic motions will provide us a powerful degree of control over the internal symmetries of the system at an atomic level. Breaking this symmetry, we measure short-lived even-order nonlinearities that would otherwise be forbidden in equilibrium. Our observations for second- and third- harmonic generation are confirmed by time-dependent density functional theory. Those simulations further extend the understanding of this symmetry-breaking effect to even higher order processes. Lastly, single-crystal graphene and graphite provide an ideal platform through which to explore time-reversal symmetry. Chiral photons, or optical beams with ellipticity and handedness, are well known to break time-reversal symmetry. While applying high-power, chiral light to graphene, the breaking of time-reversal lifts a degeneracy of the K and K’ valleys in the momentum space Brillouin zone. Lifting this degeneracy, we unveil underlying spatial symmetry properties of graphene in odd-order third- and fifth- harmonic generation which should otherwise be unobservable. We also show experimentally, for the first time, that valley polarization and population can be extracted using our technique.
- Published
- 2021
- Full Text
- View/download PDF
30. Two-boson quantum interference in time
- Author
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Nicolas J. Cerf and Michael G. Jabbour
- Subjects
Time reversal ,time reversal ,boson bunching ,FOS: Physical sciences ,Duality (optimization) ,Quantum interference ,law.invention ,Quantum amplifier ,symbols.namesake ,Pauli exclusion principle ,law ,Quantum mechanics ,Quantum ,Boson ,Physics ,Condensed Matter::Quantum Gases ,Quantum Physics ,Multidisciplinary ,quantum interference ,Généralités ,Boson bunching ,Symmetry (physics) ,Bogoliubov transformation ,Physical Sciences ,symbols ,Quantum Physics (quant-ph) ,Beam splitter - Abstract
The celebrated Hong–Ou–Mandel effect is the paradigm of two-particle quantum interference. It has its roots in the symmetry of identical quantum particles, as dictated by the Pauli principle. Two identical bosons impinging on a beam splitter (of transmittance 1/2) cannot be detected in coincidence at both output ports, as confirmed in numerous experiments with light or even matter. Here, we establish that partial time reversal transforms the beam splitter linear coupling into amplification. We infer from this duality the existence of an unsuspected two-boson interferometric effect in a quantum amplifier (of gain 2) and identify the underlying mechanism as time-like indistinguishability. This fundamental mechanism is generic to any bosonic Bogoliubov transformation, so we anticipate wide implications in quantum physics., SCOPUS: ar.j, info:eu-repo/semantics/published
- Published
- 2020
31. Parity Violating Electron Scattering and Strangeness in the Nucleon.
- Author
-
Maas, Frank E.
- Subjects
- *
ELECTRON scattering , *PROTONS , *PARTICLES (Nuclear physics) , *SCATTERING (Physics) , *PHYSICS - Abstract
A measurement of the weak form factor of the proton allows a flavor separation of the strangeness contribution to the electromagnetic form factors. The weak form factor is accessed experimentally by the measurement of a parity violating (PV) asymmetry in the scattering of polarized electrons on unpolarized protons. An extended experimental program to measure these parity violating asymmetries has been performed and is going on at different accelerators. After the first round of experiments allowing a separation of the strangeness form factors GEs and GMs at a Q2-value of 0.1 (GeV/c)2, new, preliminary results have been achieved at 0.23 (GeV/c)2. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
32. "Ultrasonic stars" for time reversal focusing using induced cavitation bubbles.
- Author
-
Pernot, Mathieu, Montaldo, Gabriel, Tanter, Mickael, and Fink, Mathias
- Subjects
- *
TIME reversal , *NUCLEAR physics , *QUANTUM theory , *CAVITATION , *HYDRODYNAMICS , *PHYSICS - Abstract
Time reversal focusing with ultrasonic arrays is a way to focus waves through heterogeneous media. It requires a reference signal either sent by a small active source embedded in the medium or backscattered by a strong scatterer acting as a passive source. The potential of this method in ultrasonic medical imaging was already envisioned for aberration corrections. However, in many practical situations it is not possible to insert an active source in the medium or to rely on the presence of a unique strong scaterrer at focus in order to generate the reference signal. In analogy with the field of adaptive optics in astronomy, we propose here to create artificial “ultrasonic stars” in the body. The trick consists in creating cavitation bubbles inside the medium using one part of the ultrasonic probe. The bubble cavitation generates a spherical wave that propagates through medium heterogeneities to a time reversal array and is used as a reference signal for the time reversal method. This novel method is here experimentally validated for aberrations corrections in tissue mimicking phantoms. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]
- Published
- 2006
- Full Text
- View/download PDF
33. A High-Frequency Active Underwater Acoustic Barrier Experiment Using a Time Reversal Mirror; Model-Data Comparison.
- Author
-
Tesei, Alessandra, Song, Hee Chun, Guerrini, Piero, Roux, Philippe, Hodgkiss, William S., Akal, Tuncay, Stevenson, Mark, and Kuperman, William A.
- Subjects
- *
TIME reversal , *UNDERWATER acoustics , *SUBMARINE signals & signaling , *ACOUSTIC properties of fluids , *OCEAN sounds , *OCEANOGRAPHY , *MARINE sciences , *PHYSICS - Abstract
An underwater acoustic barrier based upon forward scattering in a Time-Reversal Mirror (TRM) was experimentally demonstrated for the first time in 2000 by Song et al.. The barrier consisted of a TRM, a vertical receive array (VRA) and a co-located probe source working at 3,500 Hz in an ocean waveguide near the western coast of Italy. In April 2003 further barrier tests were performed by applying for the first time at sea a new method that provided the capability to focus at different depths by using only the TRM transducers without the complication of additional probe sources. An echo repeater towed by R/V Alliance crossed the barrier, emulating the field forward scattered by a possible intruder insonified by the TRM. The presence of a target between the time reversal mirror and the focus can be detected if it significantly disturbs the quiescent region. A normal mode code is used to model the sound propagation in a waveguide. This is applied to predict the unperturbed and perturbed focused acoustic field measurements conducted at sea. Model-data comparison suggests that target detection performance is reasonably predictable using a numerical propagation model. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]
- Published
- 2004
- Full Text
- View/download PDF
34. Ultrasonic Time Reversal Mirrors.
- Author
-
Fink, Mathias, Montaldo, Gabriel, and Tanter, Mickael
- Subjects
- *
TIME reversal , *UNDERWATER acoustics , *SUBMARINE signals & signaling , *ACOUSTIC properties of fluids , *OCEAN sounds , *OCEANOGRAPHY , *MARINE sciences , *PHYSICS - Abstract
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. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]
- Published
- 2004
- Full Text
- View/download PDF
35. Irreversibility and the second law.
- Author
-
Uffink, Jos
- Subjects
- *
THERMODYNAMICS , *TIME reversal , *PHYSICS - Abstract
The relation between the second law of thermodynamics and the notion of irreversibility is analysed by distinguishing three different meanings of the latter and studying how they figure in several versions of the second law. A more extensive discussion is given in [1]. [ABSTRACT FROM AUTHOR]
- Published
- 2002
36. The arrow of time in operational formulations of quantum theory
- Author
-
Carlo Rovelli, Pietro Donà, Andrea Di Biagio, Centre de Physique Théorique - UMR 7332 (CPT), and Aix Marseille Université (AMU)-Université de Toulon (UTLN)-Centre National de la Recherche Scientifique (CNRS)
- Subjects
Quantum Physics ,Physics and Astronomy (miscellaneous) ,Tension (physics) ,Physics ,QC1-999 ,media_common.quotation_subject ,FOS: Physical sciences ,quantum information ,arrow of time ,inference ,time reversal ,time reversal symmetry ,operational quantum mechanics ,01 natural sciences ,Rotation formalisms in three dimensions ,Asymmetry ,[PHYS.PHYS.PHYS-GEN-PH]Physics [physics]/Physics [physics]/General Physics [physics.gen-ph] ,Atomic and Molecular Physics, and Optics ,010305 fluids & plasmas ,Quantum mechanics ,Arrow of time ,0103 physical sciences ,Quantum Physics (quant-ph) ,010306 general physics ,media_common - Abstract
The operational formulations of quantum theory are drastically time oriented. However, to the best of our knowledge, microscopic physics is time-symmetric. We address this tension by showing that the asymmetry of the operational formulations does not reflect a fundamental time-orientation of physics. Instead, it stems from built-in assumptions about the $users$ of the theory. In particular, these formalisms are designed for predicting the future based on information about the past, and the main mathematical objects contain implicit assumption about the past, but not about the future. The main asymmetry in quantum theory is the difference between knowns and unknowns., 16 pages + references, a few diagrams. This version is to appear in Quantum. Title has changed, it used to be "Quantum information and the arrow of time''
- Published
- 2020
37. 2-D Van Atta Array of Wideband, Wideangle Slots for Radiative Wireless Power Transfer Systems
- Author
-
Mauro Ettorre, Waleed Alomar, Anthony Grbic, Institut d'Électronique et des Technologies du numéRique (IETR), Université de Nantes (UN)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA)-CentraleSupélec-Centre National de la Recherche Scientifique (CNRS), King Abdulaziz City for Science and Technology, Conseil National de la Recherche Scientifique, University of Rennes 1, Rennes, France, Université de Nantes (UN)-Université de Rennes (UR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-CentraleSupélec-Centre National de la Recherche Scientifique (CNRS), and Nantes Université (NU)-Université de Rennes 1 (UR1)
- Subjects
Physics ,Aperture ,time reversal ,Amplifier ,Acoustics ,020208 electrical & electronic engineering ,Bandwidth (signal processing) ,wireless power transfer ,020206 networking & telecommunications ,Van Atta antennas ,02 engineering and technology ,law.invention ,Antenna array ,[SPI]Engineering Sciences [physics] ,law ,Retrodirective antennas ,0202 electrical engineering, electronic engineering, information engineering ,wideband arrays ,Wireless power transfer ,Dipole antenna ,Electrical and Electronic Engineering ,Wideband ,Coaxial - Abstract
International audience; We present a 2-D Van Atta array for far-field wireless power transfer systems. The antenna array is made up of wideband, wideangle long slots. The monostatic radar cross section (RCS) of the finite array is derived by windowing the aperture field distribution of the corresponding infinite case. It is shown that for oversampled apertures, the array behaves as an ideal Van Atta reflector. Therefore, the proposed solution can collect and reradiate the total power impinging on it from a remote source over a large field of view and bandwidth. The array design is presented and validated through measurements over a relative bandwidth of 24% centered at a frequency of 5.8 GHz. The array consists of four slots, each fed by eight coaxial ports. Coaxial cables are used to connect pairs of feeds in a Van Atta configuration. A bidirectional amplifier is also introduced into the Van Atta scheme to amplify the collected energy before retransmission to a possible moving user for wireless power transfer. Off-The-shelf components are used to implement the bidirection amplifier. The amplifier is matched across the bandwidth of the array and provides 5 dB gain. Monostatic RCS measurements show that the array exhibits-10 dB beamwidths of about 118° and 80° in the E-and H-planes, over the entire bandwidth. In addition, it is shown that when the array ports are terminated with matched loads, the antenna RCS is reduced by approximately-15 dB with respect to the Van Atta case. This experimentally confirms that the array collects the total energy impinging from a remote source. © 1963-2012 IEEE.
- Published
- 2018
38. Reversal of orbital angular momentum arising from an extreme Doppler shift
- Author
-
Graham M. Gibson, Gabriel C. Spalding, Miles J. Padgett, Simon A. R. Horsley, Euan Hendry, Ermes Toninelli, and David B. Phillips
- Subjects
Angular momentum ,Negative frequency ,time reversal ,02 engineering and technology ,Rotation ,01 natural sciences ,acoustic ,symbols.namesake ,0103 physical sciences ,Supersonic speed ,010306 general physics ,Physics ,Multidisciplinary ,Doppler ,negative frequency ,Radius ,021001 nanoscience & nanotechnology ,Computational physics ,Wavelength ,orbital angular momentum ,Physical Sciences ,symbols ,0210 nano-technology ,Doppler effect ,Sign (mathematics) - Abstract
Significance The emergence of “negative” frequencies in physical systems is often accompanied by intriguing consequences. For example, supersonic motion between a source and an observer leads to a negative Doppler-shifted frequency, the physical meaning of which is time reversal of the received signal. To our knowledge, the rotational analogue of this situation—the consequences of generating negative rotationally Doppler-shifted waves—has not been studied. Here we show, using an acoustic source, that a negative rotational Doppler shift is associated with a handedness reversal of the orbital angular momentum carried by the wave. We demonstrate that this handedness reversal can occur even at significantly subsonic velocities, making our findings relevant to interactions of ultrafast rotating systems with optical frequency radiation., The linear Doppler shift is familiar as the rise and fall in pitch of a siren as it passes by. Less well known is the rotational Doppler shift, proportional to the rotation rate between source and receiver, multiplied by the angular momentum carried by the beam. In extreme cases the Doppler shift can be larger than the rest-frame frequency and for a red shift, the observed frequency then becomes “negative.” In the linear case, this effect is associated with the time reversal of the received signal, but it can be observed only with supersonic relative motion between the source and receiver. However, the rotational case is different; if the radius of rotation is smaller than the wavelength, then the velocities required to observe negative frequencies are subsonic. Using an acoustic source at ≈100 Hz we create a rotational Doppler shift larger than the laboratory-frame frequency. We observe that once the red-shifted wave passes into the “negative frequency” regime, the angular momentum associated with the sound is reversed in sign compared with that of the laboratory frame. These low-velocity laboratory realizations of extreme Doppler shifts have relevance to superoscillatory fields and offer unique opportunities to probe interactions with rotating bodies and aspects of pseudorelativistic frame translation.
- Published
- 2018
39. Current Symmetries for Particle Systems with Several Conservation Laws.
- Author
-
Grisi, Rafael and Schütz, Gunter
- Subjects
- *
CONSERVATION laws (Physics) , *STOCHASTIC analysis , *HYPERBOLA , *ENTROPY , *PHYSICS , *STATISTICS - Abstract
We consider stochastic interacting particle systems with more than one conservation law in a regime far from equilibrium. Using time reversal we derive symmetry relations for the stationary currents of the conserved quantities that are reminiscent of Onsager's reciprocity relations. These relations are valid for a very large class of particles with only some mild assumption on the decay of stationary relations and imply that the coarse-grained macroscopic dynamics is governed by a system of hyperbolic conservation laws. An explicit expression for the conserved Lax entropy is obtained. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
40. The Dirac Sea, T and C Symmetry Breaking, and the Spinor Vacuum of the Universe
- Author
-
Vadim Monakhov
- Subjects
time reversal ,Dirac (software) ,Vacuum state ,General Physics and Astronomy ,Position and momentum space ,QC793-793.5 ,Krein spaces ,01 natural sciences ,vacuum state ,alternative vacuum ,General Relativity and Quantum Cosmology ,symbols.namesake ,discrete symmetries ,0103 physical sciences ,Clifford algebra ,Quantum field theory ,010306 general physics ,Dirac sea ,Mathematical physics ,Physics ,Spinor ,charge conjugation ,010308 nuclear & particles physics ,Elementary particle physics ,Charge (physics) ,symbols ,CAR algebra ,CPT ,Dirac Sea - Abstract
We have developed a quantum field theory of spinors based on the algebra of canonical anticommutation relations (CAR algebra) of Grassmann densities in the momentum space. We have proven the existence of two spinor vacua. Operators C and T transform the normal vacuum into an alternative one, which leads to the breaking of the C and T symmetries. The CPT is the real structure operator, it preserves the normal vacuum. We have proven that, in the theory of the Dirac Sea, the formula for the charge conjugation operator must contain an additional generalized Dirac conjugation operator.
- Published
- 2021
41. Constrained Reversible System for Navier-Stokes Turbulence.
- Author
-
Jaccod, Alice and Chibbaro, Sergio
- Subjects
- *
NAVIER-Stokes equations , *TURBULENCE , *REYNOLDS number , *TIME reversal , *LARGE eddy simulation models , *PHYSICS , *STATISTICAL mechanics - Abstract
Following a Gallavotti's conjecture, stationary states of Navier-Stokes fluids are proposed to be described equivalently by alternative equations besides the Navier-Stokes equation itself. We discuss a model system symmetric under time reversal based on the Navier-Stokes equations constrained to keep the enstrophy constant. It is demonstrated through highly resolved numerical experiments that the reversible model evolves to a stationary state which reproduces quite accurately all statistical observables relevant for the physics of turbulence extracted by direct numerical simulations (DNS) at different Reynolds numbers. The possibility of using reversible models to mimic turbulence dynamics is of practical importance for the coarse-grained version of Navier-Stokes equations, as used in large-eddy simulations. Furthermore, the reversible model appears mathematically simpler, since enstrophy is bounded to be constant for every Reynolds number. Finally, the theoretical interest in the context of statistical mechanics is briefly discussed. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
42. Entanglement properties in mixed spin- systems
- Author
-
Huang, Huaixiang, Wang, Xiaoguang, Sun, Zhe, and Yang, Guohong
- Subjects
- *
QUANTUM theory , *NUCLEAR physics , *PHYSICS , *MECHANICS (Physics) - Abstract
Abstract: We obtain an exact expression of the negativity for SU(2)-invariant bipartite spin- states via the partial time reversal method. Studies of thermal states show that the threshold temperature of entanglement may be arbitrary high when is sufficient large, indicating that the entanglement is very robust against temperature. Negativities in bilinear-biquadratic system are also considered. [Copyright &y& Elsevier]
- Published
- 2008
- Full Text
- View/download PDF
43. Inherent relativistic difficulties and some basic misconceptions with certain specific physical concepts in the existing literature.
- Author
-
Arunasalam, V.
- Subjects
- *
RELATIVITY (Physics) , *PHYSICS , *GRAVITY , *COULOMB functions , *ORBITS (Astronomy) , *LORENTZ groups , *WORLD line (Physics) , *HAMILTONIAN systems - Abstract
It is shown that some basic physical concepts when carried over from Newtonian physics into relativistic physics have inherent or intrinsic difficulties that are very hard to surmount or overcome. Further, some of the misconceptions or misunderstandings in physics are also pointed out. These include: The Newtonian concept of action-at-a-distance forces (such as the Coulomb's law, restoring force of a simple harmonic oscillator or a vibrating string, Newton's law of gravity, rigid-body constraints, orbital and spin angular momentum and the associated rigid-body spatial rotations, etc.); and some basic misconceptions or misunderstandings in physics such as assuming that Dirac's relativistic Hamiltonian for the electron is Lorentz covariant even though it is the total energy which is the fourth component of the energy-momentum four vector, Dirac's claim that g =2 for the electron and Feynman's claim that the (g-2) for the electron are a direct consequence of the theory of relativity ignoring the facts that g=2 follows directly from the nonrelativistic Pauli Hamiltonian and (g-2) calculation is very much analogous to the Bethe's nonrelativistic calculation of the Lamb shift, taking for granted that the experimentally measured fundamental unit of magnetic flux is a direct verification of the "electron pairs" of the Bardeen-ooper-Schrieffer theory of low-temperature superconductivity whereas it need not imply "electron pairing," the general feeling that the canonical orbital angular momentum can only take integral values and can not take half-odd-integral values whereas it is not true in general, etc. All these exemplify some of the wrong developments and claims in the existing physics literature. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
44. Spontaneous violation of symmetry of the classical Liouville equation.
- Author
-
Lasukov, V.
- Subjects
- *
EQUATIONS , *SYMMETRY (Physics) , *PHYSICS , *TIME reversal , *SPACETIME - Abstract
An exact solution to the classical Liouville equation is derived. It is found that it can have a partial solution with a broken symmetry with respect to time. Thus, in the general case, it does not follow from the invariance of the fundamental Liouville law concerning time reversal that the past and future play similar roles. [ABSTRACT FROM AUTHOR]
- Published
- 2007
- Full Text
- View/download PDF
45. Time-Symmetric Quantum Mechanics.
- Author
-
Wharton, K.
- Subjects
- *
QUANTUM theory , *TIME reversal , *WAVE functions , *WAVE equation , *MECHANICS (Physics) , *PHYSICS - Abstract
A time-symmetric formulation of nonrelativistic quantum mechanics is developed by applying two consecutive boundary conditions onto solutions of a time- symmetrized wave equation. From known probabilities in ordinary quantum mechanics, a time-symmetric parameter P0 is then derived that properly weights the likelihood of any complete sequence of measurement outcomes on a quantum system. The results appear to match standard quantum mechanics, but do so without requiring a time-asymmetric collapse of the wavefunction upon measurement, thereby realigning quantum mechanics with an important fundamental symmetry. [ABSTRACT FROM AUTHOR]
- Published
- 2007
- Full Text
- View/download PDF
46. Radiative Wireless Power-Transfer System Using Wideband, Wide-Angle Slot Arrays
- Author
-
Anthony Grbic, Mauro Ettorre, Waleed Alomar, Institut d'Électronique et des Technologies du numéRique (IETR), Nantes Université (NU)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA)-CentraleSupélec-Centre National de la Recherche Scientifique (CNRS), Stanford Synchrotron Radiation Lightsource (SSRL SLAC), SLAC National Accelerator Laboratory (SLAC), Stanford University-Stanford University, UM-KACST Joint Center for Microwave Sensor Technology, Université de Nantes (UN)-Université de Rennes 1 (UR1), Université de Nantes (UN)-Université de Rennes (UR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), and Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-CentraleSupélec-Centre National de la Recherche Scientifique (CNRS)
- Subjects
Physics ,Directional antenna ,business.industry ,Time reversal ,020208 electrical & electronic engineering ,Bandwidth (signal processing) ,020206 networking & telecommunications ,Near and far field ,Field of view ,Van Atta antennas ,02 engineering and technology ,Physical optics ,Wideband arrays ,[SPI.TRON]Engineering Sciences [physics]/Electronics ,[INFO.INFO-NI]Computer Science [cs]/Networking and Internet Architecture [cs.NI] ,Optics ,Retrodirective antennas ,0202 electrical engineering, electronic engineering, information engineering ,Radiative transfer ,Wireless power transfer ,Electrical and Electronic Engineering ,Wideband ,business - Abstract
International audience; This paper analyzes the benefits of using wideband, wide-angle arrays in radiative wireless power-transfer systems. A physical optics (PO) code is used to investigate the focusing capabilities and operating range of two 2-D antennas: Van Atta arrays and phase-conjugate/time-reversal arrays. In the PO analysis, the antennas are assumed to be ideal mirrors, which do not backscatter the impinging energy but rather completely absorb and reemit it. Sources located in both the near and far field of the antennas are considered. It is shown that for distances larger than the mirror size, the two antennas have similar focusing capabilities. In such scenarios, a Van Atta approach is preferred over a phase-conjugate approach due to its ease of implementation. Antenna elements used to realize these arrays/mirrors are typically resonant and exhibit strong backscatter, a limited field of view, and small bandwidth. To overcome these limitations, we propose an array/mirror consisting of long slots fed by parallel plate waveguides. A spectral Green's function approach is used to derive the scattering performance of the infinite array in reception. It is shown that the array can collect the total power impinging from a remote source over a large field of view and bandwidth. The conclusions arrived at for the infinite case are extended to the finite case through full-wave simulations. It is shown that the array can refocus the energy impinging from a close source over a large bandwidth. An infinite magnetic line source is considered as an example. An accurate expression is provided for the voltage distribution across the feed lines of the array. The proposed solution paves the way toward the practical implementation of ideal Van Atta and time-reversal/ phase-conjugate mirrors. The wideband behavior of the array may enable high-power, pulsed retrodirective arrays. © 2017 IEEE.
- Published
- 2017
47. How the First Partial Transpose was Written.
- Author
-
Bruß, Dagmar and Macchiavello, Chiara
- Subjects
- *
QUANTUM theory , *PHYSICS , *STATISTICAL physics , *MATHEMATICAL statistics , *MATRICES (Mathematics) - Abstract
We tell the tale of the first writing of a partial transpose, without guaranteeing historical authenticity. [ABSTRACT FROM AUTHOR]
- Published
- 2005
- Full Text
- View/download PDF
48. Time reversal and n-qubit canonical decompositions.
- Author
-
Bullock, Stephen S., Brennen, Gavin K., and O’Leary, Dianne P.
- Subjects
- *
TIME reversal , *SPACETIME , *QUANTUM theory , *PHYSICS , *MONOTONE operators , *OPERATOR theory , *MATHEMATICAL decomposition , *MATHEMATICAL physics - Abstract
On pure states of n quantum bits, the concurrence entanglement monotone returns the norm of the inner product of a pure state with its spin-flip. The monotone vanishes for n odd, but for n even there is an explicit formula for its value on mixed states, i.e., a closed-form expression computes the minimum over all ensemble decompositions of a given density. For n even a matrix decomposition ν=k1ak2 of the unitary group is explicitly computable and allows for study of the monotone’s dynamics. The side factors k1 and k2 of this concurrence canonical decomposition (CCD) are concurrence symmetries, so the dynamics reduce to consideration of the a factor. This unitary a phases a basis of entangled states, and the concurrence dynamics of u are determined by these relative phases. In this work, we provide an explicit numerical algorithm computing ν=k1ak2 for n odd. Further, in the odd case we lift the monotone to a two-argument function. The concurrence capacity of ν according to the double argument lift may be nontrivial for n odd and reduces to the usual concurrence capacity in the literature for n even. The generalization may also be studied using the CCD, leading again to maximal capacity for most unitaries. The capacity of νxI2 is at least that of ν, so odd-qubit capacities have implications for even-qubit entanglement. The generalizations require considering the spin-flip as a time reversal symmetry operator in Wigner’s axiomatization, and the original Lie algebra homomorphism defining the CCD may be restated entirely in terms of this time reversal. The polar decomposition related to the CCD then writes any unitary evolution as the product of a time-symmetric and time-antisymmetric evolution with respect to the spin-flip. En route we observe a Kramers’ nondegeneracy: the existence of a nondegenerate eigenstate of any time reversal symmetric n-qubit Hamiltonian demands (i) n even and (ii) maximal concurrence of said eigenstate. We provide examples of how to apply this work to study the kinematics and dynamics of entanglement in spin chain Hamiltonians. [ABSTRACT FROM AUTHOR]
- Published
- 2005
- Full Text
- View/download PDF
49. Non-Materiality of Non-Locality.
- Author
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Fano, Vincenzo
- Subjects
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BELL'S theorem , *QUANTUM theory , *MECHANICS (Physics) , *ENERGY levels (Quantum mechanics) , *TIME reversal , *PHYSICS - Abstract
In the present paper we show that in a certain sense the violation of Bell’s inequality does not entail a real non-locality. We definematerialityas the capacity to be modified; and it results that in the case of the singlet state the non-locality previewed by quantum mechanics and experimentally confirmed is not material. [ABSTRACT FROM AUTHOR]
- Published
- 2004
- Full Text
- View/download PDF
50. Time-Reversed Dynamical Entropy and Irreversibility in Markovian Random Processes.
- Author
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Gaspard, Pierre
- Subjects
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ENTROPY , *THERMODYNAMICS , *MARKOV processes , *STOCHASTIC processes , *PHYSICS , *JUMP processes - Abstract
A concept of time-reversed entropy per unit time is introduced in analogy with the entropy per unit time by Shannon, Kolmogorov, and Sinai. This time-reversed entropy per unit time characterizes the dynamical randomness of a stochastic process backward in time, while the standard entropy per unit time characterizes the dynamical randomness forward in time. The difference between the time-reversed and standard entropies per unit time is shown to give the entropy production of Markovian processes in nonequilibrium steady states. [ABSTRACT FROM AUTHOR]
- Published
- 2004
- Full Text
- View/download PDF
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