94 results on '"propagation effects"'
Search Results
2. Optical Fiber and the Fiber Channel
- Author
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Antonelli, Cristian, Puttnam, Ben, Section editor, and Kawanishi, Tetsuya, editor
- Published
- 2024
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- View/download PDF
3. Spatial variability of non-ergodic GMM residuals related to source and path effects in Italy.
- Author
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BRUNELLI, G., LANZANO, G., SGOBBA, S., and LUZI, L.
- Subjects
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GROUND motion , *PREDICTION models , *EARTHQUAKES - Abstract
In this study, we exploit the advantages of non-ergodic modelling of the ground motion to map the regional characteristics of source and propagation effects in Italy. In particular, we focused on the study of source and propagation effects obtained from the decomposition of the total residuals, i.e. the logarithmic difference of ITACAext observations and the model predictions, for active crustal earthquakes in Italy. The spatial trends, obtained from interpolating the residuals, clearly showed areas where the motion was significantly different from that predicted by the reference model, and in particular was underestimated. This is the case, for example, for many events with epicentres in northern Italy and the southern Ionian Sea. In addition, the study shows that paths across the Po Valley and the Adriatic coast are characterised by slower attenuation compared to that observed in the central Apennines. In addition, a marked difference between attenuation in the volcanic domain of Etna and the Hyblaean Mountains is clearly observed. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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- View/download PDF
4. Quantum well-shape dependence of optical harmonic radiation.
- Author
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Kuang, Yue, Zhang, Chaojin, Zhao, Bo, Du, Henglei, and Liu, Chengpu
- Subjects
- *
HARMONIC generation , *QUANTUM wells , *RADIANT intensity , *RADIATION , *LASER pulses , *SYMMETRY breaking - Abstract
We theoretically investigate the spatial-non-homogeneous laser pulse propagation through the quantum well. It is shown that the odd-order and even-order harmonic generations can be found due to breaking the inversion symmetry of the system. Importantly, the spectral intensity of high-order harmonics can be enhanced by changing the propagation distances and spatial-non-homogeneity of incident laser field. Moreover, the quantum well's shape has an important influence on the peak intensities of high-order harmonic generations, which may provide a new way to improve the spectral intensity of high-order harmonic generations. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
5. Photoelastic Perturbations to the Dielectric Tensor Due to Guided Acoustic Modes
- Author
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Zadok, Avi, Diamandi, Hilel Hagai, London, Yosef, Bashan, Gil, Lotsch, H.K.V., Founding Editor, Rhodes, William T., Editor-in-Chief, Adibi, Ali, Series Editor, Asakura, Toshimitsu, Series Editor, Hänsch, Theodor W., Series Editor, Krausz, Ferenc, Series Editor, Masters, Barry R., Series Editor, Midorikawa, Katsumi, Series Editor, Venghaus, Herbert, Series Editor, Weber, Horst, Series Editor, Weinfurter, Harald, Series Editor, Kobayashi, Kazuya, Series Editor, Markel, Vadim, Series Editor, Zadok, Avi, Diamandi, Hilel Hagai, London, Yosef, and Bashan, Gil
- Published
- 2022
- Full Text
- View/download PDF
6. Propagation Effects in Optical and Wireless Communications Channels, Noise Sources, and Channel Impairments
- Author
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Djordjevic, Ivan B. and Djordjevic, Ivan B.
- Published
- 2022
- Full Text
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7. Modeling and Simulation of Electromagnetic Response Data in Multilayered Inhomogeneous Media
- Author
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Song, Xijin, Tang, Shihua, Li, Peng, He, Bo, Wu, Wei, Series Editor, Qu, Zhan, editor, and Lin, Jia'en, editor
- Published
- 2019
- Full Text
- View/download PDF
8. Harmonic Analysis in Gaseous Helium by Coherent Schrödinger-Maxwell Method
- Author
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Lei Zhang, Zhenhong Fan, and Rushan Chen
- Subjects
Gaseous helium ,harmonic analysis ,Maxwell’s wave equation ,propagation effects ,time-dependent Schrödinger equation ,Electrical engineering. Electronics. Nuclear engineering ,TK1-9971 - Abstract
This paper concentrates on harmonic analysis in gaseous helium, including microscopic generation, selective filtration and macroscopic propagation. A coherent method is proposed, with time-dependent Schrödinger equation for harmonic generation and Maxwell's wave equation for harmonic propagation. By introducing the polarization source based on the microscopic single-atom response, the macroscopic nonlinear propagation can be efficiently solved by a set of linear equations at each harmonic frequency. Using the proposed method, we numerically investigate the propagation effects of selective harmonics in gaseous helium. Our results reveal that specific harmonics allow the synthesis of an isolated attosecond pulse, which presents a high beam quality and an excellent spatial profile with Gaussian-like distribution. Moreover, the generated pulse provides a promising potential on high power defense, quantum radar and communication.
- Published
- 2019
- Full Text
- View/download PDF
9. A Frequency Offset Transmit Reference System in Dense Multipath Environments: Propagation Effects and Design Considerations.
- Author
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Bilal, Ibrahim, Meijerink, Arjan, and Bentum, Mark J.
- Abstract
Frequency offset transmit reference (FoTR)—a noncoherent spread spectrum technique—is considered in dense multipath fading environments, in the context of wideband communication. The interplay between system parameters and propagation effects is investigated. Analytical relations between key design parameters and the channel delay spread are derived, which provide a framework for determining reasonable system parameters that optimize the performance. An approximated closed-form expression for the outage probability is also obtained, which is shown to be fairly accurate for low outage probabilities. It is shown that FoTR suffers significantly from noise-enhancement, but, is nonetheless, robust against frequency-selective fading. A large value of frequency offset can significantly deteriorate the performance, particularly in environments with large channel delay spreads. This restricts the maximum data rate as well as the multiple-access capability of the scheme. Despite the limitations, FoTR can be a useful communication scheme for low data rate sensor networks deployed in dense multipath environments, particularly where the design demands a simple receiver and a low outage probability. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
10. Radio Emission from the Outer Heliosphere and Beyond
- Author
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Cairns, Iver H., Poletto, Giannina, editor, and Suess, Steven T., editor
- Published
- 2004
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11. Characteristics of femtosecond laser pulses propagating in multiply ionized rare gases.
- Author
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Toşa, Valer, Kovács, Katalin, Ursescu, Daniel, and Varjú, Katalin
- Subjects
- *
FEMTOSECOND lasers , *IONIZED gases , *ATOMIC beams , *LASER pulses , *REFRACTIVE index - Abstract
A three-dimensional non-adiabatic model in combination with a rate equation model is used to characterize high-intensity (>10 16 W/cm 2 ) femtosecond laser pulse propagation in atomic gas medium. In these conditions the atoms in the target gas will become multiply charged ions, while the laser pulse will propagate in a medium with high electron concentration created by itself. We obtain pulse characteristics in time, frequency and space domain for two representative cases: 800 nm and 267 nm (third harmonic) multi-cycle pulses which are both of practical importance. We show that the spatial-temporal variation of the refractive index in the macroscopic medium is the primary reason for pulse temporal/spectral and spatial shaping during propagation. [ABSTRACT FROM AUTHOR]
- Published
- 2017
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- View/download PDF
12. A Frequency Offset Transmit Reference System in Dense Multipath Environments
- Author
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Arjan Meijerink, Mark J. Bentum, and Ibrahim Bilal
- Subjects
Computer science ,propagation effects ,Context (language use) ,02 engineering and technology ,Data_CODINGANDINFORMATIONTHEORY ,Delay spread ,0202 electrical engineering, electronic engineering, information engineering ,Electronic engineering ,Wireless ,Frequency offset ,Fading ,Electrical and Electronic Engineering ,Wideband ,Low-power radios ,wireless sensor networks ,transmit reference ,Computer Science::Information Theory ,outage probability ,business.industry ,Applied Mathematics ,020206 networking & telecommunications ,n/a OA procedure ,Computer Science Applications ,Spread spectrum ,noise-based communication ,spread spectrum ,business ,Multipath propagation ,Communication channel - Abstract
Frequency offset transmit reference (FoTR)—a noncoherent spread spectrum technique—is considered in dense multipath fading environments, in the context of wideband communication. The interplay between system parameters and propagation effects is investigated. Analytical relations between key design parameters and the channel delay spread are derived, which provide a framework for determining reasonable system parameters that optimize the performance. An approximated closed-form expression for the outage probability is also obtained, which is shown to be fairly accurate for low outage probabilities. It is shown that FoTR suffers significantly from noise-enhancement, but, is nonetheless, robust against frequency-selective fading. A large value of frequency offset can significantly deteriorate the performance, particularly in environments with large channel delay spreads. This restricts the maximum data rate as well as the multiple-access capability of the scheme. Despite the limitations, FoTR can be a useful communication scheme for low data rate sensor networks deployed in dense multipath environments, particularly where the design demands a simple receiver and a low outage probability.
- Published
- 2020
- Full Text
- View/download PDF
13. Effects of Propagation of Narrow Bipolar Pulses, Generated by Compact Cloud Discharges, over Finitely Conducting Ground
- Author
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Vernon Cooray, M. Fernando, L. Gunasekara, and S. Nanayakkara
- Subjects
compact cloud discharges ,narrow bipolar pulses ,propagation effects ,finitely conducting ground ,Meteorology. Climatology ,QC851-999 - Abstract
Propagation effects on the narrow bipolar pulses (NBPs) or the radiation fields generated by compact cloud discharges as they propagate over finitely conducting ground are presented. The results were obtained using a sample of NBPs recorded with high time resolution from close thunderstorms in Sri Lanka. The results show that the peak amplitude and the temporal features such as the full width at half maximum (FWHM), zero-crossing time, and the time derivative of NBPs can be significantly distorted by propagation effects. For this reason, the study of peak amplitudes and temporal features of NBPs and the remote sensing of current parameters of compact cloud discharges should be conducted using NBPs recorded under conditions where the propagation effects are minimal.
- Published
- 2018
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14. Data-driven zonations for modelling the regional source and propagation effects into a Ground Motion Models in Italy.
- Author
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Brunelli, Giulio, Lanzano, Giovanni, Luzi, Lucia, and Sgobba, Sara
- Subjects
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GROUND motion , *TSUNAMI warning systems , *GEOLOGICAL modeling , *TSUNAMIS - Abstract
The main objective of this work is to provide two zonations of Italy useful to incorporate regional source and path effects in empirical Ground Motion Models (GMMs). To this end, we revise existing zonations developed for seismic and tsunami hazard studies, based on the results of a residual analysis between the observations of the ITACAext dataset and the predictions of ITA18, a GMM recently developed for Italy. The analysis consists in the decomposition of the residuals into repeatable terms, according to the well-established approach used for the calibration of non-ergodic models. Based on the spatial trend of the interpolated residuals, and geological and seismological considerations, the zonations are proposed and discussed, in the perspective of supporting regionalization of a future generation of GMMs for Italy. • The goal is to provide the tools to regionalize seismic motion in Italy. • Zonation for source effects is based on spatial variability of the event residuals. • Zonation for propagation effects is based on spatial variability of random residuals. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
15. Chirp-dependent spectral distribution for few-cycle pulses propagating through nano-semiconductor devices.
- Author
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Zhang, Chaojin and Liu, Chengpu
- Subjects
- *
SEMICONDUCTOR devices , *SYMMETRY (Physics) , *SPECTRUM analysis , *LASER beams , *QUANTUM wells , *PARAMETERS (Statistics) - Abstract
The propagation of an initially chirped incident few-cycle pulse through an ensemble of quantum wells is numerically investigated. It is found that the distribution characteristic of the transmitted spectrum sensitively depends on the incident laser parameters, especially its positive or negative chirp property. As for the incident pulse with a positive initial chirp, beyond the obvious spectral blue-shift, the transmitted spectral distribution is discrete. In contrast, as for a negative initial chirp, the spectral distribution is continuous instead. In addition, the insensitivity of chirp-dependent spectral distribution to medium symmetry character is also tested and the intensity of high-frequency spectral components enhances obviously due to the nonlinear propagation effects. [ABSTRACT FROM AUTHOR]
- Published
- 2016
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16. 近代上海平面媒体报道美国体育的作用:引导·启蒙·示范.
- Author
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倪京帅, 林恬, and 张业安
- Abstract
Copyright of Journal of Capital Institute of Physical Education is the property of Shoudu Tiyu Xueyuan and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
- Published
- 2016
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- View/download PDF
17. Effect of the rotor–stator gap variation on the tonal noise generated by axial-flow fans.
- Author
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Canepa, Edward, Cattanei, Andrea, and Mazzocut Zecchin, Fabio
- Subjects
- *
NOISE pollution , *ELECTRICAL harmonics , *AXIAL flow , *FLUID flow , *ROTORS , *MATHEMATICAL models - Abstract
The effect of the rotor–stator axial-gap on tonal noise generated by an axial-flow fan employed for automotive cooling systems has been studied. A fan equipped with a 9 blade rotor and a 18 vane stator positioned at several axial-gaps has been tested in a hemi-anechoic chamber. The acoustic measurements have been performed during rotational speed ramps. To analyze the experimental data, the propagation function, obtained by means of the spectral decomposition, has been compared with the velocity-scaled SPL and the phase angle, evaluated at the 1st and 2nd blade passing frequency harmonics. Opposite to what is commonly observed, the SPL due to the rotor–stator aerodynamic interaction does not monotonically decrease with the axial-gap and at the shortest gaps it may not be scaled with a single power of the rotational speed. The listed quantities have been plotted versus frequency, rotational speed, and axial-gap. Their analysis provides a detailed picture of the investigated phenomena and supports the assumption that the observed behavior is due to acoustic effects and not to the aerodynamic noise generating mechanism. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
18. On the validity of the Cooray formula for the evaluation of the underground horizontal electric fields of lightning.
- Author
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Khosravi-Farsani, Mojtaba, Moini, Rozbeh, Sadeghi, S. H. Hesam, and Rachidi, Farhad
- Abstract
Using a parallel implementation of the finite difference time domain (FDTD) technique, we test the accuracy of the Cooray formula in which the underground horizontal electric field is evaluated using its counterpart at the air-soil interface. This latter can be calculated using either (i) the original Cooray-Rubinstein (CR) formula in which the magnetic field at ground level is evaluated assuming the ground as a perfect conductor, (ii) taking into account propagation effects in the computation of the magnetic field. We show that, by taking into account propagation effects in the computation of the magnetic fields used in the CR formula and for ground conductivities of 0.001 S/m and higher, the underground horizontal electric field can be evaluated using the Cooray formula with acceptable accuracy. [ABSTRACT FROM PUBLISHER]
- Published
- 2012
- Full Text
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19. Graph neural network-based propagation effects modeling for detecting visual relationships among construction resources.
- Author
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Kim, Jinwoo and Chi, Seokho
- Subjects
- *
ARTIFICIAL neural networks , *DIGITAL technology , *BUILDING sites - Abstract
Detecting visual relationships among construction resources plays a pivotal role in understanding complex construction scenes and performing vision-based site monitoring and digitalization. Despite extensive efforts, the propagation effects of different resource-to-resource interactions were overlooked and thus, it is still challenging to precisely detect entangled and intertwined visual relationships from actual construction images. To address the challenge, this study proposes a semantic graph neural network approach that structuralizes construction resources and their entangled interactions in the form of a graph, and simulates the propagation effects using a neural message passing mechanism. The experimental results showed that the proposed approach achieved 77.1% F-score—11.5% higher than the performance of the baseline model. This suggests the positive impacts of the propagation effects and the applicability of the proposed approach. These findings can help understand what are actually happening at construction sites automatically and provide valuable insights for future vision-based monitoring studies. • The approach detected object-to-object visual relationships with 77.1% F-score. • Propagations effects among different object-to-object interactions were modeled. • The performance was improved by 11.5% compared to the baseline model. • Feasibility of graph neural networks was demonstrated with quantitative results. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
20. A Layer Stripping Approach for EM Reconstruction of Stratified Media.
- Author
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Caorsi, Salvatore and Stasolla, Mattia
- Subjects
- *
ELECTROMAGNETISM , *IMAGE reconstruction , *MULTILAYERS , *NONDESTRUCTIVE testing , *PERMITTIVITY , *BACKSCATTERING - Abstract
This paper presents an electromagnetic (EM) technique for the reconstruction of the physical and geometrical properties (permittivity and thickness) of stratified media. The key points of the approach, belonging to the so-called layer stripping algorithms, are the introduction of an equalization step that takes into account propagation effects, and the design of a procedure devoted to multiple reflections' removal. Furthermore, the proposed main processing block is an energy-based method able to accurately estimate amplitudes and time of delays of backscattered echoes in the time domain. A numerical analysis of the algorithm's potentialities will show that it can be successfully employed under different working conditions and in the presence of noisy data. [ABSTRACT FROM PUBLISHER]
- Published
- 2014
- Full Text
- View/download PDF
21. Propagation and Parametric Amplification in Four-Wave Mixing Processes: Intramolecular Coupling and High-Order Effects
- Author
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José Luis Paz, Patricio J. Espinoza-Montero, Marcos Loroño, Fernando Javier Torres, Lenin González-Paz, Edgar Márquez, Joan Vera-Villalobos, José R. Mora, Fernando Moncada, and Ysaias J. Alvarado
- Subjects
Physics and Astronomy (miscellaneous) ,Chemistry (miscellaneous) ,General Mathematics ,Computer Science (miscellaneous) ,Physics::Optics ,intramolecular coupling ,propagation effects ,parametric amplification - Abstract
A strong pump-power dependence of the four-wave mixing (FWM) signal for an aqueous solution of Malachite green is reported. The characteristics of the pump-power dependence of the nonlinear signal are reproduced by a theoretical model based on the coupling between pump-probe, considering signal fields and propagation effects. The effect of the intramolecular coupling on the nonlinear intensity of the FWM signal is studied using a model molecule consisting of two-coupled harmonic curves of electronic energies with minima displaced in energy and nuclear positions. Two-vibrational states are considered while including non-adiabatic effects for the two-state model. Moreover, the coupling among the field components, as well as the propagation effects, are studied by considering a constant pump-intensity. Our calculation scheme, considering both the intramolecular coupling effects in the description of the molecular structure and the effects produced by the propagation of the FWM signal along the optical length, allows the exponential dependence of the latter, as the intensity of the pumping beam increases. Our treatments do not require the inclusion of other non-resonant processes outside the RWA approximation, due to the consideration of an adiabatic basis.
- Published
- 2022
- Full Text
- View/download PDF
22. Stability of genetic effects across clonal and seedling populations of Eucalyptus globulus with common parentage.
- Author
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Costa e Silva, João, Potts, Brad M., and Tilyard, Paul
- Subjects
EUCALYPTUS globulus ,SEEDLINGS ,PLANT population genetics ,PLANT colonization ,PLANT breeding ,PLANT growth ,PLANT development - Abstract
Abstract: Eucalyptus globulus is widely planted in temperate regions of the world for pulpwood production and there are breeding programs in many countries. While breeding and deployment programs in Australia mainly use seedlings, in countries such as Chile, Portugal and Spain, a combination of seedlings and clones are used for genetic testing and plantation establishment. In the present study, we compared clones and seedlings produced from the same twenty open-pollinated families of the Jeeralang provenance of E. globulus, and randomised within the same field trial established in NW Tasmania. We specifically aimed to test whether mean performance, variance components, genetic parameters and breeding values estimated from the two propagule types were comparable. We studied the susceptibility of the juvenile foliage to leaf disease caused by Teratosphaeria nubilosa, the height at which the transition to the adult foliage occurred, as well as growth at selection and harvest ages. While the clones exhibited less disease damage, switched to the adult foliage at a slightly lower height and had less height and diameter growth than the seedlings, no significant differences in estimates of additive genetic variances and narrow-sense heritabilities between the two propagule types were detected. The additive genetic correlations estimated between the clonal and seedling populations did not differ significantly from one. The propagule type also had little effect on estimates of genetic correlations between traits. Thus, our results argue that while differences in trait means need to be taken into account, the propagation method is unlikely to affect the genetic architecture and predictions of breeding value in this species. [Copyright &y& Elsevier]
- Published
- 2013
- Full Text
- View/download PDF
23. Degree of Polarization at Horizontal Transmit: Theory and Applications for Weather Radar.
- Author
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Galletti, M., Zrnic, D. S., Melnikov, V. M., and Doviak, R. J.
- Subjects
- *
ANTENNA radiation patterns , *RADAR meteorology , *BACKSCATTERING , *RADAR polarimetry , *REMOTE sensing by radar - Abstract
This paper considers weather radar measurements at linear depolarization ratio (LDR) mode, consisting of transmission of horizontal polarization and simultaneous reception of the copolar (horizontal) and cross-polar (vertical) components of the returned wave. Such a system yields the coherency matrix, with four degrees of freedom. After a theoretical analysis of its structure and symmetries, we focus on three cross-polarization variables: LDR, cross-polar correlation coefficient at horizontal transmit (ρxh) , and degree of polarization at horizontal transmit (pH). The different properties of these variables with respect to backscattering and propagation are analyzed, together with the bias induced by antenna cross-channel coupling. It is demonstrated that the degree of polarization at horizontal transmit possesses attractive properties in terms of robustness to propagation effects and antenna cross-channel coupling. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
24. Propagation Effects Due to Finitely Conducting Ground on Lightning-Generated Magnetic Fields Evaluated Using Sommerfeld's Integrals.
- Author
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Cooray, Vernon
- Subjects
- *
MAGNETIC fields , *ELECTROMAGNETIC fields , *ELECTRIC fields ,ELECTRICITY research - Abstract
The effects of finitely conducting ground on the signature of lightning-generated magnetic fields at ground level were evaluated by numerical solution of Sommerfeld's integrals. Results are presented for distances between 10 m to 1 km from the lightning channel and for ground conductivities in the range of 0.01 and 0.0001 S/m. The results obtained from the exact theory are compared with the predictions of two frequently used analytical approximations to Sommerfeld's equations. Based on that comparison, the limits of validity of these approximate theories are obtained. [ABSTRACT FROM AUTHOR]
- Published
- 2009
- Full Text
- View/download PDF
25. Propagation and Parametric Amplification in Four-Wave Mixing Processes: Intramolecular Coupling and High-Order Effects.
- Author
-
Paz, José Luis, Espinoza-Montero, Patricio J., Loroño, Marcos, Torres, Fernando Javier, González-Paz, Lenin, Márquez, Edgar, Vera-Villalobos, Joan, Mora, José R., Moncada, Fernando, and Alvarado, Ysaias J.
- Subjects
FOUR-wave mixing ,MALACHITE green ,NUCLEAR energy ,ENVIRONMENTAL reporting ,INDUCTIVE effect - Abstract
A strong pump-power dependence of the four-wave mixing (FWM) signal for an aqueous solution of Malachite green is reported. The characteristics of the pump-power dependence of the nonlinear signal are reproduced by a theoretical model based on the coupling between pump-probe, considering signal fields and propagation effects. The effect of the intramolecular coupling on the nonlinear intensity of the FWM signal is studied using a model molecule consisting of two-coupled harmonic curves of electronic energies with minima displaced in energy and nuclear positions. Two-vibrational states are considered while including non-adiabatic effects for the two-state model. Moreover, the coupling among the field components, as well as the propagation effects, are studied by considering a constant pump-intensity. Our calculation scheme, considering both the intramolecular coupling effects in the description of the molecular structure and the effects produced by the propagation of the FWM signal along the optical length, allows the exponential dependence of the latter, as the intensity of the pumping beam increases. Our treatments do not require the inclusion of other non-resonant processes outside the RWA approximation, due to the consideration of an adiabatic basis. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
26. On the Accuracy of Several Approximate Theories Used in Quantifying the Propagation Effects on Lightning Generated Electromagnetic Fields.
- Author
-
Cooray, V.
- Abstract
The effect of finitely conducting ground on the signature of lightning generated vertical electric fields at ground level was evaluated by numerical solution of Sommerfeld's integrals. Results are presented for distances between 10 m to 1 km from the lightning channel and for ground conductivities in the range of 0.01 and 0.001 S/m. The results obtained from the exact theory are compared with the predictions of several approximate theories available in the literature. Based on that comparison the limits of validity of these approximate theories are obtained. [ABSTRACT FROM PUBLISHER]
- Published
- 2008
- Full Text
- View/download PDF
27. Propagation effects on radiation field pulses generated by cloud lightning flashes
- Author
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Cooray, Vernon
- Subjects
- *
RADIO wave propagation , *RADIATION , *LIGHTNING , *ELECTROMAGNETIC waves - Abstract
Abstract: As the electromagnetic fields propagate over finitely conducting ground, selective attenuation of the high frequencies takes place. As a result, the signatures of broad-band electromagnetic radiation fields generated by lightning flashes change as they propagate over such ground. In addition to being a function of the electrical parameters of the ground over which the electromagnetic fields propagate, these propagation effects depend on the height of their source above ground level. This makes the propagation effects on radiation fields from cloud flashes differ from those on the radiation fields generated by return strokes in ground flashes. In this paper the propagation effects on radiation field pulses of cloud flashes are illustrated and it is shown that these effects are not as severe as those of return strokes in ground flashes. [Copyright &y& Elsevier]
- Published
- 2007
- Full Text
- View/download PDF
28. Propagation effects on the electric field time derivatives generated by return strokes in lightning flashes
- Author
-
Fernando, Mahendra and Cooray, Vernon
- Subjects
- *
RADIO wave propagation , *ELECTRIC fields , *ELECTROMAGNETIC fields , *LIGHTNING - Abstract
Abstract: The effects of propagation over finitely conducting ground on the features of radiation component of the electric field time derivatives are investigated. The results show that the peak, the half-width and the risetime of the electric field time derivative change significantly in propagating over finitely conducting ground. Furthermore, any correlation that may exist between various parameters could also change significantly due to propagation effects. Consequently, in return stroke model validations using experimentally measured fields, remote sensing of return stroke current time derivatives using measured electric field time derivatives and in the calculation of induced voltages generated by lightning flashes in electrical installations the distortions caused by propagation effects on the electric field time derivatives cannot be neglected. [Copyright &y& Elsevier]
- Published
- 2007
- Full Text
- View/download PDF
29. A practical approach to correct attenuation effects in GPR data
- Author
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Xavier Neto, Pedro and Eugênio de Medeiros, Walter
- Subjects
- *
SPECTRUM analysis , *OPTICS , *DISPERSION (Chemistry) , *ABSORPTION - Abstract
Abstract: As the GPR pulse propagates in the geologic medium, it suffers attenuation as the result of absorption and dispersion, besides spherical divergence. High frequency components of the pulse suffer more pronounced effects of attenuation than low frequency components resulting in resolution loss in radargrams. The quality of the GPR images is then strongly dependent on an adequate correction of the attenuation effects. We present a practical approach to approximately correct the attenuation effects based on their influence on the amplitude and phase spectra of GPR signals. The key point of this approach is the fact that in low and moderate losses dielectric media the propagated signal suffers significant changes only in its amplitude spectrum; that is, the phase spectrum of the propagated signal remains practically unaltered for the usual travel time ranges. Based on this fact, we show using real data (both CMP and radargram) that the judicious application of the well known tools of time gain and spectral balancing can efficiently correct the attenuation effects, from the practical point of view. The proposed approach can be applied in heterogeneous media and it does not demand the precise knowledge of the attenuation parameters of the media. This approach should be understood as part of an interpretative data processing, which can be done by using the interpreter''s knowledge on the studied area and even during the fieldwork. As an additional benefit, the judicious application of spectral balancing promotes a partial deconvolution of the data without changing its phase. In this way, the spectral balancing acts in a similar way to a zero phase deconvolution. Usually, in GPR data, the resolution increase obtained with spectral balancing is greater than those obtained with spike and predictive deconvolutions. [Copyright &y& Elsevier]
- Published
- 2006
- Full Text
- View/download PDF
30. Propagation effects in spectrally resolved transient four wave mixing measurements on excitons in GaAs multiple quantum wells
- Author
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Pal, Bipul, Vengurlekar, A.S., Gopal, A.V., and Prabhu, S.S.
- Subjects
- *
EXCITON theory , *SPECTRUM analysis , *QUANTUM wells , *ULTRASHORT laser pulses - Abstract
We perform spectrally resolved degenerate four wave mixing (DFWM) measurements by resonantly exciting 1s heavy hole excitons in 8 and
17.5 nm wide GaAs multiple quantum wells (MQW) with subpicosecond laser pulses. The signal is detected in a self-diffraction mode in backward geometry. The DFWM spectra reveal a multiple peak structure, evolving into a double peak for positive delays. This may be related to the propagation effects in MQWs due to strong photon–exciton coupling. The different peaks in the DFWM spectra show a dissimilar dependence on pulse excitation intensity, delay and polarization. [Copyright &y& Elsevier]- Published
- 2004
- Full Text
- View/download PDF
31. The Fine Structure of Positive Lightning Return-Stroke Radiation Fields.
- Author
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Cooray, Vernon, Fernando, M., Gomes, C., and Sorenssen, T.
- Subjects
- *
LIGHTNING , *RADIATION , *ELECTROMAGNETIC fields , *RADIO wave propagation , *CATHODE ray oscillographs - Abstract
The electric fields generated by lightning flashes striking the North sea were measured, with a time resolution better than a few tens of nanoseconds, at Fanö island in Denmark. The measuring station was located a few tens of meters away from the high water mark at the west coast of the island. This particular location made it possible to capture, with minimal propagation effects, the electromagnetic fields from lightning flashes striking the North Sea. The waveforms were recorded by a measuring system that could provide a time resolution of about 10 ns. The data recorded had the following features. The initial rising part of the positive return-stroke fields contains a slow front followed by a fast transition. The duration of the slow front of the positive return-stroke fields had an average of 8.3 μs and its amplitude, measured as a fraction of the initial peak, had an average of 0.61. The 10%-90% rise time of the fast rising portion of the positive return-stroke fields was about 0.26 μs, on average. The average peak value of the measured radiation fields normalized to 100 km was 15.7 V/m. The mean of the peak value of the time derivative of the radiation fields was 25 V/m/μs. The full width at half maximum of the radiation field derivative had a mean of 170 ns. [ABSTRACT FROM AUTHOR]
- Published
- 2004
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32. Ku-band diurnal fade characteristics and fade event duration data from three, two-year, Earth-space radiometric experiments in Equatorial Africa.
- Author
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Allnutt, Jeremy E. and Haidara, Fatim
- Abstract
The move to provide direct to home (DTH) multi-media services from satellites requires a number of new insights to be gleaned from the propagation effects that occur along satellite-to-ground paths. Annual statistics will not be sufficient to describe the likely performance of the link, nor will they provide information on the likely customer acceptance of the DTH service. What are required are the likely number of outages due to rain attenuation in a given period, their duration, the time between the outages, and the diurnal characteristics of rain attenuation along the link. This paper presents results obtained in three, two-year, Ku-band experiments in tropical Africa on diurnal attenuation effects, as well as on rain and attenuation event duration and inter-event duration. The implications of the results are discussed. Copyright © 2000 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]
- Published
- 2000
- Full Text
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33. Compensation of laser propagation effects within solids for high harmonic generation of extreme ultraviolet radiation.
- Author
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Kim, Yong Woo, Kim, Byunggi, Choi, Seungman, Nam, Han Ku, Kim, Hyunwoong, Kim, Young-Jin, and Kim, Seung-Woo
- Subjects
- *
ULTRAVIOLET radiation , *QUARTZ crystals , *LASER pulses , *PHASE modulation , *LASERS , *HARMONIC generation - Abstract
• Compensation of the propagation effects for enhancement of the EUV harmonics yield. • Role of the band structure on the harmonics spectrum control. • Various control schemes of HHG spectra in MgO, sapphire, and quartz. • Optimization of anisotropic HHG for yield enhancement by an order of magnitude. High harmonic generation (HHG) from solids offers a convenient means of producing coherent extreme ultraviolet (EUV) radiation. However, the achievable harmonic yield is greatly affected by propagation effects that the driving laser pulse experiences with spatiotemporal distortion when passing through solids. Here, we intend to optimize EUV harmonics generated from crystals by pre-shaping the driving laser pulse via spectral phase modulation through a genetic algorithm. Our experimental results obtained from MgO, sapphire and quartz crystals demonstrate EUV yield improvements, without increasing the incident laser fluence, up to an order of magnitude along with cut-off extension and selective harmonic enhancement. As a practical tool of compensating laser propagation effects, our method is expected to facilitate solid-based HHG applications such as high-energy photon spectroscopy and multi-petahertz signal processing. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
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34. New rain rate analyses to assess rain attenuation on satellite ehf communications.
- Author
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Tattelman, Paul
- Abstract
This paper provides estimates of the frequency of occurrence, duration and probability of satellite EHF communication outages due to attenuation by rain. These can be used to determine optimum frequencies, power levels and the need for space diversity of terminals or other alternatives to maintain reliable communications. Ten years of 1 min rain rates at each of 12 U.S. cities were used in conjunction with an attenuation model to quantify communication outages at locations representing a variety of climatic regimes. Analyses of the 1 min rain rates and outage estimates at 10, 30 and 45 GHz for elevation angles of 10°, 30°, 50° and 70° are presented. [ABSTRACT FROM AUTHOR]
- Published
- 1989
- Full Text
- View/download PDF
35. An attempt to evaluate seismic hazard in Central-Southern Italy.
- Author
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Basili, A., Favali, P., Scalera, G., and Smriglio, G.
- Abstract
A method for the evaluation of seismic hazard in a given zone, taking into account both the spreading of macroseismic effects and seismic catalogue information, is applied. A data-bank of some 500 digitized isoseisms of earthquakes having occurred in Italy between 1542 and 1986 is used. The isoseismical maps are digitized considering for each degree of intensity the length of 24 spreading rays starting from the macroseismic epicenter or barycentre of the megaseismic area. These rays are separated from each other by the same angle, i.e. every isoseism is divided into 24 equal circular sectors. The year 1542 is taken as the beginning of the time span, since this is when the first seismic event occurred for which reliable isoseismal maps are available. The epicentral intensities considered lie between the VI and XI degrees of the Mercalli-Cancani-Sieberg scale (MCS). This digitized data-bank is analyzed to achieve, for each homogeneous seismogenetic zone that has been recognized, the mean azimuthal spreadings of effects for each degree of intensity as a function of the epicentral intensity. Once a mean propagation model is obtained for each zone, this is applied to seismic events of the same zone, the isoseismal maps of which are not available. A geographic grid is defined to cover the analyzed area, and for each cell of this grid it is then possible to count the number of felt events and their degree. These effects have been evaluated either on the basis of the isoseismal maps (when available) or on the basis of the mean propagations of the zone in which the single event occurred. Moreover, an index summarizing the seismic information was computed for each cell of the previous grid. All the events producing effects and their provenance are stored on files, allowing the main seismogenic zones influencing this cell to be identified. This methodology has been applied to central and southern Italy in an area between the latitudes 40.6 and 43.3 N. In particular, attention is focussed on the sample areas of Rome (given the historical and political importance of the city) and of the Sannio-Matese and Irpinia zone (in which some of the strongest earthquakes of the Apennine chain have occurred). Finally, in order to evaluate the maximum expected magnitude, extreme value statistics (Gumbel III-type) are applied to the Colli Albani area, which represents the seismogenic zone nearest to Rome. For the Sannio-Matese and Irpinia area, considering the more dangerous zone as a 'unicum', the Weibull distribution has been hypothesized to determine the mean return time for events with an intensity greater than or equal to IX. [ABSTRACT FROM AUTHOR]
- Published
- 1990
- Full Text
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36. Through-wall imaging: Historical perspective and future directions
- Author
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Baranoski, Edward J.
- Subjects
- *
SIGNAL processing , *DIAGNOSTIC imaging , *RADIO frequency , *DETECTORS - Abstract
Abstract: Through-wall imaging approaches are highly desirable for a range of applications including police, fire and rescue, first responder, and military applications. The ultimate desire of such systems is to provide detailed information in areas that cannot be seen through conventional measures. Borrowing from successes in geological and medical imaging environments, researchers have attempted to apply radio frequency (RF) and other sensing modes to penetrate wall materials and optimally estimate the content and structure of rooms and buildings. There are many propagation differences that provide unique challenges that must be addressed to make through-wall penetration sensors operationally viable. This paper outlines the historical context of early research and provides new directions for future research in the exciting interplay between electromagnetic propagation, signal processing, and knowledge-based reasoning algorithms. [Copyright &y& Elsevier]
- Published
- 2008
- Full Text
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37. Effects of Propagation of Narrow Bipolar Pulses, Generated by Compact Cloud Discharges, over Finitely Conducting Ground
- Author
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Cooray, Vernon, Fernando, M., Gunasekara, L., Nanayakkara, S., Cooray, Vernon, Fernando, M., Gunasekara, L., and Nanayakkara, S.
- Abstract
Propagation effects on the narrow bipolar pulses (NBPs) or the radiation fields generated by compact cloud discharges as they propagate over finitely conducting ground are presented. The results were obtained using a sample of NBPs recorded with high time resolution from close thunderstorms in Sri Lanka. The results show that the peak amplitude and the temporal features such as the full width at half maximum (FWHM), zero-crossing time, and the time derivative of NBPs can be significantly distorted by propagation effects. For this reason, the study of peak amplitudes and temporal features of NBPs and the remote sensing of current parameters of compact cloud discharges should be conducted using NBPs recorded under conditions where the propagation effects are minimal.
- Published
- 2018
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38. Effects of Propagation of Narrow Bipolar Pulses, Generated by Compact Cloud Discharges, over Finitely Conducting Ground
- Author
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Mahendra Fernando, Lasitha Gunasekara, Sankha Nanayakkara, and Vernon Cooray
- Subjects
Physics ,propagation effects ,Meteorologi och atmosfärforskning ,Communication Systems ,Time resolution ,lcsh:QC851-999 ,Radiation ,atmospheric_science ,Computational physics ,Full width at half maximum ,finitely conducting ground ,Amplitude ,Meteorology and Atmospheric Sciences ,narrow bipolar pulses ,Time derivative ,Thunderstorm ,lcsh:Meteorology. Climatology ,Sri lanka ,compact cloud discharges ,Kommunikationssystem - Abstract
Propagation effects on the Narrow Bipolar Pulses (NBPs) or the radiation fields generated by compact cloud discharges as they propagate over finitely conducting ground are presented. The results are obtained using a sample of NBPs recorded with high time resolution from close thunderstorms in Sri Lanka. The results show that the peak amplitude and the temporal features such as the Full Width at Half Maximum (FWHM), zero crossing time and the time derivative of NBPs can be significantly distorted by propagation effects. For this reason the study of peak amplitudes and temporal features of NBPs and the remote sensing of current parameters of compact cloud discharges should be conducted using NBPs recorded under conditions where the propagation effects are minimal.
- Published
- 2018
39. Role of Atomic and Molecular Resonances in High-order Harmonic Generation from Laser-ablated Plumes.
- Author
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Fareed, Muhammad Ashiq and Fareed, Muhammad Ashiq
- Abstract
La transcription des symboles et des caractères spéciaux utilisés dans la version originale de ce résumé n’a pas été possible en raison de limitations techniques. La version correcte de ce résumé peut être lue en PDF.High-order harmonic generation (HHG) process is explained with the so-called three-step model, where the valance electron is tunnel ionized, accelerates and photorecombines with the parent ion. In this model, it is assumed that electron’s motion is not perturbed from the atomic and molecular resonances. However, several experiments have shown that in the HHG process, the electron quantum path is perturbed from the atomic and molecular resonances that change the high-order harmonic properties. As the natural resonances are of different types (e.g., autoionizing, Giant resonance), their response for HHG is also observed differently. Several theoretical models have been proposed to explain the HHG mechanism from these resonances, but, in many cases of HHG from laser-ablated plumes (LAP), the information of the exact quantum path that the electron follows in the vicinity of these resonances was uncertain because of the lack of experimental proofs. In this thesis, we use different elements containing different types of resonances and study their role in HHG. Tin, manganese and diatomic carbon are used as nonlinear media, as these elements contain strong resonance at different energies. The resonance of tin exists at energy ~ 26.35 eV, which appears from the autoionizing state (AIS) lying above the ionization threshold. Manganese contains an inner-shell giant resonance at energy ~ 51 eV that appears mainly from 3p-3d transitions. The resonance from diatomic carbon molecules could come from molecular dissociation, or involve an AIS or bound excited state. In the first step, tin is used as a nonlinear medium for HHG to study electron interaction with the autoionizing 4d105s25p state. This AIS perturbs the HHG process and increases the intensity of a single harm
- Published
- 2017
40. Propagation effects of low frequency electromagnetic waves in production well
- Author
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Song, Xijin, Guo, Baolong, Dang, Ruirong, and Wang, Xuelong
- Published
- 2012
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41. Effects of propagation on the population dynamics of terahertz quantum cascade lasers.
- Author
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Hou, Q.S., Wang, F., Wang, C., and Cao, J.C.
- Subjects
- *
POPULATION dynamics , *QUANTUM cascade lasers , *QUANTUM theory , *LASER pulses , *ELECTRIC fields - Abstract
The spatial and temporal dependence of population dynamics caused by ultrafast π laser pulses are studied by Maxwell-Bloch equations in terahertz quantum cascade lasers with and without propagation effects. It is shown that the presence of propagation effects could decrease the flopping of population inversion and affect the oscillation intensity in recovery process. Due to the modification of total macroscopic nonlinear polarization and many-body items, local field varies not only with electron doping concentration but also with period position, which also reflected in the evolution of population dynamics. • The Maxwell-Bloch approach is proposed to research the ultrafast population dynamics in terahertz quantum cascade lasers. • With the varying of doping concentration, population dynamics shows strong temporal-spatial dependence. • The causation of the behavior is analyzed by the evolution of the electric field. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
42. Effect of the rotor-stator gap variation on the tonal noise generated by axial-flow fans
- Author
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Fabio Mazzocut Zecchin, Edward Canepa, and Andrea Cattanei
- Subjects
Engineering ,Fan noise ,Acoustics and Ultrasonics ,Rotor (electric) ,Stator ,business.industry ,Acoustics ,Phase angle ,Rotational speed ,Aerodynamics ,Rotor-stator aerodynamic interaction ,Inlet turbulence ,law.invention ,Phase delay ,Noise ,Propagation effects ,Axial compressor ,law ,Harmonics ,business ,Axial gap - Abstract
The effect of the rotor–stator axial-gap on tonal noise generated by an axial-flow fan employed for automotive cooling systems has been studied. A fan equipped with a 9 blade rotor and a 18 vane stator positioned at several axial-gaps has been tested in a hemi-anechoic chamber. The acoustic measurements have been performed during rotational speed ramps. To analyze the experimental data, the propagation function, obtained by means of the spectral decomposition, has been compared with the velocity-scaled SPL and the phase angle, evaluated at the 1st and 2nd blade passing frequency harmonics. Opposite to what is commonly observed, the SPL due to the rotor–stator aerodynamic interaction does not monotonically decrease with the axial-gap and at the shortest gaps it may not be scaled with a single power of the rotational speed. The listed quantities have been plotted versus frequency, rotational speed, and axial-gap. Their analysis provides a detailed picture of the investigated phenomena and supports the assumption that the observed behavior is due to acoustic effects and not to the aerodynamic noise generating mechanism.
- Published
- 2015
43. Phase control of the temporal envelope of an ultrashort pulse propagating in an strongly driven atomic medium
- Author
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Jean-Christophe Delagnes, M. A. Bouchene, Théorie (LCAR), Laboratoire Collisions Agrégats Réactivité (LCAR), Institut de Recherche sur les Systèmes Atomiques et Moléculaires Complexes (IRSAMC), Institut National des Sciences Appliquées - Toulouse (INSA Toulouse), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-Centre National de la Recherche Scientifique (CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut National des Sciences Appliquées - Toulouse (INSA Toulouse), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut de Recherche sur les Systèmes Atomiques et Moléculaires Complexes (IRSAMC), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées, Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche sur les Systèmes Atomiques et Moléculaires Complexes (IRSAMC), and Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)
- Subjects
Physics ,Linear polarization ,business.industry ,020209 energy ,propagation effects ,light shifts ,02 engineering and technology ,01 natural sciences ,PACS: 42.50.Gy, 42.50.Hz, 42.50.Md ,010305 fluids & plasmas ,Pulse (physics) ,Optics ,Multiphoton intrapulse interference phase scan ,Coherent control ,Distortion ,0103 physical sciences ,0202 electrical engineering, electronic engineering, information engineering ,coherent control ,Atomic physics ,Adiabatic process ,business ,Ultrashort pulse ,Envelope (waves) - Abstract
International audience; We consider a double two-level system in which each single two-level system is driven by a strong linearly polarized pulse. The system is probed by a weak pulse orthogonally polarized. We study the distortion experienced by the probe temporal envelope when the relative phase between the pump and the probe is varied. We show that pulse behavior oscillates between two regimes that corresponds to transparency and amplification respectively. Interpretation of this effect is given within adiabatic representation.
- Published
- 2011
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44. Investigation of Propagation Effects for SIGNAL (SAR FOR ICE, GLACIER AND GLOBAL DYNAMICS)
- Author
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Danklmayer, Andreas
- Subjects
Attenuation ,Propagation Effects ,SIGNAL ,SAR ,Radarkonzepte - Abstract
SIGNAL is an innovative Earth explorer mission proposal with the main objective to accurately quantify, study, and characterise topographic changes in polar regions (ice masses) and fast flowing glaciers in mountainous areas like the Alps and Himalayan regions. In contrast to Earth observation using sensors in the visible- or infrared regime of the electromagnetic spectrum, the proposed system uses microwaves which are often considered to possess the advantages of both day/night and all weather operational capabilities. Whereas the first argument is true since we are dealing with an active sensor; the second does not hold in cases for which the operating frequencies are above ~3 GHz. Indeed, the SAR performance can be significantly affected by atmospheric effects (losses), especially at unfavourable weather conditions. The principal reason for the restriction on the use of higher frequencies can be found in clear air losses (water vapour and oxygen), cloud attenuation and attenuation due to precipitation, primarily rain. The specific attenuation through rain depends on a number of parameters like the frequency, the polarization, the dropsize distribution (DSD), and rain rate. Attenuation through rain increases with frequency and for the intended frequency of 35 GHz (Ka-band) values of 5 dB/km under rain conditions of 20 mm/hr are prevalent. Depending on the location on Earth, the probability for precipitation events differs to a large extent. At higher latitudes and especially at the polar region the probability is extremely low. Thus, it is valid to conclude that only gaseous attenuation and cloud/fog attenuation will contribute to the atmospheric attenuation budget. For non-polar regions such as Europe, the influence of attenuation due to rain has to be taken into account for a certain amount of data which is far less than 10 %. In order to show how frequently measurements will be effected, pertaining statistical information is provided. The annual path attenuation versus the probability is shown for 3 different climatic regions; the polar regions, Europe and tropical regions, for comparison. As expected, the polar regions are effected the least, whereas European and Tropical regions suffer from higher yearly attenuation percentages. From an interferometric point of view, signals traversing from Earth orbiting satellites to ground are subject to delays caused by the fact that the refractive index in the atmosphere differs from one. The tropospheric delay depends on parameters like the temperature, humidity, air pressure and varies with the height of the surface relative to the platform. The main advantage of a single pass interferometric configuration considered for SIGNAL is that the time between the two acquisitions is far less than the atmospheric decorrelation time. This means that the propagation path does not significantly change between two acquisitions like in dual-pass measurement scenarios. The atmospheric budget of SIGNAL is investigated in detail and conclusions for the proposed mission are drawn.
- Published
- 2010
45. Pricipitation Effects for X- and Ka-band SAR
- Author
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Danklmayer, Andreas and Chandra, Madhukar
- Subjects
Rain attenuation ,fungi ,Propagation Effects ,Precipitation Effects ,SAR ,Radarkonzepte - Abstract
Space-borne Synthetic Aperture Radar (SAR) imaging is often considered to possess both day/night and all weather operational capabilities. Whereas the first argument is true since we are dealing with an active sensor; the second does not hold in cases for which the operating frequencies are above 3 GHz. Indeed, the SAR performance can be significantly affected by atmospheric effects (losses), especially at unfavourable weather conditions. The principal reasons for the restriction on the use of these higher frequencies can be found in clear air losses (water vapour and oxygen), cloud attenuation and attenuation due to precipitation, primarily rain.
- Published
- 2010
46. Precipitation Effects for Ka-band SAR
- Author
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Danklmayer, Andreas and Chandra, Madhukar
- Subjects
Ka-band ,Synthetic Aperture Radar (SAR) ,tropospheric effects ,propagation effects ,rain attenuation ,microwave imaging ,Radarkonzepte - Abstract
Space-borne Synthetic Aperture Radar (SAR) imaging is often considered to possess both day/night and all weather operational capabilities. Whereas the first argument is true since we are dealing with an active sensor; the second does not hold in cases for which the operating frequencies are above ~ 3 GHz. Indeed, the SAR performance can be significantly affected by atmospheric effects (losses), especially at unfavourable weather conditions. The principal reasons for the restriction on the use of these higher frequencies can be found in clear air losses (water vapour and oxygen), cloud attenuation and attenuation due to precipitation, primarily rain. The scope of this paper covers the activities performed for an ESA-study (Danklmayer, 2009 [1]) under Task 1 (Survey on Precipitation Effects for SAR) and Task 2, the quantitative assessment of the propagation effects and the associated modelling. For the Ka-band rain rates of 10 mm/h are capable to produce visible artefacts. Depending on the climatic region on Earth, the availability of the investigated Ka-band system will vary. Assuming a 5 dB acceptance of the attenuation due to rain, which corresponds to 2 mm/h at 30° incidence angle for the modelled rain cell, the availability will be better than 98% for the European regions and better than 95% for rain-forest in Brazil. Finally, measures and possibilities are suggested, how to mitigate propagation effects in SAR images, together with an outlook on remaining issues to be addressed in future studies.
- Published
- 2009
47. Comparison of Precipitation Effects in Spaceborne X- and Ka-band SAR Imaging
- Author
-
Danklmayer, Andreas and Chandra, Madhukar
- Subjects
body regions ,Synthetic Aperture Radar (SAR) ,Propagation effects ,Microwave imaging ,fungi ,Signal Attenuation ,Precipitation ,skin and connective tissue diseases ,Institut für Hochfrequenztechnik und Radarsysteme ,Radarkonzepte - Abstract
As the operating frequencies of SAR-systems are increasing, the visible distortions due to precipitation in SAR-images are becoming more frequent. This holds especially for the case of convective rain events. The German space-borne satellite TerraSAR-X has delivered a series of measurement examples, which were used to study precipitation effects in SAR-images. Based on these valuable data takes and simultaneous weather radar measurements, a quantitative estimation of precipitation effects in SAR-images is presented. In a further step, an attempt is made to extrapolate the observed effects to systems operating at higher nominal frequency-bands, i.e. Ka-band, being taken under consideration for future SAR-systems. The effects of backscattering and attenuation will be investigated. Furthermore the likelihood for precipitation effects in SAR images at Ka-band will be addressed.
- Published
- 2009
48. Precipitation Induced Signatures in SAR Images
- Author
-
Danklmayer, Andreas and Chandra, Madhu
- Subjects
body regions ,Synthetic Aperture Radar (SAR) ,Propagation effects ,Microwave imaging ,fungi ,Signal Attenuation ,Precipitation ,skin and connective tissue diseases ,Institut für Hochfrequenztechnik und Radarsysteme ,Radarkonzepte - Abstract
Active microwave SAR imaging of the Earth’s surface is commonly considered to be of all weather capability. However, as the operating frequencies of SAR-systems are increasing, visible image distortions due to heavy precipitation in SAR-images are present. This holds especially for the case of convective rain events imaged at X–band frequencies and beyond. The German spaceborne satellite TerraSAR-X delivered several measurements, which facilitate to study precipitation effects in SAR-images. Based on this SAR-images and simultaneously acquired weather radar measurements, a quantitative estimation of precipitation effects in SAR-images is presented. In a further step, a first attempt is made to extrapolate the effects observed in X-band SAR images to images acquired at higher nominal frequency bands.
- Published
- 2009
49. Propagation effects in atomic systems for ultrashort and long pulses: Control of the optical response
- Author
-
Hashmi, Faheel, Théorie (LCAR), Laboratoire Collisions Agrégats Réactivité (LCAR), Institut de Recherche sur les Systèmes Atomiques et Moléculaires Complexes (IRSAMC), Institut National des Sciences Appliquées - Toulouse (INSA Toulouse), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-Centre National de la Recherche Scientifique (CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut National des Sciences Appliquées - Toulouse (INSA Toulouse), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut de Recherche sur les Systèmes Atomiques et Moléculaires Complexes (IRSAMC), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées, Université Paul Sabatier - Toulouse III, Mohamed Aziz Bouchene(aziz@irsamc.ups-tlse.fr), Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche sur les Systèmes Atomiques et Moléculaires Complexes (IRSAMC), and Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)
- Subjects
non-adiabatic transitions ,[PHYS.PHYS.PHYS-ATOM-PH]Physics [physics]/Physics [physics]/Atomic Physics [physics.atom-ph] ,Effets de propagation ,propagation effects ,mise en forme d'impulsions ,ralentissement de la lumière ,coherent control ,transitions non-adiabatiques ,contrôle cohérent ,wave shaping ,slow light - Abstract
This thesis deals with the study of propagation effects experienced by weak light pulses as they propagate in atomic media driven by strong pulses. We explore both the ultra-short and long pulse regime and investigate the phenomena that arise at these different time scales. In the short pulse regime, a strongly driven two level atomic system presents transient light shifts, and non-adiabatic transitions occur between these adiabatic levels. We have studied a method to probe these light shifts in real time by propagating a weak probe through the medium. The light shifts enrich the spectrum of the probe and the probe gets shaped as a result. In this way a strongly driven two-level system can act as an active pulse shaper, and can introduce oscillations in the temporal profile of an ultra-short pulse at a time scale shorter than the pulse duration. We also show that by driving the system with two time delayed non-resonant strong fields, the non-adiabatic effects can be rendered phase dependent. This gives very sensitive phase control of the excited state population and can be used to formulate new techniques in interferometry. In the long pulse regime we present a new method of slowing light that can be realized in a double two-level system interacting with two orthogonally polarized light pulses that propagate along different axis. Spatio-temporal dependence of the total polarization induces a grating in the ground Zeeman coherence. The stronger of the two fields (the control field) is diffracted from this grating into the direction of the weak probe field compensating for the absorption of this latter field. A transparency window is thus created in the absorption spectrum of the probe leading to the slowing down of light. The transparency window exhibits characteristics similar to the one obtained by EIT (electromagnetic induced transparency) method. However, the important difference between our method and the traditional EIT method, is that ours doesn't rely on realizing dark state in the system. This may open the possibility of slowing down light in more complex atomic media. Moreover, when the linear absorptive response of the medium is cancelled in this manner, the nonlinear response becomes more important. In the situation where fields propagate in the same direction and have same frequency, two regimes have been investigated. For small optical depths, the effective susceptibility behaves as chi_lin exp[2 i phi] (with phi the phase difference between two fields). This renders phase control of the medium response, and the medium can be changed from an absorber to an amplifier, with normal or anomalous dispersion, by adjusting the relative phase phi. In the regime of large optical thickness, phase saturation takes place and the effective susceptibility turns into chi_lin*, changing an absorber into an amplifier without effecting the dispersive response (chi_lin is linear susceptibility).; Cette thèse concerne l'étude des effets de propagation subis par des impulsions lumineuses de faible intensité lorsqu'elles se propagent dans des systèmes atomiques soumis à des champs intenses. Nous explorons aussi bien le régime d'impulsions longues que courtes et nous analysons les phénomènes qui se produisent à ces échelles de temps différents. En régime d'impulsions ultracourtes, un système atomique à deux niveaux soumis à un champ intense présente des déplacements lumineux transitoires, et des transitions non adiabatiques se produisent entre ces états. Nous avons étudié une méthode qui permette de sonder en temps réel ces déplacements lumineux en propageant un champ sonde de faible intensité. Les déplacements lumineux enrichissent le spectre de la sonde qui se trouve ainsi modifiée. Un système à deux niveaux peut se comporter alors comme un dispositif de mise en forme et peut induire sur le profil temporel d'une impulsion ultra courte des oscillations à une échelle de temps plus courte que la durée de l'impulsion. Nous montrons aussi qu'en excitant le système avec deux impulsions intenses non résonantes et décalées dans le temps, les effets non adiabatiques peuvent être dépendant de la phase. Ceci conduit à un contrôle très sensible par la phase de la population excitée. Cet effet peut être utilisée pour créer de nouvelles techniques en interférométrie. En régime d'impulsions longues, nous présentons une nouvelle méthode de ralentissement de la lumière qui peut être réalisée dans un système à deux niveaux double interagissant avec deux impulsions de lumière polarisées orthogonalement et se propageant selon des axes différents. La dépendance spatio-temporelle de la polarisation totale induit un réseau dans la cohérence Zeeman du fondamental. Le champ le plus intense (champ de contrôle) est diffracté par ce réseau dans la direction du champ sonde de faible intensité compensant l'absorption de ce dernier. Une fenêtre de transparence est alors créée dans le spectre d'absorption de ce champ conduisant au ralentissement de la lumière. La fenêtre de transparence exhibe alors des caractéristiques similaires à ceux obtenus par la méthode EIT (electromagnetic induced transparency). Toutefois la différence importante avec la méthode EIT est que dans notre cas aucun état noir n'est créé dans le système. Ceci ouvre la voie à la possibilité de ralentir la lumière dans des systèmes plus complexes. D'autre part, quand l'absorption (linéaire) du système est éliminée, la réponse non linéaire devient plus importante. Dans la situation où les champs se propagent dans la même direction et ont même fréquence, deux régimes d'interactions ont été étudiés. Pour de faibles épaisseurs optiques, la susceptibilité effective se comporte comme chi_lin exp[2 i phi] (avec phi la différence de phase entre champs). Ceci rend alors possible le contrôle de la réponse du milieu par la phase. Le milieu peut se transformer d'un absorbant à un amplificateur avec une dispersion normale ou anormale en ajustant la phase relative phi . En régime de large épaisseur optique, la saturation de la phase se produit et la susceptibilité effective se trouve changée en chi_lin*, modifiant un absorbant en un amplificateur sans affecter la réponse dispersive.
- Published
- 2009
50. Propagation Effects in Satellite mounted Radar Remote Sensing
- Author
-
Danklmayer, Andreas
- Subjects
body regions ,Propagation effects ,Radar remote sensing ,fungi ,skin and connective tissue diseases ,attenuation ,Radarkonzepte ,SAR - Abstract
—Active microwave SAR imaging of the Earth’s surface is commonly considered to be of all weather capability. However, as the operating frequencies of SAR-systems are increasing, visible image distortions due to heavy precipitation in SAR-images may become present. This holds especially for the case of convective rain events imaged at X–band frequencies and beyond. These rain-cell signatures are thoroughly investigated, and the physical background of the related propagation effects is provided. A review of rain-cell signatures from former missions like SIR-C/X-SAR and the Shuttle Radar Topography Mission are provided. Furthermore, the German spaceborne satellite TerraSAR-X delivered several measurements, which facilitate to study precipitation effects in SAR-images. Based on this SAR-images and simultaneously acquired weather radar measurements, a quantitative estimation of precipitation effects in SAR-images is presented. In a further step, an attempt is made to extrapolate the effects observed in X-band SAR images to images acquired at higher nominal frequency bands such as Ka-band.
- Published
- 2009
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