The Experts below are selected from a list of 132 Experts worldwide ranked by ideXlab platform
K K Nandi - One of the best experts on this subject based on the ideXlab platform.
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string effect on the Relative Time Delay in the kerr sen black hole
arXiv: General Relativity and Quantum Cosmology, 2020Co-Authors: R N Izmailov, K K Nandi, Kh R Karimov, Alexander A PotapovAbstract:A well known solution of heterotic string theory is the spinning Kerr-Sen black hole (KSBH) characterized by a string parameter $\xi$. Kerr black hole is recovered at $\xi=0$. The purpose of this paper is to investigate the effect of $\xi$ on a new diagnostic of Relative Time Delay (RTD) to see how the latter deviates from that in general relativity. Assuming KSBH as the spinning lens partner in PSR-BH binary systems, which provide the best laboratory for testing the Time Delay predictions, we study here the RTD up to third PPN order in $\left(1/r\right)$ in the thin-lens approximation. We work out a useful generalization of the RTD formulas applicable to the experimentally viable \textit{finite} distance lens scales, while\ terms higher than the zeroth order are shown to contain the effect of $\xi$. We shall also relate RTD to the observable image magnification factor determined by $\beta/\theta_{E}$, where $\beta$ is the angular separation between the source and the observer and $\theta_{E}$ is the "Einstein angle" determined by an "effective" non-aligned static lens equivalent to the original aligned spinning lens. Numerical estimates for two typical binary lens systems show $\mu$sec level Delay at the zeroth order consistent with predictions in the literature. However, the string effect at higher orders is too tiny to be measurable even in the far future leading to the conclusion that the stringy and general relativity BHs are yet observationally indistinguishable.
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string effect on the Relative Time Delay in the kerr sen black hole
Annals of Physics, 2020Co-Authors: R N Izmailov, K K Nandi, Kh R Karimov, Alexander A PotapovAbstract:Abstract A well known solution of heterotic string theory is the spinning Kerr–Sen black hole (KSBH) characterized by a string parameter ξ . Kerr black hole is recovered at ξ = 0 . The purpose of this paper is to investigate the effect of ξ on a new diagnostic of Relative Time Delay (RTD) to see how the latter deviates from that in general relativity. Assuming KSBH as the spinning lens partner in PSR–BH binary systems, which provide the best laboratory for testing the Time Delay predictions, we study here the RTD up to third PPN order in 1 ∕ r in the thin-lens approximation. We work out a useful generalization of the RTD formulas applicable to the experimentally viable finite distance lens scales, while terms higher than the zeroth order are shown to contain the effect of ξ . We shall also relate RTD to the observable image magnification factor determined by β ∕ θ E , where β is the angular separation between the source and the observer and θ E is the ”Einstein angle” determined by an ”effective” non-aligned static lens equivalent to the original aligned spinning lens. Numerical estimates for two typical binary lens systems show μ sec level Delay at the zeroth order consistent with predictions in the literature. However, the string effect at higher orders is too tiny to be measurable even in the far future leading to the conclusion that the stringy and general relativity BHs are yet observationally indistinguishable.
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Relative Time Delay in a spinning black hole as a diagnostic for no hair theorem
European Physical Journal C, 2019Co-Authors: R N Izmailov, E R Zhdanov, Arunava Bhadra, K K NandiAbstract:The spinning regular black hole (spin a) metric proposed by Johannsen shares the Kerr horizon but contains independent dimensionless parameters marking deviation from the Kerr metric. Non-zero value of any of the parameters would indicate violation of the no-hair theorem. We shall find the influence of these parameters on the Relative Time Delay (not Shapiro Time Delay) treated here as a diagnostic for no-hair theorem using aligned, finite, thin-lens approximation in realistic spinning astrophysical configurations. Precise measurement of this Delay would then help us determine, from observational perspective, whether or not any of the parameters is really non-zero. We shall also point out that the aligned spinning lens is completely equivalent to a “static” lens with a fictitious lens geometry, which would enable us to re-express the Relative Time Delay components in terms of the spin a. Numerical values are tabulated for three astrophysical lens systems. The advantage of the present treatment is that it can accommodate a variety of spinning lens systems that are likely to be detected in the near future.
R N Izmailov - One of the best experts on this subject based on the ideXlab platform.
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string effect on the Relative Time Delay in the kerr sen black hole
arXiv: General Relativity and Quantum Cosmology, 2020Co-Authors: R N Izmailov, K K Nandi, Kh R Karimov, Alexander A PotapovAbstract:A well known solution of heterotic string theory is the spinning Kerr-Sen black hole (KSBH) characterized by a string parameter $\xi$. Kerr black hole is recovered at $\xi=0$. The purpose of this paper is to investigate the effect of $\xi$ on a new diagnostic of Relative Time Delay (RTD) to see how the latter deviates from that in general relativity. Assuming KSBH as the spinning lens partner in PSR-BH binary systems, which provide the best laboratory for testing the Time Delay predictions, we study here the RTD up to third PPN order in $\left(1/r\right)$ in the thin-lens approximation. We work out a useful generalization of the RTD formulas applicable to the experimentally viable \textit{finite} distance lens scales, while\ terms higher than the zeroth order are shown to contain the effect of $\xi$. We shall also relate RTD to the observable image magnification factor determined by $\beta/\theta_{E}$, where $\beta$ is the angular separation between the source and the observer and $\theta_{E}$ is the "Einstein angle" determined by an "effective" non-aligned static lens equivalent to the original aligned spinning lens. Numerical estimates for two typical binary lens systems show $\mu$sec level Delay at the zeroth order consistent with predictions in the literature. However, the string effect at higher orders is too tiny to be measurable even in the far future leading to the conclusion that the stringy and general relativity BHs are yet observationally indistinguishable.
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string effect on the Relative Time Delay in the kerr sen black hole
Annals of Physics, 2020Co-Authors: R N Izmailov, K K Nandi, Kh R Karimov, Alexander A PotapovAbstract:Abstract A well known solution of heterotic string theory is the spinning Kerr–Sen black hole (KSBH) characterized by a string parameter ξ . Kerr black hole is recovered at ξ = 0 . The purpose of this paper is to investigate the effect of ξ on a new diagnostic of Relative Time Delay (RTD) to see how the latter deviates from that in general relativity. Assuming KSBH as the spinning lens partner in PSR–BH binary systems, which provide the best laboratory for testing the Time Delay predictions, we study here the RTD up to third PPN order in 1 ∕ r in the thin-lens approximation. We work out a useful generalization of the RTD formulas applicable to the experimentally viable finite distance lens scales, while terms higher than the zeroth order are shown to contain the effect of ξ . We shall also relate RTD to the observable image magnification factor determined by β ∕ θ E , where β is the angular separation between the source and the observer and θ E is the ”Einstein angle” determined by an ”effective” non-aligned static lens equivalent to the original aligned spinning lens. Numerical estimates for two typical binary lens systems show μ sec level Delay at the zeroth order consistent with predictions in the literature. However, the string effect at higher orders is too tiny to be measurable even in the far future leading to the conclusion that the stringy and general relativity BHs are yet observationally indistinguishable.
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Relative Time Delay in a spinning black hole as a diagnostic for no hair theorem
European Physical Journal C, 2019Co-Authors: R N Izmailov, E R Zhdanov, Arunava Bhadra, K K NandiAbstract:The spinning regular black hole (spin a) metric proposed by Johannsen shares the Kerr horizon but contains independent dimensionless parameters marking deviation from the Kerr metric. Non-zero value of any of the parameters would indicate violation of the no-hair theorem. We shall find the influence of these parameters on the Relative Time Delay (not Shapiro Time Delay) treated here as a diagnostic for no-hair theorem using aligned, finite, thin-lens approximation in realistic spinning astrophysical configurations. Precise measurement of this Delay would then help us determine, from observational perspective, whether or not any of the parameters is really non-zero. We shall also point out that the aligned spinning lens is completely equivalent to a “static” lens with a fictitious lens geometry, which would enable us to re-express the Relative Time Delay components in terms of the spin a. Numerical values are tabulated for three astrophysical lens systems. The advantage of the present treatment is that it can accommodate a variety of spinning lens systems that are likely to be detected in the near future.
S B Cenko - One of the best experts on this subject based on the ideXlab platform.
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deja vu all over again the reappearance of supernova refsdal
The Astrophysical Journal, 2016Co-Authors: Patrick L Kelly, Tommaso Treu, Steven A Rodney, L G Strolger, R J Foley, Saurabh W Jha, J Selsing, G Brammer, Marusa Bradac, S B CenkoAbstract:In Hubble Space Telescope (HST) imaging taken on 2014 November 10, four images of supernova (SN) "Refsdal" (redshift z = 1.49) appeared in an Einstein-cross-like configuration (images S1–S4) around an early-type galaxy in the cluster MACS J1149.5+2223 (z = 0.54). Almost all lens models of the cluster have predicted that the SN should reappear within a year in a second host-galaxy image created by the cluster's potential. In HST observations taken on 2015 December 11, we find a new source at the predicted position of the new image of SN Refsdal approximately $8^{\prime\prime} $ from the previous images S1–S4. This marks the first Time the appearance of a SN at a particular Time and location in the sky was successfully predicted in advance! We use these data and the light curve from the first four observed images of SN Refsdal to place constraints on the Relative Time Delay and magnification of the new image (SX) compared to images S1–S4. This enables us, for the first Time, to test "blind" lens model predictions of both magnifications and Time Delays for a lensed SN. We find that the timing and brightness of the new image are consistent with the blind predictions of a fraction of the models. The reappearance illustrates the discriminatory power of this blind test and its utility to uncover sources of systematic uncertainty. From planned HST photometry, we expect to reach a precision of 1%–2% on the Time Delay between S1–S4 and SX.
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deja vu all over again the reappearance of supernova refsdal
arXiv: Cosmology and Nongalactic Astrophysics, 2015Co-Authors: Patrick L Kelly, Tommaso Treu, Steven A Rodney, L G Strolger, R J Foley, Saurabh W Jha, J Selsing, Marusa Bradac, Gabriel B Brammer, S B CenkoAbstract:In Hubble Space Telescope (HST) imaging taken on 10 November 2014, four images of supernova (SN) "Refsdal" (redshift z=1.49) appeared in an Einstein-cross--like configuration (images S1-S4) around an early-type galaxy in the cluster MACS J1149.5+2223 (z=0.54). Almost all lens models of the cluster have predicted that the SN should reappear within a year in a second host-galaxy image created by the cluster's potential. In HST observations taken on 11 December 2015, we find a new source at the predicted position of the new image of SN Refsdal approximately 8" from the previous images S1-S4. This marks the first Time the appearance of a SN at a particular Time and location in the sky was successfully predicted in advance! We use these data and the light curve from the first four observed images of SN Refsdal to place constraints on the Relative Time Delay and magnification of the new image (SX), compared to images S1-S4. This enables us, for the first Time, to test "blind" lens model predictions of both magnifications and Time Delays for a lensed SN. We find that the timing and brightness of the new image are consistent with the blind predictions of a fraction of the models. The reappearance illustrates the discriminatory power of this blind test and its utility to uncover sources of systematic uncertainty. From planned HST photometry, we expect to reach a precision of 1-2% on the Time Delay between S1-S4 and SX.
David Di Ruscio - One of the best experts on this subject based on the ideXlab platform.
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Performance Optimal PI controller Tuning Based on Integrating Plus Time Delay Models
MDPI AG, 2018Co-Authors: Christer Dalen, David Di RuscioAbstract:A method for tuning PI controller parameters, a prescribed maximum Time Delay error or a Relative Time Delay error is presented. The method is based on integrator plus Time Delay models. The integral Time constant is linear in the Relative Time Delay error, and the proportional constant is seen inversely proportional to the Relative Time Delay error. The keystone in the method is the method product parameter, i.e., the product of the PI controller proportional constant, the integral Time constant, and the integrator plus Time Delay model, velocity gain. The method product parameter is found to be constant for various PI controller tuning methods. Optimal suggestions are given for choosing the method product parameter, i.e., optimal such that the integrated absolute error or, more interestingly, the Pareto performance objective (i.e., integrated absolute error for combined step changes in output and input disturbances) is minimised. Variants of the presented tuning method are demonstrated for tuning PI controllers for motivated (possible) higher order process model examples, i.e., the presented method is combined with the model reduction step (process–reaction curve) in Ziegler–Nichols
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A Novel Process-Reaction Curve Method for Tuning PID Controllers
Norwegian Society of Automatic Control, 2018Co-Authors: Christer Dalen, David Di RuscioAbstract:A novel process-reaction curve method for tuning PID controllers for (possible) higher order processes/models is presented. The proposed method is similar to the Ziegler-Nichols process reaction curve method, viz. only the maximum slope and lag need to be identified from an open loop step response. The Relative Time Delay error (Relative Delay margin), delta is the tuning parameter. The proposed method is verified through extensive numerical simulations and is found close to optimal in many of the motivated process examples. In order to handle the wide set of process models, two model reduction modes are presented
Ralph E Hudson - One of the best experts on this subject based on the ideXlab platform.
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maximum likelihood source localization and unknown sensor location estimation for wideband signals in the near field
IEEE Transactions on Signal Processing, 2002Co-Authors: Joe C Chen, Ralph E HudsonAbstract:In this paper, we derive the maximum-likelihood (ML) location estimator for wideband sources in the near field of the sensor array. The ML estimator is optimized in a single step, as opposed to other estimators that are optimized separately in Relative Time-Delay and source location estimations. For the multisource case, we propose and demonstrate an efficient alternating projection procedure based on sequential iterative search on single-source parameters. The proposed algorithm is shown to yield superior performance over other suboptimal techniques, including the wideband MUSIC and the two-step least-squares methods, and is efficient with respect to the derived Cramer-Rao bound (CRB). From the CRB analysis, we find that better source location estimates can be obtained for high-frequency signals than low-frequency signals. In addition, large range estimation error results when the source signal is unknown, but such unknown parameter does not have much impact on angle estimation. In some applications, the locations of some sensors may be unknown and must be estimated. The proposed method is extended to estimate the range from a source to an unknown sensor location. After a number of source-location frames, the location of the uncalibrated sensor can be determined based on a least-squares unknown sensor location estimator.
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joint maximum likelihood source localization and unknown sensor location estimation for near field wideband signals
Conference on Advanced Signal Processing : Algorithms Architectures and Implemenations, 2001Co-Authors: Joe C Chen, Ralph E Hudson, Kung YaoAbstract:In this paper, we derive the maximum-likelihood (ML) location estimator for wideband sources in the near-field of a passive array. The parameters of interest are expanded to include the source range in addition to the angles in the far-field case. The ML estimator is optimized in a single step as opposed to many that are optimized separately in Relative Time-Delay and source location estimations. The ML method is capable of estimating multiple source locations, while such case is rather difficult for the Time-Delay methods. To avoid a multi-dimensional search in the ML metric, we propose an efficient alternating projection procedure that is based on sequential iterative search on single source parameters. In the single source case, the ML estimator is shown to be equivalent to maximizing the sum of the weighted cross-correlations between Time shifted sensor data. Furthermore, the ML formulation can expand the parameters to include the distance of a source to a sensor with unknown location. This provides inputs to our online unknown sensor location estimator, which is based on a least-squares fit to observations from multiple sources. The proposed algorithm has been shown to yield superior performance over other suboptimal techniques, and is efficient with respect to the derived Cramer-Rao bound. From the Cramer-Rao bound analyses, we find that better source location estimates can be obtained for high frequency signals than low frequency signals. In addition, large range estimation error results when the source signal is unknown, but such unknown parameter does not have much impact on angle estimation.