The Experts below are selected from a list of 297 Experts worldwide ranked by ideXlab platform
Dejan B. Milošević - One of the best experts on this subject based on the ideXlab platform.
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Low-Frequency Approximation for above-threshold ionization by a laser pulse: Low-energy forward rescattering
Physical Review A, 2014Co-Authors: Dejan B. MiloševićAbstract:In the context of the development of new sources of strong laser pulses in the mid-infrared region new nonperturbative methods for analysis of strong-laser-field induced or assisted atomic and molecular processes are welcome. We formulate such a theory of above-threshold ionization by a strong low-Frequency laser pulse. We call this theory the low-Frequency Approximation (LFA). A detailed derivation of the LFA, both for short and long laser pulses, is given. As an example the LFA is applied to the analysis of recently discovered low-energy structures in the above-threshold ionization spectra of atoms ionized by long-wavelength laser pulses. It was found that these low-energy structures are caused by the forward soft recollision of the ionized electrons with the parent ion which is enhanced by the Coulomb effect.
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High-order above-threshold ionization with few-cycle laser pulses: Molecular improved strong-field Approximation vs. molecular low-Frequency Approximation
Laser Physics, 2012Co-Authors: E. Hasović, Dejan B. Milošević, A. Gazibegović-busuladžić, M. Busuladžić, Wilhelm BeckerAbstract:We investigate high-order above-threshold ionization (HATI) of homonuclear diatomic molecules by a few-cycle laser pulse. In order to describe molecular HATI in ultrashort laser pulses we have modified our molecular improved strong-field Approximation (MISFA), which was developed for long laser pulses and in which the rescattering of the ionized electron off the parent ion was described using the first-order Born Approximation (1BA). Now, we introduce the so-called molecular low-Frequency Approximation (MLFA) in which the elastic rescattering amplitude is calculated exactly. The angle-resolved electron energy spectra for HATI of N2 and O2 obtained using the MLFA are compared with those obtained within the MISFA. The difference between these spectra becomes significant for larger (re)scattering angles. This is due to the fact that the exact scattering amplitude, used in the MLFA, has minima for some values of the rescattering angles that are absent in the 1BA. Also, the rescattering plateau is lower for the MLFA spectra. We investigate the influence of the carrier-envelope phase on the high-energy part of the molecular HATI spectra. As in the atomic case, the left-right (backward-forward) asymmetry is also observed in the molecular case.
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High-order above-threshold ionisation of atoms and negative ions: channel-closing effects and the low-Frequency Approximation
Journal of Modern Optics, 2011Co-Authors: B. Fetić, Dejan B. Milošević, Wilhelm BeckerAbstract:The so-called low-Frequency Approximation (LFA) is an improved version of the strong-field Approximation. The LFA describes the rescattering step of high-order above-threshold ionisation by utilising the exact field-free scattering amplitude, which has to be calculated separately. We apply the LFA to high-order above-threshold detachment of the fluorine negative ion. By comparing the so-obtained angle- and energy-resolved spectra with the exact results obtained as solutions of the time-dependent Schrodinger equation we show that the LFA is a more adequate Approximation than the so-called improved strong-field Approximation used previously. The LFA is also superior to the recently introduced quantitative rescattering (QRS) model. We show this by applying the LFA to the analysis of the intensity-dependent enhancements in above-threshold ionisation spectra of argon atoms. These enhancements can be explained as channel-closing-induced effects. In particular, we have observed and explained the behaviour of the...
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Low-Frequency Approximation for high-order above-threshold ionization
Laser Physics, 2010Co-Authors: Dejan B. Milošević, A. Čerkić, B. Fetić, E. Hasović, Wilhelm BeckerAbstract:The low-Frequency Approximation (LFA) for high-order above-threshold ionization is presented. A factorization formula for the differential ionization rate is derived and its range of validity is analyzed. The theory developed is illustrated using the example of Ar atoms. Details of the modeling of the ground state and the rescattering potential for Ar are given. In particular, it is shown, by solving the stationary Schrodinger equation, that our rescattering potential reproduces the Hartree—Fock-type ground-state wave function that we used for the LFA. Electron momentum distributions for ionization of the Ar atom by a linearly polarized laser field having intensity 2.3 × 1014 W/cm2 and wavelength 800 nm are shown. The results obtained using the improved strong-field Approximation on the one hand and the LFA on the other are compared.
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Off-shell low-Frequency Approximation for potential scattering in a strong laser field: eikonal versus [1,1] Padé Approximation
Journal of Physics B: Atomic Molecular and Optical Physics, 1997Co-Authors: Dejan B. MiloševićAbstract:Analytical and numerical results for the T-matrix and the total cross section for scattering by a Yukawa potential in a strong low-Frequency laser field are presented. They are based on our recently derived off-shell low-Frequency Approximation. The conditions under which the results by Daniele and co-workers can be applied are analysed. Expressions for the T-matrix and for the total cross section for scattering in a laser field in the eikonal Approximation are derived. The total cross section is presented in the form of an eikonal multiple scattering series as a product of two factors. One of these factors only depends on the type of the scattering potential, while the other depends on the parameters of the scattered particle and the laser field. The results obtained are in good agreement with our earlier findings derived by using the [1,1] Pade Approximation.
Jianjia Chen - One of the best experts on this subject based on the ideXlab platform.
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Energy Efficiency Analysis for the Single Frequency Approximation (SFA) Scheme
ACM Transactions on Embedded Computing Systems, 2014Co-Authors: Santiago Pagani, Jianjia ChenAbstract:Energy-efficient designs are important issues in computing systems. This article studies the energy efficiency of a simple and linear-time strategy, called the Single Frequency Approximation (SFA) scheme, for periodic real-time tasks on multicore systems with a shared supply voltage in a voltage island. The strategy executes all the cores at a single Frequency to just meet the timing constraints. SFA has been adopted in the literature after task partitioning, but the worst-case performance of SFA in terms of energy consumption incurred is an open problem. We provide comprehensive analysis for SFA to derive the cycle utilization distribution for its worst-case behaviour for energy minimization. Our analysis shows that the energy consumption incurred by using SFA for task execution is at most 1.53 (1.74, 2.10, 2.69, respectively), compared to the energy consumption of the optimal voltage/Frequency scaling, when the dynamic power consumption is a cubic function of the Frequency and the voltage island has up to 4 (8, 16, 32, respectively) cores. The analysis shows that SFA is indeed an effective scheme under practical settings, even though it is not optimal. Furthermore, since all the cores run at a single Frequency and no Frequency alignment for Dynamic Voltage and Frequency Scaling (DVFS) between cores is needed, any unicore dynamic power management technique for reducing the energy consumption for idling can be easily incorporated individually on each core in the voltage island. This article also provides an analysis of energy consumption for SFA combined with procrastination for Dynamic Power Management (DPM), resulting in an increment of 1 from the previous results for task execution. Furthermore, we also extend our analysis for deriving the Approximation factor of SFA for a multicore system with multiple voltage islands.
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energy efficient task partitioning based on the single Frequency Approximation scheme
Real-Time Systems Symposium, 2013Co-Authors: Santiago Pagani, Jianjia ChenAbstract:Energy-efficiency is a major concern in modern computing systems. For such systems, the presence of multiple voltage islands, where the voltage of each island can change independently and all cores in an island share the same supply voltage at any given time, is an expected compromise between global and per-core Dynamic Voltage and Frequency Scaling (DVFS). This paper focuses on energy minimization for a set of periodic tasks assigned on a voltage island. We present a simple and practical solution, that assigns the tasks onto cores in the island and then applies a DVFS schedule, particularly the Single Frequency Approximation (SFA) scheme. Furthermore, we provide thorough theoretical analysis of our solution, in terms of energy efficiency, against the optimal task partitioning and optimal DVFS schedule, especially for the state-of-the-art designs, that have a few number of cores per voltage island. The analysis shows that, our task partitioning scheme combined with SFA is a good and practical solution for energy efficiency. Particularly, when the number of cores in each voltage island is limited, the Approximation factor is at most 2.01 (2.29, 2.55, 2.80, respectively) when the dynamic power consumption is a cubic function of the Frequency and the islands have up to 4 (8, 16, 32, respectively) cores. Moreover, with non-negligible overhead for sleeping, further combination with any uni-core procrastination algorithm that consumes no more energy than keeping a core idle when it has no workload in its ready queue, increases the Approximation factor by at most 1.
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energy efficiency analysis for the single Frequency Approximation sfa scheme
Embedded and Real-Time Computing Systems and Applications, 2013Co-Authors: Santiago Pagani, Jianjia ChenAbstract:Energy-efficient designs are important issues in computing systems. This paper studies the energy efficiency of a simple and linear-time strategy, called Single Frequency Approximation (SFA) scheme, for periodic real-time tasks on multi-core systems with a shared supply voltage in a voltage island. The strategy executes all the cores at a single Frequency to just meet the timing constraints. SFA has been adopted in the literature after task partitioning, but the worst-case performance of SFA, in terms of energy consumption, is an open problem. We provide comprehensive analysis for SFA to derive the cycle utilization distribution for its worst-case behaviour for energy minimization. Our analysis shows that the energy consumption by using SFA for task execution is at most 1.53 (1.74, 2.10, 2.69, respectively), compared to the energy consumption of the optimal voltage/Frequency scaling, when the dynamic power consumption is a cubic function of the Frequency and the voltage island has up to 4 (8, 16, 32, respectively) cores. The analysis shows that SFA is indeed an effective scheme under practical settings, even though it is not optimal. Furthermore, since all the cores run at a single Frequency and no Frequency alignment for Dynamic Voltage and Frequency Scaling (DVFS) between cores is needed, any uni-core dynamic power management technique for reducing the energy consumption for idling can be easily incorporated individually on each core in the voltage island. This paper also provides the analysis of energy consumption for SFA, combined with the procrastination for Dynamic Power Management (DPM). Furthermore, we also extend our analysis for deriving the Approximation factor of SFA for a multi-core system with multiple voltage islands.
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RTCSA - Energy efficiency analysis for the Single Frequency Approximation (SFA) scheme
2013 IEEE 19th International Conference on Embedded and Real-Time Computing Systems and Applications, 2013Co-Authors: Santiago Pagani, Jianjia ChenAbstract:Energy-efficient designs are important issues in computing systems. This paper studies the energy efficiency of a simple and linear-time strategy, called Single Frequency Approximation (SFA) scheme, for periodic real-time tasks on multi-core systems with a shared supply voltage in a voltage island. The strategy executes all the cores at a single Frequency to just meet the timing constraints. SFA has been adopted in the literature after task partitioning, but the worst-case performance of SFA, in terms of energy consumption, is an open problem. We provide comprehensive analysis for SFA to derive the cycle utilization distribution for its worst-case behaviour for energy minimization. Our analysis shows that the energy consumption by using SFA for task execution is at most 1.53 (1.74, 2.10, 2.69, respectively), compared to the energy consumption of the optimal voltage/Frequency scaling, when the dynamic power consumption is a cubic function of the Frequency and the voltage island has up to 4 (8, 16, 32, respectively) cores. The analysis shows that SFA is indeed an effective scheme under practical settings, even though it is not optimal. Furthermore, since all the cores run at a single Frequency and no Frequency alignment for Dynamic Voltage and Frequency Scaling (DVFS) between cores is needed, any uni-core dynamic power management technique for reducing the energy consumption for idling can be easily incorporated individually on each core in the voltage island. This paper also provides the analysis of energy consumption for SFA, combined with the procrastination for Dynamic Power Management (DPM). Furthermore, we also extend our analysis for deriving the Approximation factor of SFA for a multi-core system with multiple voltage islands.
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RTSS - Energy Efficient Task Partitioning Based on the Single Frequency Approximation Scheme
2013 IEEE 34th Real-Time Systems Symposium, 2013Co-Authors: Santiago Pagani, Jianjia ChenAbstract:Energy-efficiency is a major concern in modern computing systems. For such systems, the presence of multiple voltage islands, where the voltage of each island can change independently and all cores in an island share the same supply voltage at any given time, is an expected compromise between global and per-core Dynamic Voltage and Frequency Scaling (DVFS). This paper focuses on energy minimization for a set of periodic tasks assigned on a voltage island. We present a simple and practical solution, that assigns the tasks onto cores in the island and then applies a DVFS schedule, particularly the Single Frequency Approximation (SFA) scheme. Furthermore, we provide thorough theoretical analysis of our solution, in terms of energy efficiency, against the optimal task partitioning and optimal DVFS schedule, especially for the state-of-the-art designs, that have a few number of cores per voltage island. The analysis shows that, our task partitioning scheme combined with SFA is a good and practical solution for energy efficiency. Particularly, when the number of cores in each voltage island is limited, the Approximation factor is at most 2.01 (2.29, 2.55, 2.80, respectively) when the dynamic power consumption is a cubic function of the Frequency and the islands have up to 4 (8, 16, 32, respectively) cores. Moreover, with non-negligible overhead for sleeping, further combination with any uni-core procrastination algorithm that consumes no more energy than keeping a core idle when it has no workload in its ready queue, increases the Approximation factor by at most 1.
Santiago Pagani - One of the best experts on this subject based on the ideXlab platform.
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Energy Efficiency Analysis for the Single Frequency Approximation (SFA) Scheme
ACM Transactions on Embedded Computing Systems, 2014Co-Authors: Santiago Pagani, Jianjia ChenAbstract:Energy-efficient designs are important issues in computing systems. This article studies the energy efficiency of a simple and linear-time strategy, called the Single Frequency Approximation (SFA) scheme, for periodic real-time tasks on multicore systems with a shared supply voltage in a voltage island. The strategy executes all the cores at a single Frequency to just meet the timing constraints. SFA has been adopted in the literature after task partitioning, but the worst-case performance of SFA in terms of energy consumption incurred is an open problem. We provide comprehensive analysis for SFA to derive the cycle utilization distribution for its worst-case behaviour for energy minimization. Our analysis shows that the energy consumption incurred by using SFA for task execution is at most 1.53 (1.74, 2.10, 2.69, respectively), compared to the energy consumption of the optimal voltage/Frequency scaling, when the dynamic power consumption is a cubic function of the Frequency and the voltage island has up to 4 (8, 16, 32, respectively) cores. The analysis shows that SFA is indeed an effective scheme under practical settings, even though it is not optimal. Furthermore, since all the cores run at a single Frequency and no Frequency alignment for Dynamic Voltage and Frequency Scaling (DVFS) between cores is needed, any unicore dynamic power management technique for reducing the energy consumption for idling can be easily incorporated individually on each core in the voltage island. This article also provides an analysis of energy consumption for SFA combined with procrastination for Dynamic Power Management (DPM), resulting in an increment of 1 from the previous results for task execution. Furthermore, we also extend our analysis for deriving the Approximation factor of SFA for a multicore system with multiple voltage islands.
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energy efficient task partitioning based on the single Frequency Approximation scheme
Real-Time Systems Symposium, 2013Co-Authors: Santiago Pagani, Jianjia ChenAbstract:Energy-efficiency is a major concern in modern computing systems. For such systems, the presence of multiple voltage islands, where the voltage of each island can change independently and all cores in an island share the same supply voltage at any given time, is an expected compromise between global and per-core Dynamic Voltage and Frequency Scaling (DVFS). This paper focuses on energy minimization for a set of periodic tasks assigned on a voltage island. We present a simple and practical solution, that assigns the tasks onto cores in the island and then applies a DVFS schedule, particularly the Single Frequency Approximation (SFA) scheme. Furthermore, we provide thorough theoretical analysis of our solution, in terms of energy efficiency, against the optimal task partitioning and optimal DVFS schedule, especially for the state-of-the-art designs, that have a few number of cores per voltage island. The analysis shows that, our task partitioning scheme combined with SFA is a good and practical solution for energy efficiency. Particularly, when the number of cores in each voltage island is limited, the Approximation factor is at most 2.01 (2.29, 2.55, 2.80, respectively) when the dynamic power consumption is a cubic function of the Frequency and the islands have up to 4 (8, 16, 32, respectively) cores. Moreover, with non-negligible overhead for sleeping, further combination with any uni-core procrastination algorithm that consumes no more energy than keeping a core idle when it has no workload in its ready queue, increases the Approximation factor by at most 1.
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energy efficiency analysis for the single Frequency Approximation sfa scheme
Embedded and Real-Time Computing Systems and Applications, 2013Co-Authors: Santiago Pagani, Jianjia ChenAbstract:Energy-efficient designs are important issues in computing systems. This paper studies the energy efficiency of a simple and linear-time strategy, called Single Frequency Approximation (SFA) scheme, for periodic real-time tasks on multi-core systems with a shared supply voltage in a voltage island. The strategy executes all the cores at a single Frequency to just meet the timing constraints. SFA has been adopted in the literature after task partitioning, but the worst-case performance of SFA, in terms of energy consumption, is an open problem. We provide comprehensive analysis for SFA to derive the cycle utilization distribution for its worst-case behaviour for energy minimization. Our analysis shows that the energy consumption by using SFA for task execution is at most 1.53 (1.74, 2.10, 2.69, respectively), compared to the energy consumption of the optimal voltage/Frequency scaling, when the dynamic power consumption is a cubic function of the Frequency and the voltage island has up to 4 (8, 16, 32, respectively) cores. The analysis shows that SFA is indeed an effective scheme under practical settings, even though it is not optimal. Furthermore, since all the cores run at a single Frequency and no Frequency alignment for Dynamic Voltage and Frequency Scaling (DVFS) between cores is needed, any uni-core dynamic power management technique for reducing the energy consumption for idling can be easily incorporated individually on each core in the voltage island. This paper also provides the analysis of energy consumption for SFA, combined with the procrastination for Dynamic Power Management (DPM). Furthermore, we also extend our analysis for deriving the Approximation factor of SFA for a multi-core system with multiple voltage islands.
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RTCSA - Energy efficiency analysis for the Single Frequency Approximation (SFA) scheme
2013 IEEE 19th International Conference on Embedded and Real-Time Computing Systems and Applications, 2013Co-Authors: Santiago Pagani, Jianjia ChenAbstract:Energy-efficient designs are important issues in computing systems. This paper studies the energy efficiency of a simple and linear-time strategy, called Single Frequency Approximation (SFA) scheme, for periodic real-time tasks on multi-core systems with a shared supply voltage in a voltage island. The strategy executes all the cores at a single Frequency to just meet the timing constraints. SFA has been adopted in the literature after task partitioning, but the worst-case performance of SFA, in terms of energy consumption, is an open problem. We provide comprehensive analysis for SFA to derive the cycle utilization distribution for its worst-case behaviour for energy minimization. Our analysis shows that the energy consumption by using SFA for task execution is at most 1.53 (1.74, 2.10, 2.69, respectively), compared to the energy consumption of the optimal voltage/Frequency scaling, when the dynamic power consumption is a cubic function of the Frequency and the voltage island has up to 4 (8, 16, 32, respectively) cores. The analysis shows that SFA is indeed an effective scheme under practical settings, even though it is not optimal. Furthermore, since all the cores run at a single Frequency and no Frequency alignment for Dynamic Voltage and Frequency Scaling (DVFS) between cores is needed, any uni-core dynamic power management technique for reducing the energy consumption for idling can be easily incorporated individually on each core in the voltage island. This paper also provides the analysis of energy consumption for SFA, combined with the procrastination for Dynamic Power Management (DPM). Furthermore, we also extend our analysis for deriving the Approximation factor of SFA for a multi-core system with multiple voltage islands.
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RTSS - Energy Efficient Task Partitioning Based on the Single Frequency Approximation Scheme
2013 IEEE 34th Real-Time Systems Symposium, 2013Co-Authors: Santiago Pagani, Jianjia ChenAbstract:Energy-efficiency is a major concern in modern computing systems. For such systems, the presence of multiple voltage islands, where the voltage of each island can change independently and all cores in an island share the same supply voltage at any given time, is an expected compromise between global and per-core Dynamic Voltage and Frequency Scaling (DVFS). This paper focuses on energy minimization for a set of periodic tasks assigned on a voltage island. We present a simple and practical solution, that assigns the tasks onto cores in the island and then applies a DVFS schedule, particularly the Single Frequency Approximation (SFA) scheme. Furthermore, we provide thorough theoretical analysis of our solution, in terms of energy efficiency, against the optimal task partitioning and optimal DVFS schedule, especially for the state-of-the-art designs, that have a few number of cores per voltage island. The analysis shows that, our task partitioning scheme combined with SFA is a good and practical solution for energy efficiency. Particularly, when the number of cores in each voltage island is limited, the Approximation factor is at most 2.01 (2.29, 2.55, 2.80, respectively) when the dynamic power consumption is a cubic function of the Frequency and the islands have up to 4 (8, 16, 32, respectively) cores. Moreover, with non-negligible overhead for sleeping, further combination with any uni-core procrastination algorithm that consumes no more energy than keeping a core idle when it has no workload in its ready queue, increases the Approximation factor by at most 1.
Chanan Singh - One of the best experts on this subject based on the ideXlab platform.
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A Fast and Accurate Failure Frequency Approximation for $k$ -Terminal Reliability Systems
IEEE Transactions on Reliability, 2018Co-Authors: Anoosheh Heidarzadeh, Alex Sprintson, Chanan SinghAbstract:This paper considers the problem of approximating the failure Frequency of large-scale composite $\boldsymbol{k}$ -terminal reliability systems. In such systems, the nodes ( $\boldsymbol{k}$ of which are terminals) are connected through components, which are subject to random failure and repair processes. At any time, a system failure occurs if the surviving system fails to connect all the $\boldsymbol{k}$ terminals together. We assume that each component's up times and down times follow statistically independent stationary random processes, and these processes are statistically independent across the components. In this setting, the exact computation of failure Frequency is known to be computationally intractable (NP-hard). In this paper, we present an algorithm to approximate the failure Frequency for any given multiplicative error factor that runs in polynomial time in the number of (minimal) cutsets. Moreover, for the special case of all-terminal reliability systems, i.e., where all the nodes are terminals, we propose an algorithm for approximating the failure Frequency within an arbitrary multiplicative error that runs in polynomial time in the number of nodes (which can be much smaller than the number of cutsets). Our simulation results confirm that the proposed method is much faster and more accurate than the standard Monte Carlo simulation technique for approximating the failure Frequency.
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A Fast and Accurate Failure Frequency Approximation for $k$-Terminal Reliability Systems
arXiv: Data Structures and Algorithms, 2017Co-Authors: Anoosheh Heidarzadeh, Alex Sprintson, Chanan SinghAbstract:This paper considers the problem of approximating the failure Frequency of large-scale composite $k$-terminal reliability systems. In such systems, the nodes ($k$ of which are terminals) are connected through components which are subject to random failure and repair processes. At any time, a system failure occurs if the surviving system fails to connect all the k terminals together. We assume that each component's up-times and down-times follow statistically independent stationary random processes, and these processes are statistically independent across the components. In this setting, the exact computation of failure Frequency is known to be computationally intractable (NP-hard). In this work, we present an algorithm to approximate the failure Frequency for any given multiplicative error factor that runs in polynomial time in the number of (minimal) cutsets. Moreover, for the special case of all-terminal reliability systems, i.e., where all nodes are terminals, we propose an algorithm for approximating the failure Frequency within an arbitrary multiplicative error that runs in polynomial time in the number of nodes (which can be much smaller than the number of cutsets). In addition, our simulation results confirm that the proposed method is much faster and more accurate than the Monte Carlo simulation technique for approximating the failure Frequency.
Fritz Ehlotzky - One of the best experts on this subject based on the ideXlab platform.
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Off-shell low-Frequency Approximation for potential scattering in a laser field: comparison with the Wallbank and Holmes experiments
Journal of Physics B: Atomic Molecular and Optical Physics, 1997Co-Authors: Dejan B. Milošević, Fritz EhlotzkyAbstract:We investigate the influence of the off-shell effects on the scattering processes in the presence of a laser field in view of the recent experiments by Wallbank and Holmes. In these experiments a large discrepancy between the observed data for small-angle scattering and the on-shell Kroll - Watson formula was reported. We show in the present work that the off-shell effects are not responsible for this discrepancy by presenting results for the differential cross sections obtained, using the off-shell low-Frequency Approximation and the [1,1] Pade Approximation. We model the scattering from helium and argon atoms by the scattering on a Yukawa-type potential. We show, using some examples, that higher laser field frequencies and intensities are necessary for obtaining observable off-shell effects. We also comment on possibilities of explaining the Wallbank and Holmes results. For one of these possibilities - double scattering - we compute, using our simple model, the relative differential cross sections and obtain a qualitative agreement with the experiments of Wallbank and Holmes, both for helium and argon.