Conventional ignition methods are proving to be ineffective for low-sensitivity energetic materials,highlighting the need to investigate alternative ignition systems,such as laser-based techniques.Over the past decade...Conventional ignition methods are proving to be ineffective for low-sensitivity energetic materials,highlighting the need to investigate alternative ignition systems,such as laser-based techniques.Over the past decade,lasers have emerged as a promising solution,providing focused energy beams for controllable,efficient,and reliable ignition in the field of energetic materials.This study presents a comparative analysis of two state-of-the-art ignition approaches:direct laser ignition and laser-driven flyer ignition.Experiments were performed using a Neodymium-doped Yttrium Aluminum Garnet(Nd:YAG)laser at different energy beam levels to systematically evaluate ignition onset.In the direct laser ignition test setup,the laser beam was applied directly to the energetic tested material,while laserdriven flyer ignition utilized 40 and 100μm aluminum foils,propelled at velocities ranging from 300 to 1250 m/s.Comparative analysis with the Lawrence and Trott model substantiated the velocity data and provided insight into the ignition mechanisms.Experimental results indicate that the ignition time for the laser-driven flyer method was significantly shorter,with the pyrotechnic composition achieving complete combustion faster compared to direct laser ignition.Moreover,precise ignition thresholds were determined for both methods,providing critical parameters for optimizing ignition systems in energetic materials.This work elucidates the advantages and limitations of each technique while advancing next-generation ignition technology,enhancing the reliability and safety of propulsion systems.展开更多
Joining dissimilar materials encounters significant engineering challenges due to the contrast in material properties that makes conventional welding not feasible.Magnetic Pulse Welding(MPW)offers a solidstate joining...Joining dissimilar materials encounters significant engineering challenges due to the contrast in material properties that makes conventional welding not feasible.Magnetic Pulse Welding(MPW)offers a solidstate joining technique that overcomes these issues by using impact to create strong bonds without melting the substrate materials.This study investigates the weldability of aluminum alloy Al-5754 with Al-7075 and MARS 380 steel,used in armouring solutions of defense systems,by the use of MPW.In this work,weldability windows are investigated by varying standoff distances between the coating material and its substrate(0.25-4.5 mm)and discharge energies(5-13 kJ)with both O-shape and U-shape inductors.Mechanical strength of the welded joints were assessed through single lap shear tests,identifying optimal welding parameters.Then,the velocity profiles of the flyer plates were measured using heterodyne velocimetry to understand the dynamics of the impact.Then,substructures assembled with the optimal welding conditions were subjected to ballistic testing using 7.62 mm×51 mm NATO and 9 mm×19 mm Parabellum munitions to evaluate the resilience of the welds under ballistic impact.The outcomes demonstrate that MPW effectively joins Al-5754 with both Al-7075 and MARS 380,producing robust welds capable of withstanding ballistic impacts under certain conditions.This research advances the application of MPW in lightweight ballistic protection of defense systems,contributing to the development of more resilient and lighter protective structures.展开更多
Data-driven reduced-order modeling opens new avenues of understanding,predicting,controlling,and optimizing system behavior.Simple systems may have state spaces in which sparse human-interpretable dynamical systems ca...Data-driven reduced-order modeling opens new avenues of understanding,predicting,controlling,and optimizing system behavior.Simple systems may have state spaces in which sparse human-interpretable dynamical systems can be identified.This approach has been pioneered by Brunton et al.(2016,PNAS)with sparse identification of nonlinear dynamics.Complex systems,however,cannot be expected to benefit from such simple analytical descriptions.Yet,smoothness may be exploited by analytical local descriptions.In this paper,we identify a clusterwise polynomial dynamics from time-resolved snapshot data.The full state space is partitioned into clusters with a reduced-order polynomial description for each cluster and a global patching strategy.The resulting clusterwise modeling is entirely data-driven and requires no prior knowledge of the system dynamics.We illustrate the approach on the well-known chaotic Lorenz and Rössler systems,on the more challenging chaotic fluid flow dynamics of higher state-space dimensions,on a noisy electrocardiogram signal,and finally on the time evolution of the monthly sunspot number.Clusterwise modeling offers a powerful and interpretable paradigm for dynamical modeling.Nonlinear dynamics can be approximated by assembling many simple local models of different resolutions,opening new paths to understand and control intricate nonlinearities.展开更多
An object learning and recognition system is implemented for humanoid robots to discover and memorize objects only by simple interactions with non-expert users. When the object is presented, the system makes use of th...An object learning and recognition system is implemented for humanoid robots to discover and memorize objects only by simple interactions with non-expert users. When the object is presented, the system makes use of the motion information over consecutive frames to extract object features and implements machine learning based on the bag of visual words approach. Instead of using a local feature descriptor only, the proposed system uses the co-occurring local features in order to increase feature discriminative power for both object model learning and inference stages. For different objects with different textures, a hybrid sampling strategy is considered. This hybrid approach minimizes the consumption of computation resources and helps achieving good performances demonstrated on a set of a dozen different daily objects.展开更多
The terahertz(THz)temporal waveform and spectrum from a longitudinal electrically biased femtosecond filament is studied experimentally.The initial direction of the electron motion inside the unbiased filament plasma ...The terahertz(THz)temporal waveform and spectrum from a longitudinal electrically biased femtosecond filament is studied experimentally.The initial direction of the electron motion inside the unbiased filament plasma is deduced from the transformation of the THz temporal waveform with applied fields of opposite polarities.Furthermore,a spectrum shift to lower frequency of the THz spectrum is observed in the presence of a biased field.It agrees well with theoretical predictions.展开更多
Currently, second generation intact stability criteria are being developed and evaluated by the International Maritime Organization(IMO). In this paper, we briefly present levels 1 and 2 assessment methods for the cri...Currently, second generation intact stability criteria are being developed and evaluated by the International Maritime Organization(IMO). In this paper, we briefly present levels 1 and 2 assessment methods for the criteria of pure loss of stability and parametric roll failure modes. Subsequently, we show the KG_(max) curves associated with these criteria. We compute these curves for five different types of ships and compare them with the curves embodied in the current regulations. The results show that the safety margin ensured by the first level-1 method of calculation for both pure loss of stability and parametric roll seems to be excessive in many cases. They also show that the KG_(max) given by the second level-1 method and by the level-2 method may be very similar. In some cases, the level-2 method can be more conservative than the second level-1 method, which is unanticipated by the future regulation. The KG_(max) curves associated with parametric roll confirm that the C11 container ship is vulnerable to this failure mode. The computation of the second check coefficient of parametric roll level 2(C2) for all possible values of KG reveals the existence of both authorized and restricted areas on the surface formed by both the draft and KG, which may replace the classical KG_(max) curves. In consequence, it is not sufficient to check that C2 is lower than the maximum authorized value(R_(PR0)) for a fixed ship's loading condition.展开更多
In this paper,the pricing of a Credit Default Swap(CDS)contract with multiple counterparties is considered.The pricing model takes into account the credit rating migration risk of the reference.It is a new model estab...In this paper,the pricing of a Credit Default Swap(CDS)contract with multiple counterparties is considered.The pricing model takes into account the credit rating migration risk of the reference.It is a new model established under the reduced form framework,where the intensity rates are assumed to have structural styles.We derive from it a non-linear partial differential equation system where both positive and negative correlations of counterparties and the references are considered via a single factor model.Then,an ADI(Alternating Direction Implicit)difference method is used to solve the partial differential equations by iteration.From the numerical results,the comparison of multi-counterparty CDS contract and the standard one are analyzed respectively.Moreover,the impact of default parameters on value of the contracts are discussed.展开更多
Usability is a vital characteristic in operating medical machines, especially radiological machines, such as computed tomography (CT) scans and X-rays. The more the body is exposed to it, the greater the negative effe...Usability is a vital characteristic in operating medical machines, especially radiological machines, such as computed tomography (CT) scans and X-rays. The more the body is exposed to it, the greater the negative effect has. If usability is crucial to a specific industry, it is more crucial in the medical health industry due to its tremendous effect on safety and the patient’s health. This study examines the usability of CT scans based on 14 attributes from hospitals across Saudi Arabia. The study revealed that usability consistency, visibility, minimalism, memory, and flexibility have the most usability catastrophic complaints, where the overall catastrophic rate exceeds 20%. Creating a shortcut for frequently used operations is critically important, because it has a fundamental effect in minimizing physical and mental exertion.展开更多
Among the different available wind sources, i.e. in situ measurements, numeric weather models, the retrieval of wind speed from Synthetic Aperture Radar (SAR) data is one of the most widely used methods, since it can ...Among the different available wind sources, i.e. in situ measurements, numeric weather models, the retrieval of wind speed from Synthetic Aperture Radar (SAR) data is one of the most widely used methods, since it can give high wind resolution cells. For this purpose, one can find two principal approaches: via electromagnetic (EM) models and empirical (EP) models. In both approaches, the Geophysical Model Functions (GMFs) are used to describe the relation of radar scattering, wind speed, and the geometry of observations. By knowing radar scattering and geometric parameters, it is possible to invert the GMFs to retrieve wind speed. It is very interesting to compare wind speed estimated by the EM models, general descriptions of radar scattering from sea surface, to the one estimated by the EP models, specific descriptions for the inverse problem. Based on the comparisons, some ideas are proposed to improve the performance of the EM models for wind speed retrieval.展开更多
In this paper,we present a maximum likelihood(ML)based time synchronization algorithm for Wireless Body Area Networks(WBAN).The proposed technique takes advantage of soft information retrieved from the soft demapper f...In this paper,we present a maximum likelihood(ML)based time synchronization algorithm for Wireless Body Area Networks(WBAN).The proposed technique takes advantage of soft information retrieved from the soft demapper for the time delay estimation.This algorithm has a low complexity and is adapted to the frame structure specified by the IEEE 802.15.6standard[1]for the narrowband systems.Simulation results have shown good performance which approach the theoretical mean square error limit bound represented by the Cramer Rao Bound(CRB).展开更多
This paper is mainly devoted to application of the Gaussian beam summation technique in electromagnetic simulations problem. Gaussian beams are asymptotic solutions of the Helmholtz equation within the paraxial approx...This paper is mainly devoted to application of the Gaussian beam summation technique in electromagnetic simulations problem. Gaussian beams are asymptotic solutions of the Helmholtz equation within the paraxial approximation. Since they are insensitive to ray transition region, several techniques based on Gaussian beam are used to evaluate high frequency EM wave equation, which overcome partially or fully the difficulties of singular regions (caustics, zero field in shadow zones). This paper concentrates on the explicit formulation of the electromagnetic field scattered from radar target. In this approach, when the incident field illuminates the target, the scattering is accounted in a complex weighing function. The wave field at a receiver is evaluated as superposition of Gaussian beams concentrated close to rays emerging from the target, passing through the neighbor of the receiver.展开更多
In Electronic Warfare, and more specifically in the domain of passive localization, accurate time synchronization between platforms is decisive, especially on systems relying on TDOA （time difference of arrival） and...In Electronic Warfare, and more specifically in the domain of passive localization, accurate time synchronization between platforms is decisive, especially on systems relying on TDOA （time difference of arrival） and FDOA （frequency difference of arrival）. This paper investigates this issue by presenting an analysis in terms of final localization performance of an experimental passive localization system based on off-the-shelf components. This system is detailed, as well as the methodology used to carry out the acquisition of real data. This experiment has been realized with two different kinds of clock. The results are analyzed by calculating the Allan deviation and time deviation. The choice of these metrics is explained and their properties are discussed in the scope of an airborne bi-platform passive localization context. Conclusions are drawn regarding the overall localization performance of the system.展开更多
We present the results of the first commissioning phase of the short-focal-length area of the Apollon laser facility(located in Saclay,France),which was performed with the first available laser beam(F2),scaled to a no...We present the results of the first commissioning phase of the short-focal-length area of the Apollon laser facility(located in Saclay,France),which was performed with the first available laser beam(F2),scaled to a nominal power of 1 PW.Under the conditions that were tested,this beam delivered on-target pulses of 10 J average energy and 24 fs duration.Several diagnostics were fielded to assess the performance of the facility.The on-target focal spot and its spatial stability,the temporal intensity profile prior to the main pulse,and the resulting density gradient formed at the irradiated side of solid targets have been thoroughly characterized,with the goal of helping users design future experiments.Emissions of energetic electrons,ions,and electromagnetic radiation were recorded,showing good laser-to-target coupling efficiency and an overall performance comparable to that of similar international facilities.This will be followed in 2022 by a further commissioning stage at the multipetawatt level.展开更多
The aim of this work is to study the impacts of the oil spills on the electromagnetic scattering of the ocean surfaces in bistatic and monostatic configurations. Therefore, in this paper, we will study the influence o...The aim of this work is to study the impacts of the oil spills on the electromagnetic scattering of the ocean surfaces in bistatic and monostatic configurations. Therefore, in this paper, we will study the influence of the pollutants (oil spills) on the physical and geometrical properties of sea surface. In recent literature, the study of the electromagnetic scattering from contaminated sea surface (sea surface covered by oil spill) was limited in monostatic case. In this paper, we will study this effect in bistatic configuration, which is interested in presence of pollution in sea surface. Indeed, we will start the numerical analysis of the bistatic scattering coefficients of a clean sea surface. Then, we will study the electromagnetic signature from sea surface covered by oil spills in bistatic case using the numerical Forward-Backward Method (FBM). The obtained numerical simulation of bistatic scattering coefficients of clean and contaminated sea surface is studied as a function of various parameters (frequency, incident angle, sea state, type of pollutant…). And the obtained results are also compared with those published in the literature, including those using asymptotic methods.展开更多
This study scrutinizes the thermomechanical dynamics of 3D-printed hydrofoil blades utilizing a carbon and glass bead-reinforced thermoplastic polymer.Comparative analyses underscore the pivotal role of polymer reinfo...This study scrutinizes the thermomechanical dynamics of 3D-printed hydrofoil blades utilizing a carbon and glass bead-reinforced thermoplastic polymer.Comparative analyses underscore the pivotal role of polymer reinforcement in augmenting mechanical strength and mitigating deformation and residual stress.The investigation elucidates the expeditious and cost-efficient manufacturing potential of low-cost Fused Filament Fabrication(FFF)printers for small-scale blades,revealing exemplary mechanical performance with nominal deflection and warping in the PA12-CB/GB printed blade.A comprehensive juxtaposition between Selective Laser Sintering(SLS)and FFF printing methods favors SLS due to its isotropic properties,notwithstanding remediable warping.Emphasizing the rigorous marine environment,the study cautions against the anisotropic properties of FFF-printed blades,despite their low mechanical warping.These discernments contribute to hydrofoil design optimization through numerical analysis,shedding light on additive manufacturing’s potential for small blades in renewable energy,while underscoring the imperative for further research to advance these techniques.展开更多
In this work,four samples of TiO_(2) powder materials with different structures(rutile,anatase),surface coatings and morphologies(rod,pseudo-spherical)were characterized by four partners involving complementary method...In this work,four samples of TiO_(2) powder materials with different structures(rutile,anatase),surface coatings and morphologies(rod,pseudo-spherical)were characterized by four partners involving complementary methods.With the aim of producing inter-laboratory reproducibility data,the specific surface-area,bulk density,and number size distribution were measured,yielding a satisfying agreement between partners.The equivalent diameter of constituent particles was determined from the sample volume specific surface area(VSSA)–accounting for polydispersion–and compared to electron microscopy(EM).Constituent particle diameters ranged from 15 to 225 nm according to EM analyses.The relative discrepancies between VSSA-based and EM-based diameters were found within±20%.Out of the four samples under study,TiO_(2)μ-rutile leads to a larger deviation,which was attributed to surface coating thanks to complementary analysis.Assuming that the sample is pure,an equivalent diameter based on the VSSA can be determined,provided that the shape of constituent particles is known or supposed.展开更多
The average bit-error rate （ABER） performance of free-space optical （FSO） communication links is investigated for space-shift keying （SSK） over log-normal and negative-exponential atmospheric turbulence channels...The average bit-error rate （ABER） performance of free-space optical （FSO） communication links is investigated for space-shift keying （SSK） over log-normal and negative-exponential atmospheric turbulence channels. SSK is compared with repetition codes and a single-input single-output system using multiple pulse amplitude mod- ulations. Simulation results show that the signal-to-noise ratio gain of SSK largely increases with greater spectral efficiencies and/or higher turbulence effects. A tight bound for ABER is derived based on an exact moment generation function （MGF） for negative-exponential channel and an approximate MGF for log-normal channel. Finally, extensive Monte Carlo simulations are run to validate the analytical analysis.展开更多
文摘Conventional ignition methods are proving to be ineffective for low-sensitivity energetic materials,highlighting the need to investigate alternative ignition systems,such as laser-based techniques.Over the past decade,lasers have emerged as a promising solution,providing focused energy beams for controllable,efficient,and reliable ignition in the field of energetic materials.This study presents a comparative analysis of two state-of-the-art ignition approaches:direct laser ignition and laser-driven flyer ignition.Experiments were performed using a Neodymium-doped Yttrium Aluminum Garnet(Nd:YAG)laser at different energy beam levels to systematically evaluate ignition onset.In the direct laser ignition test setup,the laser beam was applied directly to the energetic tested material,while laserdriven flyer ignition utilized 40 and 100μm aluminum foils,propelled at velocities ranging from 300 to 1250 m/s.Comparative analysis with the Lawrence and Trott model substantiated the velocity data and provided insight into the ignition mechanisms.Experimental results indicate that the ignition time for the laser-driven flyer method was significantly shorter,with the pyrotechnic composition achieving complete combustion faster compared to direct laser ignition.Moreover,precise ignition thresholds were determined for both methods,providing critical parameters for optimizing ignition systems in energetic materials.This work elucidates the advantages and limitations of each technique while advancing next-generation ignition technology,enhancing the reliability and safety of propulsion systems.
基金funded on the one hand by Agence de l'Innovation de Défense(AID)grant reference number 2021650044on the other hand by Ecole Centrale de Nantes。
文摘Joining dissimilar materials encounters significant engineering challenges due to the contrast in material properties that makes conventional welding not feasible.Magnetic Pulse Welding(MPW)offers a solidstate joining technique that overcomes these issues by using impact to create strong bonds without melting the substrate materials.This study investigates the weldability of aluminum alloy Al-5754 with Al-7075 and MARS 380 steel,used in armouring solutions of defense systems,by the use of MPW.In this work,weldability windows are investigated by varying standoff distances between the coating material and its substrate(0.25-4.5 mm)and discharge energies(5-13 kJ)with both O-shape and U-shape inductors.Mechanical strength of the welded joints were assessed through single lap shear tests,identifying optimal welding parameters.Then,the velocity profiles of the flyer plates were measured using heterodyne velocimetry to understand the dynamics of the impact.Then,substructures assembled with the optimal welding conditions were subjected to ballistic testing using 7.62 mm×51 mm NATO and 9 mm×19 mm Parabellum munitions to evaluate the resilience of the welds under ballistic impact.The outcomes demonstrate that MPW effectively joins Al-5754 with both Al-7075 and MARS 380,producing robust welds capable of withstanding ballistic impacts under certain conditions.This research advances the application of MPW in lightweight ballistic protection of defense systems,contributing to the development of more resilient and lighter protective structures.
基金supported by the National Natural Science Foundation of China(Grant Nos.12172109,12202121,and 12302293)the China Postdoctoral Science Foundation(Grant Nos.2023M730866 and 2023T160166)+1 种基金the Guangdong Basic and Applied Basic Research Foundation(Grant No.2022A1515011492)the Shenzhen Science and Technology Program(Grant Nos.JCYJ20220531095605012,KJZD20230923115210021,and 29853MKCJ202300205).
文摘Data-driven reduced-order modeling opens new avenues of understanding,predicting,controlling,and optimizing system behavior.Simple systems may have state spaces in which sparse human-interpretable dynamical systems can be identified.This approach has been pioneered by Brunton et al.(2016,PNAS)with sparse identification of nonlinear dynamics.Complex systems,however,cannot be expected to benefit from such simple analytical descriptions.Yet,smoothness may be exploited by analytical local descriptions.In this paper,we identify a clusterwise polynomial dynamics from time-resolved snapshot data.The full state space is partitioned into clusters with a reduced-order polynomial description for each cluster and a global patching strategy.The resulting clusterwise modeling is entirely data-driven and requires no prior knowledge of the system dynamics.We illustrate the approach on the well-known chaotic Lorenz and Rössler systems,on the more challenging chaotic fluid flow dynamics of higher state-space dimensions,on a noisy electrocardiogram signal,and finally on the time evolution of the monthly sunspot number.Clusterwise modeling offers a powerful and interpretable paradigm for dynamical modeling.Nonlinear dynamics can be approximated by assembling many simple local models of different resolutions,opening new paths to understand and control intricate nonlinearities.
基金The National Natural Science Foundation of China(No.60672094,60971098)
文摘An object learning and recognition system is implemented for humanoid robots to discover and memorize objects only by simple interactions with non-expert users. When the object is presented, the system makes use of the motion information over consecutive frames to extract object features and implements machine learning based on the bag of visual words approach. Instead of using a local feature descriptor only, the proposed system uses the co-occurring local features in order to increase feature discriminative power for both object model learning and inference stages. For different objects with different textures, a hybrid sampling strategy is considered. This hybrid approach minimizes the consumption of computation resources and helps achieving good performances demonstrated on a set of a dozen different daily objects.
基金Supported by the National Natural Science Foundation of China(Grant No.11574213)the Innovation Program of Shanghai Municipal Education Commission(Grant No.2017–01-07-00-07-E00007)。
文摘The terahertz(THz)temporal waveform and spectrum from a longitudinal electrically biased femtosecond filament is studied experimentally.The initial direction of the electron motion inside the unbiased filament plasma is deduced from the transformation of the THz temporal waveform with applied fields of opposite polarities.Furthermore,a spectrum shift to lower frequency of the THz spectrum is observed in the presence of a biased field.It agrees well with theoretical predictions.
文摘Currently, second generation intact stability criteria are being developed and evaluated by the International Maritime Organization(IMO). In this paper, we briefly present levels 1 and 2 assessment methods for the criteria of pure loss of stability and parametric roll failure modes. Subsequently, we show the KG_(max) curves associated with these criteria. We compute these curves for five different types of ships and compare them with the curves embodied in the current regulations. The results show that the safety margin ensured by the first level-1 method of calculation for both pure loss of stability and parametric roll seems to be excessive in many cases. They also show that the KG_(max) given by the second level-1 method and by the level-2 method may be very similar. In some cases, the level-2 method can be more conservative than the second level-1 method, which is unanticipated by the future regulation. The KG_(max) curves associated with parametric roll confirm that the C11 container ship is vulnerable to this failure mode. The computation of the second check coefficient of parametric roll level 2(C2) for all possible values of KG reveals the existence of both authorized and restricted areas on the surface formed by both the draft and KG, which may replace the classical KG_(max) curves. In consequence, it is not sufficient to check that C2 is lower than the maximum authorized value(R_(PR0)) for a fixed ship's loading condition.
基金Supported by the National Natural Science Foundation of China(11671301,12071349).
文摘In this paper,the pricing of a Credit Default Swap(CDS)contract with multiple counterparties is considered.The pricing model takes into account the credit rating migration risk of the reference.It is a new model established under the reduced form framework,where the intensity rates are assumed to have structural styles.We derive from it a non-linear partial differential equation system where both positive and negative correlations of counterparties and the references are considered via a single factor model.Then,an ADI(Alternating Direction Implicit)difference method is used to solve the partial differential equations by iteration.From the numerical results,the comparison of multi-counterparty CDS contract and the standard one are analyzed respectively.Moreover,the impact of default parameters on value of the contracts are discussed.
文摘Usability is a vital characteristic in operating medical machines, especially radiological machines, such as computed tomography (CT) scans and X-rays. The more the body is exposed to it, the greater the negative effect has. If usability is crucial to a specific industry, it is more crucial in the medical health industry due to its tremendous effect on safety and the patient’s health. This study examines the usability of CT scans based on 14 attributes from hospitals across Saudi Arabia. The study revealed that usability consistency, visibility, minimalism, memory, and flexibility have the most usability catastrophic complaints, where the overall catastrophic rate exceeds 20%. Creating a shortcut for frequently used operations is critically important, because it has a fundamental effect in minimizing physical and mental exertion.
基金National Natural Science Foundation of China(Nos.12034013,11904232)Innovation Program of Shanghai Municipal Education Commission(No.2017-01-07-00-07-E00007)。
文摘Among the different available wind sources, i.e. in situ measurements, numeric weather models, the retrieval of wind speed from Synthetic Aperture Radar (SAR) data is one of the most widely used methods, since it can give high wind resolution cells. For this purpose, one can find two principal approaches: via electromagnetic (EM) models and empirical (EP) models. In both approaches, the Geophysical Model Functions (GMFs) are used to describe the relation of radar scattering, wind speed, and the geometry of observations. By knowing radar scattering and geometric parameters, it is possible to invert the GMFs to retrieve wind speed. It is very interesting to compare wind speed estimated by the EM models, general descriptions of radar scattering from sea surface, to the one estimated by the EP models, specific descriptions for the inverse problem. Based on the comparisons, some ideas are proposed to improve the performance of the EM models for wind speed retrieval.
基金supported by the franco-chinese NSFC-ANR program under the Greencocom Project
文摘In this paper,we present a maximum likelihood(ML)based time synchronization algorithm for Wireless Body Area Networks(WBAN).The proposed technique takes advantage of soft information retrieved from the soft demapper for the time delay estimation.This algorithm has a low complexity and is adapted to the frame structure specified by the IEEE 802.15.6standard[1]for the narrowband systems.Simulation results have shown good performance which approach the theoretical mean square error limit bound represented by the Cramer Rao Bound(CRB).
文摘This paper is mainly devoted to application of the Gaussian beam summation technique in electromagnetic simulations problem. Gaussian beams are asymptotic solutions of the Helmholtz equation within the paraxial approximation. Since they are insensitive to ray transition region, several techniques based on Gaussian beam are used to evaluate high frequency EM wave equation, which overcome partially or fully the difficulties of singular regions (caustics, zero field in shadow zones). This paper concentrates on the explicit formulation of the electromagnetic field scattered from radar target. In this approach, when the incident field illuminates the target, the scattering is accounted in a complex weighing function. The wave field at a receiver is evaluated as superposition of Gaussian beams concentrated close to rays emerging from the target, passing through the neighbor of the receiver.
文摘In Electronic Warfare, and more specifically in the domain of passive localization, accurate time synchronization between platforms is decisive, especially on systems relying on TDOA （time difference of arrival） and FDOA （frequency difference of arrival）. This paper investigates this issue by presenting an analysis in terms of final localization performance of an experimental passive localization system based on off-the-shelf components. This system is detailed, as well as the methodology used to carry out the acquisition of real data. This experiment has been realized with two different kinds of clock. The results are analyzed by calculating the Allan deviation and time deviation. The choice of these metrics is explained and their properties are discussed in the scope of an airborne bi-platform passive localization context. Conclusions are drawn regarding the overall localization performance of the system.
基金The authors acknowledge the facility and the technical assistance of the national research infrastructureApollon.The authorswould also like to thank all teams of the laboratories that contributed to the success of the facility,i.e.,all of theCILEXconsortium,whichwas established to buildApollon.Thisworkwas supported by funding fromthe European Research Council(ERC)under the European Unions Horizon 2020 research and innovation program(Grant Agreement No.787539,Project GENESIS),and by Grant No.ANR-17-CE30-0026-Pinnacle from the Agence Nationale de la Recherche.We acknowledge,in the framework of ProjectGENESIS,the support provided by Extreme Light InfrastructureNuclear Physics(ELI-NP)Phase II,a project co-financed by the Romanian Government and the European Union through the European Regional Development Fund,and by the Project No.ELI-RO-2020-23,funded by IFA(Romania)to design,build,and test the neutron detectors used in this project,as well as parts of the OTR diagnostic.JIHT RAS team members are supported by the Ministry of Science and Higher Education of the Russian Federation(State Assignment No.075-00460-21-00)The study reported here was also funded by the Russian Foundation for Basic Research,Project No.20-02-00790.The work of the ENEA team members has been carried out within the framework of the EUROfusionConsortiumand has received funding from the Euratom research and training program 2014–2018 and 2019-2020 under grant agreement No.633053.
文摘We present the results of the first commissioning phase of the short-focal-length area of the Apollon laser facility(located in Saclay,France),which was performed with the first available laser beam(F2),scaled to a nominal power of 1 PW.Under the conditions that were tested,this beam delivered on-target pulses of 10 J average energy and 24 fs duration.Several diagnostics were fielded to assess the performance of the facility.The on-target focal spot and its spatial stability,the temporal intensity profile prior to the main pulse,and the resulting density gradient formed at the irradiated side of solid targets have been thoroughly characterized,with the goal of helping users design future experiments.Emissions of energetic electrons,ions,and electromagnetic radiation were recorded,showing good laser-to-target coupling efficiency and an overall performance comparable to that of similar international facilities.This will be followed in 2022 by a further commissioning stage at the multipetawatt level.
基金the EU for its support to NETMAR project where this work is in progressthe other partners of NETMAR project,and also the“Region Bretagne”for its support.
文摘The aim of this work is to study the impacts of the oil spills on the electromagnetic scattering of the ocean surfaces in bistatic and monostatic configurations. Therefore, in this paper, we will study the influence of the pollutants (oil spills) on the physical and geometrical properties of sea surface. In recent literature, the study of the electromagnetic scattering from contaminated sea surface (sea surface covered by oil spill) was limited in monostatic case. In this paper, we will study this effect in bistatic configuration, which is interested in presence of pollution in sea surface. Indeed, we will start the numerical analysis of the bistatic scattering coefficients of a clean sea surface. Then, we will study the electromagnetic signature from sea surface covered by oil spills in bistatic case using the numerical Forward-Backward Method (FBM). The obtained numerical simulation of bistatic scattering coefficients of clean and contaminated sea surface is studied as a function of various parameters (frequency, incident angle, sea state, type of pollutant…). And the obtained results are also compared with those published in the literature, including those using asymptotic methods.
文摘This study scrutinizes the thermomechanical dynamics of 3D-printed hydrofoil blades utilizing a carbon and glass bead-reinforced thermoplastic polymer.Comparative analyses underscore the pivotal role of polymer reinforcement in augmenting mechanical strength and mitigating deformation and residual stress.The investigation elucidates the expeditious and cost-efficient manufacturing potential of low-cost Fused Filament Fabrication(FFF)printers for small-scale blades,revealing exemplary mechanical performance with nominal deflection and warping in the PA12-CB/GB printed blade.A comprehensive juxtaposition between Selective Laser Sintering(SLS)and FFF printing methods favors SLS due to its isotropic properties,notwithstanding remediable warping.Emphasizing the rigorous marine environment,the study cautions against the anisotropic properties of FFF-printed blades,despite their low mechanical warping.These discernments contribute to hydrofoil design optimization through numerical analysis,shedding light on additive manufacturing’s potential for small blades in renewable energy,while underscoring the imperative for further research to advance these techniques.
文摘In this work,four samples of TiO_(2) powder materials with different structures(rutile,anatase),surface coatings and morphologies(rod,pseudo-spherical)were characterized by four partners involving complementary methods.With the aim of producing inter-laboratory reproducibility data,the specific surface-area,bulk density,and number size distribution were measured,yielding a satisfying agreement between partners.The equivalent diameter of constituent particles was determined from the sample volume specific surface area(VSSA)–accounting for polydispersion–and compared to electron microscopy(EM).Constituent particle diameters ranged from 15 to 225 nm according to EM analyses.The relative discrepancies between VSSA-based and EM-based diameters were found within±20%.Out of the four samples under study,TiO_(2)μ-rutile leads to a larger deviation,which was attributed to surface coating thanks to complementary analysis.Assuming that the sample is pure,an equivalent diameter based on the VSSA can be determined,provided that the shape of constituent particles is known or supposed.
文摘The average bit-error rate （ABER） performance of free-space optical （FSO） communication links is investigated for space-shift keying （SSK） over log-normal and negative-exponential atmospheric turbulence channels. SSK is compared with repetition codes and a single-input single-output system using multiple pulse amplitude mod- ulations. Simulation results show that the signal-to-noise ratio gain of SSK largely increases with greater spectral efficiencies and/or higher turbulence effects. A tight bound for ABER is derived based on an exact moment generation function （MGF） for negative-exponential channel and an approximate MGF for log-normal channel. Finally, extensive Monte Carlo simulations are run to validate the analytical analysis.
