Improving the utility of locally differentially private protocols for longitudinal and multidimensional frequency estimates

This paper investigates the problem of collecting multidimensional data throughout time(i.e.,longitudinal studies)for the fundamental task of frequency estimation under Local Differential Privacy(LDP)guarantees.Contrary to frequency estimation of a single attribute,the multidimensional aspect demands particular attention to the privacy budget.Besides,when collecting user statistics longitudinally,privacy progressively degrades.Indeed,the“multiple”settings in combination(i.e.,many attributes and several collections throughout time)impose several challenges,for which this paper proposes the first solution for frequency estimates under LDP.To tackle these issues,we extend the analysis of three state-of-the-art LDP protocols(Generalized Randomized Response–GRR,Optimized Unary Encoding–OUE,and Symmetric Unary Encoding–SUE)for both longitudinal and multidimensional data collections.While the known literature uses OUE and SUE for two rounds of sanitization(a.k.a.memoization),i.e.,L-OUE and L-SUE,respectively,we analytically and experimentally show that starting with OUE and then with SUE provides higher data utility(i.e.,L-OSUE).Also,for attributes with small domain sizes,we propose Longitudinal GRR(L-GRR),which provides higher utility than the other protocols based on unary encoding.Last,we also propose a new solution named Adaptive LDP for LOngitudinal and Multidimensional FREquency Estimates(ALLOMFREE),which randomly samples a single attribute to be sent with the whole privacy budget and adaptively selects the optimal protocol,i.e.,either L-GRR or L-OSUE.As shown in the results,ALLOMFREE consistently and considerably outperforms the state-of-the-art L-SUE and L-OUE protocols in the quality of the frequency estimates.

Ballistic resistance and energy dissipation of woven-fabric composite targets:Insights on the effects of projectile shape and obliquity angle

This study aims at investigating the ballistic resistance and energy absorption in woven E-glass composite panels,considering different projectile nose shapes and oblique incidence angles.To that scope,three-dimensional finite element(FE)models of both projectiles and the laminated target are developed and numerical investigations are carried out using Abaqus Explicit solver.The composite damage model’s constitutive law encompasses nonlinear material response,material properties degradation,progressive failure,and an element deletion strategy.The cohesive surface technique is used to represent the interface between two adjacent plies in the laminate,and the traction-separation law is used to characterize the behaviors of interlaminar degradation and failure.Material responses attributable to fiber rupture,matrix cracking,and plasticity caused by micro-matrix cracking due to shear loading are taken into account with suitable damage evolution laws.The computational framework is first validated against the experimental results reported in the literature by performing ballistic impact tests on the target laminate with conical,hemispherical and blunt-ended projectile,and the numerical results showed a good comparison in terms of residual velocity.Subsequently the framework is explored in simulating more complex failure mechanisms,with particular emphasis on the influence of the impact angle of obliquity,a parameter that is not usually analyzed in the literature.In that regard,the effects of normal and oblique impact on the damage morphologies and ballistic behavior of the fabric composite target in terms of energy absorption,impact contact force,and projectile residual velocity are conducted and analyzed,comparatively.The findings showed that the ballistic impact behavior of target composite is substantially influenced by projectile nose shape and incidence angle obliquity.

多物理域质子交换膜燃料电池建模仿真及实验测试

燃料电池及其应用近些年逐渐成为研究热点,对于系统级的燃料电池运行工况分析及设计,底层的燃料电池本体模型显得至关重要。相比于已有的传统经验模型,重点提出了一种一般性的多物理域燃料电池分析模型,并从电化学域、流体力学域以及热力学动态域对质子交换膜燃料电池进行了精确建模。所提出的框架性建模方法可以适用于不同型号的质子交换膜燃料电池,同时也可以进一步拓展并应用于不同种类的燃料电池。随后以Ballard NEXA 1.2 kW质子交换膜燃料电池为例,对模型在不同工况下进行了仿真,并通过实验测试验证了所提出模型的有效性和准确性。在此基础上,可以展开相应的控制策略及电池本体运行分析,从而提升燃料电池系统的运行性能和工作寿命。

Study on a new chaotic bitwise dynamical system and its FPGA implementation

In this paper, the structure of a new chaotic bitwise dynamical system （CBDS） is described. Compared to our previous research work, it uses various random bitwise operations instead of only one. The chaotic behavior of CBDS is mathemat- ically proven according to the Devaney＇s definition, and its statistical properties are verified both for uniformity and by a comprehensive, reputed and stringent battery of tests called TestU01. Furthermore, a systematic methodology developing the parallel computations is proposed for FPGA platform-based realization of this CBDS. Experiments finally validate the proposed systematic methodology.

Photo-thermal synergistic excitation:Feasible strategy to detect ethanol for wide bandgap ZIF-8at low work temperature

Zeolitic Imidazolate Framework-8(ZIF-8)material was prepared by chemical precipitation method.The microstructure and physical properties of the as-prepared samples were characterized by XRD,BET,FESEM and UV spectrophotometer.The self-made four-channel measurement device was used to test the gas sensitivity of ZIF-8 material toward ethanol gas under photo-thermal synergistic excitation.The results showed that the sample was typical ZIF-8(E_(g)=4.96 eV)with a regular dodecahedron shape and the specific surface is up to 1793 m^(2)/g.The as-prepared ZIF-8 has a gas response value of 55.04 to 100 ppm ethanol at 75℃ and it shows good gas sensing selectivity and repeated stability.The excellent gas sensitivity can be attributed to the increase of free electron concentration in the ZIF-8 conduction band by photo-thermal synergistic excitation,and the large specific surface area of ZIF-8 material provides more active sites for gas-solid surface reaction.The reaction mechanism of ZIF-8 material under multi-field excitation was also discussed.

Dynamic recrystallization behavior and strengthening mechanism of a novel Mo-Ti_(3)AlC_(2) alloy at ultrahigh temperature

Increasing the recrystallization temperature to achieve better high-temperature performance is critical in the development of molybdenum alloys for ultrahightemperature applications,such as the newest generation of multitype high-temperature nuclear reactors.In this study,an innovative strategy was proposed to improve the performance of molybdenum alloys at high temperature by using the two-dimensional MAX(where M is an early transition metal,A is an A-group element and X is C or N)ceramic material Ti_(3)AlC_(2).The relationships between flow stress,strain rate and temperature were studied.The microstructure,distribution of misorientation and evolution of dislocations in the Mo-Ti_(3)AlC_(2) alloy were analyzed.The microscopic mechanism of the Ti_(3)AlC_(2) phase in the molybdenum alloy at high temperatures was clarified.The experimental results showed that the peak flow stress of Mo-Ti_(3)AlC_(2) at 1600℃ reached 155 MPa,which was161.8% greater than that of pure Mo.The activation energy of thermal deformation of Mo-Ti_(3)AlC_(2) was as large as537 kJ·mol~(-1),which was 17.6% more than that of pure Mo.The recrystallization temperature reached 1600℃ or even higher.The topological reaction of the Ti_(3)AlC_(2) phase consumed a large amount of energy at high temperatures,resulting in increases in the deformation activation energy.Nanolayer structures of AlTi_3 and Ti-O Magneli-phase oxides(Ti_nO_(2n-1)) were formed in-situ,which relied on kink bands and interlayer slip,resulting in many dislocations during deformation.Therefore,the special two-dimensional of the structure Ti_(3)AlC_(2) ceramic inhibited the recrystallization behavior of the Mo alloy.The results of this study can provide theoretical guidance for the development of a new generation of molybdenum alloys for use in ultrahigh-temperature environments.

Controlling hydrogenation of C=C and C=O bonds in cinnamaldehyde using Pt_(1)/Ni and Pt_(1)/Co single-atom alloy catalysts

Selective hydrogenation of C=C and C=O bonds in cinnamaldehyde(CAL)to produce desired products is a challenging task due to the complex conjugate system of the two unsaturated functional groups.In this study,a simple ball milling method is presented for synthesizing Pt-based single-atom alloy catalysts(SAAs)that can function as a control switch for the selective hydrogenation of CAL into highly valuable products.

Two-photon polymerization of femtosecond high-order Bessel beams with aberration correction

In the femtosecond two-photon polymerization(2PP)experimental system,optical aberrations degrade the fabrication quality.To solve this issue,a multichannel interferometric wavefront sensing technique is adopted in the adaptive laser processing system with a single phase-only spatial light modulator.2PP fabrications using corrected high-order Bessel beams with the above solution have been conducted,and high-quality microstructure arrays of microtubes with 20μm diameter have been rapidly manufactured.The effectiveness of the proposed scheme is demonstrated by comparing the beam intensity distributions and 2PP results before and after aberration corrections.

Strong dependency of the tribological behavior of CuZr-based bulk metallic glasses on relative humidity in ambient air

Thanks to their outstanding mechanical properties,Bulk Metallic Glasses(BMGs)are new alternatives to traditional crystalline metals for mechanical and micromechanical applications including power transmission.However,the tribological properties of BMGs are still poorly understood,mostly because their amorphous nature induces counter intuitive responses to friction and wear.In the present study,four different BMGs(Cu_(47)Zr_(46)Al_(7),Zr_(46)Cu_(45)Al_(7)Nb_(2),Zr_(60)Cu_(28)Al_(12),and Zr_(61)Cu_(25)Al_(12)Ti_(2))underwent ball-on-disc friction tests against 100Cr6 steel balls(American Iron and Steel Institute(AISI)52100)at different relative humidities(RHs)ranging from 20%to 80%.Controlling humidity enabled to observe a high repeatability of the friction and wear responses of the BMG.Interestingly,the friction coefficient decreased by a factor of 2 when the humidity was increased,and the wear rate of BMGs was particularly low thanks to a 3rd-body tribolayer that forms on the BMG surface,composed of oxidized wear particles originating from the ball.The morphology of this tribolayer is highly correlated to humidity.The study also identifies how the tribolayer is built up from the initial contact until the steady state is achieved.

High-consistency proton exchange membrane fuel cells enabled by oxygen-electron mixed-pathway electrodes via digitalization design

Proton exchange membrane(PEM)fuel cell has been regarded as a promising approach to the decarbonization and diversification of energy sources.In recent years,durability and cost issues of PEM fuel cells are increasingly significant with the rapid increase of power density.However,the failure to maintain the cell consistency,as one major cause of the above issue,has attracted little attention.Therefore,this study intends to figure out the underlying cause of cell inconsistency and provide solutions to it from the perspective of multi-physics transport coupled with electrochemical reactions.The PEM fuel cells with electrodes under two compression modes are firstly discussed to fully explain the relationship of cell performance and consistency to electrode structure and multi-physics transport.The result indicates that one main cause of cell inconsistency is the intrinsic conflict between the separated transport and cooperated consumption of oxygen and electron throughout the active area.Then,a mixed-pathway electrode design is proposed to reduce the cell inconsistency by enhancing the mixed transport of oxygen and electron in the electrode.It is found that the mixing of pathways in electrodes at under-rib region is more effective than that at the under-channel region,and can achieve an up to 40%reduction of the cell inconsistency with little(3.3%)sacrificed performance.In addition,all the investigations are implemented based on a self-developed digitalization platform that reconstructs the complex physical–chemical system of PEM fuel cells.The fully observable physical information of the digitalized cells provides strong support to the related analysis.

In-situ diagnostic of femtosecond laser probe pulses for high resolution ultrafast imaging

Ultrafast imaging is essential in physics and chemistry to investigate the femtosecond dynamics of nonuniform samples or of phenomena with strong spatial variations.It relies on observing the phenomena induced by an ultrashort laser pump pulse using an ultrashort probe pulse at a later time.Recent years have seen the emergence of very successful ultrafast imaging techniques of single non-reproducible events with extremely high frame rate,based on wavelength or spatial frequency encoding.However,further progress in ultrafast imaging towards high spatial resolution is hampered by the lack of characterization of weak probe beams.For pump–probe experiments realized within solids or liquids,because of the difference in group velocities between pump and probe,the determination of the absolute pump–probe delay depends on the sample position.In addition,pulse-front tilt is a widespread issue,unacceptable for ultrafast imaging,but which is conventionally very difficult to evaluate for the low-intensity probe pulses.Here we show that a pump-induced micro-grating generated from the electronic Kerr effect provides a detailed in-situ characterization of a weak probe pulse.It allows solving the two issues of absolute pump–probe delay determination and pulse-front tilt detection.Our approach is valid whatever the transparent medium with nonnegligible Kerr index,whatever the probe pulse polarization and wavelength.Because it is nondestructive and fast to perform,this in-situ probe diagnostic can be repeated to calibrate experimental conditions,particularly in the case where complex wavelength,spatial frequency or polarization encoding is used.We anticipate that this technique will enable previously inaccessible spatiotemporal imaging in a number of fields of ultrafast science at the micro-and nanoscale.

Magnetic spin–orbit interaction of light

We study the directional excitation of optical surface waves controlled by the magnetic field of light.We theoretically predict that a spinning magnetic dipole develops a tunable unidirectional coupling of light to transverse electric(TE)polarized Bloch surface waves(BSWs).Experimentally,we show that the helicity of light projected onto a subwavelength groove milled into the top layer of a 1D photonic crystal(PC)controls the power distribution between two TE-polarized BSWs excited on both sides of the groove.Such a phenomenon is shown to be solely mediated by the helicity of the magnetic optical field,thus revealing a magnetic spin-orbit interaction of light.Remarkably,this magnetic optical effect is clearly observed via a near-field coupler governed by an electric dipole moment:it is of the same order of magnitude as the electric optical effects involved in the coupling.This opens up new degrees of freedom for the manipulation of light and offers desirable and novel opportunities for the development of integrated optical functionalities.

Subwavelength polarization optics via individual and coupled helical traveling-wave nanoantennas

Light polarization control is a key factor in modern photonics.Recent advances in surface plasmon manipulation have introduced the prospect of more compact and more efficient devices for this purpose.However,the current plasmonic-based polarization optics remain much larger than the wavelength of light,which limits the design degrees of freedom.Here,we present a plasmonic traveling-wave nanoantenna using a gold-coated helical carbon nanowire end-fired with a dipolar aperture nanoantenna.Our nonresonant helical nanoantenna enables tunable polarization control by swirling surface plasmons on the subwavelength scale and taking advantage of the optical spin–orbit interaction.Four closely packed helical traveling-wave nanoantennas(HTNs)are demonstrated to locally convert an incoming light beam into four beams of tunable polarizations and intensities,with the ability to impart different polarization states to the output beams in a controllable way.Moreover,by near-field coupling four HTNs of opposite handedness,we demonstrate a subwavelength waveplate-like structure providing a degree of freedom in polarization control that is unachievable with ordinary polarization optics and current metamaterials.

Design of high-speed and low-power finite-word-length PID controllers

ASIC or FPGA implementation of a finite word-length PID controller requires a double expertise： in control system and hardware design. In this paper, we only focus on the hardware side of the problem. We show how to design configurable fixed-point PIDs to satisfy applications requiring minimal power consumption, or high control-rate, or both together. As multiply operation is the engine of PID, we experienced three algorithms： Booth, modified Booth, and a new recursive multi-bit multiplication algorithm. This later enables the construction of finely grained PID structures with bit-level and unit-time precision. Such a feature permits to tailor the PID to the desired performance and power budget. All PIDs are implemented at register-transfer4evel （RTL） level as technology-independent reusable IP-cores. They are reconfigurable according to two compilemtime constants： set-point word-length and latency. To make PID design easily reproducible, all necessary implementation details are provided and discussed.

Rotorcraft with a 3DOF Rigid Manipulator:Quaternion-based Modeling and Real-time Control Tolerant to Multi-body Couplings

This paper proposes a simple solution for the stabilization of a mini-quadcopter carrying a 3DoF（degrees of freedom） manipulator robot in order to enhance its achievable workspace and application profile. Since the motion of the arm induces torques which degrade the stability of the system, in the present work, we consider the stabilization of both subsystems： the quadcopter and the robotic arm. The mathematical model of the system is based on quaternions. Likewise, an attitude control law consisting of a bounded quaternion-based feedback stabilizes the quadcopter to a desired attitude while the arm is evolving. The next stage is the translational dynamics which is simplified for control（nonlinear） design purposes. The aforementioned controllers are based on saturation functions whose stability is explicitly proved in the Lyapunov sense. Finally, experimental results and a statistical study validate the proposed control strategy.

Optimisation,design and characterisation of a piezoelectric micro suspension

A piezoelectric micro active suspension device has been developed for the application of active isolation of sensitive electronic devices such as frequency generators or inertial sensors.The developed strategy is based on a classical skyhook active damper but adapted and optimised to allow robust implementation onto an adaptive microelectromechanical systems(MEMS).The micro suspension is a silicon beam structure etched in a silicon on insulator(SOI)wafer and is equipped with a pair of piezoelectric transducers obtained from a lead zirconate titanante thin film sandwiched between pairs of electrodes.High performance transducers allow application of the active isolation strategy and demonstrate the possibility to implement skyhook damping with low-voltage control level.

Wafer-level vapor cells filled with laser-actuated hermetic seals for integrated atomic devices

Atomic devices such as atomic clocks and optically-pumped magnetometers rely on the interrogation of atoms contained in a cell whose inner content has to meet high standards of purity and accuracy.Glass-blowing techniques and craftsmanship have evolved over many decades to achieve such standards in macroscopic vapor cells.With the emergence of chip-scale atomic devices,the need for miniaturization and mass fabrication has led to the adoption of microfabrication techniques to make millimeter-scale vapor cells.However,many shortcomings remain and no process has been able to match the quality and versatility of glass-blown cells.Here,we introduce a novel approach to structure,fill and seal microfabricated vapor cells inspired from the century-old approach of glass-blowing,through opening and closing single-use zero-leak microfabricated valves.These valves are actuated exclusively by laser,and operate in the same way as the“make-seals”and“break-seals”found in the filling apparatus of traditional cells.Such structures are employed to fill cesium vapor cells at the wafer-level.The make-seal structure consists of a glass membrane that can be locally heated and deflected to seal a microchannel.The break-seal is obtained by breaching a silicon wall between cavities.This new approach allows adapting processes previously restricted to glass-blown cells.It can also be extended to vacuum microelectronics and vacuum-packaging of micro-electro-mechanical systems(MEMS)devices.

Artificial neural network aided real-time simulation of electric traction system

Real-time simulation-based validation plays an essential role in the early stage development of electric traction systems.The high-fidelity real-time simulation relies on the accurate modeling of the power electronics and motors and usually represents the nonlinear characteristics as many as possible while obeying the computing time constraints.In this paper,an artificial neural network(ANN)aided modeling approach is proposed for the field-programmable gate array(FPGA)-based real-time simulation to deal with the nonlinearities in permanent magnet synchronous motor(PMSM)and its drive.With the help of the ANN,the switches power losses,and the PMSM nonlinear flux linkage and electromagnetic torque can be modeled.An electro-thermal model of inverters and the finite element analysis(FEA)-based PMSM model are thus enabled in the FPGA-based real-time simulation,which can significantly improve the performances of the real-time simulation-based test bench.A two-level inverter fed PMSM drive system is modeled using the ANN-aided modeling approach and simulated in the National Instrument PXIe FlexRIO FPGA real-time system.The accuracy and effectiveness of the proposed approaches are tested and validated by comparing the results with the offline simulation tools.