Dual Time Scale Research Articles

NH<inline-formula> <tex-math notation="LaTeX">$_{3}$</tex-math> </inline-formula> Coverage Ratio Estimation of Diesel-Engine SCR Systems by a Dual Time-Scale Extended Kalman Filter

For the sake of reducing the computational load and enhancing the implementation possibility, a dual time-scale extended Kalman filter is developed in this paper. First, a conventional multistate mathematical selective catalytic reduction (SCR) model is simplified into a single-state SCR model. This simplification would reduce the computational cost a lot. Inspired by the fact that the variation of NH $_{3}$ coverage ratio between two cells changes relatively slow, then, the dual time-scale extended Kalman filter is proposed. The dual time-scales include one fast time-scale for the average NH $_{3}$ coverage ratio and a slow time-scale for the difference of NH $_{3}$ coverage ratios between the actual cell and the average value. In the dual time-scale scenario, it is unnecessary to estimate the NH $_{3}$ coverage ratio of each SCR cell every time. Finally, simulation results for a medium-duty diesel engine through the MATLAB/SIMULINK show the proposed method has good performance and lower computational load.

Detecting changes in dynamic and complex acoustic environments.

Natural sounds such as wind or rain, are characterized by the statistical occurrence of their constituents. Despite their complexity, listeners readily detect changes in these contexts. We here address the neural basis of statistical decision-making using a combination of psychophysics, EEG and modelling. In a texture-based, change-detection paradigm, human performance and reaction times improved with longer pre-change exposure, consistent with improved estimation of baseline statistics. Change-locked and decision-related EEG responses were found in a centro-parietal scalp location, whose slope depended on change size, consistent with sensory evidence accumulation. The potential's amplitude scaled with the duration of pre-change exposure, suggesting a time-dependent decision threshold. Auditory cortex-related potentials showed no response to the change. A dual timescale, statistical estimation model accounted for subjects' performance. Furthermore, a decision-augmented auditory cortex model accounted for performance and reaction times, suggesting that the primary cortical representation requires little post-processing to enable change-detection in complex acoustic environments.

A dual timescale active power coordinated scheduling framework for wind integrated power system in the presence of storage and wind forecast uncertainties

Summary This paper proposes a dual timescale active power coordinated scheduling framework to accommodate large scale wind power integration. This framework is composed of rolling scheduling, real-time scheduling and storage control. The optimization model of rolling scheduling policy is presented, which is activated every 30 min using the renewed forecast to modify the day-ahead scheduling curve. Also the optimization model of real-time scheduling is put forward, which is triggered every 15 min using the renewed forecast to modify the output of balance generators. In addition, the optimal storage control strategy is presented. The efficiency of the dual timescale active power coordinated scheduling framework is verified via the IEEE RTS bus system. Copyright © 2016 John Wiley & Sons, Ltd.

Time-dependent discrete road network design with both tactical and strategic decisions

This paper aims to model and investigate the discrete urban road network design problem, using a multi-objective time-dependent decision-making approach. Given a base network made up with two-way links, candidate link expansion projects, and candidate link construction projects, the problem determines the optimal combination of one-way and two-way links, the optimal selection of capacity expansion projects, and the optimal lane allocations on two-way links over a dual time scale. The problem considers both the total travel time and the total CO emissions as the two objective function measures. The problem is modelled using a time-dependent approach that considers a planning horizon of multiple years and both morning and evening peaks. Under this approach, the model allows determining the sequence of link construction, the expansion projects over a predetermined planning horizon, the configuration of street orientations, and the lane allocations for morning and evening peaks in each year of the planning horizon. This model is formulated as a mixed-integer programming problem with mathematical equilibrium constraints. In this regard, two multi-objective metaheuristics, including a modified non-dominated sorting genetic algorithm (NSGA-II) and a multi-objective B-cell algorithm, are proposed to solve the above-mentioned problem. Computational results for various test networks are also presented in this paper.

Degradation modeling of high temperature proton exchange membrane fuel cells using dual time scale simulation

Abstract HT-PEM fuel cells suffer from performance losses due to degradation effects. Therefore, the durability of HT-PEM is currently an important factor of research and development. In this paper a novel approach is presented for an integrated short term and long term simulation of HT-PEM accelerated lifetime testing. The physical phenomena of short term and long term effects are commonly modeled separately due to the different time scales. However, in accelerated lifetime testing, long term degradation effects have a crucial impact on the short term dynamics. Our approach addresses this problem by applying a novel method for dual time scale simulation. A transient system simulation is performed for an open voltage cycle test on a HT-PEM fuel cell for a physical time of 35 days. The analysis describes the system dynamics by numerical electrochemical impedance spectroscopy. Furthermore, a performance assessment is performed in order to demonstrate the efficiency of the approach. The presented approach reduces the simulation time by approximately 73% compared to conventional simulation approach without losing too much accuracy. The approach promises a comprehensive perspective considering short term dynamic behavior and long term degradation effects.

Diode-pumped Yb:CaF $$_2$$ 2 multipass amplifier producing 50 mJ with dynamic analysis for high repetition rate operation

The dynamic thermal issues of the Yb:CaF $$_{2}$$ crystals within a multi-tens-mJ-energy multipass amplifier operating in the 20–100 Hz repetition rate range and pumped in quasi-cw regime have been studied at different timescales. Thermal response times of the system have been precisely investigated and analyzed, for the first time to our best knowledge in such amplifiers. This study includes a dual timescale analysis: in the long-time-scale (second) with direct thermography mapping and in the millisecond range with thermal lensing in a pump-probe configuration. Very atypical positive lens behavior with fluorites will also be presented and discussed. This complete analysis is used to demonstrate the capability of $$\hbox {Yb:CaF}_{2}$$ multipass amplifier systems for operating the amplifier at 20 Hz with 57 mJ and 100 Hz with 32-mJ stable regime. Indeed, high repetition rate multipass amplifier has been realized for the first time with $$\hbox {Yb:CaF}_{2}$$ and for this energy. The results have been analyzed precisely to take into account the thermal issues and excellent beam quality, with a $$M^2$$ of 1.1. The pointing stability of 20 μrad has been measured documenting the reliability of the high repetition rate mJ amplifier.

Computation delay compensation for real time implementation of robust model predictive control

Abstract The implementation of model predictive control (MPC) requires to solve an optimization problem online. The computation time, often not negligible especially for nonlinear MPC (NMPC), introduces a delay in the feedback loop. Moreover, it impedes fast sampling rate setting for the controller to react to uncertainties quickly. In this paper, a dual time scale control scheme is proposed for linear/nonlinear systems with external disturbances. A pre-compensator works at fast sampling rate to suppress uncertainty, while the outer MPC controller updates the open loop input sequence at a slower rate. The computation delay is explicitly considered and compensated in the MPC design. Four robust MPC algorithms for linear/nonlinear systems in the literature are adopted and tailored for the proposed control scheme. The recursive feasibility and stability are rigorously analysed. Three simulation examples are provided to validate the proposed approaches.

On the KZK-type equation for modulated ultrasound fields

Abstract This study introduces a KZK-type model describing the nonlinear wave propagation due to “slowly” modulated ultrasound excitation, where the ratio between the (dominant) modulation frequency and the carrier frequency is o ( 1 ) . The model is relevant to a variety of diagnostic techniques where the acoustic radiation force, generated by a focused ultrasound beam, is used to palpate tissue locally within the focal region. An indispensable prerequisite for computing the acoustic radiation force, however, is a precise knowledge of the nonlinear wave field generated by the ultrasound transducer at hand. In this class of applications, the MHz carrier signal is commonly modulated with frequencies on the order of 10 2 ÷ 10 4 Hz which, in the context of the time-domain numerical algorithms, dramatically increases the computational effort necessary to simulate the nonlinear wave field. To alleviate the impediment, this study employs a dual time scale approach towards the development of an intermediate asymptotics solution that fits the gap between the quasi-static approximation and the full solution. Thus obtained modification of the KZK equation, which captures the leading effects of “slow” ultrasound modulation, lends itself to an effective computational treatment that makes use of suitable steady-state solutions. For generality, the asymptotic analysis deploys separate scaling parameters to describe the effects of diffraction and modulation, consequently allowing the model to (i) cover a wide range of transducer geometries, and (ii) be degenerated to the quasi-static approximation as one of its limiting cases. The formulation is accompanied by a set of numerical examples, which illustrate the applicability of the method to both “short” and “long” modulation envelopes while accounting for realistic (frequency-dependent) attenuation in a tissue.

Dual-Time Scale Photoinduced Electron Transfer from PbS Quantum Dots to a Molecular Acceptor

A combination of picosecond and microsecond transient absorption dynamics reveals the involvement of two mechanisms by which 1,4-benzoquinone (BQ) induces the decay of the excited state of PbS quantum dots (QDs): (i) electron transfer to BQ molecules adsorbed to the surfaces of PbS QDs and (ii) collisionally gated electron transfer to freely diffusing BQ. Together, these two mechanisms quantitatively describe the quenching of photoluminescence upon addition of BQ to PbS QDs in dichloromethane solution. This work represents the first quantitative study of a QD-ligand system that undergoes both adsorbed and collisionally gated photoinduced charge transfer within the same sample. The availability of a collisionally gated pathway improves the yield of electron transfer from PbS QDs to BQ by an average factor of 2.5 over that for static electron transfer alone.

Dual Time Stepping Algorithms With the High Order Harmonic Balance Method for Contact Interfaces With Fretting-Wear

Contact interfaces with dry friction are frequently used in turbomachinery. Dry friction damping produced by the sliding surfaces of these interfaces reduces the amplitude of bladed-disk vibration. The relative displacements at these interfaces lead to fretting-wear which reduces the average life expectancy of the structure. Frequency response functions are calculated numerically by using the multi-harmonic balance method (mHBM). The dynamic Lagrangian frequency-time method is used to calculate contact forces in the frequency domain. A new strategy for solving nonlinear systems based on dual time stepping is applied. This method is faster than using Newton solvers. It was used successfully for solving Nonlinear CFD equations in the frequency domain. This new approach allows identifying the steady state of worn systems by integrating wear rate equations a on dual time scale. The dual time equations are integrated by an implicit scheme. Of the different orders tested, the first order scheme provided the best results.

Attentional influences on the performance of secondary physical tasks during posture control

We examined the influence of attentional focus and cognitive load on motor performance in a dynamic stick balancing task during the maintenance of upright posture. Dynamical analyses of postural fluctuations revealed the existence of a drift and correct mechanism, with correlational structure reflecting the demands of the stick balancing task. In contrast, experimentally manipulated attentional foci (internal, external) did not influence the variability of postural or fingertip trajectories. However, dual-task cognitive stick balancing performance resulted in decreased variability of postural and fingertip time series. These results are discussed in the context of dual timescale models for posture control and stick balancing.

G-Quadruplex Folding Observed by two Photon Fluorescence Correlation Spectroscopy and Dual Time Scale

G-rich DNA sequences are known to fold upon addition of salt into a stacked well defined configuration called a quadruplex. A fluorescently labeled 5′-FAM −24-mer G-quadruplex sequence was used to explore the variation of diffusion coefficients at extremely low, low and high KCl concentrations. We found a shift in the diffusion coefficient of about 10μm2/sec toward faster diffusion from extremely low to high KCl concentrations. This shift can be related to the compact structure formed by the G-quadruplex. We have also used a fluorescent guanosine analog, 6MI, to label a 24mer that has shown folding behavior at high KCl concentrations. To explore this further, we have added in excess a sequence that complements the G-rich region to deter the formation of the G-quadruplex. The diffusion coefficient also increased from the unfolded, low KCl concentration to the high salt, G-quadruplex structure. We have constructed a dual-timescale (ps TCSPC and uS-mS FCS) photon correlation system and we are using it to explore linked changes in the fluorophores' lifetimes and the translational diffusion coefficients as they move between low and high salt environments. Part of this work was supported by NIH SCORE Grant S06 GM 060654.

Wavelet decomposed dual-time scale crystal plasticity FE model for analyzing cyclic deformation induced crack nucleation in polycrystals

A microstructure sensitive criterion for dwell fatigue crack initiation in polycrystalline alloys is proposed in this paper. Local stress peaks due to load shedding from time dependent plastic deformation fields in neighboring grains are responsible for crack initiation in dwell fatigue. A calibrated and experimentally validated crystal plasticity finite element model (CFEM) is employed for predicting slip system level stresses and strains. Vital microstructural features related to the grain morphology and crystallographic orientations are accounted for in the FEM by construction of microstructures that are statistically equivalent to those observed in OIM scans. The output of the FEM is used to evaluate the crack initiation condition in the post processing stage. The functional form of the criterion is motivated from the similarities in the stress fields and crack evolution criteria ahead of a crack tip and dislocation pile-up. A specific model is developed for estimating the pile-up length necessary for the nucleation criterion using the notion of geometrically necessary dislocations. The crack nucleation criterion is calibrated and validated by using experimental data obtained from ultrasonic crack monitoring techniques. In order to be able to model a large number of cycles to failure initiation, a dual-time scaling algorithm is proposed using wavelet induced decomposition. The algorithm decouples the governing equations into two sets of problems corresponding to two different time scales. One is a long time scale (low frequency) problem characterizing a cycle-averaged solution, while the other is a short time scale (high frequency) problem for a remaining oscillatory portion. The method significantly reduces the computational time till crack initiation.

Dual-time scale crystal plasticity FE model for cyclic deformation of Ti alloys

A dual-time scale finite element model is developed in this paper for simulating cyclic deformation in a Titanium alloy Ti-6242. The material is characterized by crystal plasticity constitutive relations. Modeling cyclic deformation using conventional time integration algorithms in a single time scale can be prohibitive for crystal plasticity computations. Typically 3D crystal plasticity based fatigue simulations found in the literature are in the range of 100 cycles. Results are subsequently extrapolated to thousands of cycles, which can lead to considerable error in fatigue predictions. However, the dual-time scale model enables simulations up to a significantly high number of cycles to reach local states of damage initiation leading to fatigue crack growth. This formulation decomposes the governing equations into two sets of problems, corresponding to a coarse time scale (low frequency) cycle-averaged problem and a fine time scale (high frequency) oscillatory problem. A statistically equivalent 3D polycrystalline model of Ti-6242 is simulated by the crystal plasticity finite element model to study the evolution of local stresses and strains in the microstructure with cyclic loading. The comparison with the single time scale reference solution shows excellent accuracy while the efficiency gained through time-scale compression can be enormous.

A fast photoswitch for minimally perturbed peptides: investigation of the trans-->cis photoisomerization of N-methylthioacetamide.

Thio amino acids can be integrated into the backbone of peptides without significantly perturbing their structure. In this contribution we use ultrafast infrared and visible spectroscopy as well as state-of-the-art ab initio computations to investigate the photoisomerization of the trans form of N-methylthioacetamide (NMTAA) as a model conformational photoswitch. Following the S2 excitation of trans-NMTAA in water, the return of the molecule into the trans ground state and the formation of the cis isomer is observed on a dual time scale, with a fast component of 8-9 ps and a slow time constant of approximately 250 ps. On both time scales the probability of isomerization to the cis form is found to be 30-40%, independently of excitation wavelength. Ab initio CASPT2//CASSCF photochemical reaction path calculations indicate that, in vacuo, the trans-->cis isomerization event takes place on the S1 and/or T1 triplet potential energy surfaces and is controlled by very small energy barriers, in agreement with the experimentally observed picosecond time scale. Furthermore, the calculations identify one S2/S1 and four nearly isoenergetic S1/S0 conical intersection decay channels. In line with the observed isomerization probability, only one of the S1/S0 conical intersections yields the cis conformation upon S1-->S0 decay. A substantially equivalent excited-state relaxation results from four T1/S0 intersystem crossing points.

Reusable Launch Vehicle Control in Multiple-Time-Scale Sliding Modes

A reusable launch vehicle control problem during ascent is addressed via multiple-time scaled continuous sliding mode control. The proposed sliding mode controller utilizes a two-loop structure and provides robust, de-coupled tracking of both orientation angle command profiles and angular rate command profiles in the presence of bounded external disturbances and plant uncertainties. Sliding mode control causes the angular rate and orientation angle tracking error dynamics to be constrained to linear, de-coupled, homogeneous, and vector valued differential equations with desired eigenvalues placement. Overall stability of a two-loop control system is addressed. An optimal control allocation algorithm is designed that allocates torque commands into end-effector deflection commands, which are executed by the actuators. The dual-time scale sliding mode controller was designed for the X-33 technology demonstration sub-orbital launch vehicle in the launch mode. Simulation results show that the designed controller provides robust, accurate, de-coupled tracking of the orientation angle command profiles in presence of external disturbances and vehicle inertia uncertainties. This is a significant advancement in performance over that achieved with linear, gain scheduled control systems currently being used for launch vehicles.

Nonlinear optical effects in chalcogenide photoresists

Both the “after-pulse effect” and the dynamic characteristics of photostructural transformations induced in glassy As0.5Se0.5 films by pulsed 532 nm excitation have been studied. The after-pulse effect investigation demonstrated more than a 103 times increase of the photosensitivity in case of pulsed excitation. Dynamic characteristics showed a dual time scale behavior and different intensity dependence of transient and long time scale signals. The obtained data indicate that the strong increase of photosensitivity following short intense pulsed light excitation is due to a two-photon effect that aids the process of structural rearrangement.

Numerical simulation of atmospheric dispersion in an urban site: Comparison with field data

This paper presents numerical simulations of tracer gas experiments performed at Porte Maillot in Paris. The Reynolds-averaged Navier-Stokes equations, combined with the dual-time scale k -epsilon turbulence model of Chen and Kim, are solved using the finite-volume code PHOENICS. Good agreement with in situ measurements is obtained. The effects of turbulence modelling, numerical diffusion, boundary conditions, turbulence and drag forces generated by traffic are investigated.

Ground and satellite observations of postdawn aurorae near the time of a sudden storm commencement

Meridian scanning photometer measurements taken in the magnetic postdawn sector at Longyearbyen, Svalbard, between 0300 and 0630 UT on December 29, 1981, are analyzed in conjunction with particle and field data retrieved during two near passes of the Dynamics Explorer 2 (DE 2) satellite. The interval included a sudden storm commencement (SSC) at 0455 UT. Pre‐SSC optical and particle measurements showed a system of arcs that are spaced at ∼1.1° intervals in magnetic latitude, embedded within the region 1 current system and span the convection reversal. The softer particle precipitation appears to have a source near the flanks of the magnetotail while the harder, more equatorward precipitation originates closer to Earth. During the SSC period the entire sky brightened, with enhanced 630.0‐nm emissions extending from the northern horizon to south of magnetic zenith; intense but spatially separated 557.7‐nm emissions dominated the southern horizon. DE 2 detected more than an order of magnitude increase and near isotropization of ring current electron fluxes, enhanced precipitation from the plasma sheet and significantly decreased auroral zone convection. Region 1/region 2 currents remained, with wavelike structures superposed. A dual timescale response to the SSC is consistent with ground and satellite measurements. On few minute travel timescales for hydromagnetic waves to pass through the system, magnetospheric particles accelerate and precipitate to increase the ionospheric conductivity. Global, field‐aligned currents change more slowly. To maintain similar field‐aligned currents with higher ionospheric conductances requires reduced electric fields. After 0520 UT the optical emissions settled into stable, but latitudinally separated, bands of 630.0‐ and 557.7‐nm emissions characteristic of cleft and plasma sheet precipitation, respectively.

Modulational instability of finite amplitude dispersive Alfvén waves

The stability of a finite amplitude plane monochromatic circularly polarized Alfvén wave is studied by using an approximate two‐fluid model obtained by performing an amplitude and dual time scale expansion in which temporal changes, observed when moving with the wave, are assumed slow. The lowest order dispersive effects and coupling terms to sound waves are of the same order. A large‐amplitude Alfvén wave obeying an approximate dispersion relation is an exact solution of the resulting model equations. Small perturbations of this solution consisting of two sideband Alfvén waves and a sound wave are then introduced. The resulting dispersion relation, which is of fourth order, is examined analytically for small wave amplitudes of the parent wave. It reveals different regions of stability and instability in a plot of wave number k0 of the unperturbed wave versus β0, the ratio of sound speed to Alfvén speed. For long wave lengths, the left‐hand polarized mode is found to be stable for β0 > 1 and the right‐hand polarized mode for β0 < 1. Modulational instability of the former mode occurs for β0 < 1 and of the latter for β0 > 1. Decay instability is predicted near β0 = 0 and β0 = 1. Formulas for growth rates and unstable wave number bands are given.