Large Time Window Research Articles

Unaffected Memory and Inhibitory Functioning Several Weeks Postpartum in Women with Pregnancy Complicated by Preeclampsia.

Several studies reported impaired cognitive functioning after pregnancy complicated by preeclampsia. The present study examined cognitive and executive functioning in women with preeclampsia at a time at which immediate effects of gestation have resolved, brain damage due to other risk factors have not yet manifested, and impairments may thus primarily occur as a result of the huge stress induced by the potentially life threatening condition. Verbal learning/memory (California Verbal Learning Test) and inhibitory functioning (Mittenecker Pointing Test) of 35 women with preeclampsia and 38 women with uncomplicated pregnancy were followed over five measurement time points during the period from 16 to 48 weeks postpartum. A further control group comprised 40 women with no history of recent pregnancy. The groups did not differ in their verbal learning/memory performance. Higher levels of currently experienced everyday-life stress were associated with poorer inhibitory control/greater stereotypy in responding, but this effect was not directly connected with pregnancy complications. Taken together, the findings do not indicate rapid-onset cognitive impairment after preeclampsia, brought about by its extremely stressful nature or other factors that take effect during gestation. Deficits observed in later life may develop on a long-term basis through late-diagnosed hypertension and unfavorable lifestyle factors. The large time window in which exaggerated cognitive decline can be prevented or mitigated should be utilized for the control of risk factors and interventions to improve lifestyle where appropriate.

Optimization of Electrooptical Sampling of THz Pulse With a Chirped Broadband Probe Pulse in Thick EO Crystal

Electrooptic (EO) sampling is a method in THz time-domain spectroscopy. In previous studies, a thick EO crystal with a broadband probe pulse is used to meet the requirements of THz detection with a large time window and high-precision frequency spectrum. However, the broadband probe pulses are significantly broadened in the time domain during the transmission in thick EO crystals due to group velocity dispersion, which distorts the EO signal. In this article, a negative prechirp of broadband (10 fs in full-width at half-maximum) laser pulse is utilized to compensate the dispersion and enhances the detected signals. In the experiments, we use an interdigital photoconductive antenna to generate typical THz pulses in the region of 0.1-3 THz. The measurement results confirm that the prechirp of -2100 fs <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> is more effective to optimize the detected signals in ZnTe crystal with a thickness of 3 mm and enhances the EO signal by 71%, and the frequency redshift caused by the filter effect of the electrooptical response function is decreased. Meanwhile, the experimental results show that the enhancements of different prechirps depend on the frequency components of THz pulses and the frequency-dependent optimization of EO sampling is effective, which is consistent with the simulation results. This technique is helpful to optimize the EO sampling in thick ZnTe crystals to obtain the large time window and higher signal-to-noise ratio of EO sampling.

Photonic RF and Microwave Integrator Based on a Transversal Filter With Soliton Crystal Microcombs

We demonstrate a photonic RF integrator based on an integrated soliton crystal microcomb source. By multicasting and progressively delaying the input RF signal using a transversal structure, the input RF signal is integrated discretely. Up to 81 wavelengths are provided by the microcomb source, which enable a large integration time window of 6.8 ns, together with a time resolution as fast as 84 ps. We perform signal integration of a diverse range of input RF signals including Gaussian pulses with varying time widths, dual pulses with varying time intervals and a square waveform. The experimental results show good agreement with theory. These results verify our microcomb-based integrator as a competitive approach for RF signal integration with high performance and potentially lower cost and footprint.

Modeling latent infection transmissions through biosocial stochastic dynamics.

The events of the recent SARS-CoV-2 epidemics have shown the importance of social factors, especially given the large number of asymptomatic cases that effectively spread the virus, which can cause a medical emergency to very susceptible individuals. Besides, the SARS-CoV-2 virus survives for several hours on different surfaces, where a new host can contract it with a delay. These passive modes of infection transmission remain an unexplored area for traditional mean-field epidemic models. Here, we design an agent-based model for simulations of infection transmission in an open system driven by the dynamics of social activity; the model takes into account the personal characteristics of individuals, as well as the survival time of the virus and its potential mutations. A growing bipartite graph embodies this biosocial process, consisting of active carriers (host) nodes that produce viral nodes during their infectious period. With its directed edges passing through viral nodes between two successive hosts, this graph contains complete information about the routes leading to each infected individual. We determine temporal fluctuations of the number of exposed and the number of infected individuals, the number of active carriers and active viruses at hourly resolution. The simulated processes underpin the latent infection transmissions, contributing significantly to the spread of the virus within a large time window. More precisely, being brought by social dynamics and exposed to the currently existing infection, an individual passes through the infectious state until eventually spontaneously recovers or otherwise is moves to a controlled hospital environment. Our results reveal complex feedback mechanisms that shape the dependence of the infection curve on the intensity of social dynamics and other sociobiological factors. In particular, the results show how the lockdown effectively reduces the spread of infection and how it increases again after the lockdown is removed. Furthermore, a reduced level of social activity but prolonged exposure of susceptible individuals have adverse effects. On the other hand, virus mutations that can gradually reduce the transmission rate by hopping to each new host along the infection path can significantly reduce the extent of the infection, but can not stop the spreading without additional social strategies. Our stochastic processes, based on graphs at the interface of biology and social dynamics, provide a new mathematical framework for simulations of various epidemic control strategies with high temporal resolution and virus traceability.

Autonomous Navigation of a Solar-Powered UAV for Secure Communication in Urban Environments with Eavesdropping Avoidance

This paper considers the navigation of a solar-powered unmanned aerial vehicle (UAV) for securing the communication with an intended ground node in the presence of eavesdroppers in urban environments. To complete this task, the UAV needs to not only fly safely in the complex urban environment, but also take into account the communication performance with the intended node and eavesdroppers. To this end, we formulate a multi-objective optimization problem to plan the UAV path. This problem jointly considers the maximization of the residual energy of the solar-powered UAV at the end of the mission, the maximization of the time period in which the UAV can securely communicate with the intended node and the minimization of the time to reach the destination. We pay attention to the impact of the buildings in the urban environments, which may block the transmitted signals and also create some shadow region where the UAV cannot harvest energy. A Rapidly-exploring Random Tree (RRT) based path planning scheme is presented. This scheme captures the nonlinear UAV motion model, and is computationally efficient considering the randomness nature. From the generated tree, a set of possible paths can be found. We evaluate the security of the wireless communication, compute the overall energy consumption as well as the harvested amount for each path and calculate the time to complete the flight. Compared to a general RRT scheme, the proposed method enables a large time window for the UAV to securely transmit data.

Anomalous dynamics on the ergodic side of the many-body localization transition and the glassy phase of directed polymers in random media

Using the non-interacting Anderson tight-binding model on the Bethe lattice as a toy model for the many-body quantum dynamics, we propose a novel and transparent theoretical explanation of the anomalously slow dynamics that emerges in the bad metal phase preceding the Many-Body Localization transition. By mapping the time-decorrelation of many-body wave-functions onto Directed Polymers in Random Media, we show the existence of a glass transition within the extended regime separating a metallic-like phase at small disorder, where delocalization occurs on an exponential number of paths, from a bad metal-like phase at intermediate disorder, where resonances are formed on rare, specific, disorder dependent site orbitals on very distant generations. The physical interpretation of subdiffusion and non-exponential relaxation emerging from this picture is complementary to the Griffiths one, although both scenarios rely on the presence of heavy-tailed distribution of the escape times. We relate the dynamical evolution in the glassy phase to the depinning transition of Directed Polymers, which results in macroscopic and abrupt jumps of the preferred delocalizing paths when a parameter like the energy is varied, and produce a singular behavior of the overlap correlation function between eigenstates at different energies. By comparing the quantum dynamics on loop-less Cayley trees and Random Regular Graphs we discuss the effect of loops, showing that in the latter slow dynamics and apparent power-laws extend on a very large time-window but are eventually cut-off on a time-scale that diverges at the MBL transition.

Traction Forces Control Cell-Edge Dynamics and Mediate Distance Sensitivity during Cell Polarization.

Traction forces are generated by cellular actin-myosin system and transmitted to the environment through adhesions. They are believed to drive cell motion, shape changes, and extracellular matrix remodeling [1-3]. However, most of the traction force analysis has been performed on stationary cells, investigating forces at the level of individual focal adhesions or linking them to static cell parameters, such as area and edge curvature [4-10]. It is not well understood how traction forces are related to shape changes and motion, e.g., forces were reported to either increase or drop prior to cell retraction [11-15]. Here, we analyze the dynamics of traction forces during the protrusion-retraction cycle of polarizing fish epidermal keratocytes and find that forces fluctuate together with the cycle, increasing during protrusion and reaching maximum at the beginning of retraction. We relate force dynamics to the recently discovered phenomenological rule [16] that governs cell-edge behavior during keratocyte polarization: both traction forces and probability of switch from protrusion to retraction increase with the distance from the cell center. Diminishing forces with cell contractility inhibitor leads to decreased edge fluctuations and abnormal polarization, although externally applied force can induce protrusion-retraction switch. These results suggest that forces mediate distance sensitivity of the edge dynamics and organize cell-edge behavior, leading to spontaneous polarization. Actin flow rate did not exhibit the same distance dependence as traction stress, arguing against its role in organizing edge dynamics. Finally, using a simple model of actin-myosin network, we show that force-distance relationship might be an emergent feature of such networks.

Time-delay signature characteristics of the chaotic output from an optoelectronic oscillator by introducing an optical feedback.

In this work, via autocorrelation function (ACF) and permutation entropy (PE) methods, we numerically investigate the time-delay signature (TDS) characteristics of the chaotic signal output from an optoelectronic oscillator (OEO) after introducing an extra optical feedback loop. The results demonstrate that, for such a chaotic system, both the optoelectronic feedback with a delay time of T1 and the optical feedback with a delay time of T2 contribute to the TDS of generated chaos. The TDS of the chaotic signal should be evaluated within a large time window including T1 and T2 by the strongest peak in the ACF curve of the chaotic signal, and the strongest peak may locate at near T1 or T2. Through mapping the evolution of the TDS in the parameter space of the optical feedback strength and time, certain optimized parameter regions for achieving a chaotic signal with a relatively weak TDS can be determined.

Longitudinal wave propagation in one-dimensional waveguides with sinusoidally varying depth

In this paper, longitudinal elastic wave propagation in one-dimensional waveguides with sinusoidally varying depth is investigated. Furthermore, different types of such waveguide designs are explored to understand their capability to attenuate the group speeds as well as the velocity amplitudes. The plane waveguide configurations with sinusoidally varying depth, of three types, namely Convex, Concave and Full, along with their combinations and variants, whose segmental depth along the length of the waveguide is modeled by a sine function having an amplitude parameter α and the half-period p, which leads to a governing differential equation with variable coefficients, are considered in this study. To study the longitudinal wave propagation in these inhomogenous waveguides, a novel superconvergent finite element formulation is developed, which gives an exact stiffness matrix. In addition to the wave propagation analysis, static and free vibration behaviors in these waveguides are also studied. The implemented superconvergent finite element formulation for these studies is validated with the commercial finite element software Abaqus. In the first part of the wave propagation analysis, abilities of the three plane waveguide configurations with sinusoidally varying depth to attenuate high amplitude and frequency waves are investigated for different values of α. Next, four different waveguides composed of Convex-Concave combinations are studied with an aim to get better attenuation. Following this, the waveguides' segmental parameters, α and p, are varied across the segments along the length of the waveguide, using a sine function and polynomial power law to see if such graded variations give better energy absorption properties compared to the plane waveguides whose parameters are unvarying. In the last part, a developed inhomogenous rod of a certain length is inserted in the middle of a uniform waveguide to study the possibility of changing the longitudinal wave propagation characteristics of the uniform waveguide. The results from the analyses show that the group speed and amplitude of the longitudinal wave in these configurations change significantly with space as well as with frequencies, especially for high values of α. The Concave and Full waveguides delay the propagation of longitudinal waves significantly, which translates into the reflected waves appearing later in the chosen large time window. The Convex waveguide and its variants reduce the wave amplitudes significantly. Building on these results, some waveguides with notable attenuation characteristics are proposed.

Serrated Behaviors and Plasticity of Nb-Alloyed Cu-Based Bulk Metallic Glasses

This paper is to disclose the plastic deformation mechanism of 3 Nb-alloyed bulk metallic glasses and composites via the analysis of serration dynamics. The as-cast alloys with 1.0 at% and 2.0 at% of Nb element display the large time window of serrated events, implying that the serrated behavior can dynamically retain in a long-time scale and thus the alloys are endowed the largest compressive plasticity. The statistic results suggest that the serrated flow of both alloys with 1.0 at% and 2.0 at% Nb element achieves the self-organized critical state. The normal probability plots were utilized to further evaluate serrated dynamics and demonstrate that large deviations from the mean value of stress drops facilitate the self-organized critical state of serrations. This work suggests that large plastic bulk metallic glasses and composites are characterized by non-normal probability of serration statistics during plastic deformation.

Prediction of Flares within 10 Days before They Occur on the Sun

Abstract Prediction of solar flares due to the effects on Earth and satellites is an important topic for scientists. We develop a method and a tool for flare prediction by applying the support vector machine classifier to unique and independent Zernike moments extracted from active region (AR) images. In the analysis, we used the Helioseismic and Magnetic Imager (HMI) line-of-sight magnetograms, the Atmospheric Imaging Assembly (AIA) ultraviolet (UV at 1600 Å) and extreme ultraviolet (EUV at 304, 171, 193, 211, 335, 94, and 131 Å) images for a period of eight years of the solar cycle 24 (2010 June to 2018 September). The power-law behavior for the frequency distribution of the large flaring time window—the time interval between the occurrence of an AR and first large flare (X- and M-class) therein—indicated that most of the large flares appeared within 150 hr. The True Skill Score (TSS) metric for the performance of the win classifier that (uses the outputs of the HMI and AIA at 193, 211, 94, and 131 Å classifiers) was obtained as 0.86 ± 0.04. We also showed that the maximum value of the TSS for prediction of large flares for the win classifiers was about 0.95 ± 0.03 on the flaring day and decreased to 0.76 ± 0.1 within 4 to 10 days before flaring.

Dealing with Cu reduction in X-ray absorption spectroscopy experiments.

In this paper we prove in the exemplary case of the amyloid-β peptide in complex with Cu(ii) that at the current low temperatures employed in XAS experiments, the time needed for collecting a good quality XAS spectrum is significantly shorter than the time after which structural damage becomes appreciable. Our method takes advantage of the well-known circumstance that the transition of Cu from the oxidized to the reduced form under ionizing radiation can be quantified by monitoring a characteristic peak in the pre-edge region. We show that there exists a sufficiently large time window in which good XAS spectra can be acquired before the structure around the oxidized Cu(ii) ion reorganizes itself into the reduced Cu(i) "resting" structure. We suggest that similar considerations apply to other cases of biological interest, especially when dealing with macromolecules in complex with transition metal ions.

Keldysh field theory of a driven dissipative Mott insulator: Nonequilibrium response and phase transitions

Understanding strongly correlated systems driven out of equilibrium is a challenging task necessitating the simultaneous treatment of quantum mechanics,dynamical constraints and strong interactions. A Mott insulator subjected to a uniform and static electric field is prototypical, raising key questions such as the fate of Bloch oscillations with increasing correlation strength, the approach to a steady state DC transport regime and the role of dissipation in it, and electric field driven phase transitions. We develop here an effective large-N Keldysh field theory for studying nonequilibrium transport in a regular one-dimensional dissipative Mott insulator system subjected to a uniform electric field. Upon abruptly turning on the electric field (a quench), a transient oscillatory current response reminiscent of Bloch oscillations is found. In the regime of small tunneling conductance the amplitude of these oscillations, over a large time window, decreases as an inverse square power-law in time, ultimately going over to an exponential decay beyond a large characteristic time that increases with N. Such a relaxation to a steady state DC response is absent in the dissipation free Hubbard chain at half filling. The steady state current at small fields is governed by large distance cotunneling, a process absent in the equilibrium counterpart. The low-field DC current has a Landau-Zener-Schwinger form but qualitatively differs from the expression for pair-production probability for the dissipation free counterpart. The breakdown of perturbation theory in the Mott phase possibly signals a nonequilibrium phase transition to a metallic phase. Our study sheds light on the approach of a driven, dissipative strongly correlated system to a nonequilibrium steady state and also provides a general analytic microscopic framework for understanding other nonequilibrium phenomena in these systems.

High performance Fe-based nanocrystalline alloys with excellent thermal stability

Fe-based alloys are an important soft magnetic material that plays a pivotal role in a variety of energy-related industrial applications, such as electric transformers, motors and converters. However, the trade-off between magnetic softness and saturation magnetization (Bs) has been hindering the development of next-generation Fe-based soft magnetic materials. In this work, we demonstrate a facile route to obtain nanostructured Fe-based alloy out of a marginal glass former, which exhibits a core-shell like nanostructure and a synergetic increase of Bs, magnetic permeability (μe) and hardness upon thermal annealing, giving rise to a unique combination of Bs > 1.83 T, μe ∼25000 and ultrahigh hardness of ∼15 GPa. In terms of the combined magnetic/mechanical properties, the nanostructured Fe-based alloy outperforms the variety of Fe-based soft magnetic alloys hitherto reported. Furthermore, compared to the existing high performance soft magnetic Fe-based nanocrystalline alloys, the core-shell like nanostructure in our Fe-based nanocrystalline alloy displays an excellent thermal stability, which offers a large time window which would facilitate materials processing for future large-scale industrial production.

Quantum-beat photoelectron-imaging spectroscopy of Xe in the VUV

Time-resolved pump-probe measurements of Xe, pumped at 133~nm and probed at 266~nm, are presented. The pump pulse prepared a long-lived hyperfine wavepacket, in the Xe $5p^5(^2P^{\circ}_{1/2})6s~^2[1/2]^{\circ}_1$ manifold ($E=$77185 cm$^{-1}=$9.57 eV). The wavepacket was monitored via single-photon ionization, and photoelectron images measured. The images provide angle- and time-resolved data which, when obtained over a large time-window (900~ps), constitute a precision quantum beat spectroscopy measurement of the hyperfine state splittings. Additionally, analysis of the full photoelectron image stack provides a quantum beat imaging modality, in which the Fourier components of the photoelectron images correlated with specific beat components can be obtained. This may also permit the extraction of isotope-resolved photoelectron images in the frequency domain, in cases where nuclear spins (hence beat components) can be uniquely assigned to specific isotopes (as herein), and also provides phase information. The information content of both raw, and inverted, image stacks is investigated, suggesting the utility of the Fourier analysis methodology in cases where images cannot be inverted.

Terahertz Electro-Optic Sampling in Thick ZnTe Crystals Below the Reststrahlen Band With a Broadband Femtosecond Laser

The method of electro-optic (EO) sampling of terahertz (THz) pulses in thick EO crystals leads to waveform distortions due to effects of phase mismatch, dispersive propagation, and absorption. In this paper, we demonstrate theoretically and experimentally that EO sampling with a broadband femtosecond (fs) laser could significantly eliminate these distortions below the Reststrahlen band. Our simulation results show that the oscillations and dips in the signals of EO response function of thick crystals are smoothed out by the broadband spectrum of the femtosecond laser. In the experiment, we use a laser with a bandwidth of 100 nm and a low temperature GaAs photoconductive antenna to generate typical THz pulses (0.1–3 THz). The measurement results confirm that a $\langle {110} \rangle $ -oriented 3-mm-thick ZnTe crystal is an attractive EO material for sampling THz pulse below 3 THz and agree with simulation results. This technique is particularly useful in areas where a large time window is needed, for example in the THz time-domain spectroscopy system.

Long-Term Event Processing over Data Streams in Cyber-Physical Systems

Event processing is a crucial cornerstone supporting the revolution of Internet of Things (IoT) and Cyber-Physical Systems (CPS) by integrating physical-layer networking and providing intelligent computation and real-time control abilities. In various IoT and CPS application scenarios, the event processing systems are required to detect complex event patterns using large time window, namely long-term events. The detection of long-term event usually leads to a large number of redundant runtime instances and calculations that significantly deteriorates the system efficiency. In this article, we propose an efficient long-term event processing model, named Long-Term Complex Event Processing (LTCEP). It leverages the semantic constraints calculus to split long-term event into sub-models. We establish a long-term query and intermediate result buffering mechanism to optimize the real-time response ability and throughput performance. Experimental results show that LTCEP can effectively reduce more than 50% redundant runtime states, which provides over 60% faster response performance and around 30% higher system throughput comparing to other selected benchmarks. The results also imply that LTCEP model has better stability and scalability in large-scale event processing applications.

Experimental study on measuring pulse duration in the far field for high-energy petawatt lasers.

We study the feasibility of measuring pulse duration in the far field in high-energy petawatt lasers using single-shot autocorrelation. This single-shot autocorrelation technique makes use of parametric upconversion in media with randomly oriented ferroelectric domains, which supports transverse second-harmonic generation with two counter-propagating fundamental beams. We show that this technique possesses a large time window, capable of measuring pulses with temporal duration ranging from a sub-picosecond to tens of picoseconds. We test the performance of this technique in the presence of multipulse structures, intensity modulations in the near field, and spatial-temporal coupling in fundamental beams. We also investigate the influence of beam pointing discrepancy on the measurement. Our study can serve as a preliminary experiment for robustly characterizing pulse duration in high-energy petawatt lasers.

Activity statistics in a colloidal glass former: Experimental evidence for a dynamical transition.

In a dense colloidal suspension at a volume fraction below the glass transition, we follow the trajectories of an assembly of tracers over a large time window. We define a local activity, which quantifies the local tendency of the system to rearrange. We determine the statistics of the time integrated activity, and we argue that it develops a low activity tail that comes together with the onset of glassy-like behavior and heterogeneous dynamics. These rare events may be interpreted as the reflection of an underlying dynamic phase transition.

Studies on Fabrication and Reliability of GaN High-Resistivity-Cap-Layer HEMT

In this paper, we systematically investigate the effect of hydrogen plasma treatment radio frequency (RF) power, treatment time, and rapid thermal annealing (RTA) on the performance of high-resistivity-cap-layer high-electron-mobility-transistor (HRCL-HEMT). It is found that high RF power contributes to obtain high drain current, but induces more damage. An appropriate RTA process not only can repair the plasma damage but also improves the static characteristics of HRCL-HEMT. Subsequently, a large hydrogen plasma treatment time window of 4 min is demonstrated with an optimized RF power of 2 W and RTA at 350 °C for 5 min. Furthermore, the thermal stability of the optimized HRCL-HEMT is investigated by high temperature test and long-term thermal stress test. No obvious degradation of ${V}_{\text {TH}}$ , ${I}_{G}$ , ${R}_{\text {SH}}$ , and dynamic ${R}_{ \mathrm{\scriptscriptstyle ON}}$ is observed in both before and after passivation devices after 1000-h thermal stress. Finally, gate reliability of the HRCL-HEMT is also analyzed by time-to-failure test. The maximum gate voltage is determined to be 6.28 V for a ten-year lifetime with a failure rate of 1% at 25 °C.