Temporal Shape Research Articles

Effect of Dual-Pulse Temporal Shaping on Ultraviolet Nanosecond Laser Damage of Fused Silica Surface in High Fluence Regime

We present the effect of dual-pulse temporal shaping on the ultraviolet nanosecond laser damage characteristics of a fused silica exit surface in a high fluence regime. The pre- and post-pulse have the opposite effects on the damage behavior at a pulse delay of 20 ns. The pre-pulse irradiation significantly increases the main-pulse threshold, making it much higher than that of the single-pulse threshold, while the post-pulse has little effect on the main-pulse threshold. For near-threshold damage sites, the pre-pulse reduces the average damage size and depth, making them smaller than those of the single-pulse, while the post-pulse drastically increases the average size and depth, making them much larger than those of the single-pulse. The average size of the damage site is monotonously increased from 43.6 µm to 127.9 µm with increasing post-pulse energy. For the pre-pulse with a shape factor of 0.61, the damage threshold of the main pulse increases with increasing delay and nearly stabilizes after 10 ns. The underlying mechanism of the temporal-shaping effect on laser damage is discussed based on the applied precursor modification to absorption enhancement, which could provide insights for studying ultraviolet laser damage of fused silica optics.

Magnetized plasma pressure filaments: Analysis of chaotic and intermittent transport events driven by drift-Alfvén modes

The origin of intermittent fluctuations in an experiment involving several interacting electron plasma pressure filaments in close proximity, embedded in a large linear magnetized plasma device, is investigated. The probability density functions of the fluctuations on the inner and outer gradient of the filament bundle are non-Gaussian and the time series contain uncorrelated Lorentzian pulses that give the frequency power spectral densities an exponential shape. A cross-conditionally averaged spatial reconstruction of a temporal event reveals that the intermittent character is caused by radially and azimuthally propagating turbulent structures with transverse spatial scales on the order of the electron skin depth. These eruption events originate from interacting pressure gradient-driven drift-Alfvén instabilities on the outer gradient and edge of the filament bundle. The temporal Lorentzian shape of the intermittent structures and exponential spectra are suggestive of deterministic chaos in the underlying dynamics; this conclusion is supported by the complexity–entropy analysis (CH-plane) that shows the experimental time series are located in the chaotic regime.

Simple or complex: How temporal landmarks shape consumer preference for food packages

Food packaging, serving as a means of marketing communication, can be presented in a simple or complex format. This work investigated the effect of start temporal landmarks (i.e., marks denoting the beginning of a period) versus end temporal landmarks (i.e., marks signaling the closure of a period) on consumers’ preferences for food packages. Three studies demonstrated that priming a start temporal landmark leads to a greater preference for food packages with simple imagery (i.e., minimalist aesthetics). In contrast, priming an end temporal landmark increases consumers’ preferences for food packages with complex imagery (i.e., ornate aesthetics). In addition, we identified an underlying mechanism in which the need for arousal mediates the impact of temporal landmarks on preference for food packages. Beyond a set of managerial implications, our findings also provide novel insights into temporal perceptions, minimalist aesthetics, and product packages.

The terroir of the finch: How spatial and temporal variation shapes phenotypic traits in DARWIN'S finches.

The term terroir is used in viticulture to emphasize how the biotic and abiotic characteristics of a local site influence grape physiology and thus the properties of wine. In ecology and evolution, such terroir (i.e., the effect of space or “site”) is expected to play an important role in shaping phenotypic traits. Just how important is the pure spatial effect of terroir (e.g., differences between sites that persist across years) in comparison to temporal variation (e.g., differences between years that persist across sites), and the interaction between space and time (e.g., differences between sites change across years)? We answer this question by analyzing beak and body traits of 4388 medium ground finches (Geospiza fortis) collected across 10 years at three locations in Galápagos. Analyses of variance indicated that phenotypic variation was mostly explained by site for beak size (η 2 = 0.42) and body size (η 2 = 0.43), with a smaller contribution for beak shape (η 2 = 0.05) and body shape (η 2 = 0.12), but still higher compared to year and site‐by‐year effects. As such, the effect of terroir seems to be very strong in Darwin's finches, notwithstanding the oft‐emphasized interannual variation. However, these results changed dramatically when we excluded data from Daphne Major, indicating that the strong effect of terroir was mostly driven by that particular population. These phenotypic results were largely paralleled in analyses of environmental variables (rainfall and vegetation indices) expected to shape terroir in this system. These findings affirm the evolutionary importance of terroir, while also revealing its dependence on other factors, such as geographical isolation.

Machine learning-based direct solver for one-to-many problems on temporal shaping of relativistic electron beams

To control the temporal profile of a relativistic electron beam to meet requirements of various advanced scientific applications like free-electron-laser and plasma wakefield acceleration, a widely-used technique is to manipulate the dispersion terms which turns out to be one-to-many problems. Due to their intrinsic one-to-many property, current popular stochastic optimization approaches on temporal shaping may face the problems of long computing time or sometimes suggesting only one solution. Here we propose a real-time solver for one-to-many problems of temporal shaping, with the aid of a semi-supervised machine learning method, the conditional generative adversarial network (CGAN). We demonstrate that the CGAN solver can learn the one-to-many dynamics and is able to accurately and quickly predict the required dispersion terms for different custom temporal profiles. This machine learning-based solver is expected to have the potential for wide applications to one-to-many problems in other scientific fields.

A novel algorithm for the generation of gap-free time series by fusing harmonized Landsat 8 and Sentinel-2 observations with PhenoCam time series for detecting land surface phenology

Vegetation phenology is one of the most sensitive indicators to environmental and climate changes. In order to characterize the seasonal variation in relatively pure or homogenous vegetation types, fine spatial resolution satellite data (≤ 30 m), such as Landsat, Sentinel-2, PlanetScope, or Harmonized Landsat and Sentinel-2 (HLS), have been increasingly applied to detect land surface phenology (LSP). However, the most critical challenge in LSP detections is the gaps in temporal satellite observations caused by noise and persistent cloud/snow cover. Therefore, this study presented a novel algorithm for generating synthetic gap-free time series at the field scale (30 m) for LSP detections. Specifically, we first developed a framework to establish a large collection of temporal shapes of vegetation growth with as many as 100 grid-based Green Chromatic Coordinate (GCC) time series in a single PhenoCam site. For a given HLS pixel, the two-band Enhanced Vegetation Index (EVI2) time series was matched and fused with the most comparable temporal GCC shape selected from the collection of PhenoCam GCC time series to generate a synthetic gap-free HLS-PhenoCam EVI2 time series, which was used to detect the 30 m phenometrics. The detected phenometrics were evaluated using manually selected and spatially matched GCC observations as well as phenology detections from HLS alone. The result indicates that the HLS-PhenoCam phenometrics are very close to the observations from PhenoCam network with a correlation coefficient (R) of 0.82–0.97, a mean absolute difference (MAD) of 2.8–3.5 days, a root mean squared error (RMSE) of 3.5–4.0 days, and a mean systematic bias (MSB) of 0.1–2.2 days. The HLS-PhenoCam detections are significantly improved relative to the HLS phenometrics that have a statistic accuracy of R = 0.57–0.78, MAD = 6.4–9.3 days, RMSE = 8.8–13.9 days, MSB = -5.2–5.9 days. The difference between HLS-PhenoCam and HLS alone LSP detections over a HLS tile could be on average larger than two weeks if high-quality observation (HQO) proportion in the annual HLS time series is <10%, which exponentially reduces with the increase of HQO in HLS observations. The analyses in this study suggest that the gap-free HLS-PhenoCam time series is able to be generated for producing high-quality phenology datasets across a local and regional scale, to bridge near-surface PhenoCam observations with satellite observations data at various scales, and to be used as a scalable phenology dataset for the validation of global MODIS and VIIRS LSP products.

Measurements of microjoule-level, few-femtosecond ultraviolet dispersive-wave pulses generated in gas-filled hollow capillary fibers.

To the best of our knowledge, we demonstrate the first time-domain measurement of µJ-level, few-fs ultraviolet dispersive-wave (DW) pulses generated in gas-filled hollow capillary fibers (HCFs) in an atmosphere environment using several chirped mirrors. The pulse temporal profiles, measured using a self-diffraction frequency-resolved optical gating setup, exhibit full width at half maximum pulse widths of 9.6 fs at 384 nm and 9.4 fs at 430 nm, close to the Fourier-transform limits. Moreover, theoretical and experimental studies reveal the strong influences of driving pulse energy and HCF length on temporal width and shape of the measured DW pulses. The ultraviolet pulses obtained in an atmosphere environment with µJ-level pulse energy, few-fs pulse width, and broadband wavelength tunability are ready to be used in many applications.

Convolution finite element method for analysis of piezoelectric materials

A new finite element scheme is proposed to analyze the elastodynamics of materials having interactions between electrical and mechanical fields. Based on coupled constitutive equations and the alternative field equations, a new form of weighted residual in terms of the convolution product is established. Next, the Galerkin formulation is utilized with a particular form of spatial–temporal shape functions. High precision for arbitrary time intervals can be attained by reducing the integral forms to a set of algebraic equations. To show the accuracy of the proposed method, several examples, including elastodynamics of 1d and 2d piezoelectric materials under various initial and boundary conditions are presented. The present contribution introduces a new solution procedure for the analysis and design of active materials.

Climatic filtering and temporal instability shape the phylogenetic diversity of European alpine floras

Alpine ecosystems are hotspots of biodiversity despite their cold climates. Here we investigate spatial patterns in the phylogenetic diversity (i.e. the degree of species relatedness) of European alpine floras and quantify the influence of climatic conditions since the late Pleistocene and historical climatic instability in shaping these patterns. We collected species‐pool data for 22 alpine regions in central and southern Europe and calculated phylogenetic diversity within and between regions using two metrics sensitive to terminal branching in the phylogeny. We regressed phylogenetic diversity against macroclimatic variables representing seasonal extremes between the Last Glacial Maximum (LGM; 21 000 years BP) and the present at 1000‐year intervals. We found the lowest phylogenetic diversity in the Carpathians and the central Alps, and the highest in the north‐eastern and southern Iberian Peninsula. Phylogenetic diversity decreased with temperature seasonality and low winter temperature. While the effect of temperature seasonality was relatively constant over time, the influence of winter temperature decreased after the LGM. We also found that phylogenetic diversity decreased with historical climatic instability. Between regions, phylogenetic diversity was mainly explained by current climatic distance rather than geographic distance, suggesting that alpine floras were primarily driven by species sorting along climatic gradients. Our results confirm the role of environmental filtering in shaping the current phylogenetic diversity of alpine floras, resulting in more closely related lineages in regions with relatively cold and unstable climates. We also highlight the importance of explicitly incorporating climatic variation through time to better understand the processes structuring the current biodiversity of alpine floras.

CNN-based neural network model for amplified laser pulse temporal shape prediction with dynamic requirement in high-power laser facility.

The temporal shape of laser pulses is one of the essential performances in the inertial confinement fusion (ICF) facility. Due to the complexity and instability of the laser propagation system, it is hard to predict the pulse shapes precisely by pure analytic methods based on the physical model [Frantz-Nodvik (F-N) equation]. Here, we present a data-driven model based on a convolutional neural network (CNN) for precise prediction. The neural network model introduces sixteen parameters neglected in the F-N equation based models to expand the representation dimension. The sensitivity analysis of the experimental results confirms that these parameters have different degrees of influence on the temporal output shapes and cannot be ignored. The network characterizes the whole physical process with commonality and specificity features to improve the description ability. The prediction accuracy evaluated by a root mean square of the proposed model is 7.93%, which is better compared to three optimized physical models. This study explores a nonanalytic methodology of combining prior physical knowledge with data-driven models to map the complex physical process by numerical models, which has strong representation capability and great potential to model other measurable processes in physical science.

Forcing Power Supply of a Xenon Flash Lamp to Create a High Power Irradiation Facility

The article describes the technical characteristics of the software-controlled power supply system for generation of second-long light pulses by means of INP‑16/580 xenon flash lamps. The amplitude-time characteristics of luminous emission in a quasi-arc mode of lamp operation are formed by computer control of temporal current pulse shape in case of large energy deposition overloads. Methods of optimisation of light and engineering characteristics were defined accounting for non-linearity of the load of the thyristor unit and ambiguity of the dependence of luminous radiation on discharge current. The data on maximum acceptable operation parameters of pulse lamps with mains supply and natural air cooling and the results of physical modelling of radiation pulses with complex shape are presented.

Modeling the Influence of Moulin Shape on Subglacial Hydrology

AbstractSubglacial models represent moulins as cylinders or cones, but field observations suggest that the upper part of moulins in the Greenland Ice Sheet has more complex shapes. These more complex shapes should cause englacial water storage within moulins to vary as a function of depth, a relationship not currently accounted for in models. Here, we use a coupled englacial‐subglacial channel model to explore how moulin shape affects depth‐dependent moulin water storage and water pressure dynamics within a subglacial channel. We simulate seven different moulin shapes across a range of moulin sizes. We find that the englacial storage capacity at the water level is the main control over the daily water level oscillation range and that depth‐varying changes in englacial water storage control the temporal shape of this oscillation. Further, the cross‐sectional area of the moulin within the daily oscillation range, but not above or below this range, controls pressures within the connected subglacial channel. Specifically, large cross‐sectional areas can dampen daily to weekly oscillations that occur in the surface meltwater supply. Our findings suggest that further knowledge of the shape of moulins around the equilibrium water level would improve englacial storage parameterization in subglacial hydrological models and aid predictions of hydrodynamic coupling.

Modulation of laser damage by temporal shaping of double picosecond pulses.

We propose a temporally shaped double-picosecond-pulse train at a sub-nanosecond scale to control the damage dynamics of optical glass. Both damage threshold and morphology are significantly modulated by pulse-train shaping. The ramp-up-shaped train effectively increases its damage threshold and decreases the damage density and size, which clearly shows that a pump pulse with optimized fluence has a strong positive modification of damage precursors. Furthermore, the temporal evolution of damage modulation is experimentally revealed by varying the interval of pump-probe pulses, and after pump exposure with optimized fluence, enhancement of the probe threshold reaches the maximum at a delay of about 260 ps.

Storage and manipulation of single x-ray photons via nuclear hyperfine splitting

We introduce a technique to store and manipulate single x-ray photons, which relies on dynamically controlled absorption via nuclear hyperfine magnetic splitting. This scheme is inherently suitable for storage, on-demand generation, and dynamical manipulation of single x-ray photons, for instance, the manipulation of the temporal shape, temporal splitting, the interference between x-ray photons, and the control of the polarization. Our approach provides more opportunities in x-ray quantum information.

Theory of two-photon absorption with broadband squeezed vacuum

We present an analytical quantum theoretic model for nonresonant molecular two-photon absorption (TPA) of broadband, spectrally multimode squeezed vacuum, including low-gain (isolated entangled photon pairs) and high-gain (bright squeezed vacuum or BSV) regimes. The results are relevant to the potential use of entangled-light TPA as a spectroscopic and imaging method. We treat the scenario that the exciting light is spatially single mode and is nonresonant with all intermediate molecular states. In the case of high gain, we find that in the case that the linewidth of the final molecular state is much narrower than the bandwidth of the exciting light, bright squeezed vacuum is found to be equally (but no more) effective in driving TPA as is a quasimonochromatic coherent-state (classical) pulse of the same temporal shape, duration, and mean photon number. Therefore, in this case the sought-for advantage of observing TPA at extremely low optical flux is not provided by broadband bright squeezed vacuum. In the opposite case that the final-state linewidth is much broader than the bandwidth of the BSV exciting light, we show that the TPA rate is proportional to the second-order intensity autocorrelation function at zero time delay ${g}^{(2)}(0)$, as expected. We derive and evaluate formulas describing the transition between these two limiting cases, that is, including the regime where the molecular linewidth and optical bandwidth are comparable, as is often the case in experimental studies. We also show that for ${g}^{(2)}(0)$ to reach the idealized form ${g}^{(2)}(0)=3+1/\overline{n}$, with $\overline{n}$ being the mean number of photons per temporal mode, it is required to compensate the dispersion inherent in the nonlinear-optical crystal used to generate the BSV.

Stimulated generation of deterministic platicon frequency microcombs

Dissipative Kerr soliton generation in chip-scale nonlinear resonators has recently observed remarkable advances, spanning from massively parallel communications, to self-referenced oscillators, and to dual-comb spectroscopy. Often working in the anomalous dispersion regime, unique driving protocols and dispersion in these nonlinear resonators have been examined to achieve the soliton and soliton-like temporal pulse shapes and coherent frequency comb generation. The normal dispersion regime provides a complementary approach to bridge the nonlinear dynamical studies, including the possibility of square pulse formation with flattop plateaus, or platicons. Here we report observations of square pulse formation in chip-scale frequency combs through stimulated pumping at one free spectral range and in silicon nitride rings with + 55 fs 2 / mm normal group velocity dispersion. Tuning of the platicon frequency comb via a varied sideband modulation frequency is examined in both spectral and temporal measurements. Determined by second-harmonic autocorrelation and cross correlation, we observe bright square platicon pulse of 17 ps pulse width on a 19 GHz flat frequency comb. With auxiliary-laser-assisted thermal stabilization, we surpass the thermal bistable dragging and extend the mode-locking access to narrower 2 ps platicon pulse states, supported by nonlinear dynamical modeling and boundary limit discussions.

Computer-Visualized Sound Parameter Analysis Method and Its Application in Vocal Music Teaching

In order to improve the quality of vocal music teaching, this paper applies the computer visualization sound parameter analysis method to vocal music teaching and discusses the scheme of parametric coding. Moreover, this paper adopts the transient signal detection mechanism to divide the signal. For frames that have detected a shock signal, frequency-domain parametric differential predictive coding can be used like temporal noise shaping (TNS) techniques. In addition, based on the short-term periodicity and short-term stationarity of speech signals, an analytical synthesis model based on harmonic decomposition is proposed. Through the simulation data analysis, it can be seen that the computer visualization sound parameter analysis method proposed in this paper has a very good application effect in vocal music teaching and can improve the quality of vocal music teaching.

Traveling Waves in Shallow Seas of Variable Depths

The problem of the existence of traveling waves in inhomogeneous fluid is very important for enabling an explanation of long-distance wave propagations such as tsunamis and storm waves. The present paper discusses new solutions to the variable-coefficient wave equations describing traveling waves in fluid layers of variable depths (1D shallow-water theory). Such solutions are obtained by using the transformation methods when variable-coefficient equations can be reduced to the constant coefficient equation when the existence of traveling waves is evident. It is shown that there is a wide class of monotonic bottom profiles (discrete set) that allow the existence of traveling waves that are not reflected in a strongly inhomogeneous water medium. Their temporal shape changes with distance, mainly near the water–land boundary (shoreline). Traveling waves can transfer the wave energy over a long distance that is often observed at the transoceanic propagation of tsunami waves.

Wind-induced changes to shoaling surface gravity wave shape

Unforced shoaling waves experience growth and changes to wave shape. Similarly, wind-forced waves on a flat-bottom likewise experience growth/decay and changes to wave shape. However, the combined effect of shoaling and wind-forcing on wave shape, particularly relevant in the near-shore environment, has not yet been investigated theoretically. Here, we consider small-amplitude, shallow-water solitary waves propagating up a gentle, planar bathymetry forced by a weak, Jeffreys-type wind-induced surface pressure. We derive a variable-coefficient Korteweg-de Vries-Burgers (vKdV-B) equation governing the wave profile's evolution and solve it numerically using a Runge-Kutta third-order finite difference solver. The simulations run until convective prebreaking -- a Froude number limit appropriate to the order of the vKdV-B equation. Offshore winds weakly enhance the ratio of prebreaking height to depth as well as prebreaking wave slope. Onshore winds have a strong impact on narrowing the wave peak, and wind also modulates the rear shelf formed behind the wave. Furthermore, wind strongly affects the width of the prebreaking zone, with larger effects for smaller beach slopes. After converting our pressure magnitudes to physically realistic wind speeds, we observe qualitative agreement with prior laboratory and numerical experiments on breakpoint location. Additionally, our numerical results have qualitatively similar temporal wave shape to shoaling and wind-forced laboratory observations, suggesting that the vKdV-B equation captures the essential aspects of wind-induced effects on shoaling wave shape. Finally, we isolate the wind's effect by comparing the wave profiles to the unforced case. This reveals that the numerical results are approximately a superposition of a solitary wave, a shoaling-induced shelf, and a wind-induced, bound, dispersive, and decaying tail.

Millisecond pulsed laser welding of AISI 316 stainless steel

Nowadays, there is an increasing demand for AISI 316 stainless steel for automotive, medical, aerospace, for tool manufacturing and for nuclear industry. Compared with continuous beam laser welding, pulse temporal shape, pulse duration and the repetition rate are fundamental parameters that have a direct influence on the quality on the welded joint [2]. The laser welding of AISI 316 stainless steel thin sheets by millisecond pulsed laser will be analysed within this research by addressing to pulsed laser parameters influence on the geometry and appearing of the welding joint. The influence of laser power, pulse duration and repetition rate were determined by tracking fusion lines on specimen’s plates and butt weld stainless steel welding were obtained by using the determined optimal welding parameters. All the parameters have a major influence on the geometrical appearance of the weld bead.