Longer Propagation Times Research Articles

Role of Initial Conditions and Meteorological Drought in Soil Moisture Drought Propagation: An Event‐Based Causal Analysis Over South Asia

AbstractThe role of meteorological droughts and initial conditions (land and atmosphere) in soil moisture drought (SMD) propagation are not yet fully understood. This work uses a drought event‐based causal framework to investigate the relative importance of meteorological drought (MD) duration and intensity and initial conditions that result in surface and rootzone SMD, considering their event‐level propagation time (PT) over South Asia. Initially, spatial variability of drought propagation is assessed by the Propagation Ratio (PR) computed based on MD counts that trigger SMD at various lags. PR depicts 2–3 months slower rootzone propagation than at surface. The gradual decrease in PR with increasing regional aridity indicates faster propagation over humid regions. The causal impact of initial conditions and MD parameters on propagating SMD are evaluated using normalized mutual information and a newly proposed normalized conditional mutual information. We found greater importance of triggering MD parameters followed by initial soil moisture condition on propagating SMD. This behavior is more evident for the surface layer propagation at shorter PT. There is a confounding effect of initial atmospheric conditions on drought propagation through initial soil moisture, depicting the significance of land‐atmosphere interactions prior to propagation. In the rootzone propagation, initial soil moisture has a greater influence on propagation, especially at longer PT, indicating the significance of soil moisture persistence. Stronger causal links obtained through the joint influence of MD parameters on SMD suggest the importance of accounting for MD duration and intensity simultaneously, which are not considered in drought index‐based propagation studies.

Hybrid Method of Uncertainty Propagation for Near-Earth Conjunction Analysis

In this research, several existing semi-analytical dynamics and uncertainty propagation techniques are combined with conjunction models to achieve fast and accurate probability of collision results. Initial Gaussian uncertainty associated with two objects is split into smaller Gaussian distributions using Gaussian mixture models to achieve mixture components that will maintain linearity over longer propagation times. These mixture components are propagated forward using second-order state transition tensors that can capture the nonlinearity in the propagation accurately by taking into account the desired dynamics. The dynamic solution and these tensors are computed using the Deprit–Lie averaging approach, including transformations between mean and osculating states, which accounts for perturbations due to solar radiation pressure and J2. This simplified dynamic system allows fast and accurate propagation by combining the speed of propagation with averaged dynamics and the accuracy of short-period variation addition. Combined, these mathematical tools are used to propagate the object’s uncertainties forward. The final distributions are compared using analytical conjunction methods to compute the probability of collision, which is then compared to the Monte Carlo result to confirm the method’s validity.

Diffuse photon remission associated with the center-illuminated-area-detection geometry. II. Approach to the time-domain model.

This part proposes a model of time-dependent diffuse photon remission for the center-illuminated-area-detection (CIAD) geometry, by virtue of area integration of the radially resolved time-dependent diffuse photon remission formulated with the master-slave dual-source scheme demonstrated in Part I for steady-state measurements. The time-domain model is assessed against Monte Carlo (MC) simulations limiting to only the Heyney-Greenstein scattering phase function for CIAD of physical scales and medium properties relevant to single-fiber reflectance (SfR) and over a 2ns duration, in compliance with the timespan of the only experimental report of SfR demonstrated with a 50µm gradient index fiber. The time-domain model-MC assessments are carried out for an absorption coefficient ranging three orders of magnitude over [0.001,0.01,0.1,1]m m -1 at a fixed scattering, and a reduced scattering coefficient ranging three orders of magnitude over [0.01,0.1,1,10]m m -1 at a fixed absorption, among others. Photons of shorter and longer propagation times, relative to the diameter of the area of collection, respond differently to the scattering and absorption changes. Limited comparisons of MC between CIAD and a top-hat geometry as the idealization of SfR reveal that the time-domain photon remissions of the two geometries differ appreciably in only the early arriving photons.

Catchment-Scale Drought Propagation Assessment in the Indus Basin of Pakistan Using a Combined Approach of Principal Components and Wavelet Analyses

Abstract This study aims to comprehend the propagation of meteorological drought [expressed by the standardized precipitation evapotranspiration index (SPEI)] into hydrological drought [expressed by the standardized runoff index (SRI)] using the combined application of principal component analysis (PCA) and wavelet analysis for a period of 39 years (1980–2018) in the Indus basin, Pakistan. PCA was used to calculate principal components of precipitation, temperature, and streamflow, which were used to systematically propagate drought from one catchment to another, resulting in a catchment-scale drought assessment. The systematic propagation of drought was useful in capturing the effects of local climate variability in the 27 catchments of the Indus basin. Wavelet analyses are used to calculate the variability of SPEI/SRI and propagation (analyzed with the wavelet coherence) from SPEI to SRI. The propagation time from SPEI to SRI was cross correlated. SPEI/SRI time series showed extreme/severe droughts in 16 out of the 39 years, where relatively weak apparent wet and drought events are observed at short periods (1 month) and apparent at longer periods (6 and 12 months). Propagation from SPEI to SRI is catchment specific, with most catchments showing transition in early years (1997–2003). Propagation rate is higher in the upper Indus basin (UIB) and lower Indus basin (LIB) than in the middle Indus basin (MIB), suggesting that climate plays an important role in drought development and propagation. Results also showed a shorter and longer propagation time in the UIB and LIB, respectively. This study has helped us understand the behavior of droughts at catchment scale and will therefore help in the development of drought mitigation plans in Pakistan and similar regions around the world.

Survey on Multi-Path Routing Protocols of Underwater Wireless Sensor Networks: Advancement and Applications

Underwater wireless sensor networks (UWSNs) are a prominent research topic in academia and industry, with many applications such as ocean, seismic, environmental, and seabed explorations. The main challenges in deploying UWSN are high ocean interference and noise, which results in longer propagation time, low bandwidth, and changes in network topology. To mitigate these problems, routing protocols have been identified as an efficient solution. Over the years, several protocols have been proposed in this direction and among them, the most popular are the ones that use multi-path propagation. However, there is a lack of compilation of studies that highlight the advancement of multi-path routing protocols of UWSN through the years. Hence, getting a heuristic idea of the existing protocols is crucial. In this study, we present a comprehensive survey of UWSNs multi-path routing protocols and categorize them into three main categories; energy-based routing protocols, geographic information-based routing protocols, and data-based routing protocols. Furthermore, we sub-classify them into several categories and identify their advantages and disadvantages. In addition, we identify the application of UWSN, open challenges and compare the protocols. The findings of our study will allow researchers to better understand different categories of UWSN multi-path routing protocols in terms of their scope, advantages, and limitations.

Efficient matrix factorisation of the modular path integral for extended systems

The modular path integral (MPI) formulation offers a numerically exact, versatile, and highly efficient approach to the quantum dynamics of extended systems characterised by a single-file arrangement of units with short-range interactions, such as hydrocarbons, molecular aggregates with exciton couplings, or spin chains. Rather than propagating the many-particle wavefunction or density matrix in time in the usual stepwise fashion, the MPI scheme proceeds by sequentially integrating over each unit after linking its quantum paths to those of its neighbour and leads to linear scaling with system length. This paper shows that the linking matrix can be further decomposed into a diagonal matrix and a product of low-dimensional matrices, which can be applied sequentially. This factorisation changes the cost scaling from L 2 to , where L is the number of quantum paths, leading to dramatic savings that are analogous to those attained by the fast Fourier transform algorithm and allowing application of the MPI procedure to systems with larger units and to longer propagation times. Applications to spin chains and to electron-vibration dynamics in a large molecular aggregate illustrate the efficiency of the algorithm.

Time intermittency in nondiffusive transport regimes of suprathermal ions in turbulent plasmas

Intermittent phenomena have long been studied in the context of nondiffusive transport across a variety of fields. In the TORPEX device, the cross-field spreading of an injected suprathermal ion beam by electrostatic plasma turbulence can access different nondiffusive transport regimes. A comprehensive set of suprathermal ion time series has been acquired, and time intermittency quantified by their skewness. Values distinctly above background level are found across all observed transport regimes. Intermittency tends to increase toward quasi- and superdiffusion and for longer propagation times of the suprathermal ions. The specific prevalence of intermittency is determined by the meandering motion of the instantaneous ion beam. We demonstrate the effectiveness of an analytical model developed to predict local intermittency from the time-average beam. This model might thus be of direct interest for similar systems, e.g., in beam physics, or meandering flux-rope models for solar energetic particle propagation. More generally, it illustrates the importance of identifying the system-specific sources of time-intermittent behavior when analyzing nondiffusive transport.

Femtosecond laser pulse control of ground state of PTCDA

With the combination of optimal control theory and multi\|configuration time-dependent Hartree（MCTDH） method, the vibrational quantum model for describing the multidimensional planar structural PTCDA molecule is constructed. Within the frame of MCTDH, the dynamics of PTCDA ground state via pump-dump process under an excitation of femtosecond laser pulse is considered. The relation of reduced control yield of target state to the shape of excitation pulses, the propagation time and the effective energy of optimal field are analyzed theoretically. The wavepacket distributions in the involved vibrational coordinates are compared with the vibrational parameters. It is found that with longer propagation time, higher control yield of target state at lower strength of optimal pulse is realized, which provides an effective method to realize the control with low energy laser pulses in experiment.

Dipolar effects on propagation of ultrashort laser pulse in one-dimensional para-nitroaniline (pNA) molecules

The dynamic behaviour of ultrashort (femtosecond) laser pulses in a molecular medium is studied by solving the full Maxwell–Bloch equations beyond the limits of the slowly varying envelope approximation and the rotating-wave approximation under the resonant and the non-resonant conditions. A one-dimensional asymmetric charge-transfer molecule, para-nitroaniline, is used as a model molecule whose electronic properties are calculated with the time-dependent hybrid density functional theory. Under the one-photon resonant condition, 4π pulse is separated into two sub-pulses. The weight of the second-harmonic component mainly contributed by the two-photon excitation becomes stronger with longer propagation time. Under the two-photon resonant condition, the separation of 4π pulse is not induced and many higher-order spectral components beyond the second-harmonic generation occur. Interestingly, when the pulse propagates for long enough, the carrier modification becomes so significant that a continuous spectrum is generated. The Fourier transform of the high-harmonic spectrum demonstrates that an even shorter laser pulse can be produced in both resonant and non-resonant propagations. The effects of permanent dipole moments on the pulse evolution are discussed.