Effect of evaporation and solutocapillary-driven flow upon motion and resultant deposition of suspended particles in volatile droplet on solid substrate

Particle motion in a volatile droplet on a solid surface, especially the behavior of particles depositing in the vicinity of a solid–liquid–gas boundary line (contact line) is focused. This phenomenon is called the ‘coffee stain problem’. Motion and deposition of the particles suspended in distilled water droplets and distilled water–ethanol mixture droplets are discussed. The spatio-temporal particle motion is analyzed by the three-dimensional particle tracking velocimetry (3D PTV). A discussion of the morphology of the particles stuck to the solid surface after the dryout of the droplet is also given.     

基于时空图卷积网络的无人机网络入侵检测方法

无人机网络相比地面网络具有节点快速移动、拓扑结构变换频繁和通信链路不可靠的特点,传统的针对地面网络的入侵检测方法难以适用。针对无人机网络的时空动态特性进行建模,提出了一种无人机网络的入侵检测方法——基于注意力机制的时空图卷积网络（ATGCN）。将图卷积网络和门控递归单元组合为时空图卷积网络,从复杂多变的数据中提取网络的时空演变特征,通过注意力机制提取和入侵检测最相关的特征,输入支持向量机进行分类预测。多个数据集的实验分析表明:所提方法能够适应无人机网络的动态性和不稳定性,相比传统检测方法准确率高且误报率低,具有良好的鲁棒性和适应性。      

The Western Crete geodetic infrastructure: Long-range power-law correlations in GPS time series using Detrended Fluctuation Analysis

The Global Positioning System makes it possible, nowadays, to measure crustal displacements with unprecedented accuracy. These measurements can improve our understanding of the spatio-temporal evolution of motion along tectonic plate boundaries, as well as deepen our comprehension for the nature of earthquake fault behavior and earthquake cycle. The Hellenic subduction zone and the earthquake-prone Crete, with large crustal motions of 3–4 cm/yr, may provide such a natural laboratory for this type of investigation. In this work, we examine the statistical structure and behavior of time series, as produced by permanent GPS sites, established on the islands of Crete and Gavdos.     

动态地球磁层的时空剖分编码

动态地球磁层时空剖分模型借鉴了广泛应用于地学大数据的地球格网模型思想，实现了面向地球磁层的动态、非规则化物理空间的多层级剖分，且剖分格网形变稳定，可以实现一定范围内地球磁层时空特性的形式化。在此基础上，对剖分得到的时空格网进行编码表达，以便于计算机存储和处理，这是构建地球磁层大规模观测数据统一管理基础时空框架的另一个关键问题。由于地球磁层特殊的时空特性，经典、单一思路的地学编码方案较难完整地反映格网间的时空关系，因此难以支持格网间的基础时空关系计算。本文融合了整数坐标编码与Morton曲线编码的基本思路，实现了对漂移壳剖分格网的高效编码方案设计，完成了动态地球磁层的时空框架构建，从而为地磁数据的高效组织和处理奠定了基础。实验证明，本文提出的编码方案编码效率较高，且可以支持高效的相邻关系计算，为动态地球磁层多源、多层级、异构的大规模观测数据的组织与计算提供了一种解决方案。      

Propagation of non-linear ion-sound pulses in dusty plasma waveguides

There are a lot of objects in space associated with dusty plasma inclusions. Such inclusions may bear a prolonged shape and behave as waveguides for ion-sound waves. In the case of space plasmas, the dust particles can possess both negative charge, due to electron attachment, and positive one, due to photoionization. In this paper the propagation of linear and non-linear ion-sound wave pulses in the dusty plasma waveguides, possessing positive charge, is studied. It has been demonstrated that non-linear dynamics of baseband pulse propagation in plasma waveguide possesses essentially non-solitonic behavior. Namely, propagation of a long ion-sound pulse leads to an excitation of a shock-like wave but not a stable localized nonlinear pulse. Also, when a Korteveg–de Vries (KdV) soliton is incident onto the dusty plasma waveguide, some part of the soliton energy is captured by the waveguide and transformed into a multi-pulse structure. Additionally, an interaction of dusty plasma inclusions with KdV soliton can lead to the occurrence of transverse instabilities of the soliton and its eventual destruction.     

Integrated drought monitoring index: A tool to monitor agricultural drought by using time-series datasets of space-based earth observation satellites

In this study, integrated drought monitoring index (IDMI) was proposed as a tool to assess and monitor the spatio-temporal dynamics of agricultural drought during the northeast monsoon season for the period from 2000 to 2016 in Tamil Nadu state, south-eastern part of Indian peninsula. The IDMI is characterized as the principal component of precipitation condition index (PCI), soil moisture condition index (SMCI), temperature condition index (TCI), and vegetation condition index (VCI) derived from time-series satellite observations of climate hazards group infra-red precipitation with stations (CHIRPS), European space agency climate change initiative (ESA-CCI) and moderate resolution imaging spectroradiometer (MODIS). The study shows that in the year 2016, about 44.4 and 17.8% of Tamil Nadu state was under extreme and severe drought conditions, respectively. Sensitivity analysis of the study shows that PCI is the most influential parameter to IDMI, followed by VCI and TCI. The validation of IDMI with 3-month standardized precipitation index (SPI) by using Pearson correlation test shows a strong positive correlation between IDMI and 3-month SPI with correlation coefficient (r) value of 0.73 and 0.77 for the wet (2005) and dry year (2016), respectively. The study clearly demonstrates the potential of IDMI derived from time-series datasets of earth observation satellites as a tool in assessment and monitoring of spatio-temporal dynamics of agricultural drought. The proposed IDMI could be effectively used as a reliable tool to monitor agricultural drought and develop its mitigation strategies to minimise the adverse effects of drought on agriculture, water resources, and livelihoods of the people.     

Ion dynamics of magnetic reconnection in the magnetotail

We discuss the kinetic processes of plasma thermalization, acceleration, and mixing in magnetic reconnection. Non-Maxwellian, gyrotropic ion distribution functions such as anisotropic ion beams in the plasma sheet boundary layer (PSBL) and counter-streaming ions (CSIs) in the plasma sheet are often observed during a plasmoid passage of a satellite in the Earth's magnetotail. Non-gyrotropic ion distribution functions are also sometimes observed just after the passage of the plasmoid. We study the behavior of non-Maxwellian ion distribution functions observed by GEOTAIL. We further study theoretically the ion dynamics by using a particle-in-cell simulation, and discuss the role of non-Maxwellian distribution functions in magnetic reconnection.     

Solitary and periodic waves in magneto–rotating plasmas: Effect of the Kappa–Cairns distributed electrons

The nonlinear propagation of ion–acoustic (IA) waves in a magneto–rotating plasma is studied by considering the Kappa-Cairns electron distribution. Employing the perturbation scheme, Korteweg–de Vries equation is derived. It is seen that both positive and negative potential solitons can be supported in the present plasma model. The numerical results reveal that the Kappa-Cairns distributed electrons modify features of the electrostatic waves significantly. The effects of non–thermal parameters, plasma rotation frequency, ion temperature, and the wave propagation angle on electrostatic solitary wave structures are also discussed here. It is found that the plasma parameters considerably influence the propagation of IA waves in rotating plasmas. Furthermore, using the bifurcation theory of planar dynamical systems to the K-dV equation, we have presented the existence of solitary and periodic traveling waves. Our study may be helpful to understand the behavior of ion–acoustic wave in the rotating plasma.     

Excitation of electrostatic plasma waves by a moving charged source in a quantum plasma

Within a quantum hydrodynamic model and using the reductive perturbation technique, the nonlinear ion-acoustic wave (IAW) excitations due to a moving charged object in an electron-pair-ion quantum plasma are studied both analytically and numerically. In such quantum plasmas we have derived forced Korteweg-de Vries (fKdV) type equation for finite amplitude nonlinear IAWs. The effect of relevant plasma parameters on solitonic excitations is investigated. Numerical simulation shows the generation of advancing solitons ahead of the forcing term traveling at a faster rate with trailing wakes behind the forcing disturbance. It is found that propagation characteristics of nonlinear excitations are significantly affected by quantum parameter. Additionally, we have pursued our analysis by extending it to account for arbitrary amplitude IA solitons, and derived a system of nonlinear differential equations which are analyzed numerically to study the dynamics. Nonlinear analysis predicts the existence of periodic and quasiperiodic nature of the nonlinear system and reveals that the transition from quasiperiodic to periodic behavior occurs due to the variation of quantum diffraction.     

Spatio-temporal analysis of ionospheric disturbances for ground based augmentation systems over a midlatitude region

Forcings from above and below the ionosphere can cause disturbances that need to be detected and corrected for navigation systems. Ground Based Augmentation Systems (GBAS) are used to give corrections to aircraft navigation systems while landing. These systems use regional ionosphere monitoring algorithms to detect the anomalies in the ionosphere. The aim of this study is to understand occurrence of ionosphere anomalies and their trends over Turkey. A comprehensive analysis of spatio-temporal variability of ionosphere is carried out for a midlatitude GPS network using Slant Total Electron Content (STEC). Differential Rate Of TEC (DROT), which is a measure of the amount of deviation of temporal derivative of TEC from its trend, is used to detect and classify the level of such disturbances. The GPS satellite tracks are grouped into north, east, west and over directions. The 24 h is divided into six time intervals. The percentage occurrence of each DROT category and the deviation from STEC trend in magnitude are calculated and grouped into satellite track directions and time intervals for 2010 (low solar activity), 2011 and 2012 (medium solar activity). The highest level of disturbances is observed in north and west directions, and during sunrise and sunset hours. The dominant periods of percentage occurrences are diurnal (22–25 h), semidiurnal (12–13 h) and terdiurnal (8–9 h) followed by quasi two-day and quasi 16-day periods. Disturbances corresponding to 50% < DROT < 70% are mostly visible during low solar activity years with magnitudes from 1 to 2 TECU. Geomagnetic storms can cause aperiodic larger scale disturbances that are mostly correlated with DROT > 70%. In 2012, the magnitude of such disturbances can reach 5 TECU. The anisotropic and dynamic nature of midlatitude ionosphere is reflected in the spatio-temporal and spectral distributions of DROT, and their percentage occurrences. This study serves a basis for future studies about development of a regional ionosphere monitoring for Turkey.     

Using GPS-SCINDA observations to study the correlation between scintillation,total electron content enhancement and depletions over the Kenyan region

This paper presents the first results of total electron content (TEC) depletions and enhancement associated with ionospheric irregularities in the low latitude region over Kenya. At the low latitude ionosphere the diurnal behavior of scintillation is driven by the formation of large scale equatorial depletions which are formed by post-sunset plasma instabilities via the Rayleigh–Taylor instability near the magnetic equator. Data from the GPS scintillation receiver (GPS-SCINDA) located at the University of Nairobi (36.8°E, 1.27°S) for March 2011 was used in this study. The TEC depletions have been detected from satellite passes along the line of sight of the signal and the detected depletions have good correspondence with the occurrence of scintillation patches. TEC enhancement has been observed and is not correlated with increases in S₄ index and consecutive enhancements and depletions in TEC have also been observed which results into scintillation patches related to TEC depletions. The TEC depletions have been interpreted as plasma irregularities and inhomogeneities in the F region caused by plasma instabilities, while TEC enhancement have been interpreted as the manifestation of plasma density enhancements mainly associated with the equatorial ionization anomaly crest over this region. Occurrence of scintillation does happen at and around the ionization anomaly crest over Kenyan region. The presence of high ambient electron densities and large electron density gradients associated with small scale irregularities in the ionization anomaly regions have been linked to the occurrence of scintillation.     

Non-parametric regional VTEC modeling with Multivariate Adaptive Regression B-Splines

In this work Multivariate Adaptive Regression B-Splines (BMARS) is applied to regional spatio-temporal mapping of the Vertical Total Electron Content (VTEC) using ground based Global Positioning System (GPS) observations. BMARS is a non-parametric regression technique that utilizes compactly supported tensor product B-splines as basis functions, which are automatically obtained from the observations. The algorithm uses a scale-by-scale model building strategy that searches for B-splines at each scale fitting adequately to the data and provides smoother approximations than the original Multivariate Adaptive Regression Splines (MARS). It is capable to process high dimensional problems with large amounts of data and can easily be parallelized. The real test data is collected from 32 ground based GPS stations located in North America. The results are compared numerically and visually with both the regional VTEC modeling generated via original MARS using piecewise-linear basis functions and another regional VTEC modeling based on B-splines.     

Interplanetary medium – A dusty plasma

The average mass of dust per volume in space equals that of the solar wind so that the interplanetary medium should provide an obvious region to study dust plasma interactions. While dust collective behavior is typically not observed in the interplanetary medium, the dust component rather consists of isolated grains screened by and interacting with the plasma. Space measurements have revealed several phenomena possibly resulting from dust plasma interactions, but most of the dust plasma interactions are at present not quantified. Examples are the production of neutrals and pick-up ions from the dust, dust impact generated field variations at spacecraft and magnetic field variations possibly caused by solar wind interacting with dust trails. Since dust particles carry a surface charge, they are exposed to the Lorentz force in the interplanetary magnetic field and for grains of sub-micrometer sizes acceleration can be substantial.     

On the initial perturbation of mesospheric dust associated irregularities by high powered radio waves

Important observational manifestations of subvisible mesospheric dust are Polar Mesospheric Summer Echoes (PMSEs) which are produced by scattering from electron irregularities produced by dust charging. It has been observed that the PMSE strength can be artificially modified by using a ground-based ionospheric heating facility to perturb the electron irregularity source region that is believed to produce PMSE. Recently it has become evident that significant diagnostic information may be available about the dust layer from the temporal behavior of the electron irregularities during the heating process which modifies the background electron temperature. Particularly interesting and important periods of the temporal behavior are during the turn-on and turn-off of the radio wave heating. Most past theoretical models and experimental investigations have concentrated primarily on the later period. The objective here is to consider the temporal behavior and possibilities for diagnostic information available during the turn-on period of the radio wave. First, approximate analytical models are developed and compared to a more accurate full computational model as a reference. Then from the temporal behavior of the electron irregularities during the turn-on of the radio wave, the analytical models are used to obtain possible diagnostic information for various charged dust and background plasma quantities.     

The characteristics of sharp (small-scale) boundaries of solar wind plasma and magnetic field structures

We investigate properties of large (>20%) and sharp (<10 min) solar wind ion flux changes using INTERBALL-1 and WIND plasma and magnetic field measurements from 1996 to 1999. These ion flux changes are the boundaries of small-scale and middle-scale solar wind structures. We describe the behavior of the solar wind velocity, temperature and interplanetary magnetic field (IMF) during these sudden flux changes. Many of the largest ion flux changes occur during periods when the solar wind velocity is nearly constant, so these are mainly plasma density changes. The IMF magnitude and direction changes at these events can be either large or small. For about 55% of the ion flux changes, the sum of the thermal and magnetic pressure are in balance across the boundary. In many of the other cases, the thermal pressure change is significantly more than the magnetic pressure change. We also attempted to classify the types of discontinuities observed.     

一种时空特征聚合的水下珊瑚礁鱼检测方法

水下监控视频中的珊瑚礁鱼检测面临着视频成像质量不高、水下环境复杂、珊瑚礁鱼视觉多样性高等困难,是一个极具挑战的视觉目标检测问题,如何提取高辨识度的特征成为制约检测精度提升的关键。提出了一种时空特征聚合的水下珊瑚礁鱼检测方法,通过设计视觉特征聚合和时序特征聚合2个模块,融合多个维度的特征以实现这一目标。前者设计了自顶向下的切分和自底向上的归并方案,可实现不同分辨率多层卷积特征图的有效聚合;后者给出了一种帧差引导的相邻帧特征图融合方案,可通过融合多帧特征图强化运动目标及其周边区域的特征表示。公开数据集上的实验表明:基于以上2个模块设计的时空特征聚合网络可以实现对水下珊瑚礁鱼的有效检测,相比于多个主流方法和模型取得了更高的检测精度。      

Ionospheric storm due to solar Coronal mass ejection in September 2017 over the Brazilian and African longitudes

Coronal mass ejection (CME) occurs when there is an abrupt release of a large amount of solar plasma, and this cloud of plasma released by the Sun has an intrinsic magnetic field. In addition, CMEs often follow solar flares (SF). The CME cloud travels outward from the Sun to the interplanetary medium and eventually hits the Earth’s system. One of the most significant aspects of space weather is the ionospheric response due to SF or CME. The direction of the interplanetary magnetic field, solar wind speed, and the number of particles are relevant parameters of the CME when it hits the Earth’s system. A geomagnetic storm is most geo-efficient when the plasma cloud has an interplanetary magnetic field southward and it is accompanied by an increase in the solar wind speed and particle number density. We investigated the ionospheric response (F-region) in the Brazilian and African sectors during a geomagnetic storm event on September 07–10, 2017, using magnetometer and GPS-TEC networks data. Positive ionospheric disturbances are observed in the VTEC during the disturbed period (September 07–08, 2017) over the Brazilian and African sectors. Also, two latitudinal chains of GPS-TEC stations from the equatorial region to low latitudes in the East and West Brazilian sectors and another chain in the East African sector are used to investigate the storm time behavior of the equatorial ionization anomaly (EIA). We noted that the EIA was disturbed in the American and African sectors during the main phase of the geomagnetic storm. Also, the Brazilian sector was more disturbed than the African sector.     

Laboratory simulation of the injection of energetic electron beams into the ionosphere—Ignition of the beam plasma discharge

Experiments, which somewhat simulate the injection of monoenergetic (several keV) electron beams into the ionosphere, have been performed in the very large (17 m × 26 m) vacuum chamber at Johnson Space Center. Typical operating ranges were: Beam current, I (0–130 mA), beam energy, E (0.5–3 kV), magnetic field, (0.3–2 G), path length, L (10–20 m), and injection pitch angle, α(0–80°). Measurements were carried out in both steady state and pulsed modes. In steady state and for constant V, B, p, L, α, the beam plasma discharge (BPD) is abruptly ignited when the beam current is increased above a critical value; at currents below critical, the beam configuration appears grossly consistent with single particle behavior. If it is assumed that each of the experiment parameters can be varied independently, the critical current required for ignition obeys the empirical relationship at p < 2 × 10^?5 torr:

$\text{I}\textcolor{red}{}\text{E}{}^{\mathrm{3/2}}\text{B}{}^{\mathrm{<mtext>0.7</mtext><mtext>pL</mtext>}}$

The BPD is characterized by 1) a large increase in the plasma production rate manifested in corresponding increases in the 3914 Å light intensity and plasma density, 2) intense wave emissions in a broad band centered at the plasma frequency and a second band extending from a few kHz up to the electron cyclotron frequency, 3) scattering of the beam in velocity space and 4) radial expansion and pitch angle scattering of the primary beam leading to the disappearance of single particle trajectory features.Measurements of the BPD critical current have been carried out with an ion thruster (Kaufman engine) to provide a background plasma, and these indicate that the presence of an ambient plasma of typical ionospheric densities has little effect on the critical current relation.Measurements of wave amplitudes over a large frequency range show that the amplitude of waves near the plasma and electron cyclotron frequencies are too small to cause or sustain BPD, and that the important instabilities are at much lower frequency (～ 3 kHz in these measurements).     

Injection of 40-kHz-modulated electron beam from the satellite: II. Excitation of electrostatic and whistler waves

Beam-plasma interaction effects are studied during the active space experiment with electron and Xe-ion beam injections in an ionospheric plasma. Permanent 40-kHz-modulated electron beam injection occurs simultaneously with a xenon-ion beam injected by the Hall-type plasma thruster operating in a square-pulse mode (100/50 s for a job/pause duration). The unusual behavior of the background charged particle fluxes and wave activity stimulated during the beam-plasma interaction have been registered by the scientific instruments onboard Intercosmos-25 station (IK-25) and Magion-3 subsatellite. The longitudinal and electromagnetic wave instabilities and their mutual relationship are considered in order to explain the observed effects. The excitation of electrostatic waves by the electron injection has been considered for different resonance conditions near the linear stability boundary. Beam-driven electromagnetic instability is responsible for the backward-propagating whistler waves excited via cyclotron resonance. Competition of these two beam instabilities is one of the subjects of the present study.     

Quality assessment of sub-Nyquist recovery from future gravity satellite missions

Drawing on experience from Gravity Recovery and Climate Experiment (GRACE) data analysis, the scientific challenges were already identified in several studies. Any future mission should focus on improvement in both precision and resolution in space and time. For future gravity missions which use high quality sensors, aliasing of high frequency time-variable geophysical signals to the lower frequency signals is one of the most serious problems. The aliasing problem and the spatio-temporal resolution are mainly restricted by two sampling theorems describing the space-time sampling of satellite missions: (i) a Heisenberg-like uncertainty theorem which states that the product of spatial resolution and time resolution is constant, and (ii) the Colombo–Nyquist rule (CNR), which requires the number of satellite revolutions in a repeat period to be at least twice a given maximum spherical harmonic degree. The CNR holds under the assumption of equal ground-track spacing, and limits the spatial resolution of the gravity solution.