Charge Cloud Research Articles

Ion accumulation by a dust cloud in a dc discharge

The ion accumulation within the negatively charged dust cloud embedded in a plasma of dc glow discharge has been studied numerically under the conditions corresponding to recent experiments. The characteristics of neon plasma in a positive column of dc discharge with various densities of micron-sized particles have been simulated by a diffusion-drift model with the use of experimental values of parameters of dust clouds. The model considers an additional gas heating associated with the presence of a dust component. It has been shown that the injection of dust particles into a plasma can either reduce the density of ions due to their recombination on dust particles or increase it due to the formation of an ion concentrator. Conditions under which the plasma-dust cloud represents an ion concentrator have been found; the density of ions in this trap can be several times higher than that in a discharge without dust particles. The method of elevating the ion density with dust particles has been shown to be more efficient than increasing the discharge current without dust particles and the value of relative overheating of the discharge with dust particles is many times less. The possibility of obtaining the desired ion density in a dust cloud at different neon pressures and the same discharge current has been demonstrated; it should be emphasized that this is impossible in a discharge without dust particles.

Impact of electrified and non-electrified clouds on the inter-seasonal characteristics of surface-based precipitation

A multi-sensor analysis of the characteristics of electrified and non-electrified clouds along with their impact on the surface-based raindrop size distribution (DSD) during the inter-seasonal phases of Indian summer monsoon over a heavy precipitation region of Western Ghat (WG) has been highlighted in the present paper. The analysis reveals that during the pre-monsoon (monsoon) months, raindrops of larger diameter dominate the rainfall evolving from the non-electrified (electrified) clouds compared to the rainfall evolving from the electrified (non-electrified) ones. The complex relationship of the convective rainfall with highly charged electrified clouds forces the smaller drops aloft and thereby allowing the larger drops to precipitate locally during the pre-monsoon season. While for the monsoon months, as most of the rainfall originates from the deep clouds, the chances of drops to break-up/evaporate is comparatively less for the precipitation evolving from electrified clouds with charged droplets with respect to the non-electrified ones. Hence, drops of larger diameter dominate the monsoon rainfall associated with lightning. Correspondingly, the paper also highlighted a case study of the changing morphology of the vertical structure of clouds and surface precipitation with the evolution of lightning during various stages of a typical rainfall event over the orographic region of WG.

Modeling Photon Counting Detector Anode Street Impact on Detector Energy Response

Accurate modeling of a photon-counting detector is essential for detector design and performance evaluation, system-level performance investigation, and image reconstruction. This modeling is complicated because various factors involve and couple together, including X-ray interactions, fluorescence X-rays escaping and absorption, primary charge cloud distribution, charge diffusion and interactions (repulsion), and charge trapping. In this article, we adapted a comprehensive detector modeling approach, which incorporates all these relevant factors into account. This approach allowed us to evaluate the impact of different physical effects on the detector energy response. In particular, we evaluated the impact of anode street impact on the detector energy response. We found the conductivity difference between the anode street surface and the bulk region within the sensor volume could significantly affect the detector energy response, including reducing peak events and increasing the low-energy tail events. As compared to without considering the anode street conductivity difference, the detection efficiency at 60 keV could be reduced by 5%-15% (40- μm street size), and 12%-33% (70- μm street size) when the threshold was varied from 45 to 57 keV.

An optimized ECG android system using data compression scheme for cloud storage

In the field of biomedical engineering, there is a lot of research being done in long term electrocardiographic (ECG) monitoring, and one of the most promising one concerns the transmission of compressed electrocardiographic signal throughout the internet, so that at the receiver side it arrives with minimum distortion, yet not demanding too much computational power from the processor to be decompressed. Other situations arrive when synchronization is a problem, and as a result may also require the storage of the signal in a cloud, for further examination by the medical staff. Another problem focuses on a reduced bandwidth for the transmission due to the huge amount of data obtained after a long term ECG monitoring of up to twelve ECG leads from the patient. In order to try solving these problems, this paper presents a ECG system using advances in Mobile Cloud Computing (MCC) focusing on its storage services, as well as concepts of ECG signal compression for an optimal processing power usage and transmission over Internet Protocol and making use of a free of charge cloud services. The task of compressing the ECG signal was made using vector quantization approach with reduced processing consumption by the mobile device. The system’s performance resulted quite suitable to be applied in patients remote ECG monitoring with very low signal distortion - maintaining its morphological information, good compression rate and reduced bandwidth for data transmission and storage. In conclusion, the system’s architecture and concepts presented here have a potential use in telemedicine systems.

Accurate contrast determination for X-ray speckle visibility spectroscopy.

X-ray speckle visibility spectroscopy using X-ray free-electron lasers has long been proposed as a probe of fast dynamics in noncrystalline materials. In this paper, numerical modeling is presented to show how the data interpretation of visibility spectroscopy can be impacted by the nonidealities of real-life X-ray detectors. Using simulated detector data, this work provides a detailed analysis of the systematic errors of several contrast extraction algorithms in the context of low-count-rate X-ray speckle visibility spectroscopy and their origins are discussed. Here, it was found that the finite detector charge cloud and pixel size lead to an unavoidable `degeneracy' in photon position determination, and that the contrasts extracted using different algorithms can all be corrected by a simple linear model. The results suggest that experimental calibration of the correction coefficient at the count rate of interest is possible and essential. Thisallows computationally lightweight algorithms to be implemented for on-the-fly analysis.

A spectroscopic Monte-Carlo model to simulate the response of pixelated CdTe based detectors

A fully spectroscopic Monte Carlo model has been developed to predict the spectroscopic performance of pixelated CdTe based detectors. The model incorporates photon attenuation by the photoelectric effect, Compton scattering and Rayleigh scattering. Charge transport equations are used to simulate the size of the electron cloud, approximated by a symmetrical two-dimensional Gaussian distribution, as it drifts to be read out at the detector anode. Direct comparisons are made between simulated data and experimentally acquired spectra from a 1 mm thick CdTe sensor coupled to the HEXITEC detector ASIC. The probability of an absorbed photon leading to charge sharing across pixels as a function of incoming photon energy is investigated. The charge cloud size was found to be dominated by cloud growth during drift for photon energies <100 keV. Furthermore, the portion of charge sharing events due to fluorescence from within the CdTe sensor is calculated—these events are distinguished from regular charge sharing events since their energy response differs. The model described is shown to give a good estimate of the total probability of charge sharing for energies up to 140 keV. CdTe sensor thickness, bias voltage, pixel size and electronic noise threshold can be adjusted to model a range of detector architectures.

Interaction between convective cloud systems and the Earth’s surface

The nature of interaction between electric fields in convective cloud systems with the underlying surface is considered. Differences in charge potentials at different points of the Earth are indicated. Modern theories about the appearance of positive and negative charges in clouds, about the development of lightning and places of their destruction are presented. Data on the influence of cloud systems depending on the properties of the Earth’s surface are presented. It is established that the interaction of cloud systems with the earth’s surface depends on the electrical properties of clouds. This interaction depends on the following factors: humidity, density, temperature, chemical and mineralogical composition, soil particle composition, structure, nature and properties of the soil solution.

Plasma expansion towards an electrically insulated surface

The problem of plasma expansion into a vacuum is revisited with the addition of a finite boundary condition; an electrically insulated surface. As plasma expands towards a charge-accumulating surface, the leading electron cloud charges the surface negatively, which in turn repels electrons and attracts ions. This plasma–surface interaction is shown to result in a feedback process which accelerates the plasma expansion. In addition, we examine the decrease in (negative) surface potential and associated near-surface electron density. To investigate this plasma coupling with an electrically floating surface, we develop an analytic model including four neighbouring plasma regions: (i) undisturbed plasma, (ii) quasi-neutral self-similar expansion, (iii) ion front boundary layer and (iv) electron cloud. A key innovation in our approach is a self-contained analytic approximation of the ion front boundary layer, providing a spatially continuous electric field model for the early phase of bounded plasma expansion.

Plasma charging effect on the nanoparticles releasing from the cavitation bubble to the solution during nanosecond Pulsed Laser Ablation in Liquid

The laser induced plasma during the nanosecond Pulsed Laser Ablation in Liquid (PLAL) plays a crucial role in the nanoparticles (NPs) formation and charging. It was demonstrated that during the plasma phase evolution, once the NPs are formed, they are charged with the excess of plasma electrons. Immediately after the plasma phase extinguishes, the NPs will be released in the induced vapor bubble, generated by the fast energy exchanges between the plasma and the liquid. The excess of charge in the NPs preserves them from the agglomeration during the bubble evolution and can induces an electrostatic pressure able to eject the particles outside the cavitation bubble.In this work, the plasma charging effect on the particle releasing in solution, during the bubble evolution, has been investigated. Temporal evolution of laser induced bubble on silver target immersed in water has been measured with the shadowgraph technique. Then, starting from the experimental bubble radius evolution, the releasing of the NPs from the cavitation bubble to the liquid has been modeled by comparing the electrostatic pressure of the charged NPs cloud and the pressure of the cavitation bubble. The following discussion proposes a new insight of the mechanism of NPs releasing in solution.

Effect of Nonzero Solid Permittivity on the Electrical Repulsion between Charged Surfaces.

The electrical repulsion between two charged solid surfaces separated by an electrolyte is studied as a function of the permittivity ϵs of the solid in the limit in which potentials are small, and the gap between the plane solid surfaces is small compared to the Debye length κ-1 within the electrolyte. The solid surfaces are uniformly charged in a central region |x|< L outside which they are uncharged. When ϵs = 0, ions from the charge cloud between the charged surfaces spill out into regions of length O(κ-1) beyond x = ± L, thereby reducing the pressure between the surfaces from that predicted by Derjaguin-Landau-Verwey-Overbeek theory for infinite, uniformly charged surfaces. When ϵs>0, ions spill out over much larger O(L) regions, thereby reducing still further both the electrical potential between the solid surfaces and the repulsive force between them. However, this reduction becomes smaller as κL becomes large.

Charged black holes in non-linear Q-clouds with O(3) symmetry

We construct charged soliton solutions around spherical charged black holes with no angular momentum in asymptotically flat spacetime. These solutions are non-linear generalizations of charged scalar clouds, dubbed Q-clouds, and they do not contradict the non-existence theorem for free (linear) scalar clouds around charged black holes. These solutions are the first examples of O(3) solutions for Q-clouds around a non-extremal and non-rotating BH in the Abelian gauge theory. We show that a solution exists with an infinitely short cloud in the limit of extremal black holes. We discuss the evolution of Q-cloud in a system with fixed total charge and describe how the existence of Q-clouds is related to the weak-gravity conjecture. The reason that the no-hair theorem by Mayo and Bekenstein cannot be applied to the massive scalar field is also discussed.

Solar radiation attenuation by aerosol: application to solar farms

The use of solar energy requires precise insolation knowledge of the considered site. Solar irradiance depends on geographical and astronomical parameters and variable characteristics of the atmosphere such as aerosol or cloud charge, which has a very important attenuation and pollution role. This study presents the estimate of the annual insolation of sites close to several solar farms. Insolation is calculated from Iqbal’s basic formulas with introduction of the total optical thickness determined by the AERONET. The PSDs and aerosol loading on an atmospheric column allowed the establishment of the attenuation-aerosol concentration relationship. The cloudless atmosphere attenuates the incident solar flux by an annual average of the order of 23.5%, where in average, about 13.73% is attributed to the aerosol, 17.75% for solar farm sites near the Sahara, and 8% for California and Arizona US sites.

Феноменология электрических разрядов, возникающих между отрицательно заряженным облаком водного аэрозоля и землёй

Studies of electrical discharges generated in the electric field of charged aerosol clouds make it possible to obtain better understanding of how lightning occurs in thunderclouds. For this purpose, an experimental setup was developed, which allows charged aerosol clouds of negative polarity to be produced. A charged aerosol cloud creates electric field strength sufficient to generate electrical discharges between this cloud and the earth. The experimental setup for obtaining an artificially produced charged aerosol cloud is briefly described. The experimental setup is equipped with a set of measuring instruments for recording the electrical and optical signals of discharges and for photographing the discharges themselves. A database has been accumulated in the course of experiments, which includes the waveforms of discharge current pulses recorded using digital oscilloscopes, the waveforms of signals from optical sensors recording the development of discharges in space and time, and the snapshots of discharges. By using the accumulated information it is possible to classify discharges that occur between artificially produced charged aerosol clouds of negative polarity and the earth by type and parameters. An analysis of the experimental data has shown that both upward and downward discharges can occur between a charged aerosol cloud and the earth, which is typical for natural lightning phenomena. The snapshots of the most characteristic types of electric discharges observed in experiments and simple models explaining the development of these discharges are studied.

WITHDRAWN

The document associated with this DOI has been withdrawn.

Performance Modeling of Silicon Carbide Photoconductive Switches for High-Power and High-Frequency Applications

In this article, we focus on the physical modeling of the nonlinear operation of intrinsic photoconductive semiconductor switches (PCSS) based on 4H-SiC using coupled electrical and optical simulations to provide performance bounds of the switch as a function of material and geometry parameters, as well as applied bias. We also conduct a full design-space exploration to identify the optimal operating and design conditions to maximize the compound metric $f_{\mathrm {op}} P_{\mathrm {out}}$ , where $f_{\mathrm {op}}$ is the maximum operating frequency, and $P_{\mathrm {out}}$ is the maximum output power the switch can provide. We quantify that a 10- $\mu \text{m}$ long and 5- $\mu \text{m}$ thick 4H-SiC PCSS can deliver output power density greater than 2W/mm at 150 GHz when triggered by a 0.325- $\mu \text{m}$ laser with intensity of 3 kW/cm2. The output power density can be significantly enhanced by increasing the optical generation rate as well as by using thicker SiC to improve its absorption characteristics. A brief discussion of signal distortion and electrostatic screening effects at high optical bias is included. Finally, we present an analytic model of charge cloud propagation and the frequency of operation based on the physics, material parameters, and geometry of the PCSS. The model accurately captures $f_{\mathrm {op}}$ of 4H-SiC PCSS over a broad range of laser spot size, device length, and electrical bias applied at the contacts.

Observation of the interactions of silver nanoparticles (AgNPs) mediated by acid in the aquatic matrices using in-situ liquid cell transmission electron microscopy

The properties of the solution matrix play a prominent role in determining the interactions between the silver nanoparticles (AgNPs) when they are present in the aquatic environment. Here, using in situ liquid cell transmission electron microscopy (LCTEM), we show that the interaction of AgNPs is predominantly affected by the solution pH. Reducing the pH in the solution will accelerate the aggregation of AgNPs due to the alteration of the charge cloud around the NPs. Aggregates formed in this scenario were non spherical and irregular shaped and were stable under the electron beam irradiation. Individual AgNPs and smaller aggregates moved randomly and approached the larger aggregates before the aggregation process came to an end. We found that during the aggregation process, the mode of jump to contact and the pairwise approach of aggregation differed according to the composition of the solution. Observations made using the LCTEM were further explained using empirical formulae. Our observation on the pH induced interactions provides important insights on predicting the behavior of AgNPs released through many anthropogenic activities in the environment.

Theoretical Problems Underlying Sprite Observations of the Planned Taranis Satellite Mission

Abstract Tool for the Analysis of Radiations from lightnings and Sprites (TARANIS) is a French Space Agency’s (CNES) satellite mission planned for launch in 2020. It is designed for investigating phenomena related to thunderstorm activity, transient luminous events (TLEs) and amongst them – red sprites. The satellite is equipped with cameras, photometers, energetic particles detectors, ion probe and electromagnetic sensors of wide frequency spectrum. It will be the most versatile satellite for measuring TLEs ever sent to space. In this article, theories that are fundamental for understanding sprites and sprites-related measurements of TARANIS mission are presented. The current state of sprites phenomenology and their possible generation mechanisms are presented. The article briefly covers streamer discharges, cloud charge structure at the TLE occurrence, electric breakdown of the air and Runaway Relativistic Electron Avalanche (RREA). At the end, TARANIS mission equipment and goals that are related to presented theories are presented.

Electron capture in collisions of Li3+ ions with ground and excited states of Li atoms**Project supported by the National Key Research and Development Program of China (Grant No. 2017YFA0402300), the National Natural Science Foundation of China (Grant No. 11774037), International Atomic Energy Agency, China (Grant No. 23196/R0), and the Science Challenge Project of China (Grant No. TZ2016001).

The electron capture processes in collisions of Li3+ ion with Li(1s22s) and Li(1s22p0,1) are investigated by using the two-center atomic orbital close-coupling method in the energy range from 0.1 keV/u to 300 keV/u. The interaction of the active electrons with the target ion is represented by a model potential. The present results for the Li3+–Li(1s22s) system are compared with the available theoretical data and general agreement is obtained for the high collision energies. It is also found that the total and partial electron capture cross sections are sensitive to the initial charge cloud alignment in the low energy region.

Study of (1 + 2)-dimensional charged string cloud with minimal geometric deformation

This paper is devoted to exploring exact charged solutions in a cloud of strings through minimal geometric deformation technique in three-dimensional gravity. For this purpose, we first evaluate the exact charged isotropic solution for static circular symmetry using Takabayashi equation of state and extend it to obtain three concrete anisotropic charged models. We investigate energy conditions as well as speed of sound constraint to check the viability of the respective solutions. It is concluded that the second model is a realistic one as it fulfills all the physical characteristics as well as stability criterion while the rest of two solutions do not satisfy the physical constraints.

A statistical field theory of salt solutions of ‘hairy’ dielectric particles

In this paper, we formulate a field-theoretical model of dilute salt solutions of electrically neutral spherical colloid particles. Each colloid particle consists of a ‘central’ charge that is situated at the center and compensating peripheral charges (grafted to it) that are fixed or fluctuating relative to the central charge. In the framework of the random phase approximation, we obtain a general expression for electrostatic free energy of solution and analyze it for different limiting cases. In the limit of infinite number of peripheral charges, when they can be modelled as a continual charged cloud, we obtain an asymptotic behavior of the electrostatic potential of a point-like test charge in a salt colloid solution at long distances, demonstrating the crossover from its monotonic decrease to damped oscillations with a certain wavelength. We show that the obtained crossover is determined by certain Fisher–Widom line. For the same limiting case, we obtain an analytical expression for the electrostatic free energy of a salt-free solution. In the case of nonzero salt concentration, we obtain analytical relations for the electrostatic free energy in two limiting regimes. Namely, when the ionic concentration is much higher than the colloid concentration and the effective size of charge cloud is much bigger than the screening lengths that are attributed to the salt ions and the central charges of colloid particles. The proposed theory could be useful for theoretical description of the phase behavior of salt solutions of metal-organic complexes and polymeric stars.