Charge Cloud Research Articles

A framework to model charge sharing and pulse pileup for virtual imaging trials of photon-counting CT

Objective.This study describes the development, validation, and integration of a detector response model that accounts for the combined effects of x-ray crosstalk, charge sharing, and pulse pileup in photon-counting detectors.Approach.The x-ray photon transport was simulated using Geant4, followed by analytical charge sharing simulation in MATLAB. The analytical simulation models charge clouds with Gaussian-distributed charge densities, which are projected on a 3×3 pixel neighborhood of interaction location to compute detected counts. For pulse pileup, a prior analytical method for redistribution of energy-binned counts was implemented for delta pulses. The x-ray photon transport and charge sharing components were validated using experimental data acquired on the CdTe-based Pixirad-1/Pixie-III detector using monoenergetic beams at 26, 33, 37, and 50 keV. The pulse pileup implementation was verified with a comparable Monte Carlo simulation. The model output without pulse pileup was used to generate spatio-energetic response matrices for efficient simulation of scanner-specific photon-counting CT (PCCT) images with DukeSim, with pulse pileup modeled as a post-processing step on simulated projections. For analysis, images for the Gammex multi-energy phantom and the XCAT chest phantom were simulated at 120 kV, both with and without pulse pileup for a range of doses (27-1344 mAs). The XCAT images were evaluated qualitatively at 120 mAs, while images for the Gammex phantom were evaluated quantitatively for all doses using measurements of attenuation coefficients and Calcium concentrations.Main results.Reasonable agreement was observed between simulated and experimental spectra with Mean Absolute Percentage Error Values (MAPE) between 10%and 31%across all incident energies and detector modes. The increased pulse pileup from increased dose affected attenuation coefficients and calcium concentrations, with an effect on calcium quantification as high as MAPE of 28%.Significance.The presented approach demonstrates the viability of the model for enabling VITs to assess and optimize the clinical performance of PCCT.

Charge Diffusion and Repulsion in Semiconductor Detectors

Semiconductor detectors for high-energy sensing (X/γ-rays) play a critical role in fields such as astronomy, particle physics, spectroscopy, medical imaging, and homeland security. The increasing need for precise detector characterization highlights the importance of developing advanced digital twins, which help optimize the design and performance of imaging systems. Current simulation frameworks primarily focus on modeling electron–hole pair dynamics within the semiconductor bulk after the photon absorption, leading to the current signals at the nearby electrodes. However, most simulations neglect charge diffusion and Coulomb repulsion, which spatially expand the charge cloud during propagation due to the high complexity they add to the physical models. Although these effects are relatively weak, their inclusion is essential for achieving a high-fidelity replication of real detector behavior. There are some existing methods that successfully incorporate these two phenomena with minimal computational cost, including those developed by Gatti in 1987 and by Benoit and Hamel in 2009. The present work evaluates these two approaches and proposes a novel Monte Carlo technique that offers higher accuracy in exchange for increased computational time. Our new method enables more realistic performance predictions while remaining within practical computational limits.

Optimizing charge transport simulation for hybrid pixel detectors

To enhance the spatial resolution of the MÖNCH 25 µm pitch hybrid pixel detector, deep learning models have been trained using both simulation and measurement data. Challenges arise when comparing simulation-based deep learning models to measurement-based models for electrons, as the spatial resolution achieved through simulations is notably inferior to that from measurements. Discrepancies are also observed when directly comparing X-ray simulations with measurements, particularly in the spectral output of single pixels. These observations collectively suggest that current simulations require optimization. To address this, the dynamics of charge carriers within the silicon sensor have been studied using Monte Carlo simulations, aiming to refine the charge transport modeling. The simulation encompasses the initial generation of the charge cloud, charge cloud drift, charge diffusion and repulsion, and electronic noise. The simulation results were validated with measurements from the MÖNCH detector for X-rays, and the agreement between measurements and simulations was significantly improved by accounting for the charge repulsion.

Extreme thunderstorm ground enhancements registered on Aragats in 2023

In 2023, a series of intense thunderstorm ground enhancements (TGEs) were recorded on Mount Aragats in Armenia, with seven events exceeding the fair-weather cosmic ray flux by more than 75%. This study comprehensively analyzes these TGEs, investigating the atmospheric conditions and electric fields contributing to their occurrence. Key insights include discovering relationships between TGE electron content and the location of atmospheric electric fields, recovering electron and gamma-ray energy spectra, and the impact of the cloud charge structure. The findings offer a deeper understanding of TGEs’ role in atmospheric physics and its synergy with high-energy astrophysics. Published by the American Physical Society 2024

Thermodynamics of a newly constructed black hole coupled with nonlinear electrodynamics and cloud of strings

This paper finds an exact singular black hole solution in the presence of nonlinear electrodynamics as the source of matter field surrounded by a cloud of strings in 4DAdS spacetime. Here, the presence of the cloud of string, the usual Bardeen solution, becomes singular. The obtained black hole solution interpolates with the AdS Letelier black hole in the absence of both the deviation parameter and magnetic charge and interpolates with the AdS Bardeen black hole in the absence of the deviation parameter and a cloud of strings parameter. We analyse the horizon structure and thermodynamics properties, including the stability of the resulting black hole, numerically and graphically. Thermodynamical quantities associated with the black hole get modified due to the nonlinear electrodynamics and cloud of strings. Moreover, we study the effect of a cloud of strings parameter, magnetic charge and deviation parameter on critical points and phase transition of the obtained black hole where the cosmological constant is treated as the thermodynamics pressure. The critical radius increases with increasing deviation parameter values and magnetic charge values. In contrast, the critical pressure and temperature decrease with increasing deviation parameters and magnetic charge values.

Self-Coagulation Theory and Related Comet- and Semi-Circle-Shaped Structures in Electronegative and Gaseous Discharging Plasmas in the Laboratory

In this work, the two-dimensional fluid models for two types of inductively coupled plasma, Ar/O2 and Ar/SF6, are numerically solved by the finite element method. Four interesting phenomena revealed by the simulations are reported: (1) comet-shaped and semi-circle-shaped structures in Ar/O2 and Ar/SF6 plasmas, respectively; (2) blue sheaths that surround the two structures; (3) the collapse and dispersion of semi-circle-shaped structures of certain Ar/SF6 plasma cations and anions when they are observed separately; and (4) the rebuilding of coagulated structures by minor cations in the Ar/SF6 plasma at the discharge center. From the simulation detail, it was found that the cooperation of free diffusion and negative chemical sources creates the coagulated structure of anions, and the self-coagulation theory is therefore built. The advective and ambipolar types of self-coagulation are put forth to explain the co-existence of blue sheath and internal neutral plasma, among which the advective type of self-coagulation extends the Bohm’s sheath theory of cations to anions, and the ambipolar type of self-coagulation originates from the idea of the ambipolar diffusion process, and it updates the recognition of people about the plasma collective interaction. During the ambipolar self-coagulation, each type of Ar/SF6 plasma cations and anions is self-coagulated, and the coagulated plasma species are then modeled as mass-point type (or point-charge type, more precisely). When the charge amounts of two point-charge models of plasma species with the same charge type are equal, the expelling effect caused by the Coulomb’s force of them leads to the collapse or dispersal of heavily coagulated species. The simulation shows that the lighter the species is, the easier it self-coagulates and the more difficult its coagulation is broken, which implies the inertia effect of density quantity. Moreover, the collapse of cation coagulation creates the spatially dispersed charge cloud that is not shielded into the Debye’s length, which indicates the anti-collective behavior of electronegative plasmas when they are self-coagulated. The rebuilt coagulated structure of minor Ar/SF6 plasma species at the discharge center and the weak coagulation of electrons in the periphery of the main coagulated structure that is under the coil are caused by the monopolar and spontaneous (non-advective) type of self-coagulation. The analysis predicts an intensity order of physically driven coagulation force, chemical self-coagulation force, and ambipolar self-coagulation force. The popular coagulated structure of the electronegative ICP sources is urgently needed to validate the experiment.

Spatial resolution improvements with finer-pitch GEMs

Gas Electron Multipliers (GEMs) are used in many particle physics experiments, employing their `standard' configuration with amplification holes of 140 μm pitch in a hexagonal pattern. However, the collection of the charge cloud from the primary ionisation electrons from the drift region of the detector into the GEM holes affects the position information from the initial interacting particle. In this paper, the results from studies with a triple-GEM detector with an X-Y-strip readout anode are presented. It is demonstrated that GEMs with a finer hole pitch of here 90 μm improve the detector's spatial resolution. Within these studies, also the impact of the front-end electronics on the spatial resolution was investigated, which is briefly discussed in the paper.

Temporal characteristics of positive cloud-to-ground flashes from tropical thunderstorms

The occurrence of positive cloud-to-ground (CG) lightning flashes proves to be a challenging task when compared to the negative CG flash which common happen in tropical region. This due to the positively charged clouds to reach higher altitudes to enable the transfer of electrical charges to the Earth's surface. With several sensors that deployed in the Malacca region (2.314077°N, 102.318282°E) such as the wide band fast and slow antenna, magnetic field sensors, and the electric field mill (EFM-100). This research study focuses on the temporal characteristics of positive CG lightning activity in the tropical region during September and October 2021. A total of 203 positive cloud-to-ground flashes were meticulously analyzed in the context of 16 thunderstorm events. Key findings highlight the consistent initiation of positive cloud-to-ground flashes through initial breakdown (IB) pulses, followed by the development of stepped leaders and subsequent return strokes. Notably, most positive cloud-to-ground events (72%) were observed as single strokes and the maximum multiplicity recorded being four subsequent return strokes. Furthermore, the analysis focuses into the temporal aspects of these lightning events, revealing average durations for various parameters, including rise-time (6.26 μs), zero-crossing (26.43 μs), pulse duration of the first RS (139.76 μs), and the interval from the first IB to the first return stroke (134.19 ms). Additionally, the recorded data from the Electric Field Mill (EFM) instruments together with Constant Altitude Plan Position Indicator (CAPPI) radar demonstrate a notable correlation. Specifically, the electric field (E-field) values exhibit a discernible increase when positive cloud-to-ground lightning events are detected near the lightning sensor.

Solution of the dark matter riddle within standard model physics: from black holes, galaxies and clusters to cosmology

It is postulated that the energy density of the (quantum) vacuum acts firstly as dark energy and secondly as a part of dark matter. Assisted by electric fields arising from a small charge mismatch in the cosmic plasma, it can condense on mass concentrations. No longer participating in the cosmic expansion, this constitutes “electro-aether-energy” (EAE), “electro-zero-point-energy” or “electro-vacuum-energy”, which solves the dark matter riddle without new physics. A radial electric field of 1 kV/m is predicted in the Galaxy. For proper electric fields, EAE can cover the results deduced with MOND. An instability allows a speedy filling of dark matter cores. Hydrostatic equilibrium in galaxy clusters is obeyed. Flowing in aether energy of explains why black holes become supermassive, do not have mass gaps and overcome the final parsec problem. Rupture of charged clouds reduces, e.g., the primordial baryon cloud to the cosmic web. The large coherence scale of the electric field acts as a scaffold for gentle galaxy formation and their vast polar structures. In galaxy merging and bars, there occurs no dynamical friction. At cosmological scales, EAE acts as pressureless dark matter. Its amount increases in time, which likely solves the Hubble tension by its late time physics. A big crunch can occur. Of the large cosmological constant injected at the Big Bang, a small part kept that form, without fine-tuning.

Atomic-scale visualization of the interlayer Rydberg exciton complex in moiré heterostructures

Excitonic systems, facilitated by optical pumping, electrostatic gating or magnetic field, sustain composite particles with fascinating physics. Although various intriguing excitonic phases have been revealed via global measurements, the atomic-scale accessibility towards excitons has yet to be established. Here, we realize the ground-state interlayer exciton complexes through the intrinsic charge transfer in monolayer YbCl3/graphite heterostructure. Combining scanning tunneling microscope and theoretical calculations, the excitonic in-gap states are directly profiled. The out-of-plane excitonic charge clouds exhibit oscillating Rydberg nodal structure, while their in-plane arrangements are determined by moiré periodicity. Exploiting the tunneling probe to reflect the shape of charge clouds, we reveal the principal quantum number hierarchy of Rydberg series, which points to an excitonic energy-level configuration with unusually large binding energy. Our results demonstrate the feasibility of mapping out the charge clouds of excitons microscopically and pave a brand-new way to directly investigate the nanoscale order of exotic correlated phases.

AI-POWERED FINANCIAL OPERATION STRATEGY FOR CLOUD COMPUTING COST OPTIMIZATION FOR FUTURE

Cloud computing has revolutionized the way groupings feature by way of manner of presenting scalable and flexible infrastructure services. However, dealing with cloud cost efficiently remains a project, as cloud environments emerge as more complex. This paper proposes an AI-powered financial operation approach for optimizing cloud computing cost. The method leverages AI algorithms to research utilization patterns, forecast future calls, and advise price-saving measures. By imposing this approach, agencies can acquire massive financial savings at the same time as ensuring the nice everyday normal performance and scalability in their cloud infrastructure. Cloud computing has obtained massive prominence in commercial enterprise because of its capacities. However, the effective management of cloud cost remains a complex agency. However, incorporating automation and Machine Learning (ML) gives a possibility to manipulate and mitigate cloud charges successfully, rendering cloud computing an additional economically viable solution. This study will investigate into the transformative effect of automation and Machine learning cloud cost optimization, providing insights into how companies can harness those technologies to curtail fees on the equal time as addressing ability implementation-demanding situations. As organizations increasingly trust upon cloud computing services for their operations, optimizing the related prices performances into a crucial factor of financial management. This paper proposes an AI-powered financial operation technique for cloud computing fee optimization. The technique leverages tool-reading algorithms to investigate historic utilization patterns, forecast future desires, and perceive capability fee-saving possibilities. It integrates with cloud service providers' APIs to continuously reveal useful resource usage and adjust provisioning ranges dynamically. Additionally, the technique includes anomaly detection strategies to discover inefficiencies or sudden spikes in utilization, permitting proactive fee management. Through the implementation of this AI-powered technique, businesses can gain huge discounts in cloud computing costs even while preserving the finest overall performance and scalability.

The magnetic field does not perform work—or does it?

We investigate the question discussed in the literature as to whether the magnetic field can perform work using two models that describe interacting magnetic dipoles. In the first model, the dipoles are realized by rigidly rotating charge clouds, whereas in the second model, one of the two dipoles is described by a real macroscopic spin density. The theoretical foundations of the second model are formulated in a recently published paper. We derive equations of motion and detailed energy balance for both models when the initial magnetic moments are parallel to the connecting line of the initial dipole positions. In this scenario the ‘large’ dipole remains stationary and generates an external magnetic field in which the ‘small’ dipole is accelerated. The answer to the title question depends on the choice of criteria for ‘work of the magnetic field’.

Induced Electromagnetic Radiation From A Charged Cloud In A Plane Gravitational Wave

For the perturbative model of a plane gravitational wave on a flat background of Minkowski space-time, electromagnetic radiation from a charged cloud in the field of a gravitational wave, detected by a remote observer, was found. It is shown that the charge density in the cloud does not change, and the radiation is generated by currents induced by the gravitational wave. The angular distribution of the radiation is obtained. If the refractive index of the cloud medium is greater than unity, Cherenkov-type radiation is generated.

Spatially regular charged black holes supporting charged massive scalar clouds

Spatially regular charged black holes supporting charged massive scalar clouds

Induced Electromagnetic Radiation from a Charged Cloud in a Plane Gravitational Wave

Induced Electromagnetic Radiation from a Charged Cloud in a Plane Gravitational Wave

The scattering map on collapsing charged spherically symmetric spacetimes

In this paper we generalise our previous results (Alford 2020 Ann. Inst. Henri Poincare 21 2031–92) concerning scattering on the exterior of collapsing dust clouds to the charged case, including in particular the extremal case. We analyse the energy boundedness of solutions φ to the wave equation on the exterior of collapsing spherically symmetric charged matter clouds. We then proceed to define the scattering map on this spacetime, and look at the implications of our boundedness results on this map. More specifically, we first construct a class of spherically symmetric charged collapsing matter cloud exteriors, and then consider solutions to the wave equation with Dirichlet (reflective) boundary conditions on the surface of these clouds. We then show that the energy of φ remains uniformly bounded going forwards or backwards in time, and that the scattering map is bounded going forwards but not backwards. Therefore, the scattering map is not surjective onto the space of finite energy on I+∪H+ . Thus there does not exist a backwards scattering map from finite energy radiation fields on I+∪H+ to finite energy radiation fields on I− for these models. These results will be used to give a treatment of Hawking radiation in a companion paper (Alford 2023 arXiv:2309.03022).

Tailoring the Function of Battery Separators via the Design of MOF Coatings

AbstractSeparators serve as critical components in batteries, bearing the responsibility for battery safety. In addition to the demand for increased flame resistance of separators, there is a growing interest in the additional functions of battery separators. In this work, a multifunctional coating integration strategy is proposed for battery separators via the versatility of metal–organic frameworks. A versatile and high‐safety MIP‐202@2320 composite separator is engineered and it is integrated into lithium–sulfur batteries. The presence of Cl− and the porous structure of MIP‐202 impart flame‐retardant characteristics and high electrolyte retention (80%) to resulting separators. Moreover, coupled with the negatively charged electron cloud formed by Cl− ions within the channels, it can selectively impede the polysulfides from migrating toward the anode, while concurrently facilitating the movement of Li+ ions. The assembled lithium–sulfur battery with MIP‐202@2320 as the separator maintains an impressive 71.8% capacity retention even after 600 cycles at a 0.5C rate. This multifunctional integration strategy not only boosts the performance of lithium–sulfur batteries but also pioneers a new direction for the design of future battery separators for different kinds of batteries.

Charge in non-thunderstorm clouds and fogs

The global atmospheric electric circuit links charge separation in thunderclouds with current flow throughout the atmosphere. This current flow causes charge accumulation on the upper and lower boundaries of clouds and fogs. Thunderclouds are therefore not the only charged clouds in the atmosphere, and other forms of clouds, especially extensive horizontal layer clouds (stratus) are much more abundant globally. To investigate possible effects of charging of natural droplets in clouds, experiments have been undertaken using corona ion emission into fogs, releasing from within and above the fog. During the corona ion release the droplet size distribution was modified, with an increase in small drops. Further, when the ions were released over the fog, the reflectivity of the fog increased by ∼2%, about 30s later.

Exploring the Use of Terrestrial Robots for Atmospheric Electricity Measurement

Measuring the electric field is a central goal in electrostatics research, such as the study of electrostatics in atmospheric processes. It serves as a key indicator for various atmospheric phenomena, including the presence of lightning, dust or charged clouds. Traditionally, electric field measurements have been conducted from static platforms, with limited mobile measurements from airborne platforms such as balloons or, more recently, Unmanned Aerial Vehicles (UAVs). Here, we explore the potential of terrestrial robots to measure the electric field with some level of autonomy, such as during supervised navigation between user-defined waypoints. We mount a field mill on a four-wheeled rover and use a Global Navigation Satellite System (GNSS) to track the position of its measurements during an outdoor survey. The robot has a depth camera for 3D terrain mapping to contextualise local field measurements. We present plans for future research, including the use of semi-autonomous identification and exploration of electrostatic ‘hotspots’; and deployment of multiple robots (e.g., six) in a ‘sparse swarm’ configuration. We consider opportunities to employ such a robot system in environmental science or space research, for instance on Mars or the moon, where an understanding of electrostatic processes could be significant for future space missions.

First experimental evaluation of a high-resolution deep silicon photon-counting sensor.

Current photon-counting computed tomography detectors are limited to a pixel size of around 0.3 to 0.5mm due to excessive charge sharing degrading the dose efficiency and energy resolution as the pixels become smaller. In this work, we present measurements of a prototype photon-counting detector that leverages the charge sharing to reach a theoretical sub-pixel resolution in the order of . The goal of the study is to validate our Monte-Carlo simulation using measurements, enabling further development. We measure the channel response at the MAX IV Lab, in the DanMAX beamline, with a 35keV photon beam, and compare the measurements with a 2D Monte Carlo simulation combined with a charge transport model. Only a few channels on the prototype are connected to keep the number of wire bonds low. The measurements agree generally well with the simulations with the beam close to the electrodes but diverge as the beam is moved further away. The induced charge cloud signals also seem to increase linearly as the beam is moved away from the electrodes. The agreement between measurements and simulations indicates that the Monte-Carlo simulation can accurately model the channel response of the detector with the photon interactions close to the electrodes, which indicates that the unconnected electrodes introduce unwanted effects that need to be further explored. With the same Monte-Carlo simulation previously indicating a resolution of around with similar geometry, the results are promising that an ultra-high resolution detector is not far in the future.