Electron Penetration Research Articles

Exclusion of Cosmic Rays from Molecular Clouds by Self-generated Electric Fields

Abstract It was recently discovered that in some regions of the Galaxy, the cosmic-ray (CR) abundance is several orders of magnitude higher than previously thought. Additionally, there is evidence that in molecular cloud envelopes, the CR ionization may be dominated by electrons. We show that for regions with high, electron-dominated ionization, the penetration of CR electrons into molecular clouds is modulated by the electric field that develops as a result of the charge they deposit. We evaluate the significance of this novel mechanism of self-modulation and show that the CR penetration can be reduced by a factor of a few to a few hundred in high-ionization environments, such as those found near the Galactic center.

Excellent photoluminescence and cathodoluminescence properties in Eu3+-activated Sr2LaNbO6 materials for multifunctional applications

Single Eu3+-activated Sr2LaNbO6 (SLN) phosphors with double-perovskite structure were successfully synthesized and their photo/cathodoluminescence properties were investigated in detail. The optimal doping concentration was confirmed to be about 0.3 mol while the concentration quenching was dominated by the dipole–dipole interaction. The optimum SLN:0.3Eu3+ phosphor exhibited good photoluminescence emission intensity, color purity, thermal stability, and quantum yield. With the help of the Judd-Oflet theory, Eu3+ ions would possess the stronger symmetry sites in SLN host lattice. Besides, the packaged red and white lighting-emitting diodes (LEDs) based on optimum sample were fabricated. Particularly, the packaged white LED device displayed good color rendering index value of 86.89 and correlated color temperature value of 4835 K. Moreover, the novel LED structure based on the SLN:0.3Eu3+-polydimethylsiloxane film having stable physicochemical structure was prepared and emitted a strong red light. Eventually, the strong cathodoluminescence intensity with large electron penetration depth was provided. These above results imply that SLN:Eu3+ phosphors with excellent photo/cathodoluminescence properties could be promised for multifunctional applications.

Impact of smart transformer voltage and frequency support in a high renewable penetration system

Increasing penetration of power electronics interfaced generation decreases the stability of the system, due to the absence of the rotational inertia in their operation. Emulation of the inertia using converter controls in combination with storages can address this issue. However, this method relies on the use of large quantities of storage to compensate power during a transient power unbalance. Instead of increasing the supply, the smart transformer (ST), with a fast response, offers the possibility to dynamically regulate the demand. This paper investigates the use of an ST to dynamically control reactive power and demand to support voltage and frequency respectively in the grid. The demand is controlled dynamically to emulate inertia. From an analysis based on a 250 kVA, 10kV/400V LV distribution network, it is shown that a demand variation in the range of 6-10% can be achieved. These results are extended to a case study based on the entire all-Island Irish Transmission system which shows that widespread use of STs with these controls could potentially facilitate a 10% increase in wind penetration without the inclusion of any other storage.

Development and Validation of Artificial Neural Network-Based Tools for Forecasting of Power System Inertia With Wind Farms Penetration

Increased penetration of power electronics interfaced renewable energy sources-based generation, for instance, wind farms, that displaces much of the conventional synchronous generation, has a profound effect on the inertia of modern/future power system networks. This article presents the development and validation of artificial neural network (ANN)-based tools, utilizing the power system variables measured by phasor measurement units through wide-area measurements systems, for estimation/forecasting of power system inertia with high penetration of wind farms. The development stage involves the correlation analysis to identify the best power system variables that can be nominated as inputs, and the training of the proposed inertia forecasting tools with the best-nominated inputs that are highly correlated with the power system inertia. Whereas, in the validation stage, the functionality of the trained ANN-based inertia forecasting tools have been validated using the hardware-in-the-loop testing facility developed at the University of Manchester. The development and validation procedures of the proposed inertia forecasting tools have been demonstrated on the IEEE 9-bus modified test system. The validation results revealed the effectiveness of the proposed inertia forecasting tools in estimating the inertia of modern/future power system networks with high penetration of wind farms.

Effect of High-Intensity Electron and Proton Fluxes on a Low-Latitude Ionosphere

Satellite experiments at low latitudes have shown that energetic (tens of keV) electrons and protons can penetrate from the Earth’s radiation belt near the equator into the ionosphere. The effect of the fluxes of these particles on the upper atmosphere and ionosphere remains understudied. In this study, local variations in the concentration of ionospheric ions in the regions of injection of electrons and protons with energies higher than 30 keV into the low-latitude ionosphere are studied using the magnetic storm of July 22, 2009, as an example. The relationship between an increase in the concentration in the F layer in the morning sector and additional ionization by fast electrons is shown. The ionospheric inhomogeneities observed in the night sector in the form of strong concentration fluctuations are caused by the action of protons. The solar-cyclic and annual variations in the frequency of the penetration of electrons and protons from the Earth’s radiation belt into the low-latitude ionosphere for the period from 1998 to 2019 are analyzed.

A model for the energy and angular distribution of x rays emitted from an x-ray tube. Part I. Bremsstrahlung production.

To develop an analytical model for bremsstrahlung production in a thick x-ray target (i.e., the x-ray tube anode) that takes into account the intrinsic bremsstrahlung angular distribution. X-ray spectrum models developed from theoretical principles have traditionally treated the angular distribution of the bremsstrahlung production as spherically uniform. This assumption stems from the rationale that electrons promptly attain a diffuse directional distribution in an x-ray target due to multiple scattering, thereby effectively masking the intrinsic bremsstrahlung angular distribution. In this work, a model that explicitly accounts for the angular distribution of the bremsstrahlung production is presented. The model combines Monte Carlo-calculated depth, energy, and angular distributions of electrons penetrating the x-ray target, and incorporates theoretical results for the differential bremsstrahlung cross section. The effects of using different simplified model assumptions for the electron penetration and the intrinsic bremsstrahlung angular distribution are analyzed for tungsten and molybdenum targets in the energy range 20-300keV. Typical assumptions of previous models are shown to introduce errors in calculated spectra. Particularly, it is shown that predictions of fluence and air kerma free-in-air can be overestimated by 15-30% (2-3% in aluminum half-value layer thickness) for clinically relevant beam qualities. The present model is able to reproduce comprehensive Monte Carlo calculations of the bremsstrahlung production generally to within 1%. The bremsstrahlung model developed in this work is an improvement over previous models in that the main features of the electron penetration and the resulting bremsstrahlung are considered in detail. The model can be used for more accurate predictions of the energy and angular distribution of x rays emitted from an x-ray tube.

Tuning the Interfacial Electronic Conductivity by Artificial Electron Tunneling Barriers for Practical Lithium Metal Batteries.

The native solid electrolyte interphase (SEI) in lithium metal batteries (LMBs) cannot effectively protect Li metal due to its poor ability to suppress electron tunneling, which may account for the increase of the SEI and even dead Li. It is desirable to introduce artificial electron tunneling barriers (AETBs) with ultrahigh insulativity and chemical stability to maintain a sufficiently low electronic conductivity of the SEI. Herein, a nanodiamond particle (ND)-embedded SEI is constructed by a self-transfer process. The ND serving as the AETB reduces the risk of electron penetration through the SEI, readjusts the electric field at the interface, and eliminates the tip effect. As a result, a dendrite-free morphology and dense massive microstructure of Li deposition are realized even with high areal capacity. Notably, full cells using ultrathin Li anodes (45 μm) and LiNi0.8Co0.1Mn0.1O2 cathodes (4.3 mA h cm-2) can cycle stably over 110 cycles, demonstrating that the AETB-embedded SEI significantly alleviates the anode pulverization and safety concerns in practical LMBs.

Dynamic Network Characteristics of Power-electronics-based Power Systems

Power flow studies in traditional power systems aim to uncover the stationary relationship between voltage amplitude and phase and active and reactive powers; they are important for both stationary and dynamic power system analysis. With the increasing penetration of large-scale power electronics devices including renewable generations interfaced with converters, the power systems become gradually power-electronics-dominant and correspondingly their dynamical behavior changes substantially. Due to the fast dynamics of converters, such as AC current controller, the quasi-stationary state approximation, which has been widely used in power systems, is no longer appropriate and should be reexamined. In this paper, for a better description of network characteristics, we develop a novel concept of dynamic power flow and uncover an explicit dynamic relation between the instantaneous powers and the voltage vectors. This mathematical relation has been well verified by simulations on transient analysis of a small power-electronics-based power system, and a small-signal frequency-domain stability analysis of a voltage source converter connected to an infinitely strong bus. These results demonstrate the applicability of the proposed method and shed an improved light on our understanding of power-electronics-dominant power systems, whose dynamical nature remains obscure.

Asymmetric carrier penetration into hexagonal boron nitride in graphene field-effect transistors

The electronic structure of graphene field-effect transistors with a hexagonal boron nitride (h-BN) gate dielectric was studied in terms of the gate electric field and dielectric thickness using the density functional theory combined with the effective screening medium method. The calculation results showed that the carrier penetration into monolayer h-BN depended on the gate voltage that injected electrons or holes into graphene. The critical voltage for hole penetration was lower than that for electron penetration. At a fixed carrier concentration, carrier penetration soon occurred with increasing h-BN thickness for hole doping.

A validation of SpekPy: A software toolkit for modelling X-ray tube spectra

PurposeTo validate the SpekPy software toolkit that has been developed to estimate the spectra emitted from tungsten anode X-ray tubes. The model underlying the toolkit introduces improvements upon a well-known semi-empirical model of X-ray emission. Materials and methodsUsing the same theoretical framework as the widely-used SpekCalc software, new electron penetration data was simulated using the Monte Carlo (MC) method, alternative bremsstrahlung cross-sections were applied, L-line characteristic emissions were included, and improvements to numerical methods implemented. The SpekPy toolkit was developed with the Python programming language. The toolkit was validated against other popular X-ray spectrum models (50 to 120 kVp), X-ray spectra estimated with MC (30 to 150 kVp) as well as reference half value layers (HVL) associated with numerous radiation qualities from standard laboratories (20 to 300 kVp). ResultsThe toolkit can be used to estimate X-ray spectra that agree with other popular X-ray spectrum models for typical configurations in diagnostic radiology as well as with MC spectra over a wider range of conditions. The improvements over SpekCalc are most evident at lower incident electron energies for lightly and moderately filtered radiation qualities. Using the toolkit, estimations of the HVL over a large range of standard radiation qualities closely match reference values. ConclusionsA toolkit to estimate X-ray spectra has been developed and extensively validated for central-axis spectra. This toolkit can provide those working in Medical Physics and beyond with a powerful and user-friendly way of estimating spectra from X-ray tubes.

Rational formation of solid electrolyte interface for high-rate potassium ion batteries

Abstract Potassium-ion batteries are one of the next-generation energy storage devices that are promising to partly replace lithium-ion batteries, especially in low-cost and large-scale application. However, the poor capacity and cycling stability do not meet the expected requirements. Herein, we synthesize a P–S co-doped flexible carbon fiber film derived from Chinese art paper, which is self-contained with SiO2 and MgO nanoparticles. Due to the uniform distribution of SiO2 and MgO on its surface, a reasonable solid electrolyte interphase (SEI) film is formed. The thin SEI layer (2–4 nm) is thick enough to prevent the electron penetration and simultaneously allows unhindered K ion intercalation/deintercalation, and it can also stabilize the interface between active material and electrolyte. Besides, the P–S co-doping can both enhance the K adsorption ability and electronic conductivity, therefore the rate capability is improved. The optimized carbon fiber film shows excellent flexibility and electrochemical performance. A capacity of 171.5 mA h g−1 at 1500 mA g−1 after 500 cycles is obtained. Even at a very high current density of 2500 mA g−1, the capacity can still reach as high as 177.3 mA h g−1. Because of its low cost and sustainability, this work will provide ideas for the development of high-performance potassium-ion battery anodes.

Grid-friendly power control for smart photovoltaic systems

The still increasing penetration of power electronics into the modern power systems challenges the entire system stability, which requires more advanced control strategies to address the issues. One of the challenges is the variability of renewable energies, including photovoltaic (PV) systems, which are generally operating with uncertainty and intermittency (non-dispatchable). In this regard, flexible power control solutions are of interest for PV systems, as an essential function of smart PV inverters, to minimize the adverse impact in grid-integration and operation. On the other hand, PV systems can be adapted to provide ancillary services, e.g., voltage and frequency support through the power control. This paper thus presents an overview of the recent advances in flexible active power control (FAPC) that enables the grid-friendly integration of smart PV systems. The demands for the FAPC are introduced from the grid’s perspective. Then, various FAPC schemes are reviewed, among which the control strategy by modifying the maximum power point tracking (MPPT) is the most feasible and efficient without any hardware modifications. This is known as the flexible power point tracking (FPPT), which is further illustrated by case studies. Additionally, a power reserve control (PRC) facilitating comprehensive voltage and frequency support to the grid is discussed in detail. Future research perspectives are also presented.

Lattice-confined Ru clusters with high CO tolerance and activity for the hydrogen oxidation reaction

An efficient catalyst for the hydrogen oxidation reaction (HOR) must maintain an oxide-free metal surface in a relatively high potential range. This requirement automatically excludes ruthenium because it is susceptible to oxidation in the hydrogen adsorption/desorption potential region. Herein we report Ru clusters partially confined in the lattice of urchin-like TiO2 crystals (Ru@TiO2) that can effectively catalyse the HOR up to a potential of 0.9 VRHE with a mass activity higher than that of a PtRu catalyst under both acidic and basic conditions. Moreover, the HOR activity of this Ru@TiO2 catalyst is not affected by 1,000 ppm CO impurity. Even at a high CO content of 10 vol%, Ru@TiO2 still selectively catalyses the HOR. Confined Ru clusters grow along the lattice of TiO2 with abundant Ru–Ti bond formation. Such atomically connected co-crystals offer efficient electron penetration from electron-rich TiO2 to Ru metal, leading to sluggish CO adsorption kinetics during the HOR. Efficient hydrogen oxidation catalysts must maintain an oxide-free metal surface in a relatively high potential range. Now, a catalyst consisting of Ru clusters partially confined in the lattice of urchin-like TiO2 crystals is shown to catalyse the reaction up to a potential of 0.9 VRHE with high mass activity and CO tolerance under both acidic and basic conditions.

Charging Effects in Al-SiO2-p-Si Structures After Low-Energy Electron Beam Irradiation

The effect of electron beam irradiation on trap charging and interface defect generation in Al/SiO2/Si structures was investigated by high-frequency capacitance–voltage measurements. Irradiation was carried out with two beam energies, at which the electron penetration depth was smaller and larger than the SiO2 thickness. The effect of applied bias, which changes the electric field inside the SiO2 film and the Si surface potential, on both the interface defect generation under the electron beam irradiation and their annealing was revealed. This showed that excess electrons generated by an e-beam play an important role in the interface defect formation. It was found that interface trap relaxation can occur even at room temperature, likely by electron tunneling from Si or hole tunneling from SiO2. The relaxation of positive bulk charge occurs at temperatures higher than 400 K via thermally stimulated carrier escape from traps. The activation energy for this process was estimated as 0.35–0.4 eV.

Fast Frequency Response From Energy Storage Systems—A Review of Grid Standards, Projects and Technical Issues

Electric power systems foresee challenges in stability due to the high penetration of power electronics interfaced renewable energy sources. The value of energy storage systems (ESS) to provide fast frequency response has been more and more recognized. Although the development of energy storage technologies has made ESSs technically feasible to be integrated in larger scale with required performance, the policies, grid codes and economic issues are still presenting barriers for wider application and investment. Recent years, a few regions and countries have designed new services to meet the upcoming grid challenges. A number of grid-scale ESS projects are also implemented aiming to trial performance, demonstrate values, and gain experience. This paper makes a review on the above mentioned aspects, including the emerging frequency regulation services, updated grid codes and grid-scale ESS projects. Some key technical issues are also discussed and prospects are outlined.

Chorus Acceleration of Relativistic Electrons in Extremely Low L‐Shell During Geomagnetic Storm of August 2018

AbstractBased on data from the Van Allen Probes and ZH‐1 satellites, relativistic electron enhancements in extremely low L‐shell regions (reaching ) were observed during August 2018 major geomagnetic storm (minimum nT). Contrary to what occurs in the outer belt, such an intense and deep electron penetration event is rare and more interesting. Strong whistler‐mode (chorus and hiss) waves, with amplitudes 81–126 pT, were also observed in the extremely low L‐shell simultaneously (reaching ) where the plasmapause was suppressed. The bounce‐averaged diffusion coefficient calculations support that the chorus waves can play a significantly important role in diffusing and accelerating the 1–3 MeV electrons even in such low L‐shells during storms. This is the first time that the electron acceleration induced by chorus waves in the extremely low L‐shell region is reported. This new finding will help to deeply understand the electron acceleration process in radiation belt physics.

Towards an Understanding of the Mode of Action of Human Aromatase Activity for Azoles through Quantum Chemical Descriptors-Based Regression and Structure Activity Relationship Modeling Analysis

Aromatase is an enzyme member of the cytochrome P450 superfamily coded by the CYP19A1 gene. Its main action is the conversion of androgens into estrogens, transforming androstenedione into estrone and testosterone into estradiol. This enzyme is present in several tissues and it has a key role in the maintenance of the balance of androgens and estrogens, and therefore in the regulation of the endocrine system. With regard to chemical safety and human health, azoles, which are used as agrochemicals and pharmaceuticals, are potential endocrine disruptors due to their agonist or antagonist interactions with the human aromatase enzyme. This theoretical study investigated the active agonist and antagonist properties of “chemical classes of azoles” to determine the relationships of azole interaction with CYP19A1, using stereochemical and electronic properties of the molecules through classification and multilinear regression (MLR) modeling. The antagonist activities for the same substituent on diazoles and triazoles vary with its chemical composition and its position and both heterocyclic systems require aromatic substituents. The triazoles require the spherical shape and diazoles have to be in proper proportion of the branching index and the number of ring systems for the inhibition. Considering the electronic aspects, triazole antagonist activity depends on the electrophilicity index that originates from interelectronic exchange interaction (ωHF) and the LUMO energy (), and the diazole antagonist activity originates from the penultimate orbital () of diazoles. The regression models for agonist activity show that it is opposed by the static charges but favored by the delocalized charges on the diazoles and thiazoles. This study proposes that the electron penetration of azoles toward heme group decides the binding behavior and stereochemistry requirement for antagonist activity against CYP19A1 enzyme.

Effect of Chiral Molecules on the Electron's Spin Wavefunction at Interfaces.

Kelvin-probe measurements on ferromagnetic thin film electrodes coated with self-assembled monolayers of chiral molecules reveal that the electron penetration from the metal electrode into the chiral molecules depends on the ferromagnet’s magnetization direction and the molecules’ chirality. Electrostatic potential differences as large as 100 mV are observed. These changes arise from the applied oscillating electric field, which drives spin-dependent charge penetration from the ferromagnetic substrate to the chiral molecules. The enantiospecificity of the response is studied as a function of the magnetization strength, the magnetization direction, and the handedness and length of the chiral molecules. These new phenomena are rationalized in terms of the chiral-induced spin selectivity (CISS) effect, in which one spin orientation of electrons from the ferromagnet penetrates more easily into a chiral molecule than does the other orientation. The large potential changes (>kT at room temperature) manifested here imply that this phenomenon is important for spin transport in chiral spintronic devices and for magneto-electrochemistry of chiral molecules.

Effects of 150–1000 eV Electron Impacts on Pure Carbon Monoxide Ices Using the Interstellar Energetic-Process System (IEPS)

Abstract Pure CO ice has been irradiated with electrons of energy in the range 150−1000 eV with the Interstellar Energetic-Process System. The main products of irradiation are carbon chains C n (n = 3, 5, 6, 8, 9, 10, 11, 12), suboxides, C n O (n = 2, 3, 4, 5, 6, 7), and C n O2 (n = 1, 3, 4, 5, 7) species. CO2 is by far the most abundant reaction product in all the experiments. The destruction cross section of CO peaks at about 250 eV, decreases with the energy of the electrons and is more than one order of magnitude higher than for gas-phase CO ionization. The production cross section of carbon dioxide has been also derived and is characterized by the competition between chemistry and desorption. Desorption of CO and of new species during the radiolysis follows the electron distribution in the ice. Low-energy electrons having short penetration depths induce significant desorption. Finally, as the ice thickness approaches the electron penetration depth the abundance of the products starts to saturate. Implications on the atmospheric photochemistry of cold planets hosting surface CO ices are also discussed.

Encapsulated cobalt nanoparticles as a recoverable catalyst for the hydrolysis of sodium borohydride

The significant challenges encountered when replacing precious-metal-based catalysts in the hydrolysis of sodium borohydride (NaBH4) are related to the low durability and efficiency of nonprecious metals. In this study, we synthesized nitrogen-doped mesoporous graphitic carbon encapsulated cobalt nanoparticles (Co@NMGC) with a core–shell structure by the carbonization of ethylenediaminetetraacetic acid (EDTA)-derived carbon. These structures were then used as catalysts for the hydrolisis of NaBH4. Among different calcination temperatures, 500 ​°C resulted in the best catalytic activity, with a hydrogen production rate of 3575 ​mL ​min−1 g−1 at 25 ​± ​0.1 ​°C and low activation energy of 35.2 ​kJ ​mol−1 for NaBH4 hydrolysis. The maximum hydrogen production rate using the cobalt-based complex catalyst was about three-fold that achieved using the pure cobalt catalyst. We found that the complex catalyst showed high durability, retaining 82.5% of the initial catalytic activity after 20 hydrolysis cycles. The catalyst was also magnetic, making it 100% recyclable. Density functional theory (DFT) calculations showed that the graphitic carbon shell promoted electron penetration from the Co nanoparticles into the graphitic carbon surface, which prevented oxidation of the Co nanoparticles, while the Co core provided better conductivity. This work provides a novel method for the synthesis of shelled-structure catalysts, which have potential applications in the hydrolysis of sodium borohydride.