Region Of High Electron Density Research Articles

Implicit particle-in-cell development for ion source plasmas

Particle-in-Cell (PIC) codes used to study plasma dynamics within ion sources typically use an explicit scheme. These methods can be slow when simulating regions of high electron density in ion sources, which require resolving the Debye length in space and the plasma frequency in time. Recent developments on fully-implicit PIC models in curvilinear geometries have shown that these spatial/time scales can be significantly decreased/increased respectively, allowing for notable speed-ups in simulation time, and thus making it a potential tool for studying the physics of ion sources. For this purpose, a charge and energy conserving implicit PIC code has been developed in 1D to determine its potential for simulating bounded plasmas. In this paper, we use this model to simulate a 1D benchmark of a bounded plasma with fixed plasma density and electron/ion temperatures. The results are shown to compare well to the benchmark and to the results using an explicit PIC code. It is shown that the total amount of macro-particles used in the simulation is a better figure of merit for accurate results than the standard particles per cell used in literature. Significant speed-ups in computation time can be achieved for high plasma densities if the accuracy requirements are relaxed. In this case, we demonstrate the ability of the implicit PIC code to speed-up simulation time by nearly a factor of 12 compared to explicit PIC.

Potansiyel JNK1 İnhibe Edici Aktiviteye Sahip 2-((4-(dimetilamino)benziliden)amino)-5-metilfenol’ün Sentezi, Teorik Çalışmaları, Sitotoksisitesi

Cisplatin, doxorubicin, hydroxycamptothecin, leucovorin, vincristine and 5-fluorouracil resistance of cancer cells are associated with the activities of C-Jun N-Terminal Kinase 1 (JNK1). Inhibition of the JNK1 by pharmacological agents could be a beneficial attempt for reversing the chemoresistance of various cancer cells. However, there is no FDA-approved JNK inhibitor for safe use in clinics in today’s clinics. In this study, a Schiff base 2-((4-(dimethylamino)benzylidene)amino)-5-methylphenol, (7S4) has been synthesized and characterized by 1H, 13C-NMR, FT-IR and elemental analysis. The stable geometry of 7S4 has been determined by DFT method with Gaussian09 program (B3LYP/6-311g++(d,p))). The Gibbs Free energies, stable tautomer forms, H-bond, Mulliken charges, dipole moment, natural bond orbital (NBO), HOMO, LUMO and band gap energy (EGAP), molecular electrostatic potential (MEP) and solvent accessibility surface areas (SASA) have been calculated. Drug-likeness, anticancer and JNK1 inhibitory activities of 7S4 have been evaluated. Enol tautomer form of trans 7S4 was characterized as the most stable structure. 7S4 was observed to be a reactive compound in chemical reactions with a low EGAP value. In addition, high and low electron density regions of 7S4 are responsible for the establishment of chemical bonds in biological systems. 7S4 exhibited strong druggability with the agreement on Lipinski, Ghose, Veber, Egan, and Muegge rules. Cytotoxicity tests and molecular docking revealed that 7S4 poses a potential JNK1 inhibitor activity.

Effect of ionic liquid as corrosion inhibitor for 6061 aluminium alloy-(electrochemical and quantum chemical approaches)

ABSTRACT Ionic liquid 1,3-dimethylimidazolium dimethyl phosphate (DIDP) is used as a possible green inhibitor for the corrosion control of 6061 aluminium alloy in 0.25 mol/L HCl is described in the study. Study involved electrochemical methods carried out at various temperatures by changing the concentrations of DIDP. Kinetic and thermodynamic parameters were determined using the Arrhenius rate law and transition state equations, respectively. Physisorption of the inhibitor takes place and the adsorption follows Freundlich isotherm. Surface morphology was studied by scanning electron microscopy (SEM), atomic force microscopy (AFM), and energy-dispersive X-ray analysis (EDAX) techniques. Quantum chemical studies were done by the density functional theory (DFT). The maximum inhibition efficiency of DIDP on 6061 aluminium alloy was about 78% for the concentration of 1000 ppm at 303 K. The mechanistic aspects of DIDP adsorption onto the metal surface were supported by quantum chemical studies. HOMO and LUMO of the optimized structure and quantum chemical descriptors confirmed the adsorption of the inhibitor on the metal surface. Mulliken charge population was used to identify the DIDP molecule’s high electron density region, and Fukui indices confirmed the interaction between metal and inhibitor.

Evaluation of Fe XIV Intensity Ratio for Electron Density Diagnostics by Laboratory Measurements

The intensity ratio of Fe XIV 264.765A/274.203A is useful to determine the electron density of solar corona, and the relationship between the electron density and the intensity ratio obtained from a model should be evaluated using laboratory plasmas to estimate the electron density more precisely. We constructed a new collisional–radiative model (CR-model) for Fe XIV (an Al-like iron ion) by considering the processes of proton-impact excitation and electron-impact ionization to the excited states of a Mg-like iron ion. The atomic data used in the CR-model were calculated using the HULLAC atomic code. The model was evaluated based on laboratory experiments using a compact electron beam ion trap, called CoBIT, and the Large Helical Device (LHD). The measured Fe XIV 264.785 Å/274.203 Å line intensity ratio with CoBIT was 1.869 ± 0.036, and it agreed well with our CR-model results. Concurrently, the measured ratio using LHD was larger than the results of our CR-model and CHIANTI. The estimated electron densities using our CR-model agreed with those from CHIANTI within a factor of 1.6–2.4 in the range of ne≈1010−11cm−3. Further model development is needed to explain the ratio in a high-electron density region.

2-D Simulation of the Electron Density Characteristics of a Special Plasma Device

The purpose of this article is to study the influence of different powers, pressures, frequencies, and gases on the electron density distribution in special structures. A simulation model is established, and the electronic density in a special capacitance coupled plasma (CCP) device is calculated over the power range of 0-10 kW, pressure range of 0-50 Pa, and frequency range of 13.56-300 MHz. The results show that the power is a logarithmic function of the electron density in helium and argon plasmas, and the peak value for the electron density occurs in the diffusion region. At a certain power, collisions between particles increase with increasing pressure, which leads to an increase in electron density. However, the high electron density region in the helium plasma is concentrated near the electrode, while the high density region in the argon plasma moves from the center of the device to the electrode with increasing gas pressure. At the same time, the increase in the power frequency increases the ionization rate, and energy is transferred to the electrons, which increases the electron density. However, the rate of increase in the electron density decreases with increasing power frequency at the same voltage and pressure. With increasing power frequency, the 2-D electron density distribution in the argon and helium plasmas is found to vary in a similar way to that found for increasing pressure.

Modification of Martian Ionosphere

To partially meet the communication requirements in Mars, low-frequency ground-to-ground communication is likely to be used in the future and hence, it is desirable to increase electron density in the Martian ionosphere. As a convenient means to this, we have proposed and explored the production of high electron density regions in the Martian atmosphere in daytime by suspension of low work function dust, specifically Cs-coated bronze in the atmosphere. Equations of the kinetics of the dusty air in sunlight have been introduced and a numerical estimate of the daytime electron density at 60-100 km heights has been obtained as a function of the dust parameters. Photoelectric emission from dust and accretion of electrons and ions on dust particles play the key role in getting the desired electron density at high altitudes (60-100 km). A discussion of the numerical results has been given with conclusions.

Polar-Nonpolar Interfaces of Normal Bicontinuous Cubic Phases in Nonionic Surfactant/Water Systems Are Parallel to the Gyroid Surface.

We investigated the structures of normal (type I) bicontinuous cubic phases in hexa-, hepta-, and octaethylene glycol dodecyl ether/water mixtures by small-angle X-ray crystallography of single-crystal domains. Reconstructed electron densities showed that the hydrophilic chains with high electron density are confined to a film centered on the surface of the Gyroid (a triply periodic minimal surface), while hydrophobic chains with low electron density are distributed within the pair of interwoven labyrinths carved out by the Gyroid. Further, the local minimum within the high electron density region, due to bulk water, coincides precisely with the Gyroid. This minimum is less pronounced in mixtures with longer ethylene glycol chains, consistent with their decreased water content. Our analysis clearly shows that the polar-nonpolar interfaces are parallel to the Gyroid surface in all mixtures. The repulsive hydration or overlapping force between the pair of facing monolayers of ethylene glycol chains on either side of the Gyroid surface is the likely origin of the parallel interfaces.

Internal structures of the ion-scale flux rope associated with dayside magnetopause reconnection

Ion-scale magnetic flux ropes have been observed in the reconnection diffusion region. In this paper, we show a typical ion-scale flux rope observed by the Magnetospheric Multiscale spacecraft at the subsolar magnetopause. The most intriguing feature of this flux rope is that the rapid variations of electron density are correlated with the changes of electron temperature and pitch angle distribution inside the flux rope. In the region of low electron density, the perpendicular temperature is higher than parallel temperature. Furthermore, the electrons within higher energies (>70 eV) are mainly trapped near pitch angle $\sim 90^{\circ}$, but electrons with lower energies (<70 eV) are missing. However, in the region of high electron density, perpendicular temperature is lower than the parallel temperature. In addition, the pitch angle of electrons with higher energies is essentially field-aligned, and the fluxes of electrons with lower energies rapidly increase. It implies that the coexistence of different magnetic field line topologies inside the ion-scale flux rope is responsible for the observed electron pitch angle distributions within the flux rope. These results can be useful for understanding the reconnection process in three-dimension and the generation mechanism of the ion-scale flux rope.

Synthesis and Characterization of Plasmon-Enhanced SERS Substrate Based on Au-Ag Alloy-Coated, Large-Area Photonic (Methyl Methacrylate+Styrene) Co-Polymer

Enhancement of surface-enhanced Raman scattering (SERS) by metal nanoparticles has attracted considerable interest on account of their widespread popularity of SERS-based measurements and devices ranging from life science until materials science. Current study focuses on noble metal SERS substrates with attempting to achieve high and enhanced effect by describe a plasmon-enhanced SERS substrate based on gold-silver, alloy-coated co-polymer (methyl methacrylate-styrene) colloidal sphere. Copolymer was synthesised via surfactant-free emulsion polymerization and was successfully produced a homogeneous colloidal spheres. The homogenous spheres of copolymer would promote periodic array upon fabrication and more, introducing the copolymer medium had improved the thermal degradation of the material compare to single polymer. Gold-silver alloy nanospheres was synthesised via one pot reduction method using citrate stabilizer. The nanoalloy obtained are well within the nanoscale domain (&lt;100 nm) supported by the maximum surface plasmon resonance peak at 436 nm using UV-Visible spectroscopy. The perfect combination of our proposed alloy nanoparticles and copolymer present an ability to enhance Raman scattering by higher than 90 %. The region of high electron density of the substrate is expected to develop a new opportunities for SERS detections in wide analytical area.

Stimulated Brillouin scattering of backward stimulated Raman scattering

The rescattering of backward stimulated Raman scattering (BSRS) by stimulated Brillouin scattering (SBS) is found in the high electron density region by relativistic Vlasov-Maxwell simulation and particle-in-cell (PIC) simulation, where the BSRS is in the regime of absolute instability and dominates in all the scatterings. Both one dimension (1D) Vlasov simulation and two dimension (2D) PIC simulation have been given to verify that there exists SBS of BSRS in the regime of absolute instability for BSRS. The SBS of BSRS will be even stronger than forward stimulated Raman scattering (FSRS) and SBS in regime of absolute instability for BSRS. Thus, besides Langmuir decay instability and laser energy absorption, the SBS of BSRS is also an important saturation mechanism of BSRS in high electron density region.

Probing the location of the unpaired electron in spin-orbit changing collisions of NO with Ar.

Understanding the molecular forces that drive a reaction or scattering process lies at the heart of molecular dynamics. Here, we present a combined experimental and theoretical study of the spin-orbit changing scattering dynamics of oriented NO molecules with Ar atoms. Using our crossed molecular beam apparatus, we have recorded velocity-map ion images and extracted differential and integral cross sections of the scattering process in the side-on geometry. We observe an overall preference for collisions close to the N atom in the spin-orbit changing manifold, which is a direct consequence of the location of the unpaired electron on the potential energy surface. In addition, a prominent forward scattered feature is observed for intermediate, even rotational transitions when the atom approaches the molecule from the O-end. The appearance of this peak originates from an attractive well on the A' potential energy surface, which efficiently directs high impact parameter trajectories towards the region of high unpaired electron density near the N-end of the molecule. The ability to orient molecules prior to collision, both experimentally and theoretically, allows us to sample different regions of the potential energy surface(s) and unveil the associated collision pathways.

Synthesis, spectroscopic investigation, molecular docking and DFT studies of novel (2Z,4Z)-2,4-bis(4-chlorobenzylidene)-5-oxo-1-phenylpyrrolidine-3-carboxylic acid (BCOPCA)

The synthesized compound (2Z,4Z)-2,4-bis(4-chlorobenzylidene)-5-oxo-1-phenylpyrrolidine-3-carboxylic acid (BCOPCA) was characterised by Ultraviolet, FT-Infra Red, 1H, 13C Nuclear Magnetic Resonance and mass spectroscopy. The compound was further subjected to quantum chemical calculations at the level of density functional theory (DFT) using 6-31G (d,p) basis sets method with B3LYP and CAM-B3LYP hybrid functionals. The intramolecular interactions, polarizability, hyperpolarizability and nonlinear optical properties of the title compound were also incorporated in the study. The total first static hyperpolarizability (β0 = 19.477 × 10−30 and 16.924 × 10−30 esu) value was also computed and indicated the title molecule as an interesting forthcoming NLO material. The other thermodynamic properties (entropy, heat capacity and zero vibrational energy) were also discussed. The study also includes NBO computations, complete vibrational assignments, Mulliken charges, UV–Visible spectral analysis and HOMO–LUMO energies. The regions of low and high electron density were obtained from MESP and ESP maps. The calculated parameters for BCOPCA using aforementioned functions are harmonious with the experimental findings. The in-vitro antimicrobial activity and molecular docking studies of BCOPCA were also done and showed a good correlation.

A Possible Role for Singlet Oxygen in the Degradation of Various Antioxidants. A Meta-Analysis and Review of Literature Data.

The thermodynamic parameters Eact, ΔH≠, ΔS≠, and ΔG≠ for various processes involving antioxidants were calculated using literature kinetic data (k, T). The ΔG≠ values of the antioxidants’ processes vary in the range 91.27–116.46 kJmol−1 at 310 K. The similarity of the ΔG≠ values (for all of the antioxidants studied) is supported to be an indication that a common mechanism in the above antioxidant processes may be taking place. A value of about 10–30 kJmol−1 is the activation energy for the diffusion of reactants depending on the reaction and the medium. The energy 92 kJmol−1 is needed for the excitation of O2 from the ground to the first excited state (1Δg, singlet oxygen). We suggest the same role of the oxidative stress and specifically of singlet oxygen to the processes of antioxidants as in the processes of proteinaceous diseases. We therefore suggest a competition between the various antioxidants and the proteins of proteinaceous diseases in capturing singlet oxygen’s empty π* orbital. The concentration of the antioxidants could be a crucial factor for the competition. Also, the structures of the antioxidant molecules play a significant role since the various structures have a different number of regions of high electron density.

A meta-analysis and review examining a possible role for oxidative stress and singlet oxygen in diverse diseases.

From kinetic data (k, T) we calculated the thermodynamic parameters for various processes (nucleation, elongation, fibrillization, etc.) of proteinaceous diseases that are related to the β-amyloid protein (Alzheimer's), to tau protein (Alzheimer's, Pick's), to α-synuclein (Parkinson's), prion, amylin (type II diabetes), and to α-crystallin (cataract). Our calculations led to ΔG≠ values that vary in the range 92.8-127 kJ mol-1 at 310 K. A value of ∼10-30 kJ mol-1 is the activation energy for the diffusion of reactants, depending on the reaction and the medium. The energy needed for the excitation of O2 from the ground to the first excited state (1Δg, singlet oxygen) is equal to 92 kJ mol-1 So, the ΔG≠ is equal to the energy needed for the excitation of ground state oxygen to the singlet oxygen (1Δg first excited) state. The similarity of the ΔG≠ values is an indication that a common mechanism in the above disorders may be taking place. We attribute this common mechanism to the (same) role of the oxidative stress and specifically of singlet oxygen, (1Δg), to the above-mentioned processes: excitation of ground state oxygen to the singlet oxygen, 1Δg, state (92 kJ mol-1), and reaction of the empty π* orbital with high electron density regions of biomolecules (∼10-30 kJ mol-1 for their diffusion). The ΔG≠ for cases of heat-induced cell killing (cancer) lie also in the above range at 310 K. The present paper is a review and meta-analysis of literature data referring to neurodegenerative and other disorders.

Electric Field Modified Bunsen Flame with Variable Anode Placement

A methane–air Bunsen flame was tested under dc electric field forcing with different ring anode sizes and locations. The anodes were placed within the flame to far outside the flame, both axially and radially. The focus of the work is to understand the limit of electrode placement and its effect on the flame under a dc field. A stoichiometric flame with voltages up to 9.1 kV was tested. The electrical current and flame height were measured as a function of the bias voltage and anode location. Plasma density measurements of the unmodified flame at various axial locations were used to corroborate that anode placement at regions of high electron density caused the largest reductions in flame height. The results showed the anodes closest to the burner at 35 mm caused the largest reduction (24%) in flame height. The effect of the electric field on flame height decreased as the anode moved farther downstream of the flame or radially outward. For the same voltage, larger currents were also observed for anodes close to the burner, whereas anodes placed far outside of the flame had minimal effects on current and, consequently, on the flame height. These differences are due to the variable electron density at the anode, which limits the net current collected and the strength of the field.

Visualization of a Mammalian Mitochondrion by Coherent X-ray Diffractive Imaging

We report a three dimensional (3D) quantitative visualization of a mammalian mitochondrion by coherent x-ray diffractive imaging (CXDI) using synchrotron radiation. The internal structures of a mitochondrion from a mouse embryonic fibroblast cell line (NIH3T3) were visualized by tomographic imaging at approximately 60 nm resolution without the need for sectioning or staining. The overall structure consisted of a high electron density region, composed of the outer and inner membranes and the cristae cluster, which enclosed the lower density mitochondrial matrix. The average mass density of the mitochondrion was about 1.36 g/cm3. Sectioned images of the cristae reveal that they have neither a baffle nor septa shape but were instead irregular. In addition, a high resolution, about 14 nm, 2D projection image was captured of a similar mitochondrion with the aid of strongly scattering Au reference objects. Obtaining 3D images at this improved resolution will allow CXDI to be an effective and nondestructive method for investigating the innate structure of mitochondria and other important life supporting organelles.

Spoke rotation reversal in magnetron discharges of aluminium, chromium and titanium

The rotation of localised ionisation zones, i.e. spokes, in magnetron discharge are frequently observed. The spokes are investigated by measuring floating potential oscillations with 12 flat probes placed azimuthally around a planar circular magnetron. The 12-probe setup provides sufficient temporal and spatial resolution to observe the properties of various spokes, such as rotation direction, mode number and angular velocity. The spokes are investigated as a function of discharge current, ranging from 10 mA (current density 0.5 mA cm−2) to 140 A (7 A cm−2). In the range from 10 mA to 600 mA the plasma was sustained in DC mode, and in the range from 1 A to 140 A the plasma was pulsed in high-power impulse magnetron sputtering mode. The presence of spokes throughout the complete discharge current range indicates that the spokes are an intrinsic property of a magnetron sputtering plasma discharge. The spokes may disappear at discharge currents above 80 A for Cr, as the plasma becomes homogeneously distributed over the racetrack. Up to discharge currents of several amperes (the exact value depends on the target material), the spokes rotate in a retrograde direction with angular velocity in the range of 0.2–4 km s−1. Beyond a discharge current of several amperes, the spokes rotate in a direction with angular velocity in the range of 5–15 km s−1. The spoke rotation reversal is explained by a transition from Ar-dominated to metal-dominated sputtering that shifts the plasma emission zone closer to the target. The spoke itself corresponds to a region of high electron density and therefore to a hump in the electrical potential. The electric field around the spoke dominates the spoke rotation direction. At low power, the plasma is further away from the target and it is dominated by the electric field to the anode, thus retrograde rotation. At high power, the plasma is closer to the target and it is dominated by the electric field pointing to the target, thus rotation.

Self-consistent particle-in-cell modelling of short pulse absorption and transport for high energy density physics experiments

In order for detailed, solid density particle-in-cell (PIC) simulations to run within a reasonable time frame, novel approaches to modelling high density material must be employed. For the purposes of modelling high intensity, short pulse laser-plasma interactions, however, these approaches must be consistent with retaining a full PIC model in the low-density laser interaction region. By replacing the standard Maxwell field solver with an electric field update based on a simplified Ohm's law in regions of high electron density, it is possible to access densities at and above solid without being subject to the standard grid and time step constraints. Such a model has recently been implemented in the PIC code EPOCH. We present the initial results of a detailed two-dimensional simulation performed to compare the adapted version of the code with recent experimental results from the Orion laser facility.

Spectroscopic measurements of ablation plasma generated with laser-driven intense extreme ultraviolet (EUV) light

Material ablation by a focused Extreme ultraviolet (EUV) light is studied by comparing expanding ion properties and plasma parameters with laser ablation. The kinetic energy distributions of expanding ions from EUV and laser ablation showed different spectra implying different geometries of plasma expansion. The calculation results of plasma parameters showed that EUV energy is mostly deposited in high electron density region close to the solid density, while laser energy is deposited in low energy density region. Plasma parameters experimentally obtained from visible spectra did not show noticeable difference between EUV and laser ablation due to the corresponding low cut off density.

Comparison study of electromagnetic wave propagation in high and low pressure Ar inductively coupled plasma

The electromagnetic wave propagation in plasmas has been investigated based on the hypothetical parameters in a number of previous literature, but the results can't mirror the feature of real plasma sources for waves. In this paper, the two-dimension parameters of Ar inductively coupled plasma (ICP) are investigated under high and low pressure by multi-physics coupling analysis method. Meanwhile, the profiles of electron density are diagnosed by the Langmuir probe for comparison with the simulated. The increasing pressure induces the significant increase of oscillation frequency and collision frequency, while a large density gradient causes the more nonuniform distribution. The wave propagation in ICPs is calculated with Z-transform finite-different time-domain method. The curves of attenuation, transmission and reflection coefficient are obtained versus pressure, frequency and power. The low pressure ICP induces the relative more attenuation of wave in the frequency band (1 GHz–6 GHz), while the high pressure ICP is more effective to the frequency band (6 GHz–17 GHz). The increasing power is conductive to the attenuation within limits. The reflection is complicated due to the high degree of wave vector gradient over a wavelength. Moreover, the pseudo secondary wave source is created inside high electron density region of ICP.