Theory Of Ionization Research Articles

Correlation Characteristics Comparison of SF6 Decomposition versus Gas Pressure under Negative DC Partial Discharge Initiated by Two Typical Defects

Aimed to clarify the correlation characteristics between the internal partial discharge (PD) in negative direct current (DC) gas insulated system (GIS) and gas pressure initiated by two typical defects (i.e., free-metal particles and metal protrusion), this study on PD decomposition of sulfur hexafluoride (SF6) was investigated under different pressures on the basis of constructing a SF6 decomposition experimental platform with DC PD. Free-metal particles and metal protrusion in a GIS were simulated using a spherical-bowl electrode and a needle-plate electrode, respectively. Trends and differences in the performance of SF6 decomposition components SOF2, SO2F2, CO2, and SO2 at different pressures were compared and analyzed by experiments under different defects. Based on gas microscopic ionization theory, the relationship between the decomposition component and gas pressure was deduced and verified. The concentrations of different decomposition components were found to vary with the change in gas pressure under different defects, whereas the characteristic ratios of decomposition components versus gas pressure showed a similar trend.

An electrical super-insulator prototype of 1D gas-solid Al2O3 nanocell

High electric breakdown strength of insulating materials is essential to improving the reliability of the electricity grid, reducing the size of electric devices, saving energy, protecting the environment, and reducing costs. Traditionally, dielectric breakdown strength is increased by exploiting its dependence on the thickness of the dielectric material, based on the electron impact ionization and avalanche theory by Townsend (1900) and Seitz (1949) [9]. However, at present there has been little research addressing the role of the transverse dimension (perpendicular to the direction of the electric field) in the avalanche breakdown process, and no results about research in nanoscale. An insulation breakdown prototype of a 1D nanocell was constructed. It consisted of an air-column and Al2O3 solid wall. Based on the analysis and comparison between nanocell geometrical dimensions and avalanche physical dimensions, it was found that the properties of the 1D nanocell diverges from the gas/solid discharge theories of Townsend and Seitz. Along with the I-V results of 1D nanocell by C-AFM (Conductive-Atomic Force Microscope), it was demonstrated that electrical breakdown cannot be caused by electron avalanche in 1D nanocell. The discharge properties of Al2O3 NPT (nano pore template) with nanocells array and when it inserted into the air gap as a barrier were studied to further demonstrate the capability of 1D nanocells on the electrical characteristic of macroscale material. Results showed that the scale effect of nanocells have an obvious role in improving the dielectric breakdown voltage, with singular discharge phenomena identified. This study proposes a new super-insulator prototype of 1D nanocell and supplies a novel thought for constructing high performance nanostructured dielectrics for more wide applications, and provides a scientific basis on the interconnection among Micro-Meso-Macro scales.

Spin-dependent quantum theory of high-order above-threshold ionization

The strong-field-approximation theory of high-order above-threshold ionization of atoms is generalized to include the electron spin. The obtained rescattering amplitude consists of a direct and exchange part. On the examples of excited He atoms as well as ${\mathrm{Li}}^{+}$ and ${\mathrm{Be}}^{++}$ ions, it is shown that the interference of these two amplitudes leads to an observable difference between the photoelectron momentum distributions corresponding to different initial spin states: Pronounced minima appear for singlet states, which are absent for triplet states.

Photoionization of triatomic molecular ions by intense bichromatic circularly polarized attosecond UV laser pulses

Photoionization of triatomic molecular ions has been studied for triangular and linear geometries by bichromatic circularly polarized attosecond UV laser pulses at frequencies . Simulations are performed on the single electron molecule by numerically solving time-dependent Schrödinger equations. We measure molecular frame photoelectron momentum distributions (MFPMDs), which show spiral electron vortex patterns as functions of the helicity of the pulse and the molecular geometry. The ionization interference effects arise from multi-pathway ionization, which give rise to the modulation of multi-center photoelectron spectra. We describe these phenomena in MFPMDs based on an ultrafast delta-function ionization model and attosecond perturbation ionization theory. Interference patterns in MFPMDs reflect the helicity and symmetry of the electric fields in the attosecond ionizing pulses.

Impact ionization rate in direct gap semiconductors

We present quantum-mechanical theory of impact ionization in semiconductors with the direct band gap in \$\Gamma\$-point. It is shown that energy dependence of the impact ionization rate \$\mathcal{W}(E)\$ near a threshold \$E_{th}\$ is given by superposition of the two terms, one of which is strongly anisotropic and quadratic in \$E-E_{th}\$, while another one is isotropic and cubic in \$E-E_{th}\$. Explicit form of the coefficients in such representation is derived in the framework of the 14-band \${\bf k\cdot p}\$ model, and we claim the room temperature domination of the cubic contribution for most of the direct-gap materials with \$E_g\$ up to 1.5 eV.

Intense-Laser Solid State Physics: Unraveling the Difference between Semiconductors and Dielectrics.

Experiments on intense laser driven dielectrics have revealed population transfer to the conduction band to be oscillatory in time. This is in stark contrast to ionization in semiconductors and is currently unexplained. Current ionization theories neglect coupling between the valence and conduction band and therewith, the dynamic Stark shift. Our single-particle analysis identifies this as a potential reason for the different ionization behavior. The dynamic Stark shift increases the band gap with increasing laser intensities, thus suppressing ionization to an extent where virtual population oscillations become dominant. The dynamic Stark shift plays a role dominantly in dielectrics which, due to the larger band gap, can be exposed to significantly higher laser intensities.

Meghnad Saha and the contemporary scene

Meghnad Saha and the contemporary scene

Pathogenic Variants of Urolithiasis

The essence of Urolithiasis - one of the oldest diseases known by the mankind - is still not understood completely. For a long time the comprehension of Urolithiasis was based on matrix, colloid, ionic, inhibitory and precipitation theories. In these cases it was impossible to single out separate pathogenetic patterns. Besides, in spite of the absence of in vivo proofs the fact that new concrement nucleus forming (de novo nucleation) is only possible outside of the stone-forming metastability range should be taken into consideration for metaphilactic purposes. Fortunately, certain progress in understanding Urolithiasis started with the onset of studies devoted to detailed scrutiny of stone-forming patients’ metabolic peculiarities as well as with the introduction into clinical practice of the up-to-date digital endoscopes. Based on existing publications one may classify pathogenesis of stone-forming into 4 major groups: growth of calcium-oxalic stones on Randall’s plaques in patients with hypercalciumuria; excrescences on the of Belliny’s ducts’ “gags”; microlites forming within the internal medullar layer discharging tubules’ lumen in patients with cystineuria; stones forming in free solution. There is no doubt this classification is not the final one, neither does it exclude mixed variants, however better understanding of the aforementioned pathogenic variants would facilitate a novel view at Urolithiasis and in patients with kidney stones would increase anti-relapse measures’ effectiveness.

Weak-field versus Born-Oppenheimer asymptotics in the theory of tunneling ionization of molecules

The weak-field asymptotic theory (WFAT) and the Born-Oppenheimer approximation (BOA) provide two general approaches to the theory of tunneling ionization of molecules enabling one to treat the internuclear motion quantum mechanically on an equal footing with the electronic motion. The approaches are based on the asymptotic expansions in field strength and electron-to-nuclear mass ratio, respectively. The problem is that they yield quite different formulas for the ionization rate, which causes an ambiguity for applications in strong-field physics. A recent experimental observation of the isotope effect in tunneling ionization of hydrogen molecules [X. Wang et al., Phys. Rev. Lett. 117, 083003 (2016)] motivates us to address this theoretical ambiguity. The WFAT and BOA have different but overlapping regions of applicability in the field strength---nuclear mass plane. We link the approaches analytically, in particular showing that the rate formulas in fact coincide in the overlap region where they both apply, and compare their predictions quantitatively.

Historical overview of electrophysiological methods

It is difficult to overestimate the importance for the physiology of nerves, muscles and the central nervous system had electrophysiological studies. For the first time the idea that some kind of electrical phenomena are occurring in the animal body was expressed by L. Galvani in 1786. The basis for this was an experiment in which Galvani observed muscle contraction. Despite the fact that the studies mentioned here were fundamental, electrophysiology as an independent field of study was formed only in the mid-1940s. thanks to the classical studies of E. du Bois-Reymond. Possessing a good preparation in the field of physics, E. du Bois-Reymond greatly improved electrical measuring equipment, carried out very precise experiments and established a number of regularities characterizing electrical phenomena in muscles and nerves. V.Yu. Chagovets for the first time in world science applied the theory of electrolytic dissociation Arrhenius for electrophysiology, formulated the ionic theory of the origin of bioelectric potentials (1903) and proposed a condenser theory of electric stimulation of living tissues (1906). Summarizing, it should be noted that, despite the primitive technique of research, outstanding scientists of that time managed to create the foundations of modern knowledge in this field of science.

Time-dependent density functional theory for strong-field ionization by circularly polarized pulses

By applying time-dependent density functional theory to a two-dimensional multielectron atom subject to strong circularly polarized light pulses, we confirm that the ionization of p orbitals with defined angular momentum depends on the sense of rotation of the applied field. A simple ad-hoc modification of the adiabatic local-density exchange-correlation functional is proposed to remedy its unphysical behavior under orbital depletion.

Relativistic theory of excitation and ionization of Rydberg atomic systems in a Black-body radiation field

The combined relativistic energy approach and relativistic many-body perturbation theory with the zeroth model density functional approximation are used for computing the thermal Blackbody radiation ionization characteristics of the Rydberg atoms, in particular, the sodium and caesium in Rydberg states with n=40-100. The comparison of the calculated ionization rate values with available theoretical and experimental data is carried out.

Influence of polarity of set voltage on the properties of conductive filaments in NiO based nonvolatile memory device

In this paper, we realize the coexistence of bipolar and unipolar resistive switching (RS) in one Pt-Ir/NiO/TiB1+δ cell. The types of RS are controlled by polarity of set voltage and are free from the current compliance. Based on this coexistence, the set voltage and characters of filaments formed in RS are studied. The results show that the types of filaments also show polarity dependence on the set voltage. The positive set voltage can induce metallic filaments while the negative set voltage can result in semiconductor filaments. It reveals that the distribution of magnitude of set voltage shows abnormal polarity dependence in our devices. The combination the theory of interaction between oxygen vacancy defects and one-carrier impact ionization theory of breakdown account for these results. The influence of filament properties on RS types is also discussed.

Probing quantum systems from the inside while producing the world’s shortest optical pulses

In 1964, Professor L.V. Keldysh, with whom I share winning the Lomonosov Gold Medal, published what was to become a very influential paper. In his paper, he developed the theory of multiphoton ionization for atoms and the creation of electron-hole pairs for solids. Fifty years later, we generate the world’s shortest light pulses using electron wave packets that are extracted from rare gas atoms by an intense infrared pulse much as Professor Keldysh described. The ultrashort bursts of XUV radiation from many atoms add coherently to produce intense pulses as short as 65 attoseconds—the current world record. Similar highly nonlinear processes occur in other atoms, molecules and solids. In addition to its importance as a new source of soft X-ray radiation and ultrashort pulses, the radiation generated from ionizing material encodes information on the quantum system from which it was made. By analyzing the XUV radiation, not only can we image molecular orbitals but also determine the band structure of solids.

Exact theory and numeric results for short pulse ionization of simple model atom in one dimension

Our exact theory for continuous harmonic perturbation of a one dimensional model atom by parametric variations of its potential is generalized for the cases when (a) the atom is exposed to short pulses of an external harmonic electric field and (b) the forcing is represented by short bursts of different shape changing the strength of the binding potential. This work is motivated not only by the wide use of laser pulses for atomic ionization, but also by our earlier study of the same model which successfully described the ionization dynamics in all orders, i.e., the multi-photon processes, though being treated by the non-relativistic Schrödinger equation. In particular, it was shown that the bound atom cannot survive the excitation of its potential caused by any non-zero frequency and amplitude of the continuous harmonic forcing. Our present analysis found important laws of the atomic ionization by short pulses, in particular the efficiency of ionizing this model system and presumably real ones as well.

First-order correction terms in the weak-field asymptotic theory of tunneling ionization in many-electron systems

The many-electron weak-field asymptotic theory of tunneling ionization including the first-order correction terms in the asymptotic expansion of the ionization rate in field strength was highlighted in our recent fast track communication (Trinh et al 2015 J. Phys. B: At. Mol. Opt. Phys. 48 061003) by demonstrating its performance for two-electron atoms. Here we present a thorough derivation of the first-order terms omitted in the previous publication and provide additional numerical illustrations of the theory.

Refining the ionic surfactant micellization theory based on the law of mass action

Refining the ionic surfactant micellization theory based on the law of mass action

Improved strong-field approximation and quantum-orbit theory: Application to ionization by a bicircular laser field

A theory of above-threshold ionization of atoms by a strong laser field is formulated. Two versions of the strong-field approximation (SFA) are considered, the direct SFA and the improved SFA, which do not and do, respectively, take into account rescattering of the freed electron off the parent ion. The atomic bound state is included in two different ways: as an expansion in terms of Slater-type orbitals or as an asymptotic wave function. Even though we are using the single-active-electron approximation, multielectron effects are taken into account in two ways: by a proper choice of the ground state and by an adequate definition of the ionization rate. For the case of the asymptotic bound-state wave functions, using the saddle-point method, a simple expression for the $T$-matrix element is derived for both the direct and the improved SFA. The theory is applied to ionization by a bicircular field, which consists of two coplanar counterrotating circularly polarized components with frequencies that are integer multiples of a fundamental frequency $\ensuremath{\omega}$. Special emphasis is on the $\ensuremath{\omega}\text{\ensuremath{-}}2\ensuremath{\omega}$ case. In this case, the threefold rotational symmetry of the field carries over to the velocity map of the liberated electrons, for both the direct and the improved SFA. The results obtained are analyzed in detail using the quantum-orbit formalism, which gives good physical insight into the above-threshold ionization process. For this purpose, a specific classification of the saddle-point solutions is introduced for both the backward-scattered and the forward-scattered electrons. The high-energy backward-scattering quantum orbits are similar to those discovered for high-order harmonic generation. The short forward-scattering quantum orbits for a bicircular field are similar to those of a linearly polarized field. The conclusion is that these orbits are universal, i.e., they do not depend much on the shape of the laser field.

HYDROLYSIS OF SALTS OF DISTINCT NATURE

The ionization theory attributes this phenomena to the interaction of water ions with the ions of dissolved salts, resulting the formation of an excess of hydrogen or hydroxyl ions. The concentration of hydrogen or hydroxyl ions in water is very low, they are in equilibrium with an immense number of unionized water molecules. When one of them is bound by the ions of the salt, the equilibrium is disturbed, causing new water molecules to ionize, which leads to accumulation an excess of quantities of the other ion, making the solution react acid or alkaline. Any salt can be obtained by neutralization of acids by bases. It is natural to assume, therefore, that solutions, at least those witch are products of complete displacement of hydrogen in acids by metals, must react neutral. However, this assumption holds only for salts of strong acids and strong bases. Salts of weak acids and strong bases, or vice versa, of strong acids and weak bases, do not react neutral when dissolved in water. The methods handbook covers the basic material on the subject ”Hydrolysis of salts of distinct nature” that may reasonably be required from Ordinary Level university standard for the trade 18.03.01 “Engineering chemistry”, in particular, when making a study in Ufa State Petroleum Technological University.

Quantitative measurement of electron number in nanosecond and picosecond laser-induced air breakdown

Here we present quantitative measurements of total electron numbers in laser-induced air breakdown at pressures ranging from atmospheric to 40 barg by 10 ns and 100 ps laser pulses. A quantifiable definition for the laser-induced breakdown threshold is identified by a sharp increase in the measurable total electron numbers via dielectric-calibrated coherent microwave scattering. For the 10 ns laser pulse, the threshold of laser-induced breakdown in atmospheric air is defined as the total electron number of ∼106. This breakdown threshold decreases with an increase of pressure and laser photon energy (shorter wavelength), which is consistent with the theory of initial multiphoton ionization and subsequent avalanche processes. For the 100 ps laser pulse cases, a clear threshold is not present and only marginal pressure effects can be observed, which is due to the short pulse duration leading to stronger multiphoton ionization and minimal collisional avalanche ionization.