Presence Of Positive Ions Research Articles

Əyləc sürtünmə cütlərində ifratkeçiricilik effekti Ə.X. Canəhmədov, D.A. Volçenko, M.Ya. Cavadov, N.N. Fidrovskaya, N.A. Volçenko, D.Yu. Juravlev, V.N. Lunin

The article addresses the following issues: general principles of the state of superconductivity in brake friction pairs; isotropic and Josephson effects; paired electron and its role in superconductivity; vibrations of the crystal lattice and vortices in the metal friction element; the discussion of the results. The exciting factor for particles of various kinds in metal friction elements is pulsed normal forces in the mating of friction pairs. Conduction electrons in a metal at a low ambient temperature and its thermally stabilized state are capable of forming pairs that unite particles with equal, oppositely directed impulses. For this to happen, there must be an attraction between the electrons. Behavior and connections of pairs of electrons and the interaction of their energy levels with the nodes of the crystal lattice of a metal friction element. The presence of positive ions in the crystal lattice ensures that a moving electron attracts nearby ions, they shift towards it and create a local excess of positive charge. A locally polarized region attracts another electron, which moves towards the first one. Elastic vibrations of the crystal lattice are the movement of phonons-quanta of sound waves. In this case, electrons are attracted, emitting and absorbing phonons. Between electrons and vibrations of the crystal lattice occurring directly by the attraction of the lattice of electrons prevailing over the Coulomb collision. The emergence of mechanical and magnetic vortices, when the transport current fields exceed the minimum limit of its intensity, magnetic vortices are born near the surface and migrate deep into the metal friction element. Keywords: braking device, friction pairs, metal friction element, superconductivity, electric, magnetic field.

Investigation of the Dielectric Properties of the Insulating Gas of Commercial Gas-Filled Surge Arresters

Based on the experimental results of dynamic breakdown voltage and electrical breakdown time delay, the dielectric properties of insulating gas commercial gas-filled surge arresters were analyzed. Data for dynamic breakdown voltage obtained by the method of stepwise increase of voltage whose rise rates ranged from 1 to 10 V/s. It is shown that these values of voltage rise rate do not have a significant effect on the value of dynamic breakdown voltage. In order to monitor the processes caused by electrical breakdown on the dielectric properties of insulating gas of these components the electrical breakdown time delay was a measure for different values of relaxation time and applied voltage. It has been shown that the presence of positive ions, which are formed during breakdown and subsequent self-sustaining discharge with recombination time of about 1 ms, has a significant effect on the reduction the dielectric resistance of insulating gas. It has also been shown that the applied voltage whose values are close to DC-spark over-voltage has a significant effect on the delay response of these components.

Performance of proportional counters filled with Xe + 5% TMA under high count rate-pressure scaling

The total space charge effect includes the cumulative effect of positive ions created from many different avalanches. The presence of positive ions in the avalanche multiplication region reduces the gas amplification factor. The gas gain has been measured for a low and high count rate by means of the current method for sealed cylindrical proportional counters of radius b = 12.5 mm with an axially placed anode of radius a = 50 μm. The gas gain curves covered the whole gas gain region from the ionisation chamber to that close to continuous discharge. The gas gain was determined for 5,9 keV X-rays of varying intensity and of constant high radiation intensity. For any count rate there is always a critical voltage, which divides the operation range of the counter into two regions, i.e. the region in which no changes in the gas gain with a count rate are observed and the region in which the space charge of positive ions reduces the gas gain. The values of current over which a 5% reduction in gas gain is observed have been determined. The measurements were made for a mixture pressure range from 294 hPa to 1800 hPa. The obtained results, which are presented here, can be favourable for micromegas-TPC operating in an Xe-TMA mixture.

Thermally Induced Variation of the Turn-ON Voltage of an Indium–Gallium–Zinc Oxide Thin-Film Transistor

The thermal processing of an indium–gallium–zinc oxide (IGZO) thin-film transistor (TFT) with annealing-induced source/drain (S/D) regions was found to induce a negative shift in the turn-ON voltage ( $V_{\mathrm{\scriptscriptstyle ON}})$ of the TFT. Such shifts are consistent with the presence of positive ions, and correlated with the detection of indium, gallium, and zinc, in the dielectric layer adjacent to the channel region. The origin of these species is attributed to the thermally induced dissociation of the IGZO in the S/D regions of the TFT, and the subsequent migration of some of the dissociated species to the dielectric layer above the channel region. It was found that the process-induced shifts in $V_{\mathrm{\scriptscriptstyle ON}}$ depended on not only the heat-treatment condition but also the structural configuration of the TFT. Since the thermal processes are practically unavoidable during the fabrication of an IGZO TFT and it is unlikely the dissociation of IGZO is unique to the present device architecture, attention must be paid to the effects of the potential migration of such ionic species on the device characteristics, regardless of the transistor structure.

Space-charge effects and gain in Cherenkov free-electron lasers

This paper presents a quantum mechanical treatment to study the growth rate characteristics of Cherenkov free-electron laser. For this purpose, we basically use the single-particle model in which the dynamics of a single electron in the presence of the laser field is analyzed. The inclusions of the space-charge (collective) effects are considered by taking into account the static electric field of neighboring electrons in the dynamics formulations. An analytical expression for the gain per pass in the Cherenkov laser is derived. It is shown that the space-charge effects depend mainly on the operating wavelength, the electron density, and the electron beam neutralization due to the possible presence of positive ions. We discuss the validity boundaries of the interaction mode evolved from the single-particle regime to the collective regime. Using quantum mechanical concepts, we finally present a formula for calculating the inclusion of the spontaneous emission power.

Antihydrogen trapping assisted by sympathetically cooled positrons

Antihydrogen, the bound state of an antiproton and a positron, is of interest for use in precision tests of nature's fundamental symmetries. Antihydrogen formed by carefully merging cold plasmas of positrons and antiprotons has recently been trapped in magnetic traps. The efficiency of trapping is strongly dependent on the temperature of the nascent antihydrogen, which, to be trapped, must have a kinetic energy less than the trap depth of . In the conditions in the ALPHA experiment, the antihydrogen temperature seems dominated by the temperature of the positron plasma used for the synthesis. Cold positrons are therefore of paramount interest in that experiment. In this paper, we propose an alternative route to make ultra-cold positrons for enhanced antihydrogen trapping. We investigate theoretically how to extend previously successful sympathetic cooling of positrons by laser-cooled positive ions to be used for antihydrogen trapping. Using simulations, we investigate the effectiveness of such cooling in conditions similar to those in ALPHA, and discuss how the formation process and the nascent antihydrogen may be influenced by the presence of positive ions. We argue that this technique is a viable alternative to methods such as evaporative and adiabatic cooling, and may overcome limitations faced by these. Ultra-cold positrons, once available, may also be of interest for a range of other applications.

Ambient air particle transport into the effluent of a cold atmospheric-pressure argon plasma jet investigated by molecular beam mass spectrometry

Ambient air species, which are transported into the active effluent of an atmospheric-pressure plasma jet result in highly reactive oxygen and nitrogen species (RONS). Especially for the envisaged application field of plasma medicine, these RONS are responsible for strong biological responses. In this work, the effect of ambient air transport into the effluent of an atmospheric-pressure plasma argon jet on the on-axis densities of nitrogen, oxygen and argon was investigated by means of absolutely calibrated molecular beam mass spectrometry (MBMS). According to biomedical experiments a (bottomless) Petri dish was installed in front of the MBMS. In the following, the near flow field is referring to the region close to the nozzle exit and the far flow field is referring to the region beyond that. The absolute on-axis densities were obtained by three different methods, for the near flow field with VUV-absorption technique, for the far flow field with the MBMS and the total flow field was calculated with a computational fluid dynamics (CFD) simulation. The results of the ambient air particle densities of all independent methods were compared and showed an excellent agreement. Therefore the transport processes of ambient air species can be measured for the whole effluent of an atmospheric-pressure plasma jet. Additionally, with the validation of the simulation it is possible in future to calculate the ambient species transport for various gas fluxes in the same turbulent flow regime. Comparing the on-axis densities obtained with an ignited and with a non-ignited plasma jet shows that for the investigated parameters, the main influence on the ambient air species transport is due to the increased temperature in the case when the jet is switched on. Moreover, the presence of positive ions (e.g. ) formed due to the interaction of plasma-produced particles and ambient air species, which are transported into the effluent, is shown.

Homogeneous and heterogeneous nucleation of water vapor: A comparison using molecular dynamics simulation

Using simple point charge/extended potential for water–water and a potential model for ion–water interaction, homogeneous and heterogeneous nucleation of water vapor are investigated with molecular dynamics simulation at 350K under supersaturation ratio of 8.9341 and 6.5000. The simulation results show the size and sign preference for ions, which is the rate of nucleation is higher for smaller negative ions. In spite of previous works which the position of ion was fixed in the center of a spherical cluster and the nucleation rate was derived from cluster formation free energy, we consider the ion as the second component which can move with no limitation on its position and the nucleation rate is calculated directly from the simulation data. The effect of supersaturation of water vapor on nucleation rate in presence of positive ions is also studied which indicates the important role of the ion presence in the nucleation process at low supersaturations.

Analysis of statistical nature of electrical breakdown time delay in nitrogen at 6.6 mbar pressure in presence of positive ions and N(4S) atoms

AbstractOn the basis of the mean value of electrical breakdown time delay $ \overline t_d $ and the standard deviation of electrical breakdown time delay σ dependence on the afterglow period τ, the mechanisms which dominantly influence to breakdown initiation in nitrogen were separated. It was shown that the positive ions formed in mutual collision of long‐lived metastable molecules have a dominant role in breakdown initiation for τ values up to 70 ms. The metastable molecules were derived from previous breakdown and discharge. In this case σ ≪ td and the total time delay td is approximately equal to formative time tf which decreases in value with the increase of overvoltage. When positive ions have a dominant role in the breakdown initiation the Gaussian distribution describes data of td ≈ tf very well. For τ > 1 s, N (4S) atoms formed in previous breakdown and discharge, have a dominant role in the breakdown initiation. Then, σ ≈$ \overline t_d $ and Laue's distribution, which is valid for statistical time delay ts, describes td data very well (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Lone pair versus bonding pair electrons: The mechanism of electronic polarization of water in the presence of positive ions

It is commonly accepted that the water molecules in the first solvation shell of a positive ion are strongly polarized because of an elongation of the oxygen lone pair orbitals along the ion-oxygen direction and this is commonly considered the dominant effect. Recent experimental and theoretical works have instead suggested that this is not the dominant aspect and that the problem is by far more complicated. Consistent with the picture given above, here we show that, in particular, an equally important role into the polarization process is played by the bonding pair electrons located along the internal oxygen-hydrogen bond. We also provide some arguments which suggest that the main reason of such a behavior is due to the distortion of the molecular orbitals caused by the interaction between non-hydrogen-bonded water molecules in the first solvation shell of the ion.

Destabilization and aggregation of aqueous humic acids solution by metal ions

The aggregation of soil humic acid (HA) after addition of cations was investigated by nephelometric measurements of HA solution turbidity. Here we show that aggregation is promoted by the presence of positive ions in the solution and that the order of increasing effectiveness in turbidity follows Schulze-Hardy rule. Also, the obtained results indicate that the cation with the largest ionic radius within a common valence is the most effective coagulant. Influence of unions follows the sequence: chloride < nitrate < sulphate, but it is insignificant comparing the influence of cation. This confirms that HA molecules are of negative charge.

X-Ray Microanalysis of Insulators in the ESEM

Abstract We have investigated the affect of accelerating voltage (E0), pressure (P), GSED bias (VGSED), field line geometry and specimen conductivity on the landing energy of the primary beam in an XL30 ESEM. The landing energy of the primary beam can be measured by using the Duane-Hunt cut-off energy, EDH, in EDS X-ray spectra. We present experimental evidence that the landing energy of the primary beam can be significantly altered when analyzing insulators in an ESEM. Shifts in EDH result from electric fields produced by the presence of positive ions in the ESEM chamber and electrons trapped in the bulk. No shift in EDH was observed with conductive specimens at all E0 and P. Changes in the landing energy of the primary beam can significantly effect the relative intensity of characteristic peaks in EDS spectra measured in the ESEM (Figure 1). The magnitude and sign of the shift in EDH is determined by E0 and P for a specific insulator specimen and stage geometry.

Article

The quadrupole ion trap mass spectrometer is of great interest for chemical analysis. Nevertheless, negative ion studies using in situ ionization (negative ions created inside the ion trap) are difficult and limited. This paper describes the difficulties that occurred during negative ion analysis when using a commercial gas chromatography quadrupole ion trap mass spectrometer (GC/MS) system. Detection problems, due to simultaneous trapping of both positive and negative ions, are explained by the large kinetic energies of the ejected ions. Negative ion formation, produced by electron capture, is limited by the fundamental RF field, which imparts high kinetic energy to the electrons, precluding the possibility that the electrons will reach the thermal energies needed for electron capture processes. In addition, simultaneous confinement of negative and positive ions affects the recorded mass spectra. Space charge potentials that exist inside the ion trap (due to the ionization conditions necessary to detect negative ions) induce the destabilization of positive ions at higher m/z ratios, while negative ions in the same m/z range are stabilized. Moreover, loss of resolution and decalibration could occur for negative ions when they are ejected in the presence of positive ions with higher m/z ratios. At the very least, ion-ion reactions could limit the observation of negative ions. The understanding of these phenomena, viz. detection, formation, and simultaneous confinement, will permit the proposal of solutions for negative ion analysis with quadrupole ion trap mass spectrometers using in situ ionization.Key words: mass spectrometry, quadrupole ion trap, negative ion, perfluorotributylamine, space charge.

Structural and electrical properties of lattice-matched Ca0.44Sr0.56F2/GaAs structures grown by molecular beam epitaxy

Single-crystalline, lattice-matched (Ca, Sr)F2 films have been grown by molecular beam epitaxy (MBE) on GaAs(100) and (111) As substrates. The ratio of the Rutherford backscattering yields from the fluoride films in the aligned normal direction to a random direction, or χmin, is 0.03 for a (100) sample and 0.05 for a (111) sample, indicating excellent epitaxy. In fact, the χmin of 0.03 for the (100) sample is the best of all reported as-grown fluoride films on the (100) surface of a semiconductor. It is nearly the same as χmin from a bulk single-crystalline fluoride. For the (111) sample, channeling measurements show that the film has the same orientation as the substrate, i.e., type A. Plan-view transmission electron microscopy confirms these results. Electrical measurements show that the film has a resistivity of 3×1014 Ω cm and breakdown fields of 7×105 to 3×106 V/cm. At room temperature I–V and C–V curves show various amounts of hysteresis that is completely eliminated at low temperature, indicating the presence of positive ions.

SCLC diode thin film rate monitor

The injection of a vapour beam into a thermionic vacuum diode in a Kingdom cage type configuration modifies the diode characteristics considerably. The anode current increases on injection, the increase being dependent on the anode voltage. This is attributed to the partial neutralization of the space charge by the presence of positive ions in the vapour beam (produced by the electron bombardment in the Kingdon cage configuration). The increase in the plate current in the space charge region of the diode is linearly proportional to the number of atoms in the vapour beam for various metal evaporants at low rates of evaporation. A theory to explain the neutralization effect has been developed. The observed effect lends itself to a useful device to monitor the vapour beam density and, therefore, the evaporation and deposition rates of materials. Vapour beam densities as low as 10 13/cm 2 sec and hence deposition rates as low as 0.1 Å/sec can be measured. Unlike the ionization gauge type of monitor, this device is not seriously affected by the presence of background (ambient) gases during vacuum evaporation.

Potential distribution in a gas filled planar diode

The approximative theory taking into account the electron space charge, initial velocities of the electrons emitted with Maxwellian distribution and their elastic collisions with neutral gas particles has been applied to the gas filled planar diode. The presence of positive ions was not considered. As a result, the differential equation for the dimensionless potential has been obtained. Using its solutions the potential distribution and the current-voltage characteristics can be determined.

INVESTIGATIONS OF CHARGED WATER DROPS

Charged water drops were suspended in a nonuniform a.c. field and observed through the microscope visually and by high-speed photography. The initial drop size was approximately 100µ. The drop shrank by evaporation and became unstable at approximately 40µ. The evaporation of stable drops and the behavior of unstable drops were studied. The rates of changes of mass and charge were determined at various temperatures, and the activation energy for the evaporation was determined. The evidence indicates that ions are ejected from an unstable drop, and that a burst of ions occurs in the evaporation of a stable drop under these conditions. The removal of water molecules from the evaporating drop is not rate-determining under these conditions. The drop evaporated rapidly at −26°C. and became unstable repeatedly without freezing.

BREAKDOWN OF A RADIO-FREQUENCY DISCHARGE IN THE PRESENCE OF A SUPERIMPOSED d-c. FIELD

Breakdown voltages have been determined in the case of some rare gases (He, Ne, A) and oxygen at a constant pressure (10 mm Hg) when excited simultaneously by a radio-frequency field (frequency 10 Mc/sec) and a variable d-c. field. It is found in all cases that the breakdown voltage is higher when both the fields are present than when the gases are excited by the radio-frequency field alone and the breakdown voltage gradually increases with the increase of the applied d-c. field. The variation of breakdown field with d-c. field is of the same nature in all of the gases studied. A theoretical expression for the breakdown voltage in the presence of both the r-f. and d-c. fields has been deduced from the theory of electrical discharge by Kihara (1952) together with the expression of equivalent length as deduced by Varnerin and Brown (1950). The theoretical expression cannot explain satisfactorily the experimental results, and the rate of rise of breakdown voltage in the d-c. field as obtained from theory is smaller than that obtained from experimental results. The discrepancy has been ascribed partly to the uncertainty in the values of the numerical constants introduced by Kihara and also to the increase of diffusion caused by the presence of positive ions—a factor which has not been taken into consideration in the present treatment.

Noise in reflex klystrons and backward-wave oscillators

The paper describes a.m. and f.m. direct-detection and superheterodyne noise spectrum measurements on various types of backward-wave oscillator and reflex klystron. A procedure has been developed by which the individual a.m., f.m. and background noise components can be separated. The results show that the predominant component at low sideband frequencies is f.m. noise and at high sideband frequencies is background noise. The a.m. noise is not a significant component. The presence of positive ions in the beam of a backward-wave oscillator causes noise peaks at frequencies near 1 Mc/s and an increase of modulation noise over a wide frequency range. Positive ions can be relatively easily removed by transverse ion drainage. Large noise peaks may also be generated at frequencies near those of spurious oscillations. The results of measurements of carrier frequency deviation, and of correlation between a.m. and f.m. noise, and between modulation and beam noise are also given.

Surface films and field emission of electrons

Experimental investigation of the cold electron emission from metals covered with thin ( ~ 10 -7 cm) tarnish films in gases shows that substantial emission ( ~ 10 5 electrons/s) can be produced by comparatively low applied electric fields ( ~ 10 4 V/cm). The results are consistent with the view that the electrons emitted are extracted from the metal substrate by the high electric field set up across the thin surface film when covered with a layer of positive ions, the presence of positive ions on the thin film being essential to the emission mechanism which follows a field law; this high emission does not occur when the thin surface tarnish film is absent. A theory based on this view is given and quantitative agreement with the experimental data is obtained. The applications of these results to the problems of the initiation of electrical discharges in general, including the electrical breakdown mechanism at high gas pressures as well as the initiation of micro-arcs at electrical contacts, are indicated. Comparison of the field emission from a mechanically polished surface with that from an electrolytically polished surface shows that the surface smoothness obtainable by the two methods of polishing can be of the same order.