VI Ions Research Articles

Data on Stark Broadening of N VI Spectral Lines

Data on Stark broadening parameters, spectral line widths, and shifts for 15 multiplets of N VI, whose spectral lines are broadened by collisions with electrons, protons, alpha particles (He III) and B III, B IV, B V and B VI ions, are presented. They have been calculated using the semiclassical perturbation theory, for temperatures from 50,000 K to 2,000,000 K, and perturber densities from 1016 cm−3 up to 1024 cm−3. The data for e, p and He III are of particular interest for the analysis and modelling of atmospheres of hot and dense stars, as, e.g., white dwarfs, and for investigation of their spectra, and data for boron ions are used for analysis and modelling of laser-driven plasma in proton–boron fusion research.

Stark Broadening of N VI Spectral Lines

Stark broadening parameters, line widths and shifts, for 15 N VI multiplets are calculated using semiclassical perturbation theory for temperatures from 50,000 K to 2,000,000 K, and perturber density of 1016 cm−3. As perturbers have been taken electrons, protons and He III ions (alpha particles), which are of interest particularly for white dwarfs. Moreover, B III, B IV, B V and B VI ions have been taken as well, due to their significance for proton-boron fusion investigations. An example of the importance of Stark broadening in comparison with thermal Doppler broadening in atmospheres of spectral class DO white dwarfs is also presented. The obtained results are of interest particularly for white dwarf atmospheres modelling and analysis and synthesis of their spectra as well as for laser driven plasma in proton-boron fusion investigations.

THE ROLE OF MHD WAVES IN HEATING OF THE SOLAR CORONA

Observations in the Solar North Polar Coronal Hole (NPCH) show that this region has high temperature values (10^6-10^8 K). At this temperature, the coronal plasma loses energy to the transition region below through heat conduction and optically thin emission. It is still a matter of debate how to replace this lost energy in the solar corona and how to maintain the observed temperature values. In this study, we aimed to study the wave theory, which is an important model proposed for the heating problem of the solar corona in NPCH. We assumed a model based on Alfvén/ion cyclotron resonance process with O VI ions by using quasi-linear approximation in NPCH and solve the magnetohydrodynamic (MHD) equations for O VI assuming that the non-thermal contribution to the temperature. Using a Matlab code, we performed 3D MHD numerical solutions of Alfvén waves. Our results show that the damping length scales (0.2-1.8 R) and energy flux densities (10^5-10^7 erg/cm^2 s) of Alfvén waves are similar for both plumes and interplumes in NPCH. As a result of our study, we present the contribution of MHD waves that will cause the acceleration of the solar wind and the heating of the solar corona.

The Potential of Cellulose from the Sugar Palm (Arenga Pinnata) Seed Shell for Removal of Cr(Vi) Ions

Cr (VI) is persistent, bio-accumulative, toxic metal, unable to decompose in the environment, and accumulates in the human body through the food chain. The Cr(VI) ions can remove in aqueous solution by adsorption technique with cellulose extracted. Extract of cellulose were prepare from palm (Arenga pinnata) seed shell using acidified H2SO4 and bleaching methods. The cellulose have contained the hydroxyl (–OH) functional groups in structure, it can be an adsorbent for heavy metal ions. Cellulose was obtained with delignification and bleaching methods to break the bond between lignin and cellulose. The cellulose extracted were characterized by Fourier Transformation Infra-Red (FT-IR) and Scanning Electron Microscopy - Energy Dispersive X-Ray (SEM)-EDX. The adsorption process was conducted using pH, contact time, and concentration of Cr(VI) ions. The results showed that the optimum pH was obtained at pH 3 with an adsorption capacity is 0.88 mg/g. The optimum contact time was obtained at 120 minutes with an adsorption capacity is 0.89 mg/g. The optimum concentration was obtained at a concentration of 200 ppm with an adsorption capacity is 20.34 mg/g

Isotherm Studies of Adsorption of Cr (Vi) Ions onto Coconut Husk

In this study, the application of ground coconut husk GCH for removal of Cr (VI) from its aqueous solution was investigated. Several batch experiments were carried out with different values of test conditions including sorbent concentration, contact time, temperature and pH. The results obtained showed that adsorption of Cr (VI) followed Freundlich isotherm model. Dubinin-Radushkevich isotherm revealed that adsorption of the three metal ions principally followed chemical adsorption process. Adsorption kinetics was best described by pseudo-second order. Thermodynamic studies revealed that adsorption of Cr (VI) were endothermic process since ∆H was positive. Adsorption of Cr (VI) was spontaneous as evident from the negative value ∆G. Uptake of metal ion from their aqueous solution increases with increase in pH but decreases slightly at pH of 8.

Coronal Pseudo-Streamer and Bipolar Streamer Observed by SOHO/UVCS in March 2008

The last solar minimum is characterized by several peculiar aspects and by the presence of a complex magnetic topology with two different kinds of coronal streamers: pseudo-streamers and bipolar streamers. Pseudo-streamers or unipolar streamer are coronal structures which separate coronal holes of the same polarity, without a current sheet in the outer corona; unlike bipolar streamer that separate coronal holes of opposite magnetic polarity. In this study, two examples of these structures have been identified in the period of Carrington rotation 2067, by applying a potential-field source-surface extrapolation of the photospheric field measurements. We present a spectroscopic analysis of a pseudo-streamer and a bipolar streamer observed in the period 12-17 March 2008 at high spectral and spatial resolution by the Ultraviolet Coronagraph Spectrometer (UVCS; Kohl et al., 1995) onboard Solar and Heliospheric Observatory (SOHO). The solar wind plasma parameters, such as kinetic temperature, electron density and outflow velocity, are inferred in the extended corona (from 1.7 to 2.1 Rsun) analysing the O VI doublet and Ly alpha line spectra. The coronal magnetic topology is taken into account and has been extrapolated by a 3D magneto-hydrodynamic model of the global corona. The results of the analysis show some peculiarities of the pseudo-streamer physical parameters in comparison with those obtained for bipolar streamers: in particular, we have found higher kinetic temperature and higher outflow velocities of O VI ions and lower electron density values. In conclusion, we point out that pseudo-streamers produce a "hybrid" type of outflow that is intermediate between slow and fast solar wind and they are a possible source of slow/fast wind in not dipolar solar magnetic field configuration.

The Photocatalytic Interaction of Cr(Vi) Ions and Phenol on Polymer-modified TiO2Under Visible Light Irradiation

The Photocatalytic Interaction of Cr(Vi) Ions and Phenol on Polymer-modified TiO₂Under Visible Light Irradiation

Ion–Cyclotron Resonance Frequency Interval Dependence on the O VI Ion Number Density in the North Polar Coronal Hole 1.5R–3R Region

The frequency intervals in which O VI ions get in resonance with ion–cyclotron waves are calculated using the kinetic model, for the latest six values found in literature on O VI ion number densities in the 1.5R–3R region of the NPCH. It is found that the common resonance interval is 1.5 kHz to 3 kHz. The R-variations of wave numbers necessary for the above calculations are evaluated numerically, solving the cubic dispersion relation with the dielectric response derived from the quasi-linear Vlasov equation for the left-circularly polarized ion-cyclotron waves.

Excitation cross-sections by electron impact for O V and O VI levels

Radiative atomic and electron impact excitation data for O V and O VI ions have been calculated. The radiative atomic data have been calculated with the AUTOSTRUCTURE code. Besides the onebody and the two-body fine structure interactions, the two-body non-fine structure operators of the Breit–Pauli Hamiltonian, namely contact spin–spin, two-body Darwin and orbit–orbit are incorporated in AUTOSTRUCTURE. The scattering problem has been treated in the Breit–Pauli distorted wave approximation using the same code AUTOSTRUCTURE .T he OV atomic calculations have been extended from 46 to 92 levels. We have calculated excitation cross-sections for the O V 2s 2 −2s2p and the O VI 2s−2p transitions at energies near the corresponding excitation threshold regions. We have also calculated collision strengths for transitions from the most important levels for collisional excitation at electron energies up to 120 Ry for O V and up to 140 Ry for O VI. Our results have been compared with the available theoretical/experimental ones and a satisfactory agreement has been found between them.

DETECTION OF DIFFUSE X-RAY EMISSION FROM PLANETARY NEBULAE WITH NEBULAR O VI

The presence of O VI ions can be indicative of plasma temperatures of a few times 10^5 K that is expected in heat conduction layers between the hot shocked stellar wind gas at several 10^6 K and the cooler (~10,000 K) nebular gas of planetary nebulae (PNe). We have used FUSE observations of PNe to search for nebular O VI emission or absorption as a diagnostic of conduction layer to ensure the presence of hot interior gas. Three PNe showing nebular O VI, namely IC 418, NGC 2392, and NGC 6826, have been selected for Chandra observations and diffuse X-ray emission is indeed detected in each of these PNe. Among the three, NGC 2392 has peculiarly high diffuse X-ray luminosity and plasma temperature compared with those expected from its stellar wind's mechanical luminosity and terminal velocity. The limited effects of heat conduction on the plasma temperature of a hot bubble at the low terminal velocity of the stellar wind of NGC 2392 may partially account for its high plasma temperature, but the high X-ray luminosity needs to be powered by processes other than the observed stellar wind, probably caused by the presence of an unseen binary companion of the CSPN of NGC 2392. We have compiled relevant information on the X-ray, stellar, and nebular properties of PNe with a bubble morphology and found that the expectations of bubble models including heat conduction compare favorably with the present X-ray observations of hot bubbles around H-rich CSPNe, but have notable discrepancies for those around H-poor [WR] CSPNe. We note that PNe with more massive central stars can produce hotter plasma and higher X-ray surface brightness inside central hot bubbles.

Ion-cyclotron resonance with streaming bi-Maxwellian distribution

We investigate the effect of bulk velocity of the solar wind on the propagation characteristics of ion-cyclotron waves (ICWs). Our model is based on the kinetic theory. We solve the Vlasov equation for O VI ions and obtain the dispersion relation of ICWs. Refractive index of the medium for a streaming bi-Maxwellian velocity distribution proved to be higher than that of the bi-Maxwellian velocity distribution. The bulk velocity of the solar polar coronal holes’ plasma increases the value of the refractive index by a factor of 1.5 (3) when the residual contribution is included (neglected). The ratio of the refractive index of interplume lanes to the plume lanes at the coronal base is also higher than we found for the bi-Maxwellian velocity distribution, i.e. kinterplume/kplume=2.5.

Ion-cyclotron waves in solar coronal hole

We investigate the effect of the plume/interplume lane (PIPL) structure of the solar polar coronal hole (PCH) on the propagation characteristics of ion-cyclotron waves (ICW). The gradients of physical parameters determined by SOHO and TRACE satellites both parallel and perpendicular to the magnetic field are considered with the aim of determining how the efficiency of the ICR process varies along the PIPL structure of PCH. We construct a model based on the kinetic theory by using quasi-linear approximation. We solve the Vlasov equation for O VI ions and obtain the dispersion relation of ICW. The resonance process in the interplume lanes is much more effective than in the plumes, agreeing with the observations which show the source of fast solar wind is interplume lanes. The solution of the Vlasov equation in PIPL structure of PCH, the physical parameters of which display gradients along and perpendicular direction to the external magnetic field, is thus obtained in a more general form than the previous investigations.

Visible light driven photocatalysis in chromate(VI)/TiO 2 systems—Improving stability of the photocatalyst

Titanium dioxide photosensitization to visible light can be observed in the presence of chromate(VI) ions adsorbed at the surface of TiO 2. The resulting materials do not show, however, sufficient stability and photostability—chromium(VI) species desorb from the surface and can be reduced to chromium(III). The stability of such systems has been improved by TiO 2 impregnation with fluorochromate(VI), K[CrO 3F], instead of K 2Cr 2O 7, yielding yellow F-Cr VI@TiO 2 material. Fluorides playing the role of anchors enable stronger adsorption of chromates at titanium dioxide. Also composites of water insoluble chromates(VI) with TiO 2 release significantly lower amounts of Cr VI ions. Such materials have been synthesized according to two main strategies—the first one involves precipitation of water insoluble chromates in the presence of TiO 2 particles (MCrO 4@TiO 2) while the second strategy comprises of TiO 2 synthesis in the presence of insoluble chromate particles (TiO 2@MCrO 4). Visible light induced photocatalytic activity of synthesized materials was studied in the process of 4-chlorophenol (4-CP) oxidation. A considerable photocatalytic activity was observed in the case of F-Cr VI@TiO 2 and TiO 2@MCrO 4 type materials (M n+ : Ba 2+, Co 2+, Mn 2+, Cr 3+). Among the composites the highest photoreactivity was shown by TiO 2@CoCrO 4 (1.7% Cr VI, mol/mol, calcined at 450 °C) and TiO 2@Cr 2(CrO 4) 3 (5% Cr VI, mol/mol, calcined at 450 °C).

MHD waves in the solar north polar coronal hole

AbstractThe effects, hitherto not treated, of the temperature and the number density gradients, both in the parallel and the perpendicular direction to the magnetic field, of O VI ions, on the MHD wave propagation characteristics in the solar North Polar Coronal Hole are investigated. We investigate the magnetosonic wave propagation in a resistive MHD regime where only the thermal conduction is taken into account. Heat conduction across the magnetic field is treated in a non‐classical approach wherein the heat is assumed to be conducted by the plasma waves emitted by ions and absorbed at a distance from the source by other ions. Anisotropic temperature and the number density distributions of O VI ions revealed the chaotic nature of MHD standing wave, especially near the plume/interplume lane borders. Attenuation length scales of the fast mode is shown not to be smoothly varying function of the radial distance from the Sun (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Novel graphical method for the simultaneous determination of stability constant and molar absorptivity of some metal - Chrome Azurol S complexes

Stability constants and molar absorptivities of complexes formed by Chrome Azurol S (tri sodium salt of 3-sulpho-2:6-dichloro-3:3'-dimethyl-4-hydroxy-fuschsone-5:5-dicarboxy acid) with metal ions like Al III , Sc, Cu II , Th IV and U VI ions have been determined by a novel graphical method in which neither the concentration of ligand has to be kept high in comparison to the concentration of metal ion nor any term has to be omitted to get the linear equation.

Studies on interaction of molybdenum(VI) with modified lignocellulosics using a novel spectrophotometric method

A new adsorbent (PGPEP-COOH) bearing carboxylate functional group was prepared through graft co-polymerization of acrylic acid onto pulverized Phyllanthus emblica planks using ferrous sulphate/H 2 O 2 redox initiator system. The adsorbent obtained was tested for the uptake of molybdenum(VI) from aqueous solutions. The efficiency of the PGPEP-COOH to remove Mo VI ions at different time of contact, initial adsorbate concentration, adsorbent dose, pH, ionic strength and temperature was studied by batch experiments. The amount of molybdeitum(VI) in aqueous system was determined using a very simple and sensitive method of estimation using potassium hexacyanoferrate(II). Reddish brown solution of the molybdenum complex at pH 3.2 shows absorption maximum at 390 nm. To establish the most appropriate correlation for adsorption equilibrium, isotherm studies were performed using Langmuir, Freundlich and Redlich-Peterson models. The suitability of isotherm models was compared using linear least square fitting. Experimental kinetic data were described using a diffusion controlled first order reversible model and diffusion coefficient was evaluated at different temperatures. Applying Eyring equation thermodynamic parameters were calculated. PGPEP-COOH adsorbed 99.2% Mo VI from a solution of 10 μmol dm -3 concentration at 303 K. Desorption and regeneration studies of the adsorbent under different conditions were also studied.

The Effect of Anticoagulants on the Distribution of Chromium VI in Blood Fractions

Metal-on-metal resurfacing arthroplasty is associated with elevated circulating levels of cobalt and chromium ions. To establish the long-term safety of metal-on-metal resurfacing arthroplasty, it has been recommended that during clinical follow-up of these patients, the levels of these metal ions in blood be monitored. In this article, we provide information on the distribution of chromium VI ions (the predominant form of chromium released by cobalt-chrome alloys in vivo and in vitro) in blood fractions. Chromium VI is predominantly partitioned into red blood cells compared with plasma (analysis of variance, P < .05). The extent of accumulation in red blood cells is influenced by the anticoagulant used to collect the blood, with EDTA giving a lower partitioning into red cells compared with sodium citrate and sodium heparin.

The Funnel Geometry of Open Flux Tubes in the Low Solar Corona Constrained by O vi and Ne viii Outflow

Model calculations show that observed outflow velocities of order 7-10 km/s of C IV and O VI ions, and 15-20 km/s of Ne VIII ions, are not only consistent with models of the solar wind from coronas holes, but also place unique constraints on the degree of flow tube expansion as well as the location of the expansion in the transition region/lower corona.

Luminescence of isoelectronically ion‐implanted SiO2 layers

AbstractScanning electron microscopy (SEM) and cathodoluminescence (CL) in combination with scanning transmission electron microscopy (STEM) have been used to investigate thermally grown amorphous silicon dioxide layers implanted isoelectronically with group IV ions (C+, Si+, Ge+, Sn+, Pb+) as well as with group VI ions (O+, S+, Se+). Besides the main luminescent centers in a‐SiO2 layers: the red R luminescence (650 nm; 1.9 eV) of the non‐bridging oxygen hole centers (NBOHC), the blue B (460 nm; 2.7 eV) and the UV (290 nm; 4.3 eV) band of the oxygen deficient centers (ODC), in ion implanted silica additional emission bands are observed. E.g. in Ge+ implanted layers a huge violet band appears at 410 nm (3.1 eV) increasing with the thermal annealing process due to formation of Ge dimers, trimers or higher aggregates, finally leading to destruction of the luminescence centers by further growing to Ge nanoclusters. The Ge cluster size is shown by STEM cross section micrographs.Generally, group IV element implantation and partial substitution of silicon increases the luminescence in the blue/violet region whereas group VI elements and additional oxygen increase the intensity in the red region, confirming the association of the blue and the red luminescence with oxygen deficient centers and oxygen excess centers, respectively. Thus, the cathodoluminescence spectra of sulfur and oxygen implanted SiO2 layers under special conditions show besides the characteristic luminescence bands a multimodal structure beginning in the green region at 500 nm and extending up to the near infrared region at 820 nm. The energy step differences of the sublevels amount in the average 120 meV and indicate vibronic‐electronic transitions, probably of O2– interstitial molecules. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Transition Region Emission and Energy Input to Thermal Plasma during the Impulsive Phase of Solar Flares

The energy released in a solar flare is partitioned between thermal and nonthermal particle energy and lost to thermal conduction and radiation over a broad range of wavelengths. It is difficult to determine the conductive losses and the energy radiated at transition region temperatures during the impulsive phases of flares. We use UVCS measurements of O VI photons produced by five flares and subsequently scattered by O VI ions in the corona to determine the 5.0 ≤ log T ≤ 6.0 transition region luminosities. We compare them with the rates of increase of thermal energy and the conductive losses deduced from RHESSI and GOES X-ray data using areas from RHESSI images to estimate the loop volumes, cross-sectional areas, and scale lengths. The transition region luminosities during the impulsive phase exceed the X-ray luminosities for the first few minutes, but they are smaller than the rates of increase of thermal energy unless the filling factor of the X-ray-emitting gas is ~0.01. The estimated conductive losses from the hot gas are too large to be balanced by radiative losses or heating of evaporated plasma, and we conclude that the area of the flare magnetic flux tubes is much smaller than the effective area measured by RHESSI during this phase of the flares. For the 2002 July 23 flare, the energy deposited by nonthermal particles exceeds the energy radiated in X-rays, the energy radiated at transition region temperatures, and the rate of increase of the thermal energy.