Double Ion Research Articles

Importance of the Number of Acid Molecules and the Strength of the Base for Double-Ion Formation in (H2SO4)m·Base·(H2O)6 Clusters

Sulfuric acid and water clusters are important for new particle formation in the atmosphere. Recent experimental studies demonstrate that critical clusters in diverse atmospheric environments contain two acid molecules and may also include additional N-containing molecules (i.e., a base). We use first-principles molecular dynamics simulations to show that the presence of two sulfuric acid molecules in (H2SO4)m x base x (H2O)6 clusters is always sufficient to form a double ion, whereas a single acid molecule, even in the presence of a base, is not.

Inter-annual stability of oligopeptide patterns of Planktothrix rubescens blooms and mass mortality of Daphnia in Lake Hallwilersee

During mass developments of Planktothrix rubescens, the biomass of this cyanobacterium was collected over a period of four consecutive years (2002–2005) from Lake Hallwilersee, Switzerland. To avoid any shifts in analytical separation and sensitivity, the biomasses were extracted with 60% aqueous methanol at the end of the investigation period and were analysed within 1 week by LC-ESMS. A new mass spectrometric method to quantify oligopeptides was introduced. The sum of all major molecular species (quasi-molecular ion, double charged ion, adducts, dimers and molecular ions that had lost a water molecule) rather than just the signal of the quasi-molecular ion was used to determine the total abundance of oligopeptides. This procedure has become necessary because the variable presence of inorganic ions and the varying conditions of the mass spectrometric source strongly affect the formation of the different molecular species. Several anabaenopeptins, oscillapeptins and planktocyclins were found. [Asp 3, Dhb 7]microcystin-RR was the major microcystin. The oligopeptide patterns were relatively stable over the investigation period of 4 years. In June 2005, a mass mortality of Daphnia was observed. The dead Daphnia, which floated on the surface of the lake, were collected and analysed for oligopeptides. Planktocyclin and planktocyclin sulfoxide, which belong to the major cyclic peptides in P. rubescens, were found in the carcasses of Daphnia, but microcystins were missing. Live zooplankton of the epilimnion was represented by both Daphnia and copepods, while the patches of dead zooplankter on the lake surface were free of copepods and contained only Daphnia. Protease inhibitors rather than microcystins are discussed as the major bioactive compounds for grazer defence of P. rubescens.

The influence of Rydberg states on the photodissociation of nitrous oxide

The absolute photoabsorption cross section and the photoionization quantum efficiency of nitrous oxide have been measured from the ionization threshold to 21 eV, using a double ion chamber and monochromated synchrotron radiation, and these have enabled the absolute photodissociation cross section to be deduced. Variations in the photoionization quantum efficiency in the vicinity of a Rydberg state have allowed the competition between predissociation and autoionization in the decay of the super-excited state to be investigated. The photodissociation cross section exhibits prominent structure which correlates with known Rydberg series. Dispersed fluorescence techniques have been employed to identify the electronically excited neutral molecular species (N2 B 3Πg and NO B 2Π) formed through photodissociation of N2O. Fluorescence excitation spectra due to the N2 B 3Πg → A 3Σ+u and the NO B 2Π → X 2Π transitions following excitation of N2O have been recorded and the features in these spectra have been compared with the corresponding structure in the photodissociation spectrum. The N2 B 3Πg fragments are produced directly through photodissociation of the parent molecule. However, at low excitation energies the NO B 2Π fragments are formed only through secondary reactions. The five Rydberg series converging onto the N2O+ C 2Σ+g limit are considered in detail because each series exhibits a specific decay mechanism.

Fragmentation of sputtered Si n O m + clusters: Release kinetic and dissociation energies

The spectra of kinetic energies of positive SinOm+ cluster ions (n = 2–5, m = 2–7) have been measured using a double focusing ion microanalyzer with reverse geometry at instants 10−5 to 10−4 s after emission. The dissociation energies have been determined within the evaporative ensemble model and the theory of unimolecular decay reactions. The results obtained are compared with the binding energies of neutral SinOm clusters.

Effects of magnetic field topography on ion thruster discharge performance

Traditional magnetic field design techniques for dc ion thrusters typically focus on closing a sufficiently high maximum closed magnetic contour, Bcc, inside the discharge chamber. In this study, detailed computational analysis of several modified NSTAR thruster 3-ring and 4-ring magnetic field geometries reveals that the magnetic field line shape as well as Bcc determines important aspects of dc ion thruster performance (i.e. propellant efficiency, beam flatness and double ion content). The DC-ION ion thruster model results show that the baseline NSTAR configuration traps the primary electrons on-axis, which leads to the high on-axis plasma density peak and high double ion content observed in experimental measurements. These problems are further exacerbated by simply increasing Bcc and not changing the field line shape. Changing the field line shape to prevent on-axis confinement (while maintaining the NSTAR baseline Bcc) improves thruster performance, improves plasma uniformity and lowers double ion content. For these favorable field line geometries, we observe further improvements to performance with increased Bcc, while maintaining plasma uniformity and low double ion content. These improvements derive from the fact that the field lines guide the high-energy primaries to regions where they are most efficiently used to create ions while a higher Bcc prevents the loss of ions to the anode walls. Therefore, it is recommended that the ion thruster designer first establish a divergent field line shape that ensures favorable beam flatness, low double ion content and reasonable performance; then the designer may adjust the Bcc to attain desirable performance and stability for the target discharge plasma conditions.

Response to “Comment on ‘Free energy simulations of single and double ion occupancy in gramicidin A’ ” [J. Chem. Phys. 128, 227101 (2008)

We respond to the criticism that one-dimensional (1D) construction of the potential of mean force (PMF) of ions in channels is flowed. Comparison of the 1D PMF results in the gramicidin A channel with independent free energy difference calculations obtained by using the free energy perturbation and thermodynamic integration methods shows complete agreement, thus providing a justifications for the 1D PMF approximation.

Synthesis and Biological Studies of 35‐Deoxy Amphotericin B Methyl Ester

The use of molecular editing in the elucidation of the mechanism of action of amphotericin B is presented. A modular strategy for the synthesis of amphotericin B and its designed ana- logues is developed, which relies on an efficient gram-scale synthesis of various subunits of amphotericin B. A novel method for the coupling of the mycosa- mine to the aglycone was identified. The implementation of the approach has enabled the preparation of 35- deoxy amphotericin B methyl ester. In- vestigation of the antifungal activity and efflux-inducing ability of this am- photericin B congener provided new clues to the role of the 35-hydroxy group and is consistent with the in- volvement of double barrel ion chan- nels in causing electrolyte efflux.

Serum proteomic profiling of obese patients: correlation with liver pathology and evolution after bariatric surgery

Objective:Chronic liver diseases, including cirrhosis, may develop in obese patients. Steatosis and non-alcoholic steatohepatitis (NASH) are risk factors for progression to fibrosis. To date, diagnosis of steatosis and NASH relies...

Study on Process of Ion Implantation on AZ31 Magnesium Alloy

Ti ion and C ion is implanted into AZ31 magnesium alloy surface by metal vapor vacuum arc (MEVVA) implanter operating with a modified cathode. This metal arc ion source has a broad beam and high current capabilities. Implantation energy is fixed at 45K eV and dose is 9×1017 cm-2 and 3×1017 cm-2 respectively. Through ion implantation, Ti ion implantation layer approximately 1000nm thick is directly formed on the surface of AZ31 magnesium alloy, by which its surface property is greatly improved. Microstructure, the component distribution and phase composition are analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The property of hardness of the ion implantation layer was studied by HMV-1T Vickers micro hardness tester. The results show that Ti ion implantation layer of a magnesium alloy surface is mainly composed of TiO2, MgO and a little of TiO. The Ti-C double ions implantation layer is composed of MgO, TiC. The hardness of ion implantation layer is improved.

Ultratrace analysis of Antarctic snow samples by reaction cell inductively coupled plasma mass spectrometry using a total-consumption micro-sample-introduction system

In this work, a new sensitive procedure for the determination of ultratrace elements in snow samples based on quadrupole ICP-MS has been developed. After filtration through a 0.5 microm PTFE membrane (for dissolved element determination) or acidification with 0.5% nitric acid (for acid dissolvable element determination), the analytes were preconcentrated by sample volume reduction and analysed by ICP-MS. Micro-samples were efficiently introduced into the plasma source at 20 microl min(-1) uptake rate by using a PFA micronebulizer coupled to an evaporation chamber of the torch integrated sample introduction system (TISIS). As a result, the amount of sample required was about one order of magnitude lower than that required with a conventional liquid sample introduction system. In order to improve the transport efficiency, the TISIS chamber was electrically-heated at 70 degrees C and a sheathing gas stream was used to protect the aerosol from the chamber walls. Under these conditions, negative solvent plasma effects were no more severe than for conventional systems, because the total solvent plasma load was 20 mg min(-1). The operating parameters were optimized to obtain maximum sensitivity, while limiting oxides and double charge ion formation. The polyatomic interferences were removed by applying the dynamic reaction cell (DRC) technique, using ammonia as the reaction gas. Under the optimized conditions, limits of detection ranged from 0.02 to 4.5 pg g(-1), allowing the determination of Cr, V, Fe, Mn, Pb, Zn, Cd, Co and Cu in Antarctic snow samples. Signal repeatability was lower than 10% which prevented the use of an internal standard. Precision of the procedure ranged from 2.0% to 5.6%. The accuracy of the method was verified by the analysis of both certified reference water and surface snow samples collected in coastal and inland areas of Antarctica. The DRC program used, the short wash out and signal stabilization times registered under these conditions led to a 10 h(-1) sample throughput.

Synthesis and welding of H-doped and N-doped carbon nanowires

A efficient and novel experimental method for synthesis and welding of amorphous carbon nanowires (ACNWs) by using double ion irradiations and heat-treatment is described. Experimental samples were characterized using high resolution transmission electron microscopy (HR-TEM). The results demonstrate that the proper combination of double ion irradiations and heat-treatment may make the multiwalled carbon nanotubes (MWCNTs) to become amorphous carbon nanowiro, thus enabling the welding of crossed ACNWs. In addition, the atomic evolution in carbon structural phase transformation is briefly discussed in connection with the current prevailing ideas.

Effect of Base Impurity Concentration on DC Characteristics of Double Ion Implanted 4H-SiC BJTs

ABSTRACTDouble ion implanted 4H-SiC bipolar junction transistors (BJTs) are fabricated by Al and N ion implantation to the base and emitter. The current gain of 3 is obtained at the base Al concentration of 1 × ∼ 1017 /cm3. The collector current as a function of the base Gummel number suggests that double ion implanted 4H-SiC BJT operates in the intrinsic region below the emitter in the low injection level. The high base resistance restricts the base current at VBE as low as 3 V.

Formation of nanoparticles in soda-lime glasses by single and double ion implantation

Structural characteristics and optical properties of monometallic and bimetallic Ag and Au nanoparticles in the surface region of soda-lime glass fabricated by ion implantation have been studied by transmission electron microscopy and optical spectroscopy. As a result it has been found that both, implantation dose and process temperature, strongly influence the metal nanoparticle formation governed by ion diffusion and metal precipitation as well as the involved stress generation around the particles. Thus, the mean size of metal nanoparticles and the width of the particle containing region beneath the glass surface increase with increasing temperature as well as implanted dose. Upon sequential high-dose double implantation to form bimetallic Ag–Au nanoparticles a rather complex configuration has been obtained. Particles of sizes above a threshold of 5–10nm exhibit distinct image contrast features indicating the development of central voids whose sizes are proportional to the outer particle diameter.

Free energy simulations of single and double ion occupancy in gramicidin A

Simultaneous occupancy of the two binding sites in gramicidin A by monovalent cations is a well known property of this channel, but the energetic feasibility of this process in molecular dynamics simulations has not been established so far. Here the authors study the energetics of single and double ion occupancy in gramicidin A by constructing the potential of mean force for single and pair of cations. As representatives of small and large ions, they consider both Na+ and K+ ions in the calculations. Binding constants of ions are estimated from the free energy profiles. Comparisons with the experimental results indicate 3-4 kT discrepancy in the binding energies. They also study the coordination of the ions in their respective binding sites and the dynamic behavior of the channel water during the double ion binding process.

Synthesis of diamond nanocrystals by double ions (40Ar+,C2H+6) bombardment

We demonstrate experimentally that an irradiation-induced transformation of multiwalled carbon nanotubes to diamond nanocrystals (DNC) can be realized with double ions (40Ar+，C2H+6) bombardment. This approach is expected to form a new route for synthesis of DNC. The idea of multi-ion irradiation may also be valid for other materials and be used for fabricating nanostructures.

Cascade decays and final charge-state distribution of single K-vacancy and double K-vacancy magnesium ions

Based on the conclusion that the contribution of correlated decay of two vacancies in atoms is small，the de-excitation process of Mg1+(1s-1) hollow magnesium ions with single K-vacancy and Mg2+(1s-2) double K-vacancy were treated by applying the radiative-single Auger - double Auger cascade model（RACDA）. The final-charge-state distribution(FCSD) of these hollow ions were calculated，and compared with that obtained with the radiative-single Auger cascade model（RAC）. The probability of tetravalent ion production via the de-excitation of Mg1+(1s-1) obtained by RACDA model is considerable，but tetravalent ion is not produced in the by RAC model. The probability of hexavalent ion production via the de-excitation of Mg2+(1s-2) obtained by RACDA model is very large，but hexavalent ion is not produced in the RAC model.

High precision titanium isotope measurements on geological samples by high resolution MC-ICPMS

A method has been developed for the precise and reproducible measurement of Ti isotopes in natural materials using high resolution MC-ICPMS. Instrumental mass fractionation is internally corrected using 49Ti/ 47Ti. Replicate measurements of synthetic standard solutions, terrestrial rocks, and the carbonaceous chondrite Allende yield a long-term reproducibility (2 σ) of 0.28 ɛ, 0.34 ɛ, and 0.28 ɛ for 50Ti/ 47Ti, 48Ti/ 47Ti, and 46Ti/ 47Ti, respectively. Isobaric interferences from 46,48Ca +, 50V +, 50Cr +, and doubly charged Zr can be corrected for reliably in separated Ti solutions with Ca/Ti < 5, V/Ti < 0.3, Cr/Ti < 0.2, and Zr/Ti < 1, respectively. Such elemental ratios are achieved easily in most samples using the anion-exchange procedure presented. Single and double charged polyatomic ions can either be resolved, e.g., 14N 36Ar +, or do not compromise the measurements. The method has been successfully applied to terrestrial rocks, meteorites, and various mineral separates. Terrestrial samples and standards agree within analytical uncertainties but are consistently different from the recommended values of Niederer et al. [F.R. Niederer, D.A. Papanastassiou, G.J. Wasserburg, Geochim. Cosmochim. Acta 45 (1981) 1017] with the largest effect on 50Ti/ 47Ti. The new results provide evidence that the recommended terrestrial 50Ti/ 47Ti is not well constrained; our data are higher by ∼13 ɛ than the recommended value. Better agreement is found with the values recommended by Heydegger et al. [H.R. Heydegger, J.J. Foster, W. Compston, Earth Planet. Sci. Lett. 58 (1982) 406]. Our best estimate for the isotopic composition of terrestrial Ti (relative to 49Ti/ 47Ti = 0.749766) is: 50Ti/ 47Ti = 0.73010, 48Ti/ 47Ti = 10.06884, and 46Ti/ 47Ti = 1.09325. This corresponds to an atomic weight of 47.877, significantly different from the value of 47.867 recommended by IUPAC. A 50Ti/ 47Ti anomaly for bulk Allende of 3.37 ± 0.51 ɛ is found, while for 48Ti/ 47Ti and 46Ti/ 47Ti the data are identical to the terrestrial value within the uncertainties. This is consistent with other recently reported differences between the bulk Earth and chondrites in neutron-rich nuclides.

Nano-mechanical properties of BCN/CN/BN multilayer films

Hard coatings based on BCN/CN/BN multilayer films were deposited on Si substrates using a double ion beam sputtering system. The multilayers were obtained by sequential sputtering of BN, C and B 4C targets and simultaneous bombardment of the growing films with low energy nitrogen ions. The multilayers were characterized by Auger electron spectroscopy (AES) depth profiles in order to get a quantitative analysis of the components in the different layers. In the interface BCN/CN, Factor Analysis was used to deconvolute the different chemical states of the components and to evaluate the physical and chemical characteristics of the multilayer with respect to their practical applications. In this work, we have studied the composition, morphology, hardness and wear resistance of the films. The mean grain size of the structures of the different coatings, as well as the root mean square (RMS) surface roughness, was measured by AFM.

Double Layers and Ion Phase-Space Holes in the Auroral Upward-Current Region

The dynamic evolution of the boundary between the ionosphere and auroral cavity is studied using 1D and 2D kinetic Vlasov simulations. The initial distributions of three singly ionized species (H+, O+, e-) are determined from space-based observations on both sides of an inferred strong double layer. The kinetic simulations reproduce features of parallel electric fields, electron distributions, ion distributions, and wave turbulence seen in satellite observations in the auroral upward-current region and, for the first time, demonstrate that auroral acceleration can be driven by a parallel electric field supported, in part, by a quasistable, strong double layer. In addition, the simulations verify that the streaming interaction between accelerated O+ and H+ populations continuously replenished by the double layer provides the free energy for the persistent formation of ion phase-space holes.

Reconstruction of Ionization Density Distribution in Hall Thruster Channel from Ion Energy Spectrum of Plasma Jet

Propellant ionization in the Hall thruster discharge channel is a significant process and has strong influence on the thruster's efficiency. In this work, the functional relation has been established between the ionization density distribution and the function of the ion energy distribution through the basic equations governing the ion flow in the Hall thruster channel and the method achieved for reconstructing the ionization density distribution inside the channel by ordinary plasma diagnosis of the potential distribution and ion energy spectrum of the plasma jet. The ionization density distributions of single and double charged ions in an ATON-thruster channel have been reconstructed according to the experimental data of the potential distribution along the axis of the channel and the ion energy spectrum of the plasma jet. The agreement between the calculation and experimental results of the percentage of double charged ions proves the validity of our method achieved in this work.