Negative ion formation and evolution in atmospheric pressure corona discharges between point-to-plane electrodes with arbitrary needle angle

The change in the distribution pattern of negative ions HO^–, NO_x^-_{x}^{-} and CO_x^-_{x}^{-} observed on arbitrary point-to-plane electrode configuration has been investigated by varying the angle of needle to the plane electrode, under atmospheric pressure corona discharge conditions. The stationary inhomogeneous electric field distributions between the point-to-plane electrodes with arbitrary needle angle were calculated. The experimental and theoretical results obtained suggested that the negative ion evolutions progress along field lines established between the electrodes with arbitrary configurations and the resulting terminal ion formation on a given field line is attributable to the electric field strength on the needle tip surface where the field line arose. The NO_x^-_{x}^{-} and CO_x^-_{x}^{-} ions were dominantly produced on the field lines arising from the needle tip apex region with the highest electric field strength, while the field lines emanating from the tip peripheral regions with lower field strength resulted in the formation of the HO^– ion.     

Field evaporation of a Hf-Mo alloy

The field evaporation of a Hf-Mo alloy (15 wt. % Hf) is investigated using a time-of-flight atom probe. A moderately heated tip detects an impurity of Hf and Mo oxides on the surface. Thermofield microprotrusions grown at T=1440–1850 K in an electric field (retarding to electrons) of intensity E=(3.2–5)×10⁷ V/cm are analyzed at room temperature and above. Zh. Tekh. Fiz. 68, 69–73 (March 1998)     

Time-resolved photoelectron spectroscopy on small tungsten cluster anions

We have studied the dynamics of photoexcited tungsten cluster anions W_n^-\mathrm{W}_{n}^{-} (n=3,4,…,14) by means of time-resolved two-photon photodetachment spectroscopy. At an excitation energy of h ν _pump=1.56 eV the photoinduced dynamics is mainly dominated by fast electronic relaxation processes. For the smallest clusters, i.e., W₃^-\mathrm{W}_{3}^{-}, W₄^-\mathrm{W}_{4}^{-}, and W₅^-\mathrm{W}_{5}^{-}, individual relaxation channels have been identified and resolved on a timescale well below 100 fs. The time constants for the decay of nascent and secondary electrons have been deduced from a Bloch model. Complete thermalization takes place for all clusters on a timescale of ∼1 ps.     

Energy dependence of the saturation scale and the charged multiplicity in pp and AA collisions

A natural framework to understand the energy dependence of bulk observables from lower energy experiments to the LHC is provided by the Color Glass Condensate, which leads to a “geometrical scaling” in terms of an energy-dependent saturation scale Q _s. The measured charged multiplicity, however, seems to grow faster ( ~ ?s^0.3{\sim}\sqrt{s}^{0.3}) in nucleus–nucleus collisions than it does for protons ( ~ ?s^0.2{\sim} \sqrt{s}^{0.2}), violating the expectation from geometric scaling. We argue that this difference between pp and AA collisions can be understood from the effect of DGLAP evolution on the value of the saturation scale, and is consistent with gluon saturation observations at HERA.     

Diffusion Coefficients of Several Rhodamine Derivatives as Determined by Pulsed Field Gradient–Nuclear Magnetic Resonance and Fluorescence Correlation Spectroscopy

Rhodamine derivatives are popular, photostable fluorophores that are used in a number of fluorescent based techniques, including fluorescence correlation spectroscopy (FCS). Indeed, in FCS, both rhodamine 6G (R6G) and rhodamine 110 (R110) are used as calibration standards to determine the dimensions of the instrument confocal volume. In spite of a requirement for precise values of the diffusion coefficients, literature values are scarce and vary over an order of magnitude. In this paper, the diffusion coefficients of four rhodamine fluorophores (rhodamine 6G (R6G), rhodamine B (RB), rhodamine 123 (R123), rhodamine 110 (R110)) were determined by pulsed field gradient nuclear magnetic resonance (PFG-NMR) spectrometry and then validated by comparison with fluorescence correlation spectroscopy. With the objective of validating the FCS calibration, diffusion coefficients of several dextrans and a polystyrene nanoparticle were also determined and compared with literature values or theoretical values that were based upon the Stoke–Einstein equation. The work presented here lead us to conclude that the diffusion coefficients for R6G and R110 have generally been underestimated in the literature. We propose revised values of 4.4 × 10⁻¹⁰ m² s⁻¹ for R110 and 4.0 × 10⁻¹⁰ m² s⁻¹ for R6G. Using the revised D value for R110 to calibrate the FCS instrument, diffusion coefficients have then been systematically determined for different conditions of pH, ionic strength and concentration. To correct for differences due to solvent effects (D₂O vs. H₂O), an isotopic correction factor, of 1.23, was determined from both FCS and from the solvent auto-diffusion coefficients obtained by NMR.     

Effect of low-level Ge additions on the superconducting transition in PbTe:Tl

A study is reported of the effect of low-level germanium additions (∼0.01–0.1 at. %) on the parameters of the superconducting transition, viz. the critical temperature T _c, the second critical magnetic field H _c2, and in PbTe doped with 2 at. % Tl, which are derived from the dependence of the electrical resistivity of a sample on temperature (0.4–4.2 K) and magnetic field (0–1.3 T). The discontinuity revealed by experimental data is related to the onset of a Ge-induced structural phase transition. Fiz. Tverd. Tela (St. Petersburg) 40, 1204–1205 (July 1998)     

Cross section and rate coefficient calculations for electron impact excitation, ionisation and dissociation of the X 1Σg+, c 3Πu, a 3Σ g+, e 3Σu+ and B′1Σu+ states of H2

The weighted total cross section (WTCS) theory has been applied to the electron-H₂ collision to obtain excitation, ionisation and dissociation cross section and rate coefficients of the X ¹S_g⁺^{1}\!\Sigma _{g}^{+}, c ³P_u^{3}\!\Pi _{u}, a ³S_g⁺^{3}\!\Sigma _{g}^{+}, e $^{3}\!\Sigma _{u}^{+}$^{3}\!\Sigma _{u}^{+} and B^{′ 1}S_u⁺^{1}\!\Sigma _{u}^{+} states. Calculation has been performed in the temperature range 1500 K–15000 K. Rate coefficients are calculated from WTCS assuming Maxwellian energy distribution functions for electrons and heavy particles. Thermal equilibrium results are presented and fitting parameters (a, b and c) are given for each reaction rate coefficient: k(θ) = a (θ^b) exp(-c/θ).     

Field desorption microscopy of the 〈111〉 trihedral angle of a reconstructed tungsten tip

The surface structure near the 〈111〉 trihedral angle, which forms in an electric-field-heated tungsten tip, is studied by field electron microscopy, continuous-mode field desorption microscopy, and high-temperature field evaporation microscopy. The shape and structure of the surface depend on the temperature, field, and time. The angle is formed by three {011} planes, with the (111) plane at its vertex being retained in the form of a triangle or a hexagon with randomly arranged atomic clusters. The edges between {011} faces represent long and narrow {112} planes having longitudinal or transverse steps. In the absence of field evaporation, the edges and angle sharpen, becoming monoatomic. Field evaporation from the angle or microprotrusions on the edges extends these edges and causes transverse steps to appear on them. The explanation of the changes in the shape and structure of the surface is based on considering the competition of surface diffusion, crystal growth in an electric field, and field evaporation.     

An ab initio molecular dynamics study of ionic conductivity in hexagonal lithium lanthanum titanate oxide La0.5Li0.5TiO3

To date, the fastest lithium ion-conducting solid electrolytes known are the perovskite-type ABO₃ oxide, with A = Li, La and B = Ti, lithium lanthanum titanate (LLTO) Li_3x La_{( 2 \mathord}

Theoretical studies on dielectronic recombination of neonlike gold and its effects on plasma ionization balance and radiation energy

The dielectronic recombination (DR) of neonlike gold ions is investigated employing the flexible atomic code based on the relativistic configuration interaction method, and its influence on the ionization balance and radiation energy in high-temperature plasma is also studied. The total resonance strength for LMM configuration complex is in a good agreement with the experimental measurement and other theoretical works. The DR rate coefficients are calculated and compared with the three-body recombination and radiative recombination rate coefficients. The DR process is the dominant recombination mechanism of Ne-like gold ions for plasma with temperature T_e≥6.5 keV and density n_e≤2×10²² cm^-3, which is close to the condition of X-ray conversion region in the inertial confinement fusion. Moreover, the DR satellite spectra of LMM, LMN and LMO resonances are simulated, and compared with the intensities of the corresponding resonance lines induced by the electron impact excitation. The intensity ratio of the satellite line 3D’ [(2p⁵_3/23d_3/23d_5/2)_J=5/2[(2p^{5}_{3/2}3d_{3/2}3d_{5/2})_{J=5/2}–(2p⁶3d_3/2) _J=3/2](2p^{6}3d_{3/2})_{ J=3/2}] and the resonance line 3D [(2p⁵_3/23d_5/2)_J=1[(2p^{5}_{3/2}3d_{5/2})_{J=1}–(2p⁶)_J=0](2p^{6})_{J=0}] is given, which can be applied for diagnostics of plasma temperature.     

Temperature dependence of magnetic properties and change of specific heat in perovskite ErCrO3 chromites

In this paper, the temperature dependence of magnetic properties and specific heat are systematically investigated for perovskite ErCrO₃ chromites. The results show that there exists a strong temperature dependence of magnetic ordering and phase coexistence in the region of low temperature. Specifically, ErCrO₃ possesses the long-range antiferromagnetic ordering and the appearance of weak ferromagnetism, occurring at T _N =133 K. In the range of higher temperature, above 133.0 K, the reciprocal of magnetic susceptibility χ ⁻¹ behaves linearly, indicating a typical Curie–Weiss behavior fitted. The effective magnetic moment μ _eff=10.57μ _B and asymptotic paramagnetic Curie temperature T _cw=−30 K, which suggests the predominance of antiferromagnetic interactions in ErCrO₃ chromites. Around T _SR≈22 K, ErCrO₃ undergoes a spin reorientation from \varGamma ₄(G_x,A_y,F_z;F^R_z)\varGamma _{4}(G_{x},A_{y},F_{z};F^{R}_{z}) to \varGamma ₁(A_x,G_y,C_z;C^R_z)\varGamma _{1}(A_{x},G_{y},C_{z};C^{R}_{z}) or Γ ₁(0). Also, the stability of the ferromagnetic Γ ₄ phase increases with increasing applied field. Furthermore, the ac susceptibilities exhibit frequency-independent anomalies near 133 K and the coexistence of the magnetic configuration \varGamma ₂(F_x,G_y,C_z;F^R_x,C^R_y)\varGamma _{2}(F_{x},G_{y},C_{z};F^{R}_{x},C^{R}_{y}) and Γ ₄. Combining the magnetic properties and the specific-heat measurements, this current magnetization can be interpreted from the interaction between C ^r3+–Cr³⁺, Cr³⁺–Er³⁺ and Er³⁺–Er³⁺.     

Plasma with two-negative ions and immobile dust particles: planar and non-planar ion-acoustic wave propagation

By using the hydrodynamic equations of positive and two negative ions, Boltzmann electron density distribution, and Poisson equation with immobile positive/negative dust particles, a cylindrical Korteweg-de Vries (CKdV) equation is derived for small but finite amplitude ion-acoustic waves. At the critical total negative ion concentration and/or the critical density rate of the second-negative ions, the pulses collapse at this limit as nonlinearity fails to balance dispersion. Then the CKdV equation is not appropriate to describe the system. Therefore, the modified CKdV (MCKdV) and extended CKdV (ECKdV) equations are derived at the critical plasma compositions and in the vicinity of the critical plasma compositions, respectively. The physical parameters of two plasma environments (e.g., Xe⁺–F^-–SF₆^-_{6}^{-} and Ar⁺–F^-–SF₆^-_{6}^{-} plasmas) are examined on the wave phase velocity and the nonlinear localized pulse profile. The latter should satisfy necessary condition to exist. The localized pulse of Ar⁺–F^-–SF₆^-_{6}^{-} plasma is much spiky than Xe⁺–F^-–SF₆^-_{6}^{-} plasma. Thus, the mass ratio of the negative-to-positive ions is focused upon and it emphasizes to play an important role on the pulse profile. Dependence of the geometrical divergence on the pulse profile is also investigated, which indicates that the localized pulse damps with time. The implications of our results agrees with the experimental observations.     

A method to study polydispersity of humic acid from fluorescence quenching by Cu<Superscript>2+</Superscript> ions

The spectral dependence of Stern–Volmer constants (K_SV^lK_{SV}^{\lambda} ) for fluorescence quenching by Cu²⁺ ions in a standard sample of humic acid (HA) (IHSS) with monochromatic excitation (λ_ex = 337.1 nm) conditions has been studied in the spectral range 400–600 nm. This is interpreted within a concept implying that HA macromolecules possess the property of polydispersity, which means that fluorophore-containing sites are different in terms of chemical nature and spatial accessibility. Modeling data show that the minimum number of spectral components required for the simulated spectral dependence of K_SV^lK_{SV}^{\lambda} to agree as closely as possible with that observed experimentally is three.     

Direct and indirect detection of dark matter in D6 flavor symmetric model

We study fermionic dark matter in a non-supersymmetric extension of the standard model with a family symmetry based on D₆ ×[^(Z)]₂×Z₂D_{6} \times\hat{Z}_{2}\times Z_{2}. In our model, the final state of the dark matter annihilation is determined to be e ⁺ e ⁻ by the flavor symmetry, which is consistent with the PAMELA result. At first, we show that our dark matter mass should be within the range of 230 GeV–750 GeV in the WMAP analysis combined with μ→eγ constraint. Moreover, we simultaneously explain the experiments of direct and indirect detection, by simply adding a gauge and D ₆ singlet real scalar field. In the direct detection experiments, we show that the lighter dark matter mass ≃230 GeV and the lighter standard model Higgs boson ≃115 GeV are in favor of the observed bounds reported by CDMS II and XENON100. In the indirect detection experiments, we explain the positron excess reported by PAMELA through the Breit–Wigner enhancement mechanism. We also show that our model is consistent with there being no antiproton excess, as suggested by PAMELA.     

Analysis of the <Emphasis Type="Italic">Y</Emphasis>(4140) and related molecular states with QCD sum rules

In this article, we assume that there exist scalar D^*[`(D)]<sup>*</sup>{D}^{\ast}{\bar {D}}^{\ast}, D<sub>s</sub><sup>*</sup>[`(D)]_s^*{D}_{s}^{\ast}{\bar{D}}_{s}^{\ast}, B^*[`(B)]<sup>*</sup>{B}^{\ast}{\bar {B}}^{\ast} and B<sub>s</sub><sup>*</sup>[`(B)]_s^*{B}_{s}^{\ast}{\bar{B}}_{s}^{\ast} molecular states, and study their masses using the QCD sum rules. The numerical results indicate that the masses are about (250–500) MeV above the corresponding D ^*–[`(D)]<sup>*</sup>{\bar{D}}^{\ast}, D <sub>s</sub> <sup>*</sup>–[`(D)]_s^*{\bar {D}}_{s}^{\ast}, B ^*–[`(B)]<sup>*</sup>{\bar{B}}^{\ast} and B <sub>s</sub> <sup>*</sup>–[`(B)]_s^*{\bar {B}}_{s}^{\ast} thresholds, the Y(4140) is unlikely a scalar D_s^*[`(D)]<sub>s</sub><sup>*</sup>{D}_{s}^{\ast}{\bar{D}}_{s}^{\ast} molecular state. The scalar D<sup>*</sup>[`(D)]^*D^{\ast}{\bar{D}}^{\ast}, D_s^*[`(D)]<sub>s</sub><sup>*</sup>D_{s}^{\ast}{\bar{D}}_{s}^{\ast}, B<sup>*</sup>[`(B)]^*B^{\ast}{\bar{B}}^{\ast} and B_s^*[`(B)]<sub>s</sub><sup>*</sup>B_{s}^{\ast}{\bar{B}}_{s}^{\ast} molecular states maybe not exist, while the scalar D￠<sup>*</sup>[`(D)]^￠*{D'}^{\ast}{\bar{D}}^{\prime\ast}, D_s^￠*[`(D)]<sub>s</sub><sup>￠*</sup>{D}_{s}^{\prime\ast}{\bar{D}}_{s}^{\prime\ast}, B<sup>￠*</sup>[`(B)]^￠*{B}^{\prime\ast}{\bar{B}}^{\prime\ast} and B_s^￠*[`(B)]_s^￠*{B}_{s}^{\prime\ast}{\bar{B}}_{s}^{\prime\ast} molecular states maybe exist.     

The direct precipitation of rhabdophane (REEPO<Subscript>4</Subscript>·<Emphasis Type="Italic">n</Emphasis>H<Subscript>2</Subscript>O) nano-rods from acidic aqueous solutions at 5–100 °C

The precipitation of lanthanum and neodymium phosphate phases from supersaturated aqueous solutions at pH ~1.9 was studied at 5, 25, 50, and 100 °C in batch reactors for up to 168 h. Crystalline La and Nd–rhabdophane phases precipitated immediately upon mixing of the initial aqueous La or Nd and PO₄ solutions. Changes in aqueous PO₄ and Rare Earth Element (REE) concentrations during the experiments were determined by ICP-MS and UV–Vis spectrophotometry, while the resulting solids were characterized via powder XRD, SEM, TEM, and FTIR. All precipitated crystals exhibited a nano-rod morphology and their initial size depended on temperature and REE identity. At 5 °C and immediately after mixing the La and Nd–rhabdophane crystals averaged ~44 and 40 nm in length, respectively, while at 100 °C lengths were ~105 and 94 nm. After 168 h of reaction, the average length of the La and Nd rhabdophanes increased by 23 and 53% at 5 °C and 11 and 59% at 100 °C, respectively. The initial reactive solutions in all experiments had activity quotients for rhabdophane precipitation: \textREE ³⁺ + \textPO₄^{3 -} + n\textH₂ \textO = \textREEPO₄ ·  n\textH₂ \textO {\text{REE}}^{ 3+ } + {\text{PO}}_{4}^{3 - } + n{\text{H}}_{2} {\text{O}} = {\text{REEPO}}_{4} \cdot\;n{\text{H}}_{2} {\text{O}} of ~10^−20.5. This activity quotient decreased with time, consistent with rhabdophane precipitation. The rapid equilibration of rhabdophane supersaturated solutions and the progressive rhabdophane crystal growth observed suggests that the REE concentrations of many natural waters may be buffered by rhabdophane precipitation. In addition, this data can be used to guide crystallization reactions in industrial processes where monodisperse and crystalline La or Nd rhabdophane materials are the target.     

<Superscript>4</Superscript>He<Superscript>3</Superscript>H<Superscript>2</Superscript>H three-body model of the <Superscript>9</Superscript>Be nucleus

Within the framework of the single-channel approximation, an {αtd} model of the ⁹ Be nucleus is presented. A comparative analysis of the t ⁶ Li wave functions describing relative motion of bound states constructed in {ααn} and {αtd} cluster representations is carried out on the example of calculations of the ⁹ Be(γ,t₀)⁶ Li process characteristics. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 85–89, January, 2008.     

Oxygen adsorption on the tungsten (110) plane. Electron impact and thermal desorption at high temperatures

When a layer of oxygen on the (110) plane of tungsten at coverages O/W≦0.5 is heated from 100 K, O⁺ evolution under electron impact becomes almost negligible at 600 K. On further heating, however, a slow, temperature-dependent evolution of O⁺ current is observed atT≳1500 K. For O/W>0.3 there is also desorption under massive bombardment. Once an equilibrium value of O⁺ current has been established, there is rapid adjustment to the appropriate equilibrium value when the temperature changes in the range 1500–1700 K. On cooling toT<1000 K, O⁺ decreases rapidly; on reheating toT>1500 K, O⁺ increases slowly again. Above 1700 K there is thermal desorption which is also reflected in the O⁺ signal. These facts indicate that there is a slow activated evolution of an electron sensitive state above 1500 K, from a reconstructed state formed by heating the low temperature layer toT≧1000 K. The latter state seems to be reformed on cooling below 1500 K.     

Preequilibrium thermofield microprotrusions as effective field point sources of electrons and ions

Field emission methods are employed for studying the conditions of formation, crystallographic localization, and emissive properties of preequilibrium thermofield microprotrusions for a number of refractory metals. Individual preequilibrium microprotrusions can be easily obtained using a W emitter of the ordinary 〈110〉 orientation; however, the number of such protrusions on the surface changes with time in the course of ionic emission, as well as their emission parameters (the parameters and the number of microprotrusions do not change in the case of electron emission). Trihedral angles of the rearranged tip, which are formed in the {111} regions, exhibit higher stability to ionic emission. A single trihedral angle stably emitting ions and located on the geometrical axis of the emitter can easily be obtained with the help of a W emitter with the 〈111〉 orientation. Two stable preequilibrium microprotrusions arranged symmetrically about the axis of the emitter in the {111} regions can be obtained using a Ta emitter of the conventional 〈110〉 orientation. Such microprotrusions virtually do not change the emission parameters during long-term extraction of ionic current.     

From Weak to Strong Coupling in ABJM Theory

The partition function of N=6{\mathcal{N}=6} supersymmetric Chern–Simons-matter theory (known as ABJM theory) on \mathbbS³{\mathbb{S}^3} , as well as certain Wilson loop observables, are captured by a zero dimensional super-matrix model. This super–matrix model is closely related to a matrix model describing topological Chern–Simons theory on a lens space. We explore further these recent observations and extract more exact results in ABJM theory from the matrix model. In particular we calculate the planar free energy, which matches at strong coupling the classical IIA supergravity action on AdS₄×\mathbbC\mathbbP³{{\rm AdS}_4\times\mathbb{C}\mathbb{P}^3} and gives the correct N ^3/2 scaling for the number of degrees of freedom of the M2 brane theory. Furthermore we find contributions coming from world-sheet instanton corrections in \mathbbC\mathbbP³{\mathbb{C}\mathbb{P}^3} . We also calculate non-planar corrections, both to the free energy and to the Wilson loop expectation values. This matrix model appears also in the study of topological strings on a toric Calabi–Yau manifold, and an intriguing connection arises between the space of couplings of the planar ABJM theory and the moduli space of this Calabi–Yau. In particular it suggests that, in addition to the usual perturbative and strong coupling (AdS) expansions, a third natural expansion locus is the line where one of the two ’t Hooft couplings vanishes and the other is finite. This is the conifold locus of the Calabi–Yau, and leads to an expansion around topological Chern–Simons theory. We present some explicit results for the partition function and Wilson loop observables around this locus.