Scaling and universality in models of step bunching: the “C<Superscript>+</Superscript>–C<Superscript>-</Superscript>” model

We recently introduced a novel model of step flow crystal growth – the so-called “C⁺–C^-” model [B. Ranguelov et al., C.R. Acad. Bulgare Sci. 60, 389 (2007)]. In this paper we aim to develop a complete picture of the model’s behaviour in the framework of the notion of universality classes. The basic assumption of the model is that the reference (“equilibrium”) densities used to compute the supersaturation might be different on either side of a step, so C_L/C_R ≠ 1 (L/R stands for left/right in a step train descending from left to right), and that this will eventually cause destabilization of the regular step train. Linear stability analysis considering perturbation of the whole step train shows that the vicinal is always unstable when the condition C_L /C_R >1 is fulfilled. Numerical integration of the equations of step motion combined with an original monitoring scheme(s) results in obtaining the exact size- and time- scaling of the step bunches in the limit of long times (including the numerical prefactors). Over a broad range of parameters the surface morphology is characterized by the appearance of the minimal interstep distance at the beginning of the bunches (at the trailing edge of the bunch) and may be described by a single universality class, different from those already generated by continuum theories [A. Pimpinelli et al., Phys. Rev. Lett. 88, 206103 (2002), J. Krug et al., Phys. Rev. B 71, 045412 (2005)]. In particular, the scaling of the minimal interstep distance l_min in the new universality class is shown to be l_min = (S_n /N)^1/(n+1), where N is the number of steps in the bunch, n is the exponent in the step-step repulsion law U ~ 1/d₀ ⁿ for two steps placed a distance d₀ apart and S_n is a combination of the model parameters. It is also shown that N scales with time with universal exponent 1/2 independent of n. For the regime of slow diffusion it is obtained for the first time that the time scaling depends only on the destabilization parameter C_L/C_R. The bunching outside the parameter region where the above scaling exists cannot be assigned to a specific universality class and thus should be considered non-universal.     

Interaction of Cu cluster anions (Cu<Superscript>-</Superscript><Subscript>n</Subscript>, n = 8–11) with oxygen

The reaction of oxygen with Cu cluster anions consisting of 6–11 atoms was studied by means of Time-of-Flight mass (TOF) spectroscopy and Ultraviolet Photoelectron Spectroscopy (UPS). Using molecular oxygen, we found that a Cu^-_n cluster (n=6-11) can react only with one single oxygen molecule, which adsorbs molecularly, implying that the clusters studied here are less reactive towards oxygen chemisorption compared to the smaller clusters (n<5). This result indicates that chemical properties can alter significantly with increasing cluster size. Depending on the cluster source conditions, different cluster structures and reactivity patterns were found. These results are used to qualitatively describe the chemisorption energetics of oxygen on Cu cluster anions.     

Λ<Subscript>b</Subscript>→Λℓ<Superscript>+</Superscript>ℓ<Superscript>-</Superscript> decay in universal extra dimensions

We study the exclusive Λ_b→Λℓ⁺ℓ^- decay in the Appelquist, Chang, Dobrescu model with a single universal extra dimension. We investigate the sensitivity of the branching ratio, lepton polarization and forward–backward asymmetry to the compactification parameter 1/R. We obtain the result that the branching ratio for the Λ_b→Λℓ⁺ℓ^- (ℓ=μ,τ) decay changes about 25% compared to the SM value when 1/R=250 GeV, and the zero position of the forward–backward asymmetry is shifted to the left compared to the SM result. Therefore, measurement of the branching ratio of Λ_b→Λℓ⁺ℓ^- decay and determination of the zero position of are very useful in looking for new physics in the framework of the UED models. PACS 12.60.-i; 13.30.-a; 14.20.Mr     

Potential energy of <Superscript>∞</Superscript>H<Stack><Subscript>2</Subscript><Superscript>-</Superscript></Stack>(<Superscript>2</Superscript>∑<Stack><Subscript>u</Subscript><Superscript>+</Superscript></Stack> in the bound-state region

An accurate calculation of the lowest negative electronic state of H ₂ ^- (fixed nuclei) is reported using the CCSD(T) method and doubly augmented cc-pv5z basis set. Comparison has been made with the reference data by Senekowitsch et al. [Chem. Phys. Lett. 111 (1984) 211]. Owing to larger size of the basisset and inclusion of triple excitations, no vertical shift in this work is necessary to reproduce the asymptotics of H + H ^-. In addition, the effect of basis-set truncation is estimated, based on the complete-basis-set extrapolation method. The contribution of correlated electron-proton motion to the electron-energy curve for H₂ ^– dynamics is pointed out.Dedicated to Prof. Jií Horáek on the occasion of his 60th birthday.     

Analysis of the vector form factors f<Superscript>+</Superscript><Subscript>Kπ</Subscript>(Q<Superscript>2</Superscript>) and f<Superscript>-</Superscript><Subscript>Kπ</Subscript>(Q<Superscript>2</Superscript>) with light-cone QCD sum rules

In this article, we calculate the vector form factors f⁺ _Kπ(Q²) and f^- _Kπ(Q²) within the framework of the light-cone QCD sum rule approach. The numerical values of f⁺ _Kπ(Q²) are compatible with existing theoretical calculations, and the central value of f⁺ _Kπ(0) (f⁺ _Kπ(0)=0.97) is in excellent agreement with the values from chiral perturbation theory and lattice QCD. The values of |f^- _Kπ(0)| are very large compared to the theoretical calculations and experimental data, and they cannot give any reliable prediction. At large momentum transfer with Q² > 5 GeV², the form factors f⁺ _Kπ(Q²) and |f^- _Kπ(Q²)| can either show the asymptotic behavior of or decrease more quickly than ; more experimental data are needed to select the ideal sum rules. PACS 12.38.Lg; 12.38.Bx; 12.15.Hh     

Stereodynamics of the reaction He+H<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack> → HeH<Superscript>+</Superscript> + H: a theoretical study

Quasiclassical trajectory method for the title reaction He +H₂⁺ → HeH⁺ + H was carried out on the potential energy surface which was revised by Aquilanti et al. [Chem. Phys. Lett. 469, 26 (2009)]. The initial vibrational quantum number of reactant was set as v=1, v=2 and v=3. Stereodynamics information of the reaction was obtained, such as the distributions of product angular momentum P(θ _r ), P(ϕ _r ),p(ϕ _r , θ _r ) and the two commonly used polarization-dependent differential cross sections (PDDCSs) (2π/σ)(dσ ₀₀/dω _t ) and (2π/σ)(dσ ₂₀/dω _t ), to get the alignment and orientation of product molecules. The results show that the influence of both the collision energy and vibrational quantum number (v) to the reaction are highly sensitive.     

Spectroscopic characteristics of anionic centers in α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> crystals bombarded by Cu<Superscript>+</Superscript> and Ti<Superscript>+</Superscript> ions

We have studied the effect of bombardment by Cu⁺ and Ti⁺ ions with energy 30 keV on the optical absorption and luminescence of F centers in oxygen-deficient aluminum oxide. We have shown that in the induced optical absorption spectra there are six components of gaussian shape, which can be assigned to absorption bands of F⁺, F², and F₂⁺ centers. We have established that bombardment of the samples by ion beams has a weak effect on the thermoluminescence parameters in the 3.0 eV and 2.4 eV bands, while in the 3.8 eV luminescence band for F⁺ centers, the thermoluminescent response increases considerably. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 3, pp. 422–424, May–June, 2008.     

Charge transfer in energetic Li<Superscript>2+</Superscript>–H and He<Superscript>+</Superscript>–He<Superscript>+</Superscript> collisions

The total cross sections for charge transfer in Li²⁺-H and He⁺-He⁺ collisions have been calculated, using the four body first Born approximation with correct boundary conditions (CB1-4B) and four body continuum distorted wave method (CDW-4B) in the energy range 10–5000 keV/amu. The role of dynamic electron correlations is examined as a function of the impact energy. The present results call for additional experimental data at higher impact energies than presently available.     

<Superscript>10</Superscript>B–<Superscript>11</Superscript>B isotope substitution and superconductivity in ZrB<Subscript>12</Subscript>

The specific heat of the ZrB₁₂ compound in the normal and superconducting states (T _C ≈ 6 K) has been studied in the 1.9–7 K temperature range for high-quality single crystals with different relative contents of boron isotopes. For Zr¹⁰B₁₂, Zr^natB₁₂, and Zr¹¹B₁₂ dodecaborides, the electron density of states and the electronphonon coupling constant, λ_e-ph ∼ 0.4, are found. The dependence of the thermodynamic and upper critical fields, as well as of the Ginzburg-Landau parameter (κ = 0.8–1.14) on temperature and isotope composition is determined. The results suggest the existence of the magnetic field induced phase transition at T* = 4–5 K, which is not related to the transition from type-I to type-II superconductivity. The possibilities of the existence of two-gap superconductivity and a structural phase transition at T* in zirconium dodecaboride are discussed.     

Emission spectroscopy of the A<Superscript>1</Superscript>Π–X<Superscript>1</Superscript>Σ<Superscript>+</Superscript> system of AlH

The high-resolution emission spectrum of the A¹ Π–X¹Σ⁺ transition of AlH was observed in the 18 000–25 000 cm^-1 spectral region using a conventional spectroscopic technique. The AlH molecules were excited in an Al hollow-cathode lamp filled with a mixture of Ne carried gas and a trace amount of NH₃. The emission from the discharge was observed with a plane grating spectrograph and recorded by a photomultiplier tube. In total 163 transition wave numbers belonging to six bands (0-0,1 and 1-0,1,2,3) were precisely measured and rotationally analysed. In the final fit the present data have been combined with available high-resolution measurements of the vibration-rotation bands by White et al. [J. Chem. Phys. 99, 8371 (1993)]. This procedure enabled extracting molecular constants for the A¹ Π and X¹ Σ⁺ states of AlH. A very slight local perturbation has been discovered in the v=1 vibration level of the A¹ Π state at J=5. This was probably caused by the interaction with the a³Π state.     

Multi electron capture processes in slow collisions between X<Superscript>7+</Superscript> (X = N,O and Ne) ions with C<Subscript>60</Subscript>

Electron capture processes in collision between slow X⁷⁺ (X = N, O and Ne) ions and C₆₀ fullerene have been investigated using coincident measurements of the number n of ejected electrons, the mass and charge of the multicharged C₆₀ ^r+ recoil ions and their fragments C_m ⁱ⁺ and the final charge state of the outgoing projectiles X^(q-s)+ ( ). The collision velocity is about 0.4 a.u. The partial cross-sections σ_r ^s , corresponding to r electrons transferred to the projectile with only s electrons stabilized, have been measured. Cross-sections for collisions “inside” and those “outside” the C₆₀ cage have been separated by analyzing the kinetic energy of the outgoing projectile. The mean final charge state for frontal collisions has been measured to 3.1, 2.6 and 2.5 for N⁷⁺, O⁷⁺ and Ne⁷⁺ respectively. These results show the importance of the core effect on the stabilisation processes of captured electrons.     

(EC + β<Superscript>+</Superscript>) decays of the 11/2<Superscript>-</Superscript> isomer and 1/2<Superscript>+</Superscript> ground state of <Superscript>143</Superscript>Dy

The 1/2⁺ ground state and a 11/2^- isomer of very neutron-deficient isotope ¹⁴³Dy were produced by irradiation of an enriched target of ¹⁰⁶Cd with ⁴⁰Ca and studied by using a helium-jet fast tape-transport system in combination with proton-γ, X-γ and γ-γ coincidence measurements. A simple ( EC + β⁺) decay scheme of ^143mDy with a half-life of 3.0(3) s and a tentative ( EC + β⁺) decay scheme of ^143gDy with a half-life of 5.6(10) s are proposed. As a by-product, the 347- and 545-keV γ transitions in ¹³⁸Sm following the β-delayed proton emission of ¹³⁹Gd decay and the 323-keV γ transition in ¹³⁹Eu following the β-delayed proton emission of ¹⁴⁰Tb decay could be observed for the first time. Received: 20 August 2002 / Accepted: 28 October 2002 / Published online: 11 February 2003 RID="a" ID="a"e-mail: xsw@ns.lzb.ac.cn Communicated by D. Schwalm     

Electrochemical immune bioassay for the antigen–antibody interaction based on [Fe(CN)<Subscript>6</Subscript>]<Superscript>4-/3-</Superscript> and [AuCl<Subscript>4</Subscript>]<Superscript>-</Superscript> ions-derivated biomimetic interface

A simple and sensitive electrochemical immune bioassay for the detection of hepatitis B surface antigen (HBsAg), as a model, was developed based on [Fe(CN)₆]^4-/3- and [AuCl₄]^- ions-derivated biomimetic interface in this study. A layer of [Fe(CN)₆]^4-/3- film (i.e., Prussian blue, PB) was initially electrodeposited onto a glassy carbon electrode, and then [AuCl₄]^- ions were reduced under the potentiostat to form gold nanoparticles on the PB film. Finally, hepatitis B surface antibody (HBsAb) was adsorbed onto the nanogold surface. The performance and factors influencing the immunosensor were assessed and optimized. The proposed immunosensor exhibits a specific response to HBsAg in the range of 2.13–314.3 ng∙ml^-1 with a detection limit of 0.42 ng∙ml^-1. In addition, the developed immunosensor shows high sensitivity, good reproducibility, and long-term stability. Importantly, the ions-derivated biomimetic interface could be further extended for the immobilization of other proteins and biocompound.     

Mechanism of the oxidation and combustion of normal paraffin hydrocarbons: Transition from C<Subscript>1</Subscript>–C<Subscript>6</Subscript> to C<Subscript>7</Subscript>H<Subscript>16</Subscript>

A previously proposed algorithm for constructing an optimal mechanism of the high- and low-temperature oxidation and combustion of normal paraffin hydrocarbons was used, which includes the major processes that determine the rate of reaction and the formation of the main intermediate and final products. The mechanism has the status of a nonempirical detailed mechanism, since all the constituent elementary reactions have a kinetic substantiation. The mechanism has two specific features: it included no reactions of so-called double addition of oxygen and no isomeric compounds and derivatives thereof as intermediate species. Realization of this algorithm leads to fairly compact models, a circumstance important for studies of chemical processes involving paraffin hydrocarbons C _n with large n. Previously, based on this algorithm, compact mechanisms of oxidation and combustion of propane, n-butane, n-pentane, and n-hexane were constructed. In this paper, we develop a nonempirical detailed mechanism of oxidation and combustion of n-heptane. The most important feature of the new mechanism is its ability to predict the staging of the process in the form of cool and blue flames at low autoignition temperatures. A comparison of the simulation results with the available experimental data is conducted.     

Mechanisms of the oxidation and combustion of normal alkanes: Transition from C<Subscript>1</Subscript>–C<Subscript>5</Subscript> to C<Subscript>6</Subscript>H<Subscript>14</Subscript>

A previously proposed algorithm of constructing optimal mechanisms of the low- and high-temperature oxidation and combustion of normal alkanes was applied to n-hexane. The proposed mechanism can be considered a nonempirical detailed mechanism, since all the constituent reactions have a solid kinetic substantiation. The mechanism features two main peculiarities: it contains no reactions of double oxygen addition (first to the peroxide radical and then to its isomerized form) and (2) involves no isomeric compounds and derivatives thereof. Application of the algorithm to n-hexane made it possible to create a new compact kinetic mechanism. The mechanism was demonstrated to correctly describe the multistage character of low-temperature self-ignition: the appearance of a cool and then a blue flame.