Electronic excitation energies in TiO<Subscript>2</Subscript> in the fluorite phase

The ab initio pseudopotential method within the generalized gradient approximation (GGA) and quasiparticle approximation has been used to investigate the electronic properties of titanium dioxide in the rutile, anatase, and fluorite structures, respectively. Here we present the GW approximation for the electronic self-energy, which allows to calculate excited-state properties, especially electronic band structures. For this calculation, good agreement with the experimental results for the minimum band gaps in rutile and anatase phase is obtained. In the fluorite phase we predict that titanium dioxide will be an indirect (Γ to X) wide band-gap semiconductor (2.367 or 2.369 eV) and the properties remain to be confirmed by experiment.     

Thermally activated dewetting of organic thin films: the case of pentacene on SiO<Subscript>2</Subscript> and gold

The morphology of pentacene organic thin films deposited on SiO₂ and Au(111) surfaces using organic molecular beam deposition (OMBD) has been characterized by a multi-technique approach. Among the techniques applied were X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), scanning electron microscopy (SEM) and thermal desorption spectroscopy (TDS). Our rather detailed studies reveal that on both substrates the growth is strongly influenced by dewetting and islanding phenomena, yielding very rough surfaces. Surprisingly, substantial changes in the morphology were observed also after deposition on room-temperature samples on a time scale of several hours. The rather extensive set of in situ XPS data was analyzed in the framework of a simple model, which allows us to derive rather detailed information on the roughness parameters.     

Comment on the recent COMPASS data on the spin structure function <Emphasis Type="Italic">g</Emphasis><Subscript>1</Subscript>

We examine the recent COMPASS data on the spin structure function g ₁ singlet. We show that it is rather difficult to use the data in the present form in order to draw conclusions on the initial parton densities. However, our tentative estimate is that the data better agree with positive than with negative initial gluon densities.     

Two Parton Shower Background for Associate <Emphasis Type="Italic">W</Emphasis> Higgs Production

The estimates of the background for the associate W Higgs production, which stems from the two parton shower production, leads to a background which is of the order of the signal for the non-perturbative contribution. In the perturbative approach the background turns out to be small. This background does not depend on the rapidity difference between the W and the pair, while the signal peaks when the rapidity difference is zero. Detailed calculations for the enhanced diagrams’ contribution to this process are presented, and it is shown that the overlapping singularities, being important theoretically, lead to a small contribution for the LHC range of energies.     

Continuous-wave intracavity Raman laser at 1179.5 nm with SrWO<Subscript>4</Subscript> Raman crystal in diode-end-pumped Nd:YVO<Subscript>4</Subscript> laser

We report a continuous-wave intracavity Raman laser at 1179.5 nm with a SrWO₄ Raman crystal in a diode-end-pumped Nd:YVO₄ laser. The highest output power of 2.23 W is obtained at the laser diode power of 21.2 W corresponding to the slope efficiency of 17.3% and a diode-to-stokes optical conversion efficiency of 10.5%. The dependence of the Raman laser performance on the pump polarization is also studied. The measured Raman thresholds are about 9.3 and 8.3 W in the diode pump laser power for the a- and b-polarized configurations, respectively. The Raman gain coefficients of the c-cut SrWO₄ crystal for a- and b-polarized pumps are estimated to be about 4.9 and 4.7 cm/GW, respectively.     

A quantum long time energy red shift: a contribution to varying <Emphasis Type="Italic">α</Emphasis> theories

By analyzing the survival probability amplitude of an unstable state we show that the energy corrections to this state in the long (t→∞) and relatively short (lifetime of the state) time regions are different. It is shown that in the considered model the above corrections decrease to zero as t→∞. It is hypothesized that this property could be detected by analyzing the spectra of distant astrophysical objects. The above property of unstable states may influence the measured values of possible deviations of the fine structure constant α as well as other astrophysical and cosmological parameters.     

Electron diffraction study of various lattice defects in a Bi<Subscript>4</Subscript>Ge<Subscript>3</Subscript>O<Subscript>12</Subscript> crystal

Lattice defects in a scintillation detector made of Bi₄Ge₃O₁₂ (BGO) could severely impact detector efficiency via non-radiative transfer of electron excitation, thus making thorough investigations of these defects highly important. Here we present a combined experimental and theoretical study of two- and three-dimensional defects in a Czochralski-grown BGO crystal. Upon examination by transmission electron microscopy the selected-area electron diffraction (SAED) patterns in two neighboring parts of the specimen reveal different kinds of two- and three-dimensional defects. Three sub-grains misoriented at 2.47° with reference to each other and probable presence of stacking faults lying in {011} planes were observed in the first examined local area. The SAED image taken from an area in the close neighborhood is much more complicated and is explained in terms of the superposition of reflections from: (i) a partially textured GeO₂ second-phase inclusion; (ii) the basic lattice of BGO and (iii) a superlattice-like structure based on the BGO lattice. The atomic structure of such a superlattice-like structure was theoretically modeled and the corresponding simulated SAED patterns were found to be in good agreement with the experimentally observed one.     

Necessary and Sufficient Condition for Greenberger-Horne-Zeilinger Diagonal States to Be Full <Emphasis Type="Italic">N</Emphasis>-partite Entangled

We show that any N-qubit state which is diagonal in the Greenberger-Horne-Zeilinger basis is full N-qubit entangled state if and only if no partial transpose of the multiqubit state is positive with respect to any partition.     

Synthesis of SmAlO<Subscript>3</Subscript> nanocrystalline powders by polymeric precursor method

SmAlO₃ nanocrystalline powders were successfully synthesized by the polymeric precursor method using ethylenediaminetetraacetic acid as a chelating agent. The precursor and the derived powders were characterized by thermogravimetry analysis (TG) and differential scanning calorimetry analysis (DSC), infrared spectroscopy (IR), X-ray diffractometry (XRD) and transmission electron microscopy (TEM). The results showed that pure SmAlO₃ powder with orthorhombic perovskite structure could be synthesized at 800°C for 2 h without formation of any intermediate phase. The average particle size of the powder synthesized at 900°C was as low as 28 nm. Subsequently, the bulk SmAlO₃ ceramics were prepared at various sintering temperatures using the synthesized powders calcined at 900°C for 2 h as starting materials. The sintering experiments indicated that the sample sintered at 1550°C for 2 h exhibited the highest relative density of 97.2% and possessed the best microwave dielectric properties of ε _r=20.94, Q×f=78600 GHz and τ _f=−71.8 ppm/°C.     

Another tetraquark structure in the <Emphasis Type="Italic">π</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">χ</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis>1</Subscript> invariant mass distribution

In this article, we assume that there exists a scalar hidden charm tetraquark state in the π ⁺ χ _c1 invariant mass distribution, and we study its mass using the QCD sum rules. The numerical result M _Z =(4.36±0.18) GeV is consistent with the mass of the Z(4250). The Z(4250) may be a tetraquark state, but other possibilities, such as a hadro-charmonium resonance and a molecular state, are not excluded.     

<Emphasis Type="Italic">PT</Emphasis> symmetry and Hermitian Hamiltonian in the local supercritical pomeron model

The local reggeon field theory is studied perturbatively taking advantage of the PT symmetry in the Hamiltonian formulation. In the lowest non-trivial order we show that the pomeron interactions renormalize the slope. In the same order we find a non-local pair potential acting between pomerons, which has a singular structure. However, the analysis of the scattering operator shows that at small coupling constant bound states do not appear so that the two-particle spectrum is not changed.     

<Emphasis Type="Italic">J</Emphasis>/<Emphasis Type="Italic">ψ</Emphasis> suppression and <Emphasis Type="Italic">p</Emphasis><Subscript><Emphasis Type="Italic">T</Emphasis></Subscript> spectra in RHIC and LHC energy collisions

In a hydrodynamic model, we have studied J/ψ production in Au+Au/Cu+Cu collisions at RHIC energy, GeV. At the initial time, J/ψ’s are randomly distributed in the fluid. As the fluid evolves in time, the free streaming J/ψ’s are dissolved if the local fluid temperature exceeds a threshold temperature T _J/ψ . Sequential melting of charmonium states (χ _c , ψ ^′ and J/ψ), with melting temperatures , T _J/ψ ≈2T _c and feed-down fraction F≈0.3, explains the PHENIX data on the centrality dependence of J/ψ suppression in Au+Au collisions. J/ψ p _T spectra and the nuclear modification factor in Au+Au collisions are also well explained in the model. The model however overpredicts the centrality dependence of J/ψ suppression in Cu+Cu collisions by 20–30%. The J/ψ p _T spectra are underpredicted by 20–30%. The model predicts that in central Pb+Pb collisions at LHC energy,  GeV, J/ψ’s are suppressed by a factor of ∼10. The model predicted a J/ψ p _T distribution in Pb+Pb collisions at LHC is similar to that in Au+Au collisions at RHIC.     

Tests of analytical hadronisation models using event shape moments in e<Superscript>+</Superscript>e<Superscript>−</Superscript> annihilation

Predictions of analytical models for hadronisation, namely the dispersive model, the shape function and the single dressed gluon approximation, are compared with moments of hadronic event shape distributions measured in e⁺e⁻ annihilation at centre-of-mass energies between 14 and 209 GeV. In contrast to Monte Carlo models for hadronisation, analytical models require to adjust only two universal parameters, the strong coupling and a second quantity parametrising non-perturbative corrections. The extracted values of α _S are consistent with the world average and competitive with previous measurements. The variance of event shape distributions is compared with predictions given by some of these models. Limitations of the models, probably due to unknown higher order corrections, are demonstrated and discussed.     

Angular distributions in the decays of the triplet <Emphasis Type="Italic">D</Emphasis><Subscript>2</Subscript> state of charmonium directly produced in polarized proton–antiproton collisions

Using the helicity formalism, we calculate the combined angular distribution function of the two gamma photons and the electron in the cascade process \({\bar{p}p}\to{}^{3}{D}_{2}\to\chi_{J}+\gamma_{1}\to(\psi +\gamma_{2})+\gamma_{1}\to({e}^{+}+{e}^{-})+\gamma_{1}+\gamma_{2}\) (J=0,1,2), when \({\bar{p}}\) and p are arbitrarily polarized. We also present the partially integrated angular distribution functions in six different cases. Our results show that by measuring the two-particle angular distribution of γ ₁ and γ ₂ and that of γ ₁ and e ^?, one can determine the relative magnitudes as well as the relative phases of all the helicity amplitudes in the two radiative decay processes ³ D ₂→χ _J +γ ₁ and χ _J →ψ+γ ₂.     

<Emphasis Type="Italic">Z</Emphasis><Superscript>′</Superscript> boson signal at Fermilab-Tevatron and CERN-LHC in a 331 model

We analyse the possibilities to detect a new Z ^′ boson in di-electron events at Tevatron and LHC in the framework of the 331 model with right-handed neutrinos. We also study other fermions and Higgs events as final state at LHC. Using collision data collected by the CDF II detector at Fermilab Tevatron, we find that the 331 Z ^′ boson is excluded with masses below 920 GeV. For an integrated luminosity of 100 fb⁻¹ at LHC, and considering a central value GeV, we obtain the invariant-mass distribution in the process pp→Z ^′→e ⁺ e ⁻, where a huge peak, corresponding to 800 signal events/(20 GeV), is found above the SM background. The number of di-electron events vary from 50000 to 2400 in the mass range of –2000 GeV. We also obtain branching ratios and cross sections in other fermion and Higgs channels at LHC, where a heavy top quark T exhibits the biggest ratio with m _T =300 GeV.     

Protons flow in Pb+Pb collisions at 40 <Emphasis Type="Italic">A</Emphasis> GeV energy

For Pb+Pb collisions at 40 A GeV energy, we calculate the side-ward and elliptic differential flow of protons in the microscopic relativistic transport simulation model. We compare our results with the recent data from the NA49 Collaboration as a function of transverse momenta, rapidity and centrality. We find that the side-ward and elliptic flow agree reasonably well with the experimental data with and without momentum-dependent potentials in the simulation model.     

Search for resonant absorption of solar axions emitted in M1 transition in <Superscript>57</Superscript>Fe nuclei

A search for resonant absorption of 14.4 keV solar axions by a ⁵⁷Fe target was performed. The Si(Li) detector placed inside the low-background setup was used to detect the γ-quanta appearing in the deexcitation of the 14.4 keV nuclear level: A+⁵⁷Fe→⁵⁷Fe^*→⁵⁷Fe+γ. The new upper limit for the hadronic axion mass has been obtained of m _A ≤159 eV (95% c.l.) (S=0.5, z=0.56).     

Characterization of 1.06 μm optical vortex laser based on a side-pumped Nd:GdVO<Subscript>4</Subscript> bounce oscillator

We directly produced for the first time a high-power 1.06 μm vortex mode from a diode-pumped Nd:GdVO₄ bounce amplifier. A maximum output of 17.8 W was achieved for a pump power of 55 W. The corresponding optical efficiency from the diode to the output was above 30%.     

Growth and characterization of nanostructured anatase phase TiO<Subscript>2</Subscript> thin films prepared by DC reactive unbalanced magnetron sputtering

Titanium dioxide thin films were deposited on three different unheated substrates by unbalanced magnetron sputtering. The effects of the sputtering current and deposition time on the crystallization of TiO₂ thin films were studied. The TiO₂ thin films were deposited at three sputtering current values of 0.50, 0.75, and 1.00 A with different deposition times of 25, 35, and 45 min, respectively. The surface morphology of the films was investigated by atomic force microscopy (AFM). The structure was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The film thickness was determined by field emission scanning electron microscopy (FE-SEM), and the optical property was evaluated with spectroscopic ellipsometry. The results show that polycrystalline anatase films were obtained at a low sputtering current value. The crystallinity of the anatase phase increases as the sputtering current increases. Furthermore, nanostructured anatase phase TiO₂ thin films were obtained for all deposition conditions. The grain size of TiO₂ thin films was in the range 10–30 nm. In addition, the grain size increases as the sputtering current and deposition time increase.     

Optical switching studies of an azobenzene rigidly linked to a hexa-<Emphasis Type="Italic">peri</Emphasis>-hexabenzocoronene derivative in solution and at a solid–liquid interface

Arrays of test structures consisting of sub-150 nm wide beams were lithographically fabricated in poly(methyl methacrylate) (PMMA) and used to measure the elastic mechanical properties of the material. Capillary forces that arise during the drying of rinse liquids from the test structures caused the nanoscale polymer beams to deform. The initial capillary forces were defined by the test structure geometry, and the magnitudes of the forces were quantified using a two-dimensional Young–Laplace equation. The deformation of the nanostructured beams was measured experimentally and compared to a model based on continuum-level bending beam mechanics, thereby enabling the calculation of the Young’s modulus (E) of the material. For PMMA beams greater than 100 nm in width E was calculated to be 5.1 GPa at room temperature, which corresponds closely to the elastic modulus of bulk PMMA. The Young’s moduli of structures with dimensions less than 100 nm were measured to be less than the bulk value and the origin of the decrease is discussed in terms of dimension dependent properties and polymer degradation during fabrication. The polymer nanostructures also were determined to mechanically deform more readily with increasing characterization temperature. PACS 62.25.+g; 68.35.Gy; 81.16.Nd