Rapidity dependence of multiplicity fluctuations and correlations in high-energy nucleus–nucleus interactions

The multiplicity fluctuations of the produced pions were studied using scaled variance method in ¹⁶O–AgBr interactions at 2.1 AGeV, ²⁴Mg–AgBr interactions at 4.5 AGeV, ¹²C–AgBr interactions at 4.5 AGeV, ¹⁶O–AgBr interactions at 60 AGeV and ³²S–AgBr interactions at 200 AGeV at two different binning conditions. In the first binning condition, the rapidity interval was varied in steps of one centring about the central rapidity until it reached 14. In the second case, the rapidity interval was increased in steps of 1.6 up to 14.4. Multiplicity distributions and their scaled variances were presented as a function of the dependence on the rapidity width for both the binning conditions. Multiplicity fluctuations were found to increase with the increase of rapidity interval and later found to saturate at larger rapidity window for all the interactions and in both the binning conditions. Multiplicity fluctuations were found to increase with the energy of the projectile beam. The values of the scaled variances were found to be greater than one in all the cases in both the binning conditions indicating the presence of correlation during the multiparticle production process in high-energy nucleus–nucleus interactions. Experimental results were compared with the results obtained from the Monte Carlo simulated events for all the interactions. The Monte Carlo simulated data showed very small values of scaled variance suggesting very small fluctuations for the simulated events. Experimental results obtained from ¹⁶O–AgBr interactions at 60 AGeV and ³²S–AgBr interactions at 200 AGeV were compared with the events generated by Lund Monte Carlo code (FRITIOF model). FRITIOF model failed to explain the multiplicity fluctuations of pions emitted from ¹⁶O–AgBr interactions at 60 AGeV for both the binning conditions. However, the experimental data agreed well with the FRITIOF model for ³²S–AgBr interactions at 200 AGeV.     

Real-time propagators at finite temperature and chemical potential

We derive a form of spectral representations for all bosonic and fermionic propagators in the real-time formulation of field theory at finite temperature and chemical potential. Besides being simple and symmetrical between the bosonic and the fermionic types, these representations depend explicitly on analytic functions only. This property allows for a simple evaluation of loop integrals in the energy variables over propagators in this form, even in the presence of chemical potentials, which is not possible for their conventional form.     

Laser-induced film ejection at interfaces: Comparison of the dynamics of liquid and solid films

The ejection dynamics of nanometer-thin fluid isopropanol and solid CO₂ films are investigated. The films are deposited on a silicon substrate, which is rapidly heated by a nanosecond laser pulse (Nd:YAG, 532 nm). A small fraction of material at the interface evaporates and the film on top is ejected as an intact layer. The kinetic energies of the two different films with thicknesses between 100 nm and 1 μm give an insight into the dynamics of a flying lamella.     

Quantum effects of potential fluctuations in GaAs δ-doping superlattices

The electronic and optical properties of δ-doping n-i-p-i superlattices are strongly influenced by the random distribution of donors and acceptors within the doping layers. A Monte-Carlo method is applied to investigate the resulting potential fluctuations and local changes of energy levels and wavefunctions. We study disorder effects on the density of states, the capacitance and the intraband absorption coefficient as a function of excitation level. In addition, the luminescence spectra are calculated and compared to electroluminescence measurements. Excellent agreement is achieved without using any fitting parameters, if the local wavefunction shrinkage of the tail states is included. While contributions of different subbands cannot be resolved in the luminescence, the simulation of conduction band (CB) intraband absorption confirms that this is possible using resonant Raman scattering.     

Nonlinear coefficient and temperature dependence of the refractive index of lithium niobate crystals in the terahertz regime

The effective nonlinear coefficient d _eff of lithium niobate is determined to be 94 pm/V for a process that converts infrared light to 1.35 THz radiation. This value is inferred from the performance of a continuous-wave, singly-resonant optical parametric oscillator, in which the cavity-enhanced signal wave of a primary parametric process acts as a pump wave for a cascaded process, generating terahertz waves. To quantify the nonlinear coefficient, the coupled wave equations including absorption are evaluated. Furthermore, from our measurements we also determine the temperature dependence of the refractive index to be dn _THz/dT=0.0013/K around 1.4 THz.     

Optical and structural characterization of iron oxide and cobalt oxide thin films at 800 nm

We report on optical and structural properties of α-Fe₂O₃ and Co₃O₄ thin films, grown by direct oxidation of pure metal films deposited on soda-lime glass. Structural characteristics and morphology of the films were investigated by X-ray diffraction, atomic force microscopy, and scanning electron microscopy. Linear optical absorption, and linear refraction as well as nonlinear optical properties were investigated. The third-order optical susceptibilities were measured applying the Thermally managed Z-scan technique using a Ti: sapphire laser (150 fs; 800 nm). The results obtained for the Co₃O₄ film were \( \text{Re} \chi^{\left( 3 \right)} \) = ?(5.7 ± 2.4) ×10^?9 esu and \( \text{Im} \chi^{(3)} \) = ?(1.8 ± 0.2) ×10^?8 esu while for the α-Fe₂O₃ film we determined \( \text{Re} \chi^{(3)} \) = +(6.6 ± 2.4) ×10^?10 esu and \( \text{Im} \chi^{(3)} \) = +(2.2 ± 0.4) ×10^?10 esu.     

Simultaneous flow field and fuel concentration imaging at 4.8 kHz in an operating engine

High-speed particle image velocimetry (PIV) and planar laser induced fluorescence (PLIF) techniques are combined to acquire flow field and fuel concentration in a spray-guided spark-ignited direct-injection (SG-SIDI) engine under motored and fired operation. This is a crucial step to enable studies that seek correlations between marginal engine operation (misfires or partial burns) and local, instantaneous mixture and flow conditions. Correlated flow and fuel data are extracted from a 4 mm×4 mm sub-region directly downstream the spark plug to characterize the in-cylinder conditions next to the spark plug during the spray and ignition event. Values of equivalence ratio, velocity magnitude, shear strain rate, and vorticity all increase during the spray event and decrease an order of magnitude during the duration of the spark event.     

Composition dependence of optical and electrical characteristics in flash evaporated Pb1−xHgxTe films

Structural, optical and electrical analyses of flash evaporated lead-mercury telluride films indicate that under appropriate conditions of growth ternary Pb_1−xHg_xTe compounds are formed in the single phase crystalline films. Optical band gaps of the crystalline films, grown on substrates at temperatures (Ts) of 25 and 100°C, are observed to decrease with increase in mercury concentration in the films. The optical gap decreases between 0.27 and 0.14 eV in the 0.07 ⩽x⩽ 0.50 Ts of 25°C films and between 0.23 and 0.09 eV in the Ts of 100°C 0.07 ⩽x⩽ 0.93 films. Activation energy values, calculated from electrical conductivity measurements, indicate that between 350 and 500 K, the conduction is mainly due to thermally generated charge carriers, whereas impurity conduction dominates at temperatures <250K. All crystalline films are observed to be photoconducting.     

Orbital Electron Capture Rate and Time Modulation of H- and He-like Ions in a Storage-Ring

We have studied in a heavy ion storage ring the orbital electron capture decays of H- and He-like ¹⁴⁰Pr and ¹⁴²Pm ions and found that the H-like ions with one electron in the K-shell decay 1.49(8) and 1.44(6) times faster, than the corresponding He-like ions with two electrons in the K-shell. This result is explained by spin statistics due to the hyperfine structure of the H-like ions.     

Particle resonance in the Dirac equation in the presence of a delta interaction and a perturbative hyperbolic potential

We show that the energy spectrum of the one-dimensional Dirac equation, in the presence of an attractive vectorial delta potential, exhibits a resonant behavior when one includes an asymptotically spatially vanishing weak electric field associated with a hyperbolic tangent potential. We solve the Dirac equation in terms of Gauss hyper-geometric functions and show explicitly how the resonant behavior depends on the strength of the electric field evaluated at the support of the point interaction. We derive an approximate expression for the value of the resonances and compare the results calculated for the hyperbolic potential with those obtained for a linear perturbative potential. Finally, we characterize the resonances with the help of the phase shift and the Wigner delay time.     

Heavy-quark mass dependence in global PDF analyses and 3- and 4-flavour parton distributions

We study the sensitivity of our recent MSTW 2008 NLO and NNLO PDF analyses to the values of the charm- and bottom-quark masses, and we provide additional public PDF sets for a wide range of these heavy-quark masses. We quantify the impact of varying m _c and m _b on the cross sections for W, Z and Higgs production at the Tevatron and the LHC. We generate 3- and 4-flavour versions of the (5-flavour) MSTW 2008 PDFs by evolving the input PDFs and α _S determined from fits in the 5-flavour scheme, including the eigenvector PDF sets necessary for calculation of PDF uncertainties. As an example of their use, we study the difference in the Z total cross sections at the Tevatron and LHC in the 4- and 5-flavour schemes. Significant differences are found, illustrating the need to resum large logarithms in $Q^{2}/m_{b}^{2}$ by using the 5-flavour scheme. The 4-flavour scheme is still necessary, however, if cuts are imposed on associated (massive) b-quarks, as is the case for the experimental measurement of $Zb\bar{b}$ production and similar processes.     

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⁺.     

Amplitude,wavevector and frequency dependence of magnetic fluctuations in YBa2Cu3O6+δ

Polarized neutrons and polarization analysis were used to determine the total amplitude of magnetic fluctuations in tetragonal YBa₂Cu₃O₆₊ for energies below 30 meV, both in the magnetically ordered state below and in the paramagnetic state above the Neél temperature. An energy analysis of the local magnetic correlation function (=S(r=0,)) was performed. The wavevector dependence of the energy integrated correlation function at high temperatures is dominated by local (i.e.q-independent) fluctuations. Total intensity, energy and wavevector dependence are substantially different from those of stable moments with quasi two-dimensional couplings. Magnetic amplitude fluctuation might be responsible for the observed behaviour.     

A study of an exciton in a quantum dot with Woods–Saxon potential

A theoretical study of an exciton confined in a quantum dot with the Woods–Saxon potential is presented. The great advantage of our methodology is that it enables confinement regimes by varying two parameters in the model potential. Calculations are made by using the method of the numerical diagonalization of the Hamiltonian matrix within the effective-mass approximation. The binding energies of the ground (L=0$L=0$) and first excited (L=1$L=1$) states are obtained as functions of the dot radius. Based on the computed energies and wave functions, the linear, the third-order nonlinear and the total optical absorption coefficients have been examined between the ground and the first excited states. The results are presented as a function of the incident photon energy for the different values of the dot radius and the barrier slope. It is found that the binding energy and the optical properties of the excitons in a quantum dot are strongly affected by the dot radius and the barrier slope of the confinement potential.     

Marginal Distribution of Wigner Function in Mesoscopic RLC Circuit at Finite Temperature and Its Application

By means of the Weyl correspondence and Wigner theorem the marginal distribution of Wigner function in mesoscopic RLC circuit at finite temperature was discussed. Here we endow the Wigner function with a new physical meaning, i.e., its marginal distributions’ statistical average for q ²/(2C) and p ²/(2L) are the temperature-related energy stored in capacity and in inductance of the mesoscopic RLC circuit, respectively.     

The interplay of superconductivity and localization in Nd2−xCexCuO4+δ single crystal films

The influence of nonstoichiometric disorder on the in-plane resistivity and SC-transition has been investigated for Nd_2−xCe_xCuO_4+δ single crystal films (x=0.15 and 0.18). It is shown that with increasing of δ the in-plane normal state resistivity increases (the mean free path diminishes) and SC-transition temperature decreases with essential broadening of the transition region. The observed evolution from homogeneous metallic (and superconducting) Nd_2−xCe_xCuO_4+δ system to inhomogeneous dielectric one is described as Anderson-type disorder-induced transition in a two-dimensional electron system.     

Stability of the scalar potential and symmetry breaking in the economical 3-3-1 model

A detailed study of the criteria for stability of the scalar potential and the proper electroweak symmetry breaking pattern in the economical 3-3-1 model, is presented. For the analysis we use and improve a method previously developed to study the scalar potential in the two-Higgs-doublet extension of the standard model. A new theorem related to the stability of the potential is stated. As a consequence of this study, the consistency of the economical 3-3-1 model emerges.     

Influence of the donor concentration on the decay kinetics of sensitized phosphorescence of 1,3,5-triphenylbenzene in toluene at 77 K

Dependence of the kinetics of sensitized phosphorescence (SP) of 1,3,5-triphenylbenzene (1,3,5-TPB) on the concentration of the energy donor – benzophenone (BP) – is studied in toluene at 77 K. An increase in the SP decay rate of 1,3,5-TPB with concentration is established. It is demonstrated that the reason for the increase in the decay rate is the increased radiative deactivation rate constant of triplet excitations caused by exchange interactions. The coefficient characterizing the exponential dependence of the radiative deactivation rate constant for triplet excitations of 1,3,5-TPB on the intermolecular distance in the donor-acceptor pair is determined.     

Effects of chromophore concentration and film thickness on thermo-optic properties of electro-optic fluorinated polyimide films

Electro-optic(EO)effect and thermo-optic(TO)effect are jointly considered on the basis of field-induced and temperature-affected perturbations of the operating point in waveguide components.TO coefficients of EO fluorinated polyimide films with side-chain azobenzene chromophore were measured by attenuated- total-reflection(ATR)technique at different temperatures with TE-and TM-polarized lights,respectively. It is found that the absolute values of TO coefficients increase with the increments of both chromophore concentration and film thickness,but the polarization dependence of TO coefficients increases with the increment of chromophore concentration and decreases with the increment of film thickness.