Theoretical and experimental study of Fe/Cr nanometric quasiperiodic multilayers

An experimental and theoretical study of magnetization curves of Fe/Cr nanometric magnetic films grown with the structure of the quasiperiodic Fibonacci sequence is presented. Fe ferromagnetic films with interfilm exchange coupling provided by intervening Cr non-ferromagnetic layers were grown on MgO (100) by dc magnetron sputtering at 300 ^°C. The magnetization curves were investigated using the magneto-optical Kerr effect with the external field applied along the easy axis. The theoretical approach for this system is based on a realistic phenomenological model that includes the following contributions to free magnetic energy: Zeeman, cubic magneto-crystalline anisotropy, as well as bilinear and biquadratic exchange energies. Our numerical results are in very good agreement with the experimental data.     

Pauli Correlation Effect for the Elastic Scattering of Protons by Different Nuclei at 800 MeV

The angular distributions of the elastic scattering of protons at an energy of 800 MeV by ¹⁶O and ²⁰Ne nuclei are described in terms of the optical model scattering theory. Single folding model is applied to calculate the optical potential taking the effective nucleon-nucleon interaction to be in two forms. One form includes the zero-range pseudo-potential term and the other includes a two-body Pauli correlation function. Analytical expressions for the real part of the optical potential are obtained for both forms. The imaginary part of the optical potential is taken to be of the Woods-Saxon's shape. It is found that introducing the Pauli correlation function improves the agreement with the experimental data for the elastic scattering differential cross-sections of protons with the target nuclei ¹⁶O and ²⁰Ne.     

Theoretical and experimental investigation of a waveguide CO2 laser with radio-frequency excitation

A comprehensive experimental and theoretical study of the optimization of a continuous-wave radiofrequency (rf) excited CO₂ waveguide laser is presented. The numerical simulation includes the modelling of the gas-discharge plasma parameters like the plasma impedance and energy deposition, the laser kinetics and finally the influence of the resonator feedback on the lasing process. Along with this theoretical study, an extensive experimental research program enabled us to optimize the laser performance of the CO₂ waveguide laser. As a result, a total output power of 42 W and a specific output power of 1.1 W/cm were obtained.     

Response function of the CdZnTe SPEAR detector

The response function of the SPEAR CdZnTe detector developed by eV Microelectronics was studied in detail. This compact detector includes a CdZnTe crystal and a preamplifier. It is operational at room temperature. The energy range of the detector is between 10 keV and 1 MeV, and its relative resolution is less than 4% at 122 keV. The goal of our study was to establish an empirical analytical approximation of the response function to be used in Monte Carlo simulations (e.g. for spectrum unfolding). Various radionuclides were used for the study. The energy spectrum obtained from the detector not only showed smooth peaks but also had a tail on the low‐energy side of the peak. This tail part was more prominent at higher energies. By using the experimental spectrum for various nuclides such as ²⁴¹Am, ¹⁰⁹Cd, ⁵⁷Co and ¹³⁷Cs, the parameters required to replicate the experimental response with a peak plus exponential model were evaluated. Copyright © 2011 John Wiley & Sons, Ltd.     

Effects of band non-parabolicity on electron drift velocity in silicon above room temperature

Electron drift velocity in silicon is studied at and above room temperature (300, 370 and 430 K) as function of field strength (up to 60 $\text{kV}\text{cm}\text{)}$ and orientation (〈111〉 and 〈100〉). Experimental data show a small anisotropy even at the highest considered temperature, while saturation is well evidenced only at 300 K with the field oriented along the (111) axis. The data are interpreted with theoretical Monte Carlo calculations. The model includes non-parabolicity of the band, and a non-parabolicity parameter α = 0.5 eV^?1 is suggested by the comparison of theoretical and experimental results.     

Analysis of gaseous mixtures with multifrequency NH3 laser spectrometer

The first results of quantitative analysis of gaseous mixtures with aid of laser spectrometer, based on a pulsed NH₃ laser with optical pump of the TEA CO₂ laser are reported. In the first part the general properties of the NH₃ laser are briefly described along with a theoretical model and some results of numerical modeling. The main difference of the laser is simultaneous multifrequency generation. In the second part of the paper, results of measurements of partial pressures of multicomponent admixtures in atmospheric pressure air are presented. It is experimentally shown, that at least four-component admixture can be analyzed with this type of spectrometer. This result can be used as preliminary step in development of a new type of remote laser spectrometer.     

Calculation of the imaginary part of the heavy ion potential

The paper contains a numerical evaluation of the expressions for the absorptive potential in heavy ion reactions given earlier. With a standard folding expression for the real part of the ion-ion potential general good agreement is found with experimental data for the angular distributions of elastic and inelastic scattering. Special interest is attached to the case of ¹⁶O + ²⁸Si where the calculated imaginary potential is very small at low bombarding energies.     

Computerprogramm zur interaktiven Auswertung von 15N-tracerkinetischen Stoffwechselexperimenten

The theoretical concept of the computer program is based on the compartment theory for the 3-pool model using single pulse administration of the tracer. The code estimates the model parameters by means of the non-linear method of least squares fit under steady state conditions. Furthermore the parameters of the protein metabolism are calculated. The program works interactively and allows reading and modifying the experimental ¹⁵N tracer data via terminal and controlling the program.     

Light-scattering studies of the dynamical behaviour of liquid 4He close to the λ-line

The paper begins with a review of experiments carried out by the present authors and their collaborators to determine by light scattering the dynamic structure factor of liquid ⁴He at temperatures close to the superfluid transition. This review includes details of the experimental techniques and reports a number of new sets of experimental results ; it concentrates particularly on the low-frequency part of the dynamic structure factor (the second-sound Brillouin doublet and the Rayleigh line), and the results cover both the hydrodynamic and the critical regimes for one particular value of the wave-vector. A comparison is made with the results of other authors, particularly those of Greytak and his collaborators. Following this presentation of the experimental data, an attempt is made to describe the dynamical behaviour of helium near the superfluid transition in terms of simple physical pictures, and then to use these pictures as the basis of simple calculations. The results often seem to agree surprisingly well with experiment, although the agreement may well be fortuitous; this part of the paper is frankly speculative and ought not to be taken too seriously. Comparison is made with the results of rigorous theoretical work, including recent attempts to apply the techniques of the renormalization group ; although these latter attempts have led to a degree of success, some of the results obtained seem to be in serious disagreement with experiment.     

Spin-lattice relaxation by solitons in 13C enriched iodine doped trans-poly acetylene

An experimental study of NMR spin-lattice relaxation of ¹³C in enriched, iodine doped, polyacetylene is presented together with a theoretical analysis of the results based on the existence of solitons in this system. The good agreement with this model and the numerical values obtained here and those measured by different experimental techniques support firmly the applicability of the soliton picture to I₂ doped polyacetylene.     

Towards e+e-→3 jets at NNLO by sector decomposition

A method based on sector decomposition has been developed to calculate the double real radiation part of the process e⁺e^-→3 jets at next-to-next-to-leading order. It is shown in an example that the numerical cancellation of soft and collinear poles works well. The method is flexible enough to include an arbitrary measurement function in the final Monte Carlo program, such that it allows one to obtain differential distributions for different kinds of observables. This is demonstrated by showing three-, four- and five-jet rates at order α_s ³ for a subpart of the process.     

Experimental and numerical modelling of the fluid flow in the continuous casting of steel

This article gives an overview of recent research activities with respect to the mold flow in the continuous casting of steel in presence of DC magnetic fields. The magnetic fields appear to be an attractive tool for controlling the melt flow in a contactless way. Various kinds of magnetic systems are already in operation in industrial steel casting, but the actual impact on the melt flow has not been sufficiently verified by experimental studies. The rapid development of innovative diagnostic techniques in low-melting liquid metals over the last two decades enables new possibilities for systematic flow measurements in liquid metal model experiments. A new research program was initiated at HZDR comprising three experimental facilities providing a LIquid Metal Model for continuous CASTing of steel (LIMMCAST). The facilities operate in a temperature range from room temperature up to 400^°C using the low-melting alloys GaInSn and SnBi, respectively. The experimental program is focused on quantitative flow measurements in the mold, the submerged entry nozzle and the tundish. Local potential probes, Ultrasonic Doppler Velocimetry (UDV) and Contactless Inductive Flow Tomography (CIFT) are employed to measure the melt flow. The behavior of two-phase flows in case of argon injection is investigated by means of the Mutual Inductance Tomography (MIT) and X-ray radioscopy. The experimental results provide a substantial data basis for the validation of related numerical simulations. Numerical calculations were performed with the software package ANSYS-CFX with an implemented RANS-SST turbulence model. The non-isotropic nature of MHD turbulence was taken into account by specific modifications of the turbulence model. First results of the LIMMCAST program reveal important findings such as the peculiar, unexpected phenomenon that the application of a DC magnetic field may excite non-steady, non-isotropic large-scale flow oscillations in the mold. Another important result of our study is that electrical boundary conditions, namely the wall conductivity ratio, have a serious influence on the mold flow while it is exposed to an external magnetic field.     

Thoughts on polarimetry for 3He beams at RHIC

The Relativistic Heavy Ions Collider (RHIC) has accelerated polarized proton beams for physics since 2001. As part of the future eRHIC program and in order to enhance access to the down quark, a program to accelerate polarized ³He in the AGS and RHIC is envisioned. To that end, a polarized ³He source is being built at MIT. This will be installed on the BNL EBIS source in preparation for injection into the booster and AGS. As an early exercise, in June 2012, unpolarized ³He beams have been accelerated in the AGS. This paper will peruse some potential ideas for ³He polarimetry and calibration that could be utilized at the AGS as well as RHIC. The current proton polarimetry program serves as a guide.     

Weak radiative hyperon decays in the pole model

We compute the parity conserving and parity violating amplitudes of the weak radiative hyperon decays in a pole model which includes negative parity intermediate states. The matrix elements are determined from experimentally known quantities and also evaluated in a nonrelativistic quark model. We find good numerical agreement with the data for the decay Σ⁺→P+γ and obtain predictions for the other decays where experimental information has been scarce up to now.     

A test of the fish bone optical model onα-16O scattering

The recently proposed fish bone optical model is tested on0α-¹⁶ O scattering. Using a microscopic interaction similar to that of resonating group calculations the characteristic rotational bands in²⁰Ne as well as the gross structure of the elastic differential cross section are reproduced. It is shown that the fish bone optical model can be extended by inclusion of a phenomenological imaginary part. A numerical comparison with the corresponding double folding model and with the Saito model confirms the theoretical prediction that the fish bone optical model is a further step towards inclusion of the effect of the Pauli principle in the optical model.     

A melt depth prediction model for quality control of laser surface glazing of inhomogeneous materials

This paper reports on an investigation into the development of an analytical model for the quality control of laser marking/engraving of clay tiles using a high-power diode laser (HPDL). An analytical model for the laser melting of inhomogeneous workpieces with parabolic melt pool geometry being assumed was developed. The theoretical results were compared with the experimental data. The predicted melt pool depth and the experimental values were in close correlation with the parameter for values less than 15 Wmm⁻¹ s^−1/2, in spite of simplifications introduced in the model. At the relatively large values of parameter the assumption of parabolic melt pool shape and one-dimensional heat transfer no longer holds true.     

Study of the broadening of the rotational Raman lines of CO2 perturbed by rare gases

This paper presents the results of an experimental and theoretical study of the broadening of the rotational Raman lines of the linear molecule CO₂ perturbed by rare gases: helium, neon and argon. In the first part, the experimental set-up and the method to deduce linewidths from the spectra are presented. This method is similar to that used by Welsh et al. although we take into account the contribution of the molecules in the (01¹0) vibrational state for which the rotational quantum number J can be odd. The results for the pressure broadening coefficient are then given for several values of J. We then briefly recall how one can derive collision cross sections from the measured linewidths. The second part is devoted to an attempt to interpret the experimental results in terms of the theory of the Raman linewidths developed by Van Kranendonk. After recalling briefly the assumptions used in that theory and discussing the intermolecular potentials that are used, we present the results of numerical calculations performed with several types of anisotropic interaction potentials between CO₂ and the atom of rare gas. We reach the conclusion that the approximate methods used by Van Kranendonk (matrix elements of the evolution operator S computed by second order perturbation theory) are probably inadequate to calculate the effect of elastic collisions that disorient the molecule. It is suggested that it might be advantageous to consider anisotropic forces of shorter range than the anisotropic London dispersion forces derived from an r^-6 potential.     

Laser diagnostics of ultrasonic outgassing of an insulating liquid

The efficiency of hydrogen evolution from transformer oil into a vacuum and into air under normal pressure is studied for the case when the oil is exposed to focused ultrasonic radiation. The study is performed by the method of spectroscopy of biharmonic-pumping coherent anti-Stokes Raman scattering (CARS) based on stimulated Raman scattering (SRS). Ultrasonic radiation at a frequency of 1.76 MHz is excited by a spherical piezoceramic transducer mounted on the bottom of the vessel and is focused on the surface of the oil. This causes the intense stirring of the oil with the formation of a fountain. The room-temperature diffusion coefficient of hydrogen in the transformer oil, 10⁻⁷ m²/s, is found by approximating experimental data by a theoretical relationship for hydrogen evolution into air. It is shown that ultrasonic radiation with a power density of 2.2 kW/m² accelerates diffusion processes ten-to fifteen-fold.