Nichtlokale Potentiale im Einteilchen-Modell des Atomkerns

In the nonlocal part of the single particle potential of bound nucleons the Gaussian nonlocality, which was used in earlier papers, is replaced by a Yukawa- and an exponential potential. The nonlocal parameters are fitted to the nucleon scattering experiments and the results are used for a calculation of single particle levels of Pb²⁰⁹ and Pb²⁰⁷. The nonlocality required by the Pauli-exclusion-principle is compared with the phenomenological approach. It turns out that the form of this nonlocality is essentially given by the supposed nucleon-nucleon potential. The range of this potential is determined by the experimentally known energy-dependence of the single particle potential.     

Atomic parity violation in a single trapped radium ion

Atomic parity violation (APV) experiments are sensitive probes of the electroweak interaction at low energy. These experiments are competitive with and complementary to high-energy collider experiments. The APV signal is strongly enhanced in heavy atoms and it is measurable by exciting suppressed (M1, E2) transitions. The status of APV experiments and theory are reviewed as well as the prospects of an APV experiment using one single trapped Ra^?+? ion. The predicted enhancement factor of the APV effect in Ra^?+? is about 50 times larger than in Cs atoms. However, certain spectroscopic information on Ra^?+? needed to constrain the required atomic many-body theory, was lacking. Using the AGOR cyclotron and the TRI??P facility at KVI in Groningen, short-lived ^212???214Ra^?+? ions were produced and trapped. First ever excited-state laser spectroscopy was performed on the trapped ions. These measurements provide a benchmark for the atomic theory required to extract the electroweak mixing angle to sub-1% accuracy and are an important step towards an APV experiment in a single trapped Ra^?+? ion.     

Robust synchronization and anti-synchronization of identical Φ6 oscillators via adaptive sliding mode control

The main goal of this paper is to propose the single input robust adaptive sliding mode controllers to accomplish synchronization and anti-synchronization between two identical Φ⁶ Duffing or Van der Pol oscillators with unmodel dynamics and external disturbances. Unlike directly eliminating the nonlinear dynamics by active control and sliding mode control in the literature, the proposed sliding mode controllers include the equivalent control part, which is only proportional to the synchronized error states, and the switching control part, where the discontinuous control functions have adaptive feedback gains. Sufficient conditions are provided based on the Lyapunov stability theorem and numerical simulations are performed to verify the effectiveness of presented schemes.     

Ventilation naturelle d'un local par une grande ouverture extérieure : Calcul à l'aide d'un code de champ

This paper is dedicated to the numerical study of natural ventilation in a room through a large external opening using the CFD code Fluent. Bidimensional numerical simulations are performed for wind speeds up to 5.55 m·s⁻¹ (20 km·h⁻¹). We propose a two-step solution procedure with grid refinement. When combined with appropriate thermal boundary conditions, this technique appears very efficient at limiting local convergence problems. Through an analysis of the flow pattern in the cavity, we qualitatively explain those results and define a critical Archimedes number. Calculated air change rates are compared to values deduced from empirical correlations of the literature. Agreement is in general poor, which can be explained by the differences between the conditions of our simulations and those of the experiments that lead to those correlations. However, from our simulations, we derived very clear correlations between the air change coefficient and the Archimedes number. In the last part, our results are compared with published data from two experiments. Agreement, in terms of air change coefficient, is within 26 % on average with the Porto test cell data which is closest to our numerical conditions. One should be careful about the transposition of our results to different ventilation scenarios.     

The atom-surface interaction potential for He-NaCl: A model based on pairwise additivity

The recently developed semi-empirical model of Fowler and Hutson is applied to the He-NaCl atom-surface interaction potential. Ab initio self-consistent field calculations of the repulsive interactions between He atoms and in-crystal Cl⁻ and Na⁺ ions are performed. Dispersion coefficients involving in-crystal ions are also calculated. The atom-surface potential is constructed using a model based on pairwise additivity of atom-ion forces. With a small adjustment of the repulsive part, this potential gives good agreement with the experimental bound state energies obtained from selective adsorption resonances in low-energy atom scattering experiments. Close-coupling calculations of the resonant scattering are performed, and good agreement with the experimental peak positions and intensity patterns is obtained. It is concluded that there are no bound states deeper than those observed in the selective adsorption experiments, and that the well depth of the He-NaCl potential is 6.0 ± 0.2 meV.     

Microwave photoconductivity relaxation time in a bifacial silicon solar cell base in the vicinity of a p-n junction

Microwave photoconductivity relaxation time depending on light intensity is studied in n ⁺-p-p ⁺ silicon solar cells. The results from experiments performed under conditions of open-circuit and short-circuit currents are in agreement with the simulated data. The relaxation times of microwave photoconductivity are found for a part of the base region adjacent to the n ⁺-p junction.     

用于10Gb/s传输系统的电吸收调制器与分布反馈激光器集成光源

采用超低压(22×１０^２Pa)选择区域生长(selective area growth, SAG)金属有机化学气相沉积(metal-organic chemical vapor deposition, MOCVD)技术成功制备了应变型InGaAsP/InGaAsP电吸收调制器(electroabsorption modulator, EAM)与分布反馈激光器(distribute feedback laser, DFB)单片集成光源的新型光电器件.实验结果表明，采用该技术制备的集成器件表现出了良好的性能：激射阈值为19 mA，出光功率接近7 mW，边模抑制比(side-mode suppression ratio, SMSR)大于40 dB，将该集成器件出射光耦合进普通单模光纤后进行测量，获得了16 dB的消光比，器件3 dB响应带宽达到了10 GHz以上.将该集成器件完全封装后成功进行了10 Gb/s非归零码(non-return zero, NRZ)的传输实验：在误码率为10^-10的传输条件下于普通单模光纤中传输了53.3 km，色散代价小于1.5 dB，动态消光比大于8 dB，且眼图清晰张开. 关键词： 超低压 选择区域生长 集成光电子器件 10 Gb/s     

The source galerkin method for scalar field theory

This is part I of a two-part series on the Source Galerkin method. This approach is based on the differential formulation of quantum field theory. On a finite lattice, the functional differential equations for a theory in the presence of an external source becomes a set of coupled differential equations for the generating functional Z. Systematic approximations to these equations are found using the Galerkin method. Calculations are straightforward to perform, and are executed rapidly compared to Monte Carlo. The bulk of the computation involves a single matrix inversion. In addition, bosons and fermions are treated in a symmetric manner. In this paper, we consider power series solutions for scalar field theory in D = 2, 3,4. Propagators and mass gaps are calculated for a number of systems. The calculations in this paper were made on a work station of modest power using a fourth order polynomial expansion for lattices of size 8², 4³, 2⁴ in 2D 3D, and 4D. In part II we consider the fermionic formulation.     

Broadband Polarization Transfer under Magic-Angle Spinning: Application to Total Through-Space-Correlation NMR Spectroscopy

A pulse sequence is described that leads to a broadband recoupling of the dipolar interaction in magic-angle-spinning solid-state NMR experiments of¹³C spins. The sequence is based on a combination of rotating frame and laboratory frame transfer periods. The recovered dipolar interaction is only weakly dependent on spectral parameters but is a faithful measure for the internuclear distances. Furthermore, a pure zero-quantum term is recovered (of the type found in static “spin-diffusion” experiments). This makes the pulse sequence particularly suited for incorporation into two-dimensional total through-space correlation experiments that deliver simultaneous information about all dipolar couplings in a single 2D experiment. It is found that the necessary decoupling from abundant protons is best performed in two steps: first, the strong homonuclear couplings between the high-γ spins are averaged by Lee–Goldburg irradiation and, second, the heteronuclear dipolar interaction is averaged by the combined application of an RF field to the low-γ spins and magic-angle sample spinning. Phase-inversion and amplitude attenuation in the rotating frame and refocusing pulses in the laboratory frame part of the pulse sequence are introduced to achieve an optimum chemical-shift offset-independence and for the suppression of unwanted double-quantum transitions. The design principles are explained in detail. Finally, the pulse scheme is applied to total-correlation spectroscopy of a uniformly labeled amino acid. The experimental cross-peak intensities are in qualitative agreement with the known crystal structure of the model compound.     

Interaction between recoil-implanted111In impurities and radiation damage in silver

We report a study of the impurity-radiation damage interaction for In in silver. Time-differential perturbed angular correlation experiments were carried out on¹¹¹Cd, the radioactive daughter of¹¹¹In produced and recoiled in Ag following the¹⁰⁹Ag(, 2n)¹¹¹In nuclear reaction. All irradiations were performed at 80 K. The dose-rate and annealing temperature dependences of the defect-induced quadrupole interaction on¹¹¹Cd were investigated. Clear differences are observed between the effects of correlated damage (the impurity interacting with the damage created by its own recoil) and uncorrelated damage (where the impurity is submitted to the influence of other damage cascades). In the former case (low dose-rate experiments), about 6% of the¹¹¹In impurities are subject to a well-defined quadrupole interaction which is ascribed to a near-neighbor vacancy. This proportion is temperature-independent up to 500 K, but the amplitude of the quadrupole frequency is reduced by a factor of three between 300 and 400 K. Assuming vacancy release by the impurity, this would lead to a binding energy of 0.34(15) eV. The remainder of the¹¹¹In nuclei are subject to a distribution of quadrupole interactions presumably due to a statistical repartition of lattice defects at some distance from the impurities. The width of the distribution changes upon annealing: a clear transition takes place at 200 K, which is the divacancy mobility threshold in Ag deduced from resistivity experiments. When cascade overlap occurs (high dose-rate experiments), no impurity-defect trapping is evidenced but a distribution of quadrupole interactions due to surrounding damage is still found. From these experiments, an order of magnitude of the damage cascade size is deduced. Our results are discussed in terms of available information on the impurity-damage interaction in various hosts; a compilation of all results on the impurity-vacancy interaction known to us is also presented in the paper.This work is part of a Ph.D. Thesis submitted by L. Thomé to Université Paris-Sud.     

On the possibility of highly selective detection of rare isotopic atoms by means of resonant laser light pressure

The application of laser deceleration and monochromatization of atoms in the schemes of single atom fluorescent detection is examined. The analysis performed shows that the use of resonant-light pressure in experiments with atomic beams enables one to obtain an ultimate value of detection selectivity that ranges from 10¹³ to 10¹⁶.     

Synthesis and decay properties of superheavy atoms in nuclear reactions induced by stable and radioactive ion beams

This talk consists of two parts. The first one presents the results of investigations performed in 1998-2000 in Dubna on the synthesis of superheavy nuclei in reactions induced by ⁴⁸Ca ions. The radioactive decay properties of the nuclei, indicating a considerable increase in the α-decay and spontaneous fission half-lives of the isotopes of elements 110-116 when approaching the closed neutron shell at N = 184, are given. In the second part the possible ways of advancing into the region of more neutron-rich nuclei, using stable and radioactive ion beams, are discussed. Since so far no intense radioactive ion beams are available, some experiments with stable beams are considered as a test for the suggested ideas. Received: 1 May 2001 / Accepted: 4 December 2001     

In-water gas combustion for thrust production

The paper presents the results of experimental study for hydrodynamic processes occurring during combustion of a stoichiometric mixture propane-oxygen in combustion chambers with different configurations and submerged into water. The pulses of force acting upon a thrust wall were measured for different geometries: cylindrical, conic, hemispherical, including the case of gas combustion near a flat thrust wall. After a single charge of stoichiometric mixture propane-oxygen is burnt near the thrust wall, the process of cyclic generation of force pulses develops. The first pulse is generated due to pressure growth during gas combustion, and the following pulses are the result of hydrodynamic pulsations of the gaseous cavity. Experiments demonstrated that efficient generation of thrust occurs if all bubble pulsations are used during combustion of a single gas combustion. In the series of experiments, the specific impulse on the thrust wall was in the range 10⁴–10⁵ s (10⁵–10⁶ m/s) with account for positive and negative components of impulse.     

Whispering gallery mode dielectric resonators in EMR spectroscopy above 150 GHz: Problems and perspectives

At frequencies above 150 GHz conventional microwave techniques become unsuitable for electron magnetic resonance (EMR) spectroscopy applications. Quasi-optical techniques are the general frame into which the different approaches to high-field high-frequency EMR (HF²-EMR) have been developed. Beyond the single-pass approach the existing HF²-EMR spectrometers make use of Fabry-Perot resonators. In this paper the use of an alternative resonating structure on the basis of the use of whispering gallery mode dielectric resonators is shown. The physics of these resonators and their implementation in a HF²-EMR probe head are described. Their use in HF²-EMR experiments performed on standard samples is described and the results of these experiments critically discussed in order to have insight into the open problems of the employed spectrometer; the more promising solutions to these problems, actually under development, are briefly outlined.     

Reinvestigation of the magnetic structure of Ca3Mn2Ge3O12

Precise neutron diffraction experiments performed on powdered antiferromagnetic garnet Ca₃Mn₂Ge₃O₁₂ lead to a complex non collinear magnetic structure. In the absence of magnetic field, it is three dimensional with eight spin directions and belongs to ¹I_41/a. At a critical magnetic field spin-flop mechanism occurs with a lowering of the magnetic symmetry which becomes triclinic. In addition to tetragonal anisotropy, both single ion orthorhombic anisotropy and its antisymmetrical counterpart for definite pairs of ions are required to explain both the observed structure and its behaviour in a magnetic field.     

Symmetry and surface energy coefficients with an effective interaction

Symmetry energy coefficients in the first and second order have been estimated by using an effective interaction developed in a previous paper. The rearrangement contribution to the first-order symmetry energy coefficient has also been estimated. The effect of neutron excess on the first- and second-order single particle energies of nuclear matter have been studied by determining the isotopic spin dependent part of the single particle potential. The 1s state single particle energies of²⁰⁸Pb and¹⁶O have been estimated from the single particle energy of nuclear matter by incorporating the values of the isotopic spin dependent part of the single particle potential. The surface energy coefficient has been determined by using the semi-infinite model in the Thomas Fermi approach.Financial assistance from University Grants Commission, New Delhi, is gratefully acknowledged. The authors are also grateful to Professor K. C. Pande and Dr. S. P. Pandya for helpful suggestions.     

Study of the oxygen electrode reaction using mixed conducting oxide surface layers. Part II: Small signal analysis

The oxygen gas electrode has been studied for a number of mixed conducting oxide surface layers on top of Gd₂Zr₂O₇ (TGZO) solid electrolytes. In part II of this paper we present the results of frequency dispersion measurements for the electrode reaction, supplying additional information to the results of current-overvoltage experiments presented in part I. For both kinds of experiments the same trends were observed for the electrode polarization. Best results are obtained for a surface layer of TGZO, while p-type mixed conducting oxides give less decreased values of the electrode polarization. High electrode capacitances were found in the case of mixed conducting surface layers (about 700 F/m²). The electrode reactions follow a Butler-Volmer type of equation. Most probably a diffusion process is rate controlling the overall charge transfer process.     

The structure of He and the neutron electric form factor from polarization observables

As there are no free neutron targets one has to resort to the nuclear targets deuterium or helium. In order to reduce nuclear effects blurring the information on nuclear form factors the technique of double polarization experiments had been developed. Recent experiments at MAMI measuring the electric form factor of the neutron are discussed. In addition, other single and double nucleon knockout experiments are described which support the buildup of a consistent interpretation of nuclear structure in ³He.     

Sound insulation of domestic roofing systems—Part 2

In the first part of this series of papers,² tests carried out on the ceiling component of a roofing system were described. In this second part, the experiments conducted on various types of roof component are outlined. The effect of coupling the ceiling and roof components to form the complete roofing system will be the central theme of the third and final part.     

Study of the oxygen electrode reaction using mixed conducting oxide surface layers. Part I: Experimental methods and current-overvoltage experiments

The oxygen gas electrode has been studied for a number of mixed conducting oxide surface layers on top of Gd₂Zr₂O₇ (TGZO) solid electrolytes. In part II of this paper we present the results of frequency dispersion measurements for the electrode reaction, supplying additional information to the results of current-overvoltage experiments presented in part I. For both kinds of experiments the same trends were observed for the electrode polarization. Best results are obtained for a surface layer of TGZO, while p-type mixed conducting oxides give less decreased values of the electrode polarization. High electrode capacitances were found in the case of mixed conducting surface layers (about 700 F/m²). The electrode reactions follow a Butler-Volmer type of equation. Most probably a diffusion process is rate controlling the overall charge transfer process.