Experimental study of the energy dependence of transmission in photoelectron spectrometers

The present study describes an experiment which allows determination of the transmission of any photoelectron spectrometer using AlKα radiation. The procedure is based on the energy independence of transmission in an iron-free, magnetic-type spectrometer. The relative line intensifies for Ag measured using such an instrument are used as a reference data set. The transmission of a VG ESCALAB-5 spectrometer has been determined and found to be proportional to E in the constant retarding ratio mode, and proportional to E^?q, with q = 0.4 ± 0.05, in the constant analyser-energy mode, for energies usually encountered in XPS.     

Numerical and experimental validation of a hybrid finite element-statistical energy analysis method

The finite element (FE) and statistical energy analysis (SEA) methods have, respectively, high and low frequency limitations and there is therefore a broad class of "mid-frequency" vibro-acoustic problems that are not suited to either FE or SEA. A hybrid method combining FE and SEA was recently presented for predicting the steady-state response of vibro-acoustic systems with uncertain properties. The subsystems with long wavelength behavior are modeled deterministically with FE, while the subsystems with short wavelength behavior are modeled statistically with SEA. The method yields the ensemble average response of the system where the uncertainty is confined in the SEA subsystems. This paper briefly summarizes the theory behind the method and presents a number of detailed numerical and experimental validation examples for structure-borne noise transmission.     

A new scheme of K-labeling for torsion-rotation energy levels in low-barrier molecules

The problem of attaching K rotational quantum number labels after the second diagonalization step in the ρ-axis-method treatment of methyl-top internal rotation problems is considered. A new partially computer-automated labeling scheme for K-labeling is proposed. The scheme is rather simple and does not require any information other than that provided by the numerical eigenvectors obtained after diagonalization of the torsion-rotation Hamiltonian matrix. It assumes that within a given K stack, torsion-rotation eigenfunctions vary slowly when J changes by unity. The basic idea is thus to search for similarities in basis-set composition in torsion-rotation eigenvectors belonging to adjacent J values. In such a way, torsion-rotation states of adjacent J values having the same value of K are connected. This allows one to transfer a given K-label from lower J values, where it can be determined easily (either from eigenvector composition or from energy-ordering considerations), to higher J values, which are characterized by extensive basis-set mixing. The approach was successfully applied to the K-labeling problem of prolate (acetaldehyde, methanol, and ethyl acetamidoacetate) and oblate (acetic acid, acetamide) rotors characterized by significant torsion-rotation interactions in their spectra. The scheme gives correct K-labels for eigenvectors in the majority of cases. The problems with the remaining cases are mainly caused by localized avoided crossing interactions, which can be fixed relatively easily in manual mode using a graphical visualization of the torsion-rotation energy level diagram.     

Validity diagrams of statistical energy analysis

This paper is concerned with the validity domain of statistical energy analysis (SEA) which is defined in terms of four criteria. The mode count N and the modal overlap M must be high, the normalized attenuation factor and the coupling strength γ must be small. The application of dimensional analysis on the governing equations of plates gives the space of dimensionless parameters in which the validity domain of SEA must be delimited. This domain is discussed on the basis of geometry of the surfaces delimiting it. The diagrams of validity of SEA are introduced and discussed. A numerical simulation on a couple of rectangular plates coupled along one edge illustrates the theoretical approach.     

Electron mean free paths as a function of kinetic energy: A substrate overlayer investigation of polyparaxylylene films on gold using A Ti Kα X-ray source

Using the substrate overlayer technique with a Ti Kα_1,2 X-ray source (hν = 4510 eV) electron mean free paths λ have been determined for in situ deposited polyparaxylylene films. By monitoring the attenuation of signals arising from the substrate Au 4f, 4d, 4p, 3d and 3p core levels excited by the Ti Kα X-ray source and for the Au 4f and 4d levels excited by Cu Lα X-rays (hν = 929.7 eV) mean free paths have been determined in the kinetic energy range ～443–～59O eV. The present results are compared with those reported previously for lower kinetic energies using Mg Kα_1,2 and Al Kα_1,2 photon sources. The results indicate that at kinetic energies of ～4000 eV the typical sampling depth using a Ti Kα source is ～ 150 Å.     

Anomalous temperature dependence of the energy gap of AgGaS2

The lowest energy gap Eg of AgGaS₂ in the temperature range from 4.2 to 300° K was determined from the reflectivity, photoluminescence and absorption measurements. Below ～ 80° K the temperature coefficient of the energy gap is +6 × 10^-5eV/°K. Above ～80° K the sign of the coefficient reverses and the value is -1.8 × 10^-4eV/°K. The positive value is explained with the lattice dilation effect being the dominant mechanism for the energy gap variation at lower temperatures than ～80°K.     

The high-density symmetry energy in heavy ion collisions

The nuclear symmetry energy as a function of density is rather poorly constrained theoretically and experimentally both below saturation density, but particularly at high density, where very few relevant experimental data exist. We discuss observables which could yield information on this question, in particular, proton-neutron flow differences, and the production of pions and kaons in relativistic heavy ion collisions. For the meson production we investigate particularly ratios of the corresponding isospin partners π⁻/π⁺ and K⁰/K⁺, where we find that the kaons are an interesting probe to the symmetry energy. In this case we also discuss the influence of various choices for the kaon potentials or in-medium effective masses.     

The prediction of airborne sound transmission between two rooms using first-order flanking paths

Airborne sound transmission between adjacent rooms can be predicted using the Standard EN 12354-1 (ISO 15712-1), which is equivalent to a first-order approximation of statistical energy analysis (SEA). This paper analyses airborne sound transmission between adjacent rooms in a masonry building, by comparing results obtained from EN 12354-1 to SEA predictions and measurements. It is shown that the restriction of the Standard to first-order flanking paths can lead to large errors in predictions when compared to measurements and SEA results taking into account all transmission paths. This is observed both for individual flanking paths and overall transmission between rooms, for which the Standard provides results similar to those obtained by the first-order approximation of SEA. The paper also looks at possible reasons why previous studies using the approach in EN 12354 have generally shown good agreement with measurements.     

Active vibration control on a quarter-car for cancellation of road noise disturbance

In this paper, a methodology is presented for the cancellation of road noise, from the analysis of vibration transmission paths for an automotive suspension to the design of an active control system using inertial actuators on a suspension to reduce the vibrations transmitted to the chassis. First, experiments were conducted on a Chevrolet Epica LS automobile on a concrete test track to measure accelerations induced on the suspension by the road. These measurements were combined with experimental Frequency Response Functions (FRFs) measured on a quarter-car test bench to reconstruct an equivalent three dimensional force applied on the wheel hub. Second, FRFs measured on the test bench between the three-dimensional driving force and forces at each suspension/chassis linkage were used to characterize the different transmission paths of vibration energy to the chassis. Third, an experimental model of the suspension was constructed to simulate the configuration of the active control system, using the primary (disturbance) FRFs and secondary (control) FRFs also measured on the test bench. This model was used to optimize the configuration of the control actuators and to evaluate the required forces. Finally, a prototype of an active suspension was implemented and measurements were performed in order to assess the performance of the control approach. A 4.6 dB attenuation on transmitted forces was obtained in the 50–250 Hz range.     

Electron transport in dirty multi-channel systems

We study the temperature dependence of the conductance and of the conductivity of a doped two-chain ladder system in the presence of a barrier or of a low impurity concentration, respectively, focusing on the effects of electronelectron interaction. Like in the purely 1-D case, the conductance vanishes at low temperature when the Luttinger-liquid exponent Kρ+ (for even-charge modes) is smaller than unity, despite the presence of dominant superconducting correlations. However, there is a region of repulsive interaction where perfect transmission across the barrier occurs. This is due to a renormalization of Kρ+ produced by the difference in Fermi velocities of the bonding and antibonding bands.     

A hybrid approach for predicting the distribution of vibro-acoustic energy in complex built-up structures

Finding the distribution of vibro-acoustic energy in complex built-up structures in the mid-to-high frequency regime is a difficult task. In particular, structures with large variation of local wavelengths and/or characteristic scales pose a challenge referred to as the mid-frequency problem. Standard numerical methods such as the finite element method (FEM) scale with the local wavelength and quickly become too large even for modern computer architectures. High frequency techniques, such as statistical energy analysis (SEA), often miss important information such as dominant resonance behavior due to stiff or small scale parts of the structure. Hybrid methods circumvent this problem by coupling FEM/BEM and SEA models in a given built-up structure. In the approach adopted here, the whole system is split into a number of subsystems that are treated by either FEM or SEA depending on the local wavelength. Subsystems with relative long wavelengths are modeled using FEM. Making a diffuse field assumption for the wave fields in the short wave length components, the coupling between subsystems can be reduced to a weighted random field correlation function. The approach presented results in an SEA-like set of linear equations that can be solved for the mean energies in the short wavelength subsystems.     

Multipole expansion of the vibration transmission between a source and a receiver

The vibrational power transmitted by N forces applied, for example, by a machine upon isolators is regarded as the power transmitted by N independent poles of vibration: e.g., monopole, dipole, etc. The machine or source of vibration moves in a set of vibrational poles. The receiver is defined by a set of polar mobilities or impedances. The power transmission expressions were implemented on a practical structure, one using the source acceleration to measure the power transmitted by the isolators, the other using the receiving structure to estimate the magnitude of power by all sources of vibration, including the airborne noise.     

Cost-effective radio over fiber system for multi service wireless signal

The feasibility of the simultaneous transmission of several wireless signals over a cost-effective Radio over Fiber (RoF) link is investigated. A RoF link simulation tool is presented and applied to validate the experimental results in the case of the transmission of two wireless signals, one compliant to Universal Mobile Telecommunications Service (UMTS) and one to Worldwide Interoperability for Microwave Access (WiMAX) standards. The cross-talk between the transmitted signals is showed and related to the RoF transmitter's characteristic in terms of frequency chirping. Both for uplink and downlink of the wireless signal RoF distribution system practical design aspects are finally evidenced.     

The effect of random errors on a large statistical energy analysis model

The framework of analysis known as Statistical Energy Analysis has many important applications particularly in systems where detailed information is not available. As a result of the approximations made, to simplify the calculations, random error can be introduced into the SEA model. For large systems this gives rise to uncertainty in the energy levels. It is shown that the effect of these errors on the model depends on the “shape” of the model. A compact model dominated by short paths is less affected than a model controlled by long paths. In either case the ratio of the average error in the resultant energy level to the average error in the coupling loss factor decreases as the errors increase. This means that large models may be used with confidence even when based on data that is known to be approximate.     

A method for solving reaction and bound-state few-body problems: A > 3

A method for solving the few-body problems is described, which is based on the expansion in a small parameter: ratio of the potential energy to the kinetic energy for the states with the hyperspherical numbers K exceeding some value K ₀. The initial problem is reduced to that with modified dynamics in the subspace with K ≤ K ₀ without expansion in the basis functions at K > K ₀.     

Evaluation of activation energy by means of different trap spectroscopy techniques

Correlations are deduced for the asymmetry and the halfwidth of a signal peak which correspond to a discrete level using different “isothermal” trap spectroscopy techniques. Using only the temperature $\text{T}$ of the scan peak maximum and the halfwidth δ = T₂ ? T₁ the activation energy can then be determined: $\text{E =}\text{T}{}^2\text{/(δT}{}_{\mathrm{K}}\text{)}$, where T_K(=4500?6000 KeV^-1) is given numerically for certain frequently applied trap spectroscopy techniques. T_K is the result of a complete mathematical treatment of the kinetic equation.     

Response variance prediction in the statistical energy analysis of built-up systems

In the statistical energy analysis (SEA) of high frequency noise and vibration, a complex engineering structure is represented as an assembly of subsystems. The response of the system to external excitation is expressed in terms of the vibrational energy of each subsystem, and these energies are found by employing the principle of power balance. Strictly the computed energy is an average taken over an ensemble of random structures, and for many years there has been interest in extending the SEA prediction to the variance of the energy. A variance prediction method for a general built-up structure is presented here. Closed form expressions for the variance are obtained in terms of the standard SEA parameters and an additional set of parameters alpha(k) that describe the nature of the power input to each subsystem k, and alpha(ks) that describe the nature of the coupling between subsystems k and s. The theory is validated by comparison with Monte Carlo simulations of plate networks and structural-acoustic systems.     

On the surface energy of compressible nuclei

The specific nuclear surface energy σ as a function of the central density n_c is shown to behave in a way opposite to that of the saturation curve; in particular, σ is maximum at the saturation density. Starting from the energy of a compressible nucleus, we find after deriving a simple expression for the second derivative of σ, a formula for thecompressibility modulus K_A of finite nuclei which contains, besides the saturation density and the bulk value K_∞, only some well-known surface parameters.     

Chaotic motion at the emergence of the time averaged energy decay

A system plus environment conservative model is used to characterize the nonlinear dynamics when the time averaged energy for the system particle starts to decay. The system particle dynamics is regular for low values of the N environment oscillators and becomes chaotic in the interval 13≤N≤15, where the system time averaged energy starts to decay. To characterize the nonlinear motion we estimate the Lyapunov exponent (LE), determine the power spectrum and the Kaplan-Yorke dimension. For much larger values of N the energy of the system particle is completely transferred to the environment and the corresponding LEs decrease. Numerical evidence shows the connection between the variations of the amplitude of the particles energy time oscillation with the time averaged energy decay and trapped trajectories.     

Elastic unitarity and the K-matrix in a Lorentz covariant representation of the NN interaction

A Lorentz covariant representation of the NN t-matrix has been obtaained over the energy range from 150 to 500 MeV by solving the integral equation that connects the t-matrix with the K-matrix. The K-matrix is expanded in a complete set of on-shell Lorentz invariant amplitudes represented phenomenologically by isoscalar and isovector “meson” exchanges. The real part of the K-matrix is fit over the energy range from 150 to 500 MeV using coupling strengths that are allowed to vary quadratically with energy. Above the pion production threshold at T_lab = 280 MeV, the real K-matrix is supplemented by an imaginary part with linear energy dependence. The K-matrix parameters are fit to thesmost recent (January 1999) Arndt amplitudes [R.A. Arndt, D. Roper, VPI and SU Scattering Analysis Interactive Dial-in Program and Data Base]. Direct and exchange contributions to the K-matrix are handled explicitly in the formalism. The resulting t-matrix satisfies elastic unitary below the pion production threshold and contains non-local terms that are not present in direct Love-Franey parameterizations of the t-matrix. Results are given for the NN amplitudes and compared with both the Arndt amplitudes and amplitudes obtained from a direct fit of the t-matrix [O.V. Maxwell, Nucl. Phys. A 600 (1996) 509]. Results are also given for a selected set of np and pp observables.