Phonons localises dus a une monocouche de xenon en epitaxie sur la surface (0001) du graphite

We compute, by a simple method, the acoustical phonons due to the adsorption of a xenon monolayer on the (0001) surface of a graphite crystal. We show that the band of acoustical localized phonons is quasi-flat and very close to the Einstein's frequency associated to the vibrations polarized in the direction normal to the (0001) plane. The consequences of these features are discussed.     

High-spin states in 59Ni

High-spin states in ⁵⁹Ni have been investigated via the study of in-beam γ-rays following the reactions ⁵⁰Cr(¹²C, 2pn)⁵⁹Ni (26–58 MeV) and ⁵⁶Fe(α, n)⁵⁹Ni (10, 15, 22.5 MeV). The spins of previously known levels have been confirmed or determined for the first time, in particular for those at $\text{3376.8}\text{keV}\text{(J =}\text{11}\text{2}\text{)}\text{and}\text{4141.3}\text{keV}\text{(J =}\text{13}\text{2}\text{or}\text{15}\text{2}\text{)}$. New states have been established and their spin determined, at $\text{1739.2}\text{keV}\text{(J =}\text{9}\text{2}\text{), 2349.2}\text{keV}\text{(J =}\text{11}\text{2}\text{), 2535.5}\text{keV}\text{(J =}\text{13}\text{2}\text{), 4455.4}\text{keV}\text{(J =}\text{13}\text{2}\text{), 4947.5}\text{keV}\text{(J =}\text{15}\text{2}\text{)}\text{and}\text{5251.7}\text{keV}\text{(J =}\text{13}\text{2}\text{or}\text{15}\text{2}\text{)}$. The resulting ⁵⁹Ni decay scheme is discussed in the framework of nuclear models.     

Méthode simple de calcul des variations de l'entropie de vibration et des déplacements carrés moyens des atomes dues aux défauts dans les cristaux

We give a simple and analytic method for the calculation of the variations of the vibration entropies and mean-square displacements due to the defects in crystals. The results are in good agreement with the experimental data and with the exact methods values.     

Restoring force and dynamic loadings identification for a nonlinear chain-like structure with partially unknown excitations

Most of the currently employed vibration-based identification approaches for structural damage detection are based on eigenvalues and/or eigenvectors extracted from dynamic response measurements, and strictly speaking, are only suitable for linear system. However, the inception and growth of damage in engineering structures under severe dynamic loadings are typical nonlinear procedures. Consequently, it is crucial to develop general structural restoring force and excitation identification approaches for nonlinear dynamic systems because the restoring force rather than equivalent stiffness can act as a direct indicator of the extent of the nonlinearity and be used to quantitatively evaluate the absorbed energy during vibration, and the dynamic loading is an important factor for structural remaining life forecast. In this study, based on the instantaneous state vectors and partially unknown excitation, a power series polynomial model (PSPM) was utilized to model the nonlinear restoring force (NRF) of a chain-like nonlinear multi-degree-of-freedom (MDOF) structure. To improve the efficiency and accuracy of the proposed approach, an iterative approach, namely weighted adaptive iterative least-squares estimation with incomplete measured excitations (WAILSE-IME), where a weight coefficient and a learning coefficient were involved, was proposed to identify the restoring force of the structure as well as the unknown dynamic loadings simultaneously. The response measurements of the structure, i.e., the acceleration, velocity, and displacement, and partially known excitations were utilized for identification. The feasibility and robustness of the proposed approach was verified by numerical simulation with a 4 degree-of-freedom (DOF) numerical model incorporating a nonlinear structural member, and by experimental measurements with a four-story frame model equipped with two magneto-rheological (MR) dampers mimicking nonlinear behavior. The results show the proposed approach by combining the PSPM and WAILSE-IME algorithm is capable of effectively representing and identifying the NRF of the chain-like MDOF nonlinear system with partially unknown external excitations, and provide a potential way for damage prognosis and condition evaluation of engineering structures under dynamic loadings which should be regarded as a nonlinear system.     

Large Eddy Simulation of a Propagating Turbulent Premixed Flame

A large eddy simulation of a turbulent premixed flame propagatingthrough a chamber containing a square obstruction is presented anddiscussed. The governing equations for compressible, reacting flowsare Favre filtered and turbulence closure is achieved using thedynamic Smagorinsky subgrid model. A simple flame surface densitymodel based on the flamelet concept is employed for the subgrid scalereaction rate. The simulation gives very good agreement with experimentalresults for the speed and the shape of the flame as it propagates throughthe chamber. The peak pressures, however, are underpredicted by20–30%. Reasons for this are discussed and it is concluded that amore sophisticated combustion model is required for complex flowssuch as this one, if a more accurate prediction of the pressureis to be achieved.     

Calculation of the phonon contribution to the specific heat of an overlayer-film substrate at low temperatures

Using the Green function method, we calculate the vibrational specific heat C_v produced by an overlayer-film substrate interface at low temperatures. A variation law in T³ is found and the dependence of C_v upon the film thickness is determined analytically.     

Data-based Identification of nonlinear restoring force under spatially incomplete excitations with power series polynomial model

One of the present barriers to the realization of structural health monitoring is the lack of efficient and general identification methodologies for dealing with nonlinearity, because a priori knowledge of the nature and mathematical form of the nonlinearities of typical engineering structures are usually unknown. The studies on the identification of restoring force, which can be considered as a direct indicator of the extent of the nonlinearity, have received increasing attention in recent years. In this paper, the nonlinear restoring force (NRF) was estimated by using a power series polynomial, and each coefficient of the polynomial was identified by means of standard least-square techniques. No information about the system was needed, and only the applied excitations and the corresponding response time series were used for the identification. Two different cases, in which the system was under complete and incomplete excitations, were investigated. Moreover, the effect of noise level was also taken into consideration. The feasibility and robustness of the proposed approach were verified via a 2-degree-of-freedom (DOF) lumped-mass numerical model, and experimental tests on a 4-story shear building with magneto-rheological (MR) dampers which served to simulate nonlinear behavior. The results show that the proposed data-based method is capable of identifying the NRF in a chain-like multi-degree-of-freedom engineering structures without any assumptions on the structural parameters, and provides a promising way for damage detection in the presence of structural nonlinearities.     

A detailed experimental investigation of well-defined,turbulent evaporating spray jets of acetone

This paper aims at investigating the detailed structure of turbulent non-reacting dilute spray flows using advanced laser diagnostics. A simple spray jet nozzle is designed to produce a two-phase slender shear flow in a co-flowing air stream with well-defined boundary conditions. The carrier flow is made intentionally simple and easy to model so that the focus can be placed on the important aspects of droplet dispersion and evaporation, as well as turbulence–droplet interactions. Phase Doppler interferometry is employed to record droplet quantities, while planar laser-induced fluorescence imaging is applied separately to obtain acetone vapour data. Measurements are conducted for four acetone spray jets in air at several axial stations starting from the nozzle exit. The combined liquid and vapour mass fluxes of acetone integrated across the jet at downstream locations agree satisfactorily with the total mass flow rate of acetone injected.     

The robustness of an efficient probabilistic data-based tool for simulating the non-stationary response of non-linear systems

The stochastic response of dynamic systems has been an area of considerable interest for some time in the analysis of risk and structural reliability. The authors, in previous work, have developed a method which can analyze the response of linear multi-degree-of-freedom systems to completely general data-based non-stationary excitations in a highly efficient and analytical form. The authors extended this work to non-linear system response by using equivalent linearization techniques. This paper explores the range of application of the extension to the analysis of non-linear systems through the use of real and simulated data-sets. In particular, sensitivity issues of non-Gaussianity of the excitation data, and the degree of response non-linearity of the dynamic system, are investigated for their effect on the estimated response using this equivalent linearization-based approach.