Influence of polymer molecular weight on the chemical modifications induced by UV laser ablation

This paper investigates the influence of polymer molecular weight (M(W)) on the chemical modifications of poly(methyl methacrylate), PMMA, and polystyrene, PS, films doped with iodonaphthalene (NapI) and iodophenanthrene (PhenI), following irradiation at 248 nm (KrF excimer laser, 20 ns fwhm and hybrid excimer-dye laser, 500 fs fwhm) and at 308 nm (XeCl excimer laser, 30 ns fwhm). The changes of intensity and position of the polymer Raman bands upon irradiation provide information on cleavage of the polymer bonds. Degradation of PMMA, which is a weak absorbing system at 248 nm, occurs to a higher extent in the case of a larger M(W), giving rise to the creation of unsaturation centers and to degradation products. For highly absorbing PS, no degradation is observed upon irradiation with a KrF laser. Consistently irradiating doped PS at 308 nm, where the absorption is low, induces degradation of the polymer. Results provide direct support for the bulk photothermal model, according to which ejection requires a critical number of broken bonds. In the case of irradiation of doped PMMA with pulses of 248 nm and 500 fs, neither degradation nor dependence with polymer M(W) are observed, indicating that mechanisms involved in the femtosecond laser ablation differ from those operating in the case of nanosecond laser ablation. Participation of multiphoton/avalanche processes is proposed.     

Estimation of aerodynamic noise generated by forced compressible round jetsEstimation du bruit d'origine aérodynamique rayonné par des jets ronds forcés compressibles

An acoustic numerical code based on Ligthill's analogy is combined with large-eddy simulations techniques in order to evaluate the noise emitted by subsonic $(M=0.7)$ and supersonic $(M=1.4)$ round jets. We show first that, for centerline Mach number $M=0.9$ and Reynolds number $\mathit{Re}=3.6\times {10}^3$, acoustic intensities compare satisfactorily with experimental data of the literature in terms of levels and directivity. Afterwards, high Reynolds number $(\mathit{Re}=3.6\times {10}^4)$ free and forced jets at Mach 0.7 and 1.4 are studied. Numerical results show that the jet noise intensity depends on the nature of the upstream mixing layer. Indeed, the subsonic jet is 4 dB quieter than the free jet when acting on this shear layer by superposing inlet varicose and flapping perturbations at preferred and first subharmonic frequency, respectively. The maximal acoustic level of the supersonic jet is, on the other hand, 3 dB lower than the free one with a flapping upstream perturbation at the second subharmonic. The results reported in this paper confirm previous works presented in the literature demonstrating that jet noise may be modified according to the inlet conditions. To cite this article: M. Maidi, C. R. Mecanique 334 (2006).     

Enhanced core polarization in (70)Ni and (74)Zn

The reduced transition probabilities B(E2;0(+) --> 2(+)(1)) of the neutron-rich (74)Zn and (70)Ni nuclei have been measured by Coulomb excitation in a (208)Pb target at intermediate energy. These nuclei have been produced at Grand Accélérateur National d'Ions Lourds via interactions of a 60A MeV (76)Ge beam with a Be target. The B(E2) value for (70)Ni(42) is unexpectedly large, which indicates that neutrons added above N=40 strongly polarize the Z=28 proton core. In the Zn isotopic chain, the steep rise of B(E2) values beyond N=40 continues up to (74)Zn(44). The enhanced proton core polarization in (70)Ni is attributed to the monopole interaction between the neutron in the g(9/2) and protons in the f(7/2) and f(5/2) spin-orbit partner orbitals. This interaction could result in a weakening of magicity in (78)Ni(50).     

Decay solution for the renewal equation with diffusion

In this paper we consider age structured equation with diffusion under nonlocal boundary condition and nonnegative initial data. We prove existence, uniqueness and the positivity of the solution to the above problem. Our main result is to get an exponential decay of the solution for large times toward such a study state. To this end we prove a weighted Poincaré–Wirtinger’s type inequality in unbounded domain.     

Linear and Bilinear Multiplier Operators for the Dunkl Transform

The main purpose of this article is to study the L _p -boundedness of linear and bilinear multiplier operators for the Dunkl transform in the one dimensional case.     

Exp-function method for the exact solutions of fifth order KdV equation and modified Burgers equation

In this paper, we implemented the exp-function method for the exact solutions of the fifth order KdV equation and modified Burgers equation. By using this scheme, we found some exact solutions of the above-mentioned equations.     

Coupled Galerkin and parameterization methods for optimal control of discretely connected parallel beams

Galerkin and wavelet methods for optimal boundary control of a couple of discretely connected parallel beams are proposed. First, the problem with boundary controls is converted into a problem with distributed controls. The problem is, then, reduced by a Galerkin-based approach into determining the optimal control of a linear time-invariant lumped parameter system, which will be solved by a wavelet-based method using Legendre wavelets. The integration-operational matrix and Kronecker product are utilized to significantly simplify the optimization problem into a system of linear equations. A numerical example is presented to demonstrate the applicability and the efficiency of the proposed method.