Effect and importance of static-load on airflow resistivity determination and its consequences on dynamic stiffness

Airflow resistivity is a physical parameter which characterizes porous and fibrous sound absorbent materials. It is well-known that such property allows the evaluation of the acoustic behaviour of sound absorbent materials in various fields of application, including automotive noise mitigation, architectural acoustics and building acoustics. In structure-borne sound insulation, airflow resistivity is essential for the evaluation of the dynamic stiffness of porous and fibrous resilient insulating materials used as underlay in floating floors.However, an inconsistency between the dynamic stiffness and the airflow resistivity test conditions can be recognized. In order to evaluate dynamic stiffness of a resilient material, a static load of about 2 kPa is applied, while in airflow resistivity determination this condition is not explicitly required. As a result, the density of analyzed material, in dynamic stiffness and airflow measurements, is different. Since these two quantities are correlated, it is necessary to measure materials under the same conditions of applied static load.In this work the effects of static load (or density after compression) in airflow resistivity determination of various porous and fibrous resilient materials are investigated, and the consequent influence on dynamic stiffness is discussed. A simply empirical relation between density and airflow resistivity is also put forth.The main focus of this paper is to propose an harmonization among requirements of the Standards in order to prevent significant errors in dynamic stiffness determination and incorrect evaluations of the acoustic behaviour.     

静电场对静止液体压强的影响

论述了由于静电场的存在,在大气压力场中,静止液体内任意两点间的压强差与重力和静电场力的关系.     

Existence and multiplicity results for singular quasilinear elliptic equation on unbounded domain

In this paper, we are interested in the existence and multiplicity results of solutions for the singular quasilinear elliptic problem with concave–convex nonlinearities (0.1) where is an unbounded exterior domain with smooth boundary ?Ω, 1 < p < N,0 ≤ a < (N ? p) ∕ p,λ > 0,1 < s < p < r < q = pN ∕ (N ? pd),d = a + 1 ? b,a ≤ b < a + 1. By the variational methods, we prove that problem 0.1 admits a sequence of solutions u_k under the appropriate assumptions on the weight functions H(x) and H(x). For the critical case, s = q,h(x) = | x | ^{? bq}, we obtain that problem 0.1 has at least a nonnegative solution with p < r < q and a sequence of solutions u_k with 1 < r < p < q and J(u_k) → 0 as k → ∞ , where J(u) is the energy functional associated to problem 0.1 . Copyright © 2013 John Wiley & Sons, Ltd.     

Improved sensitivity of headspace gas chromatography for organic aromatic compounds

Summary The effect of adding an electrolyte and increasing the temperature on the preconcentration of volatile compounds in headspace analysis has been investigated. Quantification of the interactive effects of temperature and addition of salt on the vapor concentration is of interest for the determination of trace organic impurities in pharmaceutical base materials. This study was undertaken to investigate the quantitative effects of the addition of salts alcohols, and acetone, and of increasing the temperature on the vapor concentrations and distribution coefficients of volatile aromatic compounds (benzene, toluene, ando-xylene). It was found that the concentration of aromatic compound residues in the headspace could be increased by adding an inert salt to the water, but this effect was not very significant because of the low orginal solubility of the aromatic compounds in water. The reverse effect can be achieved by use of polar organic additives; this can be explained by the high polarizability of aromatic compounds and their greater solubility in the presence of these solvents. Presented at Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 1–3, 1999.     

A note on static spaces and related problems

In this paper we study static spaces introduced in Hawking and Ellis (1975)  [1], Fischer and Marsden (1975) [3] and Riemannian manifolds possessing solutions to the critical point equation introduced in Besse (1987)  [11], Hwang (2000)  [12]. In both cases, on the manifolds there is a function satisfying a particular Ricci–Hessian type equation (1.6). With an idea similar to that used in Cao et al. (2012)  [15], [16], we have made progress in solving the problem raised in Fischer and Marsden (1975)  [3] of classifying vacuum static spaces and in proving the conjecture proposed in Besse (1987)  [11] concerning manifolds admitting solutions to the critical point equation in general dimensions. We obtain even stronger results in dimension 3.     

Influence of cubic nonlinearity on the dispersion relation for long waves on a water surface

The influence of cubic nonlinearity on the dispersion relation for long waves on a water surface is analyzed. In the long wavelength limit, it is shown that the dispersion relation is not affected by the cubic terms. The results are compared with the dispersion relation for stationary solutions to the Korteweg—de Vries equation.     

Undulation instability in two-dimensional foams of magnetic fluid

Two-dimensional magnetic fluid foams are cellular structures whose framework is made of magnetic fluid. The features of these equilibrated patterns are driven by a control parameter: the amplitude of the applied magnetic field. When the latter is rapidly increased, an instability occurs: the walls between cells undulate. Such an instability has also been observed in other 2D cellular structures, which exist for instance in Langmuir monolayers or in magnetic garnets thin films. In this paper we give a theoretical analysis of this instability, the issues of which are shown to be well confirmed by experiments and numerical simulations. Received: 13 October 1997 / Received in final form: 28 January 1998 / Accepted: 9 March 1998     

Magnetization dynamics below of EuO and EuS

Between 4.2 K and the Curie temperatures of the cubic Heisenberg ferromagnets EuS and EuO, their homogeneous dynamic susceptibilities have been investigated by means of a broad-band reflectometer operating from 0.1 GHz to 40 GHz. For internal magnetic fields larger than the anisotropy fields H A ( T ) of both materials, their static susceptibilities exhibit a -divergence, which reveals quantitatively the dominance of dipolar-anisotropic spin-wave fluctuations. displays a Lorentzian shape the damping frequency of which obeys scaling in terms of .The scaling function agrees quantitatively with work by Frey and Schwabl [#!FS88!#] for dipolar Heisenberg ferromagnets at temperatures above T_c. Building upon their approach, the resonance frequency of the Lorentzian can be related to a memory effect in the damping determined by the large value of the relaxation rate of the longitudinal magnetization fluctuations . For EuS, this relation is substantiated directly by inelastic neutron scattering. All these features reveal the hitherto uncovered importance of the dipolar anisotropic fluctuations below T_c of ferromagnets. Received: 4 March 1998 / Accepted: 12 May 1998