The influence of slits on sound transmission through a lightweight partition

In this paper the influence on sound reduction index of the length and the depth of sound leaks at the perimeter of lightweight partitions was examined. It was shown that the most important decrease on sound reduction index is caused by the first slit between lightweight partition and one of the structural members. When the length of the slit is increased, the decrease on sound reduction index is less significative. Calculated results show the same effects as measured ones.     

The interaction between poly(N-isopropylacrylamide) and salts in aqueous media: The “salting-out” phenomenon as studied by attenuated total reflection/fourier transform infrared spectroscopy

The effect of two strong salting-out salts (Na₂SO₄ and K₂SO₄) on the temperature-induced phase-separation process in aqueous solutions of poly(N-isopropylacrylamide) (PNIPA) was examined by attenuated total reflectance/Fourier transform infrared spectroscopy, differential scanning calorimetry, and viscosity measurements. On the basis of these measurements, a detailed scenario of the phase-separation process was deduced. The phase-separation scenario of solutions containing PNIPA and water was altered in the presence of sulfate ions. Here, the sulfate ions induced partial intrachain collapse, manifested by a relatively compact structure well below the lower critical solution temperature. This led to a more gradual, smooth phase transition, with temperature-resolved intrachain collapse and interchain aggregation and a lesser extent of hysteresis. Although at the macrolevel one may not be able to differentiate among various scenarios altering the solvent into a poor solvent, the aforementioned microlevel measurements provided a way to expose the difference between raising the temperature and adding cosolutes. Follow-up studies on the effect of salting-in salts will be presented. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 33–46, 2004     

Optimal Investment in a Levy Market

In this paper we consider the optimal investment problem in a market where the stock price process is modeled by a geometric Levy process (taking into account jumps). Except for the geometric Brownian model and the geometric Poissonian model, the resulting models are incomplete and there are many equivalent martingale measures. However, the model can be completed by the so-called power-jump assets. By doing this we allow investment in these new assets and we can try to maximize the expected utility of these portfolios. As particular cases we obtain the optimal portfolios based in stocks and bonds, showing that the new assets are superfluous for certain martingale measures that depend on the utility function we use.     

Characterization of NOx species in dehydrated and hydrated Na- and Ba-Y, FAU zeolites formed in NO2 adsorption

Adsorbed ionic NO_x species formed upon the interaction of NO₂ with dehydrated or hydrated Na- and Ba-Y, FAU zeolites were characterized using FT-IR/TPD, solid state NMR, and XANES techniques. NO₂ disproportionates on both dehydrated catalyst materials forming NO⁺ and NO₃⁻ species. These ionic species are stabilized by their interactions with the negatively charged zeolite framework and the charge compensating cations (Na⁺ and Ba²⁺), respectively. Although the nature of the adsorbed NO_x species formed on the two catalysts is similar, their thermal stabilities are strongly dependent on the charge compensating cations. In the presence of water in the channels of these zeolite materials new paths open for reactions between NO⁺ and H₂O, and NO₂ and H₂O, resulting in significant changes in the adsorbed ionic species observed. These combined spectroscopic investigations afforded the understanding of the interactions between water and NO₂ on these zeolite catalysts.     

X-ray diffraction study of some mesogenic copper, nickel and vanadyl complexes

We present a comparative study of various metallomesogenic complexes, using X-ray diffraction methods. For a given ligand linked to different metal atoms (Cu, Ni, VO), the nature of this central atom influences mainly the magnetic susceptibilities of the mesophases. With different ligands, which keep the close neighbourhood of the metal atom unchanged, the apparent length of the mesogenic unit is longer for short ligands than for longer ones. This unexpected behaviour is qualitatively well explained by taking into account the global shape of the different complexes.     

Estimation of the aggregation number and core radius of microemulsions

Summary A simple working method for the estimation of the aggregation numbers and core radii from weight measurements of sodium bis-2-ethylhexylsulphosuccinate (aerosol-OT orAOT)/decane/water microemulsions of several compositions is proposed.Starting out from the hypotheses that (i) the density of the water inside the droplets is the same as that of free water, (ii) all the surfactant is localized as interface, and (iii) the penetration of the organic phase into the interface is negligible, values for the aggregation number and core radii comparable to those determined using more sophisticated methods were obtained.The results/methodological simplicity ratio may be of great advantage in kinetic work on reaction mechanisms in microemulsions.

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Abschätzung von Aggregationszahl und Radius von Mikroemulsionen

Zusammenfassung Es wird eine einfache Methode zur Abschätzung von Aggregationszahl und Core-Radius von Mikroemulsionen aus Gewichtsmessungen von Natriumbis-2-ethylhexylsulphosuccinat (aerosol-OT oderAOT)/Decan/Wasser-Mikroemulsionen verschiedener Zusammensetzung vorgeschlagen. Unter den Annahmen, daß (i) die Dichte von Wasser innerhalb der Aggregationen die gleiche als bei freiem Wasser ist, (ii) das ganze Emulsionsmittel in der Grenzfläche vorliegt und (iii) das Eindringen der organischen Phase in die Grenzfläche vernachlässigbar ist, können Werte für Aggregationszahlen und Core-Radien erhalten werden, die durchaus mit entsprechenden Werten aus aufwendigeren Methoden vergleichbar sind. Das Leistungsverhältnis (Ergebnisse/geringer Aufwand) ist sehr vorteilhaft und macht die Methode für kinetische Arbeiten zur Bestimmung von Reaktionsmechanismen in Mikroemulsionen interessant.