Synthesis and physical properties of layered silicates/polyurethane nanocomposites

Samples of polyurethane nanocomposites were synthesized using diphenylmethane diisocyanate, poly(ε‐caprolactone) diol, di(ethylene glycol), and a clay functionalized by hydroxyl groups. The inorganic content in the hybrids was 2 wt %, 4 wt %, and 8 wt %. The X‐ray analysis showed that exfoliation occurred for clay content equal to 2% (w/w), whereas for higher contents, the inorganic phase rearranges in an intercalated structure. FTIR analysis suggested that the degree of hydrogen bonding in the hard segments was greatly reduced because of the amount of silicate layers and their dispersion. The dynamic‐mechanical analysis showed that the presence of clay lamellae extends very much the temperature range before the hard domain transition, causing the loss of mechanical consistency of the samples. It is less than 100 °C for the pure polymer, and increases up to 200 °C for the nanocomposites. The permeability of water vapor decreases linearly with inorganic content up to 4% of inorganic phase, and levels off at higher concentrations. The permeability behavior, at low activities, is largely dominated by the diffusion phenomenon. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2454–2467, 2005     

A new contribution to nonlinear stability of a discrete velocity model

For a class of discrete velocity models of kinetic theory we prove exponential nonlinear conditional stability of the constant basic state in the slab [0, 1].     

Precise measurement of Γ(K→e ν(γ))/Γ(K→μ ν(γ)) and study of K→e ν γ

We present a precise measurement of the ratio R _K =Γ(K→e ν(γ))/Γ(K→μ ν(γ)) and a study of the radiative process K→e ν γ, performed with the KLOE detector. The results are based on data collected at the Frascati e ⁺ e ^? collider DAΦNE for an integrated luminosity of 2.2 fb^?1. We find R _K =(2.493±0.025_stat±0.019_syst)×10^?5, in agreement with the Standard Model expectation. This result is used to improve constraints on parameters of the Minimal Supersymmetric Standard Model with lepton flavor violation. We also measured the differential decay rate dΓ(K→e ν γ)/dE _γ for photon energies 10<E _γ < 250 MeV. Results are compared with predictions from theory.     

Heat Convection of Compressible Viscous Fluids. II

We consider steady heat convections of compressible viscous fluids in the horizontal strip domain ${z_0 < z < z_0 + 1}$ under the gravity. Pattern formations are shown uniformly for ${z_0 \geq Z_0}$ . The limit of them as ${Z_0 \rightarrow + \infty}$ is that of Oberbeck-Boussinesq equations.     

High resolution FESEM and TEM reveal bacterial spore attachment.

Transmission electron microscopy (TEM) studies in the 1960s and early 1970s using conventional thin section and freeze fracture methodologies revealed ultrastructural bacterial spore appendages. However, the limited technology at that time necessitated the time-consuming process of imaging serial sections and reconstructing each structure. Consequently, the distribution and function of these appendages and their possible role in colonization or pathogenesis remained unknown. By combining high resolution field emission electron microscopy with TEM images of identical bacterial spore preparations, we have been able to obtain images of intact and sectioned Bacillus and Clostridial spores to clearly visualize the appearance, distribution, resistance (to trypsin, chloramphenicol, and heat), and participation of these structures to facilitate attachment of the spores to glass, agar, and human cell substrates. Current user-friendly commercial field emission scanning electron microscopes (FESEMs), permit high resolution imaging, with high brightness guns at lower accelerating voltages for beam sensitive intact biological samples, providing surface images at TEM magnifications for making direct comparisons. For the first time, attachment structures used by pathogenic, environmental, and thermophile bacterial spores could be readily visualized on intact spores to reveal how specific appendages and outer spore coats participated in spore attachment, colonization, and invasion.     

A precise determination of the electroweak mixing angle from semileptonic neutrino scattering

The cross-section ratio of neutral-current and charged-current semileptonic interactions of muon-neutrinos on isoscalar nuclei has been measured with the result:R ^v =0.3093±0.0031 for hadronic energy larger than 4 GeV. From this ratio we determined the electroweak mixing angle sin² θ _W , wherem _c is the charm-quark mass in GeV/c². Comparison with direct measurements ofm _w andm _z determines the radiative shift of the intermediate boson mass Δr=0.077±0.025(exp.)±0.038(syst.), in agreement with the prediction. Assuming the validity of the electroweak standard theory we determined ?=0.990?0.013(m _c ?1.5)±0.009(exp.)±0.003(theor.).     

Analogical model for mechanical vibrations in flue organ pipes inferred by independent component analysis

Several experiments have been performed to investigate the mechanical vibrations associated with an organ pipe. The measurements have been made by using laser Doppler vibrometry, a well-known not-invasive optical measurement technique that is very widely used in structural dynamics. The recorded signals are analyzed by using a well-established decomposition method in time domain, i.e., independent component analysis. Asymptotic dynamics methods to recognize low-dimensional dynamic system associated with this wave field is then considered. The full-toned recorded signals appear decomposed into three independent components. The independent components are nonlinear due to the fractal dimension of the attractor. These results for the mechanic vibrational field are compared with those of the acoustic one. It is interesting to note that the two fields have many common characteristics. Finally, a low-dimensional dynamic system that reproduces the main characteristics of the mechanical wave field in the time and frequency domains is introduced.     

The group and the minimal polynomial of a graph

This paper presents some results linking the minimal polynomial of the adjacency matrix of a graph with its group structure. An upper bound on the order of the group is derived for graphs whose minimal and characteristic polynomials are identical. It is also shown that for a graph with transitive group, the degree of the minimal polynomial is bounded above by the number of orbits of the stabilizer of any given element. Finally, the order of the group of a point-symmetric graph with a prime number of points is shown to depend on the degree of the minimal polynomial, and an algorithm for constructing such a group is given.     

An evolution problem for a non-linear hyperbolic-parabolic system

This work concerns the initial-boundary value problem for a non-linear hyperbolic-parabolic system which governs the motion of a large class of mechanical systems.