Synthesis and evaluation of properties of novel poly(benzimidazole‐amide)s

Novel aromatic polyamides have been prepared by a combination of diacids containing preformed benzimidazole rings and aromatic diamines. By the phosphorylation method of polycondensation, polymers of high molecular weight (inherent viscosities between 0.81 and 2.13 dL/g) were obtained, which showed good solubility in polar aprotic solvents. The combination of aromatic amide linkages and benzimidazole rings along the polymer chain endowed the polymers with high thermal resistance and excellent mechanical properties. Glass transition temperatures fell in the range of 290–330 °C as measured by differential scanning calorimetry, and initial decomposition temperatures under nitrogen were over 480 °C as measured by thermogravimetric analysis. Some polymer films showed outstanding tensile strength (over 150 MPa) and moduli (up to 5 GPa). The presence of benzimidazole rings in the current polyamides greatly enhanced their hydrophilicity in comparison with classical wholly aromatic polyamides; thus, although aromatic polyamide films normally show water sorption values of only 4–8%, some of the current poly(benzimidazole amide)s show water sorption up to 19% in a 65% relative humidity atmosphere. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7566–7577, 2008     

Fluctuations and correlations in the string clustering approach

The fluctuations due to the clustering of color sources can explain the behaviour of the scaled multiplicity variance and transverse momentum fluctuations with centrality. They also predict a nonmonotonic behaviour with centrality for the multiplicity associated to high-p_T events. The clustering of color sources gives rise to an increase in the long-range correlations with centrality as well as to a supression at high centrality with respect to superposition models.     

Nonsaturation of the J/psi suppression at large transverse energy in the comovers approach

We explore the phenomenology of the localized gravity model of Randall and Sundrum where a 5-dimensional nonfactorizable geometry generates the gauge hierarchy by an exponential function called a warp factor. The Kaluza-Klein (KK) tower of gravitons in this scenario has different properties from those in factorizable models. We derive the KK graviton interactions with the standard model fields and obtain constraints from their direct production at hadron colliders as well as from virtual KK exchanges. We study the KK spectrum in e(+)e(-) annihilation and show how to determine the model parameters if the first KK state is observed.     

The surface energy of kaolinite

The surface energy of kaolinite was determined from the water adsorption isotherm, the water/kaolinite contact angle, and the surface tension of water, using a formula obtained by combining the Young equation with the general equation of pair interaction. This formula could be represented by a polynomial function whose roots gave one real value of 252.57±2.75 mJ m^–2 for the surface energy of kaolinite. An important feature of the procedure for obtaining this energy is the use of the Young equation to determine the range in which the value of the surface energy lies.     

Unusual Multilayered Structures in Poly(ethylene oxide)/Laponite Nanocomposite Films

Summary: The unusual structure of poly(ethylene oxide) (PEO) and Laponite clay in transparent nanocomposite films was investigated using scanning electron, atomic force, and optical microscopy, and X‐ray scattering. Each method is sensitive to different aspects of structural features and together they measure the resulting morphology and shear‐induced orientation. On nanometer length scales, clay platelets were found to orient in bundles while polymer crystallinity was suppressed. Microscopy led to the observation of unexpected and highly oriented multilayers on the micron length scale.

Scanning electron microscopy image of the freeze‐fractured surface of a poly(ethylene oxide)–Laponite film: the view on top of the x–y plane.     

A transmission electron microscopy study of composition in Si1− x Ge x /Si (001) quantum dots

A finite-element programme has been developed to model strain relaxation in the case of epitaxial Si_{1? x} Ge _x /Si coherent quantum dots either with or without compositional inhomogeneities. The resulting elastic displacement fields are used to calculate the intensity of dynamical plan view TEM images of such quantum dots. Various types of linear or parabolic compositional inhomogeneities are studied. TEM images of quantum dots with such inhomogeneities are calculated as well as those of quantum dots with a homogeneous composition. They are then compared with experimental images. It is shown how the analysis of the main features of these experimental images (black/white lobes and moiré-like fringes) enables us to determine the conditions in which it is possible to distinguish quantum dots with a homogeneous composition from those with compositional inhomogeneity.     

Existence and Comparison Results for First Order Periodic Implicit Difference Equations with Maxima

In this paper, we establish comparison results (maximum principles) which allow us to use the monotone method and the method of upper and lower solutions in order to build convergent sequences to the solutions of difference equations of the type j u k = f k , u k +1 , max l ] { k m h +1,…, k +1} u l , k ] I , u 0 = u T , with j u k = u k +1 m u k , I ={0,1,…, T m 1} and f ] C ( I 2 R 2 R , R ).     

Existence of positive solutions for nth-order periodic difference equations

This paper is devoted to the study of difference equations coupled with periodic boundary value conditions. We deduce the existence of at least one positive solution provided that the nonlinear part of the equation satisfies some monotonicity assumptions and the existence of a positive upper solution. The result is obtained from a new fixed point theorem based on the classical Krasnoselskii's cone expansion/contraction theorem and the constant sign properties of the related Green's function.     

Results on MeV-scale dark matter from a gram-scale cryogenic calorimeter operated above ground

Models for light dark matter particles with masses below 1 GeV/c\(^2\) are a natural and well-motivated alternative to so-far unobserved weakly interacting massive particles. Gram-scale cryogenic calorimeters provide the required detector performance to detect these particles and extend the direct dark matter search program of CRESST. A prototype 0.5 g sapphire detector developed for the \(\nu \)-cleus experiment has achieved an energy threshold of \(E_{th}=(19.7\pm 0.9)\) eV. This is one order of magnitude lower than for previous devices and independent of the type of particle interaction. The result presented here is obtained in a setup above ground without significant shielding against ambient and cosmogenic radiation. Although operated in a high-background environment, the detector probes a new range of light-mass dark matter particles previously not accessible by direct searches. We report the first limit on the spin-independent dark matter particle-nucleon cross section for masses between 140 and 500 MeV/c\(^2\).