Ultragraphs and shift spaces over infinite alphabets

In this paper we further develop the theory of one-sided shift spaces over infinite alphabets, characterizing one-step shifts as edge shifts of ultragraphs and partially answering a conjecture regarding shifts of finite type (we show that there exist shifts of finite type that are not conjugate, via a conjugacy that is eventually finite periodic, to an edge shift of a graph). We also show that there exist edge shifts of ultragraphs that are shifts of finite type, but are not conjugate to a full shift, a result that is not true for edge shifts of graphs. One of the key results needed in the proofs of our conclusions is the realization of a class of ultragraph C*-algebras as partial crossed products, a result of interest on its own.     

Structural characterization of ZnO/ Er2O3 core/shell nanowires

Zinc oxide/erbium oxide core/shell nanowires are of great potential value to optoelectronics because of the possible demonstration of laser emission in the 1.5 μm range. In this paper we present a convenient technique to obtain structures of this composition. ZnO core nanowires were first obtained by a vapor–liquid–solid (VLS) method using gold as a catalyst. ZnO nanowires ranging from 50 to 100 nm in width were grown on the substrates. Erbium was incorporated into these nanowires by their exposure to Er(tmhd)₃ at elevated temperatures. After annealing at 700 C in air, the nanowires presented 1.54 μm emission when excited by any of the lines of an Ar⁺ laser. An investigation of nanowire structure by HRTEM indicates that indeed the cores consist of hexagonal ZnO grown in the 001 direction while the surface contains randomly oriented Er₂O₃ nanoparticles. EXAFS analysis reveals that the Er atoms possess a sixfold oxygen coordination environment, almost identical to that of Er₂O₃. Taken collectively, these data suggest that the overall architectures of these nanowires are discrete layered ZnO/ Er₂O₃ core/shell structures whereby erbium atoms are not incorporated into the ZnO core geometry.     

Toward bias minimization in acoustic feedback cancellation systems

A novel technique for bias suppression within acoustic feedback cancellation systems is proposed. This is achieved based on the use of all-pass filters in the forward part of the hearing aid. The poles of these filters are made time-varying, which results in a frequency response with constant magnitude and varying phase. This is a desired feature of the proposed approach, since the results from human psychoacoustics show that the human ear is not sensitive to moderate phase perturbations. The derivation of the proposed algorithms for the time variation of the location of the poles of all pass filters is based on a rigorous analysis of the phenomenon of bias in acoustic systems. Practical issues, such as the dependence of the steady-state error on the order of the all-pass filter, the number of varying poles, and their standard deviation are examined and strategies for the variation of the poles are introduced. Results obtained from a simulated hearing aid are provided to support the analysis. The quality of the processed audio signals is evaluated through subjective tests.     

Composition of Egyptian nerolì oil

The bitter orange flower oil (or neroli) is an essential product, largely used in perfumery. Neroli is obtained by hydrodistillation or steam distillation, from the flowers of bitter orange (Citrus aurantium L.). Since a long time neroli production is limited and its cost on the market is considerably high. The annual production in Tunisia and Morocco is ca. 1500 Kg, representing more than 90% of the worldwide production. A small amount ofneroli is also produced in Egypt, Spain and Comorros (not exceeding 150 kg totally). Due to the high cost, the producers and the users have tried to obtain less expensive products, with odor characters close to that of neroli oil to be used as substitute and sometimes as adulterants of the genuine oil. In this study are investigated five samples of Egyptian neroli oils produced in 2008 and 2009, in the same industrial plant, declared genuine by the producer. For all the samples the composition was determined by GC/FID and by GC/MS-LRI; the samples were also analyzed by esGC to determine the enantiomeric distribution of twelve volatiles and by GC-C-IRMS for the determination of the delta13C(VPDB) values of some mono and sesquiterpene hydrocarbons, alcohols and esters. The analytical procedures allowed to quantitatively determining 86 components. In particular the variation of the composition seems to be dependent on the period of production. In fact, the amount of linalool decreases from March to April while linalyl acetate presents an opposite trend, increasing in the same period. The RSD determined for the delta13C(VPDB) are very small (max. 3.89%), ensuring the authenticity of all samples. The results are also discussed in function of the limits provided by the European Pharmacopoeia (EP) (2004), AFNOR (1995) and ISO (2002) regulations for genuine neroli oils.     

Study of structural and dynamic properties of liquid phenyltrimethoxysilane

Herein, we present a combined experimental and computational study of liquid phenyltrimethoxysilane. A femtosecond time-resolved optical Kerr effect experiment has been performed to study the rotational diffusion of the molecule. A new all-atoms molecular model of the compound, based on the OPLS force field, has been developed to reproduce the rotational diffusion time constant and other physical and dynamic properties available in the literature. The density obtained from the simulations is 1074 ± 4 kg m(-3), which is within 1% of the experimental value of 1062 kg m(-3). The viscosity from the simulations is 1.6 ± 0.1 mPa s while the experimental value is 2.1 mPa s. The average bulk dipole moment of 1.8 ± 0.5 Debye obtained from the simulation matches the experimental value of 1.77 Debye. The average relative dielectric constant from the simulations is 3.86 ± 0.04, which is within 13% of the experimental value (4.4). The rotational diffusion time of the dipole moment obtained from the simulations is 20.39 ± 0.06 ps, which is in excellent agreement with the experimental value of 20 ± 1 ps obtained from our measurements. The new model has also been used to calculate structural and dynamic properties of the molecule not yet determined experimentally.     

Stability improvement of Cu3(BTC)2 metal-organic frameworks under steaming conditions by encapsulation of a Keggin polyoxometalate

Cu(3)(BTC)(2) with an incorporated Keggin polyoxometalate was demonstrated to be stable under steaming conditions up to 483 K, while the isostructural HKUST-1 degrades and transforms into [Cu(2)OH(BTC)(H(2)O)](n)·2nH(2)O from 343 K onwards.     

Coarse-graining MARTINI model for molecular-dynamics simulations of the wetting properties of graphitic surfaces with non-ionic, long-chain, and T-shaped surfactants

We report on a molecular dynamics investigation of the wetting properties of graphitic surfaces by various solutions at concentrations 1-8 wt. % of commercially available non-ionic surfactants with long hydrophilic chains, linear or T-shaped. These are surfactants of length up to 160 A?. It turns out that molecular dynamics simulations of such systems ask for a number of solvent particles that can be reached without seriously compromising computational efficiency only by employing a coarse-grained model. The MARTINI force field with polarizable water offers a framework particularly suited for the parameterization of our systems. In general, its advantages over other coarse-grained models are the possibility to explore faster long time scales and the wider range of applicability. Although the accuracy is sometimes put under question, the results for the wetting properties by pure water are in good agreement with those for the corresponding atomistic systems and theoretical predictions. On the other hand, the bulk properties of various aqueous surfactant solutions indicate that the micellar formation process is too strong. For this reason, a typical experimental configuration is better approached by preparing the droplets with the surfactants arranged in the initial state in the vicinity of contact line. Cross-comparisons are possible and illuminating, but equilibrium contact angles as obtained from simulations overestimate the experimental results. Nevertheless, our findings can provide guidelines for the preliminary assessment and screening of surfactants. Most importantly, it is found that the wetting properties mainly depend on the length and apolarity of the hydrophobic tail, for linear surfactants, and the length of the hydrophilic headgroup for T-shaped surfactants. Moreover, the T-shaped topology appears to favor the adsorption of surfactants onto the graphitic surface and faster spreading.