Dielectric properties of thin-film ZrO<Subscript>2</Subscript> up to 50 GHz for RF MEMS switches

The dielectric properties of zirconium dioxide (ZrO₂) ceramic thin films were characterized up to 50 GHz using coplanar waveguides (CPWs) and metal–insulator–metal (MIM) capacitors with top circular electrodes. The ZrO₂ films were deposited using a chemical solution onto high-resistivity Si wafers and metal layers. The real part of the dielectric constant of approximately 22 and 26 was extracted at 50 GHz for CPW and MIM structures, respectively, and the loss tangent was approximately 0.09 at 50 GHz. C–V and I–V measurements were carried out to determine low-frequency and DC dielectric properties. The measurement results indicate that ZrO₂ is a promising material to be used as a dielectric layer for radio-frequency (RF) microelectromechanical systems (MEMS) capacitive switches.     

Simple eigenvalues for the Steklov problem in a domain with a small hole. A functional analytic approach

Let be a bounded open domain of . Let denote the outward unit normal of . We assume that the Steklov problem Δu = 0 in and on has a simple eigenvalue of . Then we consider an annular domain obtained by removing from a small‐cavity size of ε > 0, and we show that under proper assumptions there exists a real valued and real analytic function defined in an open neighborhood of (0,0) in and such that is a simple eigenvalue for the Steklov problem Δu = 0 in and on for all ε > 0 small enough, and such that . Here denotes the outward unit normal of , and δ_2,2 ≡ 1 and δ_2,n ≡ 0 if n ≥ 3. Then related statements have been proved for corresponding eigenfunctions. Copyright © 2013 John Wiley & Sons, Ltd.     

Differences in porous characteristics of styrenic monoliths prepared by controlled thermal polymerization in molds of varying dimensions

Nitroxide‐mediated polymerization was used as a model system for preparing styrenic monolithic materials with significant mesopore contents in different mold formats, with the aim of assessing the validity of pore characterization of capillary monoliths by analysis of parallel bulk polymerized precursor solution. Capillary monoliths were prepared in 250 μm id fused silica tubes (quadruplicate samples, in total 17 m), and the batch polymerizations were carried out in parallel in 100 μL microvials and regular 2 mL glass vials, both in quintuplicate. The monoliths recovered from the molds were characterized for their meso‐ and macroporous properties by nitrogen sorptiometry (three repeated runs on each sample), followed by a single analysis by mercury intrusion porosimetry. A total of 14 monolith samples were thus analyzed. A Grubbs' test identified one regular vial sample as an outlier in the sorptiometric surface area measurements, and data from this sample were consequently excluded from the pore size calculations, which are based on the same nitrogen sorption data, and also from the mercury intrusion data set. The remaining data were subjected to single factor analyses of variance analyses to test if the porous properties of the capillary monoliths were different from those of the bulk monoliths prepared in parallel. Significant differences were found between all three formats both in their meso‐ and macroporous properties. When the dimension was shrunk from conventional vial to capillary size, the specific surface area decreased from 52.2±4.7 to 34.6±1.7 m²/g. This decrease in specific surface area was accompanied by a significant shift in median diameter of the through‐pores, from 310±3.9 to 544±13 nm. None of these differences were obvious from the scanning electron micrographs that were acquired for each sample type. The common practice of determining the mesopore characteristics from analysis of samples prepared by parallel bulk polymerization and looking for changes in the macropore structure by visual assessment of SEMs are therefore both rather questionable, at least for monoliths of the kind used in this study.     

The First Synthesis of a Ribo-Hexos-5-Ulose: the L-Enantiomer

ABSTRACT

The title compound, previously unreported in either enantioform, and its 2,6-di-O-benzyl derivative have been synthesized through a stereocontrolled epimerization at C-2 of 6-O-protected methyl 3,4-O-isopropylidene-5-C-methoxy-β-D-galactopyranosides. The epimerization, performed through a high yielding sequence of oxidation-reduction owing to the cooperative role of the equatorial C-1 aglycon and the steric hindrance of the isopropylidene group, turned out to be completely diastereoselective. Whereas the unprotected L-ribo-hexos-5-ulose exists, as proved by NMR in D₂O, in five main tautomeric forms in a ratio of about 4:2:2:1:1, only two anomeric 1,4-furanosic forms are present at equilibrium in its 2,6-di-O-benzyl derivative, in ratios ranging from 10:1 to 7:3, depending on the prevalence of D₂O or CD₃CN in the solvent mixture.     

Spectral stability of the Robin Laplacian

We consider the Robin Laplacian in two bounded regions Ω₁ and Ω₂ of ℝ ^N with Lipschitz boundaries and such that Ω₂ ⊂ Ω₁, and we obtain two-sided estimates for the eigenvalues λ _n,2 of the Robin Laplacian in Ω₂ via the eigenvalues λ _{n, 1} of the Robin Laplacian in Ω₁. Our estimates depend on the measure of the set difference Ω\Ω₂ and on suitably defined characteristics of vicinity of the boundaries ∂Ω₁ and ∂Ω₂, and of the functions defined on ∂Ω₁ and on ∂Ω₂ that enter the Robin boundary conditions.     

On the angular shape of van der Waals dimers of small polar molecules

Ab initio calculations on twenty van der Waals dimers of small polar molecules at the experimentally observed intermolecular separation R, using Hartree-Fock molecular moments, show that the minima in the electrostatic interaction expanded up to R⁻⁶ converges to angular structures which are close to those observed experimentally for such complexes.     

Properties of an entropy-based signal receiver with an application to ultrasonic molecular imaging

Qualitative and quantitative properties of the finite part, H(f), of the Shannon entropy of a continuous waveform f(t) in the continuum limit are derived in order to illuminate its use for waveform characterization. Simple upper and lower bounds on H(f), based on features of f(t), are defined. Quantitative criteria for a priori estimation of the average-case variation of H(f) and log E(f), where E(f) is the signal energy of f(t) are also derived. These provide relative sensitivity estimates that could be used to prospectively choose optimal imaging strategies in real-time ultrasonic imaging machines, where system bandwidth is often pushed to its limits. To demonstrate the utility of these sensitivity relations for this application, a study designed to assess the feasibility of identification of angiogenic neovasculature targeted with perfluorocarbon nanoparticles that specifically bind to alpha(v)beta3-integrin expression in tumors was performed. The outcome of this study agrees with the prospective sensitivity estimates that were used for the two receivers. Moreover, these data demonstrate the ability of entropy-based signal receivers when used in conjunction with targeted nanoparticles to elucidate the presence of alpha(v)beta3 integrins in primordial neovasculature, particularly in acoustically unfavorable environments.     

Wave propagation in multi-wire strands by wavelet-based laser ultrasound

Methods based on guided ultrasonic waves are gaining increasing attention for the non-destructive inspection and condition monitoring of multi-wire strands used in civil structures such as prestressing tendons and cable stays. In this paper we examine the wave propagation problem in seven-wire strands at the level of the individual wires comprising the strand. Through a broad-band, laser ultrasonic setup and a time—frequency wavelet transform processing, longitudinal and flexural waves are characterized in terms of dispersive velocity and frequency-dependent attenuation. These vibrating frequencies propagating with minimal losses are identified as they are suitable for long-range inspection of the strands. In addition, the wave transmission spectra are found to be sensitive to the load level, suggesting the potential for continuous load monitoring in the field.