New insights on amorphous silicon-nitride microcavities

All amorphous silicon-nitride planar optical microcavities operating in the visible range have been grown by plasma enhanced chemical vapor deposition. The luminescence intensity of the N-rich silicon-nitride layer from a microcavity with 6 period distributed Bragg reflectors (DBRs) is two order of magnitude higher than that of the luminescent layer without the cavity. Moreover, a strong directionality of the microcavities emission can be observed. Such results can be ascribed to the anisotropic optical density of states induced in the Fabry–Perot structure. The quality factors of the resonators are strictly correlated to the number of periods of the DBRs.     

Stochastic phase lockings in a relaxation oscillator forced by a periodic input with additive noise: A first-passage-time approach

Noise effects on phase lockings in a system consisting of a piecewise-linear van der Pol relaxation oscillator driven by a periodic input are studied. The problem of finding the period of the oscillator is reduced to the first-passage-time problem of the Ornstein-Uhlenbeck process with time-varying boundary. The probability density functions of the first-passage time are used to define the operator which governs a transition of an input phase density after one cycle of the oscillator. Phase lockings in a stochastic sense are investigated on the basis of the density evolution by the operator.     

Experimental indications for the response of the spectators to the participant blast

Precise momentum distributions of identified projectile fragments, formed in the reactions 238U+Pb and 238U+Ti at 1A GeV, are measured with a high-resolution magnetic spectrometer. With increasing mass loss, the velocities first decrease as expected from previously established systematics, then level off, and finally increase again. Light fragments are on the average even faster than the projectiles. This finding is interpreted as the response of the spectators to the participant blast. The reacceleration of projectile spectators is sensitive to the nuclear mean field and provides a new tool for investigating the equation of state of nuclear matter.     

A biofunctional polymeric coating for microcantilever molecular recognition

An innovative route to activate silicon microcantilevers (MCs) for label free molecular recognition is presented. The method consists in coating the underivatized MCs with a functional ter-polymer based on N,N-dimethylacrylamide (DMA) bearing N-acryloyloxysuccinimide (NAS) and 3-(trimethoxysilyl)propyl-methacrylate (MAPS), two functional monomers that confer to the polymer the ability to react with nucleophilic species on biomolecules and with glass silanols, respectively. The polymer was deposited onto MCs by dip coating. Polymer coated MCs were tested in both static and dynamic modes of actuation, featuring detection of DNA hybridization as well as protein/protein interaction. In the dynamic experiments, focused on protein detection, the MCs showed an average mass responsivity of 0.4 Hz/pg for the first resonant mode and of 2.5 Hz/pg for the second resonant mode. The results of the static experiments, dedicated to DNA hybridization detection, allowed for direct estimation of the DNA duplex formation energetics, which resulted fully consistent with the nominal expected values. These results, together with easiness and cheapness, high versatility, and excellent stability of the recognition signal, make the presented route a reliable alternative to standard SAM functionalization (for microcantilevers (MCs) and for micro-electro-mechanical systems (MEMS) in general).     

A generalized integro-differential theory of nonlocal elasticity of n-Helmholtz type—part II: boundary-value problems in the one-dimensional case

Meccanica - This paper is the second in a series of two that deal with a generalized theory of nonlocal elasticity of n-Helmholtz type. This terminology is motivated by the fact that the...     

Mechanism of imidazole catalysis in the curing of epoxy resins

The mechanism of imidazole catalysis in the curing of epoxy resins was studied using the PGE/1-methylimidazole, 2-methylimidazole, and 1,2-dimethylimidazole model systems and another model system based on trichloromethylethylene oxide. It was demonstrated that imidazolium systems, generated in the curing reaction, show an inherent instability leading to cleavage of an N? C bond or the 2-C? H bond (2-unsubstituted imidazoles). Fourier-transform infrared spectroscopy was used to follow specific changes in the IR spectrum of the curing mixture during polymerization. The identification of carbonyl absorptions occurring during the polymerization led to the conclusion that ketone formation is a general occurrence in the cure of epoxides with nitrogen compounds. We have also shown that imidazoles are regenerated during the curing process by at least two routes. One pathway for the regeneration of the catalyst involves N-dealkylation of the imidazole via a substitution process. Another route, β-elimination, afforded carbonyl compounds, which account for the previously unexplained appearence of infrared bands in the 1650–1770 cm^?1 region during the curing process. These investigations demonstrated the true catalytic function of the imidazole. Possible mechanisms for the regeneration of the catalyst are also suggested.     

Experimental evidence of guided-resonances in photonic crystals with aperiodically ordered supercells

We report on the first experimental evidence of guided resonances (GRs) in photonic crystal slabs based on aperiodically ordered supercells. Using Ammann-Beenker (quasiperiodic, eightfold symmetric) tiling geometry, we present our study on the fabrication, experimental characterization, and full-wave numerical simulation of two representative structures (with different filling parameters) operating at near-IR wavelengths (1300-1600 nm). Our results show a fairly good agreement between measurements and numerical predictions and pave the way for the development of new strategies (based on, e.g., the lattice symmetry breaking) for GR engineering.