Captured and cross-linked palladium nanoparticles

Polystyrene-poly(ethylene glycol) resin-captured cross-linked palladium nanopaticles were prepared via a straightforward route, and their heterogeneous behavior was truly confirmed by various tests. They were applied to aqueous Suzuki cross-coupling reactions with various aryl bromides and recycled up to six times without loss of activity.     

Microcapsules made of weak polyelectrolytes: templating and stimuli-responsive properties

Hollow microcapsules composed of the weak polyelectrolytes poly(allylamine hydrochloride) (PAH) and poly(methacrylic acid) (PMA) are templated on silicon oxide particles using the layer-by-layer adsorption. The colloidal template is removed with a buffer system of hydrofluoric acid and ammonium fluoride. With this buffer system, the template can be dissolved in mild pH conditions, where the polymeric layers are still stable. The morphology and the thickness of the resulting capsules are investigated with atomic force microscopy. The resulting hollow capsules show pH-dependent properties. The shells are stable over a broad pH range and swell and immediately dissolve for pH values below 2.3 and above 11. If the molecular weight of the poly(methacrylic acid) is increased, the enhanced entanglement of the polymers results in a reversible swelling of the capsules at low and at high pH. The swelling degree is probed with confocal laser scanning microscopy. In addition to the pH-dependent size variations, the different ionization degree of poly(methacrylic acid) as a function of pH is used for the selective binding of calcium ions.     

Complete characterization of periodic optical sources by use of sampled test-plus-reference interferometry

An interferometric technique measuring the time-dependent electric field of a periodic optical source that uses samples of its interference with a reference source of short optical pulses is presented. Compared with other test-plus-reference techniques such as spectral interferometry and Fourier-transform spectroscopy, the technique is applicable when the signal under test and the reference signal do not originate from the same source. It is highly sensitive and allows the direct real-time characterization of optical sources and the extraction of a coherent periodic signal in an incoherent background.     

Interferometric technique for measuring broadband ultrashort pulses at the sampling limit

We present a new technique for measuring ultrashort optical pulses by use of spectral phase interferometry for direct electric-field reconstruction that is suitable for large bandwidth pulses. The method does not require generation of a replica of the pulse to be measured and encodes the spectral phase information in a spatial interference pattern. A major advantage of this method is that the spectral sampling saturates the Whittaker-Shannon bound. Moreover, the technique allows for the characterization of some types of space-time coupling. An experimental demonstration of the technique is presented.     

Auditory processing of real and illusory changes in frequency modulation (FM) phase

Auditory processing of frequency modulation (FM) was explored. In experiment 1, detection of a tau-radians modulator phase shift deteriorated as modulation rate increased from 2.5 to 20 Hz, for 1- and 6-kHz carriers. In experiment 2, listeners discriminated between two 1-kHz carriers, where, mid-way through, the 10-Hz frequency modulator had either a phase shift or increased in depth by deltaD% for half a modulator period. Discrimination was poorer for deltaD = 4% than for smaller or larger increases. These results are consistent with instantaneous frequency being smoothed by a time window with a total duration of about 110 ms. In experiment 3, the central 200-ms of a 1-s 1-kHz carrier modulated at 5 Hz was replaced by noise, or by a faster FM applied to a more intense 1-kHz carrier. Listeners heard the 5-Hz FM continue at the same depth throughout the stimulus. Experiments 4 and 5 showed that, after an FM tone had been interrupted by a 200-ms noise, listeners were insensitive to the phase at which the FM resumed. It is argued that the auditory system explicitly encodes the presence, and possibly the rate and depth, of FM in a way that does not preserve information on FM phase.     

Steady light diffusion application to rheology: a new tool for the characterization of concentrated suspensions

We present new developments of steady light diffusion applied to rheology. Though many techniques allow the structural investigation of diluted or transparent media, very few give direct information on optically dense systems. The technique proposed here is based on the diffusion approximation and is thus valid for sheared, time-dependent flows.After recalling important theoretical results, we show the techniques ability to determine typical sizes and orientation of structures in shear flows for various concentrated suspensions (emulsions, and an industrial softener). In particular, it is able to demonstrate the effect of shear on the orientation of anisotropic objects. Moreover, the use of simple structural models incorporating the measured anisotropy allows good predictions of experimental rheological measurements. This new technique, applicable to a wide range of colloidal systems, is very helpful to characterize the shear induced structural organization of optically dense materials.This paper was presented at the first Annual European Rheology Conference (AERC) held in Guimarães, Portugal, September 11-13, 2003.     

Fiber-optic-based absolute displacement sensors at 1500 nm by means of a variant of channeled spectrum signal recovery

An absolute displacement-sensing system based on channeled spectrum processing capable of simultaneous interrogation of fiber Bragg gratings and fiber-optic interferometric sensors is presented in which the role of the optical spectrometer is performed by a scanning Fabry-Perot filter. We demonstrate a resolution of +/-50 nm with an estimated dynamic range of 1 part in 10(5).     

Redox-triggered molecular movement in a multicomponent metal complex in solution and in the solid state

The Cu(I) and Cu(II) complexes of the new 1,8-diferro-cenylmethyl-4,11-dimethyl-1,4,8,11-tetraazacyclotetra-decane ligand (denoted L) have been isolated and characterized by X-ray structure determination and electrochemical studies. The Cu(I) complex presents an unprecedented stability toward dioxygen. The two complexes adopt two energetically distinct and stable geometries, which differ mainly by the relative positioning of the substituents above or below the cyclam plane. Triggered by a copper-centered electron transfer, a fast and reversible motion of the noncoordinating subunits is obtained in homogeneous solution and in the solid state.