Interdigital transducer for acousto-optic tunable filter on LiNbO3

Interdigital transducers on X-cut Y-propagating lithium niobate generate parasitic Bleustein-Gulyaev waves which reduce the acoustic efficiency. An increased number of electrode pairs improves the efficiency and an AOTF driven by an RF electric power of only 6 mW can be realised     

Length-expander composite transducer and resonator excited by a perpendicular electric field

A model is developed for length-expander composite transducers and resonators excited by a perpendicular electric field. Theoretical and experimental results are reported for several structures of resonators made with metal and lithium niobate as piezoelectric materials.     

Crystalline morphology at the interface between polyethylene‐grafted glass and polyethylene

Adhesion measurements performed on a polyethylene (PE)‐grafted‐glass interface showed that the structure of the PE free chains (matrix) was an important parameter. The fracture energy was higher for interfaces prepared from a linear matrix, such as high‐density polyethylene (HDPE), than for those from a branched PE [low‐density polyethylene (LDPE)]. Therefore, the microstructure of the grafted PE/PE matrix interface or interphase was investigated as a function of the molar masses of the connectors and the structure (linear or branched) of the free PE matrix chains. As the grafted chains were linear, a cocrystalline structure with free chains of the HDPE matrix was generated. PE connecting chains led to a low capacity for cocrystallization with LDPE. Cocrystallization was studied with blends based on functionalized PE chains and PE matrices. These blends were assumed to be miscible, as substantiated by a single differential scanning calorimetry (DSC) peak. The DSC analyses were confirmed by wide‐angle X‐ray scattering, which revealed a crystalline orientation of the chains in the interphase, that is, in the vicinity of the glass surface. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 214–229, 2003     

The sulphided state of nickel molybdenum catalysts supported on zirconia and aluminates

Characterization of the sulphided Ni-MoS₂ state supported on various carriers (aluminates, zirconia) has been undertaken in order to study the influence of the carrier on the genesis of the promoted active phase, refered to as the “NiMoS” phase. The influence of the sulphidation temperature on the stability of nickel associated in that phase has also been explored. The basis of comparison is a classical Ni-MoS₂-alumina catalyst. In all these systems nickel interacts with molybdenum sulphide (decoration like position) but the “NiMoS” phase appears less stable on zirconia. On these aluminate and zirconia carriers, the charge transfer from nickel to molybdenum sulphide, as evidenced by the shifts of the active IR band of adsorbed carbon monoxide, has been found to be weaker than on the alumina supported catalyst. Such a carrier effect has been correlated with thiophene HDS activity results and discussed in terms of morphological effects as revealed by HREM.     

Rheological properties of organoclay suspensions in epoxy network precursors

This paper deals with the evolution of the state of dispersion of organically modified montmorillonites in epoxy or amine precursors. The epoxy prepolymer is a diglycidyl ether of bisphenol A (DGEBA) and the curing agent is an aliphatic diamine with a polyoxypropylene backbone (Jeffamine D2000). The clay dispersion is evaluated at the platelet scale (nanoscopic scale) from X-ray spectrometry [wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS)] and at the aggregates scale (microscopic scale) from rheological analysis. The organoclays used form gels in the monomers above the percolation threshold if no shear is applied and present a mechanical gel/sol transition when shear stress increases. Gel strength and viscosity at high shear rates are linked to the nanometric state of dispersion and reveal the existence of two different organizations depending on organoclay/monomer interactions:

(i) When the clay shows good interactions with the monomer, a significant swelling of the clay galleries by the monomer is obtained. These swollen particles lead to formation of weak gels which after shearing give high relative viscosity fluids.

(ii) When the clay develops poor interactions with the monomer, the clay tends to reduce its exchange surface with the monomer and leads to a strongly connected gel. Shear breaks down this physical network leading to a very low relative viscosity fluid composed of nonswollen particles keeping a high aspect ratio.

     

Preparation and activity of a sulfided Co-Mo/Al2O3 catalyst prepared by thermodecomposition of Co(CO)3NO

IR characterization and activity measurements of a sulfided Co-Mo/Al₂O₃ catalyst (3.6% CoO; 14% MoO₃) prepared by thermodecomposition of Co(CO)₃NO on a sulfided Mo/Al₂O₃ sample are compared to those of the conventional Co-Mo/Al₂O₃ industrial catalyst. The ex-carbonyl preparation leads to a higher degree of promotion for the Co-Mo couple, as evidenced by a two-fold increase in HDS activity and by a more intense signal of adsorbed CO on the promoted sites. On the other hand, the hydrogénation activity is not sensitive to the method of preparation.     

Preparation and stabilization of high specific area zirconia carriers

Zirconia samples have been prepared by precipitation from an aqueous solution of zirconyl nitrate followed by calcination in flowing air at temperatures up to 970 K. The textural properties (S_BET and pore size distribution) of these zirconia powders were very sensitive to the activation procedure. Calcination in carefully controlled conditions at 770 K yielded crystallized zirconia with surface area (S_BET ≈ 130 m² g⁻¹) and porosity suitable for use as a catalyst carrier.

Zirconia samples doped with yttrium, nickel or aluminium were obtained by impregnation of the amorphous hydrous oxide. For solids calcined at 770–970 K, the surface area and thermal stability were improved, but the porosity was lower.     

Tapping sensitivity to processing in short-term memory.

Examined the interference between finger tapping and searching in short-term memory (STM). 20 Ss (mean age 22.4 yrs) memorized a set of digits and then executed a series of 17 taps separated by 2 sec subjective time intervals. During each interval, a probe was presented for comparison with the items in the memory set. The amount of processing in STM was varied from series to series by manipulating the number of items in the memory set. Results show that mean duration and variability of intertap intervals increased proportionally with memory set size. This effect is explained as interference between STM processing and the timing component of the tapping performance. The authors suggest that tapping sensitivity to memory load indicates that, under some conditions, variations in tapping performance are valid indicators of STM processing requirements of a concurrent primary task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

New TE/TM polarisation splitter made in Ti:LiNbO/sub 3/ using X-cut and Z-axis propagation

A new TE/TM integrated polarisation splitter made on LiNbO/sub 3/ for an isotropic cut has been investigated. The principles of operation and measurement characteristics are presented. At 1.3 mu m wavelength, a polarisation extinction ratio of 25 dB has been obtained.<>