A CDMA2000 zero-IF receiver with low-leakage integrated front-end

This paper describes a highly integrated CDMA 2000 US-CEL band (880-MHz) receiver. The single-chip zero-IF design incorporates all receiver signal-path functions including the low-noise amplifier (LNA) on a single die. The complete receiver design exceeds the stringent linearity and local oscillator (LO) leakage requirements for this standard arising from the coexistence with narrow-band FM signals. The integrated LNA achieves 1.0-dB noise figure with +9-dBm IIP3 at high gain, and by maintaining LO leakage to the antenna port well below -80 dBm at all gain settings, no external LNA is required. The receiver is fabricated in a 0.25-/spl mu/m 40-GHz f/sub t/ BICMOS technology, and occupies 3 mm/sup 2/.     

Structural features of U6 snRNA and dynamic interactions with other spliceosomal components leading to pre-mRNA splicing

In the spliceosome, the pre-mRNA, U2 and U6 snRNAs fold into a catalytic structure exhibiting striking similarities with domain V and VI of group II introns. Building of this tripartite structure implies that an evolutionary conserved base pairing between U4 and U6 snRNAs should be disrupted to allow potentially U6 catalytic residue to interact with U2 snRNAs and the pre-mRNA. The steps leading to U4/U6 disruption have been recently discovered and have been shown to involve a modification of the 3' end of U6 snRNA and the hnRNP C protein.     

Control of the morphology of waterborne nanocomposite films

Nanocomposite materials are prepared by drying a mixed colloidal suspension of film‐forming latex and silica. The dispersion state of the silica particles in the dry film controls the properties. We describe, with the help of some examples, how the colloidal stability of the particles in the mixed suspension dictates the final morphology of the dry film. Next, some recent work aimed at controlling the morphology by means of formulation additives is described. Such additives are either surfactants or polymer dispersants (block copolymers) which stabilize the particles (latex and/or silica) in the drying suspension. As a result of the mixing‐and‐drying preparation process, suitable additives are necessarily different from the conventional dispersants used in the formulation of composites prepared by means of melt‐processing. Copyright © 2004 Society of Chemical Industry     

Investigating Density Distributions for Tablets of Different Geometry During the Compaction of Pharmaceuticals

The axial and radial powder movements during the compaction process were investigated using flat- and curved-face punches for the case of single-ended axial strain applications. The density distributions in microcrystalline cellulose tablets were determined experimentally using a colored layer technique and digital image analysis. Nondestructive topography measurements were taken to assess the variation in surface roughness of the tablets and relate this to the forming pressure and density distribution. Results showed that the tablets produced were highly nonhomogeneous with high density regions in the "top corners" (adjacent to the moving punch surface) and "middle bottom half" for the flat-face tablets. For instance, at 92.7 MPa, density values were recorded at greater than 1.2 g/cc in the high density regions and greater than 0.6 g/cc in low density regions with regards to experimental results. High density regions were noted in the corners where the powder was in contact with the die wall for the curved-face tablets; both axial and radial powder movement was seen to be taking place. Surface topography and surface form results also showed that the geometric location of the corresponding surfaces of the tablets were relocated after the compaction process due to elastic recoil and stress relief.     

Electrode biomaterials based on immobilized laccase. Application for enzymatic reduction of dioxygen

Three different methods of immobilization of the laccase enzyme have been studied by measuring the enzyme activity of the bioelectrode and its catalytic efficiency for dioxygen reduction in the presence of the 2,2′-azinobis (3-ethylbenzothiazoline-6-sulfonate) diammonium salt (ABTS) as a redox mediator. One approach has consisted in laccase entrapment in polypyrrole matrix electrogenerated on the electrode surface. The two other approaches have concerned the grafting of laccase on an original aminopolypyrrole film and the complexation of laccase with avidin and biotin reagents. The laccase activity and the catalytic current of dioxygen reduction have demonstrated the efficiency of covalent grafting to aminopolypyrrole film. The polymer thickness was a key parameter of the catalytic efficiency and stability of this type of biocathode.     

Residual stresses in aluminium alloy friction stir welds

Residual stresses are detrimental to the fatigue, fracture and corrosion resistance of welds. The literature on residual stress measurements in aluminium alloy friction stir welds is reviewed. The results of a large number of longitudinal residual stress measurements performed by the slitting method on friction stir welds in 2024-T3, 6082-T6 and 5754-H111 aluminium alloys are compared and their origin discussed. From the current investigation, it can be derived that the type of machine used for welding has only little influence on the residual stress profile. The influence of alloy type and welding parameters on the magnitude of the residual stresses and the shape of their distribution across the weld is investigated. Their magnitude is far below the room temperature yield strength of the base material. A distribution with an ??M-shape?? is always found on age hardenable structural alloys (albeit more pronounced in 6082-T6 alloy than in 2024-T3 alloy), while a ??plateau?? is found in the case of the strain hardenable 5754 H111 alloy. The low magnitude and the differences in distribution of the longitudinal residual stress are attributed mainly to the microstructural changes in the weld centre and are discussed based on the hardness profiles performed across the welds. The paper also discusses the reasons why those results are in disagreement with a number of numerical simulations from the literature that do not account for the influence of the welding thermomechanical history on the material microstructure and properties.     

Space–Time Coding Techniques With Bit-Interleaved Coded Modulations for MIMO Block-Fading Channels

The space-time bit-interleaved coded modulation (ST-BICM) is an efficient technique to obtain high diversity and coding gain on a block-fading multiple-input multiple-output (MIMO) channel. Its maximum-likelihood (ML) performance is computed under ideal interleaving conditions, which enables a global optimization taking into account channel coding. Thanks to a diversity upper bound derived from the Singleton bound, an appropriate choice of the time dimension of the space-time coding is possible, which maximizes diversity while minimizing complexity. Based on the analysis, an optimized interleaver and a set of linear precoders, called dispersive nucleo algebraic (DNA) precoders are proposed. The proposed precoders have good performance with respect to the state of the art and exist for any number of transmit antennas and any time dimension. With turbo codes, they exhibit a frame error rate which does not increase with frame length.