The transfer of TEM00 and TEM01 beams through a hard-aperture

Abstract

We determine the far-field divergence angle θ ₀₀ (θ ₀₁) resulting from the diffraction of a TEM₀₀ (TEM₀₁) beam incident on a circular aperture. It is demonstrated that, with a suitable choice of the aperture radius, the ratio θ ₀₁/θ ₀₀ is enhanced to about 2, while its value is 1.64 without the aperturing effect. It is shown that this effect allows high discrimination between TEM₀₀ and TEM₀₁ modes either in the case of a spatial filter or in the case of an apertured resonator.     

Modification of porous carbon tubes with enzymes: application for biofuel cells

Enzyme biocatalyst assemblies on electrode surfaces can be used to construct efficient membrane-less biofuel cells. The present study reports on the construction of biocatalytic oxygen electrodes based on the modification of porous carbon tubes with laccase and 2,2′-azinobis-(3-ethylbenzothiazoline−6-sulfonate) (ABTS²⁻) as mediator, co-immobilized within electrochemically polymerized films. Porous carbon tubes are used as original conducting support for enzyme incorporation and for the transport of dissolved dioxygen solution via diffusive flow through the porosity. The activity of the laccase immobilized on the porous carbon support is determined. Performance of the biocathodes towards the reduction of dioxygen to water is demonstrated by chronoamperometry at +0.4 V vs. Ag/AgCl in citrate/phosphate buffer pH 3. Moreover, the current–voltage behaviour of the biocathodes show high current densities at pH 3 (a current peak equal to 280 μA cm⁻² for the biocathode based on both entrapped laccase and mediator) and a low oxygen reduction overvoltage compared to platinum electrode.     

Characterization of chirped pulses with the fractional-order Fourier transformation.

We show that the fractional-order Fourier transformation (FRT) is a suitable method to describe chirped pulses submitted to group-velocity dispersion in a linear dispersive medium. Amplitudes exhibiting different chirp coefficients are easily separated with the FRT, although they are temporally superposed.     

Spatial Scheduling With Interference Cancellation in Multiuser MIMO Systems

This paper proposes a novel downlink spatial scheduling algorithm in multiuser multiple-input-multiple-output (MIMO) systems, which selects a good combination of terminals and base station's (BS's) transmit beams so that the BS's beams nullify interstream interference at the selected terminals. In the derivation process, we reveal the new property that the optimization problem of downlink spatial scheduling is equivalent to that of uplink scheduling under the BS's zero-forcing beamforming. Using this property, an efficient downlink scheduling algorithm is presented, applying the principle of an uplink scheduling algorithm. Numerical results show that the presented spatial scheduling achieves a much higher system throughput than a multiuser MIMO system without spatial scheduling or with conventional spatial scheduling by linear processing. We also present a realistic control structure to achieve the uplink and downlink spatial scheduling in time-division duplex systems.     

Dual tunable wavelength Er,Yb:glass laser for terahertz beatfrequency generation

Dual tunable wavelength operation of Er,Yb:phosphate glass laser is reported. The spatial separation of the laser eigenstates and the use of two properly designed intracavity etalons permit one to tune the two wavelengths independently from 1540.5 to 1562.7 nm. The generated beat note, monitored using a Michelson interferometer, is experimentally shown to be adjustable from dc to 2.7 THz. The linewidth of this beat note is found to be less than 10 kHz. Several applications are discussed     

Regeneration of rat calvarial defects using a bioabsorbable membrane technique: influence of collagen cross-linking

The aim of the present study was to examine the influence of cross-linking on collagen membranes used for guided bone regeneration of calvarial defects in rats. In 48 Wistar rats, divided equally into 4 groups, 1 control and 3 experimental, standardized transosseous circular calvarial defects were made midparietally. In the control group, the defect was only covered by the soft tissue flap while in the 3 experimental groups, 3 differently cross-linked collagen membranes were interposed between the osseous defect and the overlying flap before suturing. The healing was assessed at 10, 20, and 30 days after surgery. The results showed that augmenting the degree of collagen cross-linking diminished the membrane resorption rate. Compared to the sham-operated sites, the membrane protected defects showed significantly more bone regeneration (on average 4 times more) as attested by histology and measured by histomorphometric analysis. Although the bone gain seemed to augment with increasing degrees of cross-linking, the results within the 3 experimental groups were not statistically different. Since longer healing periods might have been necessary to substantiate results within experimental groups, a study is currently undertaken to evaluate this aspect. This study demonstrated the efficacy of collagen membranes in guiding bone regeneration, as well as the importance of the type and degree of cross-linking.     

Direct evidence for dissociated megakaryocytic chimaerism in a Wiskott-Aldrich patient successfully allografted

We report a Wiskott-Aldrich patient who underwent allogeneic bone marrow transplantation from his HLA-identical sister at the age of 25. Conditioning regimen consisted of cyclophosphamide (180 mg/kg) and thoraco-abdominal irradiation (6 Grays). Cytogenetic follow-up revealed rapid and complete lymphoid chimaerism, but prolonged mixed bone marrow chimaerism. Correlative interphase cytogenetics performed on bone marrow smears using dual-colour fluorescence in situ hybridization with X and Y specific probes showed that the proportion of donor cells was significantly higher within megakaryocytes than in other lineages. This patient therefore presented with dissociated lineage engraftment, which is not exceptional in congenital diseases and aplastic anaemia, but has not previously been described in Wiskott-Aldrich syndrome. Bone marrow transplantation was successful despite this delayed engraftment which ensured adequate production in the involved cell lines.     

p53 antibodies in the saliva of patients with squamous cell carcinoma of the oral cavity

A significant age dependence of the risk of complete heart block complicating radiofrequency ablation of the AV nodal slow pathway was noticed, with no patients <45 years of age experiencing this complication.     

Characterization of yttria-stabilized zirconia thin films deposited by electron beam evaporation on silicon substrates

Structure, phase composition and electrical conductivity of thin yttria-stabilized zirconia (YSZ) films deposited by electron beam evaporation on a silicon (1 0 0) substrate at different temperatures i.e. room temperature (r.t.), 700 and 830°C, as well as the quality of the YSZ–Si interface have been investigated. The phase composition was verified by Raman spectroscopy and by infrared (i.r.) transmission measurements. The structure of films changed in agreement with their electrical conductivity depending on the deposition temperature. Both structure and thereby electrical conductivity were influenced by the high concentration of Y2O3 stabilizer used and by the post-deposition thermal treatment of films. The deposition temperature was also important in determining the quality of the YSZ–Si interface and hence the accessible sweep of the surface potential. The capacitance–voltage characteristics of the metal–insulator–semiconductor (MIS) structures incorporating YSZ films measured at r.t. showed hysteresis and positive shifts of the flat-band voltages. © 1998 Chapman & Hall