Increase in laser repetition rate by spectral selection

An experimental and theoretical study into the use of Fabry-Perot etalons as static repetition rate upconverters outside the laser cavity is discussed. It is shown that the output repetition rate can be increased up to 12 times while maintaining high average power     

High speed BiCMOS current mode differential track-and-hold circuit

A new principle for a high speed BiCMOS differential track-and-hold circuit based on current mode processing is presented, and simulation results are given. The main characteristics are an acquisition time of 5.5 ns for 8 bit precision and a small-signal bandwidth of 1 GHz     

Multichannel FM-TV transmission using an engineered 1.3 μmpraseodymium-doped fluoride fibre amplifier

The authors report the first use of a praseodymium-doped fluoride fibre amplifier (PDFFA) in a 24 TV channel FM-SCM transmission experiment. Twenty-four analogue FM-SCM-TV channels were amplified by a PDFFA without any observable degradation in picture quality. By using a single PDFFA as a post-amplifier, transmission over 104 km of `standard' 1.3 μm optimised fibre was demonstrated with a total loss budget of 45 dB. By using the same PDFFA as an inline amplifier, a loss budget of 53 dB was achieved     

Improved performance of subcarrier multiplexed multichannel AM-VSBvideo signal transmission using Pr3+-doped fluoride fibreamplifier

The performance of 40 channel AM-VSB video signal transmission using a Pr³⁺-doped fluoride fibre amplifier (PDFA) was examined. The PDFA improves the loss budget by 10 dB for 52 dB CNR, and distortion levels almost satisfy the CATV trunk line specifications. The video quality degradation after PDFA amplification was `imperceptible' in subjective tests     

Fluorescence flow cytometry of human leukocytes in the detection of LDL receptor defects in the differential diagnosis of hypercholesterolemia

A flow-cytometric method with fluorescence-labeled monoclonal antibodies (MABs) against the low density lipoprotein (LDL) receptor (C7A MAB) or 3,3'-dioctadecylindocarbocyanin-iodide (DiI) LDL has been developed that allows the quantification of LDL receptors on leukocytes and the identification of patients with familial hypercholesterolemia (FH) within 48 hours. Leukocytes were isolated from 10 mL anticoagulated blood by density gradient centrifugation. To induce maximal expression of LDL receptors, mononuclear cells were preincubated with either phytohemagglutinine (PHA) or lipoprotein-deficient serum (LPDS). LPDS-treated monocytes provided a more homogeneous cell population with regard to LDL receptor activity than did the PHA-treated lymphocytes; they also provided a greater discrimination between the fluorescence of the receptor probes and cellular autofluorescence. The C7A MAB was able to compete for DiI LDL binding by about 40%. In competition with unlabeled LDL, DiI LDL revealed linear binding, indicating an affinity similar to native LDL. The binding characteristics of DiI LDL were also similar to 125I-LDL binding. LDL isolated from familial defective apolipoprotein B-100 was not able to compete for DiI LDL binding on monocytes, whereas native LDL reduced it by about 80%. In monocytes from FH heterozygous patients, the cellular mean fluorescence using either C7A MAB or DiI LDL at 4 degrees C was 30% to 70%; in FH homozygotes, cellular mean fluorescence was less than 20% of that in monocytes from normal individuals. In patients with familial defective apolipoprotein B-100 antibody binding was normal, but one patient's own LDL failed to compete with normal DiI LDL for 4 degrees C binding on U937 test monocytes. Patient monocytes having internalization defects showed normal 4 degrees C DiI LDL binding, but at 20 degrees C cell-associated fluorescence was reduced by about 40%. In our study 384 hypercholesterolemic patients (preselected according to serum cholesterol levels, clinical symptoms, and family history) were analyzed for LDL receptor expression using the C7A MAB-based assay. In 71.8% of the patients with cholesterol levels higher than 300 mg/dL, an LDL receptor deficiency was observed. Apolipoprotein E isoforms and lipoprotein[a] were found to be independent from the LDL receptor status. In some patients with high cholesterol levels but normal LDL receptor expression with the C7A MAB assay, LDL receptor defects could be diagnosed when either reduced binding or internalization of DiI LDL or familial defective apolipoprotein B-100 was detected.(ABSTRACT TRUNCATED AT 400 WORDS)     

Cuprates intermediate between one and two dimensions

The key elements in all known cuprate superconductors are lightly doped CuO_i-planes. Recently a new homologous series of compounds Sr_n–1Cu_n+1O_2n have been reported in which the planes contain a parallel array of line defects which form a trellis lattice with ladder-segments of the square lattice weakly coupled through triangular line defects. The width of the ladder segments is determined by the parameter n and varies from single chains to arbitrarily wide ladders. The magnetic properties of undoped compounds will be dominated by the properties of the ladders. Heisenberg s = 1/2 ladders can have a spin liquid groundstate with a spin gap if the number of rungs is odd so that a short range RVB groundstate is predicted for such trellis lattices. Using a t-J model to describe the doped material leads to the prediction of a d-wave RVB superconducting groundstate with a large spin gap.