South Pole Telescope optics

The South Pole Telescope is a 10 m diameter, wide-field, offset Gregorian telescope with a 966-pixel, millimeter-wave, bolometer array receiver. The telescope has an unusual optical system with a cold stop around the secondary. The design emphasizes low scattering and low background loading. All the optical components except the primary are cold, and the entire beam from prime focus to the detectors is surrounded by cold absorber.     

Comparison of the measured and predicted crack propagation behaviour of Zr–2.5Nb pressure tube material

The crack propagation behaviour of Zr–2.5Nb pressure tube material was studied through comparison of the measured and predicted behaviour. Three-dimensional finite element simulations of compact tension and burst specimens were performed using the crack tip opening angle (CTOA) as a fracture criterion to allow for crack propagation. To obtain reasonable agreement with the measured force, crack extension, displacement, and crack tunnelling behaviour from compact tension simulations, a non-constant CTOA profile was required. This CTOA profile was then used as the crack propagation criterion in simulations of burst specimens where it was again found that there was reasonable agreement obtained with experiment.     

Transmission of precise phase coherent optical signals using a VCSEL stabilization system

To improve the time and frequency reference standards used for radio astronomy and high precision atomic physics applications, we describe a novel stable frequency transmission technique. The approach uses a vertical-cavity surface-emitting laser (VCSEL) based phase correction actuator. Using a frequency mixing process for feedback control, the phase noise induced along the 26 km G.655 optical fibre link was actively reduced. This was achieved by using a 1 310 nm dither controlled VCSEL phase error correction actuator together with the inherent chromatic dispersion properties of the fibre. The technique corrects phase noise and optical signal drift along the fibre at the transmission end. Fractional frequency instabilities across the G.655 fibre link of 4.44×10-12 at 1 s and 4.86×10-14 at 104 s are successfully reported.     

Simultaneous 45.2 Gbit/s 4-PAM data and 8 GHz reference frequency clock signal transmission over DWDM VCSEL channels for optical interconnects

In this paper, we propose and experimentally demonstrate a vertical cavity surface emitting laser (VCSEL)-based simultaneous 45.2 Gbit/s (2×22.6 Gbit/s) 4-PAM data and 8 GHz (2×4 GHz) phase modulated reference frequency (RF) clock signal transmission dense wavelength division multiplexing (DWDM) system for optical interconnects. Two low-cost power-efficient 10 G VCSEL channels with central wavelengths at 1 550.71 nm and 1 551.11 nm are separately modulated with 22.6 Gbit/s 4-PAM data, therefore doubling the channel bit rate. Carrier spectral efficiency per channel is further maximized by exploiting the phase attribute in transmission of a 4 Hz RF clock signal. To further maximize the network capacity, the two VCSEL channels are densely multiplexed at 0.4 nm spacing. We therefore experimentally achieve the network data rate of 45.2 Gbit/s with 8 GHz phase modulated RF clock signal. The results show that receiver sensitivities of ?11.02 dBm and ?9.98 dBm are experimentally achieved for VCSEL channels of 1 550.71 nm and 1 551.11 nm respectively without the phase modulated RF clock signal. However, the introduction of a phase modulated clock signal contributes to a maximum interference penalty of 0.57 dBm and 0.41 dBm for the considered channels respectively. Simultaneous distribution of transmission data and reference clock signal over shared network structure maximizes the carrier spectral efficiency and network capacity with low cost.     

Specific modifications of phosphatidylinositol and nonesterified fatty acid fractions in cultured porcine cardiomyocytes supplemented with n-3 polyunsaturated fatty acids

Mechanisms for the antiarrhythmic effect of n−3 polyunsaturated fatty acids (PUFA) are currently being investigated using isolated cardiac myocytes. It is still not known whether the incorporation of n−3 PUFA into membrane phospholipids is a prerequisite for its protective action or if n−3 PUFA exert antiarrhythmic effects in their nonesterified form as demonstrated by recent studies. Adult porcine cardiomyocytes were grown in media supplemented with arachidonic acid (AA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). After 24 h, analysis of total lipids showed that the myocytes were enriched with the respective fatty acids compared to control cells. Large proportions of all three fatty acids supplemented (69% AA, 72% DHA, and 66% EPA) remained unesterified. Fatty acid analysis of total phospholipids (PL) revealed that the incorporation of EPA and DHA, though small, was significantly different (P<0.05) from that of the control cells. The PL fraction was further separated into phosphatidylinositol (Pl), phosphatidylethanolamine, phosphatidylcholine, and phosphatidylserine to study the pattern of incorporation of the fatty acids in these fractions. It became apparent that EPA and DHA were selectively incorporated into the Pl fraction. This study demonstrates that in adult porcine cardiomyocytes, the n−3 PUFA supplementation selectively modulates two important lipid fractions, nonesterified fatty acid and Pl, which were implicated in the mechanisms of prevention of cardiac arrhythmias.     

New techniques for genetic development of a class of fuzzycontrollers

Presents three novel techniques for enhancing the power of a genetic algorithm (GA) used to design fuzzy systems: a new context-dependent coding (CDC) technique, a simple chromosome reordering operator to maximize efficiency, and the coevolution of controller set tests to force competence in all areas of state space. These measures are shown to lead to a considerable improvement over conventional GAs when used to design controllers for a standard problem, such as the cart-pole problem. We use an analysis of GAs by L. Altenberg (1994) to determine a performance measure that demonstrates that our coding scheme and reordering operator improve the ability of the GA to organize itself and evolve chromosomal structures that not only produce high scores, but improve the search efficiency of the genetic operators. We investigate the algorithm in a controller to provide parallel parking maneuvers for mobile robots. It is shown that the controllers developed are robust to the systematic errors that inevitably arise when controllers are transferred from a simulated environment to the real world     

Temperature dependence of the photoluminescence properties and band gap energy of InxGa1−xAs/GaAs quantum wells

The effective band gap energy of In_xGa_1−xAs/GaAs strained quantum wells (QWs) is investigated by photoluminescence spectroscopy (PL) in the range 12–295 K. The temperature dependence of the band gap energy of strained QWs correlates well with that of bulk In_xGa_1−xAs of similar composition. Deviations from the band gap variation of bulk material at low temperatures (12–90 K) are interpreted in terms of exciton localization. The differences ΔE(12 K) between the measured PL peak energies and the expected transition energies at 12 K (obtained by simulating the measured temperature dependence of the PL peak positions by the well-known Varshni relation) are suggested to be closely related to the Stokes shifts that often exist between PL and PL excitation spectra of QWs. A linear relation is found between the PL full-width at half-maximum measured at 12 K and ΔE for a range of QWs prepared under different growth conditions. Excitonic recombination is inferred to be dominant in the PL transitions at the highest temperatures investigated—even at room temperature.     

The influence of 5-azacytidine on the condensation of the short arm of rye chromosome 1R in Triticum aestivum L. root tip meristematic nuclei

This paper describes the effects of 5-azacytidine on the condensation state of rye (Secale cereale L.) chromatin introduced into the wheat genome (Triticum aestivum L. cv. Beaver). The wheat cultivar Beaver carries a translocation between the short arm of rye chromosome 1R (1RS) and the long arm of wheat chromosome 1B (1BL/1RS). 1RS can be detected using genomic in situ hybridisation and carries a ribosomal DNA (rDNA) locus that can be simultaneously detected using multiple labelling strategies. The rDNA locus divides 1RS into a distal region that is gene rich and a proximal region that is gene poor and highly methylated. 1RS also carries a large block of subtelomeric heterochromatin. The drug, which acts to inhibit DNA methylation in plants, has three pronounced effects on interphase nuclei. (1) It induces aberrant condensation of the rye subtelomeric heterochromatin and in many cases induces sister chromatid separation in the subtelomeric heterochromatin of G2 nuclei. (2) Nuclei trisomic for 1RS are observed at low frequency in treated material and are probably a consequence of aberrant sister chromatid separation or condensation. (3) The drug alters normal condensation of 1RS euchromatin. However, contrary to expectation the effect is not simply to induce decondensation. The proximal region of the arm actually condenses at low levels of drug administration while the distal region remains unaltered or increases its decondensation state. Increasing the concentration of 5-azacytidine induces a biphasic response and at the highest concentration used all regions of the arm show signs of decondensation. Thus the influence of the drug on chromatin condensation depends on the genomic structure.     

The measurement of metabolisable energy in samples of oats,barley and wheat using chicks

For each of the cereals oats, barley and wheat, metabolisable energy concentrations were estimated in 16 samples of known origin and chemical composition. Each sample was fed at three levels of substitution with a fishmeal/vitamin supplement. There was not a significant difference in metabolisable energy concentration among individual samples within the barley and wheat groups. Significant differences found among values for the oat samples did not seem to correlate in any meaningful way with chemically determined components. The overall mean values with standard deviations found for oats, barley and wheat respectively were 11.9±0.29, 12.6±0.23 and 13.6 ± 0.29 MJ kg^?1 dry matter. These results are discussed and compared with values published recently for laying hens and roosters and with average figures from tables of feedingstuffs composition in current use.