20-nm optical wavelength conversion using nondegenerate four-wavemixing

Wavelength conversion of optical signals over 20 nm is demonstrated using highly nondegenerate four-wave mixing in a semiconductor traveling-wave optical amplifier. This technique has the potential for extremely-high-speed operation and allows continuous tuning of both input and output wavelengths over the amplifier gain bandwidth. It is demonstrated that, even for such a large wavelength conversion range, it is possible to obtain conversion efficiencies in excess of -10 dB and high extinction ratios. The feasibility of the technique is demonstrated by system measurements at 622 Mb/s, showing a 1.1-dB power penalty at 10^-9 bit error rate (BER)     

Picosecond optical studies of 2D electron - 2D phonon dynamics

We describe recent developments in time-resolved optical measurements of electron-phonon interactions in quantum wells which reveal the fundamental two-dimensional properties of the process. Picosecond photoluminescence experiments show enhanced energy relaxation in narrow quantum wells. Time-resolved Raman measurements of inter- and intra-subband relaxation of electrons reveal the participation of confined optical phonons; in narrow quantum wells there is strong coupling to interface phonons.     

Disulphide structure of a sunflower seed albumin: conserved and variant disulphide bonds in the cereal prolamin superfamily

Disulphide mapping of a methionine-rich 2S albumin from sunflower seeds showed four intra-chain disulphide bonds which are homologous with those in a related heterodimeric albumin from lupin seeds (conglutin delta). Similar conserved disulphide bonds are also present in alpha-gliadin and gamma-gliadin storage proteins of wheat, but a lower level of conservation is present in a further related group of proteins, the cereal inhibitors of alpha-amylase and trypsin. These differences may relate to the different functions of the proteins.     

Pressure dependence of hole mobility in In1?xGaxAsyP1?y and its relation to alloy scattering

Pressure-induced changes in the hole mobility of the quaternary alloy In1?xGaxAsyP1?y up to 15 kbar indicate that alloy scattering plays an important part in the determination of the low field hole mobility.     

Temperature dependence of the Gunn threshold in GaAs

Measurement of the temperature dependence of the threshold for transferred electron instabilities in GaAs gives (1/IP(300))×(dIP/dT=?2.4±0.2×10?3 K?1, independent of carrier concentration The threshold field decreases with decreasing T and depends on carrier concentration. Reasonable agreement is obtained with Monte Carlo calculations based on ?-L-X ordering.     

40 Gbit/s transmission over 202 km of standard fibre using midspanspectral inversion

The authors demonstrate for the first time the transmission of a 4×10 Gbit/s OTDM data sequence over two unrepeatered links of 100 km of nondispersion shifted fibre. The experiment is enabled using midspan spectral inversion and electroabsorption modulator sources and demultiplexers, and results in a record bit-rate-distance product of 8.1 Tbit/s km for a single channel over standard fibre     

Immunological characterisation of barley polypeptides in lager foam

Eight monoclonal antibodies (mAb) recognising barley polypeptides have been identified from a library developed to wheat prolamins. The specificity or the mAb has been determined using enzyme-linked immunosorbent assay (ELISA) and immunoblotting. Six were of broad specificity, recognising D, B, C and γ-hordeins to varying degrees by both techniques. IFRN 0610 preferentially recognised γ-hordeins by ELISA but was highly specific for this hordein group by immunoblotting. Another mAb, IFRN 0624, bound to a M_r ∽ 18000 polypeptide belonging to the CM protein (trypsin/α-amylase inhibitor) family by immunoblotting. This, or a related protein, was detected by 0624 in all hordein fractions using ELISA. These mAb, together with two others described previously and found to recognise the repeat motif of C hordein, were used in ELISA and immunoblot analysis of Octyl-Sepharose fractions of lager foam. Hordein polypeptides were found in all foam fractions, indicating that much foam protein originates from the malt. The CM-like protein was found present in a virtually unmodified form. In contrast, the repeat motif of C hordein was not detected, indicating that it had either been destroyed or masked by other beer constituents. The foam stabilising agent, propylene glycol alginate (PGA), increased the apparent hydrophobicity of hordein fragments suggesting that at least part of the activity of PGA is mediated by interactions with the hordein components of foam.     

Biotechnology of Wheat Quality

Wheat gluten proteins are largely responsible for the visco-elastic properties that allow doughs to be processed into bread and various other food products including cakes, biscuits (cookies), pasta and noodles. Detailed biochemical and biophysical studies are revealing details of the molecular structures and interactions of the individual gluten proteins, and their roles in determining the functional properties of gluten. In particular, one group of gluten proteins, the high molecular weight (HMW) subunits of glutenin, have been studied in detail because of their role in determining the strength (elasticity) of doughs. The development of robust transformation systems for bread wheat is now allowing the role of the HMW subunits to be explored experimentally, by manipulating their amount and composition in transgenic plants. Such studies should lead to improvement of the processing properties of wheat for traditional end uses and the development of novel end uses in food processing or as raw material for other industries. © 1997 SCI.     

An overview of Internet protocols

In a very short period of time, the Internet has risen from being viewed as a peculiarity of the defence and academic community of the late sixties to become a significant component of many of our working and home lives. The possible impact of this technology has the futurists talking of the collapse of national borders, the bypass of tax systems and traditional commerce and the emancipation of the individual from the clutches of government, corporations and the boundaries of culture, gender and physical constraints. Most users' experience of the Internet is through browser software and applications such as e-mail, World Wide Web, Newsgroups and media plug-ins. Beneath this glossy, graphical, multimedia world exists the architectural and protocol components which have enabled the Internet evolution to reach into so many parts of everday life in such a short time. The aim of this paper is to outline some of these components, their characteristics and limitations, and their ongoing development to address those limitations and add new capabilities. Even though an overview of Internet protocols is included in this paper, basic knowledge of Internet technology is assumed.