Topology of a store-and-forward net

Bounds are obtained for the minimum average delay of equal-length messages in a store-and-forward net when the traffic level is low. Specific network topologies are shown to achieve the bound when the traffic is also uniform.     

A new topological model of the cardiac sarcolemmal Na+-Ca2+ exchanger

The current topological model of the Na+-Ca2+ exchanger consists of 11 transmembrane segments with extracellular loops a, c, e, g, i, and k and cytoplasmic loops b, d, f, h, and j. Cytoplasmic loop f, which plays a role in regulating the exchanger, is large and separates the first five from the last six transmembrane segments. We have tested this topological model by mutating residues near putative transmembrane segments to cysteine and then examining the effects of intracellular and extracellular applications of sulfhydryl-modifying reagents on exchanger activity. To aid in our topological studies, we also constructed a cysteineless Na+-Ca2+ exchanger. This mutant is fully functional in Na+ gradient-dependent 45Ca2+ uptake measurements and displays wild-type regulatory properties. It is concluded that the 15 endogenous cysteine residues are not essential for either activity or regulation of the exchanger. Our data support the current model by placing loops c and e at the extracellular surface and loops d, j, and l at the intracellular surface. However, the data also support placing Ser-788 of loop h at the extracellular surface and Gly-837 of loop i at the intracellular surface. To account for these data, we propose a revision of the model that places transmembrane segment 6 in cytoplasmic loop f. Additionally, we propose that putative transmembrane segment 9 does not span the membrane, but may form a "P-loop"-like structure.     

Light-handed Regulation of Telecommunications--The Unfortunate Experiment

This article traces the recent history of telecommunications in New Zealand from a Government-owned monopoly to a privately-owned infrastructure having the legal hallmarks of a free market. If, in a small economy, the deregulated utility still owns the local loop, the lesson to be drawn from the New Zealand experience is that it will continue to exercise monopoly power unless there is the political will and a properly funded regulator to curb its worst excesses. A free market in telecommunication services is essential for the early take up of broadband Internet.     

Balloon-borne disposable radiometer for cloud detection

A low cost, disposable instrument for measuring solar radiation during meteorological balloon flights through cloud layers is described. Using a photodiode detector and low thermal drift signal conditioning circuitry, the device showed less than 1% drift for temperatures varied from +20 °C to -35 °C. The angular response to radiation, which declined less rapidly than the cosine of the angle between the incident radiation and normal incidence, is used for cloud detection exploiting the motion of the platform. Oriented upwards, the natural motion imposed by the balloon allows cloud and clear air to be distinguished by the absence of radiation variability within cloud, where the diffuse radiation present is isotropic. The optical method employed by the solar radiation instrument has also been demonstrated to provide higher resolution measurements of cloud boundaries than relative humidity measurements alone.     

Tensile strength of eutectic,directionally solidified alloys based on the Co?Cr?C-system

The influence of various alloy elements on tensile strength of the eutectic, directionally solidified superalloy 73 C was determined. The tensile properties of the base alloy had been increased by Al, Y and C as alloying elements, while Ni and Ti showed a decreasing effect (alloy softening). However, ductility and thermo-fatigue behaviour had been influenced in a positive way be these elements. The specific mechanisms caused by the different elements are discussed.     

A prospective study of gastric and oesophageal carcinoma

A prospective study of carcinoma of the stomach and oesophagus has been carried out for 2 1/2 years. Seventy-three cases of carcinoma of the stomach, and 16 cases of carcinoma of the oesophagus have been documented. For carcinoma of the stomach, operability rate was 72-6% and resectability rate was 41-9%; overall survival was poor, 20-9% at 12 months. For those who underwent resection, survival at 12 months was 45-5%. No cases of early gastric cancer are among those studied. For carcinoma of the oesophagus, four patients had a resection, and only one has survived for more than 12 months. In the clinical sphere there is a need for early endoscopic as well as radiological investigation of dyspeptic symptoms. In the research field there is a need for studies of chemotherapy in combination with surgery in the initial treatment of gastric carcinoma.