The extended quadratic residue code is the only (48,24,12) self-dual doubly-even code

An extremal self-dual doubly-even binary (n,k,d) code has a minimum weight d=4/spl lfloor/n/24/spl rfloor/+4. Of such codes with length divisible by 24, the Golay code is the only (24,12,8) code, the extended quadratic residue code is the only known (48,24,12) code, and there is no known (72,36,16) code. One may partition the search for a (48,24,12) self-dual doubly-even code into three cases. A previous search assuming one of the cases found only the extended quadratic residue code. We examine the remaining two cases. Separate searches assuming each of the remaining cases found no codes and thus the extended quadratic residue code is the only doubly-even self-dual (48,24,12) code.     

Non-equilibrium particle motion in the vicinity of a single blade

The motion of sand particles close to a single moving blade was investigated using Positron Emission Particle Tracking (PEPT) during the period in which the free bed surface profile was evolving to an equilibrium shape. The area affected by the blade was divided into active and inactive regions and these were analysed separately. The characteristic heart-shape of the active region in the plan view was determined. An approximately 10-particle-diameter wide velocity transition zone is found between the two regions. While the tracer particle is in the inactive region moving away from the blade, the time dependence of the axial displacement is well described by a logarithmic relationship. The probability of particle movement towards the centre of the blade was quantified using a “central tendency” index. The calculated central tendency shows maxima at each side of the blade. The separation of the two maxima, which indicates the width of the active region, increases with fill level but is independent of rotational speed.     

Diffusion bonding of ferritic oxide dispersion strengthened alloys to austenitic superalloys

The superior high temperature mechanical strength and oxidation resistance of ferritic oxide dispersion strengthened (ODS) tubular alloys are compromised by the difficulties encountered in joining. Conventional fusion welding techniques generate a weld fusion zone which is devoid of the mechanical strength exhibited by the base material. Therefore, more sophisticated solid state joining techniques, such as diffusion bonding, must be employed when joining ODS materials. This paper describes a series of solid state diffusion bonding experiments carried out between two tubular ferritic ODS alloys and two high temperature austenitic alloys. Careful control of bonding conditions produced pressure retaining joints between one of the tubular ODS alloys and both austenitic alloys. The successful joint design was incorporated into the manufacture of a tubular creep component, which enabled a series of internally pressurized creep tests to be carried out. The microstructure developed at the bond interface of each of the four separate material couples is described and the high temperature performance of the pressure retaining joints is discussed.     

Role of Ponded Turbidity Currents in Reservoir Trap Efficiency

The capacity to store water in a reservoir declines as it traps sediment. A river entering a reservoir forms a prograding delta. Coarse sediment (e.g., sand) deposits in the fluvial topset and avalanching foreset of the delta, and is typically trapped with an efficiency near 100%. The trap efficiency of fine sediment (e.g., mud), on the other hand, may be below 100%, because some of this sediment may pass out of the reservoir without settling out. Here, a model of trap efficiency of mud is developed in terms of the mechanics of a turbidity current that plunges on the foreset. The dam causes a sustained turbidity current to reflect and form a muddy pond bounded upstream by a hydraulic jump. If the interface of this muddy pond rises above any vent or overflow point at the dam, the trap efficiency of mud drops below 100%. A model of the coevolution of topset, foreset, and bottomset in a reservoir that captures the dynamics of the internal muddy pond is presented. Numerical implementation, comparison against an experiment, and application to a field-scale case provide the basis for a physical understanding of the processes that determine reservoir trap efficiency.     

Strength of synaptic transmission at neuromuscular junctions of crustaceans and insects in relation to calcium entry

Crustacean and insect neuromuscular junctions typically include numerous small synapses, each of which usually contains one or more active zones, which possess voltage-sensitive calcium channels and are specialized for release of synaptic vesicles. Strength of transmission (the number of quantal units released per synapse by a nerve impulse) varies greatly among different endings of individual neurons, and from one neuron to another. Ultrastructural features of synapses account for some of the physiological differences at endings of individual neurons. The nerve terminals that release more neurotransmitter per impulse have a higher incidence of synapses with more than one active zone, and this is correlated with more calcium build-up during stimulation. However, comparison of synaptic structure in neurons with different physiological phenotypes indicates no major differences in structure that could account for their different levels of neurotransmitter release per impulse, and release per synapse differs among neurons despite similar calcium build-up in their terminals during stimulation. The evidence indicates differences in calcium sensitivity of the release process among neurons as an aspect of physiological specialization.     

Transconductance and mobility of Si:B delta MOSFETs

Delta-doped MOSFETs have been fabricated in MBE-grown silicon using for the first time boron as the dopant within the delta layer. Current-voltage characteristics have been measured, and secondary ion mass spectrometry (SIMS) is used to confirm the location of the delta layer and the extent of layer broadening by diffusion during processing. Precise threshold voltages of the devices are difficult to determine since the devices (which all operate in depletion mode) take several volts to switch off. Transconductances of the devices have been measured, and it is shown how analysis of these results can yield estimates of the carrier mobility for transport along the delta layers despite the uncertainty in the threshold voltage. A clear transition is observed in the results which is attributed to the formation of a parasitic surface-channel field-effect transistor, providing conclusive evidence that the devices are conducting along a delta channel for part of the measured range of applied gate biases     

Thoughts on the present and future of pediatric neurosurgery. Skull base surgery, spinal instrumentation, and neuroendoscopy

As part of a series of essays about the first 25 years of the International Society for Pediatric Neurosurgery--what we have accomplished and where we have been--I have decided to turn my attention to where we are now and where we are going. A corollary to consider, perhaps, is where we should be going. In other words, what is the appropriate relationship between pediatric neurosurgery and general neurosurgery?     

Presence of enamel on the incisors of the llama (Lama glama) and alpaca (Lama pacos)

Cytoplasmic aggregation is an early resistance-associated event that is observed in potato tissues either after penetration of an incompatible race of Phytophthora infestans, the potato late blight fungus, or after treatment with hyphal wall components (HWC) prepared from P. infestans. In potato cells in suspension culture, the number of cells with cytoplasmic aggregation increased upon treatment with HWC, but such an increase was suppressed by treatment with cytochalasin D prior to treatment with HWC. This result suggested that cytoplasmic aggregation in cultured potato cells might be connected with the association of actin filaments. To identify the molecular basis of cytoplasmic aggregation, we purified actin and actin-related proteins by affinity chromatography on a column of immobilized DNase I from cultured potato cells and isolated proteins of 43 kDa, 32 kDa and 22 kDa. Analysis of the amino-terminal amino acid sequences indicated that the 43 kDa, 32 kDa and 22 kDa proteins were potato actin, basic chitinase and osmotin-like protein, respectively. This conclusion was supported by the results of Western blotting analysis of the 43 kDa and 32 kDa proteins with antibodies against actin and basic chitinase. Binding analysis with actin coupled to actin-specific antibodies and biotinylated actin suggested that the 32 kDa and 22 kDa proteins had actin-binding activity. In addition, examination of biomolecular interactions using an optical biosensor confirmed the binding of chitinase to actin. These results imply the possibility that basic chitinase and osmotin-like protein might be involved in cytoplasmic aggregation, hereby participating. In the potato cell's defense against attack by pathogen.