Linear solutions for cryptographic nonlinear sequence generators

This letter shows that linear Cellular Automata based on rules 90/150 generate all the solutions of linear difference equations with binary constant coefficients. Some of these solutions are pseudo-random noise sequences with application in cryptography: the sequences generated by the class of shrinking generators. Consequently, this contribution show that shrinking generators do not provide enough guarantees to be used for encryption purposes. Furthermore, the linearization is achieved through a simple algorithm about which a full description is provided

STEREO and Wind Observations of Intense Cyclotron Harmonic Waves at the Earth's Bow Shock and Inside the Magnetosheath

We present the first observations of electron cyclotron harmonic waves at the Earth's bow shock from STEREO and Wind burst waveform captures. These waves are observed at magnetic field gradients at a variety of shock geometries ranging from quasi-parallel to nearly perpendicular along with whistler mode waves, ion acoustic waves, and electrostatic solitary waves. Large amplitude cyclotron harmonic waveforms are also observed in the magnetosheath in association with magnetic field gradients convected past the bow shock. Amplitudes of the cyclotron harmonic waves range from a few tens to more than 500 millivolts/meter peak-peak. A comparison between the short (15 meters) and long (100 meters) Wind spin plane antennas shows a similar response at low harmonics and a stronger response on the short antenna at higher harmonics. This indicates that wavelengths are not significantly larger than 100 meters, consistent with the electron cyclotron radius. Waveforms are broadband and polarizations are distinctively comma-shaped with significant power both perpendicular and parallel to the magnetic field. Harmonics tend to be more prominent in the perpendicular directions. These observations indicate that the waves consist of a combination of perpendicular Bernstein waves and field-aligned waves without harmonics. A likely source is the electron cyclotron drift instability which is a coupling between Bernstein and ion acoustic waves. These waves are the most common type of high-frequency wave seen by STEREO during bow shock crossings and magnetosheath traversals and our observations suggest that they are an important component of the high-frequency turbulent spectrum in these regions

Observation of a westward travelling surge from satellites at low, medium and high altitudes

The motion of discontinuity; electric potential and current structure of the event; energy source and flow; wave-particle interactions; and particle acceleration are addressed using wave, electron, ion mass spectrometer, dc electric field, and magnetic field observation from the Isee-1, NOAA-6, and the 1976-059 geostationary satellite

THE DEVELOPMENT OF HIGH PLASTICITY CLAY SOILS THROUGH WEATHERING OF DEVONIAN SLATES IN SOUTH DEVON

Cattell, A.C. 1998. The development of high plasticity clay soils through weathering of Devonian slates in south Devon. Geoscience in south-west England, 9, 209-213. Clay-rich subsoils are developed from Devonian slates across south Devon. Weathering of the slate causes a progressive disaggregation to silty clay, with little change in the clay mineralogy. Although the clay size fraction (and hence plasticity) of individual soil samples varies with the degree of breakdown of slate clasts, the plasticity of completely weathered material is controlled by the mineralogy of the parent slate. Soils on Lower Devonian slates almost all have low to intermediate plasticity, those developed on Upper Devonian slates have intermediate to high plasticity, whilst very high plasticities soils only occur on Middle Devonian slates. These types are geographically widespread: Upper Devonian purple slates in Plymouth and Newton Abbot produce indistinguishable soils 40 km apart, and pale yellow high plasticity soils are developed on Middle Devonian slates in Torquay, Dartington and Plympton. Previous work has shown that most slates, including Middle Devonian, have the clay assemblage illite + chlorite +/-kaolinite. New data presented here show that the highest plasticity soils are restricted to particular Middle Devonian slates which have low Fe and Mg and high Al, and consequently have the assemblage illite + kaolinite. The non-chloritic slate unit is widespread but its extent remains to be determined. A.C.Cattell, Rodney Broom Associates