Departure characteristics of the large-scale circulation are studied in relation to extreme drought and flood years in northeastern Brazil identified from a collective of long-term rainfall stations and series of river discharge. Ship observations during 191 1--72 compiled with a one degree square resolution and extending between 30"N and 30"s from the African coast to the eastern Pacific form a major observational basis.The rainy season of northeastern Brazil is narrowly centred around March/April and is related to the southernmost seasonal migration of a lower-tropospheric confluence axis over the adjacent eastern tropical Atlantic. The 'S&cas' of CearA province are characterized by an equatorward expansion of the South Atlantic, and a poleward retraction of the North Atlantic, highassociated with a northward displacement of the enclosed near-equatorial trough of low pressure. Concurrently, the zonally oriented bands of maximum cloudiness and precipitation frequency stay farther north, the North Atlantic trades weaken, and the South Atlantic trades become stronger than in the long-term mean. The sea surface temperature pattern during a deficient rainy season in northeast Brazil is characterized by positive departures in a broad band across the North Atlantic and in the eastern Pacific, and anomalously cold waters in most of the South and equatorial Atlantic. During abundant rainy seasons in northeast Brazil, departure patterns are approximately inverse to those typical of drought years.A strong negative linkage exists between northeast Brazil rainfall and sea surface temperature along the Ecuador/Peru coast. This seems to be caused by inverse long-term pressure variations over the eastern South Pacific and South Atlantic oceans, which in turn may be part of large-scale mass adjustments of the Southern Oscillation type.Development of the equatorward expansions of the North and South Atlantic highs, pre-season precipitation in northeast Brazil and the Guayanas, and location of the cloudiness and precipitation belts over the adjacent western tropical Atlantic, are among the more promising predictors for seasonal foreshadowing of extreme rainy season behaviour in northeast Brazil.

Using only the known short-distance behavior of quantum chromodynamics it is possible to prove that, for sufficiently large quark mass m , and fixed antiquark mass, the dimeson ( Q 2 q 2 ) must be stable against strong decay into two mesons. The binding energy is $ m a f [ l + O ( m -I ) ] . We then study systems in which Q is c or b, using the many-body confining interaction that comes from a Born-Oppenheimer approximation to the MIT bag model. The calculations were performed using the Green's-function Monte Carlo method. The 1+ isoscalar dimeson T ( b b z d ) is bound by -70 MeV with respect to two B mesons; it can only decay weakly, therefore. The calculations of the dimesons ( c c q q ' ) and ( b c q q ' ) are more uncertain, but indicate that the latter may also be bound.

We prove that, at the frequencies generally proposed for extracranial stimulation of the brain, it is not possible, using any superposition of external current sources, to produce a three-dimensional local maximum of the electric field strength inside the brain. The maximum always occurs on a boundary where the conductivity jumps in value. Nevertheless, it may be possible to achieve greater two-dimensional focusing and shaping of the electric field than is currently available. Towards this goal we have used the reciprocity theorem to present a uniform treatment of the electric field inside a conducting medium produced by a variety of sources: an external magnetic dipole (current loop), an external electric dipole (linear antenna), and surface and depth electrodes. This formulation makes use of the lead fields from magneto- and electroencephalography. For the special case of a system with spherically symmetric conductivity, we derive a simple analytic formula for the electric field due to an external magnetic dipole. This formula is independent of the conductivity profile and therefore embraces spherical models with any number of shells. This explains the "insensitivity" to the skull's conductivity that has been described in numerical studies. We also present analytic formulas for the electric field due to an electric dipole, and also surface and depth electrodes, for the case of a sphere of constant conductivity.

Electrical conductivities of compact, spongiosum, and bulk layers of the live human skull were determined at varying frequencies and electric fields at room temperature using the four-electrode method. Current, at higher densities that occur in human cranium, was applied and withdrawn over the top and bottom surfaces of each sample and potential drop across different layers was measured. We used a model that considers variations in skull thicknesses to determine the conductivity of the tri-layer skull and its individual anatomical structures. The results indicate that the conductivities of the spongiform (16.2-41.1 milliS/m), the top compact (5.4-7.2 milliS/m) and lower compact (2.8-10.2 milliS/m) layers of the skull have significantly different and inhomogeneous conductivities. The conductivities of the skull layers are frequency dependent in the 10-90 Hz region and are non-ohmic in the 0.45-2.07 A/m2 region. These current densities are much higher than those occurring in human brain.

We have found weak long-range antiferromagnetic order in the quasi-two-dimensional insulating oxide KCr 3 ͑OD͒ 6 ͑SO 4 ͒ 2 which contains Cr 3ϩ Sϭ3/2 ions on a kagomé lattice. In a sample with Ϸ76% occupancy of the chromium sites the ordered moment is 1.1(3) B per chromium ion which is only one-third of the Néel value g B Sϭ3 B . The magnetic unit cell equals the chemical unit cell, a situation which is favored by interplane interactions. Gapless quantum spin fluctuations (⌬/k B Ͻ0.25 K) with a bandwidth of 60 K ӷT N ϭ1.6 K are the dominant contribution to the spin correlation function S(Q,) in the ordered phase.