Sparse coding and decorrelation in primary visual cortex during natural vision

Theoretical studies suggest that primary visual cortex (area V1) uses a sparse code to efficiently represent natural scenes. This issue was investigated by recording from V1 neurons in awake behaving macaques during both free viewing of natural scenes and conditions simulating natural vision. Stimulation of the nonclassical receptive field increases the selectivity and sparseness of individual V1 neurons, increases the sparseness of the population response distribution, and strongly decorrelates the responses of neuron pairs. These effects are due to both excitatory and suppressive modulation of the classical receptive field by the nonclassical receptive field and do not depend critically on the spatiotemporal structure of the stimuli. During natural vision, the classical and nonclassical receptive fields function together to form a sparse representation of the visual world. This sparse code may be computationally efficient for both early vision and higher visual processing.     

Ecdysone analog: conversion to alpha ecdysone and 20-hydroxyecdysone by an insect

The tritium-labeled synthetic ecdysone analog Delta(7)-5beta-cholestene-2beta,-3beta,14alpha-triol-6-one terminated diapause when injected into diapausing tobacco hornworm pupae and was converted into tritium-labeled alpha-ecdysone and tritium-labeled 20-hydroxyecdysone. About half of the crystalline alpha-ecdysone and 20-hydroxyecdysone isolated from the tobacco hornworms 7(1/2) to 8(1/2) days after injection was derived from endogenous steroid precursors and half from the transformation of the synthetic ecdysone analog.     

Cell-autonomous recognition of the rust pathogen determines rp1-specified resistance in maize

The Rp1 gene of maize determines resistance to the leaf rust pathogen Puccinia sorghi. X-ray treatment of heterozygous (Rp1 Oy/rp1 oy) maize embryos generated seedlings with yellow sectors lacking. Rp1. Yellow sectored seedlings inoculated with rust spores gave rust pustule formation in yellow (Rp1-lacking) sectors and hypersensitive resistance in green tissues, thereby demonstrating that the Rp1 gene product is cellautonomous in its action. In cases where the hypersensitive reaction was initiated in green (Rp1) tissue next to a yellow sector, the hypersensitive response appeared to be propagated poorly, if at all, through Rp1-lacking cells.     

Flow Characteristics of Human Erythrocytes through Polycarbonate Sieves

We used polycarbonate sieves with uniform cylindrical pores (2.4 to 6.8 microns in diameter) to filter suspensions of human erythrocytes (mean major diameter is 7.2 microns) in Eagle-albumin solution. With 6.8-micron sieves the pressure-flow curves are convexed to the pressure-axis at low pressures and become linear with high pressures. With 4.5-micron sieves, however, the pressure-flow relationship is linear throughout the range of study. In both types of sieves, flow rate is reduced progressively with increasing concentration of red blood cells (RBC) over a range of 0.5 to 95 percent. The resistance to flow of RBC suspensions is higher in 4.5-micron than in 6.8-micron pores. With filter pore diameters of 3.0 microns or more, the RBC concentration in the filtrate was 100 percent of that in the solution being filtered, but only 70 percent with 2.4-micron pores. The observed critical pore diameter for 100 percent cell transmission agrees with theoretical calculation based on the assumption that the RBC membrane is deformable but nonextensible. The importance of cell deformation in the passage of RBC's through small pores is shown by the inability of RBC hardened in acetaldehyde to pass pores with 6.8-micron diameter.     

Observed flow compensation associated with the MOC at 26.5 degrees N in the Atlantic

The Atlantic meridional overturning circulation (MOC), which provides one-quarter of the global meridional heat transport, is composed of a number of separate flow components. How changes in the strength of each of those components may affect that of the others has been unclear because of a lack of adequate data. We continuously observed the MOC at 26.5 degrees N for 1 year using end-point measurements of density, bottom pressure, and ocean currents; cable measurements across the Straits of Florida; and wind stress. The different transport components largely compensate for each other, thus confirming the validity of our monitoring approach. The MOC varied over the period of observation by +/-5.7 x 10(6) cubic meters per second, with density-inferred and wind-driven transports contributing equally to it. We find evidence for depth-independent compensation for the wind-driven surface flow.