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We give a ncw method for direct reconstruction of threc-dimcnsional objects from a fcw electron micrographs taken at angles which nced not exceed a range of 60 degrees. Thc method works for totally asymmctric objects, and rcquircs littlc computer timc or storage. It is also applicable to X-ray photography. and may greatly reduce the exposurc compared to(More)
Two forces are necessary and sufficient to produce the transformation of the newt neural plate from a hemispheric sheet of cells one cell thick to a keyhole shape. These forces are: (1) a regionally programmed shrinkage of the surface of the neural plate (accomplished by contraction of the apical surfaces of the neural plate cells and elongation of these(More)
The practical performance of algebraic reconstruction techniques (ART) for computed tomography (CT) depends heavily on the order in which the projections are considered. Complete orthogonalization, notwithstanding its theoretical justification, is not feasible because the computational time is prohibitive. The authors report here a scheme that yields the(More)
In a previous report we presented a novel ART technique with the projections arranged and accessed in a multilevel scheme (MLS) for efficient algebraic image reconstruction, but whether the scheme is still superior in real situations where the data are noisy is unknown. In this paper, we make a detailed comparison between MLS and the other two conventional(More)
In the face of increasing CO 2 emissions from conventional energy (gasoline), and the anticipated scarcity of crude oil, a worldwide effort is underway for cost-effective renewable alternative energy sources. Here, we review a simple line of reasoning: (a) geologists claim that much crude oil comes from diatoms; (b) diatoms do indeed make oil; (c)(More)
There are situations in the natural sciences and medicine (e.g. in electron microscopy and X-ray photography) in which it is desirable to estimate the gray levels of a digital picture at the individual points from the sums of the gray levels along straight lines (projections) at a few angles. Usually, in such situations, the picture is far from determined(More)
We predicted, and have now observed, a surface contraction wave in axolotl (Ambystoma mexicanum) embryos that appears to coincide temporally and spatially with primary neural induction and homoiogenetic induction, and with involution of the chordomesoderm. The wave starts from a focus anterior to the dorsal lip of the blastopore and spreads as an ellipse,(More)
We have discovered a series of expansion and contraction, solitary waves that correlate with discrete steps of differentiation in the urodele amphibian axolotl embryo (Ambystoma mexicanum). Here we examine in detail the proposition that the blastopore is a set of differentiation waves. We superimposed the image of the axolotl fate map onto our digitized(More)