Distribution of tissue progenitors within the shield region of the zebrafish gastrula

The zebrafish has emerged as an important model system for the experimental analysis of vertebrate development because it is amenable to genetic analysis and because its optical clarity allows the movements and the differentiation of individual cells to be followed in vivo. In this paper, we have sought to characterize the spatial distribution of tissue progenitors within the outer cell layers of the embryonic shield region of the early gastrula. Single cells were labeled by iontophoretic injection of fluorescent dextrans. Subsequently, we documented their position with respect to the embryonic shield and their eventual fates. Our data show that progenitor cells of the neural, notochordal, somitic and endodermal lineages were all present within the embryonic shield region, and that these progenitors were arranged as intermingled populations. Moreover, close to the midline, there was evidence for significant biases in the distribution of neural and notochord progenitors between the layers, suggesting some degree of radial organization within the zebrafish embryonic shield region. The distributions of tissue progenitors in the zebrafish gastrula differ significantly from those in amphibians; this bears not only on interpretations of mutant phenotypes and in situ staining patterns, but also on our understanding of morphogenetic movements during gastrulation and of neural induction in the zebrafish

Characterizing the zebrafish organizer: microsurgical analysis at the early-shield stage

The appearance of the embryonic shield, a slight thickening at the leading edge of the blastoderm during the formation of the germ ring, is one of the first signs of dorsoventral polarity in the zebrafish embryo. It has been proposed that the shield plays a role in fish embryo patterning similar to that attributed to the amphibian dorsal lip. In a recent study, we fate mapped many of the cells in the region of the forming embryonic shield, and found that neural and mesodermal progenitors are intermingled (Shih, J. and Fraser, S.E. (1995) Development 121, 2755–2765), in contrast to the coherent region of mesodermal progenitors found at the amphibian dorsal lip. Here, we examine the fate and the inductive potential of the embryonic shield to determine if the intermingling reflects a different mode of embryonic patterning than that found in amphibians. Using the microsurgical techniques commonly used in amphibian and avian experimental embryology, we either grafted or deleted the region of the embryonic shield. Homotopic grafting experiments confirmed the fates of cells within the embryonic shield region, showing descendants in the hatching gland, head mesoderm, notochord, somitic mesoderm, endoderm and ventral aspect of the neuraxis. Heterotopic grafting experiments demonstrated that the embryonic shield can organize a second embryonic axis; however, contrary to our expectations based on amphibian research, the graft contributes extensively to the ectopic neuraxis. Microsurgical deletion of the embryonic shield region at the onset of germ ring formation has little effect on neural development: embryos with a well-formed and well-patterned neuraxis develop in the complete absence of notochord cells. While these results show that the embryonic shield is sufficient for ectopic axis formation, they also raise questions concerning the necessity of the shield region for neural induction and embryonic patterning after the formation of the germ ring

Thermal analysis of cathode and anode regimes of an MPD arc Summary report, Jun. 1965 - Jan. 1967

Thermal analysis of anode and cathode heat transfer in magnetohydrodynamic electric arc

GRID3D-v2: An updated version of the GRID2D/3D computer program for generating grid systems in complex-shaped three-dimensional spatial domains

In order to generate good quality systems for complicated three-dimensional spatial domains, the grid-generation method used must be able to exert rather precise controls over grid-point distributions. Several techniques are presented that enhance control of grid-point distribution for a class of algebraic grid-generation methods known as the two-, four-, and six-boundary methods. These techniques include variable stretching functions from bilinear interpolation, interpolating functions based on tension splines, and normalized K-factors. The techniques developed in this study were incorporated into a new version of GRID3D called GRID3D-v2. The usefulness of GRID3D-v2 was demonstrated by using it to generate a three-dimensional grid system in the coolent passage of a radial turbine blade with serpentine channels and pin fins

Optimal quantum algorithm for polynomial interpolation

We consider the number of quantum queries required to determine the coefficients of a degree-d polynomial over GF(q). A lower bound shown independently by Kane and Kutin and by Meyer and Pommersheim shows that d/2+1/2 quantum queries are needed to solve this problem with bounded error, whereas an algorithm of Boneh and Zhandry shows that d quantum queries are sufficient. We show that the lower bound is achievable: d/2+1/2 quantum queries suffice to determine the polynomial with bounded error. Furthermore, we show that d/2+1 queries suffice to achieve probability approaching 1 for large q. These upper bounds improve results of Boneh and Zhandry on the insecurity of cryptographic protocols against quantum attacks. We also show that our algorithm's success probability as a function of the number of queries is precisely optimal. Furthermore, the algorithm can be implemented with gate complexity poly(log q) with negligible decrease in the success probability. We end with a conjecture about the quantum query complexity of multivariate polynomial interpolation.Comment: 17 pages, minor improvements, added conjecture about multivariate interpolatio

Numerical simulation of the flow and fuel-air mixing in an axisymmetric piston-cylinder arrangement

The implicit factored method of Beam and Warming was employed to describe the flow and the fuel-air mixing in an axisymmetric piston-cylinder configuration during the intake and compression strokes. The governing equations were established on the basis of laminar flow. The increased mixing due to turbulence was simulated by appropriately chosen effective transport properties. Calculations were performed for single-component gases and for two-component gases and for two-component gas mixtures. The flow field was calculated as functions of time and position for different geometries, piston speeds, intake-charge-to-residual-gas-pressure ratios, and species mass fractions of the intake charge. Results are presented in graphical form which show the formation, growth, and break-up of those vortices which form during the intake stroke and the mixing of fuel and air throughout the intake and compression strokes. It is shown that at bore-to-stroke ratio of less than unity, the vortices may break-up during the intake stroke. It is also shown that vortices which do not break-up during the intake stroke coalesce during the compression stroke. The results generated were compared to existing numerical solutions and to available experimental data

Vortex motion in axisymmetric piston-cylinder configurations

By using the Beam and Warming implicit-factored method of solution of the Navier-Stokes equations, velocities were calculated inside axisymmetric piston cylinder configurations during the intake and compression strokes. Results are presented in graphical form which show the formation, growth and breakup of those vortices which form during the intake stroke by the jet issuing from the valve. It is shown that at bore-to-stroke ratio of less than unity, the vortices may breakup during the intake stroke. It is also shown that vortices which do not breakup during the intake stroke coalesce during the compression stroke

A VLSI design for a systolic Viterbi decoder

A systolic Viterbi decoder for convolutional codes is developed. This decoder uses the trace-back method to reduce the amount of data needed to be stored in registers. It is shown that this new algorithm requires a smaller chip size and achieves a faster decoding time than other existing methods