The evolution of the vertebrate cerebellum: absence of a proliferative external granule layer in a non-teleost ray-finned fish.

The cerebellum represents one of the most morphologically variable structures in the vertebrate brain. To shed light on its evolutionary history, we have examined the molecular anatomy and proliferation of the developing cerebellum of the North American paddlefish, Polyodon spathula. Absence of an external proliferative cerebellar layer and the restriction of Atonal1 expression to the rhombic lip and valvular primordium demonstrate that transit amplification in a cerebellar external germinal layer, a prominent feature of amniote cerebellum development, is absent in paddlefish. Furthermore, expression of Sonic hedgehog, which drives secondary proliferation in the mouse cerebellum, is absent from the paddlefish cerebellum. These data are consistent with what has been observed in zebrafish and suggest that the transit amplification seen in the amniote cerebellum was either lost very early in the ray-finned fish lineage or evolved in the lobe-finned fish lineage. We also suggest that the Atoh1-positive proliferative valvular primordium may represent a synapomorphy (shared derived character) of ray-finned fishes. The topology of valvular primordium development in paddlefish differs significantly from that of zebrafish and correlates with the adult cerebellar form. The distribution of proliferative granule cell precursors in different vertebrate taxa is thus the likely determining factor in cerebellar morphological diversity.This work was funded by the BBSRC (BB/I021507/1 to R.J.T.W; BB/F00818X/1 to C.V.H.B.), and the Fisheries Society of the British Isles (Small Research Grant to M.S.M.).This is the final version of the article. It was first available from Wiley via http://dx.doi.org/10.1111/ede.1206

Heavy-Light Decay Constants: Conclusions from the Wilson Action

We report on the results of a MILC collaboration calculation of $f_B$, $f_{B_s}$, $f_D$, $f_{D_s}$ and their ratios. We discuss the most important errors in more detail than we have elsewhere.Comment: LATTICE98(heavyqk) 3 latex pages and 3 postscript figures. The perturbative correction calculated by Kuramashi has been adjusted to take into account the fact that we match to the continuum at the kinetic mass of the heavy meson, not the pole mass. This produces a 2 to 4 MeV change in final results for decay constants, and has negligible effect on decay constant ratio

Properties of the a1 Meson from Lattice QCD

We determine the mass and decay constant of the $a_1$ meson using Monte Carlo simulation of lattice QCD. We find $M_{a_1} = 1250 \pm 80$ MeV and $f_{a_1} = 0.30 \pm 0.03 ~({\rm GeV})^2$, in good agreement with experiment.Comment: 9 page uu-encoded compressed postscript file. version appearing in Phys. Rev. Lett. 74 (1995) 459

The BKB_K Kaon Parameter in the Chiral Limit

We introduce four-point functions in the hadronic ladder resummation approach to large $N_c$ QCD Green functions. We determine the relevant one to calculate the $B_K$ kaon parameter in the chiral limit. This four-point function contains both the large momenta QCD OPE and the small momenta ChPT at NLO limits, analytically. We get $\hat B_K^\chi = 0.38 \pm 0.15$. We also give the ChPT result at NLO for the relevant four-point function to calculate $B_K$ outside the chiral limit, while the leading QCD OPE is the same as the chiral limit one.Comment: 17 page

Linear approach to the orbiting spacecraft thermal problem

We develop a linear method for solving the nonlinear differential equations of a lumped-parameter thermal model of a spacecraft moving in a closed orbit. Our method, based on perturbation theory, is compared with heuristic linearizations of the same equations. The essential feature of the linear approach is that it provides a decomposition in thermal modes, like the decomposition of mechanical vibrations in normal modes. The stationary periodic solution of the linear equations can be alternately expressed as an explicit integral or as a Fourier series. We apply our method to a minimal thermal model of a satellite with ten isothermal parts (nodes) and we compare the method with direct numerical integration of the nonlinear equations. We briefly study the computational complexity of our method for general thermal models of orbiting spacecraft and conclude that it is certainly useful for reduced models and conceptual design but it can also be more efficient than the direct integration of the equations for large models. The results of the Fourier series computations for the ten-node satellite model show that the periodic solution at the second perturbative order is sufficiently accurate.Comment: 20 pages, 11 figures, accepted in Journal of Thermophysics and Heat Transfe

High-Precision Lattice QCD Confronts Experiment

We argue that high-precision lattice QCD is now possible, for the first time, because of a new improved staggered quark discretization. We compare a wide variety of nonperturbative calculations in QCD with experiment, and find agreement to within statistical and systematic errors of 3% or less. We also present a new determination of alpha_msbar(Mz); we obtain 0.121(3). We discuss the implications of this breakthrough for phenomenology and, in particular, for heavy-quark physics.Comment: 2 figures, revte

Orbitally excited and hybrid mesons from the lattice

We discuss in general the construction of gauge-invariant non-local meson operators on the lattice. We use such operators to study the $P$- and $D$-wave mesons as well as hybrid mesons in quenched QCD, with quark masses near the strange quark mass. The resulting spectra are compared with experiment for the orbital excitations. For the states produced by gluonic excitations (hybrid mesons) we find evidence of mixing for non-exotic quantum numbers. We give predictions for masses of the spin-exotic hybrid mesons with $J^{PC}=1^{-+},\ 0^{+-}$, and$2^{+-}$.Comment: 31 pages, LATEX, 8 postscript figures. Reference adde

The continuum limit in the quenched approximation

Previous work at $6/g^2=5.7$ with quenched staggered quarks is extended with new calculations at 5.85 and 6.15 on lattices up to $32^3\times 64$. These calculations allow a more detailed study of extrapolation in quark mass, finite volume and lattice spacing than has heretofore been possible. We discuss how closely the quenched spectrum approaches that of the real world.Comment: 4 pages, uuencoded compressed PostScript, contribution to Lattice '9