36,983 research outputs found
The effects of growth factors on multicellular spheroids formed by chick embryonic retinal cells
Retinal cells from chick embryos aged 7.5 days of gestation were cultured for two months in a non-adherent suspension culture dish to study the effects of growth factors and co-culture with retinal pigment epithelial cells on their differentiation. Dissociated retinal cells became cellular aggregates (multicellular spheroids) within a day, and rosettes were formed in the spheroids after 2 days. Ultrastructurally, neurons of the rosettes developed connecting cilia, ellipsoids (accumulation of mitochondria), and external limiting membrane, indicative of their differentiation into photoreceptor cells. Epidermal growth factor enhanced the expression of rhodopsin by rosette-forming neurons, while basic fibroblast growth factor induced the growth of Mueller cells at 4 weeks, and their transdifferentiation into lens-epithelial-like cells at 8 weeks. Co-culture of retinal cells with retinal pigment epithelial cells enhanced the formation of rosettes in spheroids. Multicellular spheroids formed in a dish for suspension culture would provide a convenient in vitro system to examine differentiation and transdifferentiation of the retina.</p
Some Additional Solutions of Conformal Turbulence
We made a careful study of Polyakov's Diofantian equations for 2D turbulence
and found several additional CFTs which meet his criterion. This fact implies
that we need further conditions for CFT in order to determine the exponent of
the energy spectrum function.Comment: 7 pages, UT-62
Zariski Quantization as Second Quantization
The Zariski quantization is one of the strong candidates for a quantization
of the Nambu-Poisson bracket. In this paper, we apply the Zariski quantization
for first quantized field theories, such as superstring and supermembrane
theories, and clarify physical meaning of the Zariski quantization. The first
quantized field theories need not to possess the Nambu-Poisson structure.
First, we construct a natural metric for the spaces on which Zariski product
acts in order to apply the Zariski quantization for field theories. This metric
is invariant under a gauge transformation generated by the Zariski quantized
Nambu-Poisson bracket. Second, we perform the Zariski quantization of
superstring and supermembrane theories as examples. We find flat directions,
which indicate that the Zariski quantized theories describe many-body systems.
We also find that pair creations and annihilations occur among the many bodies
introduced by the Zariski quantization, by studying a simple model. These facts
imply that the Zariski quantization is a second quantization. Moreover, the
Zariski quantization preserves supersymmetries of the first quantized field
theories. Thus, we can obtain second quantized theories of superstring and
supermembranes by performing the Zariski quantization of the superstring and
supermembrane theories.Comment: 18 pages, 2 figure
Tachyon condensation and Boundary States in Bosonic String
We discuss tachyon configuration for the unoriented bosonic string theory
which produces a bosonic string theory with SO(32) gauge symmetry in ten
dimensions. It is closely related to the tachyon condensation scenario proposed
by A. Sen. We also give the boundary state description of the tachyon
condensation process, with some emphasis on the r\^ole of orbifold conformal
field theory.Comment: Proceeding of the talk given at YITP workshop ``Tachyon condensation
and boundary state''(October 27-29, 1999), latex fil
Spatial structure of Cooper pairs in nuclei
We discuss the spatial structure of the Cooper pair in dilute neutron matter
and neutron-rich nuclei by means of the BCS theory and the
Skyrme-Hartree-Fock-Bogioliubov model, respectively. The neutron pairing in
dilute neutron matter is close to the region of the BCS-BEC crossover in a wide
density range, giving rise to spatially compact Cooper pair whose size is
smaller than the average interaparticle distance. This behavior extends to
moderate low density ( of the saturation density) where the
Cooper pair size becomes smallerst ( fm). The Cooper pair in finite
nuclei also exhibits the spatial correlation favoring the coupling of neutrons
at small relative distances r \lesim 3 fm with large probability.
Neutron-rich nuclei having small neutron separation energy may provide us
opportunity to probe the spatial correlation since the neutron pairing and the
spatial correlation persists also in an area of low-density neutron
distribution extending from the surface to far outside the nucleus.Comment: 13 pages, 5 figures, chapter in "Fifty Years of Nuclear BCS", eds.
R.A. Broglia and V.Zelevinsk
Collective Excitations and Pairing Effects in Drip-Line Nuclei -- Continuum RPA in Coordinate-Space HFB --
We discuss novel features of a new continuum RPA formulated in the
coordinate-space Hartree-Fock-Bogoliubov framework. This continuum
quasiparticle RPA takes into account both the one- and two-particle escaping
channels. The theory is tested with numerical calculations for monopole, dipole
and quadrupole excitations in neutron-rich oxygen isotopes near the drip-line.
Effects of the particle-particle RPA correlation caused by the pairing
interaction are discussed in detail, and importance of the selfconsistent
treatment is emphasized.Comment: PTPTeX, 10 pages, 8 figures, talk at the Yukawa International Seminar
2001 (YKIS01) on "Physics of Unstable Nuclei", November 5-10, 2001, Kyoto,
Japa
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