1,091 research outputs found
Establishment of pluripotent cell lines from vertebrate species - Present status and future prospects
Pluripotent embryonic stem (ES) cells are undifferentiated cell lines derived from early embryos and are capable of unlimited undifferentiated proliferation in vitro. They retain the ability to differentiate into all cell types including germ cells in chimeric animals in vivo, and can be induced to form derivatives of all three germ layers in vitro. Mouse ES cells represent one of the most important tools in genetic research. Major applications include the targeted mutation of specific genes by homologous recombination and the discovery of new genes by gene trap strategies. These applications would be of high interest for other model organisms and also for livestock species, However, in spite of tremendous research activities, no proven ES cells colonizing the germ line have been established for vertebrate species other than mouse a nd chicken thus far. This review summarizes the current status of deriving pluripotent embryonic stem cell lines from vertebrates and recent developments in nuclear transfer technology, which may provide an alternative tool for genetic modification of livestock animals. Copyright (C) 1999 S. Karger AG, Basel
The Models of Strategic Interaction between Network and Generating Companies at Electricity Transmission Market
The paper considers the strategic interaction between network and generating companies at electricity transmission market within the simplest electric power system with two nodes. The four possible variants of the market organization are investigated: guaranteed regulated and non-regulated network monopoly, network monopoly facing potential competition from the independent network company or generating company. The possible consequences and by-effects of vertical unbundling, in particular, influence of such a regulation on the prices and network transfer capabilities, are analyzed. It is shown that the elimination of monopolistic preferences on electric power transmission with the possibility of network objects building and operation by the generating companies is an effective mechanism for electricity price reduction.oligopoly, monopoly, strategic interaction, potential competition, Nash equilibrium, electricity transmission market
Use of insulin to increase epiblast cell number: towards a new approach for improving ESC isolation from human embryos
Human embryos donated for embryonic stem cell (ESC) derivation have often been cryopreserved for 5–10 years. As a consequence, many of these embryos have been cultured in media now known to affect embryo viability and the number of ESC progenitor epiblast cells. Historically, these conditions supported only low levels of blastocyst development necessitating their transfer or cryopreservation at the 4–8-cell stage. As such, these embryos are donated at the cleavage stage and require further culture to the blastocyst stage before hESC derivation can be attempted. These are generally of poor quality, and, consequently, the efficiency of hESC derivation is low. Recent work using a mouse model has shown that the culture of embryos from the cleavage stage with insulin to day 6 increases the blastocyst epiblast cell number, which in turn increases the number of pluripotent cells in outgrowths following plating, and results in an increased capacity to give rise to ESCs. These findings suggest that culture with insulin may provide a strategy to improve the efficiency with which hESCs are derived from embryos donated at the cleavage stage.Jared M. Campbell, Michelle Lane, Ivan Vassiliev, and Mark B. Nottl
On polynomially integrable domains in Euclidean spaces
Let be a bounded domain in with smooth boundary. Denote
the Radon transform of
the characteristic function of the domain i.e., the
dimensional volume of the intersection with the hyperplane If the domain is an ellipsoid, then the function
is algebraic and if, in addition, the dimension is odd, then
is a polynomial with respect to Whether odd-dimensional
ellipsoids are the only bounded smooth domains with such a property? The
article is devoted to partial verification and discussion of this question
PP-waves with torsion and metric-affine gravity
A classical pp-wave is a 4-dimensional Lorentzian spacetime which admits a
nonvanishing parallel spinor field; here the connection is assumed to be
Levi-Civita. We generalise this definition to metric compatible spacetimes with
torsion and describe basic properties of such spacetimes. We use our
generalised pp-waves for constructing new explicit vacuum solutions of
quadratic metric-affine gravity.Comment: 17 pages, LaTeX2
A teleparallel model for the neutrino
The main result of the paper is a new representation for the Weyl Lagrangian
(massless Dirac Lagrangian). As the dynamical variable we use the coframe, i.e.
an orthonormal tetrad of covector fields. We write down a simple Lagrangian -
wedge product of axial torsion with a lightlike element of the coframe - and
show that variation of the resulting action with respect to the coframe
produces the Weyl equation. The advantage of our approach is that it does not
require the use of spinors, Pauli matrices or covariant differentiation. The
only geometric concepts we use are those of a metric, differential form, wedge
product and exterior derivative. Our result assigns a variational meaning to
the tetrad representation of the Weyl equation suggested by J.B.Griffiths and
R.A.Newing.Comment: 4 pages, REVTe
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