- Full text PDF available (16)
As in other clitellate annelids, embryonic development in the oligochaete Tubifex is characterized by the generation of five bilateral pairs of teloblasts (designated M, N, O, P and Q), which serve as embryonic stem cells to produce germ bands on either side of the embryo. A large part of the tissues comprising body segments has been assigned to the… (More)
Ectodermal segmentation in the oligochaete annelid Tubifex is a process of separation of 50-microm-wide blocks of cells from the initially continuous ectodermal germ band (GB), a cell sheet consisting of four bandlets of blast cells derived from ectoteloblasts (N, O, P and Q). In this study, using intracellular lineage tracers, we characterized the… (More)
In embryos of clitellate annelids (i.e. oligochaetes and leeches), four ectodermal teloblasts (ectoteloblasts N, O, P and Q) are generated on either side through a stereotyped sequence of cell divisions of a proteloblast, NOPQ. The four ectoteloblasts assume distinct fates and produce bandlets of smaller progeny cells, which join together to form an… (More)
We consider, in an abstract form, a system of " quantum particles " coupled to a Bose field. It is shown that, under suitable hypotheses, the composed system can have a ground state even if the uncoupled particle system has no ground state.
We present new classes of time operators of a Hamiltonian H (a self-adjoint operator) with discrete eigenvalues which may be degenerate. Moreover we formulate necessary and sufficient conditions for H to have time operators, determining the general form of them. As corollaries, non-existence theorems of time operators for some classes of H are derived.
We consider a model of quantum particles coupled to a massless quantum scalar eld, called the massless Nelson model, in a non-Fock representation of the time-zero elds which satisfy the canonical commutation relations. We show that the model has a ground state for all values of the coupling constant even in the case where no infrared cutoo is made. The… (More)
Regularities and higher order regularities of ground states of quantum field models are investigated through the fact that asymptotic annihilation operators vanish ground states. Moreover a sufficient condition for the absence of a ground state is given.
Let (T, H) be a weak Weyl representation of the canonical commutation relation (CCR) with one degree of freedom. Namely T is a symmetric operator and H is a self-adjoint operator on a complex Hilbert space H satisfying the weak Weyl relation: For all t ∈ R (the set of real numbers), e −itH D(T) ⊂ D(T) (i is the imaginary unit and D(T) denotes the domain of… (More)
We consider two kinds of stability (under a perturbation) of the ground state of a self-adjoint operator, being concerned with (i) the sector to which the ground state belongs and (ii) the uniqueness of the ground state. As an application to the Wigner-Weisskopf model which describes one mode fermion coupled to a quantum scalar eld, we prove in the massive… (More)