Nonadiabatic Effects in Quantum-Classical Molecular Dynamics

In molecular dynamics applications there is a growing interest in mixed quantum-classical models. The article is concerned with the so-called QCMD model. This model describes most atoms of the molecular system by the means of classical mechanics but an important, small portion of the system by the means of a wavefunction. We review the conditions under which the QCMD model is known to approximate the full quantum dynamical evolution of the system. In most quantum-classical simulations the Born-Oppenheimer model (BO) is used. In this model, the wavefunction is adiabatically coupled to the classical motion which leads to serious approximation deficiencies with respect to non-adiabatic effects in the fully quantum dynamical description of the system. In contrast to the BO model, the QCMD model does include non-adiabatic processes, e.g., transitions between the energy levels of the quantum system. It is demonstrated that, in mildly non-adiabatic scenarios, so-called surface hopping extensi..

Non-immunological enhancement of tumour transplantability in x-irradiated host animals.

MSC-10 tumour cells (derived from a chemically induced pulmonary squamous-cell carcinoma in DBA/2 mice) were inoculated intramuscularly into thymectomized, X-irradiated isogeneic mice, either 48 h or 6 weeks after thymectomy and X-irradiation. Normal mice and immunologically reconstituted mice served as controls. A marked enhancement in frequency of tumour takes was observed in all groups of animals inoculated with tumour cells 48 h after whole:-body X-irradiation, whether thymectomized, immunologically reconstituted or not. The TD50 decreased to less than 1/10 of that observed in unirradiated controls. When mice were inoculated with tumour cells 6 weeks after X-irradiation, the incidence of tumour takes was similar to that of unirradiated controls, including the thymectomized-irradiated group, which was still severely immunodeficient as measured by antibody formation and skin graft rejection. The experiments indicate that whole-body X-irradiation creates a condition that favours tumour cell survival or growth. This "permissive state" exists only shortly after X-irradiation and is not correlated with the host's level of immunocompetence

Properties of rat tracheal epithelial cells separated based on expression of cell surface alpha-galactosyl end groups.

We used Griffonia (bandeiraea) simplicifolia I (GS I) lectin and flow cytometry to isolate subsets of rat tracheal epithelial cells based on the presence or absence of cell surface alpha-galactosyl end groups. These fractions were designated GS I-positive and -negative, respectively. Ninety-eight percent of the cells in the GS I-positive fraction expressed cell surface alpha-galactosyl end groups; 95% had immunocytochemically detectable keratin 14-related protein (a basal cell marker) and 98% lacked alcian blue-periodic acid-Schiff (AB-PAS)-stained cytoplasmic granules. More than 90% of the GS I-positive cells had a high nuclear-to-cytoplasm ratio, had tonofilaments, and lacked organelles characteristic of other differentiated cell types; they were thus classified as basal cells. In bioassays, the GS I-positive fraction had a colony-forming efficiency greater than or equal to that of native tracheal cell suspensions, and the cells were able to repopulate denuded tracheal grafts with ciliated, secretory, and basal cells. More than 99% of the cells in the GS I-negative fraction lacked cell surface alpha-galactosyl end groups, 98% did not stain for keratin 14-related protein, 54% had significant numbers of AB-PAS-stained cytoplasmic granules, and 16% were identified as ciliated cells. The GS I-negative fraction had a lower colony-forming efficiency than the GS I-positive fraction but, it too, was able to repopulate denuded tracheal grafts with a complete mucociliary epithelium. These results show that both GS I-positive and -negative cells had the potential to proliferate and differentiate into the major tracheal cell types