Starting from a three-level atom coupled to two modes of radiation field, we derive a Raman-coupled Hamiltonian by a unitary transformation, evaluated perturbatively in coupling constants. The Rabi oscillation frequency and the collapse and revival times of the atomic coherence are found to have strikingly different photon-intensity dependence than those found previously.PACS number(s): 42.50.Hz, 42.50.Ar

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A procedure has been developed to yield infectious elementary bodies of the lymphogranuloma venereum strains LGV 434 and 404 of Chlamydia trachomatis, labelled during intracellular growth in HeLa 229 cells. The final preparation, obtained after velocity sedimentation of a polycarbonate membrane-filtered sample through a sucrose gradient, is free of host proteins and, more importantly, of chlamydia1 reticulate bodies. Using such purified preparations, it was found that the association of LGV 434 elementary bodies with HeLa 229 cultures was unaffected by the pretreatment of the host cells with a variety of lectins or with neuraminidases from Clostridium perfringens and Vibrio cholerae. The association was inhibited by dextran sulphate and by mild trypsin treatment of HeLa cultures. Treatment of purified elementary bodies with trypsin, chymotrypsin, neuraminidases and a variety of carbohydrates and lectins did not produce any change in the rate of association with HeLa cultures. Heat-inactivated elementary bodies were significantly less able to associate with the host cells.

Several aspects of the adherence of purified elementary bodies (EB) of Chlamydia trachomatis to HeLa and to McCoy cells were examined using different techniques, including an ELISA. Serovar-specific, biotinylated monoclonal antibodies were used to detect cell-bound chlamydiae. In addition, purified chlamydiae were biotinylated and their adherence properties were studied. The assays were done at 4 "C to exclude the energy-dependent internalization of the cell-bound EB and host-cell membrane recycling that occur at 37 "C. Saturation kinetics were routinely observed at 4 "C, and the rate of adherence remained linear for approximately 60 min. Lineweaver-Burk analysis of the kinetics data showed that adherence of any one serovar was competitively inhibited by other serovars of C. trachomatis. This competition for the same receptor on the two alternative hosts, HeLa and McCoy, was also seen when the adherence assays were done at 37°C in the presence of sodium azide, an energy poison that inhibits endocytosis of cell-bound chlamydiae. Chlamydiae exposed to 56 "C for 5 min, or treated with low doses of trypsin, failed to exhibit competitive inhibition, having suffered considerable loss of the ability to adhere to host-cells. These data suggest that heat-and trypsin-labile chlamydial moieties participate in the adherence reaction, and that oculo-genital serovars of C. trachomatis, including that of lymphogranuloma venereum, attach to the same receptor on the host-cell membrane.

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that STR does not rule out such objects. Now, the momentum 4-vector of a Tachyon is necessarily space-like and consequently, the sign of energy no longer Lorentz-invariant. Thus a Tachyon will be found to have negative energy in certain inertial frames. The authors noted that in the latter, the sign of time-intervals will also be reversed. A negative energy Tachyon traveling backward in time could now be reinterpreted as a positive energy particle traveling forward in time. This reinterpretation could be done consistently as was shown by several examples. A quantum field theory of free spinless Tachyons was suggested by Feinberg (1967). M. Arons and Sudarshan reexamined this model and showed that the model did not possess invariance under the Poincaré group. An alternative version was constructed by them that possessed the desired invariance property but no local commutativity. Subsequently, Dhar and Sudarshan constructed a model of a neutral scalar Tachyon with Yukawa coupling to Fermions. The model had unusual features such as the emission of a Tachyon by a Fermion as a real process and the need for an additional non-local interaction. Prof. Sudarshan, in association with J. Narlikar, studied Tachyons in the context of cosmology in 1976. One of their conclusions is that any primordial Tachyons that might have been created at the beginning are unlikely to have survived to the present era.