The Hamiltonian of an king quantum chain with a square-root-increasing transverse magnetic field is exactly diagonalized and its spectrum determined by the zeros of Charlier polynomials. We compute also the magnetization at zem temperature as a function of the position in closed form.

In a semi-insulating GaAs (S.I. GaAs) diode with an ohmic cathode, a negative differential resistance (NDR) appears at a field as low as 2 kV/cm. In the NDR region, luminescence with a broad spectrum is observed. The luminescence area is localized just in front of the anode. These results are explained on the basis of the avalanche injection effect in S.I. GaAs material. The electron temperature estimated from the luminescent spectrum is 3200 K. The avalanche multiplication is discussed in terms of the low-field avalanche scheme.

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In the present study, we examined the in vitro effect of Cryptococcus neoformans on the production of interleukin-12 (IL-12) and IL-10 by murine macrophages. At a dose of 1 x 10(5), 1 x 10(6) or 1 x 10(7) ml-1, a highly virulent strain of C. neoformans (strain YC-11) suppressed the production of IL-12p40 by a murine macrophage cell line, J774.1 stimulated with lipopolysaccharide (LPS) and interferon (IFN)-gamma, while the production of IL-10 was not inhibited, but rather slightly augmented. The suppression of IL-12p40 production did not change by neutralizing anti-IL-10 mAb. A direct contact of C. neoformans with macrophages was largely involved in this inhibitory effect, since placement of a 0.45 micron pore membrane between the organism and macrophages prevented such effect. On the other hand, the culture supernatant of YC-11 did not inhibit macrophage IL-12p40 production when used at a lower dose, which contained an equivalent amount of capsular polysaccharide to that in the supernatant of YC-11 cultured at 1 x 10(5) or 1 x 10(6) ml-1, although it showed a small suppression at higher doses. Our results suggest that C. neoformans may suppress the induction of Th1 responses by inhibiting macrophage IL-12 production predominantly through a direct contact-dependent mechanism and to a lesser extent by a certain soluble factor(s) released from this microorganism.

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