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Abstract:  The propagation of long waves of finite amplitude at the interface of two viscous fluids in the presence of interfacial tension is examined. The effect of capillarity on the shape of the waves at the interface of two superposed fluids is investigated for a wide range of density differences, viscosity ratios and imposed pressure gradients. It is found that in planar geometry surface tension stabilizes the interfacial disturbances. Attention is given to the case in which the upper fluid is more dense and comprises a thin film above the lower fluid. With the heavier fluid on the top the flow pattern is always unstable when surface tension effects are neglected. In this case the interfacial waves do not grow forever and reach a finite amplitude only when the interfacial tension is greater than a critical value.

Bone marrow transplantation from unrelated donors is being used increasingly for the treatment of patients with leukemia and several other hematologic disorders. Selection of unrelated bone marrow donors currently relies on serological HLA identity and negative mixed lymphocyte reactions between donor/recipient pairs. As serological HLA-DP typing is not feasible, we used the HLA-DPB1 oligonucleotide typing method to investigate whether the current selection procedure can guarantee complete MHC class II identity. In 40 consecutive patients, one third (62/193) serologically HLA-A, -B, -C, -DR and -DQ identical donors were found to be MLC negative with a relative response below 5%. HLA-DPB1 oligonucleotide typing of these MLC negative donors revealed that again only one third (20/62) was also identical for DP with their presumptive recipients. In the majority of pairs a disparity in graft-versus-host direction or in host-versus-graft direction of at least one allele was seen. These data indicate that in spite of the strict MLC criteria used, the current procedure did not warrant complete MHC class II identity. This implies that oligotyping for DPB1 can improve matching and should be introduced for typing of volunteers. We speculate that DP differences may contribute to the higher incidence of graft -versus-host disease or graft rejection in unrelated transplants.