Combined pancreatic islet and kidney transplantation in a child with unstable type 1 diabetes and end-stage renal disease.

Islet transplantation after successful kidney transplantation is a recognized treatment for adults with diabetes and end-stage renal disease (ESRD), but has not been considered an option in the pediatric population. To our knowledge, we report the first combined islet and kidney transplant in a child. The patient was born with bilateral renal hypoplasia and was diagnosed with type 1 diabetes mellitus at age 13 months. He had erratic glycemic control and hypoglycemia unawareness. At 6 years of age, the child safely underwent simultaneous islet and live donor kidney transplantation. Although function of the islet graft was transient, the combined transplant provided significant benefits in terms of glucose control and overall growth and development. Such an approach represents a viable treatment option for pediatric patients with ESRD and unstable diabetes.

Model for the voltage steps in the breakdown of the integer quantum Hall effect.

In samples used to maintain the U.S. resistance standard the breakdown of the dissipationless integer quantum Hall effect occurs as a series of dissipative voltage steps. A mechanism for this type of breakdown is proposed, based on the generation of magnetoexcitons when the quantum Hall fluid flows past an ionized impurity above a critical velocity. The calculated generation rate gives a voltage step height in good agreement with measurements on both electron and hole gases. We also compare this model to a hydrodynamic description of breakdown.

Landau-level spectroscopy of a two-dimensional electron system by tunneling through a quantum dot.

A single InAs self-assembled quantum dot is incorporated in the barrier of a tunnel diode and used as a spectroscopic probe of an adjacent two-dimensional electron system from the Fermi energy to the subband edge. We obtain quantitative information about the energy dependence of the quasiparticle lifetime. For magnetic field B, applied parallel to the current, we observe peaks in the current-voltage characteristics I(V) corresponding to the formation of Landau levels. Close to filling factor nu=1 we observe directly the exchange enhancement of the Lande g factor.