Adsorption and two-body recombination of atomic hydrogen on 3^3He-4^4He mixture films

We present the first systematic measurement of the binding energy $E_a$ of hydrogen atoms to the surface of saturated $^3$He-$^4$He mixture films. $E_a$ is found to decrease almost linearly from 1.14(1) K down to 0.39(1) K, when the population of the ground surface state of $^3$He grows from zero to $6\times10^{14}$ cm$^{-2}$, yielding the value $1.2(1)\times 10^{-15}$ K cm$^2$ for the mean-field parameter of H-$^3$He interaction in 2D. The experiments were carried out with overall $^3$He concentrations ranging from 0.1 ppm to 5 % as well as with commercial and isotopically purified $^4$He at temperatures 70...400 mK. Measuring by ESR the rate constants $K_{aa}$ and $K_{ab}$ for second-order recombination of hydrogen atoms in hyperfine states $a$ and $b$ we find the ratio $K_{ab}/K_{aa}$ to be independent of the $^3$He content and to grow with temperature.Comment: 4 pages, 4 figures, all zipped in a sigle file. Submitted to Phys. Rev. Let

In situ functionalization of graphene

While the basal plane of graphene is inert, defects in it are centers of chemical activity. An attractive application of such defects is towards controlled functionalization of graphene with foreign molecules. However, the interaction of the defects with reactive environment, such as ambient, decreases the efficiency of functionalization and makes it poorly controlled. Here, we report a novel approach to generate, monitor with time resolution, and functionalize the defects in situ without ever exposing them to the ambient. The defects are generated by an energetic argon plasma and their properties are monitored using in situ Raman spectroscopy. We find that these defects are functional, very reactive, and strongly change their density from ≈1 × 1013 cm−2 to ≈5 × 1011 cm−2 upon exposure to air. We perform the proof of principle in situ functionalization by generating defects using the argon plasma and functionalizing them in situ using ammonia functional. The functionalization induces the n-doping with a carrier density up to 5 × 1012 cm−2 in graphene and remains stable in ambient conditions

Arterio-enteric fistula in failed enteric-drained pancreas transplants: an impending danger

Enteric drainage is the preferred method of exocrine diversion in simultaneous kidney-pancreas transplantation. Because of improvements in immunosuppression, enteric drainage has become the preferred method of pancreas transplantation in general. Although associated with less potential complications than bladder-drained pancreas, potentially lethal arterio-enteric fistulas in the setting of nonfunctioning allografts represent a constant threat. We herein present a case report, a review of the literature, and a call for caution