Protocolos de selección y estudio del donante y receptor aplicables a la práctica chilena, en trasplante de intestino

ResumenLa insuficiencia intestinal se define como la pérdida de la autonomía nutricional debido a disfunción intestinal. Su única opción de tratamiento adecuado es la Nutrición Parenteral Total Central. El trasplante de intestino se presenta como una alternativa de tratamiento.Los resultados iniciales del trasplante de intestino evidenciaron una alta incidencia de rechazo, infección y complicaciones técnicas que frenaron el desarrollo de esta técnica, sin embargo con la disminución de los problemas técnicos por la experiencia acumulada y la mejoría de los tratamientos inmunosupresores los resultados mejoraron en forma importante. Si bien en Chile la experiencia es limitada la indicación para su realización existe y aumenta debido al interés creciente por los buenos resultados demostrados a nivel mundial.En este breve artículo se revisan las indicaciones y contraindicaciones del procedimiento, el estudio del receptor y del donante, la técnica de procuramiento y se analizan los resultados actuales y las perspectivas futuras.SummaryIntestinal insufficiency is defined as the loss of nutricional autonomy as a result of intestinal malfunction. The only adequate treatment option is Total Central Parenteral Nutrition. Intestinal transplantation is proposed as a treatment alternative.Initial intestinal transplantation results showed a high incidence of rejection, infection and technical complications that stunted the development of this technique. Results have however greatly improved with the enhancement of immunosuppressive therapy and increased experience which has led to a subsequent decrease in technical problems.Even though Chile has limited experience, the demand for intestinal transplantation exists and increases due to a rising interest brought about by the good results presented worldwide.This short article addresses the indications and contraindications of this procedure, receptor and donor studies, the procurement technique and also analyzes current results and future prospects

Josephson junction array type I-V characteristics of quench-condensed ultra thin films of Bi

In this communication we report studies of d.c current-voltage (I-V) characteristics of ultra thin films of Bi, quench condensed on single crystal sapphire substrates at T = 15K. The hysteretic I-V characteristics are explained using a resistively and capacitively shunted junction (RCSJ) model of Josephson junction arrays. The Josephson coupling energy($E_J$) and the charging energy($E_c$) are calculated for different thickness($d$) values. A low resistance state is found in the low current regime below the critical current, $I_c$. This resistance $R_0$ is found to have a minimum at a particular thickness ($d_c$) value. Reflection High Energy Electron Diffraction (RHEED) studies are done on these films. A distinct appearance of a diffuse ring near $d_c$ is observed in the diffraction images, consistent with the recent STM studies(Ekinci and Valles, PRL {\bf 82}(1999) 1518). These films show an irreversible annealing when temperature is increased. The annealing temperature ($T_a$) also has a maximum at the same thickness. Althoguh the R$_s$ vs T of quench condensed Bi films suggest that the films are uniform, our results indicate that even in thick films, the order parameter is not fully developed over the complete area of the film. These results are discussed qualitatively.Comment: 6 pages, 6 figure

Inter- and Intragranular Effects in Superconducting Compacted Platinum Powders

Compacted platinum powders exhibit a sharp onset of diamagnetic screening at $T \simeq 1.9$ mK in zero magnetic field in all samples investigated. This sharp onset is interpreted in terms of the intragranular transition into the superconducting state. At lower temperatures, the magnetic ac susceptibility strongly depends on the ac field amplitude and reflects the small intergranular critical current density $j_{c}$. This critical current density shows a strong dependence on the packing fraction f of the granular samples. Surprisingly, $j_{c}$ increases significantly with decreasing f ($j_{c}(B=0, T=0) \simeq 0.07$ A/cm$^{2}$ for f = 0.67 and $j_{c}(B=0, T=0) \simeq 0.8$ A/cm$^{2}$ for f = 0.50). The temperature dependence of $j_{c}$ shows strong positive curvature over a wide temperature range for both samples. The phase diagrams of inter- and intragranular superconductivity for different samples indicate that the granular structure might play the key role for an understanding of the origin of superconductivity in the platinum compacts.Comment: 11 pages including 9 figures. To appear in Phys. Rev. B in Nov. 0