Bose-Einstein condensation of exciton polaritons.

Phase transitions to quantum condensed phases--such as Bose-Einstein condensation (BEC), superfluidity, and superconductivity--have long fascinated scientists, as they bring pure quantum effects to a macroscopic scale. BEC has, for example, famously been demonstrated in dilute atom gas of rubidium atoms at temperatures below 200 nanokelvin. Much effort has been devoted to finding a solid-state system in which BEC can take place. Promising candidate systems are semiconductor microcavities, in which photons are confined and strongly coupled to electronic excitations, leading to the creation of exciton polaritons. These bosonic quasi-particles are 10(9) times lighter than rubidium atoms, thus theoretically permitting BEC to occur at standard cryogenic temperatures. Here we detail a comprehensive set of experiments giving compelling evidence for BEC of polaritons. Above a critical density, we observe massive occupation of the ground state developing from a polariton gas at thermal equilibrium at 19 K, an increase of temporal coherence, and the build-up of long-range spatial coherence and linear polarization, all of which indicate the spontaneous onset of a macroscopic quantum phase.

[Oculocutaneous albinism: clinical, historical and anthropological aspects]. / L'albinisme oculocutané: mises au point clinique, historique et anthropologique.

Albinism represents a group of inherited abnormalities of the melanin pigment system in which the synthesis of melanin is absent or reduced, generalized (oculocutaneous albinism) or localised (ocular albinism). Recent molecular studies provide insight into the pathophysiological processes of pigmentation regulation and help our understanding of the genetic heterogeneity of human albinism. It rarely affects Europeans, frequently Africans, only a minority of Amerindians, who nevertheless, when an ethnic group is concerned, presents one of the highest incidence in the world. Historically, the African albinos were used as an alibi by the European theologians to support Adam's descent of humanity and by naturalists to affirm the alleged superiority of the white men. Anthropological data are mainly issued from Amerindians with contradictories attitudes towards albinos: both acceptance and rejection. Only the Kuna of Panama have given albinos a major place in their mythology, although in reality they frequently reject them.

Nutrition and immunity after peritoneovenous drainage of intractable ascites in cirrhotic patients.

Severe malnutrition and related impaired cell-mediated immunity are commonly found in cirrhotic patients with intractable ascites and may be responsible for the poor prognosis of these patients. The effects of LeVeen peritoneovenous shunting of ascites on protein reserves and cell-mediated immunity were studied in 31 cirrhotic patients with intractable ascites over a period of 1 year following operation. Arm-muscle circumference, serum albumin, and transferrin levels markedly increased and became close to the normal values. In the same period, delayed hypersensitivity improved. Although the lymphocyte count and the absolute T cell concentration in peripheral blood remained low after peritoneovenous shunting, the in vitro lymphoblastic transformation in response to phytohemagglutinin was augmented. An increased capacity to eat normal meals and the resumption of a good appetite due to the discontinuation of a salt-restricted diet seemed to be the most important factors in the dramatic improvement in the nutritional status of these patients. Restriction from heavy alcohol use may have also contributed, although the patients had already stopped drinking for several months before operation. Improvement in cell-mediated immunity might have been secondary to the increase in protein reserves.