Exciton-polariton topological insulator.

Topological insulators-materials that are insulating in the bulk but allow electrons to flow on their surface-are striking examples of materials in which topological invariants are manifested in robustness against perturbations such as defects and disorder1. Their most prominent feature is the emergence of edge states at the boundary between areas with different topological properties. The observable physical effect is unidirectional robust transport of these edge states. Topological insulators were originally observed in the integer quantum Hall effect2 (in which conductance is quantized in a strong magnetic field) and subsequently suggested3-5 and observed6 to exist without a magnetic field, by virtue of other effects such as strong spin-orbit interaction. These were systems of correlated electrons. During the past decade, the concepts of topological physics have been introduced into other fields, including microwaves7,8, photonic systems9,10, cold atoms11,12, acoustics13,14 and even mechanics15. Recently, topological insulators were suggested to be possible in exciton-polariton systems16-18 organized as honeycomb (graphene-like) lattices, under the influence of a magnetic field. Exciton-polaritons are part-light, part-matter quasiparticles that emerge from strong coupling of quantum-well excitons and cavity photons19. Accordingly, the predicted topological effects differ from all those demonstrated thus far. Here we demonstrate experimentally an exciton-polariton topological insulator. Our lattice of coupled semiconductor microcavities is excited non-resonantly by a laser, and an applied magnetic field leads to the unidirectional flow of a polariton wavepacket around the edge of the array. This chiral edge mode is populated by a polariton condensation mechanism. We use scanning imaging techniques in real space and Fourier space to measure photoluminescence and thus visualize the mode as it propagates. We demonstrate that the topological edge mode goes around defects, and that its propagation direction can be reversed by inverting the applied magnetic field. Our exciton-polariton topological insulator paves the way for topological phenomena that involve light-matter interaction, amplification and the interaction of exciton-polaritons as a nonlinear many-body system.

[A study of initial antiretroviral therapy effectiveness, survival and safety in HIV+ patients]. / Estudio de la efectividad, supervivencia y seguridad de las terapias antirretrovirales de inicio en pacientes VIH+.

OBJECTIVE: To study initial antiretroviral therapies indicated for HIV-infected patients during the 2001-2003 period regarding effectiveness, survival and safety. METHOD: A descriptive, retrospective study of clinical and drug-related variables of naïve HIV-infected patients through pharmacotherapeutic history. RESULTS: Mean CD4+ lymphocytes counts were 209.6 cells/mm3. Pneumonia by Pneumocystis carinii was the most commonly found condition at antiretroviral treatment onset. Most commonly used therapies included those based on a non-nucleoside reverse transcriptase inhibitor (NNRTI) combined with two nucleoside reverse transcriptase inhibitors (NRTIs). The longest mean survival was achieved by using combinations of three nucleoside reverse transcriptase inhibitors. The primary reason for initial antiretroviral therapy discontinuation were adverse effects, with stavudine exhibiting the poorest tolerability. CONCLUSIONS: Therapies based on non-nucleoside reverse transcriptase inhibitors and protease inhibitors (PIs) have shown similar effectiveness to increase CD4+ cell counts. Regarding viral load decreases, protease inhibitors were most effective. Therapies using three nucleoside reverse transcriptase inhibitors resulted in peak survival.

[Cross-hypersensitivity syndrome between antiepileptic drugs: report of a case]. / Síndrome de hipersensibilidad cruzado entre antiepilépticos: a propósito de un caso.

Antiepileptic hypersensitivity syndrome (SHA) is a rare (1/1.000 to 1/10.000 in new exposures) but potentially life-threatening syndrome that occurs after exposure to an anticonvulsant, most commonly the aromatic ones such as phenytoin, carbamazepine or phenobarbital. Clinical features of this syndrome include cutaneous reactions, fever, lymphadenopaties, eosinophilia and internal organ involvement (mainly liver, but also kidney, CNS, heart or lung). We present a case report of a 61-year-old woman treated with phenobarbital who developed a cutaneous eruption attributed to this drug. Treatment was changed to phenytoin and after 17 days the patient developed cutaneous rash, eosinophilia and an increase in transaminase levels. The high rate of cross-sensitivity between aromatic anticonvulsants (40-80%) suggests a link between a hypersensitivity reaction to phenytoin and the previous reaction to phenobarbital.