Polariton fluids for analogue gravity physics.

Analogue gravity enables the study of fields on curved space-times in the laboratory. There are numerous experimental platforms in which amplification at the event horizon or the ergoregion has been observed. Here, we demonstrate how optically generating a defect in a polariton microcavity enables the creation of one- and two-dimensional, transsonic fluid flows. We show that this highly tuneable method permits the creation of horizons. Furthermore, we present a rotating geometry akin to the water-wave bathtub vortex. These experiments usher in the possibility of observing stimulated as well as spontaneous amplification by the Hawking, Penrose and Zeld'ovich effects in fluids of light. This article is part of a discussion meeting issue 'The next generation of analogue gravity experiments'.

[Diagnosis of postpartum abdominal pain: about a rare case of portal vein thrombosis]. / Orientation diagnostique devant des douleurs abdominales du post-partum: à propos d'un cas rare de thrombose portale.

We report the management of patient with acute abdominal pain in the immediate post-partum caesarean section performed in the context of preeclampsia. Acute portal vein thrombosis is diagnosed, in a patient with no personal or family history of venous thrombosis. Blood tests showed a protein C and S deficiencies. Portal vein thrombosis is an extremely rare occurrence in pregnancy and postpartum.

Polariton-generated intensity squeezing in semiconductor micropillars.

The generation of squeezed and entangled light fields is a crucial ingredient for the implementation of quantum information protocols. In this context, semiconductor materials offer a strong potential for the implementation of on-chip devices operating at the quantum level. Here we demonstrate a novel source of continuous variable squeezed light in pillar-shaped semiconductor microcavities in the strong coupling regime. Degenerate polariton four-wave mixing is obtained by exciting the pillar at normal incidence. We observe a bistable behaviour and we demonstrate the generation of squeezing near the turning point of the bistability curve. The confined pillar geometry allows for a larger amount of squeezing than planar microcavities due to the discrete energy levels protected from excess noise. By analysing the noise of the emitted light, we obtain a measured intensity squeezing of 20.3%, inferred to be 35.8% after corrections.

Motion of spin polariton bullets in semiconductor microcavities.

The dynamics of optical switching in semiconductor microcavities in the strong coupling regime is studied by using time- and spatially resolved spectroscopy. The switching is triggered by polarized short pulses which create spin bullets of high polariton density. The spin packets travel with speeds of the order of 10(6) m/s due to the ballistic propagation and drift of exciton polaritons from high to low density areas. The speed is controlled by the angle of incidence of the excitation beams, which changes the polariton group velocity.

Spin rings in bistable planar semiconductor microcavities.

A remarkable feature of exciton-polaritons is the strongly spin-dependent polariton-polariton interaction, which has been predicted to result in the formation of spin rings in real space [Shelykh, Phys. Rev. Lett. 100, 116401 (2008)]. Here we experimentally demonstrate the spin bistability of exciton polaritons in an InGaAs-based semiconductor microcavity under resonant optical pumping. We observe the formation of spin rings whose size can be finely controlled in a spatial scale down to the micrometer range, much smaller than the spot size. Demonstration of optically controlled spin patterns in semiconductors opens way to the realization of spin logic devices and spin memories.

Functionally abnormal stromal cells and megakaryocyte size, ploidy, and ultrastructure in Sl/Sld mice.

The first goal of the present studies was to determine if Sl/Sld megakaryocytes have features in common with the macrocytic megakaryocytes that genetically normal mice produce in response to acute platelet depletion. The second was to test the hypothesis that megakaryocyte abnormalities in Sl/Sld mice are due to genetically determined hemopoietic stromal cell abnormalities. Sizes and ploidies of mature Sl/Sld megakaryocytes were measured. Macrocytosis and a shift to higher ploidy values were found compared with normal. Within ploidy groups 16N-64N, Sl/Sld megakaryocytes were larger than normal megakaryocytes of the same ploidy. Transmission electron microscopy revealed that Sl/Sld megakaryocyte nuclei contain more and larger nucleoli, and the chromatin was more dispersed than in normal megakaryocyte nuclei of comparable maturity. Asynchronous megakaryocyte cytoplasmic maturation was found. Sl/Sld macrophages were also ultrastructurally abnormal. Megakaryocytic macrocytosis was reproduced in long-term bone marrow cultures in which the adherent layer was formed by Sl/Sld cells. It was the same if cultures were recharged with Sl/Sld or +/+ hemopoietic cells. Previously reported ambiguities in mixed cell cultures were avoided by recharging the adherent layers with only a million cells. These results were correlated with previously published observations. Sl/Sld megakaryocytes have features in common with megakaryocytes from acutely thrombocytopenic animals. One feature, macrocytosis, appears to be due to abnormal Sl/Sld stromal cells that are reproduced as adherent layer cells in long-term cultures. The responsible stromal cells in Sl/Sld mice may be counterparts of megakaryocytopoietic regulatory cells in the marrow stroma of normal animals.

Independence of megakaryocyte number and size in long-term cultures of normal mouse marrow.

Megakaryocytopoiesis was evaluated in long-term cultures of normal murine marrow to determine whether the number and size of megakaryocytes were independent or interdependent. Numbers of megakaryocytes and granulocytes varied widely in different experiments, due, in part, to varying concentrations of hydrocortisone in the culture medium. The sizes of acetylcholinesterase-positive cells were the same in cultures with as much as a 20-fold difference in megakaryocyte numbers. These results indicate that, in the closed culture system containing normal stromal cells, megakaryocyte size and number are not reciprocal as they were in many previously reported cultures of S1/S1d mouse marrow. The results suggest that separate stromal functions may determine precursor cell proliferation and nuclear endomitosis in megakaryocytes in vitro. The relationship of these findings to regulation of megakaryocytopoiesis in vivo remains speculative.

Mean platelet volume: the need for a reference method.

The time course of artifactual effects due to anticoagulants, specimen temperature, and interval between venipuncture and analysis on platelet volume measurements was evaluated. Split specimens were analyzed using hydrodynamic focusing, and platelet distributions were computed using a least-squares fit to a log-normal distribution. Significant artifacts resulted from exposure to EDTA, cooling to room temperature, and delay in exposure to anticoagulant. The artifactual effect of EDTA is extreme and time dependent. Collection of blood in Buffered Citrate, Acid Citrate Dextrose, or Pyridoxal-5'-phosphate supplemented Citrate yielded stable and equivalent results with rapid anticoagulation and incubation at 37 degrees C for up to six hours.

Macrocytic megakaryocytes in cultures of S1/S1d bone marrow.

The thrombocytopoietic system of S1/S1d mice is characterized by macromegakaryocytosis and megakaryocytopenia, but the mechanisms responsible for reciprocal abnormalities of megakaryocyte number and size are unknown. These mice have a genetically determined abnormality of their hemopoietic microenvironment that can, in part, be reproduced as abnormal adherent stromal cells in bone marrow cultures. Cultures of bone marrow were therefore done to determine if the megakaryocytic abnormalities of S1/S1d marrow would also be reproduced in them. Cultures composed entirely of S1/S1d cells showed persistent macrocytosis of megakaryocytes when compared with cultures of normal +/+ marrow. At various times of culture, there were also reduced numbers of megakaryocytes, total cells, and granulocytes in the supernatants of S1/S1d cultures. Mixed cultures of S1/S1d and +/+ cells yielded inconclusive findings. The fact that macromegakaryocytosis occurred in cultures of S1/S1d marrow strongly suggests that its in vivo determinants were, in part, reproduced in culture.

Megakaryocytopoiesis in irradiated, splenectomized mice.

The hypomegakaryocytic state that develops after exposure to sublethal doses of ionizing radiation was evaluated in splenectomized and intact mice. The percentage reduction of marrow megakaryocytes was greater than that of platelets at comparable times post-irradiation. After initial recovery a secondary drop in platelet counts occurred earlier in intact than in splenectomized mice. The average size of mature megakaryocytes was found to be increased, due primarily to marked reductions in megakaryocytes of smaller size. These results indicate that the spleen acts more to reduce than to increase the platelet count after exposure to sublethal doses of whole body radiation and that megakaryocyte size may be increased by reduction in numbers of small megakaryocytes without an increase in large megakaryocytes.