We present the first results from the polarimetry mode of the Gemini Planet Imager (GPI), which uses a new integral field polarimetry architecture to provide high contrast linear polarimetry with minimal systematic biases between the orthogonal polarizations. We describe the design, data reduction methods, and performance of polarimetry with GPI. Point spread function subtraction via differential polarimetry suppresses unpolarized starlight by a factor of over 100, and provides sensitivity to circumstellar dust reaching the photon noise limit for these observations. In the case of the circumstellar disk around HR 4796A, GPI's advanced adaptive optics system reveals the disk clearly even prior to PSF subtraction. In polarized light, the disk is seen all the way in to its semi-minor axis for the first time. The disk exhibits surprisingly strong asymmetry in polarized intensity, with the west side 9 times brighter than the east side despite the fact that the east side is slightly brighter in total intensity. Based on a synthesis of the total and polarized intensities, we now believe that the west side is closer to us, contrary to most prior interpretations. Forward scattering by relatively large silicate dust particles leads to the strong polarized intensity on the west side, and the ring must be slightly optically thick in order to explain the lower brightness in total intensity there. These findings suggest that the ring is geometrically narrow and dynamically cold, perhaps shepherded by larger bodies in the same manner as Saturn's F ring.

The ability of muscarinic cholinergic receptors (mAChRs) to regulate the volume-sensitive efflux of two organic osmolytes, namely, taurine and D-aspartate, from human SH-SY5Y neuroblastoma cells has been examined. Incubation of the cells with hypoosmolar buffers resulted in an efflux of both osmolytes, with the threshold for release occurring at approximately 225 mOsM for taurine and D-aspartate. Inclusion of oxotremorine-M (Oxo-M), a muscarinic agonist, resulted in a marked enhancement of the volume-dependent efflux of both osmolytes and increased the threshold osmolarity for taurine and D-aspartate release to 340 (isotonic) and 320 mOsM, respectively. Maximum agonist stimulation of osmolyte release (350% of basal) was observed in the range of 225 to 250 mOsM. Oxo-M-stimulated osmolyte efflux was inhibited by muscarinic antagonists with a rank order of ,4]benzodiazepin-6-one, a pharmacological profile identical to that obtained for M 3 mAChRstimulated phosphoinositide hydrolysis. Agonist-stimulated efflux of both osmolytes could be inhibited by inclusion of either anion channel blockers known to inhibit the volume-sensitive organic anion channel (VSOAC) or by a tyrosine kinase inhibitor ␣-cyano-(3,4-dihydroxy)cinnamonitrile. The results indicate that the activation of M 3 mAChRs on SH-SY5Y neuroblastoma facilitates the ability of these cells to respond to very limited reductions in osmolarity via a release of osmolytes. mAChR-stimulated osmolyte efflux is mediated via a VSOAC and seems to require the activity of a tyrosine kinase.Although most cells possess homeostatic mechanisms for the maintenance of cell volume, these are particularly important to cells in the central nervous system (CNS) because of restrictions of the skull. Even modest alterations in brain volume can have profound effects on cell-cell signaling because the spatial relationship between neurons, astrocytes, and the extracellular space becomes compromised. Brain swelling, which can occur in response to conditions such as hyponatremia, inappropriate secretion of antidiuretic hormone, or after polydypsia, can lead to the compression of small blood vessels, and subsequently, cerebral anoxia and ischemia. Death can result from the displacement of brain parenchyma through the foramen magnum and the ensuing cardiac and respiratory arrest (Pasantes-Morales et al., 2000). To counter these deleterious changes, neural cells initially restore their osmotic balance via a loss of K ϩ and Cl Ϫ ions. However, because large changes in ion concentrations can adversely impact excitability, cells subsequently use "compatible" or nonperturbing organic osmolytes to counter changes in osmolarity without compromising cell function. In the CNS, the three quantitatively major organic osmolytes are taurine, glutamate, and myo-inositol. Organic osmolytes are released from neural cells via a volume-sensitive organic anion channel (VSOAC), a channel that has been extensively characterized both electrophysiologically and pharmacologically, although its molecular s...

With two large deformable mirrors with a total of more than 7000 actuators that need to be driven from the measurements of six 60x60 LGS WFSs (total 1.23Mpixels) at 800Hz with a latency of less than one frame, NFIRAOS presents an interesting real-time computing challenge. This paper reports on a recent trade study to evaluate which current technology could meet this challenge, with the plan to select a baseline architecture by the beginning of NFIRAOS construction in 2014. We have evaluated a number of architectures, ranging from very specialized layouts with custom boards to more generic architectures made from commercial off-the-shelf units (CPUs with or without accelerator boards). For each architecture, we have found the most suitable algorithm, mapped it onto the hardware and evaluated the performance through benchmarking whenever possible. We have evaluated a large number of criteria, including cost, power consumption, reliability and flexibility, and proceeded with scoring each architecture based on these criteria. We have found that, with today's technology, the NFIRAOS requirements are well within reach of off-theshelf commercial hardware running a parallel implementation of the straightforward matrix-vector multiply (MVM) algorithm for wave-front reconstruction. Even accelerators such as GPUs and Xeon Phis are no longer necessary. Indeed, we have found that the entire NFIRAOS RTC can be handled by seven 2U high-end PC-servers using 10GbE connectivity. Accelerators are only required for the off-line process of updating the matrix control matrix every ~10s, as observing conditions change.

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