The Imaging Magnetograph eXperiment (IMaX) for the Sunrise balloon-borne solar observatory

The Imaging Magnetograph eXperiment (IMaX) is a spectropolarimeter built by four institutions in Spain that flew on board the Sunrise balloon-borne telesocope in June 2009 for almost six days over the Arctic Circle. As a polarimeter IMaX uses fast polarization modulation (based on the use of two liquid crystal retarders), real-time image accumulation, and dual beam polarimetry to reach polarization sensitivities of 0.1%. As a spectrograph, the instrument uses a LiNbO3 etalon in double pass and a narrow band pre-filter to achieve a spectral resolution of 85 mAA. IMaX uses the high Zeeman sensitive line of Fe I at 5250.2 AA and observes all four Stokes parameters at various points inside the spectral line. This allows vector magnetograms, Dopplergrams, and intensity frames to be produced that, after reconstruction, reach spatial resolutions in the 0.15-0.18 arcsec range over a 50x50 arcsec FOV. Time cadences vary between ten and 33 seconds, although the shortest one only includes longitudinal polarimetry. The spectral line is sampled in various ways depending on the applied observing mode, from just two points inside the line to 11 of them. All observing modes include one extra wavelength point in the nearby continuum. Gauss equivalent sensitivities are four Gauss for longitudinal fields and 80 Gauss for transverse fields per wavelength sample. The LOS velocities are estimated with statistical errors of the order of 5-40 m/s. The design, calibration and integration phases of the instrument, together with the implemented data reduction scheme are described in some detail.Comment: 17 figure

Few-core spatial-mode multiplexers/demultiplexers based on evanescent coupling

The multiplexing and demultiplexing of the spatialmodes of few-mode fiber is demonstrated using few-core couplers. The mode combination/separation is achieved through mode-selective evanescent coupling. In particular, multiplexers/demultiplexers for three fiber modes are simulated that use either circular (fiber) or rectangular (planar) cores. The demultiplexing can be made independent of the spatial-orientations of the fiber modes by judicious choice of core configuration.Nicolas Riesen, John D.Love, and John W. Arkwrigh

Few-mode elliptical-core fiber data transmission

Spatial mode-division-multiplexing is seen as paramount to overcoming the bandwidth limitations of single-mode fiber. In this letter, spatial-multiplexing of polarization-maintaining, elliptical-core fiber is proposed using asymmetric Y-junctions. Asymmetric Y-junctions also allow for straightforward wavelength- and polarization-multiplexing. Numerical beam propagation method simulations are used to demonstrate the functioning of a three-mode elliptical-core fiber data link, which could easily be extended to more modes. The multiplexing of multiple spatial modes could potentially see multifold increases in fiber capacity.Nicolas Riesen, John D. Love, and John W. Arkwrigh

Roles of three distinct neurogenic motor patterns during pellet propulsion in guinea-pig distal colon

KEY POINTS:Enteric neural circuits enable isolated preparations of guinea-pig distal colon to propel solid and fluid contents by a self-sustaining neuromechanical loop process. In addition there are at least three neural mechanisms which are not directly involved in propulsion: cyclic motor complexes, transient neural events and distal colon migrating motor complexes. In excised guinea-pig colon we simultaneously recorded high resolution manometry, video-imaging of colonic wall movements and electrophysiological recordings from smooth muscle, which enabled us to identify mechanisms that underlie the propulsion of colonic content. The results show that the intermittent propulsion during emptying of the multiple natural faecal pellets is due to the intermittent activation of cyclic motor complexes and this is facilitated by transient neural events. Loss or dysfunction of these activities is likely to underlie disordered gastrointestinal transit. ABSTRACT:It is well known that there are different patterns of electrical activity in smooth muscle cells along different regions of the gastrointestinal tract. These different patterns can be generated by myogenic and/or neurogenic mechanisms. However, what patterns of electrical activity underlie the propulsion of natural faecal content remains unknown, particularly along the large intestine, where large quantities of water are reabsorbed and semi-solid faeces form. In this study, we developed a novel approach which enables for the first time the simultaneous recording of high resolution intraluminal manometry, electrophysiology from the smooth muscle, and spatio-temporal video imaging of colonic wall movements. Using this approach we were able to reveal the nature of enteric neuromuscular transmission and patterns of motor activity responsible for the movement of content. Three distinct neurogenic patterns of electrical activity were recorded even in the absence of propulsive movement. These were the cyclic motor complexes (CMCs), the transient neural events (TNEs) and the slowly propagating distal colonic migrating motor complexes (DCMMCs). We present evidence that the initiation of pellet propulsion is due to a cyclic motor complex (CMC) occurring oral to the pellet. Furthermore, we discovered that the intermittent propulsion of natural faecal pellets is generated by intermittent activation of CMCs; and this propulsion is facilitated by hexamethonium-sensitive TNEs. However, TNEs were not required for propulsion. The findings reveal the patterns of electrical activity that underlie propulsion of natural colonic content and demonstrate that propulsion is generated by a complex interplay between distinct enteric neural circuits.Marcello Costa, Lauren J. Keightley, Lukasz Wiklendt, TimothyJ.Hibberd, JohnW.Arkwright, Taher Omari, DavidA.Wattchow, Vladimir Zagorodnyuk, SimonJ.H.Brookes, Phil G. Dinning, and Nick J. Spence