Far-infrared observations of a massive cluster forming in the Monoceros R2 filament hub

We present far-infrared observations of Monoceros R2 (a giant molecular cloud at approximately 830 pc distance, containing several sites of active star formation), as observed at 70 μm, 160 μm, 250 μm, 350 μm, and 500 μm by the Photodetector Array Camera and Spectrometer (PACS) and Spectral and Photometric Imaging Receiver (SPIRE) instruments on the Herschel Space Observatory as part of the Herschel imaging survey of OB young stellar objects (HOBYS) Key programme. The Herschel data are complemented by SCUBA-2 data in the submillimetre range, and WISE and Spitzer data in the mid-infrared. In addition, C18O data from the IRAM 30-m Telescope are presented, and used for kinematic information. Sources were extracted from the maps with getsources, and from the fluxes measured, spectral energy distributions were constructed, allowing measurements of source mass and dust temperature. Of 177 Herschel sources robustly detected in the region (a detection with high signal-to-noise and low axis ratio at multiple wavelengths), including protostars and starless cores, 29 are found in a filamentary hub at the centre of the region (a little over 1% of the observed area). These objects are on average smaller, more massive, and more luminous than those in the surrounding regions (which together suggest that they are at a later stage of evolution), a result that cannot be explained entirely by selection effects. These results suggest a picture in which the hub may have begun star formation at a point significantly earlier than the outer regions, possibly forming as a result of feedback from earlier star formation. Furthermore, the hub may be sustaining its star formation by accreting material from the surrounding filaments

A simple role of coral-algal symbiosis in coral calcification based on multiple geochemical tracers

Light-enhanced calcification of reef-building corals, which eventually create vast coral reefs, is well known and based on coral-algal symbiosis. Several controversial hypotheses have been proposed as possible mechanisms for connecting symbiont photosynthesis and coral calcification, including pH rise in the internal pool, role of organic matrix secretion, and enzyme activities. Here, based on the skeletal chemical and isotopic compositions of symbiotic and asymbiotic primary polyps of Acropora digitifera corals, we show a simple pH increase in the calcification medium as the predominant contribution of symbionts to calcification of host corals. We used the symbiotic and asymbiotic primary polyps reared for 10 days at four temperatures (27, 29, 31, and 33 °C), five salinities (34, 32, 30, 28, and 26), and four pCO2 levels (<300, 400, 800, and 1000 µatm). As a result of analyzing multiple geochemical tracers (U/Ca, Mg/Ca, Sr/Ca, δ18O, δ13C, and δ44Ca), a clear and systematic decrease in skeletal U/Ca ratio (used as a proxy for calcification fluid pH) was observed, indicating a higher pH of the fluid in symbiotic compared to asymbiotic polyps. In contrast, Mg/Ca ratios (used as a tentative proxy for organic matrix secretion) and δ44Ca (used as an indicator of Ca2+ pathway to the fluid) did not differ between symbiotic and asymbiotic polyps. This suggests that organic matrix secretion related to coral calcification is controlled mainly by the coral host itself, and a transmembrane transport of Ca2+ does not vary according to symbiosis relationship. Skeletal δ18O values of both symbiotic and asymbiotic polyps showed offsets between them with identical temperature dependence. Based on a newly proposed model, behavior of δ18O in the present study seems to reflect the rate of CO2 hydration in the calcifying fluid. Since CO2 hydration is promoted by enzyme carbonic anhydrase, the offset of δ18O values between symbiotic and asymbiotic polyps is attributed to the differences of enzyme activity, although the enzyme is functional even in the asymbiotic polyp. Symbiotic δ13C values in the temperature and salinity experiments were higher compared to those in the asymbiotic polyps due to photosynthesis, although photosynthetic δ13C signals in the pCO2 experiment were masked by the dominant δ13C gradient in dissolved inorganic carbon in seawater caused by 13C-depletd CO2 gas addition in the higher pCO2 treatments. Sr/Ca ratios showed a negligible relationship according to variation of temperature, salinity, and pCO2, although it might be attributed to relatively large deviations of replicates of Sr/Ca ratios in the present study. Overall, only the U/Ca ratio showed a significant difference between symbiotic and asymbiotic polyps throughout all experiments, indicating that the critical effect on coral calcification caused by symbiotic algae is the increase of pH of the calcifying fluid by photosynthesis

Path Planning for Mobile Robot Navigation using Voronoi Diagram and Fast Marching

For navigation in complex environments, a robot need s to reach a compromise between the need for having efficient and optimized trajectories and t he need for reacting to unexpected events. This paper presents a new sensor-based Path Planner w hich results in a fast local or global motion planning able to incorporate the new obstacle information. In the first step the safest areas in the environment are extracted by means of a Vorono i Diagram. In the second step the Fast Marching Method is applied to the Voronoi extracted a reas in order to obtain the path. The method combines map-based and sensor-based planning o perations to provide a reliable motion plan, while it operates at the sensor frequency. The m ain characteristics are speed and reliability, since the map dimensions are reduced to an almost uni dimensional map and this map represents the safest areas in the environment for moving the robot. In addition, the Voronoi Diagram can be calculated in open areas, and with all kind of shaped obstacles, which allows to apply the proposed planning method in complex environments wher e other methods of planning based on Voronoi do not work.This work has been supported by the CAM Project S2009/DPI-1559/ROBOCITY2030 I