Gaia data release 1, the photometric data

CONTEXT. This paper presents an overview of the photometric data that are part of the first Gaia data release. AIMS. The principles of the processing and the main characteristics of the Gaia photometric data are presented. METHODS. The calibration strategy is outlined briefly and the main properties of the resulting photometry are presented. RESULTS. Relations with other broadband photometric systems are provided. The overall precision for the Gaia photometry is shown to be at the milli-magnitude level and has a clear potential to improve further in future releases

The Formation of Collective Silk Balls in the Spider Mite Tetranychus urticae Koch

Tetranychus urticae is a phytophagous mite that forms colonies of several thousand individuals. These mites construct a common web to protect the colony. When plants become overcrowded and food resources become scarce, individuals gather at the plant apex to form a ball composed of mites and their silk threads. This ball is a structure facilitating group dispersal by wind or animal transport. Until now, no quantitative study had been done on this collective form of migration. This is the first attempt to understand the mechanisms that underlie the emergence and growth of the ball. We studied this collective behaviour under laboratory conditions on standardized infested plants. Our results show that the collective displacement and the formation of balls result from a recruitment process: by depositing silk threads on their way up to the plant apex, mites favour and amplify the recruitment toward the balls. A critical threshold (quorum response) in the cumulative flow of mites must be reached to observe the emergence of a ball. At the beginning of the balls formation, mites form an aggregate. After 24 hours, the aggregated mites are trapped inside the silk balls by the complex network of silk threads and finally die, except for recently arrived individuals. The balls are mainly composed of immature stages. Our study reconstructs the key events that lead to the formation of silk balls. They suggest that the interplay between mites' density, plant morphology and plant density lead to different modes of dispersions (individual or collective) and under what conditions populations might adopt a collective strategy rather than one that is individually oriented. Moreover, our results lead to discuss two aspects of the cooperation and altruism: the importance of Allee effects during colonization of new plants and the importance of the size of a founding group

Gaia Data Release 2: Photometric content and validation

Aims. We describe the photometric content of the second data release of the Gaia project (Gaia DR2) and its validation along with the quality of the data. Methods. The validation was mainly carried out using an internal analysis of the photometry. External comparisons were also made, but were limited by the precision and systematics that may be present in the external catalogues used. Results. In addition to the photometric quality assessment, we present the best estimates of the three photometric passbands. Various colour-colour transformations are also derived to enable the users to convert between the Gaia and commonly used passbands. Conclusions. The internal analysis of the data shows that the photometric calibrations can reach a precision as low as 2 mmag on individual CCD measurements. Other tests show that systematic effects are present in the data at the 10 mmag level

Managing bridge scour risk using structural health monitoring

Scour is the leading cause of bridge failures worldwide. In the United States, 22 bridges fail every year, whereas in the UK scour contributed significantly to the 138 bridge collapses recorded in the last century. In Scotland, there are around 2,000 bridges susceptible to scour. Scour assessments are currently based on visual inspections, which are expensive, time-consuming, and the information collected is qualitative. However, monitoring an entire infrastructure network against scour is not economically feasible. A way to overcome this limitation is to install monitoring systems at critical locations, and then extend the pieces of information gained to the entire asset through a probabilistic approach. This paper proposes a Decision Support System (DSS) for bridge scour management that exploits information from a limited number of scour monitoring systems to achieve a more confined estimate of the scour risk for a bridge network. A Bayesian network (BN) is used to describe conditional dependencies among the involved random variables. The BN allows estimating, and updating, the scour depth distributions using information from monitoring of scour depth and river flow characteristics. Data collected by the monitoring system and BN's outcomes are then used to inform a decision model and thus support transport agencies’ decision frameworks. A case study consisting of several road bridges in Scotland is considered to demonstrate the functioning of the DSS. The BN is found to estimate accurately the scour depth at unmonitored bridges, and the decision model provides higher values of scour thresholds compared to the ones implicitly chosen by the transport agencies

Hirschsprung\u2019s Disease

Hirschsprung\u2019s disease (HD) or \u201ccongenital megacolon\u201d is a congenital developmental disorder characterized by the absence of ganglion cells in the distal intestine with variable proximal extension. HD affects approximately 1 / 5,000 live births and is more common in males (M: F = 4: 1). According to the proximal extension is possible to indentify different forms of HD: ultrashort, short segment or classical form, long segment and total colonic aganglia. Most children with HD (50-90%) are diagnosed in the neonatal period. Typically the infant with HD is born at term and present with failure to pass meconium.When there is a clinical suspicion of HD, diagnostic investigations to be performed include: radiologic evaluation (plain radiographs, barium enema), anorectal manometry, rectal full-thickness biopsy or serum-muscle and / or rectal biopsy by suction (Rectal Suction biopsy - RSB).There are numerous surgical techniques described for the treatment of HD. The most commonly performed, and therefore considered \u201cthe major pull-through procedures\u201d, are: Swenson rectosigmoidectomy, Duhamel retrorectal transanal pull-through, Rehbein pull-through with anterior colorectal anastomosis, Soave rectosigmoidectomy with aseptic endorectal colon pull-through.Early postoperative complication is represented by colo-anal anastomosis dehiscence (3.2%) which, if not massive, is solvable conservatively. Late postoperative complications are HAEC and colo-anal anastomosis stenosis.On rare occasions the child may require a RedoPT procedure. Indication for RedoPT in the recent review was most commonly for a retained aganglionosis/transition zone pathology (RA/TZP; 71% overall ). Other indications included stricture/obstructing Duhamel pouch (19%), excessively tight cuff (8%), twisted-PT (4%). Operative approach can vary widely and is heavily dependent on type of complication, underlying pathology, previous surgical history as well as surgeon preference as to the type of repair. Complications are quite similar after redo-PT compared to primary PT in experienced hands but stooling outcomes are significantly worse compared to those after a primaryPT. Importantly, continence is still retained in the majority of children