The fast transient sky with Gaia

The ESA Gaia satellite scans the whole sky with a temporal sampling ranging from seconds and hours to months. Each time a source passes within the Gaia field of view, it moves over 10 CCDs in 45 s and a lightcurve with 4.5 s sampling (the crossing time per CCD) is registered. Given that the 4.5 s sampling represents a virtually unexplored parameter space in optical time domain astronomy, this data set potentially provides a unique opportunity to open up the fast transient sky. We present a method to start mining the wealth of information in the per CCD Gaia data. We perform extensive data filtering to eliminate known on-board and data processing artefacts, and present a statistical method to identify sources that show transient brightness variations on ~2 hours timescales. We illustrate that by using the Gaia photometric CCD measurements, we can detect transient brightness variations down to an amplitude of 0.3 mag on timescales ranging from 15 seconds to several hours. We search an area of ~23.5 square degrees on the sky, and find four strong candidate fast transients. Two candidates are tentatively classified as flares on M-dwarf stars, while one is probably a flare on a giant star and one potentially a flare on a solar type star. These classifications are based on archival data and the timescales involved. We argue that the method presented here can be added to the existing Gaia Science Alerts infrastructure for the near real-time public dissemination of fast transient events.Comment: 10 pages, 5 figures and 5 tables; MNRAS in pres

Effects of magnesium sulphate on liver ischemia/reperfusion injury in a rat model

Aim: To investigate the protective efficacy of magnesium sulphate in a model of rat liver ischemia-reperfusion (I/R) injury. Method: 32 adult female Wistar-Albino rats (250 to 350 g) were used in this experimental study. Rats were divided into 4 groups according to liver ischemia and magnesium sulfate application methods. Group 1 (C); control, group 2 (M); magnesium sulphate, group 3 (I/R); liver I/R, group 4 (I/R+M); I/R + magnesium sulphate treated. The blood samples were centrifuged for the study of aspartate aminotransferase (AST), alanine aminotransferase, prothrombin time (PT), international normalized ratio (INR) troponin I, total antioxidant status (TAS), total oxidant status (TOS) assays. The livers of the animals were removed at the end of the study and samples were taken for histopathological examination. Results: AST and INR values were significantly decreased in I/R+M group compared to I/R group. There was no significant difference in ALT values of the groups. Although not statistically significant, the TAS values were increased in I/R + M group compared to I/R group rats. In addition, the value of TOS was found to be lower in I/R + M group rats. In the histopathological examination, the mean values of apoptosis and necrosis were lower in the IR+M group compared to the IR group. Conclusion: The main finding of the present study suggested that magnesium sulphate pretreatment moderately decreased the liver damage through its anti-inflammatory and anti-oxidant effects in a rat model of liver I/R

FAST STEREO PAIR GENERATION USING SRTM REGISTRATION AND OPTICAL FLOW

In Digital Surface Model generation applications, obtaining stereo correspondences is a crucial step. The geometry of stereo image generation causes significant disparities between match points. Unlike the pinhole camera model, in pushbroom sensor images, search is less structured, since there exists no epipolar geometry. This situation brings significant computational load over the stereo correspondence generation step. In this study, a fast sparse stereo pair generation scheme is presented. This approach uses SRTM data, RPC coefficients and quadratic polynomial interpolation to generate an estimate for the geodetic coordinates of each pixel in the reference image. Harris corner detector is used to generate many feature points in the reference image. The geodetic coordinate estimates at these feature points are projected onto the second image using RPC coefficients and this projection is taken as an initial estimate for a pyramidal Kanade-Lucas-Tomasi (KLT) optical flow estimation method. Since the initial estimates for optical flow are quite reliable, the resulting match points are obtained using more precise spatio-temporal derivatives during optical flow estimation step. The pyramidal nature of the optical flow estimation method allows quite fast and promising results, even for cluttered and perspective-distorted regions, which are usually difficult to mark manually. On satellite images, the accuracy of the geodetic coordinate estimates and the success of the proposed pair generation scheme are presented through experiments. The differences for urban and rural areas are also investigated. The limits of the KLT algorithm for satellite stereo match generation and the potential of the method are discussed. Based on the experiments, it is shown that the proposed approach gives quite reliable sparse stereo correspondences for urban and rural areas in relatively small execution time

Preparing for Gaia Searches for Optical Counterparts of Gravitational Wave Events during O4

The discovery of gravitational wave (GW) events and the detection of electromagnetic counterparts from GW170817 has started the era of multimessenger GW astronomy.The field has been developing rapidly and in this paper,we discuss the preparation for detecting these events with the ESA Gaia satellite,during the 4th observing run of the LIGO-Virgo-KAGRA (LVK) collaboration that has started on May 24,2023. Gaia is contributing to the search for GW counterparts by a new transient detection pipeline called GaiaX. In GaiaX, a new source appearing in the field of view of only one of the two telescopes on-board Gaia is sufficient to send out an alert on the possible detection of a new transient. Ahead of O4, an experiment was conducted over a period of about two months. During the two weeks around New Moon in this period of time, the MeerLICHT (ML) telescope located in South Africa tried (weather permitting) to observe the same region of the sky as Gaia within 10 minutes. Any GaiaX detected transient was published publicly. ML and Gaia have similar limiting magnitudes for typical seeing conditions at ML. At the end of the experiment, we had 11861 GaiaX candidate transients and 15806 ML candidate transients, which we further analysed and the results of which are presented in this paper. Finally, we discuss the possibility and capabilities of Gaia contributing to the search for electromagnetic counterparts of gravitational wave events during O4 through the GaiaX detection and alert procedure.Comment: 13 pages, 9 figures; Submitted to MNRA

Effect of indentation load and time on knoop and vickers microhardness tests for enamel and dentin

The aim of this study was to determine the effect of variations in indentation load and time on the Knoop and Vickers hardness numbers (KHN and VHN) for enamel and dentin. Twenty molar teeth were divided into twenty enamel and twenty dentin specimens. Each specimen was tested using a Knoop or Vickers microhardness tester at different loads and times. The difference in hardness between the groups was analyzed with two-way ANOVA followed by a Tukey test. The results revealed that a difference of indentation time did not influence the microhardness number of enamel and dentin. The KHN values of enamel and the VHN values of dentin were affected by variation of test loads. Therefore, the tooth hardness number for different loads may not be acceptable for comparison