2,210 research outputs found

    Progenitor delay-time distribution of short gamma-ray bursts: Constraints from observations

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    Context. The progenitors of short gamma-ray bursts (SGRBs) have not yet been well identified. The most popular model is the merger of compact object binaries (NS-NS/NS-BH). However, other progenitor models cannot be ruled out. The delay-time distribution of SGRB progenitors, which is an important property to constrain progenitor models, is still poorly understood. Aims. We aim to better constrain the luminosity function of SGRBs and the delay-time distribution of their progenitors with newly discovered SGRBs. Methods. We present a low-contamination sample of 16 Swift SGRBs that is better defined by a duration shorter than 0.8 s. By using this robust sample and by combining a self-consistent star formation model with various models for the distribution of time delays, the redshift distribution of SGRBs is calculated and then compared to the observational data. Results. We find that the power-law delay distribution model is disfavored and that only the lognormal delay distribution model with the typical delay tau >= 3 Gyr is consistent with the data. Comparing Swift SGRBs with T90 > 0.8 s to our robust sample (T90 < 0.8 s), we find a significant difference in the time delays between these two samples. Conclusions. Our results show that the progenitors of SGRBs are dominated by relatively long-lived systems (tau >= 3 Gyr), which contrasts the results found for Type Ia supernovae. We therefore conclude that primordial NS-NS systems are not favored as the dominant SGRB progenitors. Alternatively, dynamically formed NS-NS/BH and primordial NS-BH systems with average delays longer than 5 Gyr may contribute a significant fraction to the overall SGRB progenitors.Comment: 8 pages, 6 figures, Astron. Astrophys. in pres

    Photometric Stereo-Based Depth Map Reconstruction for Monocular Capsule Endoscopy

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    The capsule endoscopy robot can only use monocular vision due to the dimensional limit. To improve the depth perception of the monocular capsule endoscopy robot, this paper proposes a photometric stereo-based depth map reconstruction method. First, based on the characteristics of the capsule endoscopy robot system, a photometric stereo framework is established. Then, by combining the specular property and Lambertian property of the object surface, the depth of the specular highlight point is estimated, and the depth map of the whole object surface is reconstructed by a forward upwind scheme. To evaluate the precision of the depth estimation of the specular highlight region and the depth map reconstruction of the object surface, simulations and experiments are implemented with synthetic images and pig colon tissue, respectively. The results of the simulations and experiments show that the proposed method provides good precision for depth map reconstruction in monocular capsule endoscopy

    Efficient point cloud corrections for mobile monitoring applications using road/rail-side infrastructure

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    Light Detection and Ranging (LiDAR) systems are known to capture high density and accuracy data much more efficiently than other surveying methods. Therefore they are used for many applications, e.g. mobile mapping and surveying, 3D modelling, hazard detection, etc. However, while the accuracy of the laser measurements is very high, the accuracy of the resulting 3D point cloud is greatly affected by the geo-referencing accuracy. This is especially problematic for mobile laser scanning systems, where the LiDAR is installed on a moving platform, e.g. a vehicle, and the point cloud is geo-referenced by the data provided by a navigation system. Owing to the complexity of the surrounding environments and external conditions, the accuracy of the navigation system varies and thereby changes the quality of the point cloud. Conventional methods for correcting the point cloud accuracy either rely heavily on manual work or semi-automatic registration methods. While they can provide geo-referencing under different conditions, each has their own problems. This paper presents a semi-automated geo-referencing trajectory correction method by extracting features from the pre-processed point cloud and integrating this information to reprocess the navigation trajectory which is then able to produce better quality point clouds. The method deals with the changing errors within a point cloud dataset, and reducing the trajectory error from metre level to decimetre level, improving the accuracy by at least 56%. The accuracy of the regenerated point cloud then becomes suitable for many accuracy-demanding monitoring and change detection applications

    Study on the relationship between expression patterns of cocaine-and amphetamine regulated transcript and hormones secretion in porcine ovarian follicles

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    Background: Cocaine-and amphetamine regulated transcript (CART) is an endogenous neuropeptide, which is widespread in animals, plays a key role in regulation of follicular atresia in cattle and sheep. Among animal ovaries, CART mRNA was firstly found in the cattle ovaries. CART was localized in the antral follicles oocytes, granulosa and cumulus cells by immunohistochemistry and in situ hybridization. Further research found that secretion of E2 was inhibited in granulosa cells with a certain dose of CART, the effect depends on the stage of cell differentiation, sug- gesting that CART could play a crucial role in regulating follicle atresia. The objective of this study was to character- ize the CART expression model and hormones secretion in vivo and vitro in pig follicle granulosa cells, preliminarily studied whether CART have an effect on granulosa cells proliferation and hormones secretion in multiparous animals such as pigs. Methods: The expression levels of CART mRNA in granulosa cells of different follicles were analyzed using qRT-PCR technology. Immunohistochemistry technology was used to localize CART peptide. Granulosa cells were cultured in medium supplemented with different concentrations of CART and FSH for 168 h using Long-term culture system, and observed using a microscope. The concentration of Estradiol (E2) and progesterone (P) in follicular fluids of different test groups were detected by enzyme linked immunosorbent assay (ELISA). Results: Results showed that expression level of CART mRNA was highest in medium follicles, and significantly higher than that in large and small follicles (P \u3c 0.05). Immunohistochemical results showed that CART were expressed both in granulosa cells and theca cells of large follicles, while CART were detected only in theca cells of medium and small follicles. After the granulosa cells were cultured for 168 h, and found that concentrations of E2 increase with concen- trations of follicle-stimulating hormone (FSH) increase when the CART concentration was 0 ╬╝M. And the concentra- tion of FSH reached 25 ng/mL, the concentration of E2 is greatest. It shows that the production of E2 needs induction of FSH in granulosa cells of pig ovarian follicles. With the increasing of CART concentrations (0.01, 0.1, 1 ╬╝M), E2 con- centration has a declining trend, when the FSH concentrations were 25 and 50 ng/mL in the medium, respectively. Conclusions: These results suggested that CART plays a role to inhibit granulosa cells proliferation and E2 production, which induced by FSH in porcine ovarian follicular granulosa cells in vitro, but the inhibition effect is not significant. So we hypothesis CART maybe not a main local negative regulatory factor during porcine follicular development, which is different from the single fetal animals

    Histopathologic changes of Reis-B├╝cklers corneal dystrophy

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    AIM: To explore the histopathologic changes of Reis-B├╝cklers corneal dystrophy(RBCD). METHODS: Cornea buttons were obtained from patients in 1 pedigree who underwent lamella keratoplasty. Sections with HE and special staining which included symplectic blue staining and Masson staining and Congo red staining were observed under light microscope. Two normal cornea specimens(donated corneas from eye bank)were used as control. RESULTS: In those patients, the bowman's membrane disappeared. The main lesion was in bowman's membrane through HE staining, positive through PAS Congo red staining and Masson staining, negative through symplectic blue staining.CONCLUSION: The Reis - B├╝cklers corneal dystrophy is characterized as geographic map-like lesion of bowman's membrane, and the abnormal extracellular deposit is amyloid protein fiber
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