Phase-resolved optical and X-ray spectroscopy of low-mass X-ray binary X1822-371

(Abridged) X1822-371 is the prototypical accretion disc corona X-ray source, a low-mass X-ray binary viewed at very high inclination, thereby allowing the disc structure and extended disc coronal regions to be visible. We study the structure of the accretion disc in X1822-371 by modelling the phase-resolved spectra both in optical and X-ray regime. We analyse high time resolution optical ESO/VLT spectra of X1822-371 to study the variability in the emission line profiles. In addition, we use data from XMM-Newton space observatory to study phase-resolved as well as high resolution X-ray spectra. We apply the Doppler tomography technique to reconstruct a map of the optical emission distribution in the system. We fit multi-component models to the X-ray spectra. We find that our results from both the optical and X-ray analysis can be explained with a model where the accretion disc has a thick rim in the region where the accretion stream impacts the disc. The behaviour of the H_beta line complex implies that some of the accreting matter creates an outburst around the accretion stream impact location and that the resulting outflow of matter moves both away from the accretion disc and towards the centre of the disc. Such behaviour can be explained by an almost isotropic outflow of matter from the accretion stream impact region. The optical emission lines of HeII 4686 and 5411 show double peaked profiles, typical for an accretion disc at high inclination. However, their velocities are slower than expected for an accretion disc in a system like X1822-371. This, combined with the fact that the HeII emission lines do not get eclipsed during the partial eclipse in the continuum, suggests that the line emission does not originate in the orbital plane and is more likely to come from above the accretion disc, for example the accretion disc wind.Comment: 10 pages, 13 figures, accepted for publication in A&

Understanding forecast verification statistics

Although there are numerous reasons for performing a verification analysis, there are usually two general questions that are of interest: are the forecasts good, and can we be confident that the estimate of forecast quality is not misleading? When calculating a verification score, it is not usually obvious how the score can answer either of these questions. Some procedures for attempting to answer the questions are reviewed, with particular focus on p-values and confidence intervals. P-values are shown to be rather unhelpful in answering either question, especially when applied to probabilistic verification scores, and confidence intervals are to be preferred. However, confidence intervals cannot reveal biases in the value of a score that arises from an inadequate experimental design for testing on truly out-of-sample observations. Some specific problems with cross validation are highlighted. Finally, in the interests of increasing the insight into forecast strengths and weaknesses and in pointing towards methods for improving forecast quality, a plea is made for a more discriminating selection of verification procedures than has been adopted to date

Inhibitory effects of Yangzheng Xiaoji on angiogenesis and the role of the focal adhesion kinase pathway

Angiogenesis is an essential event during the excessive growth and metastatic spread of solid tumours. Anti-angiogenic agents have become a new choice of therapy for patients with cancer. In the present study, we investigated the potential effect of Yangzheng Xiaoji, a traditional Chinese medicinal formula presently used in the treatment of several solid tumours including liver cancer and gastric cancer, on angiogenesis, in vitro. The human vascular endothelial cell line HECV was used. A Matrigel-based sandwich tubule formation assay was employed to assess in vitro angiogenesis, a colorimetric method for assessing in vitro cell growth. Electric cell-substrate impedance sensing (ECIS) was used to evaluate the adhesion and migration of endothelial cells. The effects on activation of focal adhesion kinase (FAK) were evaluated using western blotting and immunofluorescence methods. Yangzhen Xiaoji extract DME25 significantly inhibited tube formation (p=0.046 vs control). This was seen together with a concentration-dependent inhibition on cell-matrix adhesion and cellular migration. It was demonstrated that the focal adhesion kinase (FAK) inhibitor PF557328 had a significant synergistic effect on DME25-induced inhibition of cell adhesion, migration and tube formation. The study showed that DME25 inhibited the phosphorylation of FAK in endothelial cells. In conclusion, Yangzhen Xiaoji has a marked effect on angiogenesis, in vitro and that this effect is at least partly mediated by the focal adhesion kinase (FAK) pathway

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Applying Data Mining Methods to Understand User Interactions within Learning Management Systems: Approaches and Lessons Learned

This article describes our processes for analyzing and mining the vast records of instructor and student usage data collected by a learning management system (LMS) widely used in higher education, called Canvas. Our data were drawn from over 33,000 courses taught over three years at a mid-sized public Western U.S. university. Our processes were guided by an established data mining framework, called Knowledge Discovery and Data Mining (KDD). In particular, we use the KDD framework in guiding our application of several educational data mining (EDM) methods (prediction, clustering, and data visualization) to model student and instructor Canvas usage data, and to examine the relationship between these models and student learning outcomes. We also describe challenges and lessons learned along the way

Quantifying solar superactive regions with vector magnetic field observations

The vector magnetic field characteristics of superactive regions (SARs) hold the key for understanding why SARs are extremely active and provide the guidance in space weather prediction. We aim to quantify the characteristics of SARs using the vector magnetograms taken by the Solar Magnetic Field Telescope at Huairou Solar Observatory Station. The vector magnetic field characteristics of 14 SARs in solar cycles 22 and 23 were analyzed using the following four parameters: 1) the magnetic flux imbalance between opposite polarities, 2) the total photospheric free magnetic energy, 3) the length of the magnetic neutral line with its steep horizontal magnetic gradient, and 4) the area with strong magnetic shear. Furthermore, we selected another eight large and inactive active regions (ARs), which are called fallow ARs (FARs), to compare them with the SARs. We found that most of the SARs have a net magnetic flux higher than 7.0\times10^21 Mx, a total photospheric free magnetic energy higher than 1.0\times10^24 erg/cm, a magnetic neutral line with a steep horizontal magnetic gradient (\geq 300 G/Mm) longer than 30 Mm, and an area with strong magnetic shear (shear angle \geq 80\degree) greater than 100 Mm^2. In contrast, the values of these parameters for the FARs are mostly very low. The Pearson \c{hi}2 test was used to examine the significance of the difference between the SARs and FARs, and the results indicate that these two types of ARs can be fairly distinguished by each of these parameters. The significance levels are 99.55%, 99.98%, 99.98%, and 99.96%, respectively. However, no single parameter can distinguish them perfectly. Therefore we propose a composite index based on these parameters, and find that the distinction between the two types of ARs is also significant with a significance level of 99.96%. These results are useful for a better physical understanding of the SAR and FARComment: 9 pages, 3 figures, 2 table

Stable isotopic labeling in proteomics

Labeling of proteins and peptides with stable heavy isotopes (deuterium, carbon-13, nitrogen-15, and oxygen-18) is widely used in quantitative proteomics. These are either incorporated metabolically in cells and small organisms, or postmetabolically in proteins and peptides by chemical or enzymatic reactions. Only upon measurement with mass spectrometers holding sufficient resolution, light, and heavy labeled peptide ions or reporter peptide fragment ions segregate and their intensity values are subsequently used for quantification. Targeted use of these labels or mass tags further leads to specific monitoring of diverse aspects of dynamic proteomes. In this review article, commonly used isotope labeling strategies are described, both for quantitative differential protein profiling and for targeted analysis of protein modifications