IDENTIFICATION OF TREATED-COLOR FRESHWATER CULTURED PEARLS

Ta τελευταία 30 χρόνια η ζήτηση των χρωματιστών μαργαριταριών (όπου είναι σπανιότερα από τα λευκά) έχει ανέβει κατακόρυφα. Αποτέλεσμα αυτού είναι η εισροή στην αγορά μαργαριταριών με τεχνητό χρώμα, η αναγνώριση των οποίων απασχολεί έντονα τους γεμμολόγους. Για την αναγνώριση, τα μαργαριτάρια εξετάζονται μακροσκοπικά και μικροσκοπικά, γίνονται μετρήσεις φθορισμού σε ακτίνες-Χ (EDXRF) και τέλος μελετώνται οι ακτινογραφίες τους. Με τη χρήση ωστόσο των παραπάνω μεθόδων δεν καθίσταται, πάντα, εφικτή η αναγνώριση των τεχνητά χρωματισμένων μαργαριταριών. Παλαιότερες έρευνες έδειξαν ότι η φασματοσκοπία Raman είναι χρήσιμη στην αναγνώριση των χρωστικών ουσιών των μαργαριταριών γλυκού νερού. Στη παρούσα εργασία παρουσιάζονται μετρήσεις του φαινομένου Raman, με τη χρήση πράσινου laser, σε 35 φυσικά και 15 τεχνητά χρωματισμένα δείγματα. Όλα τα φάσματα Raman των φυσικά χρωματισμένων δειγμάτων παρουσιάζουν δύο κορυφές, όπου είναι χαρακτηριστικές για τις πολυακετυλενικές χρωστικές ουσίες. Αυτές οι κορυφές είναι παρούσες, ανεξαρτήτως του χρώματος των δειγμάτων, και οφείλονται στη δόνηση τάσης (stretching) των μορίων του των διπλών δεσμών άνθρακα (C—C) -στα 1530(±25) cm'1- και των μονών δεσμών άνθρακα (CC) -στα 1130(±10) cm'1- των χρωστικών ουσιών. Στη παρούσα εργασία προτείνεται ότι  η πιθανή απουσία των παραπάνω κορυφών Raman σε ένα χρωματιστό μαργαριτάρι γλυκού νερού αποτελεί απόδειξη ότι το χρώμα του μαργαριταριού αυτού είναι τεχνητό.Demand for colored pearls has grown during the last thirty years. Colored pearls are rarer than white ones. Thus treated-color pearls have entered the marketplace and their identification became a challenge for the gemologists. With only the help of visual observation, EDXRF and X-radiography, methods that are used today for pearls identification, it is not always easy to identify them. Previous studies, have established that Raman scattering is useful to detect pigments in cultured freshwater pearls. The present study is based on the measurement of the Raman spectroscopy of 35 natural colored freshwater pearls and 15 treated-color freshwater pearls, covering a wide range of typical colors for this material, with green excitation. All natural- color pearls show the two major Raman resonance features of polacetyenic pigments assigned to C=C stretching-at about 1530(±25) cm'1- and C-C stretching - at about 1130(±10) cm' -, regardless of their specific hue. In this paper it is proposed that the absence of these Raman features prove the artificial origin of pigments in a colored freshwater cultured pearl

Deep XMM-Newton observations of the northern disc of M31. I. Source catalogue

We carried out new observations of two fields in the northern ring of M31 with XMM-Newton with two exposures of 100 ks each and obtained a complete list of X-ray sources down to a sensitivity limit of ~7 x 10^34 erg s^-1 (0.5 - 2.0 keV). The major objective of the observing programme was the study of the hot phase of the ISM in M31. The analysis of the diffuse emission and the study of the ISM is presented in a separate paper. We analysed the spectral properties of all detected sources using hardness ratios and spectra if the statistics were high enough. We also checked for variability. We cross-correlated the source list with the source catalogue of a new survey of the northern disc of M31 carried out with Chandra and Hubble (Panchromatic Hubble Andromeda Treasury, PHAT) as well as with other existing catalogues. We detected a total of 389 sources, including 43 foreground stars and candidates and 50 background sources. Based on the comparison to the Chandra/PHAT survey, we classify 24 hard X-ray sources as new candidates for X-ray binaries (XRBs). In total, we identified 34 XRBs and candidates and 18 supernova remnants (SNRs) and candidates. Three of the four brightest SNRs show emission mainly below 2 keV, consistent with shocked ISM. The spectra of two of them also require an additional component with a higher temperature. The SNR [SPH11] 1535 has a harder spectrum and might suggest that there is a pulsar-wind nebula inside the SNR. We find five new sources showing clear time variability. We also studied the spectral properties of the transient source SWIFT J004420.1+413702, which shows significant variation in flux over a period of seven months (June 2015 to January 2016) and associated change in absorption. Based on the likely optical counterpart detected in the Chandra/PHAT survey, the source is classified as a low-mass X-ray binary.Comment: Accepted for publication in A&

Web user interface design strategy: Designing for device independence

Until recently, Web services were available only through a desktop web browser. Nowadays, methods of access move beyond the desktop computer towards ubiquitous access through portable devices. As a consequence, users have the chance to interact with a growing diversity of computing devices such as PDAs, smart phones, etc., with diverse characteristics that tend to replace conventional laptop and desktop computers. User interface designers, on the other hand, strive to design usable interfaces to cater for the diverse requirements of these devices. The design strategy proposed in this paper aims at assisting user interface designers in designing for diverse devices recommending a specific line of activities in the process of design. A case study of application of the proposed design strategy is presented, outlining its advantages

Comparative performance of selected variability detection techniques in photometric time series

Photometric measurements are prone to systematic errors presenting a challenge to low-amplitude variability detection. In search for a general-purpose variability detection technique able to recover a broad range of variability types including currently unknown ones, we test 18 statistical characteristics quantifying scatter and/or correlation between brightness measurements. We compare their performance in identifying variable objects in seven time series data sets obtained with telescopes ranging in size from a telephoto lens to 1m-class and probing variability on time-scales from minutes to decades. The test data sets together include lightcurves of 127539 objects, among them 1251 variable stars of various types and represent a range of observing conditions often found in ground-based variability surveys. The real data are complemented by simulations. We propose a combination of two indices that together recover a broad range of variability types from photometric data characterized by a wide variety of sampling patterns, photometric accuracies, and percentages of outlier measurements. The first index is the interquartile range (IQR) of magnitude measurements, sensitive to variability irrespective of a time-scale and resistant to outliers. It can be complemented by the ratio of the lightcurve variance to the mean square successive difference, 1/h, which is efficient in detecting variability on time-scales longer than the typical time interval between observations. Variable objects have larger 1/h and/or IQR values than non-variable objects of similar brightness. Another approach to variability detection is to combine many variability indices using principal component analysis. We present 124 previously unknown variable stars found in the test data.Comment: 29 pages, 8 figures, 7 tables; accepted to MNRAS; for additional plots, see http://scan.sai.msu.ru/~kirx/var_idx_paper

Velocity asymmetries in YSO jets: Intrinsic and extrinsic mechanisms

It is a well established fact that some YSO jets (e.g. RW Aur) display different propagation speeds between their blue and red shifted parts, a feature possibly associated with the central engine or the environment in which the jet propagates. In order to understand the origin of asymmetric YSO jet velocities, we investigate the efficiency of two candidate mechanisms, one based on the intrinsic properties of the system and one based on the role of the external medium. In particular, a parallel or anti-parallel configuration between the protostellar magnetosphere and the disk magnetic field is considered and the resulting dynamics are examined both in an ideal and a resistive magneto-hydrodynamical (MHD) regime. Moreover, we explore the effects of a potential difference in the pressure of the environment, as a consequence of the non-uniform density distribution of molecular clouds. Ideal and resistive axisymmetric numerical simulations are carried out for a variety of models, all of which are based on a combination of two analytical solutions, a disk wind and a stellar outflow. We find that jet velocity asymmetries can indeed occur both when multipolar magnetic moments are present in the star-disk system as well as when non-uniform environments are considered. The latter case is an external mechanism that can easily explain the large time scale of the phenomenon, whereas the former one naturally relates it to the YSO intrinsic properties. [abridged]Comment: accepted for publication in A&

VET students into technology companies: a microlearning digital course to train critical thinking skills

This microlearning course is designed to support VET graduates or students, especially those with fewer opportunities, who join a technology company at the beginning of their professional career. It has been developed within the framework of the Erasmus + project “VET STUDENTS İNTO TECHNOLOGY COMPANİES: A VET students mobility network in the technological sector through a virtual environment with specific materials for critical thinking”. This is an intiative co-financed by the Erasmus + Programme, with a personalized digital course format, to take into account both the previous training of the VET student or graduate and the type of company they will join. The course has in its sights to develop in the VET student the specific competences required by the technology company to address the problems typical of fields of leading technology innovation, as well as fitting in multidisciplinary teams. To do this, this course generates an innovative methodology in which the education itinerary is built based on previous knowledge of the student and the needs and work field of the technology company. Besides its contents strengthen critical thinking as an essential mechanism for work in both dynamic and technology sectors. For that purpose, the student is asked a series of questions in the form of problems that, in addition to being related to the study plans of VET studies, require for their solution the search for information, its analysis and many times the making of a decision or adopting a personal position on it. We aim with our training projects, within the Erasmus + program, to convince students that they are capable of going further and further in the development of their professional skills being the technology sector an acceptable option for them, making their work increasingly valuable for their inclusion, for their own personal development, for that of the company in which they work and for society. But for this certain skills are required, and one of the most important is learning to learn autonomously and to accurately analyse the information received and the decisions that are made from it. It is generally true that the problems that one encounters in professional practice are not going to be the ones that you were taught in your VET studies. Vocational training has to head for equipping students with the necessary tools to face the new problems that they will face in their job and to grow professionally every day. We intend to show how valuable critical thinking skills are in analysing our way of thinking and making decisions. In this paper we present examples of the exercises included in the course, how their approach and the processes that have led to a solution relate with the standards of critical thinking and the different levels of help that are offered to the student for their solution. The course is accessible from a digital educational software “ON YOUR SIDE: VIRTUAL ASSISTANT FOR EUROPEAN MOBILITIES IN TECHNOLOGICAL CENTERS” developed in the framework of this Erasmus+ project in order to develop cooperative work between students with fewer opportunities doing their internships in technology companies and their inclusion in new job posts. We will also present this software in a very summarized way in this article.This work has been funded by the Erasmus + program within the 2019-1-ES01-KA202-064569 project, Spanish Service for the Internationalization of Education (SEPIE