A multiple objective test assembly approach for exposure control problems in computerized adaptive testing

Overexposure and underexposure of items in the bank are serious problems in operational computerized adaptive testing (CAT) systems. These exposure problems might result in item compromise, or point at a waste of investments. The exposure control problem can be viewed as a test assembly problem with multiple objectives. Information in the test has to be maximized, item compromise has to be minimized, and pool usage has to be optimized. In this paper, a multiple objectives method is developed to deal with both types of exposure problems. In this method, exposure control parameters based on observed exposure rates are implemented as weights for the information in the item selection procedure. The method does not need time consuming simulation studies, and it can be implemented conditional on ability level. The method is compared with Sympson Hetter method for exposure control, with the Progressive method and with alphastratified testing. The results show that the method is successful in dealing with both kinds of exposure problems

Chemical compositions of stars in two stellar streams from the Galactic thick disk

We present abundances for 20 elements for stars in two stellar streams identified by Arifyanto & Fuchs (2006, A&A, 449, 533): 18 stars from the Arcturus stream and 26 from a new stream, which we call AF06 stream, both from the Galactic thick disk. Results show both streams are metal-poor and very old (10$-$14 Gyrs) with kinematics and abundances overlapping with the properties of local field thick disk stars. Both streams exhibit a range in metallicity but with relative elemental abundances that are identical to those of thick disk stars of the same metallicity. These results show that neither stream can result from dissolution of an open cluster. It is highly unlikely that either stream represents tidal debris from an accreted satellite galaxy. Both streams most probably owe their origin to dynamical perturbations within the Galaxy.Comment: 10 figures, Accepted for publication in MNRA

A blending of computer-based assessment and performance-based assessment: Multimedia-Based Performance Assessment (MBPA). The introduction of a new method of assessment in Dutch Vocational Education and Training (VET)

Innovation in technology drives innovation in assessment. Since the introduction of computer-based assessment (CBA), a few decades ago, many formerly paper-and-pencil tests have transformed in a computer-based equivalent. CBAs are becoming more complex, including multimedia and simulative elements and even immersive virtual environments. In Vocational Education and Training (VET), test developers may seize the opportunity provided by technology to create a multimedia-based equivalent of performance-based assessment (PBA), from here on defined as multimedia-based performance assessment (MBPA). MBPA in vocational education is an assessment method that incorporates multimedia (e.g. video, illustrations, graphs, virtual reality) for the purpose of simulating the work environment of the student and for creating tasks and assignments in the assessment. Furthermore, MBPA is characterized by a higher amount of interactivity between the student and the assessment than traditional computer-based tests. The focal constructs measured by MBPA are the same as are currently assessed by performance-based assessments. Compared to automated delivery of item-based tests, MBPA realizes the full power of ICT. In the present article we will therefore discuss the current status of MBPA, including examples of our own research on MBPA. We provide an argument for the use of MBPA in vocational education too

Item Selection Methods Based on Multiple Objective Approaches for Classifying Respondents Into Multiple Levels

Computerized classification tests classify examinees into two or more levels while maximizing accuracy and minimizing test length. The majority of currently available item selection methods maximize information at one point on the ability scale, but in a test with multiple cutting points selection methods could take all these points simultaneously into account. If for each cutting point one objective is specified, the objectives can be combined into one optimization function using multiple objective approaches. Simulation studies were used to compare the efficiency and accuracy of eight selection methods in a test based on the sequential probability ratio test. Small differences were found in accuracy and efficiency between different methods depending on the item pool and settings of the classification method. The size of the indifference region had little influence on accuracy but considerable influence on efficiency. Content and exposure control had little influence on accuracy and efficienc

Characterization of human UTF1, a chromatin-associated protein with repressor activity expressed in pluripotent cells

AbstractIn mice, during early embryonic development UTF1 (undifferentiated embryonic cell transcription factor 1) is expressed in the inner cell mass of blastocysts and in adult animals expression is restricted to the gonads. (Embryonic) Cells expressing UTF1 are generally considered pluripotent, meaning they can differentiate into all cell types of the adult body. In mouse it was shown that UTF1 is tightly associated with chromatin and that it is required for proper differentiation of embryonic carcinoma and embryonic stem cells. In this study we functionally characterized the human UTF1 protein. We show with localization, subnuclear fractionation, and strip-FRAP analyses that human UTF1 is a tightly DNA-associated protein with transcriptional repressor activity. Our data identify human UTF1 as a pluripotency-associated chromatin component with core histone-like characteristics

New triple systems in the RasTyc sample of stellar X-ray sources

During the study of a large set of late-type stellar X-ray sources, we discovered a large fraction of multiple systems. In this paper we investigate the orbital elements and kinematic properties of three new spectroscopic triple systems as well as spectral types and astrophysical parameters (T_eff, log g, vsin i, log N(Li)) of their components. We conducted follow-up optical observations, both photometric and spectroscopic at high resolution, of these systems. We used a synthetic approach and the cross-correlation method to derive most of the stellar parameters. We estimated reliable radial velocities and deduced the orbital elements of the inner binaries. The comparison of the observed spectra with synthetic composite ones, obtained as the weighted sum of three spectra of non-active reference stars, allowed us to determine the stellar parameters for each component of these systems. We found all are only composed of main sequence stars. These three systems are certainly stable hierarchical triples composed of short-period inner binaries plus a tertiary component in a long-period orbit. From their kinematics and/or Lithium content, these systems result to be fairly young.Comment: Accepted for publication in A&A (on July 22, 2008

Dynamical Masses of Young Stars in Multiple Systems

We present recent measurements of the orbital motion in the young binaries DF Tau and ZZ Tau, and the hierarchical triple Elias 12, that were obtained with the Fine Guidance Sensors on the HST and at the Keck Observatory using adaptive optics. Combining these observations with previous measurements from the literature, we compute preliminary orbital parameters for DF Tau and ZZ Tau. We find that the orbital elements cannot yet be determined precisely because the orbital coverage spans only about 90 degr in position angle. Nonetheless, the range of possible values for the period and semi-major axis already defines a useful estimate for the total mass in DF Tau and ZZ Tau, with values of 0.90{+0.85}{-0.35} M_sun and 0.81{+0.44}{-0.25} M_sun, respectively, at a fiducial distance of 140 pc.Comment: 26 pages, 9 figures, accepted for publication in A

New high-sensitivity, milliarcsecond resolution results from routine observations of lunar occultations at the ESO VLT

(Abridged) Lunar occultations (LO) are a very efficient and powerful technique, that achieves the best combination of high angular resolution and sensitivity possible today at near-infrared wavelengths. Given that the events are fixed in time, that the sources are occulted randomly, and that the telescope use is minimal, the technique is very well suited for service mode observations. We have established a program of routine LO observations at the VLT observatory, especially designed to take advantage of short breaks available in-between other programs. We have used the ISAAC instrument in burst mode, capable of producing continuous read-outs at millisecond rates on a suitable subwindow. Given the random nature of the source selection, our aim has been primarily the investigation of a large number of stellar sources at the highest angular resolution in order to detect new binaries. Serendipitous results such as resolved sources and detection of circumstellar components were also anticipated. We have recorded the signal from background stars for a few seconds, around the predicted time of occultation by the Moon's dark limb. At millisecond time resolution, a characteristic diffraction pattern can be observed. Patterns for two or more sources superimpose linearly, and this property is used for the detection of binary stars. The detailed analysis of the diffraction fringes can be used to measure specific properties such as the stellar angular size and the presence of extended light sources such as a circumstellar shell. We present a list of 191 stars for which LO data could be recorded and analyzed. Results include the detection of 16 binary and 2 triple stars, all but one of which were previously unknown. The projected angular separations are as small as 4 milliarcseconds and magnitude differences as high as ?K=5.8 mag...Comment: 10 pages, 3 figures, to be published in A&

Do we ruin the moment? Exploring the design of novel capturing technologies

Copyright © 2015 ACM. By capturing our experiences we often strive to better remember them in the future. However, the act of media capturing also influences these same experiences in the present, an area which is underexplored. This paper describes a study with the aim to inform the design of novel media capturing strategies. Adopting an approach of defamiliarization based on intervention and reflection, we strive to gain insights in the influences of future capturing technologies on the experience of a day out. We conducted an exploratory study in which 28 students went on a day out and used a variety of capturing strategies. Individual and group reflections on the experience during this day identified several important aspects that media capturing influences: engagement, perception & attention and social activity. The paper concludes with implications for design and proposes three potential future directions for media capturing, that instead of disturbing the moment enhance the experience