1,371 research outputs found
A method for optimal image subtraction
We present a new method designed for optimal subtraction of two images with
different seeing. Using image subtraction appears to be essential for the full
analysis of the microlensing survey images, however a perfect subtraction of
two images is not easy as it requires the derivation of an extremely accurate
convolution kernel. Some empirical attempts to find the kernel have used the
Fourier transform of bright stars, but solving the statistical problem of
finding the best kernel solution has never really been tackled. We demonstrate
that it is possible to derive an optimal kernel solution from a simple least
square analysis using all the pixels of both images, and also show that it is
possible to fit the differential background variation at the same time. We also
show that PSF variations can also be easily handled by the method. To
demonstrate the practical efficiency of the method, we analyzed some images
from a Galactic Bulge field monitored by the OGLE II project.
We find that the residuals in the subtracted images are very close to the
photon noise expectations. We also present some light curves of variable stars,
and show that, despite high crowding levels, we get an error distribution close
to that expected from photon noise alone. We thus demonstrate that nearly
optimal differential photometry can be achieved even in very crowded fields. We
suggest that this algorithm might be particularly important for microlensing
surveys, where the photometric accuracy and completeness levels could be very
significantly improved by using this method.Comment: 8,pages, 4 Postscript figures, emulateapj.sty include
Wavelength Dependent PSFs and their impact on Weak Lensing Measurements
We measure and model the wavelength dependence of the PSF in the Hyper
Suprime-Cam (HSC) Subaru Strategic Program (SSP) survey. We find that PSF
chromaticity is present in that redder stars appear smaller than bluer stars in
the and -bands at the 1-2 per cent level and in the and
-bands at the 0.1-0.2 per cent level. From the color dependence of the PSF,
we fit a model between the monochromatic PSF trace radius, , and wavelength
of the form . We find values of between -0.2
and -0.5, depending on the epoch and filter. This is consistent with the
expectations of a turbulent atmosphere with an outer scale length of m, indicating that the atmosphere is dominating the chromaticity. We
find evidence in the best seeing data that the optical system and detector also
contribute some wavelength dependence. Meyers and Burchat (2015) showed that
must be measured to an accuracy of not to dominate the
systematic error budget of the Large Synoptic Survey Telescope (LSST) weak
lensing (WL) survey. Using simple image simulations, we find that can be
inferred with this accuracy in the and -bands for all positions in the
LSST field of view, assuming a stellar density of 1 star arcmin and that
the optical PSF can be accurately modeled. Therefore, it is possible to correct
for most, if not all, of the bias that the wavelength-dependent PSF will
introduce into an LSST-like WL survey.Comment: 14 pages, 10 figures. Submitted to MNRAS. Comments welcom
Development of an mHealth platform for HIV Care: gathering user perspectives through co-design workshops and interviews
Background: Despite advances in testing and treatment, HIV incidence rates within European countries are at best stable or else increasing. mHealth technology has been advocated to increase quality and cost-effectiveness of health services while dealing with growing patient numbers. However, studies suggested that mHealth apps are rarely adopted and often considered to be of low quality by users. Only a few studies (conducted in the United States) have involved people living with HIV (PLWH) in the design of mHealth.
Objective: The goal of this study was to facilitate a co-design process among PLWH and clinicians across 5 clinical sites in the European Union to inform the development of an mHealth platform to be integrated into clinical care pathways. We aimed to (1) elicit experiences of living with HIV and of working in HIV care, (2) identify mHealth functionalities that are considered useful for HIV care, and (3) identify potential benefits as well as concerns about mHealth.
Methods: Between January and June 2016, 14 co-design workshops and 22 semistructured interviews were conducted, involving 97 PLWH and 63 clinicians. Data were analyzed thematically and iteratively, drawing on grounded theory techniques.
Results: Findings were established into 3 thematic clusters: (1) approaching the mHealth platform, (2) imagining the mHealth platform, and (3) anticipating the mHealth platformâs implications. Co-design participants approached the mHealth platform with pre-existing concerns arising from their experiences of receiving or providing care. PLWH particularly addressed issues of stigma and questioned how mHealth could enable them to manage their HIV. Clinicians problematized the compatibility of mHealth with existing information technology systems and questioned which patients should be targeted by mHealth. Imagining the potential of mHealth for HIV care, co-design participants suggested medical functionalities (accessing test results, managing medicines and appointments, and digital communication channels), social functionalities (peer support network, international travel, etc), and general features (security and privacy, credibility, language, etc). Co-design participants also anticipated potential implications of mHealth for self-management and the provision of care.
Conclusions: Our approach to co-design enabled us to facilitate early engagement in the mHealth platform, enabling patient and clinician feedback to become embedded in the development process at a preprototype phase. Although the technologies in question were not yet present, understanding how users approach, imagine, and anticipate technology formed an important source of knowledge and proved highly significant within the technology design and development process
Attitudes Toward Business Ethics And Degree Of Opinion Leadership Of Future Managers In The United States, Finland, And China
The purpose of this study was to compare the attitudes towards business ethics of future managers in three countries: the United State, Finland, and China, and determine whether business ethics attitudes differed by the students major, class year, GPA, gender, age, and the number of ethics and religious studies courses completed. Additionally the relationship between the degree of opinion leadership and ethical attitudes was examined to determine if opinion leaders exhibited different attitudes towards business ethics
Attitudes, Perceptions, and Tendencies of the Iranian Students in Medical Fields towards Cheating and Academic Dishonesty
     Background and Objectives: Despite universities initiating different controlling systems, cheating is still rampant and a global phenomena. One side of the problem of cheating involves the attitudes, perceptions and tendencies of the university students towards cheating and academic misconduct. The present survey seeks to elaborate on the above aspects among the students at one of the most important universities in Tehran, Iran. Methods and Sample: The study has benefitted from the translated and validated version of the questionnaire used by Lupton and Chapman (2002). The sample included 386 students studying at Shahid Beheshti University of Medical Sciences (SBMU) in Tehran in different fields of medical sciences.  Findings and Discussion: The survey has found some very interesting results on what Iranian university students think of cheating and academic dishonesty, despite all the controlling systems used in assigning homework and initiating mid-term and final exams. Almost 81.1 % of the female students and 85.2 % of male students did not consider âgiving the exam answers to someone at the following semesterâ an act of cheating. Moreover, 72.2 % of students responded that they had not cheated. Interestingly, 65.4 % of the respondents have admitted that they had given information of a previous exam to another student. The results showed that sex did not have any role in cheating and academic dishonesty (p=0.826)
Spectroscopy of Quasar Candidates from SDSS Commissioning Data
The Sloan Digital Sky Survey has obtained images in five broad-band colors
for several hundred square degrees. We present color-color diagrams for stellar
objects, and demonstrate that quasars are easily distinguished from stars by
their distinctive colors. Follow-up spectroscopy in less than ten nights of
telescope time has yielded 22 new quasars, 9 of them at , and one with
, the second highest-redshift quasar yet known. Roughly 80% of the
high-redshift quasar candidates selected by color indeed turn out to be
high-redshift quasars.Comment: 4 pages, 3 figures, to appear in the proceedings of "After the Dark
Ages: When Galaxies were Young (the Universe at 2<z<5)", 9th Annual October
Astrophysics Conference in Marylan
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