2,970 research outputs found

### The effect of imperfect corrections of PSF anisotropy on cosmic shear measurements

Current measurements of the weak lensing signal induced by large scale
structure provide useful constraints on a range of cosmological parameters.
However, the ultimate succes of this technique depends on the accuracy with
which one can correct for the effect of the Point Spread Function (PSF). In
this paper we examine the accuracy of the PSF anisotropy correction using
images of fields with a large number of stars. The ellipticity correlation
function of the residuals is studied to quantify the effect of imperfect
corrections for PSF anisotropy on cosmic shear studies. These imperfections
occur on the chip scale and consequently the systematic signal decreases
rapidly with increasing angular scale. Separation of the signal into ``E''
(curl-free) and ``B'' (curl) components can help to identify the presence of
residual systematics, but in general, the amplitude of the ``B''-mode is
different from that of the ``E''-mode. The study of fields with many stars can
be beneficial in finding a proper description of the variation of PSF
anisotropy, and consequently help to significantly improve the accuracy with
which the cosmic shear signal can be measured. We show that with such an
approach it is feasible that the accuracy of future cosmic shear studies is
limited by the statistical noise introduced by the intrinsic shapes of the
sources. In particular, the prospects for accurate measurements of the cosmic
shear signal on scales larger than ~10 arcminutes are excellent.Comment: submitted to MNRAS, 8 page

### Is There a Learning Gap?

This semester I student taught within a School Corporation in Northwest Indiana. I taught at two different elementary schools, School A and School B. Although the curriculum is the same across both schools, the students at each school are different.
School A has a higher income rate and also has lower enrollment for ethnic students.
School B has more students enrolled in the special education program and more students enrolled in the free and reduced lunch program.
My goal is to figure out if students from both schools will learn the same given the same instruction

### Patient Perception of Negative Non-Invasive Prenatal Testing Results

Non-invasive prenatal testing (NIPT) uses cell-free fetal DNA to assess for fetal aneuploidy during pregnancy. NIPT has higher detection rates and positive predictive values than previous methods; however, NIPT is not diagnostic. Studies suggest patients may underestimate the limitations of prenatal screening. Therefore, we conducted a prospective cross-sectional study of ninety-four women from genetic counseling clinics in Houston, Texas to assess patient understanding of the residual risk for aneuploidy after receiving a negative NIPT. The majority of participants (66%) understood the residual risk for Down syndrome following negative NIPT; however, 34% of participants indicated that negative NIPT completely eliminated the risk. Individuals with at least four years of college education were more likely to understand that NIPT does not eliminate the chance of trisomy 13/18 (p=0.012) and sex chromosome abnormality (p=0.039), and were more likely to understand which conditions NIPT tests for (p=0.021), compared to women with less formal education. These data demonstrate that despite the recent implementation of NIPT into obstetric practice, the majority of women are aware of its limitations after genetic counseling. However, clinicians may need to consider alternative ways to communicate the limitations of NIPT to those women with less formal education to ensure understanding

### Precision Weak Gravitational Lensing Using Velocity Fields: Fisher Matrix Analysis

Weak gravitational lensing measurements based on photometry are limited by
shape noise, the variance in the unknown unlensed orientations of the source
galaxies. If the source is a disk galaxy with a well-ordered velocity field,
however, velocity field data can support simultaneous inference of the shear,
inclination, and position angle, virtually eliminating shape noise. We use the
Fisher Information Matrix formalism to forecast the precision of this method in
the idealized case of a perfectly ordered velocity field defined on an
infinitesimally thin disk. For nearly face-on targets one shear component,
$\gamma_\times$, can be constrained to $0.003\frac{90}{I_0}\frac{25}{n_{\rm
pix}}$ where $I_0$ is the S/N of the central intensity pixel and $n_{\rm pix}$
is the number of pixels across a diameter enclosing 80\% of the light. This
precision degrades with inclination angle, by a factor of three by
$i{=}50^\circ$. Uncertainty on the other shear component, $\gamma_+$, is about
1.5 (7) times larger than the $\gamma_\times$ uncertainty for targets at
$i=10^\circ$ ($50^\circ$). For arbitrary galaxy position angle on the sky,
these forecasts apply not to $\gamma_+$ and $\gamma_\times$ as defined on the
sky, but to two eigenvectors in $(\gamma_+, \gamma_\times,\mu)$ space where
$\mu$ is the magnification. We also forecast the potential of less expensive
partial observations of the velocity field such as slit spectroscopy. We
conclude by outlining some ways in which real galaxies depart from our
idealized model and thus create random or systematic uncertainties not captured
here. In particular, our forecast $\gamma_\times$ precision is currently
limited only by the data quality rather than scatter in galaxy properties
because the relevant type of scatter has yet to be measured.Comment: Accepted to ApJ, 17 pages, 14 figures. Diff from v1: added Sec 3.1 on
degeneracies and Appendix with simulations confirming Fisher result

### Shaping Attitudes Toward Science in an Introductory Astronomy Class

At many universities, astronomy is a popular way for non-science majors to
fulfill a general education requirement. Because general-education astronomy
may be the only college-level science course taken by these students, it is the
last chance to shape the science attitudes of these future journalists,
teachers, politicians, and voters. I report on an attempt to measure and induce
changes in science attitudes in my general-education astronomy course. I
describe construction of the attitude survey, classroom activities designed to
influence attitudes, and give numerical results indicating a significant
improvement. In contrast, the literature on attitudes in introductory physics
courses generally reports stagnation or decline. I briefly comment on some
plausible explanations for this difference.Comment: v2 includes a copy of the surve

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