News and Events

Yifan Dong
Please join us for a colloquium titled “Unraveling Ultrafast Charge Transfer Dynamics in Organic Solar Cells” at 12:00 PM in C215 ESC.
Thumbnail of A Picturesque Equinox Sunset
What's that at the end of the road? The Sun. Many towns have roads that run east-west, and on two days each year, the Sun rises and sets right down the middle. Today, in some parts of the world (tomorrow in others), is one of those days: an equinox. Not only is this a day of equal night ("aequus"-"nox") and day time, but also a day when the sun rises precisely to the east and sets due west. Displayed here is a picturesque rural road in Alberta, Canada that runs approximately east-west. The featured image was taken during the September Equinox of 2021, but the geometry remains the same every year. In many cultures, this March equinox is taken to be the first day of a season, typically spring in Earth's northern hemisphere, and autumn in the south. Does your favorite street run east-west? Tonight, at sunset, you can find out with a quick glance.
Mount Timpanogos with sky above
Check current conditions and historical weather data at the ESC.
Image for Steve Summers' Insights for Students
Alumni Steve Summers answers interview questions for current students
Image for Wesley Morgan Doubles AP Physics Enrollment
Y Magazine recognizes finalist for the 2023 National Science Foundation’s Presidential Award of Excellence in Mathematics and Science Teaching
Image for BYU Women in Physics Students Thrive at CUWiP
Conference for Undergraduate Women in Physics provides support and opportunities for female BYU physics students

Selected Publications

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BYU Authors: Darin Ragozzine, published in Astron. J.

We present the methods and results from the discovery and photometric measurement of 26 bright VR > 24 trans-Neptunian objects (TNOs) during the first year (2019–20) of the DECam Ecliptic Exploration Project (DEEP). The DEEP survey is an observational TNO survey with wide sky coverage, high sensitivity, and a fast photometric cadence. We apply a computer vision technique known as a progressive probabilistic Hough transform to identify linearly moving transient sources within DEEP photometric catalogs. After subsequent visual vetting, we provide a photometric and astrometric catalog of our TNOs. By modeling the partial lightcurve amplitude distribution of the DEEP TNOs using Monte Carlo techniques, we find our data to be most consistent with an average TNO axis ratio b/a < 0.5, implying a population dominated by non-spherical objects. Based on ellipsoidal gravitational stability arguments, we find our data to be consistent with a TNO population containing a high fraction of contact binaries or other extremely non-spherical objects. We also discuss our data as evidence that the expected binarity fraction of TNOs may be size-dependent.

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BYU Authors: Mitchell C. Cutler, Mylan R. Cook, Mark K. Transtrum, and Kent L. Gee, published in J. Acoust. Soc. Am.

Separating crowd responses from raw acoustic signals at sporting events is challenging because recordings contain complex combinations of acoustic sources, including crowd noise, music, individual voices, and public address (PA) systems. This paper presents a data-driven decomposition of recordings of 30 collegiate sporting events. The decomposition uses machine-learning methods to find three principal spectral shapes that separate various acoustic sources. First, the distributions of recorded one-half-second equivalent continuous sound levels from men's and women's basketball and volleyball games are analyzed with regard to crowd size and venue. Using 24 one-third-octave bands between 50 Hz and 10 kHz, spectrograms from each type of game are then analyzed. Based on principal component analysis, 87.5% of the spectral variation in the signals can be represented with three principal components, regardless of sport, venue, or crowd composition. Using the resulting three-dimensional component coefficient representation, a Gaussian mixture model clustering analysis finds nine different clusters. These clusters separate audibly distinct signals and represent various combinations of acoustic sources, including crowd noise, music, individual voices, and the PA system.

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BYU Authors: Michael D. Joner, published in Astrophys. J.

We fit the UV/optical lightcurves of the Seyfert 1 galaxy Mrk 817 to produce maps of the accretion disk temperature fluctuations delta T resolved in time and radius. The delta T maps are dominated by coherent radial structures that move slowly (v c) inward and outward, which conflicts with the idea that disk variability is driven only by reverberation. Instead, these slow-moving temperature fluctuations are likely due to variability intrinsic to the disk. We test how modifying the input lightcurves by smoothing and subtracting them changes the resulting delta T maps and find that most of the temperature fluctuations exist over relatively long timescales (hundreds of days). We show how detrending active galactic nucleus (AGN) lightcurves can be used to separate the flux variations driven by the slow-moving temperature fluctuations from those driven by reverberation. We also simulate contamination of the continuum emission from the disk by continuum emission from the broad-line region (BLR), which is expected to have spectral features localized in wavelength, such as the Balmer break contaminating the U band. We find that a disk with a smooth temperature profile cannot produce a signal localized in wavelength and that any BLR contamination should appear as residuals in our model lightcurves. Given the observed residuals, we estimate that only similar to 20% of the variable flux in the U and u lightcurves can be due to BLR contamination. Finally, we discus how these maps not only describe the data but can make predictions about other aspects of AGN variability.

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BYU Authors: A. V. Mosenkov, S. K. H. Bahr, and Z. Shakespear, published in Astron. Astrophys.

Polar-ring galaxies are photometrically and kinematically decoupled systems that are highly inclined to the major axis of the host. These galaxies have been explored since the 1970s, but the rarity of these systems has made such systematic studies difficult. However, over 250 good candidates have been identified. In this work, we examine a sample of over 18 000 galaxies from the Sloan Digital Sky Survey (SDSS) Stripe 82 for the presence of galaxies with polar structures. Using deep SDSS Stripe 82, DESI Legacy Imaging Surveys, and Hyper Suprime-Cam Subaru Strategic Program, we selected 53 good candidate galaxies with photometrically decoupled polar rings, 9 galaxies with polar halos, 6 galaxies with polar bulges, and 34 possibly forming polar-ring galaxies, versus 13 polar-ring candidates previously selected in Stripe 82. Our results suggest that the occurrence rate of galaxies with polar structures may be significantly underestimated, as revealed by the deep observations, and may amount to 1-3% of non-dwarf galaxies.

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BYU Authors: Samuel Bellows and Timothy W. Leishman, published in J. Audio Eng. Soc.

Directivity measurements characterize the angular dependence of source-radiated fields, often through discrete measurements made over a spherical surface. Despite the AES56-2008 (r2019) dual-equiangular standard's ubiquity for directivity applications, no well-known spherical quadrature rule directly applies to its sampling scheme. However, this work shows how Clenshaw-Curtis--type Chebyshev quadrature rules adapt efficiently to equiangular spherical integration. Numerical experiments compare the reliability of Chebyshev, Chebshev-Lobatto, and Chebyshev-Radau quadrature rules for sampled pressure fields. The results show that significant aliasing effects do not occur until nearly twice the previously assumed limit. They also highlight the benefits of the AES approach of equivalent polar and azimuthal angle sampling intervals.

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BYU Authors: D. Hodge, T. Buckway, R. Camacho, E. Christie, A.M. Hardy, M. Ware, and R.L. Sandberg, published in Results Phys.

We present measurements of X-ray Parametric Down Conversion at the Advanced Photon Source synchrotron facility. Using an incoming pump beam at 22 keV, we observe the simultaneous, elastic emission of down-converted photon pairs generated in a diamond crystal. The pairs are detected using high count rate silicon drift detectors with low noise. Production by down-conversion is confirmed by measuring time–energy correlations in the detector signal, where photon pairs within an energy window ranging from 10 to 12 keV are only observed at short time differences. By systematically varying the crystal misalignment and detector positions, we obtain results that are consistent with the constant total of the down-converted signal. Our maximum rate of observed pairs was 130/h, corresponding to a conversion efficiency for the down-conversion process of 5.3±0.5×10−13.