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 NGC 7714: Starburst after Galaxy Collision
Is this galaxy jumping through a giant ring of stars? Probably not. Although the precise dynamics behind the featured image is yet unclear, what is clear is that the pictured galaxy, NGC 7714, has been stretched and distorted by a recent collision with a neighboring galaxy. This smaller neighbor, NGC 7715, situated off to the left of the frame, is thought to have charged right through NGC 7714. Observations indicate that the golden ring pictured is composed of millions of older Sun-like stars that are likely co-moving with the interior bluer stars. In contrast, the bright center of NGC 7714 appears to be undergoing a burst of new star formation. The featured image was captured by the Hubble Space Telescope. NGC 7714 is located about 130 million light years away toward the constellation of the Two Fish (Pisces). The interactions between these galaxies likely started about 150 million years ago and should continue for several hundred million years more, after which a single central galaxy may result.
Mount Timpanogos with sky above
Check current conditions and historical weather data at the ESC.
Image for Sommerfeldts Called as Mission Leaders
Professor Scott and Lisa Sommerfeldt in Missouri Independence Mission
Image for Sounding out the Deep: Traci Neilsen’s Trip to the North Atlantic
A recent research adventure took Dr. Traci Neilsen and two students to the North Atlantic Ocean. Neilsen, an associate professor of physics at BYU, and her team apply artificial intelligence to noises in the ocean to classify the seabed.
Image for Reveling in Uncertainty
Despite the inherent time constraints of engaging undergraduate and graduate students in research, Scott Bergeson enjoys teaching this “seek and find” principle to his students, a principle that has become his philosophy for life.

Selected Publications

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BYU Authors: Benjamin Francis and Mark K. Transtrum, published in Adv. Electron. Mater.

Superconducting radio-frequency (SRF) resonators are critical components for particle accelerator applications, such as free-electron lasers, and for emerging technologies in quantum computing. Developing advanced materials and their deposition processes to produce RF superconductors that yield n & omega; surface resistances is a key metric for the wider adoption of SRF technology. Here, ZrNb(CO) RF superconducting films with high critical temperatures (T-c) achieved for the first time under ambient pressure are reported. The attainment of a T-c near the theoretical limit for this material without applied pressure is promising for its use in practical applications. A range of T-c, likely arising from Zr doping variation, may allow a tunable superconducting coherence length that lowers the sensitivity to material defects when an ultra-low surface resistance is required. The ZrNb(CO) films are synthesized using a low-temperature (100 - 200 & DEG;C) electrochemical recipe combined with thermal annealing. The phase transformation as a function of annealing temperature and time is optimized by the evaporated Zr-Nb diffusion couples. Through phase control, one avoids hexagonal Zr phases that are equilibrium-stable but degrade T-c. X-ray and electron diffraction combined with photoelectron spectroscopy reveal a system containing cubic & beta;-ZrNb mixed with rocksalt NbC and low-dielectric-loss ZrO2. Proof-of-concept RF performance of ZrNb(CO) on an SRF sample test system is demonstrated. BCS resistance trends lower than reference Nb, while quench fields occur at approximately 35 mT. The results demonstrate the potential of ZrNb(CO) thin films for particle accelerators and other SRF applications.

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BYU Authors: Sharisse Poff, Daniel Tebbs, Robert C. Davis, and Shiuh–hua Wood Chiang, published in 2023 Intermountain Engineering, Technology and Computing (IETC), (Provo, UT, May 2023).

The ability to monitor a varying impedance has a range of applications, including the measurement of biological properties using bioimpedance analysis. For this type of impedance monitoring, the human heartbeat plays a role, motivating a desire to monitor pulsatile impedance changes. A four-point circuit for pulsatile impedance monitoring is designed, simulated, and built on a PCB. The circuit design is described. The circuit's ability to measure constant impedance across frequency and extract lumped element values is characterized. Using a photoresistor setup, the circuit's response to pulsatile impedance variation ranging from 500 Ω to 70 kΩ is measured and analyzed. The measured circuit settling time for an impedance change as large as 70 kΩ is 40 milliseconds, sufficient speed for heartbeat-rate pulsatile impedance monitoring.

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BYU Authors: G. Apolonio, A. Bugg, K. Epps, M. D. Joner, M. Spencer, and J. B. Trump, published in Astrophys. J.

We study the broadband emission of Mrk 501 using multiwavelength observations from 2017 to 2020 performed with a multitude of instruments, involving, among others, MAGIC, Fermi's Large Area Telescope (LAT), NuSTAR, Swift, GASP-WEBT, and the Owens Valley Radio Observatory. Mrk 501 showed an extremely low broadband activity, which may help to unravel its baseline emission. Nonetheless, significant flux variations are detected at all wave bands, with the highest occurring at X-rays and very-high-energy (VHE) γ-rays. A significant correlation (>3σ) between X-rays and VHE γ-rays is measured, supporting leptonic scenarios to explain the variable parts of the emission, also during low activity. This is further supported when we extend our data from 2008 to 2020, and identify, for the first time, significant correlations between the Swift X-Ray Telescope and Fermi-LAT. We additionally find correlations between high-energy γ-rays and radio, with the radio lagging by more than 100 days, placing the γ-ray emission zone upstream of the radio-bright regions in the jet. Furthermore, Mrk 501 showed a historically low activity in X-rays and VHE γ-rays from mid-2017 to mid-2019 with a stable VHE flux (>0.2 TeV) of 5% the emission of the Crab Nebula. The broadband spectral energy distribution (SED) of this 2 yr long low state, the potential baseline emission of Mrk 501, can be characterized with one-zone leptonic models, and with (lepto)-hadronic models fulfilling neutrino flux constraints from IceCube. We explore the time evolution of the SED toward the low state, revealing that the stable baseline emission may be ascribed to a standing shock, and the variable emission to an additional expanding or traveling shock.

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BYU Authors: Logan T. Mathews, Alan T. Wall, and Kent L. Gee, published in AIAA AVIATION Forum, (San Diego, CA, June 2023).

Understanding the acoustic source characteristics of supersonic jets is vital to accurate noise field modeling and jet noise reduction strategies. This paper uses advanced, coherence- based partial field decomposition methods to characterize the acoustic sources in an installed, supersonic GE F404 engine. Partial field decomposition is accomplished using an equivalent source reconstruction via acoustical holography. Bandwidth is extended through the application of an array phase-unwrapping and interpolating scheme. The optimized-location virtual references method is used, and variations on this method are discussed. Apparent source distributions and source-related partial fields are shown as a function of frequency. Local maxima are observed in holography reconstructions at the nozzle lipline, distinct in frequency and space. It is hypothesized that the first local maximum may relate to noise generated by large-scale turbulence structures around and downstream of the supersonic core tip. Other local maxima are correlated primarily with Mach wave radiation originating from throughout the shear layer and into the region downstream of the potential core tip but before the end of the supersonic core. Source-elucidating decompositions show that the order and behavior of the decomposition lends to the local maxima being related to distinct source mechanisms, while between the local maxima, there is a combination of mechanisms active, which is likely the cause of spatiospectral lobes observed previously with other full-scale, supersonic jets.

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BYU Authors: Tyce Olaveson, Kent L. Gee, and Jon Johnson, published in AIAA AVIATION Forum, (San Diego, CA, June 2023).

Spatiospectral lobes are features identified in the noise fields radiated from full-scale tactical aircraft that are unseen in lab-scale experiments. Prior studies have explored lobe frequency-domain characteristics, but a joint time-frequency domain (JTFD) analysis has the potential to further explore these phenomena and connect them to source-related events. This paper applies an event-based beamforming technique to acoustical data collected at a 120-microphone array near a T-7A-installed F404 engine. The algorithm correlates time domain events between pairs of adjacent microphones to find an event propagation direction and then ray traces to the jet centerline to identify an apparent source location. A wavelet transform is used to identify frequency triggers tied to the spatiospectral lobes to gain insights. It is shown that the source responsible for the spatiospectral lobes is composed of multiple, overlapping sources each with a different peak radiation angle. Events are also observed in the time-frequency domain, and it is found that there is an underlying temporal structure reminiscent of mode switching seen with lab-scale jet screech. Using a Markov-style analysis, this temporal structure is characterized. It is found that spectral peaks related to the spatiospectral lobes are composed of discrete but randomly distributed temporospectral events, each with a frequency-dependent directivity.

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BYU Authors: Matthew A. Christian and Kent L. Gee, published in AIAA AVIATION Forum, (San Diego, CA, June 2023)

This paper describes investigations into convective Mach number and its relationship to maximum radiation angle for an installed afterburner-capable military jet engine. The convective Mach number describes the velocity of coherent structures in the turbulent mixing layer of a jet. For supersonic jets, this parameter should be useful in predicting the maximum noise radiation angle. However, of the several definitions of the convective Mach number, none have been successful in predicting the peak radiation angle of all jets. In this paper, physicsbased and empirically derived convective Mach numbers are calculated from data collected from a T-7A-installed GE F404 engine and are compared against measured maximum noise directivity angles. Of the physics-based definitions, the T-7A data how the convective Mach number associated with Oertel’s first family of instability waves predicts the maximum radiation angle within 6° over a range of engine conditions. Additionally, the so-called “Oertel convective Mach number,” which has successfully predicted peak directivity angles in rocket noise studies, is a relatively poor predictor of the T-7A maximum directivity angle. An empirical formulation of the convective Mach number suggests that, for the T-7A, the “convective velocity” of coherent structures in the shear layer is about 60% of the fullyexpanded centerline velocity for supersonic engine conditions. Evaluating this empirical definition of the convective Mach number using data from other jet noise studies shows that the acoustic Mach number appears to be the best predictor of the convective velocity. Finally, a frequency-dependent study of the convective Mach number at afterburner shows the peak directivity angle is roughly constant at low and high frequencies, while the frequencies associated with the transition from the potential core to the supersonic core show the greatest change in directivity.