HD 4915: A Maunder Minimum Candidate

We study the magnetic activity cycle of HD 4915 using the \ion{Ca}{2} H \& K emission line strengths measured by Keck I/HIRES spectrograph. The star has been observed as a part of California Planet Search Program from 2006 to present. We note decreasing amplitude in the magnetic activity cycle, a pattern suggesting the star's entry into a Magnetic Grand Minimum (MGM) state, reminiscent of the Sun's Maunder and Dalton Minima. We recommend further monitoring of the star to confirm the grand minimum nature of the dynamo, which would provide insight into the state of the Sun's chromosphere and the global magnetic field during its grand minima. We also recommend continued observations of H \& K emission lines, and ground or space based photometric observations to estimate the sunspot coverage.Comment: To be submitted to AAS Journals; comments welcom

Astrophysical Insights into Radial Velocity Jitter from an Analysis of 600 Planet-search Stars

Radial velocity (RV) detection of planets is hampered by astrophysical processes on the surfaces of stars that induce a stochastic signal, or "jitter," which can drown out or even mimic planetary signals. Here, we empirically and carefully measure the RV jitter of more than 600 stars from the California Planet Search sample on a star by star basis. As part of this process, we explore the activity–RV correlation of stellar cycles and include appendices listing every ostensibly companion-induced signal we removed and every activity cycle we noted. We then use precise stellar properties from Brewer et al. to separate the sample into bins of stellar mass and examine trends with activity and with evolutionary state. We find that RV jitter tracks stellar evolution and that in general, stars evolve through different stages of RV jitter: the jitter in younger stars is driven by magnetic activity, while the jitter in older stars is convectively driven and dominated by granulation and oscillations. We identify the "jitter minimum"—where activity-driven and convectively driven jitter have similar amplitudes—for stars between 0.7 and 1.7 M⊙ and find that more-massive stars reach this jitter minimum later in their lifetime, in the subgiant or even giant phases. Finally, we comment on how these results can inform future RV efforts, from prioritization of follow-up targets from transit surveys like TESS to target selection of future RV surveys

Calculating the Conformal Modulus of Complex Tori and an Application to Graph Theory

In 1985 William Thurston conjectured that conformal mappings could be approximated using infintessimal circles. With this, the area of mathematics called Cirle Packing was born. The advantage of this technique is that it gives a computational method of understanding manifolds. In particular, we attempt to gain some insight of complex tori via Circle Packing. In practice, it is difficult to imagine what these tori look like. Computational techniques of Circle Packing will help us visualise these tori as points in moduli space by beginning with an initial triangulation of the torus. We then experiment with triangulations on a set number of vertices

Heterogeneous multithreaded computing

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1995.by Howard J. LuM.Eng

Some Bright Stars with Smooth Continua for Calibrating the Response of High Resolution Spectrographs

When characterizing a high resolution echelle spectrograph, for instance for precise Doppler work, it is useful to observe featureless sources such as quartz lamps or hot stars to determine the response of the instrument. Such sources provide a way to determine the blaze function of the orders, pixel-to-pixel variations in the detector, fringing in the system, and other important characteristics. In practice, however, many B or early A stars do not provide a smooth continuum, whether because they are not rotating rapidly enough or for some other reason. In fact, we have found that published rotational velocities and temperatures are not a specific and sensitive guide to whether a star's continuum will be smooth. A useful resource for observers, therefore, is a list of "good" hot stars: bright, blue stars known empirically to have no lines or other spectral features beyond the Balmer series with minima below 95% of the continuum. We have compiled a list of such stars visible from Northern Hemisphere telescopes. This list includes all stars listed in the Yale Bright Star Catalog (Hoffleit & Jaschek 1991) as being single with V 175 km/s, and declination > -30, and many other hot stars that we have found useful for calibration purposes. The list here of "bad" stars may also be of interest in studies of hot, slowly rotating stars

The Puzzle of Humility and Disparity

Suppose that you are engaging with someone who is your oppressor, or someone who espouses a heinous view like Nazism or a ridiculous view like flat-earthism. In contexts like these, there is a disparity between you and your interlocutor, a dramatic normative difference across which you are in the right and they are in the wrong. As theorists of humility, we find these contexts puzzling. Humility seems like the *last* thing oppressed people need and the *last* thing we need in dealing with those whose views are heinous or ridiculous. Responding to such people via humility seems uncalled for, even inappropriate. But how could this be, given that humility is a *virtue*? The purpose of the paper is to explore this puzzle. We explain what the puzzle is and then attempt to draw some lessons from it: first, the lesson that the importance of humility is limited in several ways, and second, the lesson that humility nonetheless has several important roles to play, even for people who are in the right in contexts of disparity

The Relationships of Perceived Supervisor and Peer Support on Job Embeddedness and Turnover Intent in Special Operations Post COVID-19

The COVID-19 pandemic created a societal recalculation based on a situation where mass populations were sent into isolation. Research noted the need for meaningfulness and intimacy creating a psychological imbalance that resulted in withdrawal from work and a reinvestment in higher priorities, called the Great Resignation. These cascading effects continue to negatively impact morale and performance, something that U.S. Special Operations cannot afford as the premier global combatant command. From a pool of 140 Special Operations participants data was collected through an anonymous survey to quantitatively assess correlational relationships among perceived peer support, perceived supervisor support, job embeddedness, and turnover intent in post-pandemic Special Operations. This study concluded that high levels of perceived supervisor support and perceived peer support have a significant relationship with turnover intent, further analysis revealed the strongest relationship nested within perceived supervisor support. Further synthesis of data revealed a significant correlation between perceived peer support, perceived supervisory support, and job embeddedness. The study also concluded that perceived peer support had the strongest relationship with job embeddedness. This concept finds Scriptural grounding in the relationships between Christ, His disciples, and their interactions. Solomon famously addressed the importance of peer support when he stated that “iron sharpens iron”

Circles Minimize most Knot Energies

We define a new class of knot energies (known as renormalization energies) and prove that a broad class of these energies are uniquely minimized by the round circle. Most of O'Hara's knot energies belong to this class. This proves two conjectures of O'Hara and of Freedman, He, and Wang. We also find energies not minimized by a round circle. The proof is based on a theorem of G. Luko on average chord lengths of closed curves.Comment: 15 pages with 3 figures. See also http://www.math.sc.edu/~howard