Publications

We report the development of a tandem chemoenzymatic transformation that combines alkene metathesis with enzymatic epoxidation to provide aryl epoxides. The development of this one-pot reaction required substantial protein and reaction engineering to improve both selectivity and catalytic activity. Ultimately, this reaction converts a mixture of alkenes into a single epoxide product in high enantioselectivity and moderate yields and illustrates both the challenges and benefits of tandem catalysis combining organometallic and enzymatic systems.

We worked to ensure race, ethnic, and/or other types of diversity in the recruitment of human participants. We worked to ensure that the study questionnaires were prepared in an inclusive way. We worked to ensure sex and gender balance in the recruitment of human participants. One or more of the authors of this paper self-identifies as a member of one or more historically underrepresented racial and/or ethnic groups in science. One or more of the authors of this paper self-identifies as a member of one or more historically underrepresented sexual and/or gender groups in science. One or more of the authors of this paper self-identifies as living with a disability. One or more of the authors of this paper received support from a program designed to increase minority representation in science.

Research suggests that altered emotion processing may be one important pathway linking social risk factors and depressive symptoms. We examined the extent to which neural response to negatively valenced social information might help to account for the relationship between social risk and depressive symptoms in youth. Forty‐nine youth were scanned while identifying the emotional valence of words that connoted social status. They also completed questionnaires assessing self‐reported social risk factors and depressive symptoms. Mediation analysis revealed that reduced dorsolateral prefrontal cortex activity in response to negative social status words explained the positive association between social risk and depressive symptoms. These findings suggest that social risk factors present during adolescence may contribute to depressive symptoms by influencing the neural substrates of emotion processing.

One of the strongest predictors for osteoporosis is peak bone mass. Interventions to augment peak bone mass have yet to be developed. β-Ecdysone (βEcd), a natural steroid-like compound produced by arthropods to initiate metamorphosis, is believed to have androgenic effects and so may be used to augment bone mass.The purpose of this study was to use both male and female (1) gonadal-sufficient; and (2) -insufficient mice to investigate sex differences in terms of bone development and structure after βEcd administration.Two-month-old male and female Swiss-Webster mice were randomized to receive either vehicle or βEcd (0.5 mg/kg) for 3 weeks. In a separate experiment to evaluate the effects of βEcd on sex hormone-deficient mice, gonadectomy was performed in male (orchiectomy [ORX]) and female mice (ovariectomy [OVX]). Sham-operated and the ORX/OVX mice were then treated for 3 weeks with βEcd. Primary endpoints for the study were trabecular bone structure and bone strength.In male mice, the trabecular bone volume was 0.18±0.02 in the placebo-treated (PL) and 0.23±0.02 in the βEcd-treated group (p<0.05 versus PL); and 0.09±0.01 in the ORX group (p<0.05 versus PL) and 0.12±0.01 in the ORX+βEcd group. Vertebral bone strength (maximum load) was 43±2 in PL and 51±1 in the βEcd-treated group (p<0.05 versus PL); and 30±4 in the ORX group (p<0.05 versus PL) and 37±3 in the ORX+βEcd group. In female mice, trabecular bone volume was 0.23±0.02 in PL and 0.26±0.02 in the βEcd-treated group (p<0.05 versus PL); and 0.15±0.01 in the OVX group (p<0.05 versus PL) and 0.14±0.01 in the OVX+βEcd group. Maximum load of the vertebrae was 45±2 in PL and 48±4 in the βEcd-treated group; and 39±4 in the OVX group (p<0.05 versus PL) and 44±4 in the OVX+βEcd group.These findings suggest the potential use of βEcd in the augmentation of bone mass in growing male and female mice. It may also partially prevent the detrimental effects of gonadectomy on trabecular bone.Our results support the potential use of βEcd or nature products that are rich in βEcd to augment peak bone mass. βEcd may differ from the other anabolic hormone treatments that may have severe side effects such as serious cardiac complications. However, its effects on humans remain to be determined.

Abstract We present optical photometry and spectra of supernova (SN) 2022hrs (distance ∼ 19 Mpc). It was classified as a Type Ia SN (SN Ia) based on its optical spectra, which exhibited high velocities in both Si ii and Ca ii absorption lines. The light curve of SN 2022hrs was typical of an SN Ia, with a peak magnitude of 13.01 ± 0.30 in B and a time interval of 14.5 days between detection and peak; its optical spectra are also normal. It is a standard SN Ia with no evidence of circumstellar material.

view Abstract Citations (110) References (75) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS SN 1961V: an Extragalactic Eta Carinae Analog? Goodrich, Robert W. ; Stringfellow, Guy S. ; Penrod, G. Donald ; Filippenko, Alexei V. Abstract We have obtained spectra of the site of the unique Type V supernova SN 1961V in NGC 1058, and of two nearby H II regions. Broad (FWHM ~ 2100 km s^-1^) Hα emission, with a luminosity of 2 x 10^36^ ergs s^-1^, is detected at the position of SN 1961V. SN 1961V is thus the first historical extragalactic object classified as a supernova to be optically recovered. The "east H II region," about 1.6" northeast of SN 1961V, is a small high-excitation H II region, with strong [O II], [N II], and [S II] lines for its excitation, and no detectable continuum. The temperature of the ionizing star must be greater than 45,000 K, but the H II region requires only a small fraction of the ionizing flux that such a star would produce. We argue that the east region is probably ionized by the SN 1961V progenitor, some 60 pc distant, and intercepts only a fraction of the ionizing flux from that star. The nearby "west H II region" is an intermediate-age supernova remnant, similar in its optical and radio properties to the most luminous supernova remnants in M31 and M33, but is not obviously associated with SN 1961V. We believe that SN 1961V was not a supernova (the explosion of a massive star at the end of its life) but the superoutburst of a luminous blue variable--an exaggerated η Carinae-type outburst of a very massive, evolved star near the end of core hydrogen burning. The long plateau in the light curve following outburst, at nearly the same brightness as the preoutburst star, suggests that the progenitor survived the outburst and was seen for more than 4 years afterward. It eventually faded because of the formation of optically thick dust in the ejecta, which amounts to only ~1-10 M_sun_. The progenitor is one of the most massive and luminous known stars, with a zero-age main-sequence (ZAMS) mass >~240 M_sun_ and a current mass >~170 M_sun_. The major reduction in mass is a direct result of mass lost during core hydrogen burning through a wind, and perhaps previous large episodic events. The hot underlying star should therefore now be of type Of/WN, like the S Doradus star R127 in the Large Magellanic Cloud but several times more luminous. During outburst the star had the spectrum and colors of an F supergiant, formed in an extended optically thick wind, and was thus optically very bright, partly at the expense of a changing bolometric correction. In addition, considerable thermal radiation was apparently liberated from the material ejected by the star, resulting in the energetic outburst observed. Such a star can account for both the high excitation of the nearby east H II region and the extreme visual brightness of the progenitor without requiring an unreasonably high mass or luminosity. Our observed Hα flux from the site of SN 1961V suggests a circumstellar extinction of A_v_ ~ 5 mag, if the surviving star resembles η Car. The present brightness of the star should be near V ~ 27 mag with a large uncertainty. The infrared brightness should be much higher. Publication: The Astrophysical Journal Pub Date: July 1989 DOI: 10.1086/167646 Bibcode: 1989ApJ...342..908G Keywords: H Ii Regions; Light Curve; Stellar Mass Ejection; Supermassive Stars; Supernova Remnants; H Alpha Line; Interstellar Extinction; Late Stars; Stellar Evolution; Stellar Luminosity; Variable Stars; Astrophysics; NEBULAE: H II REGIONS; STARS: MASS LOSS; STARS: MASSIVE; STARS: SUPERNOVAE; STARS: VARIABLES full text sources ADS | data products SIMBAD (12) NED (5)

Abstract We observed the Seyfert 1 galaxy Mrk 817 during an intensive multiwavelength reverberation mapping campaign for 16 months. Here, we examine the behavior of narrow UV absorption lines seen in the Hubble Space Telescope/Cosmic Origins Spectrograph spectra, both during the campaign and in other epochs extending over 14 yr. We conclude that, while the narrow absorption outflow system (at −3750 km s −1 with FWHM = 177 km s −1 ) responds to the variations of the UV continuum as modified by the X-ray obscurer, its total column density (log N H = 19.5 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow/> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.13</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.61</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> cm −2 ) did not change across all epochs. The adjusted ionization parameter (scaled with respect to the variations in the hydrogen-ionizing continuum flux) is log U H = −1.0 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow/> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.3</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.1</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> . The outflow is located at a distance smaller than 38 pc from the central source, which implies a hydrogen density of n H &gt; 3000 cm −3 . The absorption outflow system only covers the continuum emission source and not the broad emission line region, which suggests that its transverse size is small (&lt; 10 16 cm), with potential cloud geometries ranging from spherical to elongated along the line of sight.

Abstract Refractory high-entropy alloys (RHEAs) hold promise for applications in extreme environments. However, conventional as-cast RHEAs are constrained by the trade-off between strength and ductility, necessitating time- and energy-intensive post-processing. Here, we propose a streamlined strategy to fabricate RHEAs via laser directed energy deposition (LDED) using elemental powder blends, eliminating the need for post heat treatments. The additively manufactured (AMed) Nb 40 Ta 25 Ti 15 Hf 15 Zr 5 alloy, characterized by a high density of intrinsic edge dislocations introduced during the thermal cycling of the process, demonstrates a remarkable tensile strength of ~497.3 MPa and a uniform elongation of ~6.8 % at 1000 °C, representing a ~ 37.8% and ~61.9% increase, respectively, over its as-cast counterparts. It is found that the intrinsic edge dislocations generated during AM process significantly enhances the alloy’s strain hardening capability at elevated temperatures. Simultaneously, the high density of edge dislocations effectively enhance material deformability through kink band formation and the stochastic nature of dislocation motion. This work presents a cost-effective pathway for the rapid fabrication of AMed RHEAs with an exceptional combination of high-temperature strength and ductility, paving the way for next-generation structural alloys in extreme environments.

Generalized Ising models, also known as cluster expansions, are an important tool in many areas of condensed-matter physics and materials science, as they are often used in the study of lattice thermodynamics, solid-solid phase transitions, magnetic and thermal properties of solids, and fluid mechanics. However, the problem of finding the global ground state of generalized Ising model has remained unresolved, with only a limited number of results for simple systems known. We propose a method to efficiently find the periodic ground state of a generalized Ising model of arbitrary complexity by a new algorithm which we term cluster tree optimization. Importantly, we are able to show that even in the case of an aperiodic ground state, our algorithm produces a sequence of states with energy converging to the true ground state energy, with a provable bound on error. Compared to the current state-of-the-art polytope method, this algorithm eliminates the necessity of introducing an exponential number of variables to counter frustration, and thus significantly improves tractability. We believe that the cluster tree algorithm offers an intuitive and efficient approach to finding and proving ground states of generalized Ising Hamiltonians of arbitrary complexity, which will help validate assumptions regarding local vs. global optimality in lattice models, as well as offer insights into the low-energy behavior of highly frustrated systems.