172 research outputs found
Examining a Peak-Luminosity/Decline-Rate Relationship for Tidal Disruption Events
We compare the luminosity, radius, and temperature evolution of the
UV/optical blackbodies for 21 well-observed tidal disruption events (TDEs), 8
of which were discovered by the All-Sky Automated Survey for Supernovae. We
find that the blackbody radii generally increase prior to peak and slowly
decline at late times. The blackbody temperature evolution is generally flat,
with a few objects showing small-scale variations. The bolometric UV/optical
luminosities generally evolve smoothly and flatten out at late times. Finally,
we find an apparent correlation between the peak luminosity and the decline
rate of TDEs. This relationship is strongest when comparing the peak luminosity
to its decline over 40 days. A linear fit yields in cgs, where
.Comment: 10 pages, 4 figures. Updated to reflect changes made in the published
ApJL version. Six new objects added to sample. Updated video description can
be found at https://youtu.be/TtZU22eyHv
Correlation of Structure, Function and Protein Dynamics in GH7 Cellobiohydrolases from \u3cem\u3eTrichoderma atroviride\u3c/em\u3e, \u3cem\u3eT. reesei\u3c/em\u3e and \u3cem\u3eT. harzianum\u3c/em\u3e
Background: The ascomycete fungus Trichoderma reesei is the predominant source of enzymes for industrial conversion of lignocellulose. Its glycoside hydrolase family 7 cellobiohydrolase (GH7 CBH) TreCel7A constitutes nearly half of the enzyme cocktail by weight and is the major workhorse in the cellulose hydrolysis process. The orthologs from Trichoderma atroviride (TatCel7A) and Trichoderma harzianum (ThaCel7A) show high sequence identity with TreCel7A, ~ 80%, and represent naturally evolved combinations of cellulose-binding tunnel-enclosing loop motifs, which have been suggested to influence intrinsic cellobiohydrolase properties, such as endo-initiation, processivity, and off-rate.
Results: The TatCel7A, ThaCel7A, and TreCel7A enzymes were characterized for comparison of function. The catalytic domain of TatCel7A was crystallized, and two structures were determined: without ligand and with thio-cellotriose in the active site. Initial hydrolysis of bacterial cellulose was faster with TatCel7A than either ThaCel7A or TreCel7A. In synergistic saccharification of pretreated corn stover, both TatCel7A and ThaCel7A were more efficient than TreCel7A, although TatCel7A was more sensitive to thermal inactivation. Structural analyses and molecular dynamics (MD) simulations were performed to elucidate important structure/function correlations. Moreover, reverse conservation analysis (RCA) of sequence diversity revealed divergent regions of interest located outside the cellulose-binding tunnel of Trichoderma spp. GH7 CBHs.
Conclusions: We hypothesize that the combination of loop motifs is the main determinant for the observed differences in Cel7A activity on cellulosic substrates. Fine-tuning of the loop flexibility appears to be an important evolutionary target in Trichoderma spp., a conclusion supported by the RCA data. Our results indicate that, for industrial use, it would be beneficial to combine loop motifs from TatCel7A with the thermostability features of TreCel7A. Furthermore, one region implicated in thermal unfolding is suggested as a primary target for protein engineering
Revealing AGNs Through TESS Variability
We used Transiting Exoplanet Survey Satellite (TESS) data to identify 29
candidate active galactic nuclei (AGNs) through their optical variability. The
high-cadence, high-precision TESS light curves present a unique opportunity for
the identification of AGNs, including those not selected through other methods.
Of the candidates, we found that 18 have either previously been identified as
AGNs in the literature or could have been selected based on emission-line
diagnostics, mid-IR colors, or X-ray luminosity. AGNs in low-mass galaxies
offer a window into supermassive black hole (SMBH) and galaxy co-evolution and
8 of the 29 candidates have estimated black hole masses . The low-mass galaxies NGC 4395 and NGC 4449 are two of our
five "high-confidence" candidates. By applying our methodology to the entire
TESS main and extended mission datasets, we expect to identify 45 more
AGN candidates, of which 26 will be new and 8 will be in low-mass
galaxies.Comment: 21 pages, 17 figures, 6 tables. Will be submitted to AAS journals.
Comments welcom
Isolation and identification of a South African lentivirus from jaagsiekte lungs
In the course of attempts to grow the jaagsiekte retrovirus in cell culture, a typical lentivirus was isolated for the first time in South Africa from adenomatous lungs. Morphologically the virus could not be distinguished from other lentiviruses, but serologically it was shown to be more closely related to visna virus than to caprine arthritis-encephalitis virus. However, a preliminary restriction enzyme analysis of the linear proviral DNA of this new lentivirus (SA-DMVV) revealed that it is significantly district from visna virus and CAEV and therefore may represent a third type of lentivirus. Antibodies to the virus were demonstrated in a number of sheep in various parts of the country, but a direct link to a disease condition was not found. Attempts to produce lung lesions by
intratracheal injection of the virus have been unsuccessful to date but a transient arthritis was produced by intra-articular inoculation. Viral replication seems to be enhanced in jaagsiekte lungs.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi.
Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.mn201
Chandra, HST/STIS, NICER, Swift, and TESS Detail the Flare Evolution of the Repeating Nuclear Transient ASASSN-14ko
ASASSN-14ko is a nuclear transient at the center of the AGN ESO 253-G003 that
undergoes periodic flares. Optical flares were first observed in 2014 by the
All-Sky Automated Survey for Supernovae (ASAS-SN) and their peak times are
well-modeled with a period of days and period derivative
of . Here we present ASAS-SN, Chandra, HST/STIS, NICER,
Swift, and TESS data for the flares that occurred in December 2020, April 2021,
July 2021, and November 2021. The HST/STIS UV spectra evolve from blue shifted
broad absorption features to red shifted broad emission features over 10
days. The Swift UV/optical light curves peaked as predicted by the timing
model, but the peak UV luminosities varied between flares and the UV flux in
July 2021 was roughly half the brightness of all other peaks. The X-ray
luminosities consistently decreased and the spectra became harder during the
UV/optical rise but apparently without changes in absorption. Finally, two
high-cadence TESS light curves from December 2020 and November 2018 showed that
the slopes during the rising and declining phases changed over time, which
indicates some stochasticity in the flare's driving mechanism. ASASSN-14ko
remains observationally consistent with a repeating partial tidal disruption
event, but, these rich multi-wavelength data are in need of a detailed
theoretical model.Comment: 25 pages, 14 figures, 4 tables; Submitted to ApJ, comments welcom
TESS Shines Light on the Origin of the Ambiguous Nuclear Transient ASASSN-18el
We analyze high-cadence data from the Transiting Exoplanet Survey Satellite
(TESS) of the ambiguous nuclear transient (ANT) ASASSN-18el. The optical
changing-look phenomenon in ASASSN-18el has been argued to be due to either a
drastic change in the accretion rate of the existing active galactic nucleus
(AGN) or the result of a tidal disruption event (TDE). Throughout the TESS
observations, short-timescale stochastic variability is seen, consistent with
an AGN. We are able to fit the TESS light curve with a damped-random-walk (DRW)
model and recover a rest-frame variability amplitude of mJy and a rest-frame timescale of days.
We find that the estimated for ASASSN-18el is broadly consistent
with an apparent relationship between the DRW timescale and central
supermassive black hole mass. The large-amplitude stochastic variability of
ASASSN-18el, particularly during late stages of the flare, suggests that the
origin of this ANT is likely due to extreme AGN activity rather than a TDE.Comment: 13 pages, 8 figures. Will be submitted to AAS journals. Comments
welcom
COol Companions ON Ultrawide orbiTS (COCONUTS). I. A high-gravity T4 benchmark around an Old White Dwarf and a re-examination of the surface-gravity dependence of the L/T transition
We present the first discovery from the COol Companions ON Ultrawide orbiTS (COCONUTS) program, a large-scale survey for wide-orbit planetary and substellar companions. We have discovered a comoving system COCONUTS-1, composed of a hydrogen-dominated white dwarf (PSO J058.9855+45.4184; d = 31.5 pc) and a T4 companion (PSO J058.9869+45.4296) at a 40farcs6 (1280 au) projected separation. We derive physical properties for COCONUTS-1B from (1) its near-infrared spectrum using cloudless Sonora atmospheric models, and (2) its luminosity and the white dwarf's age (7.3_-1.6^+2.8 Gyr) using Sonora evolutionary models. The two methods give consistent temperatures and radii, but atmospheric models infer a lower surface gravity and therefore an unphysically young age. Assuming evolutionary model parameters (T_eff=1255_-8^+6 K, log g=5.44_-0.03^+0.02 dex, R= 0.789_-0.005^+0.011 R_Jup), we find that cloudless model atmospheres have brighter Y- and J-band fluxes than the data, suggesting that condensate clouds have not fully dispersed around 1300 K. The W2 flux (4.6 μm) of COCONUTS-1B is fainter than models, suggesting non-equilibrium mixing of CO. To investigate the gravity dependence of the L/T transition, we compile all 60 known L6−T6 benchmarks and derive a homogeneous set of temperatures, surface gravities, and masses. As is well known, young, low-gravity late-L dwarfs have significantly fainter, redder near-infrared photometry and ≈200–300 K cooler temperatures than old, high-gravity objects. Our sample now reveals such gravity dependence becomes weaker for T dwarfs, with young objects having comparable near-infrared photometry and ≈100 K cooler temperatures compared to old objects. Finally, we find that young objects have a larger amplitude J-band brightening than old objects, and also brighten at H band as they cross the L/T transition.Published versio
WISE J072003.20-084651.2B Is A Massive T Dwarf
We present individual dynamical masses for the nearby M9.5+T5.5 binary WISE
J072003.20084651.2AB, a.k.a. Scholz's star. Combining high-precision
CFHT/WIRCam photocenter astrometry and Keck adaptive optics resolved imaging,
we measure the first high-quality parallactic distance (
pc) and orbit ( yr period) for this system composed of a
low-mass star and brown dwarf. We find a moderately eccentric orbit (), incompatible with previous work based on less data,
and dynamical masses of and for
the two components. The primary mass is marginally inconsistent (2.1)
with the empirical massmagnitudemetallicity relation and models of
main-sequence stars. The relatively high mass of the cold ( K) brown dwarf companion indicates an age older than a few Gyr, in
accord with age estimates for the primary star, and is consistent with our
recent estimate of 70 for the stellar/substellar
boundary among the field population. Our improved parallax and proper motion,
as well as an orbit-corrected system velocity, improve the accuracy of the
system's close encounter with the solar system by an order of magnitude. WISE
J07200846AB passed within kAU of the Sun kyr ago,
passing through the outer Oort cloud where comets can have stable orbits.Comment: accepted to A
Gender comparisons of fat talk in the United Kingdom and the United States
This study compared different forms of body talk, including "fat talk," among 231 university men and women in central England (UK; n = 93) and the southeastern United States (US; n = 138). A 2 (gender) by 2 (country) repeated measures ANOVA across types of body talk (negative, self-accepting, positive) and additional Chi-square analyses revealed that there were differences across gender and between the UK and US cultures. Specifically, UK and US women were more likely to report frequently hearing or perceiving pressure to engage in fat talk than men. US women and men were also more likely to report pressure to join in self-accepting body talk than UK women and men
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