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"Chiron"
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\"Demon has always counted on his magical medicine box to help him cure the sick beasts on Mount Olympus. But Chiron, his new healing master, insists Demon learn to find the cures on his own. Demon's new skills are soon put to the test when he must save an ailing phoenix--or face the wrath of its fiery guards!\"-- Provided by publisher.
Book
CO and Other Volatiles in Distantly Active Comets
The activity of most comets near the Sun is dominated by the sublimation of frozen water, the most abundant ice in comets. Some comets, however, are active well beyond the water-ice sublimation limit of ∼3 au. Three bodies dominate the observational record and modeling efforts for distantly active comets: the long-period comet C/1995 O1 (Hale-Bopp), and the short-period comets (with Centaur orbits) 29P/Schwassmann-Wachmann 1 and 2060 Chiron. We summarize what is known about these three objects with an emphasis on their gaseous comae. We calculate their CN/CO and CO2/CO production rate ratios from the literature and discuss implications, such as HCN and CO2 outgassing are not significant contributors to their comae. Using our own data we derive CO production rates, Q(CO), for all three objects to examine whether there is a correlation between gas production and different orbital histories and/or size. The CO measurements of Hale-Bopp (4-11 AU) and 29P are consistent with a nominal production rate of Q(CO) = 3.5 × 1029 r−2 superimposed with sporadic outbursts. The similarity of Hale-Bopp CO production rates for pre- and post-perihelion suggests that thermal inertia was not very important and therefore most of the activity is at or near the surface of the comet. We further examine the applicability of existing models in explaining the systematic behavior of our small sample. We find that orbital history does not appear to play a significant role in explaining 29P's CO production rates. 29P outproduces Hale-Bopp at the same heliocentric distance, even though it has been subjected to much more solar heating. Previous modeling work on such objects predicts that 29P should have been devolatilized over a fresher comet like Hale-Bopp. This may point to 29P having a different orbital history than current models predict, with its current orbit acquired more recently. On the other hand, Chiron's CO measurements are consistent with it being significantly depleted over its original state, perhaps due to increased radiogenic heating made possible by its much larger size or its higher processing due to orbital history. Observed spectral line profiles for several volatiles are consistent with the development and sublimation of icy grains in the coma at about 5-6 au for 29P and Hale-Bopp, and this is probably a common feature in distantly active comets, and an important source of volatiles for all comets within 5 au. In contrast, the narrow CO line profiles indicate a nuclear, and not extended, origin for CO beyond ∼4 au.
Journal Article
Antigenic and EM characterization of the Chiron experimental hepatitis C virus vaccine
The Chiron experimental HCV vaccine, the only envelope-based HCV vaccine candidate to date, was immunogenic and safe in a phase 1 trial, though its efficacy remains untested. This study examined the antigenic properties of the vaccine antigens by immunoassays and EM, revealing inconsistent presentation of AR1/5 epitopes. The vaccine elicited mainly strain-specific neutralizing antibodies in humans and non-human primates, highlighting the need for rational antigen design to improve vaccine breadth.
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Journal Article
Dynamical Environment and Stability around Centaur (2060) Chiron
A recent stellar occultation revealed that the Centaur (2060) Chiron hosts a broad disk extending beyond ∼200 km from its center, embedding three ring-like structures (Chi1R, Chi2R, and Chi3R), while a tenuous outer ring (Chi4R) lies beyond the Roche limit. Here, we present a first dynamical assessment of the system’s stability through numerical simulations of test particles, accounting for Chiron’s triaxial figure. For an equatorial ellipticity of C22 ∼ 0.02, as inferred from the most recent shape estimates, our simulations reveal a chaotic inner zone extending to ∼260 km, where particle lifetimes reach up to a year, while particles beyond ∼260 km can remain stable for at least a decade. These results suggest that the innermost portion of the disk is ephemeral and can only persist if continuously replenished. For lower ellipticity values (C22 ≲ 0.012), however, the entire disk is located within the stable region, regardless of Chiron’s mass. Under the physical parameters currently available in the literature, Chi2R is possibly linked to the 1:3 spin-orbit resonance, while Chi1R cannot be linked to the 1:2 resonance, as previously proposed, since this resonance is unstable. Instead, Chi1R and Chi3R may be associated with the 2:5 and 1:5 spin–orbit resonances, respectively. Both the 1:3 and 1:5 resonances are bifurcated, generating chaotic zones that may explain the gap in Chi2R and the longitudinal asymmetry observed in Chi3R.
Journal Article
The Rings of (2060) Chiron: Evidence of an Evolving System
The centaur (2060) Chiron has long been a candidate for hosting material in orbit, based on occultation and photometric and spectroscopic data. Here, we present a multichord stellar occultation observed on 2023 September 10 UT that reveals new and complex structures surrounding Chiron. High-cadence light curves show multiple secondary events that are best explained (when compared with a multishell interpretation) with a system of three confined rings located at average radii of 273, 325, and 438 km, the outermost of which lies beyond Chiron’s Roche limit. The rings appear coplanar, with a mean pole orientation of λ = 151∘ ± 4∘ and β = 20∘ ± 6∘. A broader, disklike structure extends from about 200 to 800 km, and a newly detected faint feature is observed at ∼1380 km. Chiron thus appears as the fourth small solar system body known for hosting a ring system. Comparisons with previous occultation events that have occurred since 1994 show that these features are not permanent. With these observations, we may witness for the first time the ongoing formation and evolution of a ring system.
Journal Article
Stellar occultations by trans-Neptunian objects
Stellar occultations provide a powerful tool to explore objects of the outer solar system. The Gaia mission now provides milli-arcsec accuracy on the predictions of these events and makes possible observations that were previously unthinkable. Occultations return kilometric accuracies on the three-dimensional shape of bodies irrespective of their geocentric distances, with the potential of detecting topographic features along the limb. From the shape, accurate values of albedo can be derived, and if the mass is known, the bulk density is pinned down, thus constraining the internal structure and equilibrium state of the object. Occultations are also extremely sensitive to tenuous atmospheres, down to the nanobar level. They allowed the monitoring of Pluto’s and Triton’s atmospheres in the last three decades, constraining their seasonal evolution. They may unveil in the near future atmospheres around other remote bodies of the solar system. Since 2013, occultations have led to the surprising discovery of ring systems around the Centaur object Chariklo, the dwarf planet Haumea and the large trans-Neptunian object Quaoar, while revealing dense material around the Centaur Chiron. This suggests that rings are probably much more common features than previously thought. Meanwhile, they have raised new dynamical questions concerning the confining effect of resonances forced by irregular objects on ring particles. Serendipitous occultations by km-sized trans-Neptunian or Oort objects have the potential to provide the size distribution of a population that suffered few collisions until now, thus constraining the history of primordial planetesimals in the 1–100 km range.
Journal Article
A Chiron approach towards the stereoselective synthesis of polyfluorinated carbohydrates
The replacement of hydroxyl groups by fluorine atoms on hexopyranose scaffolds may allow access to the discovery of new chemical entities possessing unique physical, chemical and ultimately even biological properties. The prospect of significant effects generated by such multiple and controlled substitutions encouraged us to develop diverse synthetic routes towards the stereoselective synthesis of polyfluorinated hexopyranoses, six of which are unprecedented. Hence, we report the synthesis of heavily fluorinated galactose, glucose, mannose, talose, allose, fucose, and galacturonic acid methyl ester using a Chiron approach from inexpensive levoglucosan. Structural analysis of single-crystal X-ray diffractions and NMR studies confirm the conservation of favored
4
C
1
conformation for fluorinated carbohydrate analogs, while a slightly distorted conformation due to repulsive 1,3-diaxial F···F interaction is observed for the trifluorinated talose derivative. Finally, the relative stereochemistry of multi-vicinal fluorine atoms has a strong effect on the lipophilicities (log
P
).
Polyfluorinated hexopyranoses display unique physical, chemical and biological properties, however their stereoselective synthesis is highly challenging. Here, the authors report a synthetic approach based on the chemical manipulation of inexpensive levoglucosan to obtain heavily fluorinated monosaccharides stereoselectively.
Journal Article
Practical adoption of state-of-the-art hiPSC-cardiomyocyte differentiation techniques
Human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes are a valuable resource for cardiac therapeutic development; however, generation of these cells in large numbers and high purity is a limitation in widespread adoption. Here, design of experiments (DOE) is used to investigate the cardiac differentiation space of three hiPSC lines when varying CHIR99027 concentration and cell seeding density, and a novel image analysis is developed to evaluate plate coverage when initiating differentiation. Metabolic selection via lactate purifies hiPSC-cardiomyocyte populations, and the bioenergetic phenotype and engineered tissue mechanics of purified and unpurified hiPSC-cardiomyocytes are compared. Findings demonstrate that when initiating differentiation one day after hiPSC plating, low (3 μM) Chiron and 72 x 103 cells/cm2 seeding density result in peak cardiac purity (50-90%) for all three hiPSC lines. Our results confirm that metabolic selection with lactate shifts hiPSC-cardiomyocyte metabolism towards oxidative phosphorylation, but this more \"mature\" metabolic phenotype does not by itself result in a more mature contractile phenotype in engineered cardiac tissues at one week of culture in 3D tissues. This study provides widely adaptable methods including novel image analysis code and parameters for refining hiPSC-cardiomyocyte differentiation and describes the practical implications of metabolic selection of cardiomyocytes for downstream tissue engineering applications.
Journal Article
Photometry of Centaurs and trans-Neptunian objects: 2060 Chiron (1977 UB), 10199 Chariklo (1997 CU26), 38628 Huya (2000 EB173), 28978 Ixion (2001 KX76), and 90482 Orcus (2004 DW)
Both Centaurs and trans-Neptunian objects (TNOs) are minor bodies found in the outer Solar System. Centaurs are a transient population that moves between the orbits of Jupiter and Neptune, and they probably diffused out of the TNOs. TNOs move mainly beyond Neptune. Some of these objects display episodic cometary behaviour; a few percent of them are known to host binary companions. Here, we study the light-curves of two Centaurs—2060 Chiron (1977 UB) and 10199 Chariklo (1997 CU
26
)—and three TNOs—38628 Huya (2000 EB
173
), 28978 Ixion (2001 KX
76
), and 90482 Orcus (2004 DW)—and the colours of the Centaurs and Huya. Precise,
∼
1
%
,
R
-band absolute CCD photometry of these minor bodies acquired between 2006 and 2011 is presented; the new data are used to investigate the rotation rate of these objects. The colours of the Centaurs and Huya are determined using
BVRI
photometry. The point spread function of the five minor bodies is analysed, searching for signs of a coma or close companions. Astrometry is also discussed. A periodogram analysis of the light-curves of these objects gives the following rotational periods:
5.5
±
0.4
h
for Chiron,
7.0
±
0.6
h
for Chariklo,
4.45
±
0.07
h
for Huya,
12.4
±
0.3
h
for Ixion, and
11.9
±
0.5
h
for Orcus. The colour indices of Chiron are found to be
B
−
V
=
0.53
±
0.05
,
V
−
R
=
0.37
±
0.08
, and
R
−
I
=
0.36
±
0.15
. The values computed for Chariklo are
V
−
R
=
0.62
±
0.07
and
R
−
I
=
0.61
±
0.07
. For Huya, we find
V
−
R
=
0.58
±
0.09
and
R
−
I
=
0.64
±
0.20
. Our rotation periods are similar to and our colour values are consistent with those already published for these objects. We find very low levels of cometary activity (if any) and no sign of close or wide binary companions for these minor bodies.
Journal Article