Block copolymers incorporating epoxy-reactive functionality in one block have been studied as modifiers for model epoxy resins. As observed previously with nonreactive ...poly(ethylethylene)-b-poly(ethylene oxide) (OP) copolymers, reactive poly(epoxyisoprene)-b-polybutadiene (BIxn) copolymers and poly(methyl acrylate-co-glycidyl methacrylate)-b-polyisoprene (MG-I) copolymers form ordered microstructures in blends with epoxy precursors as evidenced by small-angle X-ray scattering and transmission electron microscopy. Like OP copolymers, both types of reactive copolymer remain well-dispersed within the epoxy matrix during cure. Additionally, DSC and solubility studies suggest that these copolymers can react with the curing epoxy resin to form covalent linkages between the copolymeric microstructures and the cross-linked epoxy resin. The capability of these types of copolymers to template epoxy resin is proposed to arise from a combination of (1) the miscibility of one block with the epoxy components well into the curing process and (2) the energetic barriers to nucleation and growth of copolymer-rich regions in the epoxy matrix as network formation occurs and the epoxy molecular weight diverges.
Context.
Asteroid families with ages younger than 1 Myr offer an interesting possibility of studying the outcomes of asteroid disruptions that are little modified by subsequent evolutionary ...processes.
Aims.
We analyze a very young asteroid family associated with (18777) Hobson in the central part of the main belt. We aim at (i) understanding its peculiar size distribution, and (ii) setting an upper limit on the characteristic dispersal velocity at subkilometer sizes corresponding to the smallest visible Hobson members.
Methods.
We identified the Hobson family using an up-to-date asteroid catalog. A significant increase in the number of its known members allowed us to study their size distribution and compare it with computer simulations of catastrophic disruptions. Backward orbital integrations of the heliocentric orbits allowed us to confirm the previously suggested age of Hobson and helped to estimate limits of the ejection speed.
Results.
The Hobson family has an unusual size distribution: two nearly equal-size bodies, followed by a population of smaller asteroids, whose distribution takes a characteristic power law. There are two possibilities to explain these data. Either a canonical impact onto a single parent body, requiring fine-tuned impact conditions that have not been studied so far, or an unconventional model for the parent object of the Hobson family, namely a binary with ≃7−9 km primary and a ≃2.5 km secondary. In the latter case, the primary was disrupted, leaving behind the largest remnant (18777) Hobson and a suite of subkilometer asteroids. The second largest asteroid, (57738) 2001 UZ160, is the nearly intact satellite of the parent binary. The excellent convergence of nominal orbits of Hobson members sets an upper limit of ≃(10−20) m s
−1
for the initial dispersal velocity of the known members, which is consistent with both formation models. The Hobson family provides a so far rare opportunity of studying disruptions of small asteroids in a situation in which both the material strength and reaccumulation efficiency play an important role.
We study the orbital and physical properties of Trojan asteroids of Jupiter. We try to discern all the families previously discussed in the literature, but we conclude that there is only one ...significant family among the Trojans, namely the cluster around the asteroid (3548) Eurybates. This is the only cluster that has all of the following characteristics: (i) it is clearly concentrated in the proper-element space; (ii) the size-frequency distribution is different from that of background asteroids; (iii) we have a reasonable collisional/dynamical model of the family. Henceforth, we can consider it as a real collisional family.
We also report the discovery of a possible family around the asteroid (4709) Ennomos, composed mostly of small asteroids. The asteroid (4709) Ennomos is known to have a very high albedo pV
≃ 0.15, which may be related to the hypothetical cratering event that exposed ice. The relation between the collisional family and the exposed surface of the parent body offers a unique means to study the physics of cratering events. However, more data are needed to confirm the existence of this family and its relationship with Ennomos.
Yarkovsky footprints in the Eos family Vokrouhlický, D.; Brož, M.; Morbidelli, A. ...
Icarus (New York, N.Y. 1962),
01/2006, Letnik:
182, Številka:
1
Journal Article
Recenzirano
The Eos asteroid family is the third most populous, after Themis and Koronis, and one of the largest non-random groups of asteroids in the main belt. It has been known and studied for decades, but ...its structure and history still presented difficulties to understand. We first revise the Eos family identification as a statistical cluster in the space of proper elements. Using the most to-date catalogue of proper elements we determine a nominal Eos family, defined by us using the hierarchical-clustering method with the cut-off velocity of 55 m/s, contains some 4400 members. This unforeseen increase in known Eos asteroids allows us to perform a much more detailed study than was possible so far. We show, in particular, that most of the previously thought peculiar features are explained within the following model: (i) collisional disruption of the parent body leads to formation of a compact family in the proper element space (with characteristic escape velocities of the observed asteroids of tens of meters per second, compatible with hydrocode simulations), and (ii) as time goes, the family dynamically evolves due to a combination of the thermal effects and planetary perturbations. This model allows us to explain sharp termination of the family at the J7/3 mean motion resonance with Jupiter, uneven distribution of family members about the J9/4 mean motion resonance with Jupiter, semimajor axis distribution of large vs small members in the family and anomalous residence of Eos members inside the high-order secular resonance
z
1
. Our dynamical method also allows us to estimate Eos family age to
1.3
−0.2
+0.15
Gyr
. Several formal members of the Eos family are in conflict with our model and these are suspected interlopers. We use spectroscopic observations, whose results are also reported here, and results of 5-color wide-band Sloan Digital Sky Survey photometry to prove some of them are indeed spectrally incompatible with the family.
The multiple system V505 Sagittarii is composed of at least three stars: a compact eclipsing pair and a distant component, whose orbit is measured directly using speckle interferometry. In order to ...explain the observed orbit of the third body in V505 Sagittarii and also other observable quantities, namely the minima timings of the eclipsing binary and three different radial velocities (RVs) detected in the spectrum, we thoroughly test a fourth-body hypothesis--a perturbation by a dim, yet-unobserved object. We use an N-body numerical integrator to simulate future and past orbital evolution of three or four components in this system. We construct a suitable Delta *y2 metric from all available speckle-interferometry, minima-timings, and RV data and we scan a part of a parameter space to get at least some of the possible solutions. In principle, we are able to explain all observable quantities by the presence of a fourth body, but the resulting likelihood of this hypothesis is very low. We also discuss other theoretical explanations of the minima-timing variations. Further observations of the minima timings during the next decade or high-resolution spectroscopic data can significantly constrain the model.
Checkpoint blockade immunotherapy has improved metastatic cancer patient survival, but response rates remain low. There is an unmet need to identify mechanisms and tools to circumvent resistance. In ...human patients, responses to checkpoint blockade therapy correlate with tumor mutation load, and intrinsic resistance associates with pre-treatment signatures of epithelial mesenchymal transition (EMT), immunosuppression, macrophage chemotaxis and TGFβ signaling.
To facilitate studies on mechanisms of squamous cell carcinoma (SCC) evasion of checkpoint blockade immunotherapy, we sought to develop a novel panel of murine syngeneic SCC lines reflecting the heterogeneity of human cancer and its responses to immunotherapy. We characterized six Kras-driven cutaneous SCC lines with a range of mutation loads. Following implantation into syngeneic FVB mice, we examined multiple tumor responses to α-PD-1, α-TGFβ or combinatorial therapy, including tumor growth rate and regression, tumor immune cell composition, acquired tumor immunity, and the role of cytotoxic T cells and Tregs in immunotherapy responses.
We show that α-PD-1 therapy is ineffective in establishing complete regression (CR) of tumors in all six SCC lines, but causes partial tumor growth inhibition of two lines with the highest mutations loads, CCK168 and CCK169. α-TGFβ monotherapy results in 20% CR and 10% CR of established CCK168 and CCK169 tumors respectively, together with acquisition of long-term anti-tumor immunity. α-PD-1 synergizes with α-TGFβ, increasing CR rates to 60% (CCK168) and 20% (CCK169). α-PD-1 therapy enhances CD4 + Treg/CD4 + Th ratios and increases tumor cell pSmad3 expression in CCK168 SCCs, whereas α-TGFβ antibody administration attenuates these effects. We show that α-TGFβ acts in part through suppressing immunosuppressive Tregs induced by α-PD-1, that limit the anti-tumor activity of α-PD-1 monotherapy. Additionally, in vitro and in vivo, α-TGFβ acts directly on the tumor cell to attenuate EMT, to activate a program of gene expression that stimulates immuno-surveillance, including up regulation of genes encoding the tumor cell antigen presentation machinery.
We show that α-PD-1 not only initiates a tumor rejection program, but can induce a competing TGFβ-driven immuno-suppressive program. We identify new opportunities for α-PD-1/α-TGFβ combinatorial treatment of SCCs especially those with a high mutation load, high CD4+ T cell content and pSmad3 signaling. Our data form the basis for clinical trial of α-TGFβ/α-PD-1 combination therapy (NCT02947165).
Aims.
The orbit of the outer satellite Alexhelios of (216) Kleopatra is already constrained by adaptive-optics astrometry obtained with the VLT/SPHERE instrument. However, there is also a preceding ...occultation event in 1980 attributed to this satellite. Here, we try to link all observations, spanning 1980–2018, because the nominal orbit exhibits an unexplained shift by + 60° in the true longitude.
Methods.
Using both a periodogram analysis and an ℓ = 10 multipole model suitable for the motion of mutually interacting moons about the irregular body, we confirmed that it is not possible to adjust the respective osculating period
P
2
. Instead, we were forced to use a model with tidal dissipation (and increasing orbital periods) to explain the shift. We also analysed light curves spanning 1977–2021, and searched for the expected spin deceleration of Kleopatra.
Results.
According to our best-fit model, the observed period rate is
Ṗ
2
= (1.8 ± 0.1) × 10
−8
d d
−1
and the corresponding time-lag Δ
t
2
= 42 s of tides, for the assumed value of the Love number
k
2
= 0.3. This is the first detection of tidal evolution for moons orbiting 100 km asteroids. The corresponding dissipation factor
Q
is comparable with that of other terrestrial bodies, albeit at a higher loading frequency 2|
ω
−
n
|. We also predict a secular evolution of the inner moon,
Ṗ
1
= 5.0 × 10
−8
, as well as a spin deceleration of Kleopatra,
Ṗ
0
= 1.9 × 10
−12
. In alternative models, with moons captured in the 3:2 mean-motion resonance or more massive moons, the respective values of Δ
t
2
are a factor of between two and three lower. Future astrometric observations using direct imaging or occultations should allow us to distinguish between these models, which is important for our understanding of the internal structure and mechanical properties of (216) Kleopatra.
Aims.
The Euphrosyne asteroid family occupies a unique zone in orbital element space around 3.15 au and may be an important source of the low-albedo near-Earth objects. The parent body of this family ...may have been one of the planetesimals that delivered water and organic materials onto the growing terrestrial planets. We aim to characterize the compositional properties as well as the dynamical properties of the family.
Methods.
We performed a systematic study to characterize the physical properties of the Euphrosyne family members via low-resolution spectroscopy using the NASA Infrared Telescope Facility. In addition, we performed smoothed-particle hydrodynamics (SPH) simulations and
N
-body simulations to investigate the collisional origin, determine a realistic velocity field, study the orbital evolution, and constrain the age of the Euphrosyne family.
Results.
Our spectroscopy survey shows that the family members exhibit a tight taxonomic distribution, suggesting a homogeneous composition of the parent body. Our SPH simulations are consistent with the Euphrosyne family having formed via a reaccumulation process instead of a cratering event. Finally, our
N
-body simulations indicate that the age of the family is 280
−80
+180
Myr, which is younger than previous estimates.
We studied impact processes by means of smoothed-particle hydrodynamics (SPH) simulations. The method was applied to modelling formation of main-belt families during the cometary bombardment (either ...early or late, ∼3.85Gy ago). If asteroids were bombarded by comets, as predicted by the Nice model, hundreds of asteroid families (catastrophic disruptions of diameter D≥100km bodies) should have been created, but the observed number is only 20. Therefore we computed a standard set of 125 simulations of collisions between representative D=100km asteroids and high-speed icy projectiles (comets), in the range 8 to 15km/s. According to our results, the largest remnant mass Mlr is similar as in low-speed collisions, due to appropriate scaling with the effective strength Qeff, but the largest fragment mass Mlf exhibits systematic differences — it is typically smaller for craterings and bigger for super-catastrophic events. This trend does not, however, explain the non-existence of old families. The respective parametric relations can be used in other statistical (Monte-Carlo) models to better understand collisions between asteroidal and cometary populations.
•A set of SPH simulations was computed for high-speed (8–15 km/s) collisions.•The simulations are applicable to collisions between asteroids and comets.•The largest fragment mass M_lf exhibits systematic differences.•This trend does not, however, explain the non-existence of old families.