962 research outputs found
Olivine on Vesta as exogenous contaminants brought by impacts: Constraints from modeling Vesta's collisional history and from impact simulations
The survival of asteroid Vesta during the violent early history of the Solar
System is a pivotal constraint on theories of planetary formation. Particularly
important from this perspective is the amount of olivine excavated from the
vestan mantle by impacts, as this constrains both the interior structure of
Vesta and the number of major impacts the asteroid suffered during its life.
The NASA Dawn mission revealed that olivine is present on Vesta's surface in
limited quantities, concentrated in small patches at a handful of sites and
interpreted as the result of the excavation of endogenous olivine. Later works
raised the possibility that the olivine had an exogenous origin, based on the
geologic and spectral features of the deposits. In this work we quantitatively
explore the proposed scenario of a exogenous origin for the detected olivine to
investigate whether its presence on Vesta can be explained as a natural outcome
of the collisional history of the asteroid. We took advantage of the impact
contamination model previously developed to study the origin and amount of dark
and hydrated materials observed by Dawn on Vesta, which we updated by
performing dedicated hydrocode impact simulations. We show that the exogenous
delivery of olivine by impacts can offer a viable explanation for the currently
identified olivine-rich sites without violating the constraint posed by the
lack of global olivine signatures on Vesta. Our results indicate that no mantle
excavation is in principle required to explain the observations of the Dawn
mission and support the idea that the vestan crust could be thicker than
indicated by simple geochemical models based on the Howardite-Eucrite-Diogenite
family of meteorites.Comment: 24 pages, 6 figures, accepted for publication on the journal Icaru
The late accretion and erosion of Vesta's crust recorded by eucrites and diogenites as an astrochemical window into the formation of Jupiter and the early evolution of the Solar System
For decades the limited thickness of Vesta's basaltic crust, revealed by the
link between the asteroid and the howardite-eucrite-diogenite family of
meteorites, and its survival to collisional erosion offered an important
constraint for the study of the early evolution of the Solar System. Some
results of the Dawn mission, however, cast doubts on our understanding of
Vesta's interior composition and of the characteristics of its basaltic crust,
weakening this classical constraint. In this work we investigate the late
accretion and erosion experienced by Vesta's crust after its differentiation
and recorded in the composition of eucrites and diogenites and show that it
offers an astrochemical window into the earliest evolution of the Solar System.
In our proof-of-concept case study focusing on the late accretion and erosion
of Vesta's crust during the growth and migration of Jupiter, the water
enrichment of eucrites appears to be a sensitive function of Jupiter's
migration while the enrichment in highly-siderophile elements of diogenites
appears to be particularly sensitive to the size-frequency distribution of the
planetesimals. The picture depicted by the enrichments created by late
accretion in eucrites and diogenites is not qualitatively affected by the
uncertainty on the primordial mass of Vesta. Crustal erosion, instead, is more
significantly affected by said uncertainty and Vesta's crust survival appears
to be mainly useful to study violent collisional scenarios where highly
energetic impacts can strip significant amounts of vestan material while
limitedly contributing to Vesta's late accretion. Our results suggest that the
astrochemical record of the late accretion and erosion of Vesta's crust
provided by eucrites and diogenites can be used as a tool to investigate any
process or scenario associated to the evolution of primordial Vesta and of the
early Solar System.Comment: 21 pages, 15 figures, accepted for publication on Icaru
The rank of trifocal grassmann tensors
Grassmann tensors arise from classical problems of scene reconstruction in computer vision. Trifocal Grassmann tensors, related to three projections from a projective space of dimension k onto view spaces of varying dimensions, are studied in this work. A canonical form for the combined projection matrices is obtained. When the centers of projections satisfy a natural generality assumption, such canonical form gives a closed formula for the rank of trifocal Grassmann tensors. The same approach is also applied to the case of two projections, confirming a previous result obtained with different methods in [M. Bertolini, G. Besana, and C. Turrini, Ann. Mat. Pura Appl. (4), 196 (2016), pp. 539-553]. The rank of sequences of tensors converging to tensors associated with degenerate configurations of projection centers is also considered, giving concrete examples of a wide spectrum of phenomena that can happen
Marine anthraquinones: Pharmacological and toxicological issues
The marine ecosystem, populated by a myriad of animals, plants, and microorganisms, is an inexhaustible reservoir of pharmacologically active molecules. Among the multiple secondary metabolites produced by marine sources, there are anthraquinones and their derivatives. Besides being mainly known to be produced by terrestrial species, even marine organisms and the uncount-able kingdom of marine microorganisms biosynthesize anthraquinones. Anthraquinones possess many different biological activities, including a remarkable antitumor activity. However, due to their peculiar chemical structures, anthraquinones are often associated with toxicological issues, even relevant, such as genotoxicity and mutagenicity. The aim of this review is to critically describe the an-ticancer potential of anthraquinones derived from marine sources and their genotoxic and mutagenic potential. Marine-derived anthraquinones show a promising anticancer potential, although clinical studies are missing. Additionally, an in-depth investigation of their toxicological profile is needed before advocating anthraquinones as a therapeutic armamentarium in the oncological area
Probing the origin of the dark material on Iapetus
Among the icy satellites of Saturn, Iapetus shows a striking dichotomy
between its leading and trailing hemispheres, the former being significantly
darker than the latter. Thanks to the VIMS imaging spectrometer on-board
Cassini, it is now possible to investigate the spectral features of the
satellites in Saturn system within a wider spectral range and with an enhanced
accuracy than with previously available data. In this work, we present an
application of the G-mode method to the high resolution, visible and near
infrared data of Phoebe, Iapetus and Hyperion collected by Cassini/VIMS, to
search for compositional correlations. We also present the results of a
dynamical study on the efficiency of Iapetus in capturing dust grains
travelling inward in Saturn system to evaluate the viability of
Poynting-Robertson drag as the physical mechanism transferring the dark
material to the satellite. The results of spectroscopic classification are used
jointly with the ones of the dynamical study to describe a plausible physical
scenario for the origin of Iapetus' dichotomy. Our work shows that mass
transfer from the outer Saturnian system is an efficient mechanism,
particularly for the range of sizes hypothesised for the particles composing
the newly discovered outer ring around Saturn. Both spectral and dynamical data
indicate Phoebe as the main source of the dark material. However, we suggest a
multi-source scenario where now extinct prograde satellites and the disruptive
impacts that generated the putative collisional families played a significant
role in supplying the original amount of dark material.Comment: 20 pages, 4 tables, 11 figures, major revision (manuscript extended
and completed, figures added and corrected, new results added), minor
revision and finalization of author list, moderate revision (update of the
manuscript following reviewer's feedback and discovery of the new Saturnian
outer ring
TIE-2 expressing monocytes in human cancers.
Tumor-associated macrophages (TAM) are well known as a key player in the tumor microenvironment, which support cancer progression. More recently, a lineage of monocytes characterized by the expression of the TIE-2/Tek angiopoietin receptor identified a subset of circulating and tumor-associated monocytes endowed with proangiogenic activity. TIE-2 expressing monocytes (TEM) were found both in humans and mice. Here, we review the phenotypes and functions of TEM reported so far in human cancer and their potential use as markers of cancer progression and metastasis. Finally, we discuss the therapeutic approaches currently used or proposed to target TEM
Assessing the Economic Value of a Regional Air Quality Plan
When developing an air quality plan, environmental authorities usually devise a number of individual actions, constituted by the application of both technical (end-of-pipe) and energy efficiency measures.
They may range from the incentives to buy less polluting vehicles, to the enforcement of stricter rules on domestic heating. The assessment of the economic effectiveness for the society as a whole of the individual measures and of the overall plan requires a flexible support system able to quickly perform
air quality impact evaluations on the specific area. One such system is RIAT+, a software package developed and tested during a series of European research projects, which has been used to evaluate costs and benefits of the Lombardy Region Air Quality Plan (PRIA), constituted by about 90 different
actions to be implemented within 2020. The adoption of each measure means a certain change in the emission, which is distributed over the regional territory in different way, depending on the type of measure. A shift of the car fleet to a different EURO class, for instance, means an emission reduction only on the road network, while a reduced use of electricity may imply a lower emission of power
plants at specific sites.
To evaluate the effects of these emission changes, RIAT+ adopts a surrogate model approach, namely using a neural network calibrated on few results of a full chemical transport model. It is thus possible to rapidly evaluate the improvements in the population exposure and health and the consequent reduction of external costs.
The final economic assessment is obtained by comparing the sum of energy savings and external cost reductions with the implementation costs of the corresponding measures
Optical mapping of neuronal activity during seizures in zebrafish
Mapping neuronal activity during the onset and propagation of epileptic seizures can provide a better understanding of the mechanisms underlying this pathology and improve our approaches to the development of new drugs. Recently, zebrafish has become an important model for studying epilepsy both in basic research and in drug discovery. Here, we employed a transgenic line with pan-neuronal expression of the genetically-encoded calcium indicator GCaMP6s to measure neuronal activity in zebrafish larvae during seizures induced by pentylenetretrazole (PTZ). With this approach, we mapped neuronal activity in different areas of the larval brain, demonstrating the high sensitivity of this method to different levels of alteration, as induced by increasing PTZ concentrations, and the rescuing effect of an anti-epileptic drug. We also present simultaneous measurements of brain and locomotor activity, as well as a high-throughput assay, demonstrating that GCaMP measurements can complement behavioural assays for the detection of subclinical epileptic seizures, thus enabling future investigations on human hypomorphic mutations and more effective drug screening methods. Notably, the methodology described here can be easily applied to the study of many human neuropathologies modelled in zebrafish, allowing a simple and yet detailed investigation of brain activity alterations associated with the pathological phenotype
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