6,552 research outputs found
Systematic ranging and late warning asteroid impacts
We describe systematic ranging, an orbit determination technique especially
suitable to assess the near-term Earth impact hazard posed by newly discovered
asteroids. For these late warning cases, the time interval covered by the
observations is generally short, perhaps a few hours or even less, which leads
to severe degeneracies in the orbit estimation process. The systematic ranging
approach gets around these degeneracies by performing a raster scan in the
poorly-constrained space of topocentric range and range rate, while the plane
of sky position and motion are directly tied to the recorded observations. This
scan allows us to identify regions corresponding to collision solutions, as
well as potential impact times and locations. From the probability distribution
of the observation errors, we obtain a probability distribution in the orbital
space and then estimate the probability of an Earth impact. We show how this
technique is effective for a number of examples, including 2008 TC3 and 2014
AA, the only two asteroids to date discovered prior to impact
CVD nano-coating of carbon composites for space materials atomic oxygen shielding
The present work analyzes the possibility to employ carbon nanostructures as a basic material to prevent the erosion effects of atomic oxygen suffered by the carbon fiber reinforced polymeric material used in low earth orbit space environment. The application of thin protecting coatings to base materials is a widely used method for preventing the atomic oxygen induced erosion, and thus degradation. The generic purpose is to integrate carbon nanostructures onto carbon composites surface in order to develop the basic substrate of advanced nanocomposite for atomic oxygen protection. The final goal is the characterization of carbon nanostructures-reinforced carbon composites by means of on-ground atomic oxygen simulation facility, with the future objective to assess and optimize the process of carbon-multiscale advanced composites production. With such an aim, a wide investigation on the methane chemical vapor deposition (CVD) over catalyzed carbon fiber-based substrates has been carried out. The as grown nanostructures have been analyzed in terms of morphology, as well as regarding the main features of the resulting growth (yield, purity, homogeneity, coating uniformity, etc.) and the influence of the deposition route operating parameters (catalyst typology, gas flowing rate, growth time/temperature, etc.). A high degree of reproducibility in terms of the relationship between the carbon deposit type/yield and the main process variables (catalyst and protocol) has been thus obtained. Finally, atomic oxygen ground tests have been conducted in order to evaluate the coating process effectiveness. The on-ground test in atomic oxygen environment, with respect to the performances of the reference carbon composites (in terms of total mass loss and atomic oxygen rate of erosion), showed a worsening for the disordered carbon deposit, while an intriguing improvement was achieved by the high-yield carbon nano-filaments deposition
Focusing New Ataxia Telangiectasia Therapeutic Approaches
Ataxia Telangiectasia (AT) is a rare worldwide disease inherited as autosomal recessive with a poor prognosis in its classical form. It is characterized by neurological impairment (progressive cerebellar ataxia, axonal peripheral neuropathy, oculomotor apraxia, and movement disorders such as dystonia, choreoathetosis, myoclonus, tremor, Parkinsonism), telangiectasias, recurrent sino pulmonary infections, proneness to cancer, increased alpha-fetoprotein and decreased IgA levels and radio hypersensitivity. AT is caused by biallelic mutations in ATM gene, which plays a pivotal role in the control of cell cycle and in the response to DNA double strand break damage and chromatin changes. The management of patients, as well as prognosis, depends on the severity of the phenotype; only symptomatic therapies are by now available. Here we discuss the classical and the new therapeutic approaches in the light of the most recent reports in the literature
Quark pseudoscalar vertex and quark mass function with clover fermions : spontaneous symmetry breaking, OPE, symmetry restoration at small volume
We study the quark mass function on hypercubic lattices, in a large range of
physical volumes and cutoffs. To avoid the very large Wilson term artefact, we
exploit the relation between the quark mass function and the pseudoscalar
vertex in the continuum. We extrapolate to the chiral limit.
In function of the physical volume, we observe a striking discontinuity in
the properties of chiral extrapolation around a physical volume L_c 6
(GeV}^{-1}=1.2 fm. It is present in the quark mass function, which collapses
to zero, as well as in the pion mass and the quark condensate as directly
calculated from the pseudoscalar correlator. It is strongly reminiscent of the
phenomenon of chiral symmetry restoration observed by Neuberger and Narayanan
at around the same physical length.
In the case of spontaneous symmetry breaking, we confirm that the OPE of the
quark mass function, involving the quark condensate, is not operative at the
available momenta, even taking into account the unusually large high order
corrections to the Wilson coefficient calculated by Chetyrkin and Maier ; the
gap remains large, around a factor 2, even at the largest momenta available to
us (p \simeg GeV)Comment: 31 pages, 8 figures Comments added, one figure suppressed, various
typos correcte
Plausible home stars of the interstellar object 'Oumuamua found in Gaia DR2
The first detected interstellar object 'Oumuamua that passed within 0.25au of
the Sun on 2017 September 9 was presumably ejected from a stellar system. We
use its newly determined non-Keplerian trajectory together with the
reconstructed Galactic orbits of 7 million stars from Gaia DR2 to identify past
close encounters. Such an "encounter" could reveal the home system from which
'Oumuamua was ejected. The closest encounter, at 0.60pc (0.53-0.67pc, 90%
confidence interval), was with the M2.5 dwarf HIP 3757 at a relative velocity
of 24.7km/s, 1Myr ago. A more distant encounter (1.6pc) but with a lower
encounter (ejection) velocity of 10.7km/s was with the G5 dwarf HD 292249,
3.8Myr ago. Two more stars have encounter distances and velocities intermediate
to these. The encounter parameters are similar across six different
non-gravitational trajectories for 'Oumuamua. Ejection of 'Oumuamua by
scattering from a giant planet in one of the systems is plausible, but requires
a rather unlikely configuration to achieve the high velocities found. A binary
star system is more likely to produce the observed velocities. None of the four
home candidates have published exoplanets or are known to be binaries. Given
that the 7 million stars in Gaia DR2 with 6D phase space information is just a
small fraction of all stars for which we can eventually reconstruct orbits, it
is a priori unlikely that our current search would find 'Oumuamua's home star
system. As 'Oumuamua is expected to pass within 1pc of about 20 stars and brown
dwarfs every Myr, the plausibility of a home system depends also on an
appropriate (low) encounter velocity.Comment: Accepted to The Astronomical Journa
Determination of folic acid using biosensors: a short review of recent progress
Folic acid (FA) is the synthetic surrogate of the essential B vitamin folate, alternatively named folacin, pteroylglutamic acid or vitamin B-9. FA is an electroactive compound that helps our body to create and keep our cells healthy: it acts as the main character in a variety of synthetic biological reactions such as the synthesis of purines, pyrimidine (thus being indirectly implied in DNA synthesis), fixing and methylation of DNA. Therefore, physiological folate deficiency may be responsible for severe degenerative conditions, including neural tube defects in developing embryos and megaloblastic anaemia at any age. Moreover, being a water-soluble molecule, it is constantly lost and has to be reintegrated daily; for this reason, FA supplements and food fortification are, nowadays, extremely diffused and well-established practices. Consequently, accurate, reliable and precise analytical techniques are needed to exactly determine FA concentration in various media. Thus, the aim of this review is to report on research papers of the past 5 years (2016-2020) dealing with rapid and low-cost electrochemical determination of FA in food or biological fluid samples
Weakly bound states of polar molecules in bilayers
We investigate a system of two polarized molecules in a layered trap. The
molecules reside in adjacent layers and interact purely via the dipole-dipole
interaction. We determine the properties of the ground state of the system as a
function of the dipole moment and polarization angle. A bound state is always
present in the system and in the weak binding limit the bound state extends to
a very large distance and shows universal behavior.Comment: Presented at the 21st European Conference on Few-Body Problems in
Physics, Salamanca, Spain, 30 August - 3 September 201
- …