Context.
In meteor physics, the luminous efficiency
τ
is used to convert the meteor’s magnitude to the corresponding meteoroid’s mass. However, a lack of sufficiently accurate verification methods or ...adequate laboratory tests mean that discussions around this parameter are a subject of controversy.
Aims.
In this work, we aim to use meteor data obtained by the Fireball Recovery and InterPlanetary Observation to calculate the luminous efficiencies of the recorded meteors. We also show the limitations of the methods presented herein.
Methods.
Deceleration-based formulas were used to calculate the masses of the pre-atmospheric meteoroids. These can in turn be compared to the meteor brightnesses to assess the luminous efficiencies of the recorded objects. Fragmentation of the meteoroids is not considered within this model. Good measurements of the meteor deceleration are required.
Results.
We find
τ
-values, as well as the shape change coefficients, of 294 meteors and fireballs with determined masses in the range of 10
−6
–100 kg. The derived
τ
-values have a median of
τ
median
= 2.17%. Most of them are of the order of 0.1–10%. We present how our values are obtained, compare them with data reported in the literature, and discuss several methods. A dependence of
τ
on the pre-atmospheric velocity of the meteor,
v
e
, is noticeable with a relation of τ = 0.0023⋅
v
e
2.3
. Furthermore, a dependence of
τ
on the initial meteoroid mass,
M
e
, is found with negative linear behaviour in log–log space: τ = 0.48⋅
M
e
−0.47
.
Conclusions.
The higher luminous efficiency of fast meteors could be explained by the higher amount of energy released. Fast meteoroids produce additional emission lines that radiate more efficiently in specific wavelengths due to the appearance of the so-called second component of higher temperature. Furthermore, the negative dependence of
τ
on
M
e
implies that the radiation of smaller meteoroids is more efficient. The results of this study also show the limitations of the ablation-based model for the determination of the luminous efficiency.
Context.
The luminous efficiency,
τ
, can be used to compute the pre-atmospheric masses of meteoroids from corresponding recorded meteor brightnesses. The derivation of the luminous efficiency is ...non-trivial and is subject to biases and model assumptions. This has led to greatly varying results in the last decades of studies.
Aims.
The present paper aims to investigate how a reduction in various observational biases can be achieved to derive (more) reliable values for the luminous efficiency.
Methods.
A total of 281 meteors observed by the Fireball Recovery and InterPlanetary Observation Network (FRIPON) are studied. The luminous efficiencies of the events are computed using an ablation-based model. The relations of
τ
as a function of the pre-atmospheric meteoroid velocity,
v
e
, and mass,
M
e
, are studied. Various aspects that could render the method less valid, cause inaccuracies, or bias the results are investigated. On this basis, the best suitable meteors were selected for luminous efficiency computations.
Results.
The presented analysis shows the limits of the used method. The most influential characteristics that are necessary for reliable results for the
τ
computation were identified. We study the dependence of
τ
on the assumed meteoroid’s density,
ρ
, and include improved
ρ
-values for objects with identified meteoroid stream association. Based on the discovered individual biases and constraints we create a pre-debiased subset of 54 well-recorded events with a relative velocity change >80%, a final height <70 km, and a Knudsen number Kn < 0.01; this last value indicates that the events were observed in the continuum-flow regime. We find
τ
-values in the range between 0.012% and 1.1% for this pre-debiased subset and relations of
τ
to
v
e
and
M
e
of:
τ
=7.33⋅
v
e
−1.10
and
τ
=0.28⋅
M
e
−0.33
.
Conclusions.
The derived luminous efficiency of meteoroids depends on the assumed material density. Our results indicate that the applied debiasing method improves the analysis of
τ
from decelerated meteoroids. The underlying method is only valid for meteors in the continuum-flow regime. These events tend to have low end heights, large masses, and high deceleration.
Mini-EUSO is part of the JEM-EUSO program and operates on board the International Space Station (ISS). It is a UV-telescope with single-photon counting capability looking at nighttime downwards to ...the Earth through a nadir-facing UV-transparent window. As part of the pre-flight tests, the Mini-EUSO engineering model, a telescope with 1/9 of the original focal surface and a lens of 2.5 cm diameter, has been built and tested. Tests of the Mini-EUSO engineering model have been made in laboratory and in open-sky conditions. Laboratory tests have been performed at the TurLab facility, located at the Physics Department of the University of Turin, equipped with a rotating tank containing different types of materials and light sources. In this way, the configuration for the observation of the Earth from space was emulated, including the Mini-EUSO trigger schemes. In addition to the qualification and calibration tests, the Mini-EUSO engineering model has also been used to evaluate the possibility of using a JEM-EUSO-type detector for applications such as observation of space debris. Furthermore, observations in open-sky conditions allowed the studies of natural light sources such as stars, meteors, planets, and artificial light sources such as airplanes, satellites reflecting the sunlight, and city lights. Most of these targets could be detected also with Mini-EUSO. In this paper, the tests in laboratory and in open-sky conditions are reported, as well as the obtained results. In addition, the contribution that such tests provided to foresee and improve the performance of Mini-EUSO on board the ISS is discussed.
A unique feature of the cancer-causing mucosotropic human papillomaviruses (HPVs) is the ability of their E6 proteins to interact with a number of PDZ domain-containing cellular substrates, including ...the cell polarity regulators hDlg and hScrib. These interactions are essential for the ability of these viruses to induce malignant progression. Rhesus papillomaviruses (RhPV) are similar to their human counterparts in that they also cause anogenital malignancy in their host, the Rhesus Macaque. However, unlike HPV E6, the RhPV E6 has no PDZ-binding motif. We now show that such a motif is present on the RhPV E7 oncoprotein. This motif specifically confers PDZ-binding activity and directs the interaction of RhPV E7 with the cell polarity regulator Par3, which it targets for proteasome-mediated degradation. These results demonstrate an amazing evolutionary conservation of function between the RhPV and the HPV oncoproteins, where both target proteins of the same cell polarity control network, although through different components and pathways.
Loss of cell polarity is a fundamental process in cell transformation. Among polarity proteins, we focused on human disc large (DLG1), which is localized mainly at adherens junctions and contributes ...to the control of cell proliferation. We previously demonstrated that its expression is altered in HPV-associated cervical neoplastic lesions, but the mechanisms beyond this remain unknown. In this study, we analysed the contribution of HPV proteins to the changes in DLG1 expression in the squamous epithelium. We observed tissue and intracellular misdistribution of DLG1 when high-risk HPV-18 E7 or E6/E7 proteins were expressed in organotypic raft cultures. The viral oncoproteins induce the loss of DLG1 from the cell borders and an increase in the level of DLG1 protein, reflecting the pattern observed in cervical lesions. These findings were corroborated in cultures bearing the entire HPV-18 genome. Interestingly, changes in tissue distribution and abundance of DLG1 were also detected in organotypic cultures expressing the low-risk HPV-11 E7 or E6/E7 proteins, suggesting a conserved function among different HPV types. However, for low-risk HPVs, the subcellular localization of DLG1 at cell-to-cell contacts was predominantly maintained. This report offers new evidence, we believe, of the involvement of HPV proteins in DLG1 expression pattern and our data support previous observations regarding DLG1 expression in cervical lesions.
On May 30, 2017, at about 21 h 09 min 17 s UTC a green bright fireball crossed the sky of northeastern Italy. The fireball path was observed from some all-sky cameras starting from a mean altitude of
...81.1
±
0.2
km (Lat.
44
.
369
∘
±
0
.
002
∘
N; Long.
11
.
859
∘
±
0
.
002
∘
E) and extinct at
23.3
±
0.2
km (Lat.
45
.
246
∘
±
0
.
002
∘
N; Long.
12
.
046
∘
±
0
.
002
∘
E), between the Italian cities of Venice and Padua. In this paper, on the basis of simple physical models, we will compute the atmospheric trajectory, analyze the meteoroid atmospheric dynamics, the dark flight phase (with the strewn field) and compute the best heliocentric orbit of the progenitor body. Search for meteorites on the ground has not produced any results so far.
Testing instrument capabilities is a crucial issue for Gaia, where high level performances are expected. This activity involves many aspects: simulation of the instrument through suitable modelling, ...comparison of the models with the actual instrument, as well as producing evaluation methods, which are strictly related to the way data will be processed and calibrated. In this paper I discuss the interconnections among these aspects, and provide some example from the current testing activities.
.
At the underground laboratory of Monte dei Cappuccini (OATo-INAF) in Torino (Italy) we set up selective HPGe-NaI(Tl) spectrometers for measurements of cosmogenic radioisotopes in meteorites in ...order to study centennial-scale modulation of solar activity.
44
Ti is a suitable proxy for this timescale, but its detection is difficult due to the strong interference by naturally occurring
214
Bi. In order to optimize the extraction of the
44
Ti signal, we have developed software procedures specifically designed to improve selectivity of the Ge-NaI detectors coincidence.
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