147 research outputs found
Variation of bulk Lorentz factor in AGN jets due to Compton rocket in a complex photon field
Radio-loud active galactic nuclei are among the most powerful objects in the
universe. In these objects, most of the emission comes from relativistic jets
getting their power from the accretion of matter onto supermassive black holes.
However, despite the number of studies, a jet's acceleration to relativistic
speeds is still poorly understood.
It is widely known that jets contain relativistic particles that emit
radiation through several physical processes, one of them being the inverse
Compton scattering of photons coming from external sources. In the case of a
plasma composed of electrons and positrons continuously heated by the
turbulence, inverse Compton scattering can lead to relativistic bulk motions
through the Compton rocket effect. We investigate this process and compute the
resulting bulk Lorentz factor in the complex photon field of an AGN composed of
several external photon sources.
We consider various sources here: the accretion disk, the dusty torus, and
the broad line region. We take their geometry and anisotropy carefully into
account in order to numerically compute the bulk Lorentz factor of the jet at
every altitude.
The study, made for a broad range of parameters, shows interesting and
unexpected behaviors of the bulk Lorentz factor, exhibiting acceleration and
deceleration zones in the jet. We investigate the patterns of the bulk Lorentz
factor along the jet depending on the source sizes and on the observation angle
and we finally show that these patterns can induce variability in the AGN
emission with timescales going from hours to months.Comment: 12 pages, 16 figures, accepted to A&
Deep unsupervised domain adaptation applied to the Cherenkov Telescope Array Large-Sized Telescope
The Cherenkov Telescope Array is the next generation of observatory using
imaging air Cherenkov technique for very-high-energy gamma-ray astronomy. Its
first prototype telescope is operational on-site at La Palma and its data
acquisitions allowed to detect known sources, study new ones, and to confirm
the performance expectations. The application of deep learning for the
reconstruction of the incident particle physical properties (energy, direction
of arrival and type) have shown promising results when conducted on
simulations. Nevertheless, its application to real observational data is
challenging because deep-learning-based models can suffer from domain shifts.
In the present article, we address this issue by implementing domain adaptation
methods into state-of-art deep learning models for Imaging Atmospheric
Cherenkov Telescopes event reconstruction to reduce the domain discrepancies,
and we shed light on the gain in performance that they bring along
Localization and delocalization of charges injected in DNA
The electrical properties of DNA molecules are investigated by charge
injection and electric force microscopy experiments. Prior to injection, DNA
molecules exhibit a weak positively charged state. We probe the electrical
behaviour of DNA by measuring the localized or delocalized character of the DNA
charge states upon injection of excess charges. We show that injected charges
do not delocalize for overstretched DNA prepared by a receding meniscus
technique, while the adjunction of spermidine during the deposition leads to
relaxed DNA molecules exhibiting a charge delocalization over microns. The
interplay between charge localization/delocalization and deposition techniques
may explain that transport behaviors ranging from insulating to conductive have
been reported for DNA deposited on surfaces.Comment: To be published in Appl. Phys. Let
Performance of the Large-Sized Telescope prototype of the Cherenkov Telescope Array
The next-generation ground-based gamma-ray Cherenkov Telescope Array
Observatory (CTAO) will consist of imaging atmospheric Cherenkov telescopes
(IACTs) of three different sizes distributed in two sites. The Large-Sized
Telescopes will cover the low-energy end of the CTA energy range, starting at
about 20 GeV. After its first years of operation at the CTA northern site, the
Large-Sized Telescope prototype (LST-1) is in the final stage of its
commissioning phase, having collected a significant amount of scientific data
to date.
In this contribution, we present the physics performance of the telescope
using low-zenith Crab Nebula observations and Monte Carlo simulations
fine-tuned accordingly. We show performance figures of merit such as the energy
threshold, effective area, energy and angular resolution, and sensitivity based
on the standard Hillas-parameters approach and following the source-independent
and dependent analysis methods. The analysis threshold is estimated at 30 GeV.
The energy resolution is around 30%, and the angular resolution is 0.3 degrees
at 100 GeV. The best integral sensitivity of LST-1 is about 1.1% of the Crab
Nebula flux above 250 GeV for 50 hours of observations. We also show the
spectral energy distribution and light curve from Crab Nebula observations,
which agree with results from other IACTs and link smoothly with Fermi-LAT when
considering statistical and systematic uncertainties near the energy threshold.Comment: Presented at the 38th International Cosmic Ray Conference (ICRC
2023), 2023 (arXiv:2309.08219
Conductance switching at the nanoscale of diarylethene derivatives self-assembled monolayers on LaSrMnO
We report on the phosphonic acid route for the grafting of functional
molecules, optical switch (dithienylethene diphosphonic acid, DDA), on
La0.7Sr0.3MnO3 (LSMO). Compact self-assembled monolayers (SAMs) of DDA are
formed on LSMO as studied by topographic atomic force microscopy (AFM),
ellipsometry, water contact angle and X-ray photoemission spectroscopy (XPS).
The conducting AFM measurements show that the electrical conductance of
LSMO/DDA is about 3 decades below that of the bare LSMO substrate. Moreover,
the presence of the DDA SAM suppresses the known conductance switching of the
LSMO substrate that is induced by mechanical and/or bias constraints during
C-AFM measurements. A partial light-induced conductance switching between the
open and closed forms of the DDA is observed for the LSMO/DDA/C-AFM tip
molecular junctions (closed/open conductance ratio of about 8). We show that,
in the case of long-time exposition to UV light, this feature can be masked by
a non-reversible decrease (a factor of about 15) of the conductance of the LSMO
electrode.Comment: Full paper with supporting informatio
Effectiveness of strategies to increase the validity of findings from association studies: size vs. replication
<p>Abstract</p> <p>Background</p> <p>The capacity of multiple comparisons to produce false positive findings in genetic association studies is abundantly clear. To address this issue, the concept of false positive report probability (FPRP) measures "the probability of no true association between a genetic variant and disease given a statistically significant finding". This concept involves the notion of prior probability of an association between a genetic variant and a disease, making it difficult to achieve acceptable levels for the FPRP when the prior probability is low. Increasing the sample size is of limited efficiency to improve the situation.</p> <p>Methods</p> <p>To further clarify this problem, the concept of true report probability (TRP) is introduced by analogy to the positive predictive value (PPV) of diagnostic testing. The approach is extended to consider the effects of replication studies. The formula for the TRP after k replication studies is mathematically derived and shown to be only dependent on prior probability, alpha, power, and number of replication studies.</p> <p>Results</p> <p>Case-control association studies are used to illustrate the TRP concept for replication strategies. Based on power considerations, a relationship is derived between TRP after k replication studies and sample size of each individual study. That relationship enables study designers optimization of study plans. Further, it is demonstrated that replication is efficient in increasing the TRP even in the case of low prior probability of an association and without requiring very large sample sizes for each individual study.</p> <p>Conclusions</p> <p>True report probability is a comprehensive and straightforward concept for assessing the validity of positive statistical testing results in association studies. By its extension to replication strategies it can be demonstrated in a transparent manner that replication is highly effective in distinguishing spurious from true associations. Based on the generalized TRP method for replication designs, optimal research strategy and sample size planning become possible.</p
Kinetics of maternal immunity against rabies in fox cubs (Vulpes vulpes)
BACKGROUND: In previous experiments, it was demonstrated that maternal antibodies (maAb) against rabies in foxes (Vulpes vulpes) were transferred from the vixen to her offspring. However, data was lacking from cubs during the first three weeks post partum. Therefore, this complementary study was initiated. METHODS: Blood samples (n = 281) were collected from 64 cubs (3 to 43 days old) whelped by 19 rabies-immune captive-bred vixens. Sera was collected up to six times from each cub. The samples were analysed by a fluorescence focus inhibition technique (RFFIT), and antibody titres (nAb) were expressed in IU/ml. The obtained data was pooled with previous data sets. Subsequently, a total of 499 serum samples from 249 cubs whelped by 54 rabies-immune vixens were fitted to a non-linear regression model. RESULTS: The disappearance rate of maAb was independent of the vixens' nAb-titre. The maAb-titre of the cubs decreased exponentially with age and the half-life of the maAb was estimated to be 9.34 days. However, maAb of offspring whelped by vixens with high nAb-titres can be detected for longer by RFFIT than that of offspring whelped by vixens with relatively low nAb-titres. At a mean critical age of about 23 days post partum, maAb could no longer be distinguished from unspecific reactions in RFFIT depending on the amount of maAb transferred by the mother. CONCLUSIONS: The amount of maAb cubs receive is directly proportional to the titre of the vixen and decreases exponentially with age below detectable levels in seroneutralisation tests at a relatively early age
The development of the würde + infinitive construction in Early Modern German (1650–1800)
This paper presents a corpus-based analysis of the evolution of the würde + infinitive construction in German during the Early Modern period (1650– 1800), using newly available data from the GerManC-corpus. We demonstrate how this construction occupies a unique position orthogonal to both the tense and mood systems of German through an analysis of the syntax and semantics of würde + infinitive clauses, beginning with Modern Standard German and then subsequently with a historical focus on the late seventeenth and eighteenth centuries. Through both quantitative and qualitative analyses, we examine the contexts in which the construction occurs and see how, as it came to be used more frequently over the period in question, it encroached more and more into contexts which had been the preserve of the synthetic preterite subjunctive, even being used in some where the latter is still the norm in modern German. Thus, by the end of the eighteenth century it had become difficult to identify a clear difference in meaning and use between these forms, and the reasons why the würde + in- finitive construction may be preferred over the synthetic preterite subjunctive are by no means clear. We conclude our discussion with an overview of how the würde + infinitive construction was received in the prescriptive tradition during this key period in the standardization of German, seeing its stigmatization in some contexts in part as an attempt by prescriptive grammarians to establish an explicit and clearly justified role for it in the language
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