419 research outputs found
A photon transport problem with a time-dependent point source
We consider a time-dependent problem of photon transport in an interstellar cloud with a point photon source modeled by a Dirac δ functional. The existence of a unique distributional solution to this problem is established by using the theory of continuous semigroups of operators on locally convex spaces coupled with a constructive approach for producing spaces of generalized functions
Influence of mismatch on the defects in relaxed epitaxial InGaAs/GaAs(100) films grown by molecular beam epitaxy
Thick (∼3 μm) films of InxGa1−xAs grown on GaAs(100) substrates, across the whole composition range, have been examined by transmission electron microscopy and double‐crystal x‐ray diffraction. The results were compared with the observed growth mode of the material determined by in situ reflection high‐energy electron diffraction in the molecular beam epitaxy growth system. The quality of the material degraded noticeably for compositions up to x∼0.5 associated with an increased density of dislocations and stacking faults. In contrast, improvements in quality as x approached 1.0 were correlated with the introduction of an increasingly more regular array of edge dislocations
Regulatory Dynamics on Random Networks: Asymptotic Periodicity and Modularity
We study the dynamics of discrete-time regulatory networks on random
digraphs. For this we define ensembles of deterministic orbits of random
regulatory networks, and introduce some statistical indicators related to the
long-term dynamics of the system. We prove that, in a random regulatory
network, initial conditions converge almost surely to a periodic attractor. We
study the subnetworks, which we call modules, where the periodic asymptotic
oscillations are concentrated. We proof that those modules are dynamically
equivalent to independent regulatory networks.Comment: 23 pages, 3 figure
ESA F-Class Comet Interceptor: Trajectory design to intercept a yet-to-be-discovered comet
Comet Interceptor (Comet-I) was selected in June 2019 as the first ESA F-Class mission. In 2029+, Comet-I will hitch a ride to a Sun-Earth L2 quasi-halo orbit, as a co-passenger of ESA's M4 ARIEL mission. It will then remain idle at the L2 point until the right departure conditions are met to intercept a yet-to-be-discovered long period comet (or interstellar body). The fact that Comet-I target is thus unidentified becomes a key aspect of the trajectory and mission design. The paper first analyses the long period comet population and concludes that 2 to 3 feasible targets a year should be expected. Yet, Comet-I will only be able to access some of these, depending mostly on the angular distance between the Earth and the closest nodal point to the Earth's orbit radius. A preliminary analysis of the transfer trajectories has been performed to assess the trade-off between the accessible region and the transfer time for a given spacecraft design, including a fully chemical, a fully electric and a hybrid propulsion system. The different Earth escape options also play a paramount role to enhance Comet-I capability to reach possible long period comet targets. Particularly, Earth-leading intercept configurations have the potential to benefit the most from lunar swing-by departures. Finally, a preliminary Monte Carlo analysis shows that Comet-I has a 95–99% likelihood of successfully visit a pristine newly-discovered long period comet in less than 6 years of mission timespan
Advanced Electron Microscopy Techniques on Semiconductor Nanowires: from Atomic Density of States Analysis to 3D Reconstruction Models
Distance to range edge determines sensitivity to deforestation
It is generally assumed that deforestation affects a species consistently across space, however populations near their geographic range edge may exist at their niche limits and therefore be more sensitive to disturbance. We found that both within and across Atlantic Forest bird species, populations are more sensitive to deforestation when near their range edge. In fact, the negative effects of deforestation on bird occurrences switched to positive in the range core (>829 km), in line with Ellenberg’s rule. We show that the proportion of populations at their range core and edge varies across Brazil, suggesting deforestation effects on communities, and hence the most appropriate conservation action, also vary geographically
Efficacy of lamivudine to prevent hepatitis reactivation in hepatitis B virus-infected patients treated for non-Hodgkin lymphoma.
The association of hepatitis viruses with non-Hodgkin lymphomas
(NHL) is not rare. Several authors have reported an
exceeding prevalence of hepatitis C virus (HCV)1-3 or of
hepatitis B virus (HBV)4,5 infection in patients affected by NHL.
A sustained increase of alanine aminotransferase (ALT) associated
with high levels of HBV viremia (HBV-DNA) 1 to 2 months after
the suspension of chemotherapy has been described in patients
suffering from NHL and infected by HBV.7,8 Recently, a nucleotide
analogue (lamivudine) was shown to be beneficial in HBV-infected
patients with signs of active replication.6 The aim of this study was
to investigate the role of lamivudine to treat or to prevent hepatitis
reactivation in HBV-infected subjects suffering from NHL and
undergoing chemotherapy
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