Search results for "Flight"
showing 10 items of 372 documents
Fractional Laplacians in bounded domains: Killed, reflected, censored, and taboo Lévy flights.
2018
The fractional Laplacian $(- \Delta)^{\alpha /2}$, $\alpha \in (0,2)$ has many equivalent (albeit formally different) realizations as a nonlocal generator of a family of $\alpha $-stable stochastic processes in $R^n$. On the other hand, if the process is to be restricted to a bounded domain, there are many inequivalent proposals for what a boundary-data respecting fractional Laplacian should actually be. This ambiguity holds true not only for each specific choice of the process behavior at the boundary (like e.g. absorbtion, reflection, conditioning or boundary taboos), but extends as well to its particular technical implementation (Dirchlet, Neumann, etc. problems). The inferred jump-type …
Lévy flights and Lévy-Schrödinger semigroups
2010
We analyze two different confining mechanisms for L\'{e}vy flights in the presence of external potentials. One of them is due to a conservative force in the corresponding Langevin equation. Another is implemented by Levy-Schroedinger semigroups which induce so-called topological Levy processes (Levy flights with locally modified jump rates in the master equation). Given a stationary probability function (pdf) associated with the Langevin-based fractional Fokker-Planck equation, we demonstrate that generically there exists a topological L\'{e}vy process with the very same invariant pdf and in the reverse.
Photoemission time-of-flight spectromicroscopy of Ag nanoparticle films on Si(111)
2004
Abstract Time-of-flight photoemission electron microscopy was used to measure spatially resolved energy distribution curves of electrons emitted from Ag nanoparticle films with different mass thicknesses. Two-photon photoemission (2PPE) was induced by femtosecond laser pulse excitation with 3.1 eV photon energy and 200 fs pulse width. Regions of Ag nanoparticles with different average sizes and one region with a continuous 100 nm thick Ag film were deposited as a stepped wedge on a Si(1 1 1) substrate. Upon laser excitation the nanoparticle films exhibit a very high electron emission yield in the images, whereas the uncovered Si surface and the continuous Ag film are dark. The time-of-fligh…
Autonomic Stress Response and Perceived Effort Jointly Inform on Dual Tasking in Aging
2019
The study investigated, through neuroendocrinological, subjective and behavioral assessments, how aging individuals cope with locomotor-cognitive dual-tasking and whether physical activity habits influence the acute response to locomotor-cognitive performance. Seventy-nine healthy participants aged 55&ndash
Sequential window acquisition of all theoretical fragments versus information dependent acquisition for suspected-screening of pharmaceuticals in sed…
2019
The aquatic ecosystems are dynamic environments often affected directly or indirectly by a myriad of anthropogenic contaminants that need to be properly identified. In this study, liquid chromatography-quadrupole time-of-flight mass spectrometry (LC-QqTOF-MS) suspected-screening was applied to mussels and riverine sediment both, non-spiked and spiked with a mixture of 32 pharmaceuticals. Three data acquisition methods –sequential window acquisition of all theoretical fragment-ion spectra (SWATH), in fix (FSWATH) and variable (VSWATH) window modes and Information Dependent Acquisition (IDA)– were compared to determine the most suitable acquisition technique. The results obtained in the spike…
Latvijas Vēstures Institūta Žurnāls. 2022, Nr. 2 (117)
2022
Atbalsts LU Latvijas vēstures institūta LU ilgtermiņa saistību izpildei 2020.-2022. gadā ("Latvijas Vēstures Institūta Žurnāls")
Limited potential for bird migration to disperse plants to cooler latitudes
2021
Climate change is forcing the redistribution of life on Earth at an unprecedented velocity1,2. Migratory birds are thought to help plants to track climate change through long-distance seed dispersal3,4. However, seeds may be consistently dispersed towards cooler or warmer latitudes depending on whether the fruiting period of a plant species coincides with northward or southward migrations. Here we assess the potential of plant communities to keep pace with climate change through long-distance seed dispersal by migratory birds. To do so, we combine phenological and migration information with data on 949 seed-dispersal interactions between 46 bird and 81 plant species from 13 woodland communi…
Space medicine: use of ex vivo human respiratory mucosa in the survey of the effects of microgravity on the respiratory system
2019
In the near future, the length and scope of space travel is set to increase significantly. The number of individuals who will have access to extra-terrestrial travels is also increasing. In view of the growing international interest towards manned long-term space exploration, possible effects of exposure to microgravity conditions affecting the respiratory system are subject of interest by major space agencies (NASA and ESA primarily). Our team has developed an advanced 3d tissue model of the human bronchial mucosa within a wide research project involving several universities and space agencies at international level. The model will be used to study the structural/functional alterations of …
Flight Control Research Laboratory Unmanned Aerial System flying in turbulent air: an algorithm for parameter identification from flight data
2013
This work addresses the identification of the dynamics of the research aircraft FCRL (Flight Control Research Laboratory) used for the Italian National Research Project PRIN2008 accounting for atmospheric turbulence. The subject vehicle is an unpressurized 2 seats, 427 kg maximum take of weight aircraft. It features a non retractable, tailwheel, landing gear and a powerplant made up of reciprocating engine capable of developing 60 HP, with a 60 inches diameter, two bladed, fixed pitch., tractor propeller. The aircraft stall speed is 41.6 kts, therefore it is capable of speeds up to about 115 kts (Sea level) and it will be cleared for altitudes up to 10.000 ft. The studied aircraft is equipp…
Trajectory tracking for a Non-Conventional UAV
2008
The aim of the present paper is the design of a flight control system for a Tandem – Canard UAV, useful in the whole flight envelope, both Out of Ground Effect (OGE) and In Ground Effect (IGE) conditions. Because of the particular arrangement of the studied aircraft, a general mathematical model has been built in order to obtain non-linear analytical equations for longitudinal aerodynamic coefficients both in OGE and in IGE flight. So the dynamic behaviour of the UAV may be studied during every flight phases i.e. in the whole range of altitude. To consider the strong variation of aerodynamic parameters due to the ground effect presence, a robust control technique (LQG/LTR) has been used to …