2,473 research outputs found
The NASA-Ames Research Center stratospheric aerosol model. 2. Sensitivity studies and comparison with observatories
Sensitivity tests were performed on a one-dimensional, physical-chemical model of the unperturbed stratospheric aerosols, and model calculations were compared with observations. The tests and comparisons suggest that coagulation controls the particle number mixing ratio, although the number of condensation nuclei at the tropopause and the diffusion coefficient at high altitudes are also important. The sulfur gas source strength and the aerosol residence time are much more important than the supply of condensation nuclei in establishing mass and large particle concentrations. The particle size is also controlled mainly by gas supply and residence time. In situ observations of the aerosols and laboratory measurements of aerosols, parameters that can provide further information about the physics and chemistry of the stratosphere and the aerosols found there are provided
The NASA-AMES Research Center Stratospheric Aerosol Model. 1. Physical Processes and Computational Analogs
A time-dependent one-dimensional model of the stratospheric sulfate aerosol layer is presented. In constructing the model, a wide range of basic physical and chemical processes are incorporated in order to avoid predetermining or biasing the model predictions. The simulation, which extends from the surface to an altitude of 58 km, includes the troposphere as a source of gases and condensation nuclei and as a sink for aerosol droplets. The size distribution of aerosol particles is resolved into 25 categories with particle radii increasing geometrically from 0.01 to 2.56 microns such that particle volume doubles between categories
Environmental effects of SPS: The middle atmosphere
The heavy lift launch vehicle associated with the solar power satellite (SPS) would deposit in the upper atmosphere exhaust and reentry products which could modify the composition of the stratosphere, mesosphere, and lower ionosphere. In order to assess such effects, atmospheric model simulations were performed, especially considering a geographic zone centered at the launch and reentry latitudes
Reply to Yu Wei, Yao Zhu, and Dingwei Ye's Letter to the Editor re: Fabio Turco, Andrew Armstrong, Gerhardt Attard, et al. What Experts Think About Prostate Cancer Management During the COVID-19 Pandemic: Report from the Advanced Prostate Cancer Consensus Conference 2021. Eur Urol. 2022;82:6–11
Instalações.
Selecionando locais para as instalações. Instalações: abrigos, apriscos, baias para reprodutores, setor de manejo, sala de ordenha, quarentenario e ambulatório. Istalações para crescimento e engorda. Cercas para caprinos: convencionais e móveis. Equipamento para as instalações: comedouros, comedouros para concentrados, fenis, comedouros de concentrados e feno, comedouros conjugados as cercas, saleiro, manejo de dejetos
Water fragmentation by bare and dressed light ions with MeV energies: Fragment-ion-energy and time-of-flight distributions
The energy and time-of-flight distributions of water ionic fragments produced by impact of fast atoms and bare and dressed ions; namely, H+, Li0-3+, C1+, and C2+ are reported in this work. Fragment species as a function of emission energy and time-of-flight were recorded by using an electrostatic spectrometer and a time-of-flight mass spectrometer, respectively. An improved Coulomb explosion model coupled to a classical trajectory Monte Carlo (CTMC) simulation gave the energy centroids of the fragments for the dissociation channels resulting from the removal of two to five electrons from the water molecule. For the energy distribution ranging up to 50 eV, both the experiment and model reveal an isotropic production of multiple charged oxygen ions, as well as hydrogen ions. From the ion energy distribution, relative yields of the dissociation resulting from multiple ionization were obtained as a function of the charge state, as well as for several projectile energies. Multiple-ionization yields with charge state up to 4+, were extracted from the measurements of the time-of-flight spectra, focused on the production of single and multiple charged oxygen ions. The measurements were compared to ion-water collision experiments investigated at the keV energy range available in the literature, revealing differences and similarities in the fragment-ion energy distribution.Fil: Wolff, W.. Universidade Federal do Rio de Janeiro; BrasilFil: Luna, H.. Universidade Federal do Rio de Janeiro; BrasilFil: Schuch, R.. Alba Nova University Center; SueciaFil: Cariatore, Nelson Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Otranto, Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Turco, Federico. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Fregenal, Daniel Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Bernardi, Guillermo Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Suárez, S.. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentin
An analysis tool for collision avoidance manoeuvres using aerodynamic drag
Aerodynamic collision avoidance manoeuvres provide an opportunity for
satellites in Low Earth Orbits to reduce the risk during close encounters. With
rising numbers of satellites and objects in orbit, satellites experience close
encounters more frequently. Especially those satellites without thrusting
capabilities face the problem of not being able to performimpulsive evasive
manoeuvres. For satellites in Low Earth Orbits, though, perturbing forces due
to aerodynamic drag may be used to influence their trajectories, thus offering
a possibility to avoid collisions. This work introduces a tool for the analysis
of aerodynamic collision avoidance manoeuvres. Current space-weather data are
employed to estimate the density the satellite encounters. Achievable in-track
separation distances following a variation of the ballistic coefficient through
a change in attitude are then derived by evaluating an analytical equation from
literature. Considering additional constraints for the attitude, e.g., charging
phases, and uncertainties in the used parameters, the influence of a manoeuvre
on the conjunction geometry and the collision probability is examined. The
university satellite Flying Laptop of the University of Stuttgart is used as an
exemplary satellite for analysis, which show the general effectiveness of
evasive manoeuvres employing aerodynamic drag. First manoeuvring strategies can
be deducted and the influence of parameter uncertainties is assessed.Comment: 18 pages, 13 figure
Demographic Change and the Urban–Rural Divide: Understanding the Role of Density and Agglomeration in Fertility Transitions
Assuming fertility variations across urban–rural gradients, our study focuses on the traditional polarization in urban and rural fertility, offering a refined interpretation of demographic processes associated with population density. More specifically, we tested the intimate relationship between local fertility and population density, comparing the outcomes of a classical urban–rural model (reflecting a linear relationship between the two variables) with those of a more complex quadratic model (implying the so-called ‘suburban fertility hypothesis’) in Greece. We considered fertility dynamics in three districts (urban, suburban, and rural) of 51 Greek prefectures for the last two decades (2000–2009 and 2010–2019) and controlled for the diverging impact of local contexts at different population density levels. Taken as a measure of ‘maturity’ of regional systems, urban fertility surpassed rural fertility in almost all prefectures of Greece. An additional sign of maturity in metropolitan systems indicates that suburban birth rates are higher than urban birth rates in prefectures with high population density (Athens, Thessaloniki, Heraklion, and Patras). The regression outcomes document a specific response of fertility to regional development, evidencing a spatially differentiated shift from classical urban–rural disparities toward a more complex model with the emergence of suburban poles. From this perspective, fertility divides reflect the evolutions of socioeconomic forces (more or less rapidly) along the urban gradient
Confinement of chiral molecules in reverse micelles:FT-IR,polarimetric and VCD investigation on the state of dimethyl tartrate in sodium bis(2-ethylhexyl) sulfosuccinate reverse micelles dispersed in carbon tetrachloride
The state of d and l-dimethyl tartrate confined within dry sodium bis(2-ethylhexyl) sulfosuccinate
(AOT) reverse micelles dispersed in CCl4 has been investigated by FT-IR spectroscopy, polarimetry, and
vibrational circular dichroism (VCD). Measurements have been performed at 25 ◦C as a function of the
solubilizate-to-surfactant molar ratio (R) at a fixed AOT concentration (0.158 M). The analysis of experimental
data is consistent with the hypothesis that both enantiomers of dimethyl tartrate are mainly
entrapped in the reverse micelles and located in proximity to the surfactant head-group region. The
formation of this interesting self-organized chiral nanostructure involves some changes of the typical
H-bonding of dimethyl tartrates in the pure solid state or as monomers dispersed in CCl4 attributable to
the establishment of specific solubilizate/surfactant head-group interactions and confinement effects
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