Results 1 - 10 of 17
Results 1 - 10 of 17. Search took: 0.016 seconds
|Sort by: date | relevance|
[en] We explore the geodesic movement on an effective four-dimensional hypersurface that is embedded in a five-dimensional Ricci-flat manifold described by a canonical metric, to applying to planetary orbits in our solar system. Some important solutions are given, which provide the standard solutions of general relativity without any extra force component. We study the perihelion advances of Mercury, the Earth, and Pluto using the extended theory of general relativity. Our results are in very good agreement with observations and show how the foliation is determinant to the value of the perihelion's advances. Possible applications are not limited to these kinds of orbits. (author)
[en] Aside from recording stellar nucleosynthesis, a few elements in presolar grains can also provide insights into the galactic chemical evolution (GCE) of nuclides. We have studied the carbon, silicon, iron, and nickel isotopic compositions of presolar silicon carbide (SiC) grains from asymptotic giant branch (AGB) stars to better understand GCE. Since only the neutron-rich nuclides in these grains have been heavily in uenced by the parent star, the neutron-poor nuclides serve as GCE proxies. Using CHILI, a new resonance ionization mass spectrometry (RIMS) instrument, we measured 74 presolar SiC grains for all iron and nickel isotopes. With the CHARISMA instrument, 13 presolar SiC grains were analyzed for iron isotopes. All grains were also measured by NanoSIMS for their carbon and silicon isotopic compositions. A comparison of the measured neutron-rich isotopes with models for AGB star nucleosynthesis shows that our measurements are consistent with AGB star predictions for low-mass stars between half-solar and solar metallicity. Furthermore, our measurements give an indication on the 22Ne(,n)25Mg reaction rate. In terms of GCE, we nd that the GCE-dominated iron and nickel isotope ratios, 54Fe/56Fe and 60Ni/58Ni, correlate with their GCE-dominated counterpart in silicon, 29Si/28Si. The measured GCE trends include the Solar System composition, showing that the Solar System is not a special case. However, as seen in silicon and titanium, many presolar SiC grains are more evolved for iron and nickel than the Solar System. This con rms prior ndings and agrees with observations of large stellar samples that a simple age-metallicity relationship for GCE cannot explain the composition of the solar neighborhood.
[en] The European Space Agency (ESA) has a very active Science Programme, with many missions in operation in space, and others being studied, developed or being prepared for launch. The ESA Science missions are very diverse, ranging from astrophysics observatories to probes visiting other parts of our planetary system, studying other planets, comets and our sun. Their success would not be possible without the development and use of novel technologies. Future ESA Science missions are extensively studied before their adoption for flight, and associated technologies are developed in industrial activities funded by ESA. An elaborated technology development plan is being regularly updated, and offers opportunities for innovative companies and research institutions to contribute to the ESA Science Programme. (author)
[en] We review the field of exoplanetary biosignatures with a main focus upon atmospheric gas-phase species. Due to the paucity of data in Earth-like planetary atmospheres a common approach is to extrapolate knowledge from the Solar System and Early Earth to Earth-like exoplanets. We therefore review the main processes (e.g. atmospheric photochemistry and transport) affecting the most commonly-considered species (e.g. O2, O3, N2O, CH4 etc.) in the context of the modern Earth, Early Earth, the Solar System and Earth-like exoplanets. We consider thereby known abiotic sources for these species in the Solar System and beyond. We also discuss detectability issues related to atmospheric biosignature spectra such as band strength and uniqueness. Finally, we summarize current space agency roadmaps related to biosignature science in an exoplanet context.
[en] It is shown that basic hypotheses regarding the nature of the source of the observed gravitational anomalies lead naturally to both the baryonic Tully-Fisher relationship and the Pioneer anomaly. A theory where the gravitational field of a mass induces a gravitational field contribution from the cosmos fits well with these hypotheses. In line with this, a theory is presented where particle-antiparticle pairs exist throughout the cosmos, with a lifetime in accordance with Heisenberg's uncertainty principle. These particle-antiparticle pairs are displaced in the presence of a gravitational field and contribute to the overall gravitational field of a given mass. The modeled contribution agrees with the baryonic Tully-Fisher relationship, the Pioneer anomaly, and the absence of any anomalous gravitational field within the inner solar system. (author)
[en] Aluminium-26, a radioactive isotope with a half life of 0.72 Myr, was present in the early Solar System, as inferred from Magnesium-26 excess in meteorites. It is also detected in the Galaxy via gamma-ray observations from COMPTEL and INTEGRAL. While it is known that Al-26 is produced in stars, many uncertainties are left related to the production sites and the nuclear physics input. Past research has focused mostly on yields of Al-26 from massive single stars, both rotating and non-rotating, including their winds and supernova explosions. We focus on the yields from massive star winds, primarily Wolf-Rayet stars with masses of 30 Msun or larger, both single and in binary systems, and on the yields from non-conservative mass transfer in binary systems with primary masses starting at 15 Msun. The final goal is to discover the impact of massive binary stars on the galactic abundance of Al-26 and on the origin of the Al-26 in the early Solar System. I will present the first results of our research, focusing on a 20 Msun star and a 18+20 Msun binary system. (author)
[en] Radiative power balance of a planet in the solar system is delineated. The terrestrial powers are transformed to average global flux in an effective atmospheric column approximation, its components are delineated. The estimated and measured secular changes of the average global flux are compared to the fluxes derived from the Stefan-Boltzmann law using the observed global annual temperatures in the decades between 1880 and 2010. The conclusion of this procedure is that the radiative contribution of the greenhouse gas CO2 is some 21 ± 7 % to the observed global warming from the end of the nineteenth century excluding the feedback mechanisms playing determining role in the climate system. Stationary radiative flux transfer is treated in an air column as a function of the column density of the absorbent. Upper and lower limit of radiative forcing is given by assuming true absorption and coherent scatter of the monochromatic radiation. An integral formula is given for the outgoing long wave radiation as a function of column density of the components of greenhouse gases. (author)
[en] Highlights: • The energy output characteristics of the solar hybrid CCHP system are defined in a clear perspective. • The particle swarm optimization (PSO) algorithm is adopted to find the optimum design parameters. • The design features and the performance of solar hybrid systems under five different operation strategies are analyzed. • The comparison between the hybrid system and the conventional system is given. - Abstract: The hybridization between conventional combined cooling heating and power (CCHP) systems and solar systems has been considered as a good solution to the urgent energy and environment issues. This study develops the mathematical model of a CCHP system hybridized with PV panels and solar thermal collectors. The particle swarm optimization (PSO) algorithm is adopted to find the optimum values of design parameters. Based on the energy output characteristic of the solar hybrid CCHP system, five operation strategies of the conventional CCHP system are adjusted and applied for the solar hybrid CCHP system. The simulation work of the hybrid CCHP systems based upon a hotel building in Atlanta is carried out to find an appropriate design scheme. The results show that the hybrid CCHP system under the FEL-ECR mode is the best choice. Besides, its PESR, CO2ERR and ATCSR can reach 36.15%, 53.73% and 4.16%, respectively. Compared with a conventional CCHP system, the hybrid CCHP system achieves better energy-saving and CO2 reduction performance. However, the hybrid CCHP system consumes more annual total costs because of its high initial investment.
[en] The r-process is responsible for the production of about half of the heavy elements observed in the solar abundances. The site of the r-process was unknown until recent observations. The gravitational wave event GW170817, which was identified as a binary Neutron Star Merger (NSM), was followed by the detection of fast fading optical counterpart that is consistent with predictions for a kilonova/macronova, associated with r-process nucleosynthesis. In particular the observation of a bright, fast fading UV component, established the production of heavy element in the aftermath of the neutron star merger. Since the complicated atomic structure of lanthanides implies high opacity ejecta which would shift the wavelength of the observed light to the red, the blue color of the ejecta indicates the presence of material with relatively high electron fractions and consequently low lanthanide production. Recent mass measurements of neutron rich gallium masses affect the production of elements of the first r-process peak. We present a study of nucleosynthesis for conditions of high Ye outflows from NSMs and investigate the effect of the recently measured Ga masses and the conditions under which this could be the site for the production of the elements of the r-process abundance pattern for A < 100. (author)