排序方式： 共有16条查询结果，搜索用时 15 毫秒
1.
C. Kiss T. G. Müller E. Vilenius A. Pál P. Santos-Sanz E. Lellouch G. Marton E. Verebélyi N. Szalai P. Hartogh J. Stansberry F. Henry A. Delsanti 《Experimental Astronomy》2014,37(2):161-174
The “TNOs are Cool!: A survey of the trans-Neptunian region” is a Herschel Open Time Key Program that aims to characterize planetary bodies at the outskirts of the Solar System using PACS and SPIRE data, mostly taken as scan-maps. In this paper we summarize our PACS data reduction scheme that uses a modified version of the standard pipeline for basic data reduction, optimized for faint, moving targets. Due to the low flux density of our targets the observations are confusion noise limited or at least often affected by bright nearby background sources at 100 and 160 \(\mu \) m. To overcome these problems we developed techniques to characterize and eliminate the background at the positions of our targets and a background matching technique to compensate for pointing errors. We derive a variety of maps as science data products that are used depending on the source flux and background levels and the scientific purpose. Our techniques are also applicable to a wealth of other Herschel solar system photometric observations, e.g. comets and near-Earth asteroids. The principles of our observing strategies and reduction techniques for moving targets will also be applicable for similar surveys of future infrared space projects. 相似文献
2.
Ecological optima and tolerances with respect to autumn pH were estimated for 63 diatom taxa in 47 Finnish lakes. The methods used were weighted averaging (WA), least squares (LS) and maximum likelihood (ML), the two latter methods assuming the Gaussian response model.WA produces optimum estimates which are necessarily within the observed lake pH range, whereas there is no such restriction in ML and LS. When the most extreme estimates of ML and LS were excluded, a reasonably close agreement among the results of different estimation methods was observed. When the species with unrealistic optima were excluded, the tolerance estimates were also rather similar, although the ML estimates were systematically greater.The parameter estimates were used to predict the autumn pH of 34 other lakes by weighted averaging. The ML and LS estimates including the extreme optima produced inferior predictions. A good prediction was obtained, however, when prediction with these estimates was additionally scaled with inverse squared tolerances, or when the extreme values were removed (censored). Tolerance downweighting was perhaps more efficient, and when it was used, no additional improvement was gained by censoring. The WA estimates produced good predictions without any manipulations, but these predictions tended to be biased towards the centroid of the observed range of pH values.At best, the average bias in prediction, as measured by mean difference between predicted and observed pH, was 0.082 pH units and the standard deviation of the differences, measuring the average random prediction error, was 0.256 pH units. 相似文献
3.
Esa Hyyppä 《International Journal of Earth Sciences》1942,32(4-5):595-611
Ohne Zusammenfassung 相似文献
4.
Andreï Lecomte Michel Cathelineau Etienne Deloule Marc Brouand Chantal Peiffert Kirsti Loukola-Ruskeeniemi Esa Pohjolainen Hannu Lahtinen 《Mineralium Deposita》2014,49(4):513-533
In the central part of the Fennoscandian Shield, the Talvivaara Ni–Zn–Cu–Co deposit, hosted by Palaeoproterozoic metamorphosed black schists, contains low uranium concentrations ranging from 10 to 30 ppm. The Talvivaara black schists were deposited 2.0–1.9 Ga ago and underwent subsequent metamorphism during the 1.9–1.79 Ga Svecofennian orogeny. Anhedral uraninite crystals rimmed by bitumen constitute the main host of uranium. U–Pb secondary ion mass spectrometry dating indicates that uraninite crystals were formed between 1,878?±?17 and 1,871?±?43 Ma, during peak metamorphism. Rare earth element patterns and high Th content (average 6.38 wt%) in disseminated uraninite crystals indicate that U was concentrated during high temperature metamorphism (>400 °C). The formation of bitumen rims around uraninite may be explained by two distinct scenarios: (a) a transport of U coincident with the migration of hydrocarbons or (b) post-metamorphic formation of bitumen rims, through radiolytic polymerization of gaseous hydrocarbons at the contact with uraninite. 相似文献
5.
Biological assessment of the Zayandeh Rud River, Iran, using benthic macroinvertebrates 总被引：1，自引：0，他引：1
Mohammad Nemati Varnosfaderany Esa Ebrahimi Noorolla Mirghaffary Alireza Safyanian 《Limnologica》2010,40(3):226-232
Benthic macroinvertebrate communities from the middle of Zayandeh Rud River were analyzed monthly during 1 year at 8 stations, in order to assess changes in their diversity and richness in relation to water quality. Two major groups of sites based on similarity between macroinvertebrate communities were identified by cluster analysis. The performances of the original and revised BMWP score systems were assessed by comparing the community structure indices of benthic macroinvertebrates along with physico-chemical parameters of the water. The biotic indices (BMWP, ASPT, revised BMWP and ASPT) showed better correlation with water quality parameters than that of the richness and diversity indices. The revised ASPT had the highest correlation with water quality parameters. It seems that the application of the revised BMWP score system could be useful for assessment of the water quality in Zayandeh Rud River. 相似文献
6.
Groundwater use and policy in community water supply in Finland 总被引：2，自引：2，他引：0
Selection between ground and surface water in community water supply has been one of the key strategic questions in Finland since the early 1900s. After some cities failed to find reliable groundwater sources, many turned to surface waters. Since the 1950s the use of groundwater and artificial recharged groundwater have continuously increased. Presently their use is promoted by the government and European water policy through technical advice and financial support. It is obvious that the share of groundwater and artificial recharged groundwater will increase in the future. This requires active public response and transparency in decision-making.
Resumen Desde el principio de 1900 una de las preguntas estratégicas clave en Finlandia es la selección entre agua subterranea y de superficie para el suministro de agua de la comunidad. Muchas ciudades renunciaron al agua de superficie luego de haber fracesado en encontrar fuentes de agua subterránea confiables. Desde 1950 el uso de agua subterránea y de agua subterránea recargada artificialmente ha aumentado continuamente. Actualmente los políticas de agua del gobierno y de Europa promueven su uso por medio de asesoría técnica y apoyo financiero. Es obvio que la participación del agua subterránea y del agua subterránea recargada artificialmente va a aumentar en el futuro. Esto requiere una respuesta activa pública y transparencia en el proceso de toma de decisiones.
Resumé Le choix parmi lutilisation de leau de surface ou de leau souterraine comme source dapprovisionnement en eau potable est, depuis le début des années 1900, une question stratégique en Finlande. Suite à léchec de certaines villes à sapprovisionner en eau souterraine, plusieurs se sont tournées vers leau de surface. Depuis les années 1950, lutilisation de leau souterraine et la recharge artificielle des aquifères est en constante croissance. Actuellement, leur utilisation est encouragée par le Gouvernement ainsi que par la politique européenne de leau qui fournit une expertise technique et un soutient financier. Il est évident que les proportions occupées par lapprovisionnement en eau souterraine et la recharge artificielle vont augmenter avec le temps. Ceci requiert une participation active du public ainsi que de la transparence lors du processus décisionnel.相似文献
7.
8.
We have studied the escape and energization of several O+ populations and an population at Mars by using a hybrid model. The quasi-neutral hybrid model, HYB-Mars model, included five oxygen ion populations making it possible to distinguish photoions from oxygen ions originating from charge exchange processes and from the ionosphere.We have identified two high-energy ion components and one low-energy ion component of oxygen. They have different spatial and energy distributions near Mars. The two high-energy oxygen ion components, consisting of a high-energy “beam” and a high-energy “halo”, have different origins. (1) The high-energy (>∼100 eV) “beam” of O+ and ions are originating from the ionosphere. These ions form a highly asymmetric spatial distribution of escaping oxygen ions with respect to the direction of the convective electric field in the solar wind. (2) The high-energy (>∼100 eV) “halo” component contains O+ ions which are formed from the oxygen neutral exosphere by extreme ultraviolet radiation (EUV) and by charge exchange processes. These energetic halo ions can be found all around Mars. (3) The low energy O+ and ions (<∼100 eV) form a relatively symmetric spatial distribution around the Mars-Sun line. They originate from the ionosphere and from charge exchange processes between protons and exospheric oxygen atoms.The existence of the low- and the high-energy oxygen components is in agreement with recent in situ plasma measurements made by the ASPERA-3 instrument on the Mars Express mission. The analysis of the escaping oxygen ions suggests that the global energization of escaping planetary ions in the martian tail is controlled by the convective electric field. 相似文献
9.
Thomas Müller Zoltán Balog Markus Nielbock Tanya Lim David Teyssier Michael Olberg Ulrich Klaas Hendrik Linz Bruno Altieri Chris Pearson George Bendo Esa Vilenius 《Experimental Astronomy》2014,37(2):253-330
Celestial standards play a major role in observational astrophysics. They are needed to characterise the performance of instruments and are paramount for photometric calibration. During the Herschel Calibration Asteroid Preparatory Programme approximately 50 asteroids have been established as far-IR/sub-mm/mm calibrators for Herschel. The selected asteroids fill the flux gap between the sub-mm/mm calibrators Mars, Uranus and Neptune, and the mid-IR bright calibration stars. All three Herschel instruments observed asteroids for various calibration purposes, including pointing tests, absolute flux calibration, relative spectral response function, observing mode validation, and cross-calibration aspects. Here we present newly established models for the four large and well characterized main-belt asteroids (1) Ceres, (2) Pallas, (4) Vesta, and (21) Lutetia which can be considered as new prime flux calibrators. The relevant object-specific properties (size, shape, spin-properties, albedo, thermal properties) are well established. The seasonal (distance to Sun, distance to observer, phase angle, aspect angle) and daily variations (rotation) are included in a new thermophysical model setup for these targets. The thermophysical model predictions agree within 5 % with the available (and independently calibrated) Herschel measurements. The four objects cover the flux regime from just below 1,000 Jy (Ceres at mid-IR N-/Q-band) down to fluxes below 0.1 Jy (Lutetia at the longest wavelengths). Based on the comparison with PACS, SPIRE and HIFI measurements and pre-Herschel experience, the validity of these new prime calibrators ranges from mid-infrared to about 700 μm, connecting nicely the absolute stellar reference system in the mid-IR with the planet-based calibration at sub-mm/mm wavelengths. 相似文献
10.