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991.
Simone Lotti Teresa Mineo Christian Jacquey Silvano Molendi Matteo D’Andrea Claudio Macculi Luigi Piro 《Experimental Astronomy》2017,44(3):371-385
In this paper we are going to review the latest estimates for the particle background expected on the X-IFU instrument onboard of the ATHENA mission. The particle background is induced by two different particle populations: the so called “soft protons” and the Cosmic rays. The first component is composed of low energy particles (< 100s keV) that get funnelled by the mirrors towards the focal plane, losing part of their energy inside the filters and inducing background counts inside the instrument sensitivity band. The latter component is induced by high energy particles (> 100 MeV) that possess enough energy to cross the spacecraft and reach the detector from any direction, depositing a small fraction of their energy inside the instrument. Both these components are estimated using Monte Carlo simulations and the latest results are presented here. 相似文献
992.
R. Krivonos A. Tkachenko R. Burenin E. Filippova I. Lapshov I. Mereminskiy S. Molkov M. Pavlinsky S. Sazonov M. Gubarev J. Kolodziejczak S. L. O’Dell D. Swartz Vyacheslav E. Zavlin B. D. Ramsey 《Experimental Astronomy》2017,44(1):147-164
The Astronomical Röntgen Telescope X-ray Concentrator (ART-XC) is a hard X-ray telescope with energy response up to 30 keV, to be launched on board the Spectrum Röntgen Gamma (SRG) spacecraft in 2018. ART-XC consists of seven identical co-aligned mirror modules. Each mirror assembly is coupled with a CdTe double-sided strip (DSS) focal-plane detector. Eight X-ray mirror modules (seven flight and one spare units) for ART-XC were developed and fabricated at the Marshall Space Flight Center (MSFC), NASA, USA. We present results of testing procedures performed with an X-ray beam facility at MSFC to calibrate the point spread function (PSF) of the mirror modules. The shape of the PSF was measured with a high-resolution CCD camera installed in the focal plane with defocusing of 7 mm, as required by the ART-XC design. For each module, we performed a parametrization of the PSF at various angular distances Θ. We used a King function to approximate the radial profile of the near on-axis PSF (Θ < 9 arcmin) and an ellipse fitting procedure to describe the morphology of the far off-axis angular response (9 < Θ < 24 arcmin). We found a good agreement between the seven ART-XC flight mirror modules at the level of 10%. The on-axis angular resolution of the ART-XC optics varies between 27 and 33 arcsec (half-power diameter), except for the spare module. 相似文献
993.
994.
Michiel A. F. Knaapen 《Geo-Marine Letters》2009,29(1):17-24
Sandbanks, the largest of bed patterns in shallow sandy seas, pose a potential risk to shipping. They are also valuable elements
of natural coastal protection, dissipating the energy of waves. In the Southern Bight of the North Sea, several sandbank areas
have been reported in the literature. However, based on an objective crest–trough analysis of the bathymetry of the Dutch
continental shelf, the present study shows that sandbanks are more widespread than commonly considered. These banks are relatively
low, presumably explaining why they have not been documented before. This widespread occurrence of sandbanks in the North
Sea is in agreement with theoretical predictions based on stability analysis techniques. The possible interference between
large-scale human activity and low-amplitude open-shelf ridges implies that one should be careful not to overlook these patterns
if none should appear in a preliminary (visual) assessment. The only part of the Southern Bight in which no ridges can be
seen is a circular area with a diameter of about 50 km near the mouth of the river Rhine. Here, freshwater outflow affects
the direction of tidal ellipses and residual flow, and suppresses the formation of open ridges. 相似文献
995.
Pockmarks in the inner Oslofjord,Norway 总被引:5,自引:3,他引:2
Multibeam bathymetric surveys of the Inner Oslofjord, Norway have revealed a high density of pockmarks in the 179-km2 inner fjord area, which contains over 500 pockmarks of varying size, typically 20–50 m in diameter and 2–10 m deep. These
pockmarks have been investigated with a variety of techniques, including acoustic subbottom profiling, sedimentological and
geochemical analyses of cores, remotely operated vehicle observation, and morphometry. Both the distribution and shapes of
the pockmarks suggest that they are related to structures in the bedrock underlying relatively thin (<50 m) unconsolidated
glacial and postglacial sediments. The data provide no direct indication of a particular mode of pockmark formation, but release
of large amounts of biogenic, shallow methane seems unlikely. Several lines of evidence point to a continuous process of pockmark
formation followed by inactivity, with some pockmarks recently active whereas others have been inactive for a considerable
time. Some pockmarks are characterised by coarse sediment in their centres. The density, variety and easy access make this
pockmark field an ideal model area for pockmark research.
John S. Gray is deceased. 相似文献
996.
Jeff A. Polton 《Journal of Oceanography》2009,65(5):665-668
In a recent paper, Liu et al. (2007) formulate an expression for how surface gravity waves modify the Ekman layer energy budget. They then diagnose the
effect in the world oceans using available data. This comment addresses the formulation of the energy equation that is fundamental
to their study. 相似文献
997.
Masahiko Fujii Fei Chai Lei Shi Hisayuki Y. Inoue Masao Ishii 《Journal of Oceanography》2009,65(5):689-701
The oceanic carbon cycle in the tropical-subtropical Pacific is strongly affected by various physical processes with different
temporal and spatial scales, yet the mechanisms that regulate air-sea CO2 flux are not fully understood due to the paucity of both measurement and modeling. Using a 3-D physical-biogeochemical model,
we simulate the partial pressure of CO2 in surface water (pCO2sea) and air-sea CO2 flux in the tropical and subtropical regions from 1990 to 2004. The model reproduces well the observed spatial differences
in physical and biogeochemical processes, such as: (1) relatively higher sea surface temperature (SST), and lower dissolved
inorganic carbon (DIC) and pCO2sea in the western than in the central tropical-subtropical Pacific, and (2) predominantly seasonal and interannual variations
in the subtropical and tropical Pacific, respectively. Our model results suggest a non-negligible contribution of the wind
variability to that of the air-sea CO2 flux in the central tropical Pacific, but the modeled contribution of 7% is much less than that from a previous modeling
study (30%; McKinley et al., 2004). While DIC increases in the entire region SST increases in the subtropical and western tropical Pacific but decreases
in the central tropical Pacific from 1990 to 2004. As a result, the interannual pCO2sea variability is different in different regions. The pCO2sea temporal variation is found to be primarily controlled by SST and DIC, although the role of salinity and total alkalinity,
both of which also control pCO2sea, need to be elucidated by long-term observations and eddy-permitting models for better estimation of the interannual variability
of air-sea CO2 flux. 相似文献
998.
Hirokazu Ozaki Hajime Obata Mikio Naganobu Toshitaka Gamo 《Journal of Oceanography》2009,65(2):235-244
We measured potential temperature, salinity, and dissolved oxygen profiles from the surface to the bottom at two locations
in the north Ross Sea (65.2°S, 174.2°E and 67.2°S, 172.7°W) in December 2004. Comparison of our data with previous results
from the same region reveals an increase in potential temperature and decreases in salinity and dissolved oxygen concentration
in the bottom layer (deeper than 3000 m) over the past four decades. The changes were significantly different from the analytical
precisions. Detailed investigation of the temperature, salinity, dissolved oxygen and σ
3 value distributions and the bottom water flow in the north Ross Sea suggests a long-term change in water mass mixing balance.
That is to say, it is speculated that the influence of cool, saline, high-oxygen bottom water (high-salinity Ross Sea Bottom
Water) formed in the southwestern Ross Sea has possibly been decreased, while the influences of relatively warmer and fresher
bottom water (low-salinity Ross Sea Bottom Water) and the Adélie Land Bottom Water coming from the Australia-Antarctic Basin
have increased. The possible impact of global warming on ocean circulation needs much more investigation. 相似文献
999.
Sulfotransferase (ST) is the first enzyme discovered in association with paralytic shellfish poisoning (PSP) toxin biosynthesis in toxic dinoflagellates. This study investigates the ST activity in crude enzyme extraction of a toxic dinoflagellate species, Alexandrium tamarense CI01. The results show that crude enzyme can transfer a sulfate group from 3’-phosphoadenosine 5’-phosphosulfate (PAPS) to N-21 in the carbamoyl group of gonyautoxin 2/3 (GTX2/3) to produce C1/C2, but is inactive toward STX to produce GTX5. The crude enzyme is optimally active at pH 6.0 and 15°C. The activity is enhanced by Co2 , Mg2 , Mn2 and Ca2 individually, but is inhibited by Cu2 . Moreover, the activity shows no difference when various sulfur compounds are used as sulfate donors. These results demonstrate that the ST specific to GTX2/3 is present in the cells of A. tamarense CI01 and is involved in PSP toxin biosynthesis. In addition, the ST from different dinoflagellates is species-specific, which explains well the various biosynthesis pathways of the PSP toxins in toxic dinoflagellates. 相似文献
1000.
Seasonal change in body length of important small copepods and relationship with environmental factors in Jiaozhou Bay,China 总被引:1,自引:0,他引:1
Differences among species in prosome length and in species’ response to environmental factors do exist. Therefore, it is useful to examine prosome length for different copepod species in variable environments. Seasonal variations in prosome length of four small copepods and their copepodite stages in the Jiaozhou Bay were compared and the relative influence of temperature, salinity, and chlorophyll concentration were examined. Two peaks were found in the mean prosome length of Paracalanus parvus (in early winter and May). For Acartia bifilosa, the maximum values of all copepodites occurred mainly from February to April, and decreased to the bottom in July. Prosome length of Acartia pacifica peaked when it first appeared in June, then reached to the minimum in July. Parvocalanus crassirostris only appeared from late summer to autumn and the mean prosome length showed no clear changes. Correlations of adult prosome length with environmental factors were evaluated. For the four species, temperature was negatively correlated to prosome length except for P. crassirostris. But the different species varied markedly in their responds to temperature. A. bifilosa showed a more definite trend of size variation with temperature than P. parvus and A. pacifica. Correlations of prosome length with salinity were significantly positive for almost all the small copepods. The relationship between chlorophyll concentration and prosome length was complicated for these copepods, but for P. parvus, chlorophyll concentration was also an important affecting factor. Furthermore, investigation needs to be done on food quality for some copepod. These results are essential to estimate the biomass and the production, and to understand these small copepods’ population dynamics in this human-affected bay. 相似文献