410 research outputs found
X-ray Observation of Mars with Suzaku at Solar Minimun
Mars was observed in X-rays during April 3-5 2008 for 82 ksec with the
Japanese Suzaku observatory. Mars has been known to emit X-rays via the
scattering of solar X-rays and via the charge exchange between neutral atoms in
the exosphere and solar wind ions. Past theoretical studies suggest that the
exospheric neutral density may vary by a factor of up to 10 over the solar
cycle. To investigate a potential change of the exospheric charge exchange
emission, Mars was observed with Suzaku at solar minimum. Significant signals
were not detected at the position of Mars in the energy band of 0.2-5 keV. A 2
sigma upper limit of the O VII line flux in 0.5-0.65 keV was 4.3
ph cm s. Comparing this upper limit to the past Chandra and
XMM-Newton observations conducted near solar maximum, it was found that the
exospheric density at solar minimum does not exceed that near solar maximum by
more than 6-70 times.Comment: 17 pages, 7 figures, accepted for publication in PAS
Survival of Terrestrial N2-O2 Atmospheres in Violent XUV Environments through Efficient Atomic Line Radiative Cooling
Atmospheres play a crucial role in planetary habitability. Around M dwarfs
and young Sun-like stars, planets receiving the same insolation as the
present-day Earth are exposed to intense stellar X-rays and extreme-ultraviolet
(XUV) radiation. This study explores the fundamental question of whether the
atmosphere of present-day Earth could survive in such harsh XUV environments.
Previous theoretical studies suggest that stellar XUV irradiation is
sufficiently intense to remove such atmospheres completely on short timescales.
In this study, we develop a new upper-atmospheric model and re-examine the
thermal and hydrodynamic responses of the thermospheric structure of an
Earth-like N2-O2 atmosphere, on an Earth-mass planet, to an increase in the XUV
irradiation. Our model includes the effects of radiative cooling via electronic
transitions of atoms and ions, known as atomic line cooling, in addition to the
processes accounted for by previous models. We demonstrate that atomic line
cooling dominates over the hydrodynamic effect at XUV irradiation levels
greater than several times the present level of the Earth. Consequentially, the
atmosphere's structure is kept almost hydrostatic, and its escape remains
sluggish even at XUV irradiation levels up to a thousand times that of the
Earth at present. Our estimates for the Jeans escape rates of N2-O2 atmospheres
suggest that these 1 bar atmospheres survive in early active phases of Sun-like
stars. Even around active late M dwarfs, N2-O2 atmospheres could escape
significant thermal loss on timescales of gigayears. These results give new
insights into the habitability of terrestrial exoplanets and the Earth's
climate history.Comment: Published 2022 September 29 in Ap
Enhancement of Terrestrial Diffuse X-ray Emission Associated With Coronal Mass Ejection and Geomagnetic Storm
We present an analysis of a Suzaku observation taken during the geomagnetic
storm of 2005 August 23-24. We found time variation of diffuse soft X-ray
emission when a coronal mass ejection hit Earth and caused a geomagnetic storm.
The diffuse emission consists of fluorescent scattering of solar X-rays and
exospheric solarwind charge exchange. The former is characterized by a neutral
oxygen emission line due to strong heating of the upper atmosphere during the
storm time, while the latter is dominated by a sum of C V, C VI, N VI, N VII, O
VII, and O VIII emission lines due to the enhanced solar wind flux in the
vicinity of the exosphere. Using the solar wind data taken with the ACE and
WIND satellites,a time correlation between the solar wind and the strong O VII
line flux were investigated. We estimated necessary column densities for the
solar X-ray scattering and exospheric SWCX. From these results, we argue that a
part of the solar wind ions enter inside the magnetosphere and cause the SWCX
reaction.Comment: 33 pages, 16 figures, accepted for publication in PAS
Studies on substantially increased proteins in follicular fluid of bovine ovarian follicular cysts using 2-D PAGE and MALDI-TOF MS
BACKGROUND: The objective of this study was to identify substantially increased proteins in bovine cystic follicular fluid (FF) in order to clarify the pathology and etiology of bovine ovarian follicular cysts (BOFC). METHODS: Proteins in normal and cystic FF samples were subjected to two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) and were compared using silver stained gel images with PDQuest image analysis software. Peptides from these increased spots were analyzed by matrix assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS), and were identified based on the NCBI database by a peptide mass fingerprinting method. RESULTS: Comparative proteomic analysis showed 8 increased protein spots present in cystic FF. MS analysis and database searching revealed that the increased proteins in cystic FF were bovine mitochondrial f1-atpase (BMFA), erythroid associated factor (EAF), methionine synthase (MeS), VEGF-receptor, glyceraldehydes 3-phosphate dehydrogenase (GAPDH), heat shock protein 70 (HSP70), β-lactoglobulin (BLG) and succinate dehydrogenase Ip subunit (SD). CONCLUSION: Our results suggest that these proteins are overexpressed in BOFC, and that they may play important roles in the pathogenesis of BOFC. Furthermore, these proteins in the FF could be useful biomarkers for BOFC
Effect of Bovine Follicular Fluid Added to the Maturation Medium on Sperm Penetration in Pig Oocytes Matured In Vitro [Article]
The objective of this study was to examine the effect of bovine follicular fluid added to the matura-tion medium on sperm penetration, male pronucleus formation and polyspermy in pig oocytes fertilizedin vitro. Pig oocytes were cultured in 10 µl droplets of medium without bovine follicular fluid for 24 h.The oocytes were then cultured in 100 µl droplets of medium supplemented with 0,10 or 20% bovinefollicular fluid for further 24 h. The cultured oocytes were inseminated with boar sperm at a concentra-tion of 1×105or 106sperm/ml. When oocytes were inseminated at 1×105sperm/ml, significantly lowerproportion of penetrated oocytes was found in 20% bovine follicular fluid group compared with that in 0and 10% bovine follicular fluid groups (P<0.05). Addition of bovine follicular fluid to maturation medi-um promoted the male pronucleus formation in oocytes inseminated with 1×105sperm/ml, with a sig-nificant (P<0.05) difference in rate of oocytes with male pronuclei between 0 0x1.de8c8p-891nd 10% bovine follicu-lar fluid groups. Treatment with bovine follicular fluid during the second 24 h culture significantlydecreased the proportions of polyspermic oocytes inseminated with either of sperm concentrations.These results indicate that the presence of bovine follicular fluid in maturation medium enhances malepronucleaus formation and reduces polyspermic penetration in pig oocytes fertilized in vitro
Modeling of geocoronal solar wind charge exchange events detected with Suzaku
A model of geocoronal solar wind charge exchange (SWCX) emission was built
and compared to five Suzaku detections of bright geocoronal SWCX events. An
exospheric neutral hydrogen distribution model, charge exchange cross sections,
solar wind ion data taken with the ACE and WIND satellites, and magnetic field
models of the Earth's magnetosphere are all combined in order to predict
time-variable geocoronal SWCX emission depending on line-of-sight directions of
the Suzaku satellite. The modeled average intensities of O VII emission lines
were consistent with the observed ones within a factor of three in four out of
the five cases except for an event in which a line-of-sight direction was
toward the night side of the high-latitude magnetosheath and a major
geomagnetic storm was observed. Those of O VIII emission lines were
underestimated by a factor of three or more in all the five cases. On the other
hand, the modeled O VII and O VIII light curves reproduced the observed ones
after being scaled by ratios between the observed and modeled average
intensities. In particular, short-term variations due to line-of-sight
directions traversing cusp regions during an orbital motion of the Suzaku
satellite were reproduced. These results are discussed in the context of model
uncertainties.Comment: 47 pages, 23 figures, accepted for publication in PAS
Studies of the role of steroid hormone in the regulation of oocyte maturation in cattle
BACKGROUND: The objective of this study was to investigate whether the steroid hormone(s) secreted from cumulus-oocyte complexes (COCs) is a prerequisite for bovine oocyte maturation and cumulus expansion using aminoglutethimide (AGT), a P450 cholesterol side-chain cleavage inhibitor. METHODS: In experiment 1, COCs were cultured in maturation medium with various concentrations of AGT for 22 h to determine the effective concentration of AGT to inhibit steroid hormone secretion, meiotic maturation and cumulus expansion. In experiment 2, COCs were cultured in conditioned medium (CM) and TCM-199 medium with or without 10 mM AGT to check whether steroid hormones secreted from COCs were responsible for oocyte maturation and cumulus expansion. Experiments 3 and 4 were carried out to determine whether exogenous progesterone or estradiol-17beta was able to overcome the inhibitory effects of AGT on oocytes maturation and cumulus expansion. COCs cultured in 10 mM AGT-containing medium supplemented with various concentrations of progesterone or estradiol-17beta for 22 h were examined for oocyte maturation and cumulus expansion. RESULTS: Experiment 1 showed that a concentration of 10 mM AGT in medium was sufficient to block steroid hormone secretion, oocyte maturation and cumulus expansion, and that these inhibitory effects were fully reversible. In experiment 2, the addition of 10 mM AGT to CM did not significantly prevent oocyte maturation and cumulus expansion, implying that CM contains the steroid hormone(s) secreted from COCs, which are closely associated with oocyte maturation and cumulus expansion. The results in experiments 3 and 4 demonstrated that the addition of any concentration of progesterone or estradiol-17beta in the medium did not reduce the inhibitory effects of AGT on oocyte maturation and cumulus expansion. CONCLUSION: Our results indicate that bovine oocytes surrounded by cumulus cells are prevented from maturation and cumulus expansion through the inhibition of steroid secretion due to AGT, and that these inhibitory effects of AGT on oocyte maturation and cumulus expansions can not be overcome by the addition of either progesterone or estradiol-17beta in the medium. These observations suggest that some steroid hormone(s) other than P(4 )and E(2 )secreted from bovine COCs is essential for their meiotic maturation and cumulus expansion
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