Effect of Radiation Drag on Hoyle-Lyttleton Accretion

Hoyle-Lyttleton type accretion is investigated, by taking account of not only the effect of radiation pressure but the effect of radiation drag. We calculate the trajectories of particles for three cases: only the effect of gravity is considered (case A); the effect of radiation pressure is taken into account (case B); the effect of radiation drag as well as radiation pressure is taken into account (case C). The accretion radii for former two cases are $2GM/v_{\infty}^2$ for case A and $2GM(1-\Gamma)/v_{\infty}^2$ for case B, where M is the mass of the accreted object, $v_{\infty}$ the relative velocity, and Gamma the normalized luminosity of the accreted object. We found that the accretion radius for case C is in between those of cases A and B under the present approximation; i.e., the accretion radius decreases due to radiation pressure while it increases due to radiation drag. In addition, the accretion radius for case C becomes larger as the incident velocity becomes fast. The effect of radiation drag becomes more and more important when the velocity of the incident particle is comparable to the light speed.Comment: 11 pages, LaTeX with 6 eps figures, accepted by Publications of the Astronomical Society of Japa

Low-dimensional feedback control model that utilizes redundant degrees of freedom

The 11th International Symposium on Adaptive Motion of Animals and Machines. Kobe University, Japan. 2023-06-06/09. Adaptive Motion of Animals and Machines Organizing Committee.Poster Session P5

Reexamination of purely physical separation of the phase enriched in noble gases from the Allende meteorite

We have prepared a new sample of the "floating fraction" of the Allende meteorite and have analyzed the elemental and isotopic compositions of the noble gases to examine the properties of the separation technique. The "floating fraction" is the black fine material, which floats on the water during freeze-thaw disaggregation. The floating fraction separated in this study was enriched in noble gases, and its isotopic compositions were very similar to those of chemical residues. We thus confirmed that the physical separation is an effective method to obtain a noble-gas-rich fraction than the chemical treatment. The only major difference between our floating fraction and those previously prepared was that the former had small excesses in ^Ar and ^Xe which were supposed to be due to the contamination from small amounts of silicate like sodalite. There were some variations in the Xe-Q/Xe-HL ratios among floating fractions, suggesting that Q-and HL-components might be separable by a physical process

A preliminary report on noble gases in the Kobe (CK) meteorite: A carbonaceous chondrite fell in Kobe City, Japan

We have investigated elemental and isotopic compositions of noble gases in the newly-fallen CK chondrite, Kobe. The relatively low concentrations of primordial heavy noble gases (Kr and Xe) and the relatively high ^Xe/^Xe ratio (6.51±0.02) are similar to those found in previous studies of CK chondrites. The calculated cosmic-ray exposure age based on cosmogenic ^Ne is 41Ma, and the K-Ar age is 2.1Ga. Based on calculated exposure ages and gas retention ages of Kobe and some other CK chondrites, it is likely that they have partially lost both radiogenic and cosmogenic He by solar heating during the time of exposure. Based on the ^Ar retention age, we interpret that Kobe may also have experienced thermal events, possibly related to impacts about 2 billion years age

A laboratory experiment on the influence of aqueous alteration on noble gas compositions in the Allende meteorite

We have carried out a hydrothermal experiment on the Allende CV chondrite, in order to understand the observed noble gas loss from CM and CI chondrites, possibly caused by aqueous alteration on their parent bodies (L. B. Browning et al., Geochim. Cosmochim. Acta, 60,2621,1996; T. Nakamura et al., Geochim. Cosmochim. Acta, 63,257,1999). The Allende meteorite was disaggregated and kept with liquid water in a pressurized vessel under 15 atm of water vapor at 200℃ for a week. The abundances of helium, neon, argon, krypton and xenon in the samples have been measured by stepwise heating technique. The abundances of noble gases were decreased by 24% (He), 27% (Ne), 38% (Ar), 23% (Kr) and 34% (Xe) after the hydrothermal treatment, suggesting that the hot water treatment had contributed to reduce the concentrations of noble gases in Allende. This gas loss also affected the isotopic composition of xenon. For the 1200℃ fraction, the amount of ^Xe-HL was decreased from the sample by about 80% during the hot water treatment, while that of ^Xe-Q was decreased to a lesser extent (∿40%). This result seems to indicate that the carrier of Xe-HL is less resistant to the gas loss by the hot water alteration than phase Q for high temperature components. However, further studies are required as this trend becomes less obvious and rather similar if we take into consideration the xenon of 800℃ fraction

Neon isotopic composition of carbon residues from the Canyon Diablo iron meteorite

We analyzed noble gases in acid residues extracted from the Canyon Diablo iron meteorite by density and colloidal separation. The results do not indicate any significant variation among the samples although spallogenic noble gases were effectively removed by the treatment. The isotopic compositions of the heavy noble gases are close to those of the terrestrial atmosphere, suggesting that the samples were seriously contaminated by atmospheric noble gases during the treatment. However, the Ne isotopic ratios fall between atmospheric Ne and planetary Ne, suggesting that the primordial component of the noble gases in carbonaceous material in Canyon Diablo is planetary rather than solar

Prediction of fetal acidemia in placental abruption

BACKGROUND: To determine the major predictive factors for fetal acidemia in placental abruption. METHODS: A retrospective review of pregnancies with placental abruption was performed using a logistic regression model. Fetal acidemia was defined as a pH of less than 7.0 in umbilical artery. The severe abruption score, which was derived from a linear discriminant function, was calculated to determine the probability of fetal acidemia. RESULTS: Fetal acidemia was seen in 43 survivors (43/222, 19%). A logistic regression model showed bradycardia (OR (odds ratio) 50.34, 95% CI 11.07 – 228.93), and late decelerations (OR 15.13, 3.05 – 74.97), but not abnormal ultrasonographic findings were to be associated with the occurrence of fetal acidemia. The severe abruption score was calculated for the occurrence of fetal acidemia, using 6 items including vaginal bleeding, gestational age, abdominal pain, abnormal ultrasonographic finding, late decelerations, and bradycardia. CONCLUSIONS: An abnormal FHR pattern, especially bradycardia is the most significant risk factor in placental abruption predicting fetal acidemia, regardless of the presence of abnormal ultrasonographic findings or gestational age