Mechanism of Magnetic Flux Loss in Molecular Clouds

We investigate the detailed processes working in the drift of magnetic fields in molecular clouds. To the frictional force, whereby the magnetic force is transmitted to neutral molecules, ions contribute more than half only at cloud densities $n_{\rm H} < 10^4 {\rm cm}^{-3}$, and charged grains contribute more than 90% at $n_{\rm H} > 10^6 {\rm cm}^{-3}$. Thus grains play a decisive role in the process of magnetic flux loss. Approximating the flux loss time $t_B$ by a power law $t_B \propto B^{-\gamma}$, where $B$ is the mean field strength in the cloud, we find $\gamma \approx 2$, characteristic to ambipolar diffusion, only at $n_{\rm H} < 10^7 {\rm cm}^{-3}$. At higher densities, $\gamma$ decreases steeply with $n_{\rm H}$, and finally at $n_{\rm H} \approx n_{\rm dec} \approx {\rm a few} \times 10^{11} {\rm cm}^{-3}$, where magnetic fields effectively decouple from the gas, $\gamma << 1$ is attained, reminiscent of Ohmic dissipation, though flux loss occurs about 10 times faster than by Ohmic dissipation. Ohmic dissipation is dominant only at $n_{\rm H} > 1 \times 10^{12} {\rm cm}^{-3}$. While ions and electrons drift in the direction of magnetic force at all densities, grains of opposite charges drift in opposite directions at high densities, where grains are major contributors to the frictional force. Although magnetic flux loss occurs significantly faster than by Ohmic dissipation even at very high densities as $n_{\rm H} \approx n_{\rm dec}$, the process going on at high densities is quite different from ambipolar diffusion in which particles of opposite charges are supposed to drift as one unit.Comment: 34 pages including 9 postscript figures, LaTex, accepted by Astrophysical Journal (vol.573, No.1, July 1, 2002

Equivalency of the quality of sublethal lesions after photons and high-linear energy transfer ion beams

The quality of the sublethal damage (SLD) after irradiation with high–linear energy transfer (LET) ion beams was investigated with low-LET photons. Chinese hamster V79 cells and human squamous carcinoma SAS cells were first exposed to a priming dose of different ion beams at different LETs at the Heavy Ion Medical Accelerator in the Chiba facility. The cells were kept at room temperature and then exposed to a secondary test dose of X-rays. Based on the repair kinetics study, the surviving fraction of cells quickly increased with the repair time, and reached a plateau in 2–3 h, even when cells had received priming monoenergetic high-LET beams or spread-out Bragg peak beams as well as X-ray irradiation. The shapes of the cell survival curves from the secondary test X-rays, after repair of the damage caused by the high-LET irradiation, were similar to those obtained from cells exposed to primary X-rays only. Complete SLD repairs were observed, even when the LET of the primary ion beams was very high. These results suggest that the SLD caused by high-LET irradiation was repaired well, and likewise, the damage caused by the X-rays. In cells where the ion beam had made a direct hit in the core region in an ion track, lethal damage to the domain was produced, resulting in cell death. On the other hand, in domains that had received a glancing hit in the low-LET penumbra region, the SLD produced was completely repaired

Quantitative ultrasound (QUS) axial transmission method reflects anisotropy in micro-arrangement of apatite crystallites in human long bones: A study with 3-MHz-frequency ultrasound

Anisotropic arrangement of apatite crystallites, i.e., preferential orientation of the apatite c-axis, is known to be an important bone quality parameter that governs the mechanical properties. However, noninvasive evaluation of apatite orientation has not been achieved to date. The present paper reports the potential of quantitative ultrasound (QUS) for noninvasive evaluation of the degree of apatite orientation in human bone for the first time. A novel QUS instrument for implementation of the axial transmission (AT) method is developed, so as to achieve precise measurement of the speed of sound (SOS) in the cortex (cSOS) of human long bone. The advantages of our QUS instrument are the following: (i) it is equipped with a cortical bone surface-morphology detection system to correct the ultrasound transmission distance, which should be necessary for AT measurement of long bone covered by soft tissue of non-uniform thickness; and (ii) ultrasound with a relatively high frequency of 3 MHz is employed, enabling thickness-independent cSOS measurement even for the thin cortex by preventing guide wave generation. The reliability of the proposed AT measurement system is confirmed through comparison with the well-established direct transmission (DT) method. The cSOS in human long bone is found to exhibit considerable direction-dependent anisotropy; the axial cSOS (3870 ± 66 m/s) is the highest, followed by the tangential (3411 ± 94 m/s) and radial (3320 ± 85 m/s) cSOSs. The degree of apatite orientation exhibits the same order, despite the unchanged bone mineral density. Multiple regression analysis reveals that the cSOS of human long bone strongly reflects the apatite orientation. The cSOS determined by the AT method is positively correlated with that determined by the DT method and sensitively reflects the apatite orientation variation, indicating the validity of the AT instrument developed in this study. Our instrument will be beneficial for noninvasive evaluation of the material integrity of the human long-bone cortex, as determined by apatite c-axis orientation along the axial direction.Ishimoto T., Suetoshi R., Cretin D., et al. Quantitative ultrasound (QUS) axial transmission method reflects anisotropy in micro-arrangement of apatite crystallites in human long bones: A study with 3-MHz-frequency ultrasound. Bone, 127, 82. https://doi.org/10.1016/j.bone.2019.05.034

Determination of specific ion positions of Cr³⁺ and O²- in Cr₂O₃ thin films and their relationship to exchange anisotropy at Co/Cr₂O₃ interfaces

The structures of antiferromagnetic Cr₂O₃(0001) thin films with perpendicular exchange bias were investigated using reflection high-energy electron diffraction, X-ray reflectivity, and synchrotron X-ray diffraction. We mainly investigated the specific ion positions of Cr³⁺ and O²- in the corundum structure and discussed their relationship to the magnetic anisotropy of Cr₂O₃. The Cr₂O₃(0001) thin film grown on a Pt(111) buffer layer exhibited a perpendicular exchange anisotropy density of 0.42 mJ/m², in which the Cr³⁺ position is the primary factor in the enhancement of magnetic anisotropy due to dipolar-interaction. In contrast, the single-crystalline Cr₂O₃(0001) film grown on a α-Al₂O₃(0001) substrate featured a low exchange magnetic anisotropy of 0.098 mJ/m². In this film, the Cr³⁺ position parameter is an insignificant factor, leading to low magnetic anisotropy. The O²- ion position also differs between the two types of films, which can affect both the magnetic anisotropy energy originating from fine structures and the magneto-electric properties of Cr₂O₃.Yu Shiratsuchi, Yuuta Nakano, Nobuhito Inami, Tetsuro Ueno, Kanta Ono, Reiji Kumai, Ryoko Sagayama, and Ryoichi Nakatani, Journal of Applied Physics 123, 103903 (2018); https://doi.org/10.1063/1.5020620

Physical Properties of Dense Cores in the Rho Ophiuchi Main Cloud and A Significant Role of External Pressures in Clustered Star Formation

Using the archive data of the H13CO+ (J=1-0) line emission taken with the Nobeyama 45 m radio telescope with a spatial resolution of about 0.01pc, we have identified 68 dense cores in the central dense region of the rho Ophiuchi main cloud. The H13CO+ data also indicates that the fractional abundance of H13CO+ relative to H2 is roughly inversely proportional to the square root of the H2 column density with a mean of 1.72 x 10^{-11}. The mean radius, FWHM line width, and LTE mass of the identified cores are estimated to be 0.045 +- 0.011 pc, 0.49 +- 0.14 km/s, and 3.4 +- 3.6 Msolar, respectively. The majority of the identified cores have subsonic internal motions. The virial ratio, the ratio of the virial mass to the LTE mass, tends to decrease with increasing the LTE mass and about 60 percent of the cores have virial ratios smaller than 2, indicating that these cores are not transient structures but self-gravitating. The detailed virial analysis suggests that the surface pressure often dominates over the self-gravity and thus plays a crucial role in regulating core formation and evolution. By comparing the rho Oph cores with those in the Orion A molecular cloud observed with the same telescope, we found that the statistical properties of the core physical quantities are similar between the two clouds if the effect of the different spatial resolutions is corrected. The line widths of the rho Oph cores appear to be nearly independent of the core radii over the range of 0.01 - 0.1 pc and deviate upwards from the Heyer & Brunt relation. This may be evidence that turbulent motions are driven by protostellar outflows in the cluster environment.Comment: 45 pages, 14 figures, accepted or publication in ApJ, mpeg movies of figure 3 are available from http://quasar1.ed.niigata-u.ac.jp/~fnakamur/papers/oph1

The Molecular Outflows in the rho Ophiuchi Main Cloud: Implications For Turbulence Generation

We present the results of CO (J=3-2) and CO (J=1-0) mapping observations toward the active cluster forming clump, L1688, in the rho Ophiuchi molecular cloud. From the CO (J=3-2) and CO (J=1-0) data cubes, we identify five outflows, whose driving sources are VLA 1623, EL 32, LFAM 26, EL 29, and IRS 44. Among the identified outflows, the most luminous outflow is the one from the prototypical Class 0 source, VLA 1623. We also discover that the EL 32 outflow located in the Oph B2 region has very extended blueshifted and redshifted lobes with wide opening angles. This outflow is most massive and have the largest momentum among the identified outflows in the CO (J=1-0) map. We estimate the total energy injection rate due to the molecular outflows identified by the present and previous studies to be about 0.2 L_solar, larger than or at least comparable to the turbulence dissipation rate [~(0.03 - 0.1) L_solar]. Therefore, we conclude that the protostellar outflows are likely to play a significant role in replenishing the supersonic turbulence in this clump.Comment: 37 pages, 9 figures, accepted for publication in The Astrophysical Journa

Learning and memory in mice gestationally and lactationally exposed to 3-methylcholanthrene

研究ノート (Note

Management of Natural History collections: criteria and parameters of evaluation

[ES] Las colecciones de historia natural son una herramienta básica para la investigación científica y el estudio de la distribución en el pasado de muchas especies, así como de la propia historia de la ciencia. Además del uso científico de estas colecciones, destacan otros como el histórico, el divulgativo-pedagógico y el estético. De ahí la importancia que tiene una gestión eficaz de las mismas, la cual implica diversos aspectos, que van desde la conservación y su mantenimiento, su inventario, ordenación y procesamiento informático hasta las múltiples tareas relacionadas con su uso en consultas, visitas, préstamos científicos y participación en actividades de carácter divulgativo. En este artículo se examinan los criterios para evaluar la gestión de las colecciones de historia natural y se definen una serie de parámetros, útiles para medir el estado de una colección y su evolución en el tiempo, tanto en su crecimiento como en su uso, principalmente. Se ejemplifica todo ello en el grupo de los poliquetos, del que el Museo Nacional de Ciencias Naturales de Madrid (MNCN) cuenta con una estimable colección, y se comparan los resultados, según varios parámetros seleccionados, con los de otras colecciones de poliquetos de diversas instituciones de todo el mundo.[EN] Natural History collections are a basic and essential tool for scientific research, the study of the distribution in the past of many species of animals and plants and the History of Science. As well as the scientific aspect of these collections, stand outs other uses as the historic one, the educational and the aesthetic. All these are reasons that show the importance of an effective management of the Natural History collections as well as the several tasks related to it, as consults, visits, scientific loans and educational activities. In this article various criteria and useful parameters are provided for evaluating the curatorial state of a Natural History collection and its evolution, both in growth and use mainly. Finally, an example based on the Polychaeta, an estimable group in the Invertebrates Collection of the Museo Nacional de Ciencias Naturales of Madrid (MNCN), is provided. The results of several selected parameters are compared with other Polychaeta collections from several institutions around the world.Peer reviewe