Stability of the Accretion Flows with Stalled Shocks in Core-Collapse Supernovae

Bearing in mind the application to the theory of core-collapse supernovae, we performed a global linear analysis on the stability of spherically symmetric accretion flows through a standing shock wave onto a proto neutron star. As unperturbed flows, we adopted the spherically symmetric steady solutions to the Euler equations obtained with realistic equation of state and formulae for neutrino reaction rates taken into account. Then we solved the equations for linear perturbations numerically, and obtained the eigen frequencies and eigen functions. We found (1) the flows are stable for all modes if the neutrino luminosity is lower than $\sim 1\times 10^{52}$ ergs/s for $\dot{M}=1.0M_{\odot}/{\rm s}$. (2) For larger luminosities, the non-radial instabilities are induced, probably via the advection-acoustic cycles. Interestingly, the modes with $\ell=2$ and 3 become unstable at first for relatively low neutrino luminosities, e.g. $\gtrsim 2-3\times 10^{52}$ ergs/s for the same accretion rate, whereas the $\ell=1$ mode is the most unstable for higher luminosities, $\sim 3-7\times 10^{52}$ ergs/s. These are all oscillatory modes. (3) For still larger luminosities, $\sim 7\times 10^{52}$ ergs/s for $\dot{M}=1.0M_{\odot}/{\rm s}$, non-oscillatory modes, both radial and non-radial, become unstable. These non-radial modes were identified as convection. We confirmed the results obtained by numerical simulations that the instabilities induced by the advection-acoustic cycles are more important than the convection for lower neutrino luminosities.Comment: 46 pages, 19 figures, Accepted by Ap

Standing Accretion Shocks in the Supernova Core: Effects of Convection and Realistic EOS

We investigated the structure of the spherically symmetric accretion flows through the standing shock wave onto the proto-neutron star in the post-bounce phase of the collapse-driven supernova. We assume that the accretion flow is in a steady state controlled by the neutrino luminosity and mass accretion rate that are kept constant. We obtain solutions of the steady Euler equations for a wide range of neutrino luminosity and mass accretion rate. We employ a realistic EOS and neutrino-heating rates. More importantly, we take into account the effect of convection phenomenologically. For each mass accretion rate, we find the critical neutrino luminosity, above which there exists no steady solution. These critical points are supposed to mark the onset of the shock revival. As the neutrino luminosity increases for a given mass accretion rate, there appears a convectively unstable region at some point before the critical value is reached. We introduce a phenomenological energy flux by convection so that the negative entropy gradient should be canceled out. We find that the convection lowers the critical neutrino luminosity substantially. We also consider the effect of the self-gravity. It is found that the self-gravity is important only when the neutrino luminosity is high. The critical luminosity, however, is little affected if the energy transport by convection is taken into account.Comment: accepted by ApJ, 20 pages, 8 figure

Effects of rotation on the revival of a stalled shock in supernova explosions

In order to infer the effects of rotation on the revival of a stalled shock in supernova explosions, we investigated steady accretion flows with a standing shock. We first obtained a series of solutions for equations describing non-rotating spherically symmetric flows and confirmed the results of preceding papers that, for a given mass accretion rate, there is a critical luminosity of irradiating neutrinos, above which there exists no steady solution. Below the critical value, we found two branches of solutions; one is stable and the other is unstable against radial perturbations. With a simple argument based on the Riemann problem, we can identify the critical luminosity as the one, at which the stalled shock revives. We also obtained the condition satisfied by the flow velocity for the critical luminosity, which can be easily applied to the rotational case. If a collapsing star rotates, the accretion flow is non-spherical due to centrifugal forces. Flows are accelerated near the rotation axis whereas they are decelerated near the equatorial plane. As a result, the critical luminosity is lowered, that is, rotation assists the revival of a stalled shock. According to our calculations, the critical luminosity is $\sim25$% lower for the mass accretion rate of 1M$_{\odot}$/sec and the rotation frequency of 0.1 Hz at a radius of 1000 km than that of the spherically symmetric flow with the same mass accretion rate. We found that the condition of the flow velocity at the critical luminosity is first satisfied at the rotation axis. This suggests that the shock revival is triggered on the rotation axis and a jet-like explosion ensues.Comment: 26 pages, 10 figures, submitted to Ap

Collimated Jet or Expanding Outflow: Possible Origins of GRBs and X-Ray Flashes

We investigate the dynamics of an injected outflow propagating in a progenitor in the context of the collapsar model for gamma-ray bursts (GRBs) through two dimensional axisymmetric relativistic hydrodynamic simulations. Initially, we locally inject an outflow near the center of a progenitor. We calculate 25 models, in total, by fixing its total input energy to be 10^{51} ergs s^{-1} and radius of the injected outflow to be $7\times 10^7$ cm while varying its bulk Lorentz factor, $\Gamma_{0} = 1.05\sim 5$, and its specific internal energy, $\epsilon_0/c^2 = 0.1\sim 30$. The injected outflow propagates in the progenitor and drives a large-scale outflow or jet. We find a smooth but dramatic transition from a collimated jet to an expanding outflow among calculated models. The maximum Lorentz factor is, on the other hand, sensitive to both of $\Gamma_0$ and $\epsilon_0$; roughly $\Gamma_{\rm max} \sim \Gamma_0 (1+\epsilon_0/c^2)$. Our finding will explain a smooth transition between the GRBs, X-ray rich GRBs (XRRs) and X-ray Flashes (XRFs) by the same model but with different $\epsilon_0$ values.Comment: Comments 51 pages, 21 figures. accepted for publication in ApJ high resolution version is available at http://www.mpa-garching.mpg.de/~mizuta/COLLAPSAR/collapsar.htm

Thoracoscopic Surgery in a Patient with Multiple Esophageal Carcinomas after Surgery for Esophageal Achalasia

We present a case in which we used a thoracoscopic approach for resection of multiple esophageal carcinomas diagnosed 33 years after surgery for esophageal achalasia. A 68-year-old Japanese man had been diagnosed with esophageal achalasia and underwent surgical treatment 33 years earlier. He was examined at our hospital for annual routine checkup in which upper gastrointestinal endoscopy showed a “0-IIb+IIa” lesion in the middle esophagus. Iodine staining revealed multiple irregularly shaped iodine-unstained areas, the diagnosis of which was esophageal carcinoma. Thoracoscopic subtotal esophagectomy was performed. Esophageal carcinoma may occur many years after surgery for esophageal achalasia, even if the passage symptoms have improved. So, long-term periodic follow-up is necessary for detection of carcinoma at an earlier stage

The ABCF proteins in Escherichia coli individually cope with 'hard-to-translate' nascent peptide sequences

Organisms possess a wide variety of proteins with diverse amino acid sequences, and their synthesis relies on the ribosome. Empirical observations have led to the misconception that ribosomes are robust protein factories, but in reality, they have several weaknesses. For instance, ribosomes stall during the translation of the proline-rich sequences, but the elongation factor EF-P assists in synthesizing proteins containing the poly-proline sequences. Thus, living organisms have evolved to expand the translation capability of ribosomes through the acquisition of translation elongation factors. In this study, we have revealed that Escherichia coli ATP-Binding Cassette family-F (ABCF) proteins, YheS, YbiT, EttA and Uup, individually cope with various problematic nascent peptide sequences within the exit tunnel. The correspondence between noncanonical translations and ABCFs was YheS for the translational arrest by nascent SecM, YbiT for poly-basic sequence-dependent stalling and poly-acidic sequence-dependent intrinsic ribosome destabilization (IRD), EttA for IRD at the early stage of elongation, and Uup for poly-proline-dependent stalling. Our results suggest that ATP hydrolysis-coupled structural rearrangement and the interdomain linker sequence are pivotal for handling 'hard-to-translate' nascent peptides. Our study highlights a new aspect of ABCF proteins to reduce the potential risks that are encoded within the nascent peptide sequences. Graphical Abstrac

Crystal structure of the hemolytic lectin CEL-III isolated from the marine invertebrate Cucumaria echinata : Implications of domain structure for its membrane pore-formation mechanism

CEL-III is a Ca^＋ -dependent and galactose-specific lectin purified from the sea cucumber, Cucumaria echinata, which exhibits hemolytic and hemagglutinating activities. Six molecules of CEL-III are assumed to oligomerize to form an ion-permeable pore in the cell membrane. We have determined the crystal structure of CEL-III by using single isomorphous replacement aided by anomalous scattering in lead at 1.7 Å resolution. CEL-III consists of three distinct domains as follows: the N-terminal two carbohydrate-binding domains (1 and 2), which adopt β-trefoil folds such as the B-chain of ricin and are members of the (QXW)_3 motif family; and domain 3, which is a novel fold composed of two α-helices and one β-sandwich. CEL-III is the first Ca^ -dependent lectin structure with two β-trefoil folds. Despite sharing the structure of the B-chain of ricin, CEL-III binds five Ca^ ions at five of the six subdomains in both domains 1 and 2. Considering the relatively high similarity among the five subdomains, they are putative binding sites for galactose-related carbohydrates, although it remains to be elucidated whether bound Ca^ is directly involved in interaction with carbohydrates. The paucity of hydrophobic interactions in the interfaces between the domains and biochemical data suggest that these domains rearrange upon carbohydrate binding in the erythrocyte membrane. This conformational change may be responsible for oligomerization of CEL-III molecules and hemolysis in the erythrocyte membranes.This research was originally published in Journal of Biological Chemistry. Tatsuya Uchida, Takayuki Yamasaki, Seiichiro Eto, Hajime Sugawara, Genji Kurisu, Atsushi Nakagawa, Masami Kusunoki and Tomomitsu Hatakeyama. Crystal structure of the hemolytic lectin CEL-III isolated from the marine invertebrate Cucumaria echinata : Implications of domain structure for its membrane pore-formation mechanism. Journal of Biological Chemistry. 2004; 279, 37133-37141. © the American Society for Biochemistry and Molecular Biology

The Traditional Japanese Medicine (Kampo) Boiogito has a Dual Benefit in Cardiorenal Syndrome: A Pilot Observational Study

Article信州医学雑誌 62(2):89-97(2014)journal articl

Effects of sulfated fucan, ascophyllan, from the brown Alga Ascophyllum nodosum on various cell lines: a comparative study on ascophyllan and fucoidan.

The effects of fucose-containing sulfated polysaccharides, ascophyllan and fucoidan, isolated from the brown alga Ascophyllum nodosum, on the growth of various cell lines (MDCK, Vero, PtK(1), CHO, HeLa, and XC) were investigated. In a colony formation assay, ascophyllan and fucoidan showed potent cytotoxic effects on Vero and XC cells, while other cell lines were relatively resistant to these polysaccharides. Almost no significant effects of these polysaccharides were observed in the cell lines tested using the Alamar blue cytotoxicity assay over 48 h with varying initial cell densities (2500-20,000 cells/well) in growth medium. Interestingly, a significant growth promoting effect of ascophyllan on MDCK cells was observed, whereas treatment with fucoidan showed growth suppressive effects on this cell line under the same experimental conditions. These results suggest that ascophyllan is distinguishable from fucoidan in terms of their bioactivities. This is the first report of the growth promoting effects of a sulfated fucan on a mammalian cell line under normal growth conditions