273 research outputs found
On cosmic-ray production efficiency at supernova remnant shocks propagating into realistic diffuse interstellar medium
Using three-dimensional magnetohydrodynamics simulations, we show that the
efficiency of cosmic-ray (CR) production at supernova remnants (SNRs) is
over-predicted if it could be estimated based on proper motion measurements of
H filaments in combination with shock-jump conditions. Density
fluctuations of upstream medium make shock waves rippled and oblique almost
everywhere. The kinetic energy of the shock wave is transferred into that of
downstream turbulence as well as thermal energy which is related to the shock
velocity component normal to the shock surface. Our synthetic observation shows
that the CR acceleration efficiency as estimated from a lower downstream plasma
temperature, is overestimated by 10-40%, because rippled shock does not
immediately dissipate all upstream kinetic energy.Comment: 7 pages, 3 figures, 1 table, accepted for publication in ApJ; the
paper with full resolution images is
http://www.phys.aoyama.ac.jp/~ryo/papers/shimoda2015.pd
From Exclusive Particle to Adversative Conjunction: A Study on the Particle tasol in Tok Pisin
n/
Toward Understanding the Origin of Turbulence in Molecular Clouds: Small Scale Structures as Units of Dynamical Multi-Phase Interstellar Medium
In order to investigate the origin of the interstellar turbulence, detailed
observations in the CO J=1--0 and 3--2 lines have been carried out in an
interacting region of a molecular cloud with an HII region. As a result,
several 1,000 to 10,000 AU scale cloudlets with small velocity dispersion are
detected, whose systemic velocities have a relatively large scatter of a few
km/s. It is suggested that the cloud is composed of small-scale dense and cold
structures and their overlapping effect makes it appear to be a turbulent
entity as a whole. This picture strongly supports the two-phase model of
turbulent medium driven by thermal instability proposed previously. On the
surface of the present cloud, the turbulence is likely to be driven by thermal
instability following ionization shock compression and UV irradiation. Those
small scale structures with line width of ~ 0.6 km/s have a relatively high CO
line ratio of J=3--2 to 1--0, 1 < R(3-2/1-0) < 2. The large velocity gradient
analysis implies that the 0.6 km/s width component cloudlets have an average
density of 10^{3-4} cm^{-3}, which is relatively high at cloud edges, but their
masses are only < 0.05 M_{sun}.Comment: 12 pages, 9 figures. To be published in the Astrophysical Journa
Two functionally distinct manganese clusters formed by introducing a mutation in the carboxyl terminus of a photosystem II reaction center polypeptide, D1, of the green alga Chlamydomonas reinhardtii
AbstractTo study the function of the carboxyl-terminal domain of a photosystem II (PSII) reaction center polypeptide, D1, chloroplast mutants of the green alga Chlamydomonas reinhardtii have been generated in which Leu-343 and Ala-344 have been simultaneously or individually replaced by Phe and Ser, respectively. The mutants carrying these replacements individually, L343F and A344S, showed a wild-type phenotype. In contrast, the double mutant, L343FA344S, evolved O2 at only 20–30% of the wild-type rate and was unable to grow photosynthetically. In this mutant, PSII accumulated to 60% of the wild-type level, indicating that the O2-evolving activity per PSII was reduced to approximately half that of the wild-type. However, the amount of Mn atom detected in the thylakoids suggested that a normal amount of Mn cluster was assembled. An investigation of the kinetics of flash-induced fluorescence yield decay revealed that the electron transfer from Q−A to QB was not affected. When a back electron transfer from Q−A to a donor component was measured in the presence of 3-(3,4-dichlorophenol)-1,1-dimethylurea, a significantly slower component of the Q−A oxidation was detected in addition to the normal component that corresponds to the back electron transfer from the Q−A to the S2-state of the Mn cluster. Thermoluminescence measurements revealed that L343FA344S cells contained two functionally distinct Mn clusters. One was equivalent to that of the wild-type, while the other was incapable of water oxidation and was able to advance the transition from the S1-state to the S2-state. These results suggested that a fraction of the Mn cluster had been impaired by the L343FA344S mutation, leading to decreased O2 evolution. We concluded that the structure of the C-terminus of D1 is critical for the formation of the Mn cluster that is capable of water oxidation, in particular, transition to higher S-states
A case of generalized lymphatic anomaly causing skull-base leakage and bacterial meningitis
Generalized lymphatic anomaly (GLA) is a multifocal lymphatic malformation that affects the skin, thoracic viscera, and bones. A 7-year-old boy presented with fever and disturbance of consciousness, and bacterial meningitis was diagnosed. Computed tomography and magnetic resonance imaging revealed middle skull-base leakage due to lymphatic malformation. Past history included facial palsy due to cystic tumors in the right petrous bone 4 years before onset of meningitis. At that time, pericardial effusion had been found and GLA had been diagnosed by pericardial biopsy. He achieved complete recovery under intensive care with antibiotics and mechanical ventilation. At the 3-year follow-up, the patient was healthy with no recurrence of meningitis. We should consider GLA among the differential diagnoses for osteolytic diseases in the pediatric population
Solution structure of multi-domain protein ER-60 studied by aggregation-free SAXS and coarse-grained-MD simulation
Multi-domain proteins (MDPs) show a variety of domain conformations under physiological conditions, regulating their functions through such conformational changes. One of the typical MDPs, ER-60 which is a protein folding enzyme, has a U-shape with four domains and is thought to have different domain conformations in solution depending on the redox state at the active centres of the edge domains. In this work, an aggregation-free small-angle X-ray scattering revealed that the structures of oxidized and reduced ER-60 in solution are different from each other and are also different from those in the crystal. Furthermore, structural modelling with coarse-grained molecular dynamics simulation indicated that the distance between the two edge domains of oxidized ER-60 is longer than that of reduced ER-60. In addition, one of the edge domains has a more flexible conformation than the other
Origin of Thermal and Non-Thermal Hard X-ray Emission from the Galactic Center
We analyse new results of Chandra and Suzaku which found a flux of hard X-ray
emission from the compact region around Sgr A (r ~ 100 pc). We suppose
that this emission is generated by accretion processes onto the central
supermassive blackhole when an unbounded part of captured stars obtains an
additional momentum. As a result a flux of subrelativistic protons is generated
near the Galactic center which heats the background plasma up to temperatures
about 6-10 keV and produces by inverse bremsstrahlung a flux of non-thermal
X-ray emission in the energy range above 10 keV.Comment: to be published in PASJ, v.61, No.5, 200
- …