Abstract
We perform three-dimensional (3D) magnetohydrodynamic simulations of magnetospheric accretion in a T Tauri star to study the accretion and wind structures in the close vicinity of the star. ...The gas accreting onto the star consists of the gas from the magnetospheric boundary and the failed disk winds. The accreting gas is commonly found as a multi-column accretion, which is consistent with observations. A significant fraction of the angular momentum of the accreting flows is removed by the magnetic fields of conical disk winds and turbulent failed winds inside and near the magnetosphere. As a result, the accretion torque is significantly reduced compared to the simple estimation based on the mass accretion rate. The stellar spin affects the time variability of the conical disk wind by changing the stability condition of the magnetospheric boundary. However, the time-averaged magnetospheric radius only weakly depends on the stellar spin, which is unlike the prediction of classical theories that the stellar spin controls the magnetospheric radius through the magnetic torque. The ratio of the toroidal to the poloidal field strengths at the magnetospheric boundary, which is a key parameter for the magnetic torque, is also insensitive to the spin; it is rather determined by the disk dynamics. Considering newly found 3D effects, we obtain a scaling relation of the magnetospheric radius very similar to the Ghosh & Lamb relation from the steady angular momentum transport equation.
Context. No planets exist inside the orbit of Mercury and the terrestrial planets of the solar system exhibit a localized configuration. According to thermal structure calculation of protoplanetary ...disks, a silicate condensation line (~1300 K) is located around 0.1 au from the Sun except for the early phase of disk evolution, and planetesimals could have formed inside the orbit of Mercury. A recent study of disk evolution that includes magnetically driven disk winds showed that the gas disk obtains a positive surface density slope inside ~1 au from the central star. In a region with positive midplane pressure gradient, planetesimals undergo outward radial drift. Aims. We investigate the radial drift of planetesimals and type I migration of planetary embryos in a disk that viscously evolves with magnetically driven disk winds. We show a case in which no planets remain in the close-in region. Methods. Radial drifts of planetesimals are simulated using a recent disk evolution model that includes effects of disk winds. The late stage of planet formation is also examined by performing N-body simulations of planetary embryos. Results. We demonstrate that in the middle stage of disk evolution, planetesimals can undergo convergent radial drift in a magnetorotational instability (MRI)-inactive disk, in which the pressure maximum is created, and accumulate in a narrow ring-like region with an inner edge at ~0.7 au from the Sun. We also show that planetary embryos that may grow from the narrow planetesimal ring do not exhibit significant type I migration in the late stage of disk evolution. Conclusions. The origin of the localized configuration of the terrestrial planets of the solar system, in particular the deficit of close-in planets, can be explained by the convergent radial drift of planetesimals in disks with a positive pressure gradient in the close-in region.
Species of the genus
Streptomyces
, which constitute the vast majority of taxa within the family
Streptomycetaceae
, are a predominant component of the microbial population in soils throughout the ...world and have been the subject of extensive isolation and screening efforts over the years because they are a major source of commercially and medically important secondary metabolites. Taxonomic characterization of
Streptomyces
strains has been a challenge due to the large number of described species, greater than any other microbial genus, resulting from academic and industrial activities. The methods used for characterization have evolved through several phases over the years from those based largely on morphological observations, to subsequent classifications based on numerical taxonomic analyses of standardized sets of phenotypic characters and, most recently, to the use of molecular phylogenetic analyses of gene sequences. The present phylogenetic study examines almost all described species (615 taxa) within the family
Streptomycetaceae
based on 16S rRNA gene sequences and illustrates the species diversity within this family, which is observed to contain 130 statistically supported clades, as well as many unsupported and single member clusters. Many of the observed clades are consistent with earlier morphological and numerical taxonomic studies, but it is apparent that insufficient variation is present in the 16S rRNA gene sequence within the species of this family to permit bootstrap-supported resolution of relationships between many of the individual clusters.
C‐type lectin‐like receptor 2 (CLEC‐2) has been identified as a receptor for the platelet activating snake venom rhodocytin. CLEC‐2 elicits powerful platelet activation signals in conjunction with ...Src, Syk kinases, and phospholipase Cγ2, similar to the collagen receptor glycoprotein (GP) VI/FcRγ‐chain complex. In contrast to GPVI/FcRγ, which initiates platelet activation through the tandem YxxL motif immunoreceptor tyrosine‐based activation motif (ITAM), CLEC‐2 signals via the single YxxL motif hemi‐ITAM. The endogenous ligand of CLEC‐2 has been identified as podoplanin, which is expressed on the surface of tumour cells and facilitates tumour metastasis by inducing platelet activation. Studies of CLEC‐2‐deficient mice have revealed several physiological roles of CLEC‐2. Podoplanin is also expressed in lymphatic endothelial cells as well as several other cells, including type I alveolar cells and kidney podocytes, but is absent from vascular endothelial cells. In the developmental stages, when the primary lymph sac is derived from the cardinal vein, podoplanin activates platelets in lymphatic endothelial cells by binding to CLEC‐2, which facilitates blood/lymphatic vessel separation. Moreover, CLEC‐2 is involved in thrombus stabilisation under flow conditions in part through homophilic interactions. However, the absence of CLEC‐2 does not significantly increase bleeding tendency. CLEC‐2 may be a good target protein for novel anti‐platelet drugs or anti‐metastatic drugs having therapeutic and preventive effects on arterial thrombosis and cancer, the primary causes of mortality in developed countries. In this article, we review the mechanisms of signal transduction, structure, expression, and function of CLEC‐2.
Two-dimensional structures of medium-scale traveling ionospheric disturbances (MSTIDs) over Europe have been revealed, for the first time, by using maps of the total electron content (TEC) obtained ...from more than 800 GPS receivers of the European GPS receiver networks. From statistical analysis of the TEC maps obtained 2008, we have found that the observed MSTIDs can be categorized into two groups: daytime MSTID and nighttime MSTID. The daytime MSTID frequently occurs in winter. Its maximum occurrence rate in monthly and hourly bin exceeds 70% at lower latitudes over Europe, whereas it is approximately 45% at higher latitudes. Since most of the daytime MSTIDs propagate southward, we speculate that they could be caused by atmospheric gravity waves in the thermosphere. The nighttime MSTIDs also frequently occur in winter but most of them propagate southwestward, in a direction consistent with the theory that polarization electric fields play an important role in generating the nighttime MSTIDs. The nighttime MSTID occurrence rate shows distinct latitudinal difference: The maximum of the occurrence rate in monthly and hourly bin is approximately 50% at lower latitudes in Europe, whereas the nighttime MSTID was rarely observed at higher latitudes. We have performed model calculations of the plasma density perturbations caused by a gravity wave and an oscillating electric field to reproduce the daytime and nighttime MSTIDs, respectively. We find that TEC perturbations caused by gravity waves do not show dip angle dependencies, while those caused by the oscillating electric field have a larger amplitude at lower latitudes. These dip angle dependencies of the TEC perturbation amplitude could contribute to the latitudinal variation of the MSTID occurrence rate. Comparing with previous studies, we discuss the longitudinal difference of the nighttime MSTID occurrence rate, along with the E- and F-region coupling processes. The seasonal variation, of the nighttime MSTID occurrence rate in Europe, is not consistent with the theory that the longitudinal and seasonal variations of the nighttime MSTID occurrence could be attributed to those of the Es layer occurrence.
Abstract
Mitochondrial transcription factor A (TFAM) is essential for the maintenance, expression and transmission of mitochondrial DNA (mtDNA). However, mechanisms for the post-translational ...regulation of TFAM are poorly understood. Here, we show that TFAM is lysine acetylated within its high-mobility-group box 1, a domain that can also be serine phosphorylated. Using bulk and single-molecule methods, we demonstrate that site-specific phosphoserine and acetyl-lysine mimics of human TFAM regulate its interaction with non-specific DNA through distinct kinetic pathways. We show that higher protein concentrations of both TFAM mimics are required to compact DNA to a similar extent as the wild-type. Compaction is thought to be crucial for regulating mtDNA segregation and expression. Moreover, we reveal that the reduced DNA binding affinity of the acetyl-lysine mimic arises from a lower on-rate, whereas the phosphoserine mimic displays both a decreased on-rate and an increased off-rate. Strikingly, the increased off-rate of the phosphoserine mimic is coupled to a significantly faster diffusion of TFAM on DNA. These findings indicate that acetylation and phosphorylation of TFAM can fine-tune TFAM-DNA binding affinity, to permit the discrete regulation of mtDNA dynamics. Furthermore, our results suggest that phosphorylation could additionally regulate transcription by altering the ability of TFAM to locate promoter sites.
Abstract
The discovery of charge- and spin-density-wave (CDW/SDW) orders in superconducting cuprates has altered our perspective on the nature of high-temperature superconductivity (SC). However, it ...has proven difficult to fully elucidate the relationship between the density wave orders and SC. Here, using resonant soft X-ray scattering, we study the archetypal cuprate La
2-
x
Sr
x
CuO
4
(LSCO) over a broad doping range. We reveal the existence of two types of CDW orders in LSCO, namely CDW stripe order and CDW short-range order (SRO). While the CDW-SRO is suppressed by SC, it is partially transformed into the CDW stripe order with developing SDW stripe order near the superconducting
T
c
. These findings indicate that the stripe orders and SC are inhomogeneously distributed in the superconducting CuO
2
planes of LSCO. This further suggests a new perspective on the putative pair-density-wave order that coexists with SC, SDW, and CDW orders.
Abstract
By performing
N
-body simulations, we investigated the fundamental processes of collisions between dust aggregates composed of submicron-sized icy dust monomers. We examined the mass ...distribution of fragments in the collisional outcomes in a wide range of the mass ratio and the collision velocity between colliding dust aggregates. We derived analytic expressions of the mass distribution of large remnants and small fragments by numerical fitting to the simulation results. Our analytic formulae for masses of the large remnants can reproduce the contribution of mass transfer from a large target to a small projectile, which occurs for a mass ratio of ≳3 and is shown in a previous study. We found that the power-law index of the cumulative mass distribution of the small fragments is independent of the mass ratio and only weakly dependent on the collision velocity. On the other hand, the mass fraction of fragments of individual dust monomers decreases with an increasing total mass of colliding aggregates for a fixed mass ratio. This tendency implies that multiple hierarchical disruptive collisions (i.e., collisions between fragments, and collisions between fragments of fragments) are required for producing a large number of individual dust monomers via collisional fragmentation. Our fragment model suggests that the total geometric cross section integrated over the fragments is estimated to be about the same order as the geometric cross section of the target.
A low oxygen induction thermal plasma (LO-ITP) system was developed and a cold-welding behavior of bare fine metallic aluminum powders prepared by the system developed here was observed. This ...behavior is suitable for a metal precursor for metal matrix composites (MMC) since fine and bare metal particles may contribute to obtaining a well-dispersed state and a high relative density respectively, which lead to the enhancement of the reinforcement of MMC properties. The electric conductivity of the aluminum green pellet compacted at 200 MPa reached 2.9 × 107 S/m, which is comparable to that of bulk aluminum, indicating that the cold welding was taken place since the surface contamination layer such as an oxide may be negligibly thin. Therefore, the powder obtained in this work is expected to be useful in enhancing the reinforcement of MMC properties.
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•A new low oxygen induction thermal plasma system was developed.•Bare fine metallic Al powders were successfully prepared.•The electric conductivity of the Al green pellet reached that of bulk Al.•This system can be used as a production process for fine bare metal powders.
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