arXiv subjects

J. Ito

Publications and source records attributed to J. Ito.

5 recordsLinked to original sources

arXiv2025

TESS and ground-based observations of WZ Sge-type dwarf novae in outburst

Dwarf nova (DN) superoutbursts are accompanied by superhumps, which change their periods and profiles over a superoutburst. We present the TESS and ground-based observations of nine WZ Sge-type DNe and candidates in superoutburst. In TCP J23580961$+$5502508, ASASSN-23ba, PNV J19030433$-$3102187, V748 Hya, and ASASSN-25ci, we confirmed double-peaked oscillations called early superhumps, which are regarded as the unambiguous feature of WZ Sge-type DNe. On the other hand, the superhump and outburst properties of MO Psc and V1676 Her suggest that they may not be a member of WZ Sge-type DNe. The 2022 superoutburst of a confirmed WZ Sge-type DN TCP J05515391$+$6504346, however, lacked an early superhump phase. We find superhumps in a WZ Sge-type DN ASASSN-20mq during its rebrightening outburst. Thanks to the continuous coverage of TESS, we find the broken-powerlaw rise of the outburst light curve in V748 Hya and PNV J19030433$-$3102187, previously found in only one WZ Sge-type DN observed by Kepler. Early superhumps appeared when the system reached $\simeq40$% of the outburst peak flux. No orbital modulation from a hot spot is detected before and after this. This non-detection of orbital humps on the early rise of V748 Hya constrains that the corresponding mass transfer rate should be below $\simeq1\times10^{16}$ g s$^{-1}$, disfavouring an enhancement of a mass transfer rate by an order of magnitude or larger, even if it occurs. The contentious TESS observations also confirm the coexistence of early and ordinary superhumps during their transition and $\leq$2-cycle duration of stage A--B superhump transition in V748 Hya.

astro-ph.SR↗

arXiv2023

Momentum flux fluctuations in wall turbulence formulated along the distance from the wall

Wall turbulence has a sublayer where the mean wall-normal flux of the streamwise momentum is constant. Via the law of the wall, this mean flux is related to the wall-normal profile of the mean streamwise velocity. However, the momentum flux has large fluctuations, for which the corresponding law is yet unknown. To formulate such a law, we decompose fluctuations of the streamwise and the wall-normal velocities. These are smoothed to single out a component that would dominate the momentum flux fluctuations. It is dependent on the wall-normal distance. We relate this dependence to the wall-normal profile of the streamwise velocity variance. The resultant law is consistent with laboratory and field data across a wide range of that distance and applies readily to wall modeling of a numerical simulation.

physics.flu-dyn↗

arXiv2022

Improved upper limit on degree-scale CMB B-mode polarization power from the 670 square-degree POLARBEAR survey

We report an improved measurement of the degree-scale cosmic microwave background $B$-mode angular-power spectrum over 670 square-degree sky area at 150 GHz with POLARBEAR. In the original analysis of the data, errors in the angle measurement of the continuously rotating half-wave plate, a polarization modulator, caused significant data loss. By introducing an angle-correction algorithm, the data volume is increased by a factor of 1.8. We report a new analysis using the larger data set. We find the measured $B$-mode spectrum is consistent with the $Λ$CDM model with Galactic dust foregrounds. We estimate the contamination of the foreground by cross-correlating our data and Planck 143, 217, and 353 GHz measurements, where its spectrum is modeled as a power law in angular scale and a modified blackbody in frequency. We place an upper limit on the tensor-to-scalar ratio $r$ < 0.33 at 95% confidence level after marginalizing over the foreground parameters.

astro-ph.CO↗

arXiv2022

Momentum flux fluctuations in wall turbulence: a formula beyond the law of the wall

Within wall turbulence, there is a sublayer where the mean wall-normal flux of the streamwise momentum is constant and related to the logarithmic wall-normal profile of the mean streamwise velocity. This relation, i.e., the law of the wall, has been used to estimate the mean stress at the wall surface. However, the momentum flux exhibits large temporal fluctuations. To relate them theoretically to those of the streamwise velocity at the same position from the wall, we consider an orthogonal decomposition of the fluctuations on a plane of the streamwise and wall-normal velocities. Since a large timescale is expected for the component that would dominate the momentum flux, it is singled out by temporal smoothing. The resultant formula is consistent with time-series data of a boundary layer in a wind tunnel. We also extend the formula to thermally stratified cases.

physics.flu-dyn↗

arXiv1999

Self-organized hierarchical structure in a plastic network of chaotic units

Formation of a layered structure is studied in a globally coupled map of chaotic units with a plastic coupling strength that changes depending on the states of units globally and an external input. In the parameter region characterized by weakly chaotic and desynchronized dynamics, units spontaneously form a hierarchical structure due to the influence of the input, with regards to the coupling strength. This hierarchical structure is not fixed in time, and is successively reorganized. It is found that the distribution of lifetimes of the structure obeys a power law. The possible relevance of the present result to information processing in the brain is briefly discussed.

cond-mat.dis-nn↗