107 research outputs found
Near-wall rheotaxis of the ciliate Tetrahymena induced by the kinesthetic sensing of cilia
泳ぐ微生物が海まで流されない理由 --SDGsに欠かせない小さな生物たちの振る舞いを解明--. 京都大学プレスリリース. 2021-10-21.To survive in harsh environments, single-celled microorganisms autonomously respond to external stimuli, such as light, heat, and flow. Here, we elucidate the flow response of Tetrahymena, a well-known single-celled freshwater microorganism. Tetrahymena moves upstream against an external flow via a behavior called rheotaxis. While micrometer-sized particles are swept away downstream in a viscous flow, what dynamics underlie the rheotaxis of the ciliate? Our experiments reveal that Tetrahymena slides along walls during upstream movement, which indicates that the cells receive rotational torque from shear flow to control cell orientation. To evaluate the effects of the shear torque and propelling speed, we perform a numerical simulation with a hydrodynamic model swimmer adopting cilia dynamics in a shear flow. The swimmer orientations converge to an upstream alignment, and the swimmer slides upstream along a boundary wall. The results suggest that Tetrahymena automatically responds to shear flow by performing rheotaxis using cilia-stalling mechanics
SPIN-WAVE EXCITATIONS IN Gd AT LOW TEMPERATURES
It has been manifestly demonstrated that Gd is one of the best example to be realistically applied to the spin-wave theory of Heisenberg model for the localized magnetic moment. The magnetization of Gd has been measured in the temperature 4<T<310 K at a constant magnetic field of 6 kOe using a homemade vibrating sample magnetometer. We present an exact analysis of the spin-wave excitations for Gd. In the presence of an applied magnetic field, H, an energy gap exists in the spin-wave dispersion relation. As a consequence, the temperature dependence of the magnetization for ferromagnets must differ from the simple Bloch T³/² law. The low temperature magnetization per gram is found to obey the form: Δσ(T)/σ(0) = BZ(3/2,Tℊ/T)T³/² + CZ(5/2, Tℊ/T)T⁵/², where B and C are constants and Δσ(T) = σ(0) - σ(T). The modification factors Z(3/2, Tℊ/T) and Z(5/2, Tℊ/T) are the characteristic functions of T and the magnetic field, H. The spontaneous magnetization of ferromagnetic Gd follows BZ(3/2,Tℊ/T) T³/² relation (the modified Bloch T³/² law) with remarkable fidelity below 200 K
Submillimeter ALMA Observations of the Dense Gas in the Low-Luminosity Type-1 Active Nucleus of NGC 1097
We present the first 100 pc scale view of the dense molecular gas in the
central ~ 1.3 kpc region of the type-1 Seyfert NGC 1097 traced by HCN (J=4-3)
and HCO+ (J=4-3) lines afforded with ALMA band 7. This galaxy shows significant
HCN enhancement with respect to HCO+ and CO in the low-J transitions, which
seems to be a common characteristic in AGN environments. Using the ALMA data,
we study the characteristics of the dense gas around this AGN and search for
the mechanism of HCN enhancement. We find a high HCN (J=4-3) to HCO+ (J=4-3)
line ratio in the nucleus. The upper limit of the brightness temperature ratio
of HCN (v2=1^{1f}, J=4-3) to HCN (J=4-3) is 0.08, which indicates that IR
pumping does not significantly affect the pure rotational population in this
nucleus. We also find a higher HCN (J=4-3) to CS (J=7-6) line ratio in NGC 1097
than in starburst galaxies, which is more than 12.7 on the brightness
temperature scale. Combined from similar observations from other galaxies, we
tentatively suggest that this ratio appears to be higher in AGN-host galaxies
than in pure starburst ones similar to the widely used HCN to HCO+ ratio. LTE
and non-LTE modeling of the observed HCN and HCO+ lines using J=4-3 and 1-0
data from ALMA, and J=3-2 data from SMA, reveals a high HCN to HCO+ abundance
ratio (5 < [HCN]/[HCO+] < 20: non-LTE analysis) in the nucleus, and that the
high-J lines (J=4-3 and 3-2) are emitted from dense (10^{4.5} < n_H2 [/cc] <
10^6), hot (70 < Tkin [K] < 550) regions. Finally we propose that the high
temperature chemistry is more plausible to explain the observed enhanced HCN
emission in NGC 1097 than the pure gas phase PDR/XDR chemistry.Comment: 28 pages, 17 figures, 10 tables. Accepted to PAS
Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) VIII. A less biased view of the early co-evolution of black holes and host galaxies
We present ALMA [CII] line and far-infrared (FIR) continuum observations of
three low-luminosity quasars () discovered by our
Subaru Hyper Suprime-Cam (HSC) survey. The [CII] line was detected in all three
targets with luminosities of , about one order
of magnitude smaller than optically luminous ()
quasars. The FIR continuum luminosities range from
(3 limit) to , indicating a wide range
in star formation rates in these galaxies. Most of the HSC quasars studied thus
far show [CII]/FIR luminosity ratios similar to local star-forming galaxies.
Using the [CII]-based dynamical mass () as a surrogate for bulge
stellar mass (), we find that a significant fraction of
low-luminosity quasars are located on or even below the local relation, particularly at the massive end of the galaxy mass
distribution. In contrast, previous studies of optically luminous quasars have
found that black holes are overmassive relative to the local relation. Given
the low luminosities of our targets, we are exploring the nature of the early
co-evolution of supermassive black holes and their hosts in a less biased way.
Almost all of the quasars presented in this work are growing their black hole
mass at much higher pace at than the parallel growth model, in which
supermassive black holes and their hosts grow simultaneously to match the local
relation at all redshifts. As the low-luminosity
quasars appear to realize the local co-evolutionary relation even at , they should have experienced vigorous starbursts prior to the currently
observed quasar phase to catch up with the relation.Comment: 19 pages, 11 figures, 4 tables. Accepted for publication in
Publications of the Astronomical Society of Japan (PASJ
Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) III. Star formation properties of the host galaxies at studied with ALMA
We present our ALMA Cycle 4 measurements of the [CII] emission line and the
underlying far-infrared (FIR) continuum emission from four optically
low-luminosity () quasars at discovered by
the Subaru Hyper Suprime Cam (HSC) survey. The [CII] line and FIR continuum
luminosities lie in the ranges
and , which are at least one
order of magnitude smaller than those of optically-luminous quasars at . We estimate the star formation rates (SFR) of our targets as
. Their line and continuum-emitting
regions are marginally resolved, and found to be comparable in size to those of
optically luminous quasars, indicating that their SFR or likely gas mass
surface densities (key controlling parameter of mass accretion) are accordingly
different. The ratios of the hosts, , are fully consistent with local star-forming
galaxies. Using the [CII] dynamics, we derived their dynamical masses within a
radius of 1.5-2.5 kpc as . By
interpreting these masses as stellar ones, we suggest that these faint quasar
hosts are on or even below the star-forming main sequence at , i.e.,
they appear to be transforming into quiescent galaxies. This is in contrast to
the optically luminous quasars at those redshifts, which show starburst-like
properties. Finally, we find that the ratios of black hole mass to host galaxy
dynamical mass of the most of low-luminosity quasars including the HSC ones are
consistent with the local value. The mass ratios of the HSC quasars can be
reproduced by a semi-analytical model that assumes merger-induced black
hole-host galaxy evolution.Comment: 20 pages, 9 figures, 4 tables. Accepted for publication in PAS
A novel efficient feeder-free culture system for the derivation of human induced pluripotent stem cells
Nakagawa, M.et al. A novel efficient feeder-free culture system forthe derivation of human induced pluripotent stem cells.Sci. Rep.4, 3594; DOI:10.1038/srep03594 (2014)
Subaru Hyper Suprime-Cam View of Quasar Host Galaxies at z < 1
Active galactic nuclei (AGNs) are key for understanding the coevolution of
galaxies and supermassive black holes (SMBHs). AGN activity is thought to
affect the properties of their host galaxies, via a process called "AGN
feedback", which drives the co-evolution. From a parent sample of 1151 z < 1
type-1 quasars from the Sloan Digital Sky Survey quasar catalog, we detected
host galaxies of 862 of them in the high-quality grizy images of the Subaru
Hyper Suprime-Cam (HSC) survey. The unprecedented combination of the survey
area and depth allows us to perform a statistical analysis of the quasar host
galaxies, with small sample variance. We fit the radial image profile of each
quasar as a linear combination of the point spread function and the Sersic
function, decomposing the images into the quasar nucleus and the host galaxy
components. We found that the host galaxies are massive, with stellar mass
Mstar > 10^(10) Msun, and are mainly located on the green valley. This trend is
consistent with a scenario in which star formation of the host galaxies is
suppressed by AGN feedback, that is, AGN activity may be responsible for the
transition of these galaxies from the blue cloud to the red sequence. We also
investigated the SMBH mass to stellar mass relation of the z < 1 quasars, and
found a consistent slope with the local relation, while the SMBHs may be
slightly undermassive. However, the above results are subject to our sample
selection, which biases against host galaxies with low masses and/or large
quasar-to-host flux ratios.Comment: Accepted for publication in PAS
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