287 research outputs found
AlN/AlGaN HEMTs on AlN substrate for stable high-temperature operation
We demonstrate an AlN/AlGaN high-electron-mobility transistor (HEMT) fabricated on a free-standing AlN substrate. A metal stack,
composed of Zr/Al/Mo/Au, was found to show low contact resistivity for source and drain ohmic contacts. The fabricated AlN/AlGaN HEMT
exhibited a maximum drain current of 38 mA/mm with a threshold voltage of -3.4 V. Negligible drain current degradation was observed at temperatures from 300 to 573 K, emonstrating that our AlN/AlGaN approach on an AlN substrate is promising for stable high-temperature operation
The K2-ESPRINT Project VI: K2-105 b, a Hot-Neptune around a Metal-rich G-dwarf
We report on the confirmation that the candidate transits observed for the
star EPIC 211525389 are due to a short-period Neptune-sized planet. The host
star, located in K2 campaign field 5, is a metal-rich ([Fe/H] = 0.260.05)
G-dwarf (T_eff = 543070 K and log g = 4.480.09), based on
observations with the High Dispersion Spectrograph (HDS) on the Subaru 8.2m
telescope. High-spatial resolution AO imaging with HiCIAO on the Subaru
telescope excludes faint companions near the host star, and the false positive
probability of this target is found to be < using the open source
vespa code. A joint analysis of transit light curves from K2 and additional
ground-based multi-color transit photometry with MuSCAT on the Okayama 1.88m
telescope gives the orbital period of P = 8.2669020.000070 days and
consistent transit depths of or . The transit depth corresponds to a planetary radius of , indicating that EPIC 211525389 b is a
short-period Neptune-sized planet. Radial velocities of the host star, obtained
with the Subaru HDS, lead to a 3\sigma\ upper limit of 90 on the mass of EPIC 211525389 b, confirming its planetary nature.
We expect this planet, newly named K2-105 b, to be the subject of future
studies to characterize its mass, atmosphere, spin-orbit (mis)alignment, as
well as investigate the possibility of additional planets in the system.Comment: 11 pages, 9 figures, 4 tables, PASJ accepte
Molecular and functional characterization of an evolutionarily conserved CREB-binding protein in the Lymnaea CNS
In eukaryotes, CREB-binding protein (CBP), a coactivator of CREB, functions both as a platform for recruiting other components of the transcriptional machinery and as a histone acetyltransferase (HAT) that alters chromatin structure. We previously showed that the transcriptional activity of cAMP-responsive element binding protein (CREB) plays a crucial role in neuronal plasticity in the pond snail Lymnaea stagnalis. However, there is no information on the molecular structure and HAT activity of CBP in the Lymnaea central nervous system (CNS), hindering an investigation of its postulated role in long-term memory (LTM). Here, we characterize the Lymnaea CBP (LymCBP) gene and identify a conserved domain of LymCBP as a functional HAT. Like CBPs of other species, LymCBP possesses functional domains, such as the KIX domain, which is essential for interaction with CREB and was shown to regulate LTM. In-situ hybridization showed that the staining patterns of LymCBP mRNA in CNS are very similar to those of Lymnaea CREB1. A particularly strong LymCBP mRNA signal was observed in the cerebral giant cell (CGC), an identified extrinsic modulatory interneuron of the feeding circuit, the key to both appetitive and aversive LTM for taste. Biochemical experiments using the recombinant protein of the LymCBP HAT domain showed that its enzymatic activity was blocked by classical HAT inhibitors. Preincubation of the CNS with such inhibitors blocked cAMP-induced synaptic facilitation between the CGC and an identified follower motoneuron of the feeding system. Taken together, our findings suggest a role for the HAT activity of LymCBP in synaptic plasticity in the feeding circuitry
Neuropsychological study of amyotrophic lateral sclerosis and parkinsonism-dementia complex in Kii peninsula, Japan
Direct Imaging of a Cold Jovian Exoplanet in Orbit around the Sun-like Star GJ 504
Several exoplanets have recently been imaged at wide separations of >10 AU
from their parent stars. These span a limited range of ages (<50 Myr) and
atmospheric properties, with temperatures of 800--1800 K and very red colors (J
- H > 0.5 mag), implying thick cloud covers. Furthermore, substantial model
uncertainties exist at these young ages due to the unknown initial conditions
at formation, which can lead to an order of magnitude of uncertainty in the
modeled planet mass. Here, we report the direct imaging discovery of a Jovian
exoplanet around the Sun-like star GJ 504, detected as part of the SEEDS
survey. The system is older than all other known directly-imaged planets; as a
result, its estimated mass remains in the planetary regime independent of
uncertainties related to choices of initial conditions in the exoplanet
modeling. Using the most common exoplanet cooling model, and given the system
age of 160 [+350, -60] Myr, GJ 504 b has an estimated mass of 4 [+4.5, -1.0]
Jupiter masses, among the lowest of directly imaged planets. Its projected
separation of 43.5 AU exceeds the typical outer boundary of ~30 AU predicted
for the core accretion mechanism. GJ 504 b is also significantly cooler (510
[+30, -20] K) and has a bluer color (J-H = -0.23 mag) than previously imaged
exoplanets, suggesting a largely cloud-free atmosphere accessible to
spectroscopic characterization. Thus, it has the potential of providing novel
insights into the origins of giant planets, as well as their atmospheric
properties.Comment: 20 pages, 12 figures, Accepted for publication in ApJ. Minor updates
from the version
Subaru Imaging of Asymmetric Features in a Transitional Disk in Upper Scorpius
We report high-resolution (0.07 arcsec) near-infrared polarized intensity
images of the circumstellar disk around the star 2MASS J16042165-2130284
obtained with HiCIAO mounted on the Subaru 8.2 m telescope. We present our
-band data, which clearly exhibits a resolved, face-on disk with a large
inner hole for the first time at infrared wavelengths. We detect the
centrosymmetric polarization pattern in the circumstellar material as has been
observed in other disks. Elliptical fitting gives the semimajor axis, semiminor
axis, and position angle (P.A.) of the disk as 63 AU, 62 AU, and -14
, respectively. The disk is asymmetric, with one dip located at P.A.s
of . Our observed disk size agrees well with a previous study
of dust and CO emission at submillimeter wavelength with Submillimeter Array.
Hence, the near-infrared light is interpreted as scattered light reflected from
the inner edge of the disk. Our observations also detect an elongated arc (50
AU) extending over the disk inner hole. It emanates at the inner edge of the
western side of the disk, extending inward first, then curving to the
northeast. We discuss the possibility that the inner hole, the dip, and the arc
that we have observed may be related to the existence of unseen bodies within
the disk.Comment: 21 pages, 3 figures, published 2012 November 7 by ApJL, typo
correcte
SEEDS direct imaging of the RV-detected companion to V450 Andromedae, and characterization of the system
We report the direct imaging detection of a low-mass companion to a young,
moderately active star V450 And, that was previously identified with the radial
velocity method. The companion was found in high-contrast images obtained with
the Subaru Telescope equipped with the HiCIAO camera and AO188 adaptive optics
system. From the public ELODIE and SOPHIE archives we extracted available
high-resolution spectra and radial velocity (RV) measurements, along with RVs
from the Lick planet search program. We combined our multi-epoch astrometry
with these archival, partially unpublished RVs, and found that the companion is
a low-mass star, not a brown dwarf, as previously suggested. We found the
best-fitting dynamical masses to be and
M. We also performed spectral analysis of
the SOPHIE spectra with the iSpec code. The Hipparcos time-series photometry
shows a periodicity of d, which is also seen in SOPHIE spectra as an
RV modulation of the star A. We interpret it as being caused by spots on the
stellar surface, and the star to be rotating with the given period. From the
rotation and level of activity, we found that the system is
Myr old, consistent with an isochrone analysis ( Myr). This
work may serve as a test case for future studies of low-mass stars, brown
dwarfs and exoplanets by combination of RV and direct imaging data.Comment: 15 pages, 9 figures, 7 tables, to appear in Ap
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