66 research outputs found
Near-optimal stochastic MIMO signal detection with a mixture of t-distribution prior
Multiple-input multiple-output (MIMO) systems will play a crucial role in
future wireless communication, but improving their signal detection performance
to increase transmission efficiency remains a challenge. To address this issue,
we propose extending the discrete signal detection problem in MIMO systems to a
continuous one and applying the Hamiltonian Monte Carlo method, an efficient
Markov chain Monte Carlo algorithm. In our previous studies, we have used a
mixture of normal distributions for the prior distribution. In this study, we
propose using a mixture of t-distributions, which further improves detection
performance. Based on our theoretical analysis and computer simulations, the
proposed method can achieve near-optimal signal detection with polynomial
computational complexity. This high-performance and practical MIMO signal
detection could contribute to the development of the 6th-generation mobile
network.Comment: to be published in the 2023 IEEE Global Communications Conference
(GLOBECOM
SERENADE II: An ALMA Multi-Band Dust-Continuum Analysis of 28 Galaxies at and the Physical Origin of the Dust Temperature Evolution
We present an analysis of ALMA multi-band dust-continuum observations for 28
spectroscopically-confirmed bright Lyman-break galaxies at . Our sample
consists of 11 galaxies at newly observed in our ALMA program, which
substantially increases the number of galaxies with both rest-frame 88
and 158 continuum observations, allowing us to simultaneously
measure the IR luminosity and dust temperature for a statistical sample of
galaxies for the first time. We derive the relationship between the
UV slope () and infrared excess (IRX) for the
galaxies, and find a shallower IRX- relation compared to the
previous results at --4. Based on the IRX- relation
consistent with our results and the - relation
including fainter galaxies in the literature, we find a limited contribution of
the dust-obscured star formation to the total SFR density, at
. Our measurements of the dust temperature at , on average, supports a gentle increase of
from to --7. Using an analytic model with
parameters consistent with recent {\it{JWST}} results, we discuss that the
observed redshift evolution of the dust temperature can be reproduced by an
increase in the gas depletion timescale and decrease of the metallicity. The variety of observed at
high redshifts can also be naturally explained by scatters around the
star-formation main sequence and average mass-metallicity relation, including
an extremely high dust temperature of observed in a
galaxy at .Comment: Submitted to Ap
Energizing Star Formation: The Cosmic Ray Ionization Rate in NGC 253 Derived From ALCHEMI Measurements of HO and SO
The cosmic ray ionization rate (CRIR) is a key parameter in understanding the
physical and chemical processes in the interstellar medium. Cosmic rays are a
significant source of energy in star formation regions, which impacts the
physical and chemical processes which drive the formation of stars. Previous
studies of the circum-molecular zone (CMZ) of the starburst galaxy NGC 253 have
found evidence for a high CRIR value; times the average cosmic ray
ionization rate within the Milky Way. This is a broad constraint and one goal
of this study is to determine this value with much higher precision. We exploit
ALMA observations towards the central molecular zone of NGC 253 to measure the
CRIR. We first demonstrate that the abundance ratio of HO and SO is
strongly sensitive to the CRIR. We then combine chemical and radiative transfer
models with nested sampling to infer the gas properties and CRIR of several
star-forming regions in NGC 253 due to emission from their transitions. We find
that each of the four regions modelled has a CRIR in the range
s and that this result adequately fits the
abundances of other species that are believed to be sensitive to cosmic rays
including CH, HCO, HOC, and CO. From shock and PDR/XDR models, we
further find that neither UV/X-ray driven nor shock dominated chemistry are a
viable single alternative as none of these processes can adequately fit the
abundances of all of these species.Comment: 24 pages, 15 figures, accepted for publication in Ap
Starburst Energy Feedback Seen through HCO+/HOC+Emission in NGC 253 from ALCHEMI
Molecular abundances are sensitive to the UV photon flux and cosmic-ray ionization rate. In starburst environments, the effects of high-energy photons and particles are expected to be stronger. We examine these astrochemical signatures through multiple transitions of HCO+ and its metastable isomer HOC+ in the center of the starburst galaxy NGC 253 using data from the Atacama Large Millimeter/submillimeter Array large program ALMA Comprehensive High-resolution Extragalactic Molecular inventory. The distribution of the HOC+(1-0) integrated intensity shows its association with "superbubbles,"cavities created either by supernovae or expanding H ii regions. The observed HCO+/HOC+ abundance ratios are ∼10-150, and the fractional abundance of HOC+ relative to H2 is ∼1.5 × 10-11-6 × 10-10, which implies that the HOC+ abundance in the center of NGC 253 is significantly higher than in quiescent spiral arm dark clouds in the Galaxy and the Galactic center clouds. Comparison with chemical models implies either an interstellar radiation field of G 0 ⪆ 103 if the maximum visual extinction is ⪆5, or a cosmic-ray ionization rate of ζ ⪆ 10-14 s-1 (3-4 orders of magnitude higher than that within clouds in the Galactic spiral arms) to reproduce the observed results. From the difference in formation routes of HOC+, we propose that a low-excitation line of HOC+ traces cosmic-ray dominated regions, while high-excitation lines trace photodissociation regions. Our results suggest that the interstellar medium in the center of NGC 253 is significantly affected by energy input from UV photons and cosmic rays, sources of energy feedback.N.H. acknowledges support
from JSPS KAKENHI grant No. JP21K03634. K.S. has been
supported by grants MOST 108-2112-M-001-015 and 109-
2112-M-001-020 from the Ministry of Science and Technology,
Taiwan. Y.N. is supported by the NAOJ ALMA Scientific
Research grant No. 2017-06B. V.M.R. and L.C. are funded by
the Comunidad de Madrid through the Atracción de Talento
Investigador (Doctores con experiencia) Grant (COOL: Cosmic
Origins Of Life; 2019-T1/TIC-15379)
The ALCHEMI atlas: principal component analysis reveals starburst evolution in NGC 253
Molecular lines are powerful diagnostics of the physical and chemical
properties of the interstellar medium (ISM). These ISM properties, which affect
future star formation, are expected to differ in starburst galaxies from those
of more quiescent galaxies. We investigate the ISM properties in the central
molecular zone of the nearby starburst galaxy NGC 253 using the ultra-wide
millimeter spectral scan survey from the ALMA Large Program ALCHEMI. We present
an atlas of velocity-integrated images at a 1".6 resolution of 148 unblended
transitions from 44 species, including the first extragalactic detection of
HCNH and the first interferometric images of CH, NO, HCS. We
conduct a principal component analysis (PCA) on these images to extract
correlated chemical species and to identify key groups of diagnostic
transitions. To the best of our knowledge, our dataset is currently the largest
astronomical set of molecular lines to which PCA has been applied. The PCA can
categorize transitions coming from different physical components in NGC 253
such as i) young starburst tracers characterized by high-excitation transitions
of HCN and complex organic molecules (COMs) versus tracers of on-going star
formation (radio recombination lines) and high-excitation transitions of CCH
and CN tracing PDRs, ii) tracers of cloud-collision-induced shocks
(low-excitation transitions of CHOH, HNCO, HOCO, and OCS) versus shocks
from star-formation-induced outflows (high-excitation transitions of SiO), as
well as iii) outflows showing emission from HOC, CCH, HO, CO
isotopologues, HCN, HCO, CS, and CN. Our findings show these intensities
vary with galactic dynamics, star formation activities, and stellar feedback.Comment: 65 pages, 39 figures. Accepted for publication in ApJ
豊橋技術科学大学における学生と教員の英語学習に対する意識
This is a report based on a general survey given to undergraduate students and professors at Toyohashi University of Technology (TUT) about English education at TUT. Regarding students, the main purposes of the survey, conducted in the fall of 2005, were to find how students had studied English before enrolling in TUT, what the students thought of English teaching and learning at TUT, and how important they thought English was for their majors. As for the survey to professors, the main purposes were finding out instructor attitudes toward the teaching and learning of English at TUT and how necessary they felt the acquisition of English was for their students. In this study, attention is paid to the differences of awareness and attitudes between the professors and students toward English teaching and learning. Based on the results of this study, discussions on and refinements to the current English curriculum will be made in the near future at TUT with the aim of raising student English fluency, particularly in the areas of written and oral communication ability
Second nationwide surveillance of bacterial pathogens in patients with acute uncomplicated cystitis conducted by Japanese Surveillance Committee from 2015 to 2016: antimicrobial susceptibility of Escherichia coli, Klebsiella pneumoniae, and Staphylococcus saprophyticus
The Japanese Surveillance Committee conducted a second nationwide surveillance of antimicrobial susceptibility patterns of uropathogens responsible for acute uncomplicated cystitis (AUC) in premenopausal patients aged 16–40 years old at 31 hospitals throughout Japan from March 2015 to February 2016. In this study, the susceptibility of causative bacteria (Escherichia coli, Klebsiella pneumoniae, Staphylococcus saprophyticus) for various antimicrobial agents was investigated by isolation and culturing of organisms obtained from urine samples. In total, 324 strains were isolated from 361 patients, including E. coli (n = 220, 67.9%), S. saprophyticus (n = 36, 11.1%), and K. pneumoniae (n = 7, 2.2%). The minimum inhibitory concentrations (MICs) of 20 antibacterial agents for these strains were determined according to the Clinical and Laboratory Standards Institute (CLSI) manual. At least 93% of the E. coli isolates showed susceptibility to fluoroquinolones and cephalosporins, whereas 100% of the S. saprophyticus isolates showed susceptibility to fluoroquinolones and aminoglycosides. The proportions of fluoroquinolone-resistant and extended-spectrum β-lactamase (ESBL)-producing E. coli strains were 6.4% (13/220) and 4.1% (9/220), respectively. The antimicrobial susceptibility of K. pneumoniae was retained during the surveillance period, while no multidrug-resistant strains were identified.
In summary, antimicrobial susceptibility results of our second nationwide surveillance did not differ significantly from those of the first surveillance. Especially the numbers of fluoroquinolone-resistant and ESBL-producing E. coli strains were not increased in premenopausal patients with AUC in Japan
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