600 research outputs found
Delay Time Distribution Measurement of Type Ia Supernovae by the Subaru/XMM-Newton Deep Survey and Implications for the Progenitor
The delay time distribution (DTD) of type Ia supernovae (SNe Ia) from star
formation is an important clue to reveal the still unknown progenitor system of
SNe Ia. Here we report on a measurement of the SN Ia DTD in a delay time range
of t_Ia = 0.1-8.0 Gyr by using the faint variable objects detected in the
Subaru/XMM-Newton Deep Survey (SXDS) down to i' ~ 25.5. We select 65 SN
candidates showing significant spatial offset from nuclei of the host galaxies
having old stellar population at z ~ 0.4-1.2, out of more than 1,000 SXDS
variable objects. Although spectroscopic type classification is not available
for these, we quantitatively demonstrate that more than ~80% of these should be
SNe Ia. The DTD is derived using the stellar age estimates of the old galaxies
based on 9 band photometries from optical to mid-infrared wavelength. Combined
with the observed SN Ia rate in elliptical galaxies at the local universe, the
DTD in t_Ia ~ 0.1-10 Gyr is well described by a featureless power-law as
f_D(t_Ia) \propto t_Ia^{-1}. The derived DTD is in excellent agreement with the
generic prediction of the double-degenerate scenario, giving a strong support
to this scenario. In the single-degenerate (SD) scenario, although predictions
by simple analytic formulations have broad DTD shapes that are similar to the
observation, DTD shapes calculated by more detailed binary population synthesis
tend to have strong peaks at characteristic time scales, which do not fit the
observation. This result thus indicates either that the SD channel is not the
major contributor to SNe Ia in old stellar population, or that improvement of
binary population synthesis theory is required. Various sources of systematic
uncertainties are examined and tested, but our main conclusions are not
affected significantly.Comment: Matches the final version to be published in PASJ. A very minor bug
in the visibility time calculation has been fixed, resulting in slight
changes in the derived DTD (<~ 10%). Conclusions are not affected at all. The
font error of the labels in Fig 3 also fixe
Power-Level-Design-Aware Scalable Framework for Throughput Analysis of GF-NOMA in mMTC
Hirai T., Oda R., Wakamiya N.. Power-Level-Design-Aware Scalable Framework for Throughput Analysis of GF-NOMA in mMTC. IEEE Internet of Things Journal , (2024); https://doi.org/10.1109/JIOT.2024.3400996.This paper proposes a scalable framework to analyze the throughput of the grant-free power-domain nonorthogonal multiple access (GF-NOMA) and presents the achievable performance in the optimized offered load at each power level (called per-level offered load) by using our framework. Our analytical model reflects packet errors caused by power collisions, characterized by GF-NOMA, based on the power level design guaranteeing the required signal-to-interference-and-noise ratio (SINR). This key idea enables analyzing the throughput of a large-scale GF-NOMA system more accurately than the existing analytical models. Also, this key idea enables optimizing the per-level offered load rather than a uniform one in typical optimization problems related to the throughput: the throughput maximization or energy minimization problem with a throughput condition. Our analytical results highlight some key insights into designing future access control methods in GF-NOMA. First, our analytical model achieves an approximation error of only 0.4% for the exact throughput obtained by the exhaustive search at five power levels; the existing analytical model provides an approximation error of 25%. Next, our proposed framework highlights that the optimal per-level offered load restrictively improves the throughput above the optimally uniform per-level offered load. Finally, our proposed framework discovers a 27 more energy-efficient per-level offered load than the existing framework at five power levels while providing higher throughput than the optimally uniform per-level offered load
Association between high cardiac output at altitude and acute mountain sickness: preliminary study on Mt. Fuji
Background: Acute mountain sickness (AMS) affects around 30% of people climbing Mt. Fuji, but its pathogenesis is incompletely understood. The influence of a rapid ascent to high altitude by climbing and summiting Mt. Fuji on cardiac function in the general population is unknown, and its association with altitude sickness has not been clarified. Methods: Subjects climbing Mt. Fuji were included. Heart rate, oxygen saturation, systolic blood pressure, cardiac index (CI) and stroke volume index were measured multiple times at 120 m as baseline values and at Mt. Fuji Research Station (MFRS) at 3,775 m. Each value and its difference from the baseline value (Δ) of subjects with AMS (defined as Lake Louise Score [LLS] ≥ 3 with headache after sleeping at 3,775 m) were compared with those of non-AMS subjects. Results: Eleven volunteers who climbed from 2,380 m to MFRS within 8 h and stayed overnight at MFRS were included. Four suffered AMS. Compared with the non-AMS subjects, CI in the AMS subjects was significantly higher than that before sleeping (median [interquartile range]: 4.9 [4.5, 5.0] vs. 3.8 [3.4, 3.9] mL/min/m2; p = 0.04), and their ΔCI was significantly higher before sleeping (1.6 [1.4, 2.1] vs. 0.2 [0.0, 0.7] mL/min/m2; p < 0.01) and after sleeping (0.7 [0.3, 1.7] vs. -0.2 [-0.5, 0.0] mL/min/m2; p < 0.01). ΔCI in the AMS subjects dropped significantly after sleeping versus before sleeping (3.8 [3.6, 4.5] vs. 4.9 [4.5, 5.0] mL/min/m2; p = 0.04). Conclusions: Higher values of CI and ΔCI were observed at high altitude in the AMS subjects. A high cardiac output might be associated with the development of AMS.Ebihara T., Shimizu K., Mitsuyama Y., et al. Association between high cardiac output at altitude and acute mountain sickness: preliminary study on Mt. Fuji. Journal of Physiological Anthropology 42, 6 (2023); https://doi.org/10.1186/s40101-023-00322-7
Relationship between peak oxygen uptake and regional body composition in Japanese subjects
AbstractPurposeTo investigate the link between peak oxygen uptake and regional body composition by dual energy X-ray absorptiometry (DEXA) in Japanese subjects.MethodsA total of 93 men (42.2 ± 12.3 years old) and 106 women (43.5 ± 12.3 years old) were enrolled in this cross-sectional investigation study. Peak oxygen uptake was measured by the breath-by-breath method. Regional body composition i.e., body fat mass, lean body mass, and body fat percentage was evaluated using DEXA. In addition, metabolic risk parameters were also evaluated.ResultsPeak oxygen uptake was 37.6 ± 8.7 mL/kg/min in men and 31.1 ± 6.4 mL/kg/min in women, and decreased with age in both genders. Peak oxygen uptake was significantly correlated with total body fat percentage (men: r = −0.684, p < 0.0001; women: r = −0.681, p < 0.0001). These associations remained even after adjusting for age and total lean body mass. However, peak work rate was positively and significantly correlated with leg lean body mass.ConclusionPeak oxygen uptake was closely correlated with total body fat percentage in both genders. Aerobic exercise as well as leg resistance training might be useful for improving peak oxygen uptake in Japanese subjects
A Discovery of Rapid Optical Flares from Low-Luminosity Active Nuclei in Massive Galaxies
We report a serendipitous discovery of six very low-luminosity active
galactic nuclei (AGNs) only by optical variability in one-month baseline. The
detected flux variability is ~ 1-5% of the total luminosity of host galaxies.
Careful subtraction of host galaxy components in nuclear regions indicates that
the fractional variability (Delta F / F) of the nuclei is of order unity. At
least one of them is showing a compelling flaring activity within just a few
days, which appears to be quite different from previously known AGN
variability. We obtained spectroscopic data for the one showing the largest
flare and confirmed that it is in fact an AGN at z = 0.33 with an estimated
black hole mass of ~10^8 M_sun. As a possible interpretation, we suggest that
these activities are coming from the region around the black hole event
horizon, which is physically similar to the recently discovered near-infrared
flares of our Galactic nucleus. It is indicated that our Galaxy is not special,
and that surprisingly rapid flaring activity in optical/near-infrared bands may
be commonly hidden in nuclei of apparently normal galaxies with low Eddington
ratios, in contrast to the variability of well-studied luminous AGNs or
quasars.Comment: Accepted to ApJ Letter
Deciphering the cosmic star formation history and the Nature of Type Ia Supernovae by Future Supernova Surveys
We investigate the prospects of future supernova searches to get meaningful
constraints about the cosmic star formation history (CSFH) and the delay time
of type Ia supernovae from star formation (tau_{Ia}), based only on supernova
data. Here we parameterize the CSFH by two parameters, alpha and beta that are
the evolutionary indices (proportional to (1+z)^{alpha, beta}) at z ~
1, respectively, and quantitatively examined how well the three parameters
(alpha, beta, and tau_{Ia}) can be constrained in ongoing and future supernova
surveys. We found that the type classification of detected supernovae down to
the magnitude of I_{AB} ~ 27 is essential, to get useful constraint on beta.
The parameter tau_{Ia} can also be constrained within an accuracy of ~ 1--2
Gyr, without knowing alpha that is somewhat degenerate with tau_{Ia}. This
might be potentially achieved by ground-based surveys but depending on the
still highly uncertain type-classification by imaging data. More reliable
classification will be achieved by the SNAP mission. The supernova counts at a
magnitude level of I_{AB} or K_{AB} ~ 30 will allow us to break degeneracies
between alpha and tau_{Ia} and independently constrain all the three
parameters, even without knowing supernova types. This can be achieved by the
SNAP and JWST missions, having different strength of larger statistics and
reach to higher redshifts, respectively. The dependence of observable
quantities on survey time intervals is also quantitatively calculated and
discussed.Comment: 10 pages, 6 figures, accepted to Ap
Supernovae in the Subaru Deep Field: An Initial Sample, and Type Ia Rate, out to Redshift 1.6
Large samples of high-redshift supernovae (SNe) are potentially powerful
probes of cosmic star formation, metal enrichment, and SN physics. We present
initial results from a new deep SN survey, based on re-imaging in the R, i', z'
bands, of the 0.25 deg2 Subaru Deep Field (SDF), with the 8.2-m Subaru
telescope and Suprime-Cam. In a single new epoch consisting of two nights of
observations, we have discovered 33 candidate SNe, down to a z'-band magnitude
of 26.3 (AB). We have measured the photometric redshifts of the SN host
galaxies, obtained Keck spectroscopic redshifts for 17 of the host galaxies,
and classified the SNe using the Bayesian photometric algorithm of Poznanski et
al. (2007) that relies on template matching. After correcting for biases in the
classification, 55% of our sample consists of Type Ia supernovae and 45% of
core-collapse SNe. The redshift distribution of the SNe Ia reaches z ~ 1.6,
with a median of z ~ 1.2. The core-collapse SNe reach z ~ 1.0, with a median of
z ~ 0.5. Our SN sample is comparable to the Hubble Space Telescope/GOODS sample
both in size and redshift range. The redshift distributions of the SNe in the
SDF and in GOODS are consistent, but there is a trend (which requires
confirmation using a larger sample) for more high-z SNe Ia in the SDF. This
trend is also apparent when comparing the SN Ia rates we derive to those based
on GOODS data. Our results suggest a fairly constant rate at high redshift that
could be tracking the star-formation rate. Additional epochs on this field,
already being obtained, will enlarge our SN sample to the hundreds, and
determine whether or not there is a decline in the SN Ia rate at z >~ 1.Comment: 20 pages, 8 figures, MNRAS accepte
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