We analysed associations between exposure to nightlife businesses and severe acute respiratory syndrome coronavirus 2 PCR test results at a tertiary hospital in Tokyo between March and April 2020. A nightlife group was defined as those who had worked at or visited the businesses. We included 1517 individuals; 196 (12.9%) were categorised as the nightlife group. After propensity score matching, the proportion of positive PCR tests in the nightlife group was significantly higher than that in the non-nightlife group (nightlife, 63.8%; non-nightlife, 23.0%; P < 0.001). An inclusive approach to mitigate risks related to the businesses needs to be identified.

A super-Chandrasekhar (SC) supernova (SN) has an extremely high luminosity and a slow decline rate of the light curve in the early-phase. We present late-phase observations of the SC SN 2009dc. We find that the optical luminosity a year after maximum is much fainter than that expected from its early luminosity. We attempt to fit the analytic light curve model to the observations using Arnett's rule. The model successfully explains the light curves until 120 days. This suggests that the extremely high luminosity originates from the 56Ni decay. We suggest that the late-phase decline would be caused by dust formation. The existence of strong carbon features in early-phase spectra would support this scenario. We also find a blend of [Ca ii] and [Ni ii] in its late-phase spectrum. This indicates that the calcium is distributed in the inner layer along with nickel and iron. We conclude that the mixing may occur in the inner parts of the ejecta.

We successfully obtained the first optical spectra of the faint light echoes around Cassiopeia A and Tycho Brahe's supernova remnants (SNRs) with FOCAS and the Subaru Telescope. We conclude that Cas A and Tycho's SN 1572 belong to the Type IIb and normal Type Ia supernovae, respectively. Light echo spectra are important in order to obtain further insight into the supernova explosion mechanism of Tycho's SN 1572: how the Type Ia explosion actually proceeds, and whether accretion occurs from a companion or by the merging of two white dwarfs. The proximity of the SN 1572 remnant has allowed detailed studies, such as the possible identification of the binary companion, and provides a unique opportunity to test theories of the explosion mechanism and the nature of the progenitor. Future light-echo spectra, obtained in different spatial directions of SN 1572, will enable to construct a three-dimensional spectroscopic view of the explosion.

H and He features in photospheric spectra have rarely been used to constrain the structure of Type IIb/Ib/Ic supernovae (SNe IIb/Ib/Ic). The lines have to be modelled with a detailed non-local-thermodynamic-equilibrium (NLTE) treatment, including effects uncommon in stars. Once this is done, however, one obtains valuable hints on the characteristics of progenitors and explosions (composition, explosion energy, . . .). We have extended a radiative transfer code to compute synthetic spectra of SNe IIb, Ib and Ic. Here, we discuss our first larger set of models, focusing on the question: How much H/He can be hidden (i.e. remain undetected in photospheric spectra) in SNe Ib/Ic? For the SNe studied (relatively low Mej = 1. . .3 M⊙), we find a limit of MHe ≲ 0.1 M⊙ in SNe Ic (no unambiguous He lines). Stellar evolution models for single stars normally always yield higher masses. We suggest that low- or moderate-mass SNe Ic result from efficient envelope stripping in binaries. We propose similar studies on H/He in high-mass and extremely aspherical SNe, and observations covering the region of He I λ 20581.

Acute diarrhoea remains a major public health challenge in developing countries. We examined the role of a probiotic in the prevention of acute diarrhoea to discover if there was an effect directed towards a specific aetiology. A double-blind, randomized, controlled field trial involving 3758 children aged 1–5 years was conducted in an urban slum community in Kolkata, India. Participants were given either a probiotic drink containing Lactobacillus casei strain Shirota or a nutrient drink daily for 12 weeks. They were followed up for another 12 weeks. The primary outcome of this study was the occurrence of first episodes of diarrhoea. We assessed this during 12 weeks of intake of study agent and also for 12 weeks of follow-up. There were 608 subjects with diarrhoea in the probiotic group and 674 subjects in the nutrient group during the study period of 24 weeks. The level of protective efficacy for the probiotic was 14% (95% confidence interval 4–23, P<0·01 in adjusted model). The reduced occurrence of acute diarrhoea in the probiotic group compared to nutrient group was not associated with any specific aetiology. No adverse event was observed in children of either probiotic or nutrient groups. The study suggests that daily intake of a probiotic drink can play a role in prevention of acute diarrhoea in young children in a community setting of a developing country.

The connection between the long GRBs and Type Ic Supernovae (SNe) has revealed the interesting diversity: (i) GRB-SNe, (ii) Non-GRB Hypernovae (HNe), (iii) X-Ray Flash (XRF)-SNe, and (iv) Non-SN GRBs (or dark HNe). We show that nucleosynthetic properties found in the above diversity are connected to the variation of the abundance patterns of extremely-metal-poor (EMP) stars, such as the excess of C, Co, Zn relative to Fe. We explain such a connection in a unified manner as nucleosynthesis of hyper-aspherical (jet-induced) explosions of Pop III core-collapse SNe. We show that (1) the explosions with large energy deposition rate, Ėdep, are observed as GRB-HNe and their yields can explain the abundances of normal EMP stars, and (2) the explosions with small Ėdep are observed as GRBs without bright SNe and can be responsible for the formation of the C-rich EMP (CEMP) and the hyper metal-poor (HMP) stars. We thus propose that GRB-HNe and the Non-SN GRBs (dark HNe) belong to a continuous series of BH-forming massive stellar deaths with the relativistic jets of different Ėdep.

To determine the role of interleukin-5 (IL-5) and eosinophils in protection against Strongyloides ratti, mice treated with anti-IL-5 monoclonal antibody (mAb) were infected with S. ratti larvae. Strongyloides ratti egg numbers in faeces (EPG) in mAb treated mice were higher than those in control mice on days 6 and 7 after inoculation. The numbers of migrating worms in mAb treated mice 36 h after inoculation were higher than those observed in control mice. Intestinal worm numbers in mAb treated mice 5 days after inoculation were higher than those in control mice. These results show that eosinophils effectively protected the host against S. ratti infection by mainly the larval stage in primary infections. The involvement of eosinophils in protection against secondary infection was also examined. Before secondary infection, mice were treated with anti-IL-5 mAb and infected with S. ratti. Patent infections were not observed in either mAb treated or control Ab treated mice. The numbers of migrating worms in the head and lungs of mAb treated mice increased to 60% of that in primary infected mice. Intestinal worms were not found in mAb treated mice or in contcrol mice after oral implantation of adult worms. Eosinophils were therefore mainly involved in protection against tissue migrating worms in secondary infections.

The sheet resistance and sheet carrier concentration for Si ion implanted GaN have been investigated as a function of Si ion dosages and ion's energy using van der Pauw method and Hall effect measurement. Si ion implanted GaN is annealed at 1200 °C for 10 sec in N2 gas flow with 50 nm-thick SiNx cap layer to avoid dissociation of GaN. For Si ion energy of 30 keV, the sheet resistance is decreased from 103 to 56 ohm/sq. for the dose ranging from 1 × 1014 to 2 × 1015/cm2. For the Si dose larger than 2 × 1015/cm2, the sheet carrier concentration is saturated around 1 ×s 1015/cm2. Si ion implanted GaN with energy of 50, 80, and 120 keV at a dose of 2 × 1015/cm2 also reveal the sheet carrier concentration of about 1 × 1015/cm2 with the decrease of electron mobility. It is suggested that the implanted Si donors are strongly compensated by the residual implantation-induced defects.

We describe the discovery of HE 1327–2326, a dwarf or subgiant with $\mbox{[Fe/H]}=-5.4$. The star was found in a sample of bright metal-poor stars selected from the Hamburg/ESO survey. Its abundance pattern is characterized by very high C and N abundances. The detection of Sr which is overabundant by a factor of 10 as compared to iron and the Sun, suggests that neutron-capture elements had already been produced in the very early Galaxy. A puzzling Li depletion is observed in this unevolved star which contradicts the value of the primordial Li derived from WMAP and other Li studies. Possible scenarios for the origin of the abundance pattern (Pop. II or Pop. III) are presented as well as an outlook on future observations.

We calculate evolution, explosion and nucleosynthesis of 1000$M_{\odot}$ stars. Even such massive stars may explode at the end of their lives if they rotate. We use a 2 dimensional hydrodynamical code to take aspherisity by the effect of rotation into account. Our results show that (1) abundance pattern of ejected matter by explosion is consistent with observational data of intracluster medium gas and M82 hot gas, (2) such massive stars can supply more efficient UV photons to re-ionize HI, HeI and HeII than ordinary massive stars (less than 100 solar-masses) and (3) final black hole mass is 500 solar-mass, which is consistent of the mass scale of intermediate-mass black hole (IHBH) found in M82.

The abundance patterns of extremely metal-poor (EMP) stars provide us with important information on nucleosynthesis in supernovae (SNe) formed in a Pop III or EMP environment, and thus on the nature of the first stars in the Universe. We review nucleosynthesis yields of various types of those SNe, focusing on core-collapse (black-hole-forming) SNe with various progenitor masses, explosion energies (including Hypernovae), and asphericity. We discuss the implications of the observed trends in the abundance ratios among iron-peak elements, and the large C/Fe ratio observed in certain EMP stars with particular attention to recently discovered hyper metal-poor (HMP) stars. We show that the abundance pattern of the HMP stars with [Fe/H] <−5 and other EMP stars are in good accord with those of black-hole-forming supernovae, but not pair-instability supernovae. This suggests that black-hole-forming supernovae made important contributions to the early Galactic (and cosmic) chemical evolution. Finally we discuss the nature of First (Pop III) Stars.

We present preliminary results on the chemical abundance patterns of extremely metal-poor stars obtained during an ongoing observing program with Subaru/HDS. High-resolution, high signal-to-noise spectra have been obtained for 14 stars with [Fe/H]$\lesssim -3$. Five of them exhibit clear overabundances of carbon, a remarkable characteristic found only in the most metal-poor range. One of the carbon-rich stars, HE 1327–2326, has [Fe/H]$_{\rm NLTE}=-5.4$, the lowest Fe abundance known. No stars with ${-}5\,{<}\,$[Fe/H]$\,{<}\,{-}4$ have yet been found in our program, suggesting that quite different enrichment processes were responsible for stars with [Fe/H]$\,{<}\,{-}5$ and [Fe/H]$\,{>}\,{-}4$. While neutron-capture elements are deficient in most of our stars, one star (BS 16550–087) exhibits large enhancements of its light neutron-capture elements (Sr, Y and Zr), providing a strong constraint on models for the production of such elements in the very early Galaxy.

Stars more massive than ~ 20–25 M⊙ form a black hole at the end of their evolution. Stars with non-rotating black holes are likely to collapse ”quietly” ejecting a small amount of heavy elements (Faint supernovae). In contrast, stars with rotating black holes are likely to give rise to very energetic supernovae (Hypernovae). Nucleosynthesis in Hypernovae is characterized by larger abundance ratios (Zn,Co,V,Ti)/Fe and smaller (Mn,Cr)/Fe than normal supernovae, which can explain the observed trend of these ratios in extremely metal-poor stars. Nucleosynthesis in Faint supernovae is characterized by a large amount of fall-back. We show that the abundance pattern of the recently discovered most Fe-poor star, HE0107-5240, and other extremely metal-poor carbon-rich stars are in good accord with those of black-hole-forming supernovae, but not pair-instability supernovae. This suggests that black-hole-forming supernovae made important contributions to the early Galactic (and cosmic) chemical evolution as the First (Pop III) Supernovae.

Stars more massive than ~ 20 − 25 M⊙ form a black hole at the end of their evolution. Stars with non-rotating black holes are likely to collapse “quietly” ejecting a small amount of heavy elements (faint supernovae). In contrast, stars with rotating black holes are likely to give rise to very energetic supernovae (hypernovae). We present distinct nucleosynthesis features of these two types of “black-hole-forming” supernovae. Nucleosynthesis in hypernovae is characterized by larger abundance ratios (Zn, Co, V, Ti)/Fe and smaller (Mn, Cr)/Fe than normal supernovae, which can explain the observed trend of these ratios in extremely metal-poor stars. Nucleosynthesis in faint supernovae is characterized by a large amount of fall-back. We show that the abundance pattern of the recently discovered most Fe-poor star, HE0107-5240, and other extremely metal-poor carbon-rich stars are in good accord with those of black-hole-forming supernovae, but not pair-instability supernovae. This suggests that black-hole-forming supernovae made important contributions to the early Galactic (and cosmic) chemical evolution. Finally we discuss the nature of first (Pop III) Stars.

SN 2002ic is a unique supernova which shows the typical spectral features of Type la supernovae (SNe Ia) near maximum light, but also apparent hydrogen features that have been absent in SNe Ia (Hamuy et al. 2003). We have calculated hydrodynamical models for the interaction between the SN la ejecta and the H-rich circumstellar medium (CSM) to reproduce the observed features of SN 2002ic. Based on our modeling, possible progenitor systems of SN 2002ic are discussed.

The cosmic/galactic chemical evolutions have been modeled with the early metal enrichment by Type II supernovae (SNe II) and the delayed enrichment of Fe by Type Ia supernovae (SNe Ia). However, the exact nature of SN Ia progenitors have been obscure. Here we present the currently most plausible scenario of the progenitor binary systems of SNe Ia. This scenario involves strong winds from accreting white dwarfs, which introduces important metallicity effects, namely, low-metallicity inhibition of SNe Ia. Resultant predictions for the Galactic/cosmic chemical evolution and the cosmic SNe Ia rate are presented. Another importance of identifying the SN Ia progenitors lies in the use of SNe Ia as a “standard candle” to determine cosmological parameters. To examine whether the “evolution” of SNe Ia with redshift and metallicity is significant, we discuss how the metallicity affects the properties of the C+O white dwarfs such as the C/O ratio, and find the metallicity dependence is rather weak.

We discuss the properties of the very energetic Type Ic supernovae (SNe Ic) 1998bw and 1997ef, and of Type IIn supernova (SN IIn) 1997cy. SNe Ic 1998bw and 1997ef are characterized by their large luminosity and very broad spectral features. Their observed properties can be explained if they are very energetic SN explosions (EK ≳ 1 × 1052 erg), originating probably from the core collapse of the bare C+O cores of massive stars (~ 30–40M⊙). At late times, both the light curve and the spectra suggest that the explosion may have been asymmetric; this may help us understand the claimed connection with GRBs. Type IIn SN 1997cy is even more luminous than SN 998bw, and the light curve declines more slowly than the 56Co decay. We model such a light curve with circumstellar interaction, which requires the explosion energy of ~ 5 × 1052 erg. Because these kinetic energies of explosion are much larger than in normal core-collapse SNe, we call objects like these SNe “hypernovae”.