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Recent studies on the temperatures of red supergiants (RSGs) in the local universe provide us with an excellent observational constraint on RSG models. We calibrate the mixing length parameter by comparing model predictions with the empirical RSG temperatures in Small and Large Magellanic Clouds, Milky Way, and M31, which are inferred from the TiO band and the spectral energy distribution (SED). Although our RSG models are computed with the MESA code, our result may be applied to other stellar evolution codes, including the BEC and TWIN codes. We find evidence that the mixing length increases with increasing metallicity for both cases where the TiO and SED temperatures of RSGs are used for the calibration. Together with the recent finding of a similar correlation in lowmass red giants by Tayar et al, this implies that the metallicity dependence of the mixing length is a universal feature in post-main sequence stars of both low and high masses. Our result implies that typical Type IIP supernova (SN IIP) progenitors with initial masses of ∼ 10 − 16 M ⊙ have a radius range of 400R ⊙ R 800R ⊙ regardless of metallicity. As an auxiliary result of this study, we find that the hydrogen-rich envelope mass of SN IIP progenitors for a given initial mass is predicted to be largely independent of metallicity if the Ledoux criterion with slow semiconvection is adopted, while the Schwarzschild models predict systematically more massive hydrogen-rich envelopes for lower metallicity.

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We investigate the effects of winds on the observational properties of Type Ib and Ic supernova (SN Ib/Ic) progenitors using spectral models constructed with the non-LTE stellar atmospheric code CMFGEN. We consider SN Ib/Ic progenitor models of the final mass range of 2.16–9.09 M ⊙ having different surface temperatures and chemical compositions, and calculate the resulting spectra for various wind mass-loss rates and wind terminal velocities. We find that the progenitors having an optically thick wind would become brighter in the optical for a higher mass-loss rate (or a lower wind terminal velocity) because of the formation of the photosphere in the extended wind matter and the contribution from free–free and line emissions from the wind. As a result, for the standard Wolf-Rayet wind mass-loss rate, helium-deficient compact SN Ic progenitors would be brighter in the optical by ∼3 mag compared to the case without the wind effects. We also find that the color dependence on the photospheric temperature is non-monotonic because of the wind effects. Our results imply that inferring the progenitor mass, bolometric luminosity, and effective temperature from the optical observation using the standard stellar evolution model prediction can be misleading. By comparing our fiducial model predictions with the detection limits of the previous SN Ib/Ic progenitor searches, we conclude that a deep search with an optical absolute magnitude larger than ∼−4 is needed to directly identify most of the ordinary SN Ib/Ic progenitors. We discuss implications of our results for the observed SN Ib/Ic progenitor candidates for iPTF13bvn, SN 2019vyr, and SN 2017ein.

The electromagnetic interference (EMI) shielding effectiveness (SE) of Ultra-High Performance Concrete (UHPC) mixed with carbon nanotubes (CNTs) (UHPC/CNT composites) having a thickness of 200 mm in the frequency range of 10 kHz to 18 GHz was investigated according to IEEE-STD-299 for the first time. In addition, the effect of the size of the incident area on the SE was analyzed by comparing the SE results for two different incident areas: a small incident area of 300 × 300 mm 2 and a large incident area of 1200 × 1200 mm 2. A significant improvement in the SE of the UHPC/CNT composite was achieved by increasing the CNT content up to the percolation threshold. Experimental observations indicated that the small incident area caused a distortion of the SE in the magnetic field owing to the aperture effect, whereas it had little effect on the SE for a plane wave. Thus, to eliminate the effect of the aperture on the measurement of the SE for UHPC/CNT composites in a magnetic field, an incident area larger than 1200 × 1200 mm 2 is recommended. According to a statistical analysis of the experimental results, a practical model was proposed to estimate the SE of cementitious material for different frequency ranges. INDEX TERMS Carbon nanotube (CNT), electromagnetic interference (EMI), IEEE-STD-299, shielding effectiveness (SE), ultra-high performance concrete (UHPC).