Progenitors of Type Ib and Ic supernovae (SNe) are stripped envelope stars and provide important clues on the mass-loss history of massive stars. Direct observations of the progenitors before the supernova explosion would provide strong constraints on the exact nature of SN Ib/Ic progenitors. Given that stripped envelope massive stars can have an optically thick wind as in the case of Wolf-Rayet stars, the influence of the wind on the observational properties needs to be properly considered to correctly infer progenitor properties from pre-SN observations. Non-LTE stellar atmosphere models indicate that the optical brightness could be greatly enhanced with an optically thick wind because of lifting-up of the photosphere from the stellar surface to the wind matter, and line and free-free emissions. So far, only a limited number of SN Ib/Ic progenitor candidates have been reported, including iPTF13bvn, SN 2017ein and SN 2019yvr. We argue that these three candidates are a biased sample, being unusually bright in the optical compared to what is expected from typical SN Ib/Ic progenitors, and that mass-loss enhancement during the final evolutionary stage can explain their optical properties.

A CoCrFeNiMn high-entropy alloy (HEA), in the form of a face-centered cubic (fcc) solid solution, was processed by high-pressure torsion (HPT) to produce a nanocrystalline (nc) HEA. Significant grain refinement was achieved from the very early stage of HPT through 1/4 turn and an nc structure with an average grain size of ∼40 nm was successfully attained after 2 turns. The feasibility of significant microstructural changes was attributed to the occurrence of accelerated atomic diffusivity under the torsional stress during HPT. Nanoindentation experiments showed that the hardness increased significantly in the nc HEA during HPT processing and this was associated with additional grain refinement. The estimated values of the strain-rate sensitivity were maintained reasonably constant from the as-cast condition to the nc alloy after HPT through 2 turns, thereby demonstrating a preservation of plasticity in the HEA. In addition, a calculation of the activation volume suggested that the grain boundaries play an important role in the plastic deformation of the nc HEA where the flow mechanism is consistent with other nc metals. Transmission electron microscopy showed that, unlike conventional fcc nc metals, the nc HEA exhibits excellent microstructural stability under severe stress conditions.

Sesame (Sesamum indicum L.) is one of the oldest oil crops and is widely cultivated in Asia and Africa. The aim of this study was to assess the genetic diversity, phylogenetic relationships and population structure of 277 sesame core collection accessions collected from 15 countries in four different continents. A total of 158 alleles were detected among the sesame accessions, with the number varying from 3 to 25 alleles per locus and an average of 11.3. Polymorphism information content values ranged from 0.34 to 0.84, with an average of 0.568. These values indicated a high genetic diversity at 14 loci both among and within the populations. Of these, 44 genotype-specific alleles were identified in 12 of the 14 polymorphic simple sequence repeat markers. The core collection preserved a much higher level of genetic variation. Therefore, 10.1% was selected as the best sampling percentage from the whole collection when constructing the core collection. The 277 core collection accessions formed four robust clusters in the unweighted pair group method and the arithmetic averages (UPGMA) dendrogram, although the clustering did not indicate any clear division among the sesame accessions based on their geographical locations. Similar patterns were obtained using model-based structure analysis and country-based dendrograms, as some accessions situated geographically far apart were grouped together in the same cluster. The results of these analyses will increase our understanding of the genotype-specific alleles, genetic diversity and population structure of core collections, and the information can be used for the development of a future breeding strategy to improve sesame yield.

The numerical approach of Lee et al. [Trans. Korean Soc. Mech. Eng., A28, 816–825 (2004)] to spherical indentation technique for property evaluation of hyperelastic rubber is enhanced. The Yeoh model is adopted as the constitutive form of rubber material because it can express well large deformation and cover various deformation modes with a simple form. We first determine the friction coefficient between a rubber specimen and a spherical indenter in a practical viewpoint and perform finite element simulations for a deeper indentation depth than that selected by Lee et al. [Trans. Korean Soc. Mech. Eng., A28, 816–825 (2004)]. An optimal data acquisition spot is selected, which features sufficiently large strain energy density and negligible frictional effect. We improve then two normalized functions mapping an indentation load–displacement curve onto a strain energy density–invariant curve, the latter of which gives the Yeoh model constants. The enhanced spherical indentation approach successfully produces the rubber material properties with an average error of less than 5%. The validity of our developed approach is verified by experimental evaluation of material properties with three kinds of rubber materials.

Despite numerous previous studies, relationships between watershed land use and adjacent streams and rivers at various scales in Korea remain unclear. This study investigated the relationships between land uses and the physical, chemical, and biological characteristics of 720 sites of streams and rivers across the country. The land uses at two spatial scales, including a 1-km buffer and the base watershed management region (BWMR), were computed in a geographical information system (GIS) with a digital land use/land cover map. Characteristics of land uses at two spatial scales were then correlated with the monitored multidimensional characteristics of the streams and rivers. The results of this study indicate that land use types have significant effects on stream and river characteristics. Specifically, most characteristics were negatively correlated with the proportions of urban, rice paddy, agricultural, and bare soil areas and positively correlated with the amount of forest. The site-scale and BWMR-scale analyses suggest that BWMR land use patterns were more strongly related to ecological integrity than they were to site land use patterns. Improving our understanding of land use effects will largely depend on relating the results of site-specific studies that use similar response techniques and measures to evaluate ecological integrity. In addition, our results clearly indicate that the characteristics of streams and rivers are closely linked and that land use types differentially affect those characteristics. Thus, effective restoration and management for ecological integrity of lotic system should consider the physical, chemical, and biological factors in combination.

Conical indentation methods to determine residual stress are proposed by examining the finite element solutions based on the incremental plasticity theory. We first note that hardness depends on the magnitude and sign of residual stress and material properties and can change by up to 20% over a specific range of elastic tensile and compressive residual stress, although some prior indentation studies reported that hardness is hardly affected by residual stress. By analyzing the characteristics of conical indentation, we then select some normalized indentation parameters, which are free from the effect of indenter tip rounding. Adopting dimensional analysis, we present practical conical indentation methods for the evaluation of elastic/plastic equi- and nonequi-biaxial residual stresses. The validity of developed approaches is confirmed by applying them to the experimental evaluation of four-point bending stress.

A systematic study on the effect of sputtering deposition parameters on material properties of Al doped ZnO (ZnO:Al) films prepared by an in-line rf magnetron sputtering and on surface morphology of the films after wet etching process was carried out. For application to silicon thin film solar cells as a front electrode, the as-deposited films were surface-textured by a dilute HCl solution to improve the light scattering properties such as haze and angle resolved distribution of scattered light on the film surfaces. The microstructure of as-deposited films is affected significantly by the working pressure and film compactness decreases with increasing working pressure from 1.5 mTorr to 10 mTorr. High quality ZnO:Al films with electrical resistivity of 4.25 × 10-4 Ω cm and optical transmittance of 80% in a visible range are obtained at low working pressure of 1.5 mTorr and substrate temperature of 100℃. Crater-like surface morphologies are observed on the textured ZnO:Al films after wet etching. The size and shape of craters are closely dependent on the microstructure and film compactness of as-deposited films. Haze values of the textured ZnO:Al films are improved in a whole wavelength of 300 – 1100 nm compared to commercial SnO2:F films (Asahi U type) and incident light on the textured films is scattered effectively with 30° angle.

We report on the basic characteristics and gas sensing operation of density controlled single-walled carbon nanotube (SWCNT) thin films on poly(dimethyl siloxane) (PDMS) substrates The vacuum filteration and PDMS mold transfer method allowed the density of SWCNT distributed to have non-local uniformity. The optical transparency of the SWCNT thin films was inversely proportional to SWCNT density and conductivity. The flexible SWCNT thin film showed high mechanical stability with negligible change in conductance after being bent by 180o. We evaluated its gas sensing operation depending on SWCNT density and bias voltage. It was shown that lower SWCNT density thin films had higher sensitivity to NH3 gas, which may be due to higher exposed surface area for lower density SWCNT thin films. Also, we found that lower bias voltage devices showed faster recovery times. The results show that vacuum filteration and mold transfer method produced flexible SWCNT thin films that have stable mechanical and electrical characteristics and also stable gas sensing capabilities making them applicable to future flexible integrated sensors.

For the first time, we have taken into account the detailed systematic variation of horizontal-branch (HB) morphology with age and metallicity in our population synthesis models and they result that the integrated Hβ index is significantly affected by the presence of blue HB stars. As a matter of fact, due to the systematic HB morphology variation, it is found that Hβ does not monotonically decrease as metallicity increases at given ages, but shows a kind of wavy feature. According to our models, a systematic difference between the globular cluster system in the Milky Way Galaxy and that in NGC 1399 in the Hβ vs. Mg2 plane is explained if globular cluster systems in giant elliptical galaxies are a couple of billion years older, in the mean, than the Galactic counterpart.

We present our recent revision of model constructions for the horizontal-branch (HB) morphology of globular clusters, which suggests the HB morphology is more sensitive to age compared to our earlier models. We also present our high precision CCD photometry for the classic second parameter pair M3 and M13. The relative age dating based on this photometry indicates that M13 is indeed older than M3 by 1.7 Gyr. This is consistent with the age difference predicted from our new models, which provides a further support that the HB morphology is a reliable age indicator in most population II stellar systems.

Amorphous silicon films were prepared by dc reactive magnetron sputtering under conditions approaching the phase transition to microcrystallinity. Using TEM imaging these films were found to contain clusters of 5 to 50 nm sized Si crystallites embedded in an amorphous silicon matrix. Photocapacitance and transient photocurrent sub-band-gap optical spectra of this material appear to consist of a superposition of a spectrum typical of amorphous silicon together with an optical transition, with a threshold near 1. 1eV, that exhibits a very large optical cross section. This transition arises from valence band electrons being optically inserted into empty levels lying within the amorphous silicon mobility gap. Using modulated photocurrent methods we have determined that these states also dominate the electron deep trapping in this material. We argue that these states arise from defects at the crystalline-amorphous boundary.

We have studied the degradation kinetics of undoped a-Si:H films which contain a significant fraction of silicon microcrystallites. The degradation rate is found to be exceptionally slow in the first stage of degradation, then the defect density follows the “normal” t1/3rate and finally saturates. We present a model which relates this abnormal kinetics to the microcrystallites which are embedded in the amorphous matrix.

The hydrogenation effect was studied in the fabrication of amorphous silicon thin film transistor using APCVD technique. The inverse staggered type a-Si TFTs were fabricated with the deposited a-Si and SiO2 films by the atmospheric pressure (AP) CVD. The field effect mobility of the fabricated a-Si TFT is 0.79 cm2/Vs and threshold voltage is 5.4V after post hydrogenation. These results can be applied to make low cost a-Si TFT array using an in-line APCVD system.

We have studied the preparation and device application of a-Si by atmospheric pressure CVD using disilane. The deposition rate of a-Si increases with the partial pressure of disilane and with the total pressure. The deposition rate of APCVD a-Si is, therefore, very high compared with LPCVD. The photosensitivity of APCVD a-Si is 104 at 100mW/cm2. We have made an inverse staggered type a-Si TFT using SiO2 as a gate insulator. The on/off current ratio and field effect mobility are 105 and 0.19cm2/Vs, respectively.

We studied the layer by layer deposition technique of a-Si:H film, where the hydrogen radicals are exposed between the deposition of each layer. The effects of each layer thickness and hydrogen radical exposure time on the electrical and optical properties were studied. With the decrease of the each layer thickness, more hydrogen is involved in the network if the structure is still amorphous, but the hydrogen content is very small for microcrystal Si formed by long exposure to hydrogen radicals in between the depositions of thin layers.