Vat-polymerization 3D printing (3DP) enables the high speed printing of precise and intricate 3D models, yet it inevitably produces highly crosslinked polymers that are not easily degradable or ...recyclable. Here, the author highlights recent work that realizes the formation of fully degradable polymers based on organocatalytic vat-ring-opening photopolymerization 3DP.
Liquefaction and solidification of materials are the most fundamental changes observed during thermal phase transitions, yet the design of organic and polymeric soft materials showing isothermal ...reversible liquid-nonliquid conversion remains challenging. Here, we demonstrate that solvent-free repeatable molecular architectural transformation between liquid-star and nonliquid-network polymers that relies on cleavage and reformation of a covalent bond in hexaarylbiimidazole. Liquid four-armed star-shaped poly(n-butyl acrylate) and poly(dimethyl siloxane) with 2,4,5-triphenylimidazole end groups were first synthesized. Subsequent oxidation of the 2,4,5-triphenylimidazoles into 2,4,5-triphenylimidazoryl radicals and their coupling with these liquid star polymers to form hexaarylbiimidazoles afforded the corresponding nonliquid network polymers. The resulting nonliquid network polymers liquefied upon UV irradiation and produced liquid star-shaped polymers with 2,4,5-triphenylimidazoryl radical end groups that reverted to nonliquid network polymers again by recoupling of the generated 2,4,5-triphenylimidazoryl radicals immediately after terminating UV irradiation.The design of organic and polymeric soft materials showing isothermal reversible liquid-nonliquid conversion is challenging. Here, the authors show solvent-free repeatable molecular architectural transformation between liquid-star and non-liquid-network polymers by the cleavage and reformation of covalent bonds in the polymer chain.
It has been suggested that Fe abundances of K dwarfs derived from Fe i and Fe ii lines show considerable discrepancies, and oxygen abundances determined from high-excitation O i 7771-5 triplet lines ...are appreciably overestimated (the problem becoming more serious toward lower Teff), which, however, has not yet been widely confirmed. With the aim of clarifying this issue, we spectroscopically determined the atmospheric parameters of 148 G-K dwarfs (Hyades cluster stars and field stars) by assuming the classical Fe i/Fe ii ionization equilibrium as usual, and determined their oxygen abundances by applying the non-local thermal equilibrium spectrum fitting analysis to O i 7771-5 lines. It turned out that the resulting parameters did not show any significant inconsistency with those determined by other methods (for example, the mean differences in Teff and from the well-determined solutions of Hyades dwarfs are mostly 100 K and 0.1 dex). Likewise, the oxygen abundances of Hyades stars are around O/H ∼ +0.2 dex (consistent with the metallicity of this cluster) without exhibiting any systematic Teff-dependence. Accordingly, we conclude that parameters can be spectroscopically evaluated to a sufficient precision in the conventional manner (based on the Saha-Boltzmann equation for Fe i/Fe ii) and oxygen abundances can be reliably determined from the O i 7771-5 triplet for K dwarfs as far as stars of Teff 4500 K are concerned. We suspect that previously reported strongly Teff-dependent discrepancies may have stemmed mainly from overestimation of weak-line strengths and/or improper Teff scale.
We report the latest statistical analyses of superflares on solar-type (G-type main-sequence; effective temperature is 5100-6000 K) stars using all of the Kepler primary mission data and Gaia Data ...Release 2 catalog. We updated the flare detection method from our previous studies by using a high-pass filter to remove rotational variations caused by starspots. We also examined the sample biases on the frequency of superflares, taking into account gyrochronology and flare detection completeness. The sample sizes of solar-type and Sun-like stars (effective temperature is 5600-6000 K and rotation period is over 20 days in solar-type stars) are ∼4 and ∼12 times, respectively, compared with Notsu et al. As a result, we found 2341 superflares on 265 solar-type stars and 26 superflares on 15 Sun-like stars; the former increased from 527 to 2341 and the latter from three to 26 events compared with our previous study. This enabled us to have a more well-established view on the statistical properties of superflares. The observed upper limit of the flare energy decreases as the rotation period increases in solar-type stars. The frequency of superflares decreases as the stellar rotation period increases. The maximum energy we found on Sun-like stars is 4 × 1034 erg. Our analysis of Sun-like stars suggests that the Sun can cause superflares with energies of ∼7 × 1033 erg (∼X700-class flares) and ∼1 × 1034 erg (∼X1000-class flares) once every ∼3000 and ∼6000 yr, respectively.
Selective dye loading at the polymer/fullerene interface was studied for ternary blend bulk heterojunction solar cells, consisting of regioregular poly(3‐hexylthiophene) (RR‐P3HT), a fullerene ...derivative (PCBM), and a silicon phthalocyanine derivative (SiPc) as a light‐harvesting dye. The photocurrent density and power conversion efficiency of the ternary blend solar cells were most improved by loading SiPc with a content of 4.8 wt%. The absorption and surface energy measurements suggested that SiPc is located in the disordered P3HT domains at the RR‐P3HT/PCBM interface rather than in the PCBM and crystal P3HT domains. From the peak wavelength of SiPc absorption, the local concentration of SiPc (SiPcLocal) was estimated for the RR‐P3HT:PCBM:SiPc ternary blends. Even for amorphous films of regiorandom P3HT (RRa‐P3HT) blended with PCBM and SiPc, SiPcLocal was higher than the original content, suggesting dye segregation into the RRa‐P3HT/PCBM interface. For RR‐P3HT:PCBM:SiPc blends, SiPcLocal increased with the increase in the P3HT crystallinity. Such interfacial segregation of dye molecules in ternary blend films can be rationally explained in terms of the surface energy of each component and the crystallization of P3HT being enhanced by annealing. Notably, the solvent annealing effectively segregated dye molecules into the interface without the formation of PCBM clusters.
Selective dye loading at the polymer/fullerene interface improves the photocurrent density and power conversion efficiency of ternary blend bulk heterojunction solar cells. Such interfacial segregation of NIR‐dye molecules in ternary blend films can be rationally explained in terms of the surface energy of each component and the crystallization of polymer enhanced by annealing.
We report the latest view of Kepler solar-type (G-type main-sequence) superflare stars, including recent updates with Apache Point Observatory (APO) 3.5 m telescope spectroscopic observations and ...Gaia-DR2 data. First, we newly conducted APO 3.5 m spectroscopic observations of 18 superflare stars found from Kepler 1-minute time-cadence data. More than half (43 stars) are confirmed to be "single" stars, among 64 superflare stars in total that have been spectroscopically investigated so far in this APO 3.5 m and our previous Subaru/HDS observations. The measurements of v sin i (projected rotational velocity) and chromospheric lines (Ca ii H and K and Ca ii λ8542) support that the brightness variation of superflare stars is caused by the rotation of a star with large starspots. We then investigated the statistical properties of Kepler solar-type superflare stars by incorporating Gaia-DR2 stellar radius estimates. As a result, the maximum superflare energy continuously decreases as the rotation period Prot increases. Superflares with energies 5 × 1034 erg occur on old, slowly rotating Sun-like stars (Prot ∼ 25 days) approximately once every 2000-3000 yr, while young, rapidly rotating stars with Prot ∼ a few days have superflares up to 1036 erg. The maximum starspot area does not depend on the rotation period when the star is young, but as the rotation slows down, it starts to steeply decrease at Prot 12 days for Sun-like stars. These two decreasing trends are consistent since the magnetic energy stored around starspots explains the flare energy, but other factors like spot magnetic structure should also be considered.
We searched for superflares on solar-type stars using Kepler data with 1-min sampling in order to detect superflares with a short duration. We found 187 superflares on 23 solar-type stars whose ...bolometric energy ranges from the order of 10
32
to 10
36
erg. Some superflares show multiple peaks with the peak separation of the order of 100 to 1,000 s which is comparable to the periods of quasi-periodic pulsations in solar and stellar flares. Using these new data combined with the results from the data with 30-min sampling, we found that the occurrence frequency (dN/dE) of superflares as a function of flare energy (
E
) shows the power-law distribution (dN/dE∝
E
−
α
) with
α
∼−1.5 for 10
33
<
E
<10
36
erg which is consistent with the previous results. The average occurrence rate of superflares with the energy of 10
33
erg which is equivalent to X100 solar flares is about once in 500 to 600 years. The upper limit of energy released by superflares is basically comparable to a fraction of the magnetic energy stored near starspots which is estimated from the photometry.
We also found that the duration of superflares (
τ
) increases with the flare energy (
E
) as
τ
∝
E
0.39 ± 0.03
. This can be explained if we assume the time scale of flares is determined by the Alfvén time.
Multi-colored dye-sensitized polymer/fullerene solar cells with two different near-IR dyes, silicon phthalocyanine bis(trihexylsilyl oxide) (SiPc) and silicon naphthalocyanine bis(trihexylsilyl ...oxide) (SiNc), enhanced power conversion efficiency up to 4.3%, compared to that of the individual ternary blend solar cells with a single dye under AM1.5G illumination.
Multi-colored dye-sensitized polymer/fullerene solar cells with two different near-IR dyes, silicon phthalocyanine bis(trihexylsilyl oxide) (SiPc) and silicon naphthalocyanine bis(trihexylsilyl oxide) (SiNc), enhanced power conversion efficiency up to 4.3%, compared to that of the individual ternary blend solar cells with a single dye.
The integration of high-speed light emitters on silicon chips is an important issue that must be resolved in order to realize on-chip or interchip optical interconnects. Here, we demonstrate the ...first electrically driven ultrafast carbon nanotube (CNT) light emitter based on blackbody radiation with a response speed (1–10 Gbps) that is more than 106 times higher than that of conventional incandescent emitters and is either higher than or comparable to that of light-emitting diodes or laser diodes. This high-speed response is explained by the extremely fast temperature response of the CNT film, which is dominated by the small heat capacity of the CNT film and its high heat dissipation to the substrate. Moreover, we experimentally demonstrate 140 ps width pulsed light generation and real-time optical communication. This CNT-based emitter with the advantages of ultrafast response speeds, a small footprint, and integration on silicon can enable novel architectures for optical interconnects, photonic, and optoelectronic integrated circuits.
Aim: Omega-3 fatty acids have emerged as a new option for controlling the residual risk for coronary artery disease (CAD) in the statin era. Eicosapentaenoic acid (EPA) is associated with reduced CAD ...risk in the Reduction of Cardiovascular Events with Icosapent Ethyl-Intervention trial, whereas the Statin Residual Risk with Epanova in High Cardiovascular Risk Patients with Hypertriglyceridemia trial that used the combination EPA/docosahexaenoic acid (DHA) has failed to derive any clinical benefit. These contradictory results raise important questions about whether investigating the antiatherosclerotic effect of omega-3 fatty acids could help to understand their significance for CAD-risk reduction. Methods: The Attempts at Plaque Vulnerability Quantification with Magnetic Resonance Imaging Using Noncontrast T1-weighted Technic EPA/DHA study is a single-center, triple-arm, randomized, controlled, open-label trial used to investigate the effect of EPA/DHA on high-risk coronary plaques after 12 months of treatment, detected using cardiac magnetic resonance (CMR) in patients with CAD receiving statin therapy. Eligible patients were randomly assigned to no-treatment, 2-g/day, and 4-g/day EPA/DHA groups. The primary endpoint was the change in the plaque-to-myocardium signal intensity ratio (PMR) of coronary high-intensity plaques detected by CMR. Coronary plaque assessment using computed tomography angiography (CTA) was also investigated. Results: Overall, 84 patients (mean age: 68.2 years, male: 85%) who achieved low-density lipoprotein cholesterol levels of ＜100 mg/dL were enrolled. The PMR was reduced in each group over 12 months. There were no significant differences in PMR changes among the three groups in the primary analysis or analysis including total lesions. The changes in CTA parameters, including indexes for detecting high-risk features, also did not differ. Conclusion: The EPA/DHA therapy of 2 or 4 g/day did not significantly improve the high-risk features of coronary atherosclerotic plaques evaluated using CMR under statin therapy.
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