[en] The Portland cement industry is the main source of particulate air pollution in Kaohsiung city. Data in this study concern outdoor air pollution and the health of individuals living in communities in close proximity to Portland cement plants. The prevalence of delivery of preterm birth infants as significantly higher in mothers living within 0-2 km of a Portland cement plant than in mothers living within 2-4 km. After controlling for several possible confounders (including maternal age, season, marital status, maternal education, and infant sex), the adjusted odds ratio was 1.30 (95% I=1.09-1.54) for the delivery of preterm infants for mothers living close to he Portland cement plants, chosen at the start to be from 0 to 2 km. These data provide further support for the hypothesis that air pollution can affect he outcome of pregnancy

[en] The effects of contact electrode size on the photo-voltaic characteristics of polycrystalline-Si p-i-n solar cells have been studied, with respect to a unit-cell pitch size of 1 μm width. For the non-transparent Al contact electrode with a contact width of 0.05-0.2 μm, the short-circuit current is obviously reduced with increasing contact width, due to a larger area of optical reflection by the electrode. On the other hand, even when using a transparent ITO (indium-tin-oxide) electrode, a larger width of contact electrode may also cause a smaller short-circuit current, due to a larger area of optical absorption by the electrode. However, for this ITO electrode, the contact electrode of 0.05 μm width causes a smaller short-circuit current than that of 0.1 μm width, primarily ascribed to a smaller area for collecting carrier and a larger contact resistance. As a result, while using the ITO contact electrode to enhance the conversion efficiency of the solar cell, a proper width of contact electrode should be employed to optimize the photo-voltaic characteristics. (semiconductor devices)

[en] By using cavity ring-down absorption spectroscopy technique, we have observed the channel of Br₂ molecular elimination following photodissociation of CF₂Br₂ at 248 nm. A tunable laser beam, which is crossed perpendicular to the photolyzing laser beam in a ring-down cell, is used to probe the Br₂ fragment in the B ³Π_ou⁺-X ¹Σ_g⁺ transition. The vibrational population is obtained in a nascent state, despite ring-down time as long as 500-1000 ns. The population ratio of Br₂(v=1)/Br₂(v=0) is determined to be 0.4±0.2, slightly larger than the value of 0.22 evaluated by Boltzmann distribution at room temperature. The quantum yield of the Br₂ elimination reaction is also measured to be 0.04±0.01. This work provides direct evidence to support molecular elimination occurring in the CF₂Br₂ photodissociation and proposes a plausible pathway with the aid of ab initio potential-energy calculations. CF₂Br₂ is excited probably to the ¹B₁ and ³B₂ states at 248 nm. As the C-Br bond is elongated upon excitation, the coupling of the ¹A^'(¹B₁) state to the high vibrational levels of the ground state X-tilde ¹A^'(¹A₁) may be enhanced to facilitate the process of internal conversion. After transition, the highly vibrationally excited CF₂Br₂ feasibly surpasses a transition barrier prior to decomposition. According to the ab initio calculations, the transition state structure tends to correlate with the intermediate state CF₂Br+Br(CF₂Br···Br) and the products CF₂+Br₂. A sequential photodissociation pathway is thus favored. That is, a single C-Br bond breaks, and then the free-Br atom moves to form a Br-Br bond, followed by the Br₂ elimination. The formed Br-Br bond distance in the transition state tends to approach equilibrium such that the Br₂ fragment may be populated in cold vibrational distribution. Observation of a small vibrational population ratio of Br₂(v=1)/Br₂(v=0) agrees with the proposed mechanism

[en] High crystalline multi-walled carbon nanotubes with large inner diameters have been produced by a one-step synthesis method from ferrocene pyrolysis in a sealed pre-vacuumed quartz tube. Ferrocene serves as both catalyst and carbon source. The diameters of the as-produced carbon nanotubes have been observed by transmission electron microscope to be 40-60 nm with inner diameters of 20-40 t shells for the encapsulation experiments. The high crystallinity of the as-produced carbon nanotubes has also been characterized by Raman scattering and X-ray diffraction (XRD) measurements. (paper)

[en] By using cavity ring-down spectroscopy technique, we have observed the channel leading to Br₂ molecular elimination following photodissociation of bromoform at 248 nm. A tunable laser beam, which is crossed perpendicular to the photolysis laser beam in a ring-down cell, is used to probe the Br₂ fragment in the B ³Π_ou⁺-X ¹Σ_g⁺ transition using the range 515-524 nm. The ring-down time lasts 500 ns, so the rotational population of the Br₂ fragment may not be nascent nature, but its vibrational population should be. The vibrational population ratio of Br₂(v=1)/Br₂(v=0)=0.8±0.2 implies that the fragmented Br₂ is vibrationally hot. The quantum yield of the molecular elimination reaction is 0.23±0.05, consistent with the values of 0.26 and 0.16 reported in 234 and 267 nm photolysis of bromoform, respectively, using velocity ion imaging. A plausible photodissociation pathway is proposed, based upon this work and ab initio calculations. The A-tilde ¹A₂, B-tilde ¹E, and C-tilde ¹A₁ singlet states of bromoform are probably excited at 248 nm. These excited states may couple to the high vibrational levels of the ground state X-tilde ¹A₁ via internal conversion. This vibrationally excited bromoform readily surpasses a reaction barrier 389.6 kJ/mol prior to decomposition. The transition state structure tends to correlate with vibrationally hot Br₂. Dissociation after internal conversion of the excited states to vibrationally excited ground state should result in a large fraction of the available energy to be partitioned in vibrational states of the fragments. The observed vibrationally hot Br₂ fragment seems to favor the dissociation pathway from high vibrational levels of the ground state. Nevertheless, the other reaction channel leading to a direct impulsive dissociation from the excited states cannot be excluded

[en] The iridium(I) cyclooctadiene complex with two (3-tert-butylimidazol-2-ylidene) ligands [(H-Im"tBu)_2Ir(COD)]"+PF_6"− (C_2_2H_3_2PF_6IrN_4) has been prepared, and its crystal structure is determined by X-ray diffraction. Complex exhibits slightly distorted square planar configurations around the metal atom, which is coordinated by two H-Im"tBu ligands and one cyclooctadiene group. The new iridium carbene complex has a pair of hydrogen wing tips. The Ir−C_c_a_r_b_e_n_e bond lengths are 2.066(5) and 2.052(5) Å, and the bond angle C−Ir−C between these bonds is 95.54(19)°. The dihedral angle between two imidazol-2-ylidene rings is 86.42°.

[en] Isotropic and anisotropic NdFeB magnets were synthesized by spark plasma sintering (SPS) and SPS+HD (hot deformation), respectively, using melt-spun ribbons as the starting materials. Spark plasma sintered magnets sintered at low temperatures (<700 ⁰C) almost maintained the uniform fine grain structure inherited from rapid quenching. At higher temperatures, due to the local high-temperature field caused by the spark plasma discharge, the grain growth occurred at the initial particle surfaces and the coarse grain zones formed in the vicinity of the particle boundaries. Since the interior of the particles maintained the fine grain structure, a distinct two-zone structure was formed in the spark plasma sintered magnets. The SPS temperature and pressure have important effects on the widths of coarse and fine grain zones, as well as the grain sizes in two zones. The changes in grain structure led to variations in the magnetic properties. By employing low SPS temperature and high pressure, high-density magnets with negligible coarse grain zone and an excellent combination of magnetic properties can be obtained. An anisotropic magnet with a maximum energy product of ∼30 MG Oe was produced by the SPS+HD process. HD at 750 ⁰C did not lead to obvious grain growth and the two-zone structure still existed in the hot deformed magnets. Intergranular exchange coupling was demonstrated in the spark plasma sintered magnets and was enhanced by the HD process, which reduced the coercivity. Good temperature stability was manifested by low temperature coefficients of remanence and coercivity. The results indicated that nanocrystalline NdFeB magnets without significant grain growth and with excellent properties could be obtained by SPS and HD processes.

[en] Following photodissociation of CH₂Br₂ at 248 nm, Br₂ molecular elimination is detected by using a tunable laser beam, as crossed perpendicular to the photolyzing laser beam in a ring-down cell, probing the Br₂ fragment in the B ³Π_ou⁺-X ¹Σ_g⁺ transition. The nascent vibrational population is obtained, yielding a population ratio of Br₂(v=1)/Br₂(v=0) to be 0.7±0.2. The quantum yield for the Br₂ elimination reaction is determined to be 0.2±0.1. Nevertheless, when CH₂Br₂ is prepared in a supersonic molecular beam under cold temperature, photofragmentation gives no Br₂ detectable in a time-of-flight mass spectrometer. With the aid of ab initio potential energy calculations, a plausible pathway is proposed. Upon excitation to the ¹B₁ or ³B₁ state, C-Br bond elongation may change the molecular symmetry of C_s and enhance the resultant 1 ^1,3A^'-X-tilde¹A^' (or 1 ^1,3B₁-X-tilde¹A₁ as C_2v is used) coupling to facilitate the process of internal conversion, followed by asynchronous concerted photodissociation. Temperature dependence measurements lend support to the proposed pathway

[en] Luminescent gold nanoclusters (AuNCs) with good biocompatibility have gained much attention in bio-photonics. In addition, they also exhibit a unique photo-physical property, namely thermally activated delayed fluorescence (TADF), by which both singlet and triplet excitons can be harvested. The combination of their non-toxic material property and unique TADF behavior makes AuNCs biocompatible nano-emitters for bio-related light-emitting devices. Unfortunately, the TADF emission is quenched when colloidal AuNCs are transferred to solid states under ambient environment. Here, a facile, low-cost and effective method was used to generate efficient and stable TADF emissions from solid AuNCs under ambient environment using polyvinyl alcohol as a solid matrix. To unravel the underlying mechanism, temperature-dependent static and transient photoluminescence measurements were performed and we found that two factors are crucial for solid TADF emission: small energy splitting between singlet and triplet states and the stabilization of the triplet states. Solid TADF films were also deposited on the flexible plastic substrate with patterned structures, thus mitigating the waveguide-mode losses. In addition, we also demonstrated that warm white light can be generated based on a co-doped single emissive layer, consisting of non-toxic, solution-processed TADF AuNCs and fluorescent carbon dots under UV excitation. (paper)

[en] Heavy-metal-containing quantum dots (QDs) with engineered electronic states have been served as luminophores in luminescent solar concentrators (LSCs) with impressive optical efficiency. Unfortunately, those QDs involve toxic elements and need to be synthesized in a hazardous solvent. Recently, biocompatible, eco-friendly gold nanoclusters (AuNCs), which can be directly synthesized in an aqueous solution, have gained much attention for promising applications in ‘green photonics’. Here, we explored the solid-state photophysical properties of aqueous-solution-processed, glutathione-stabilized gold nanoclusters (GSH-AuNCs) with a ligand-to-metal charge-transfer (LMCT) state for developing ‘green’ LSCs. We found that such GSH-AuNCs exhibit a large Stokes shift with almost no spectral overlap between the optical absorption and PL emission due to the LMCT states, thus, suppressing reabsorption losses. Compared with GSH-AuNCs in solution, the photoluminescence quantum yields (PL-QYs) of the LSCs can be enhanced, accompanied with a lengthened PL lifetime owing to the suppression of non-radiative recombination rates. In addition, the LSCs do not suffer from severe concentration-induced PL quenching, which is a common weakness for conventional luminophores. As a result, a common trade-off between light-harvesting efficiency and solid-state PL-QYs can be bypassed due to nearly-zero spectral overlap integral between the optical absorption and PL emission. We expect that GSH-AuNCs hold great promise for serving as luminophores for ‘green’ LSCs by further enhancing solid-state PL-QYs. (paper)