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Major accidents such as the Space Shuttle Challenger disaster in the USA, the Bhopal Disaster in India, the Fukushima nuclear accident in Japan, and the Tianjin Port fire and explosion accident in China, have occurred all over the world. Safety scientists are always trying to understand why these accidents happened and how to prevent these accidents. Accident models and theories form the basis for many safety research fields and practices. However, there is no universally accepted model with useful elements relating to understanding accident causation, although many accident causation models exist. A new accident causation theory named the Interaction Theory of Hazard-Target System (ITHTS) is proposed based on Systems-Theoretic Accident Model and Processes (STAMP) and Risk Management Framework (RMF), which not only incorporates human, organisational and technological characteristics in the same framework, but also considers the sociological factors such as legislative, regulatory, and cultural factors. On the other hand, a new systemic accident analysis method of work systems (SAAMWS) is proposed based on ITHTS and STAMP because ITHTS cannot be applied directly in accident analysis. We choose Tianjin Port fire and explosion accident as a case study to demonstrate the explanatory power of Interaction Theory of Hazard-target System and the feasibility of the new accident analysis method. Further research needs to be done to assess the reliability and validity of this new systemic accident analysis method. [ABSTRACT FROM AUTHOR]

The photophysical properties of the natural pigment violacein extracted from an Antarctic organism adapted to high exposure levels of UV radiation were measured in a combined steady-state and time-resolved spectroscopic study for the first time. In the low-viscosity solvents methanol and acetone, violacein exhibits low fluorescence quantum yields on the order of 1 × 10-4, and femtosecond transient absorption measurements reveal excited-state lifetimes of 3.2 ± 0.2 and 4.5 ± 0.2 ps in methanol and acetone, respectively. As solvent viscosity is increased, both the fluorescence quantum yield and excited-state lifetime of this intensely colored pigment increase dramatically, and stimulated emission decays 30-fold more slowly in glycerol than in methanol at room temperature. Excited-state deactivation is suggested to occur via a molecular-rotor mechanism in which torsion about an interring bond leads to a conical intersection with the ground state. [ABSTRACT FROM AUTHOR]

Melamine may have been an important prebiotic information carrier, but its excited-state dynamics, which determine its stability under UV radiation, have never been characterized. The ability of melamine to withstand the strong UV radiation present on the surface of the early Earth is likely to have affected its abundance in the primordial soup. Here, we studied the excited-state dynamics of melamine (a proto-nucleobase) and its lysine derivative (a proto-nucleoside) using the transient absorption technique with a UV pump, and UV and infrared probe pulses. For melamine, the excited-state population decays by internal conversion with a lifetime of 13 ps without coupling significantly to any photochemical channels. The excited-state lifetime of the lysine derivative is slightly longer (18 ps), but the dominant deactivation pathway is otherwise the same as for melamine. In both cases, the vast majority of excited molecules return to the electronic ground state on the aforementioned time scales, but a minor population is trapped in a long-lived triplet state. [ABSTRACT FROM AUTHOR]

The excited-state dynamics of two cyclic DNA miniduplexes, each containing just two base pairs, are investigated using time-resolved infrared spectroscopy. As in longer DNA duplexes, intrastrand electron transfer induced by UV excitation triggers interstrand proton transfer in the alternating miniduplex containing two out-of-phase G·C base pairs. The resulting excited state decays on a time scale of several tens of picoseconds. This state is absent when one of the two G residues is substituted by 8-oxo-7,8-dihydroguanine, a modification that is suggested to disrupt base stacking, while maintaining base pairing. These findings demonstrate that a nucleobase tetramer arranged as two stacked base pairs accurately captures the interplay between intrastrand and interstrand decay channels. The similar signals seen in the miniduplexes and longer sequences suggest that excited states in the latter rapidly localize on two adjacent base pairs. [ABSTRACT FROM AUTHOR]

Femtosecond time-resolved IR spectroscopyis used to investigatethe excited-state dynamics of a dinucleotide containing an 8-oxoguanineanion at the 5′-end and neutral adenine at the 3′-end.UV excitation of the dinucleotide transfers an electron from deprotonated8-oxoguanine to its π-stacked neighbor adenine in less than1 ps, generating a neutral 8-oxoguanine radical and an adenine radicalanion. These species are identified by the excellent agreement betweenthe experimental and calculated IR difference spectra. The quantumefficiency of this ultrafast charge shift reaction approaches unity.Back electron transfer from the adenine radical anion to the 8-oxguanineneutral radical occurs in 9 ps, or approximately 6 times faster thanbetween the adenine radical anion and the 8-oxoguanine radical cation(Zhang, Y. et al. Proc. Natl. Acad. Sci. U.S.A.2014, 111, 11612–11617). The largeasymmetry in forward and back electron transfer rates is fully rationalizedby semiclassical nonadiabatic electron transfer theory. Forward electrontransfer is ultrafast because the driving force is nearly equal tothe reorganization energy, which is estimated to lie between 1 and2 eV. Back electron transfer is highly exergonic and takes place muchmore slowly in the Marcus inverted region. [ABSTRACT FROM AUTHOR]

UV radiation creates excited states in DNA that lead to mutagenic photoproducts. Photoexcitation of single-stranded DNA can transfer an electron between stacked bases, but the fate of excited states in the double helix has been intensely debated. Here, photoinduced interstrand proton transfer (PT) triggered by intrastrand electron transfer (ET) is detected for the first time by time-resolved vibrational spectroscopy and quantum mechanical calculations. Long-lived excited states are shown to be oppositely charged base pair radical ions. In two of the duplexes, the base pair radical anions are present as tautomers formed by interstrand PT. Charge recombination occurs on the picosecond time scale preventing the accumulation of damaging radicals or mutagenic tautomers. [ABSTRACT FROM AUTHOR]

During the early evolution of life, 8-oxo-7,8-dihydro-2'-deoxyguano-sine (O) may have functioned as a proto-flavin capable of repairing cyclobutane pyrimidine dimers in DNA or RNA by photoinduced electron transfer using longer wavelength UVB radiation. To investigate the ability of O to act as an excited-state electron donor, a dinucleotide mimic of the FADH2 cofactor containing O at the 5-end and 2-deoxyadenosine at the 3-end was studied by femtosecond transient absorption spectroscopy in aqueous solution. Following excitation with a UV pulse, a broadband mid-IR pulse probed vibrational modes of ground-state and electronically excited molecules in the double-bond stretching region. Global analysis of time-and frequency-resolved transient absorption data coupled with ab initio quantum mechanical calculations reveal vibrational marker bands of nucleobase radical ions formed by electron transfer from O to 2-deoxyadenosine. The quantum yield of charge separation is 0.4 at 265 nm, but decreases to 0.1 at 295 nm. Charge recombination occurs in 60 ps before the O radical cation can lose a deuteron to water. Kinetic and thermodynamic considerations strongly suggest that all nucleobases can undergo ultrafast charge separation when n-stacked in DNA or RNA. Interbase charge transfer is proposed to be a major decay pathway for UV excited states of nucleic acids of great importance for photostability as well as photoredox activity. [ABSTRACT FROM AUTHOR]

Anatase-dominated anatase/rutile mixed-phase TiO nanotubes were prepared by decorating TiO on the hydrothermally synthesized TiO-derived nanotubes via liquid phase deposition and subsequent annealing. The morphology and structure of as-prepared TiO nanotubes were characterized by transmission electron microscopy, X-ray diffraction, Raman spectra, and UV-Vis diffuse reflectance spectra. The separation efficiency of photogenerated carriers was investigated by photoluminescence spectra. The photocatalytic activity was evaluated by methyl orange decomposition under UV illumination. The results indicated that the mixed-phase TiO nanotubes consisting of anatase and rutile (82/18 w/w) were successfully fabricated. Due to the synergistic effect of mixed anatase and rutile phases, the anatase-dominated anatase/rutile mixed-phase TiO nanotubes exhibited superior photocatalytic activity. The apparent rate constant k of the photocatalytic reaction for the TiO nanotubes with and without decoration was 0.0528 and 0.0126, respectively. Graphical Abstract: Anatase/rutile mixed-phase TiO nanotubes (MNTs) were prepared by hydrothermal synthesis and subsequent annealing. And anatase-dominated anatase/rutile mixed-phase TiO nanotubes (ANTs) with superior photocatalytic performance were fabricated by decorating TiO on hydrothermally synthesized TiO-derived nanotubes via liquid phase deposition and subsequent annealing.[Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

To better understand how the solvent influences excited-state deactivation in DNA strands, femtosecond time-resolved IR (fs-TRIR) pump-probe measurements were performed on a d(AT)9·d(AT9 duplex dissolved in a deep eutectic solvent (DES) made from choline chloride and ethylene glycol in a 1:2 mol ratio. This solvent, known as ethaline, is a member of a class of ionic liquids capable of solubilizing DNA with minimal disruption to its secondary structure. UV melting analysis reveals that the duplex studied here melts at 18 °C in ethaline compared to 50 °C in aqueous solution. Ethaline has an excellent transparency window that facilitates TRIR measurements in the double-bond stretching region. Transient spectra recorded in deuterated ethaline at room temperature indicate that photoinduced intrastrand charge transfer occurs from A to T, yielding the same exciplex state previously detected in aqueous solution. This state decays via charge recombination with a lifetime of 380 ± 10 ps compared to the 300 ± 10 ps lifetime measured earlier in D2O solution. The TRIR data strongly suggest that the long-lived exciplex forms exclusively in the solvated duplex, and not in the denatured single strands, which appear to have little, if any, base stacking. The longer lifetime of the exciplex state in the DES compared to aqueous solution is suggested to arise from reduced stabilization of the charge transfer state, resulting in slower charge recombination on account of Marcus inverted behavior. [ABSTRACT FROM AUTHOR]

This study presents a novel visible light-active TiO2 nanotube anode film by sensitization with Bi2O3 nanoparticles. The uniform incorporation of Bi2O3 contributes to largely enhancing the solar light absorption and photoelectric conversion efficiency of TiO2 nanotubes. Due to the energy level difference between Bi2O3 and TiO2, the built-in electric field is suggested to be formed in the Bi2O3 sensitized TiO2 hybrid, which effectively separates the photo-generated electron-hole pairs and hence improves the photocatalytic activity. It is also found that the photoelectric conversion efficiency of Bi2O3 sensitized TiO2 nanotubes is not in direct proportion with the content of the sensitizer, Bi2O3, which should be carefully controlled to realize excellent photoelectrical properties. With a narrower energy band gap relative to TiO2, the sensitizer Bi2O3 can efficiently harvest the solar energy to generate electrons and holes, while TiO2 collects and transports the charge carriers. The new-type visible light-sensitive photocatalyst presented in this paper will shed light on sensitizing many other wide-band-gap semiconductors for improving solar photocatalysis, and on understanding the visible light-driven photocatalysis through narrow-band-gap semiconductor coupling. [ABSTRACT FROM AUTHOR]

In this study, a typical site that had been contaminated by the chemical industry in the past was selected for investigation. To reveal the pollution status, 18 organochlorine pesticides (OCPs) and seven polychlorinated biphenyls (PCBs) in the surface soil and sediment samples were analysed by gas chromatography-mass spectrometry (GC-MS). The levels of the persistent organochlorine residues in the sediment ranged from 44.59-143.29 ng/g, whereas they were 13.94-97.91 ng/g in the soil. A principal component analysis identified that PCBs and dichlorodiphenyltrichloroethanes (DDTs) were the primary sources of the organochlorine residues in the study area. The p, p'-DDT/(p, p'-DDE + p,p'-DDD) values were all below 1, which indicated that the historical inputs of the technical DDT and dicofol were the major sources of DDTs rather than recent inputs. The composition diversity of the hexachlorocyclohexane (HCH) isomers showed that the main sources in the soil were the past use of pesticides, whereas the sediment sources might be due to the historical use of technical HCHs and recent lindane inputs. The ecological risk assessment showed that ?-HCH could pose the highest risks for benthic organisms, followed by DDTs and heptachlor epoxide. These compounds are known to bio-accumulate in fatty tissues. Therefore, routine monitoring of the persistent organochlorine residues in the area is needed and the health risks to local residents should be assessed. [ABSTRACT FROM AUTHOR]

Nonstoichiometric silica with multi-active groups particles (NS-MAG particles) were first synthesized, and then added to the porous matrix of PSF to prepare a NS-MAG/PSF composite membrane through a phase inversion process. The optimum preparation conditions of NS-MAG particles were researched and determined. Then the permeation fluxes of NS-MAG/PSF membranes with different doping amount of NS-MAG particles were tested. NS-MAG/PSF" membrane, Si02/PSF membrane, and PSF" membrane were prepared respectively. These membranes were characterized by testing the tensile strength and the permeation flux. The results show that doping NS-MAG particles can better enhance the tensile strength and permeation flux of PSF membrane. [ABSTRACT FROM AUTHOR]