X-ray emission spectroscopy: a genetic algorithm to disentangle core–hole-induced dynamics

A genetic algorithm (GA) is developed and applied to make proper connections of final-state potential-energy surfaces and X-ray emission (XES) cross sections between steps in the time-propagation of H-bonded systems after a core–hole is created. We show that this modification results in significantly improved resolution of spectral features in XES with the semiclassical Kramers–Heisenberg approach which takes into account important interference effects. We demonstrate the effects on a water pentamer model as well as on two 17-molecules water clusters representing, respectively, tetrahedral (D2A2) and asymmetric (D1A1) H-bonding environments. For D2A2, the applied procedure improves significantly the obtained intensities, whereas for D1A1 the effects are smaller due to milder dynamics during the core–hole life-time as only one hydrogen is involved. We reinvestigate XES for liquid ethanol and, by properly disentangling the relevant states in the dense manifold of states using the GA, now resolve the important 3a′′ state as a peak rather than a shoulder. Furthermore, by applying the SpecSwap-RMC procedure, we reweigh the distribution of structures in the sampling of the liquid to fit to experiment and estimate the ratio between the main anti and gauche conformers in the liquid at room temperature. This combination of techniques will be generally applicable to challenging problems in liquid-phase spectroscopy.

Exploring the needs of urban producers in a rural state: A qualitative needs assessment

Urban farming is a phenomenon rising in popular­ity across the United States. Investigating the needs of urban farmers in a predominately rural state is important in informing future programming and technical assistance for these clients. This qualita­tive study used semi-structured, in-depth interviews that investigated the perceptions, needs, and expe­riences of Arkansas urban farmers and their inter­actions with the University of Arkansas Division of Agriculture Cooperative Extension Service. Inter­views were conducted with 16 urban farmers in Northwest and Central Arkansas. The interview data revealed highly individualized needs based on the operation size, years in operation, and mission of each urban farmer interviewed. While needs var­ied, some were consistent, such as market pricing, co-ops, and access to appropriate equipment. Par­ticipants also revealed a positive perception of Extension, though they cited that the organization did not always have resources specific to small-scale, sustainable farming. Building from the Com­munity Food System Development Framework for Change and informed by the AgroEcological-Educator theory, this study provides urban farm­ers’ insights and contextualizes urban farming in a predominately rural, southern state. Potential remains for increased collaboration and communi­cation between Arkansas urban farmers and Exten­sion. This article demonstrates the diverse needs of Arkansas urban farmers, which can be used by Extension and sustainable agriculture experts to inform research about urban and sustainable farmers in their respective states.

Effect of hybridized local and charge transfer molecules rotation in excited state on exciton utilization

The fluorescent molecules utilizing hybridized local and charge-transfer (HLCT) state as potential organic light-emitting diodes materials attract extensive attention due to their high exciton utilization. In this work, we have performed the density functional theory method on three HLCT-state molecules to investigate their excited-state potential energy surface (PES). The calculated results indicate the T1 and T2 energy gap is quite large, and the T2 is very close to S1 in the energy level. The large gap is beneficial for inhibiting the internal conversion between T1 and T2, and quite closed S1 and T2 energies are favor for activating the T2 → S1 reverse intersystem crossing path. However, considering the singlet excited-state PES by twisting the triphenylamine (TPA) or diphenylamine (PA) group, it can be found that the TPA or PA group almost has no influence on T1 and T2 energy levels. However, the plots of S1 PES display two kinds of results that the S1 emissive state is dominated by charge-transfer (CT) or HLCT state. The CT emission state formation would decrease the S1 energy level, enlarge the S1 and T2 gap, and impair the triplet exciton utilization. Therefore, understanding the relationship between the S1 PES and molecular structures is important for designing high-performance luminescent materials utilizing HLCT state.

A QM/MM Study on the Initiation Reaction of Firefly Bioluminescence—Enzymatic Oxidation of Luciferin

Among all bioluminescent organisms, the firefly is the most famous, with a high luminescent efficiency of 41%, which is widely used in the fields of biotechnology, biomedicine and so on. The entire bioluminescence (BL) process involves a series of complicated in-vivo chemical reactions. The BL is initiated by the enzymatic oxidation of luciferin (LH2). However, the mechanism of the efficient spin-forbidden oxygenation is far from being totally understood. Via MD simulation and QM/MM calculations, this article describes the complete process of oxygenation in real protein. The oxygenation of luciferin is initiated by a single electron transfer from the trivalent anionic LH2 (L3−) to O2 to form 1[L•2−…O2•−]; the entire reaction is carried out along the ground-state potential energy surface to produce the dioxetanone (FDO−) via three transition states and two intermediates. The low energy barriers of the oxygenation reaction and biradical annihilation involved in the reaction explain this spin-forbidden reaction with high efficiency. This study is helpful for understanding the BL initiation of fireflies and the other oxygen-dependent bioluminescent organisms.

دراسة وتحليل واقع هشاشة النظام المالي في العراق للمدة (2003-2018)

The analysis of the reality of the financial fragility of the financial system especially the banking system side of it is recent and it has become an increasingly important goal in the context of macroeconomic policy-making especially its financial and monetary parts and among the reasons that have made attention towards the issue of the fragility of the financial system and that it has priority within The concerns of financial monetary and economic policymakers around the world are the need for sudden financing operations especially investment which necessitated the study and analysis of the impact of the state of the fragility of the financial system in Iraq on the state potential or ability of the country's financial and banking system to face the necessary financing operations especially domestic investment The fragility of the financial system expresses a state of deterioration and instability of the financial system whether the banking side of it (the financial and banking institutions) or the financial market side in a manner in which it does not perform its functions efficiently especially the allocation of resources directing them or making them ready for any sudden financing that could aid the economic situation in the country