Modelling of high-temperature dark current in multi-quantum well structures from MWIR to VLWIR

In this paper, a model to calculate the dark current of quantum well infrared photodetectors at high-temperature regime is presented. The model is derived from a positive-definite quantum probability-flux and considers thermionic emission and thermally-assisted tunnelling as mechanisms of dark current generation. Its main input data are the wave functions obtained by time-independent Schrodinger equation and it does not require empirical parameters related to the transport of carriers. By means of this model, the dark current of quantum well infrared photodetectors at high-temperature regime is investigated with respect to the temperature, the barrier width, the applied electric field and the position of the first excited state. The theoretical results are compared with experimental data obtained from lattice-matched InAlAs/InGaAs, InGaAsP/InP on InP substrate and AlGaAs/GaAs structures with rectangular wells and symmetric barriers, whose absorption peak wavelengths range from MWIR to VLWIR. The corresponding results are in a good agreement with experimental data at different temperatures and at a wide range of applied electric field.     

Evaluating impacts of fish stock enhancement and biodiversity conservation actions on the livelihoods of small‐scale fishers on the Beijiang River,China

Inappropriate development and overexploitation have seriously degraded aquatic resources in China. Stakeholders identified three fish stock enhancement and biodiversity conservation scenarios for the Beijiang River: S1, increased fish restocking; S2, no fishing season and habitat conservation; and S3, strict pollution control. Potential impacts of these actions on the livelihoods of fishers were evaluated using applied economic modeling. Baseline costs and benefits came from logbooks from 30 fishers and a survey of 90 households in three villages. The financial net benefit for a household was US$1583 (￥11,160) annually, representing a 142% and 387% return on capital and operating costs, respectively. Larger catches associated with S1 and S2 generated a net benefit of US$1651 and US$1822, respectively. Strict pollution control resulting in higher catches (+20%) and lower operating costs (?20%) would increase the net benefit by 15.9% to US$1835 annually. Pollution control would benefit other resource users and is a prerequisite for ecological restoration. Recommendations for Resource Managers

• Stringent pollution control measures are essential to conserve aquatic biodiversity and enhance the livelihoods of fishers but will require considerable public and private sector investment.
• Enhanced fish stocks in the Beijiang River could benefit poor livelihoods but may not be sufficient to lift households out of poverty, aged fishers require government assistance to diversify their livelihoods, access alternative urban employment, and survive with dignity.
• Adopting the economic modeling approach presented here could enable responsible authorities to simultaneously evaluate fish stock enhancement and biodiversity conservation options.
• Broader application of the approach presented here could help ensure small‐scale inland fisheries are managed sustainably and aquatic ecosystems are restored and protected by 2020, in line with Target 6 of the United Nations’ Convention on Biological Diversity Strategic Plan for Biodiversity.

     

Mechanics of fish skin: A computational approach for bio-inspired flexible composites

Natural materials and structures are increasingly becoming a source of inspiration for the design novel of engineering systems. In this context, the structure of fish skin, made of an intricate arrangement of flexible plates growing out of the dermis of a majority of fish, can be of particular interest for materials such as protective layers or flexible electronics. To better understand the mechanics of these composite shells, we introduce here a general computational framework that aims at establishing a relationship between their structure and their overall mechanical response. Taking advantage of the periodicity of the scale arrangement, it is shown that a representative periodic cell can be introduced as the basic element to carry out a homogenization procedure based on the Hill-Mendel condition. The proposed procedure is applied to the specific case of the fish skin structure of the Morone saxatilis, using a computational finite element approach. Our numerical study shows that fish skin possesses a highly anisotropic response, with a softer bending stiffness in the longitudinal direction of the fish. This softer response arises from significant scale rotations during bending, which induce a stiffening of the response under large bending curvature. Interestingly, this mechanism can be suppressed or magnified by tuning the rotational stiffness of the scale-dermis attachment but is not activated in the lateral direction. These results are not only valuable to the engineering design of flexible and protective shells, but also have implications on the mechanics of fish swimming.     

Supramolecular Chemistry In Silico

Computational protocols capable of modelling supramolecular complexes have been evaluated. The complexation of cations by crown ethers and quaternary ammonium ions by an oxacalix[3]arene are presented as examples. In the latter case reliable qualitative results were obtained using the semi-empirical PM3 method where guest LUMO and electrostatic potential energies have been shown to correlate with experimental binding data. The optimal method for more accurate results combines semi-empirical equilibrium geometry and property calculations with single point energy calculations at the HF/6–31G* or BP/6–31G* quantum mechanical level.     

Oxidative addition transition states of Pd(0) complexes in polar solvent—a DFT study involving implicit and explicit solvation

Previous reports in the literature have suggested that concerted transition states for oxidative addition would not exist in solution. By contrast, this report describes the successful location of transition states for the oxidative addition of monoligated Pd(P^tBu₃), bisligated Pd(P^tBu₃)(MeCN), and anionic Pd(P^tBu₃)F^? complexes to C–Cl and C–OTf of an aryl chloro triflate in polar solvent (MeCN). Optimizations were done with implicit solvation and a combined implicit/explicit solvation approach in which six acetonitrile molecules were additionally involved in the optimization. The geometries obtained from optimizations employing an implicit solvation model are structurally largely analogous to those found using a combination of implicit and explicit solvation.     

CFD Simulation of Rheological Model Effect on Cuttings Transport

Foam, as a non-Newtonian fluid, plays an important role in the underbalanced drilling technique in oil field development. The rheological properties of drilling fluids, such as foam, have a direct effect on flow characteristics and hydraulic performance. Two rheological models—the Herschel–Bulkley model and power law—were fitted to two foam systems in this study. Computational fluid dynamics (CFD) was used to simulate the effect of the rheological models on solid–liquid (cuttings transport) hydraulics in concentric and eccentric annulus during the foam drilling operation. The simulation results are compared to the experimental data from previous studies. The results of CFD using the power law model are in good agreement with experimental results in horizontal annulus with respect to the Herschel–Bulkley model with relative error less than 8%. Thus, for CFD cuttings transport for simulations in inclined and horizontal annulus, it is best to use the power law's rheological model parameters.     

A Combined Spectroscopic and Theoretical Study on a Ruthenium Complex Featuring a π-Extended dppz Ligand for Light-Driven Accumulation of Multiple Reducing Equivalents

The design of photoactive systems capable of storing and relaying multiple electrons is highly demanded in the field of artificial photosynthesis, where transformations of interest rely on multielectronic redox processes. The photophysical properties of the ruthenium photosensitizer [(bpy)₂Ru( oxim-dppqp )]²⁺ ( Ru ), storing two electrons coupled to two protons on the π-extended oxim-dppqp ligand under light-driven conditions, are investigated by means of excitation wavelength-dependent resonance Raman and transient absorption spectroscopies, in combination with time-dependent density functional theory; the results are discussed in comparison to the parent [(bpy)₂Ru(dppz)]²⁺ and [(bpy)₂Ru( oxo-dppqp )]²⁺ complexes. In addition, this study provides in-depth insights on the impact of protonation or of accumulation of multiple reducing equivalents on the reactive excited states.     

Multicomponent synthesis,cytotoxicity, and computational studies of novel imidazopyridazine-based N-phenylbenzamides

A one-pot multicomponent synthesis and application of new imidazopyridazine based N-phenylbenzamides is described. An atom-economical method involving dimethyl phthalate, substituted anilines, and pyridazine-4,5-diamine provided the desired compounds in 120–150 min with 80–85% yield. The reaction was catalyzed with phosphoric acid, and glycerol was used as a safer, greener solvent. Anticancer evaluation against selected cancer cell lines revealed that compound 4e was the most active from the series and exhibited IC₅₀ values below 9.1 µM. Compounds 4h and 4d also displayed good and comparable IC₅₀ values (10.2–12.1 µM). Molecular docking and molecular dynamic studies showed that compound 4e exhibit good binding affinity and stable complex formation with ABL1-kinase protein, respectively. Additional computational predictions such as ADME and drug-likeness demonstrated the potential of the new benzamides as leads for further development.     

Effect of selected dopants on conductivity and moisture stability of Li3PS4 sulfide solid electrolyte: a first-principles study

The first principle computational screening was performed to investigate the effect of selected dopants for Li₃PS₄ sulfide solid electrolyte on its ionic conductivity and stability toward moisture. The results suggest that substitution P⁵⁺ using isovalent cations whose electronegativity (EN) value is closer to the value of S has more significant effects on the ionic conductivity, whereby W⁵⁺ and Sb⁵⁺ can improve most. Similarly, aliovalent cation substitutions with compensating changes in the lithium-ion concentration, particularly those with a lower oxidation state and higher EN, such as Cu²⁺, effectively enhance the lithium-ion conductivity in this structure. For cation dopants, it is found that ionic conductivity improvement of Li₃PS₄ is the synergetic effect of EN and oxidation number of the dopant as well as the material's lattice parameter change. Oxides of the considered cation dopants can also improve the ionic conductivity of the material but have much lower lithium-ion conductivity than the cases of cation dopants. However, the metal oxide dopants, particularly those derived from soft Lewis' acid cations, show a marginal improvement in moisture stability of the Li₃PS₄ electrolyte. The effect of halides and metal halide dopants on the lithium-ion conductivity and moisture stability of Li₃PS₄ electrolyte are also studied. It is found that metal halides are more effective than any other dopants in improving the ionic conductivity of Li₃PS₄.