Applications using simulation-optimization approaches are often limited in practice because of the high computational cost associated with executing the simulation-optimization analysis. This research proposes a nonlinearity interval mapping scheme (NIMS) to overcome the computational barrier of applying the simulation-optimization approach for a waste load allocation analysis. Unlike the traditional response surface methods that use response surface functions to approximate the functional form of the original simulation model, the NIMS approach involves mapping the nonlinear input-output response relationship of a simulation model into an interval matrix, thereby converting the original simulation-optimization model into an interval linear programming model. By using the risk explicit interval linear programming algorithm and an inverse mapping scheme to implicitly resolve nonlinearity in the interval linear programming model, the NIMS approach efficiently obtained near-optimal solutions of the original simulation-optimization problem. The NIMS approach was applied to a case study on Wissahickon Creek in Pennsylvania, with the objective of finding optimal carbonaceous biological oxygen demand and ammonia (NH4) point source waste load allocations, subject to daily average and minimum dissolved oxygen compliance constraints at multiple points along the stream. First, a simulation-optimization model was formulated for this case study. Next, a genetic algorithm was used to solve the problem to produce reference optimal solutions. Finally, the simulation-optimization model was solved using the proposed NIMS, and the obtained solutions were compared with the reference solutions to demonstrate the superior computational efficiency and solution quality of the NIMS.
A facile way to fabricate highly efficient organic light emitting devices (OLEDs) with insulator MnO as an electron injecting and transporting material was devised, which eliminates the problem of the oxidation of reactive dopants. The power efficiency of 1.1 lm/W by inserting 3-nm-thick MnO as the electron injecting layer was obtained, higher than the 0.8 lm/W efficiency for the reference device with 0.5-nm-thick LiF. A thermal co-evaporation layer containing 10% weight of MnO and tris(8-hydroxyquinolato) aluminum (Alq(3)) as the electron transporting layer showed more efficient electron transport ability, with turn-on voltage of 3.8 V, lower than 7.4 V for the intrinsic Alq3. Meanwhile, the insertion of thin MnO layer between organic photoactive layer and inorganic metal electrode significantly improved performance and stability of organic solar cell compared to device without it. The power conversion efficiency (PCE) of 2.91% by inserting 3-nm-thick MnO was obtained, higher than the 0.91% efficiency for the device without it, and 2.59% for the device with 0.5-nm-thick LiF. Charge transport of rhenium trioxide (ReO(3)) in organic electronic devices was investigated. The hole injection/transport was blocked and the electron injection/transport was enhanced with doping of ReO(3) in organic electronic devices. Thus the charge balance and efficiency of the OLED were improved, 2.7 cd/A of current efficiency (CE) at 20 mA/cm(2) for the device with ReO(3) was higher than 1.5 cd/A for the device without it. In the case of organic photovoltaic cells (OPV), the open-circuit voltage (V(oc)), 0.58 V, was higher compared to the device without ReO(3) (0.44 V) due to the improvement of interface properties. The PCE was increased to 2.27% by the combination of ReO(3) (increasing V(oc)) with poly(3,4-ethylene dioxythiophene): poly(styrene-sulfonate) (PEDOT:PSS) (improve hole transport to increase J(sc)) on the modification of the anode, higher than 1.85% for the device without ReO(3).
Researches on HO(x) radical chemistry would provide theoretical support for understanding the global climate change and regional air pollution control. At present stage, comprehensive field campaign including HO(x) radial measurements is one of the critical approaches to advance it. However, due to the very short lifetime and extremely low concentration of HO(x) in the atmosphere, direct measurement of HO(x) radical is one of most challenged works in atmospheric chemistry. This paper reviews the direct measurement techniques of the HO(x) radical, summarizes the observed dynamics range of its concentrations, introduces the current schematic diagram of the HO(x) radical chemistry and the important contributions from previous field studies, and discusses the main scientific questions that need further researches. Besides, the progress of the HO(x) radical chemistry in China is reviewed, and several potentially important research directions are pointed out.
Ambient particulate matter (PM) samples were collected on quartz filters at a rural site in central Ontario during an intensive study in 2007. The concentrations of organic carbon (OC), pyrolysis organic carbon (POC), and elemental carbon (EC) were determined by thermal analysis. The concentrations are compared to the organic aerosol mass concentration (OM) measured with an Aerodyne C-ToF Aerosol Mass Spectrometer (AMS) and to the particle absorption coefficient (b(asp)) obtained from a Radiance Research Particle Soot Absorption Photometer (PSAP). The total organic mass to organic carbon ratios (OM/OC) and specific attenuation coefficients (SAC=b(asp)/EC) are derived. Proportionality of the POC mass with the oxygen mass in the aerosols estimated from the AMS offers a potential means to estimate OM/OC from thermal measurements only. The mean SAC for the study is 3.8 +/- 0.3 m(2) g(-1). It is found that the SAC is independent of or decrease with increasing particle mass loading, depending on whether or not the data are separated between aerosols dominated by more recent anthropogenic input and aerosols dominated by longer residence time or biogenic components. There is no evidence to support an enhancement of light absorption by the condensation of secondary material to particles, suggesting that present model simulations built on such an assumption may overestimate atmospheric warming by BC.
AlGaN/GaN high-electron mobility transistor's (HEMT's) off-state breakdown is investigated using drain-current injection techniques with different injection current levels. Competitions between the source leakage and gate leakage, pure leakage and impact ionization, and source-and gate-injection-induced impact ionization during the drain-injection measurement are discussed in detail. It was found that the breakdown originates from the source/gate leakage at low drain injection levels but is dominated by source/gate-induced impact ionization process at high drain injection currents. The source-induced impact ionization usually precedes the gate-induced impact ionization in low-gate leakage devices, resulting in a premature three-terminal off-state breakdown. We also found that the gate-bias value affects the breakdown voltage in the conventional three-terminal off-state breakdown I-V measurement and should be carefully considered.
A set of conjugated oligo- and polytluorene-tethered fac-Ir(ppy)(3) complexes were synthesized, In addition to steady-state absorption and emission, time-resolved emission spectroscopy was used to systematically study the correlation of photophysical properties with chemical structures. A chain length dependency study showed that both radiative and nonradiative triplet decay rates, as well as the phosphorescence quantum yield, decreased with increasing chain length of the appended oligofluorene. Notably, the complex with oligofluorene tethered to the pyridine tiara to phenyl ring possessed a substantially higher phosphorescence quantum efficiency and shorter lifetime than those of an isomeric complex with the oligofluorene linked to the phenyl ring para to pyridine. Nonetheless, both these two oligomer complexes exhibited an excited state of mixed MLCT. (metal-to-ligand charge transfer) and LC (ligand-centered) transitions, whereas another isomeric complex having an oligofluorene appended to the phenyl ring pant to the iridium ion exhibited a particularly long triplet lifetime (> 100 mu s), indicative of a (LC)-L-3 excited state. A moderately high quantum yield (similar to 0.5) was displayed by this (LC)-L-3-featured phosphor. DEL calculations substantiated the proposition that the attachment of oligofluorene to Ir(ppy)(3) at different positions resulted in varied molecular orbitals, with different relative contribution of MLCT to the emissive excited state. Hence, photophysical properties such as radiative decay rate, lifetime, and quantum yield, etc., were all influenced by the substitution isomerism. As these results indicated that if short lifetime and fast radiative decay were desired, among different substitution patterns appending the conjugated chain to the pyridine unit was the most favorable. Thus, star-shaped complexes with an oligo- or polyfluorene tethered to each of the three pyridine units of Ir(ppy)(3) were prepared. In such a structure, the tris-cyclometalated iridium effected nearly complete intersystem crossing (ISC) in all three ligands across three fluorene units, without compromising the phosphorescence quantum yield. But the study showed that further extending the conjugated ligand resulted in partial ISC or even complete loss of capacity for ISC beyond a certain distance.