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.
The Amazon Basin provides an excellent environment for studying the sources, transformations, and properties of natural aerosol particles and the resulting links between biological processes and climate. With this framework in mind, the Amazonian Aerosol Characterization Experiment (AMAZE-08), carried out from 7 February to 14 March 2008 during the wet season in the central Amazon Basin, sought to understand the formation, transformations, and cloud-forming properties of fine-and coarse-mode biogenic aerosol particles, especially as related to their effects on cloud activation and regional climate. Special foci included (1) the production mechanisms of secondary organic components at a pristine continental site, including the factors regulating their temporal variability, and (2) predicting and understanding the cloud-forming properties of biogenic particles at such a site. In this overview paper, the field site and the instrumentation employed during the campaign are introduced. Observations and findings are reported, including the large-scale context for the campaign, especially as provided by satellite observations. New findings presented include: (i) a particle number-diameter distribution from 10 nm to 10 mu m that is representative of the pristine tropical rain forest and recommended for model use; (ii) the absence of substantial quantities of primary biological particles in the submicron mode as evidenced by mass spectral characterization; (iii) the large-scale production of secondary organic material; (iv) insights into the chemical and physical properties of the particles as revealed by thermodenuder-induced changes in the particle number-diameter distributions and mass spectra; and (v) comparisons of ground-based predictions and satellite-based observations of hydrometeor phase in clouds. A main finding of AMAZE-08 is the dominance of secondary organic material as particle components. The results presented here provide mechanistic insight and quantitative parameters that can serve to increase the accuracy of models of the formation, transformations, and cloud-forming properties of biogenic natural aerosol particles, especially as related to their effects on cloud activation and regional climate.
For CareBeijing-2006, two sites were established in urban and suburban regions of Beijing in summer 2006. Observations of O(3) and its precursors together with meteorological parameters at both sites are presented. Gross ozone production rate P(O(3)) and sensitivity to nitric oxides (NO(x)) and volatile organic compounds (VOCs) were investigated using an observation-based photochemical box model (OBM). P(O(3)) varied from nearly zero to 120 and 50 ppb h(-1) for urban and suburban sites, respectively. These rates were greater than the accumulation rates of the observed oxidant (O(3) + NO(2)) concentrations. The O(3) episodes typically appeared under southerly wind conditions with high P(O(3)), especially at the urban site. Sensitivity studies with and without measured nitrous acid (HONO) as a model constraint suggested that the estimated P(O(3)) at both sites was strongly enhanced by radical production from HONO photolysis. Both NO(x)- and VOC-sensitive chemistries existed over time scales from hours to days at the two sites. The variation in O(3)-sensitive chemistry was relatively well explained by the ratio of the average daytime total VOC reactivity (k(TVOC)) to NO, with the transition chemistry corresponding to a k(TVOC)/NO value of 2-4 s(-1) ppb(-1). Pronounced diurnal variations in the O(3) production regime were found. In the morning, conditions were always strongly VOC-limited, while in the afternoon, conditions were variable for different days and different sites. The model-calculated results were tested by measurements of H(2)O(2), HNO(3), total OH reactivity, and HO(x) radicals. The OBM was generally capable of correctly simulating the levels of P(O(3)), although it might tend to overpredict the VOC-sensitive chemistry.
Poly(3-hexylthiophene) (P3HT):1-(3-methoxycarbonyl)-propyl-1-Phenyl-(6,6)C-61 (PCBM) photovoltaic devices based on ordinary paper as substrate were fabricated. Au layer deposited on paper by RF magnetron sputtering was used as anode. The hybrid layer of LiF co-evaporated with Al was used for transparent cathode, and the light transmittance could reach to similar to 70%. By optimizing the mass proportion of LiF and Al, we could get the best papery solar cells with the short current density and open circuit voltage 0.1 mA/cm(2) and 0.39 V. respectively. The corresponding power conversion efficiency was measured to be 0.13 parts per thousand illuminated with 100 mW/cm(2) air mass 1.5 global (AM 1.5 G) simulated sunlight. (C) 2010 Elsevier B.V. All rights reserved.