Increase In I0 Research Articles

Influence of light intensity on the steady-state kinetics in tungsten trioxide particulate photoanode studied by intensity-modulated photocurrent spectroscopy

Charge-carrier dynamics during photoelectrochemical (PEC) water splitting over WO3 particulate photoanode deposited on titanium sheet (Ti/WO3) was studied using intensity-modulated photocurrent spectroscopy (IMPS). The WO3 particulate film calcined at 650 °C showed high PEC performance for water oxidation to evolve O2. In linear sweep voltammetry, the photocurrent density proportionally increased with incident light intensity (I0). This means that the incident photon-to-current conversion efficiency (IPCE) of Ti/WO3 was not dependent on I0 in voltammetry. In contrast, there was no proportional relation between I0 and the photocurrent density in chronoamperometry at a constant potential, indicating that the IPCE at steady state decreased with an increase of I0. To elucidate the effect of light intensity on the steady-state IPCE, we investigated the IMPS response of Ti/WO3 photoanodes by applying a simple branching model with respect to the photogenerated holes (h+). It was found that the recombination rate constant (krec) rather than the charge transfer rate constant (kct) significantly depends on I0 at the steady-state condition. The pseudo-first-order krec increased with an increase of I0, suggesting that recombination is increased by the accumulation of photogenerated carriers during continuous PEC water oxidation. This is the reason for the decrease in the steady-state IPCE of Ti/WO3 under high-intensity light irradiation. The effects of applied potentials on the kinetic parameters (kct and krec) were also evaluated for Ti/WO3 under different I0.

Laser sintering of Cu nanoparticles: analysis based on modified continuum-atomistic model

This paper reports on the use of molecular dynamics simulation in conjunction with a modified two-temperature model to elucidate the dynamic behavior of copper nanoparticles (Cu-NPs) undergoing laser sintering. Simulations were conducted using seven models of Cu-NP powders to investigate the means by which particle size (SP), incident laser fluence (I0), and stacking patterns (powders comprising Cu-NPs of either one or two sizes) affect the evolution of electronic temperature (Te), lattice temperature (Tl), pressure (P), and atomic density (dAN) in Cu-NP powders under the effects of laser sintering. We also studied the evolution of sintering configurations and the radial distribution function (g(r)) of Cu-NPs. In powders comprising Cu-NPs of uniform size (2 nm $$\le$$ Sp $$\le$$ 5 nm), the apparent density (d) initially increased (i.e., the powder densified) with I0 and then decreased (i.e., the powder coarsened) with a further increase in I0. Single-size powders composed of smaller Cu-NPs (Sp = 1 nm) underwent densification followed by coarsening followed by densification. Dual-size powders comprising Cu-NPs (Sp = 1 and 3 nm) underwent coarsening almost linearly with an increase in I0, due to the fact that in this model, the incident energy was sufficient to facilitate the atomic diffusion of smaller Cu particles toward larger Cu particles.

Deep tillage and residue mulch effects on productivity and water and nitrogen economy of spring maize in north-west India

Alarming decline of groundwater levels in last two decades in Punjab state of north-west India has limited the scope of high water-requiring, but otherwise profitable spring maize crop. This water limitation also calls for optimizing use of fertilizer nitrogen (N). Interventions like tillage and residue management help to address these constraints. This study examined the effects of deep tillage, irrigation, residue mulch and N regimes on root growth, water use, N uptake and productivity of spring maize in a sub-tropical environment. Combinations of two tillage systems viz., deep tillage (DT) and conventional tillage (CT), with two irrigation regimes viz., irrigation water to pan evaporation ratio of 1.0 (I1.0) and 0.5 (I0.5) in main plots; and combinations of four N rates viz., 0 (N0), 50 (N1), 100 (N2) and 150 (N3) kg ha−1 with two mulch rates viz., 0 (M0) and 6 t ha−1 (M) in subplots were randomized with three replications.Deep tillage reduced soil penetration resistance and caused denser rooting than CT. Residue mulch decreased maximum soil temperature by 3.5–8.5 °C resulting in better root growth. Root mass at silking in CTI1.0MN3 (1.46 t ha−1) was comparable to that in DTI1.0M0N3 (1.48 t ha−1) suggesting that deep tillage and mulch had similar effects. Interaction effects of irrigation and N on grain yield were significant. Mean yield increased from 4.3 t ha−1 in N0 to 7.0 t ha−1 in N3 in I1.0 regime; while in I0.5 regime, yield increased from 3.9 t ha−1 in N0 to 5.5 t ha−1 in N2 and declined thereafter. Deep tillage and mulch modified this synergism by causing greater yield increase in I0.5N3 than in I1.0N3 regime. Comparable grain yield in CTM0I1.0N3 (6.3 t ha−1) and DTM0I0.5N2 (6.2 t ha−1) indicate that same yield could be realized with less water and N in DT than in CT regime.

Interplay of Surface Recombination and Diode Geometry for the Performance of Axial p-i-n Nanowire Solar Cells.

Nanowires (NWs) with axial p-i-n junctions have been widely explored as microscopic diodes for optoelectronic and solar energy applications, and their performance is strongly influenced by charge recombination at the surface. We delineate how the photovoltaic performance of these diodes is dictated not only by the surface but also by the complex and seemingly counterintuitive interplay of diode geometry, that is, radius ( R) and intrinsic length ( Li), with the surface recombination velocity ( S). An analytical model to describe these relationships is developed and compared to finite-element simulations, which verify the accuracy and limitations of the model. The dependence of the dark saturation current ( I0), internal quantum efficiency (IQE), short-circuit current ( ISC), and open-circuit voltage ( VOC) on both geometric and recombination parameters demonstrates that no single set of parameters produces optimal performance; instead, various trade-offs in performance are observed. For instance, longer Li might be expected to produce higher ISC, yet at high values of S the ISC declines because of decreases in IQE. Moreover, longer Li produces a concurrent decline in VOC regardless of S due to increases in I0. We also find that ISC and VOC trends are radius independent, yet I0 is directly proportional to R, causing NWs with smaller R to display higher turn-on voltages. The analysis regarding the interplay of these parameters, verified by experimental measurements with various p-i-n geometries and surface treatments, provides clear guidance for the rational design of performance metrics for photodiode and photovoltaic devices.

Kinetics of Ferric Ion Reduction on Chalcopyrite and its Influence on Leaching up to 150 °C

The reduction kinetics of ferric ion on chalcopyrite in the quaternary H2SO4-Fe2(SO4)3-FeSO4-H2O system were systematically studied by cathodic potentiodynamic polarization (0.5mV/s) through a wide range of solution compositions and temperatures (25–150°C). Results reveal that all of the pseudo-polarization plots exhibit reproducible well-defined linear Tafel regions and thus the temperature dependence of various kinetic parameters, such as the exchange current density, transfer coefficient and rate constant, has been determined. The exchange current densities of the Fe3+/Fe2+ couple obtained by extrapolating the cathodic linear Tafel line to the reversible potential are on the order of 10−7-10−5 A/cm2 in the range of 25–150°C, substantially less than that on platinum due to the formation of a passive film. In general, at the same nominal Fe3+/Fe2+ ratio, increasing the temperature from 25 to 150°C was observed to give rise to an increase in i0, especially when a larger amount of free ferrous existed in the solution. Based on the obtained exchange current densities, the rate constants for ferric ion reduction were calculated, and further analysis indicates that the rate constants can be well described by the Arrhenius equation. Experimental evidence clearly shows an anomalous independent variation of Tafel slope with temperature and a corresponding unexpected increased linear variation of transfer coefficient with respect to temperature (rather than being constant throughout the investigated temperature range). Analysis by mixed potential theory indicates that in the acidic iron sulfate leaching system the control scenario highly depends on both the solution composition and temperature. The importance of the cathodic ferric ion reduction reaction on the overall leaching process is progressively increased when increasing the nominal Fe3+/Fe2+ ratio and temperature. The leaching reaction is under anodic control when the nominal Fe3+/Fe2+ ratio is around 1:1, whereas at higher nominal Fe3+/Fe2+ ratios and temperatures the reaction is under mixed control, by both anodic oxidation and cathodic reduction reactions.

Atmospheric effect of air, N2, O2, and water vapor on the ionization energy of titanyl phthalocyanine thin film studied by photoemission yield spectroscopy

The effect of atmospheric gases on the ionization energy (I) of titanyl phthalocyanine thin film was investigated by an apparatus of photoemission yield spectroscopy developed for the measurements of I for the same specimen both in vacuum and under gaseous atmosphere. It was found that the value of I is affected by the exposure to various ambient gases (i.e., air, nitrogen, and oxygen of 1 atm, and water vapor corresponding to 27% relative humidity at 300 K), and that the effect strongly depends on the gas. The ionization energies in vacuum could be determined as the onset I0 of the cube-root plot of the photoemission yield as a function of photon energy. When the sample was exposed to gases, the cube-root plot still gives an onset, but often a long tail at the low-energy side with another onset It was also observed. The first exposure to air did not affect both I0 and It much, while the following evacuation-exposure cycles caused mostly reversible decrease and increase of I0 and It by about 0.2 and 0.4 eV, respectively. Among the examined constituent gases of air, nitrogen was found to hardly affect both I0 and It except for the small temporal decrease by 0.06 eV at the first exposure. Similar trends of the change of I0 and It with those for air were found for oxygen, with the amplitudes of mostly reversible change being 0.1 eV for I0 and 0.2 eV for It. Overlapped with these changes, a slow decrease of both I0 and It, was also observed with a slope of 0.01 eV per day. For water, the trends were mostly similar with O2, except that (1) the first exposure to water vapor showed small and large changes in I0 (0.03 eV increase) and It (0.4 eV decrease) and (2) the amplitudes of the mostly reversible change of I0 (0.3 eV) and It (0.05 eV) were much larger and smaller than those for O2, respectively. A long-term decrease was also observed with a slope of 0.04 eV per day. These results indicate that the atmospheric effect by ambient air on I is mainly caused by water vapor, although oxygen also makes significant contribution. Since the observed trends are rather complex, there seem to be multiple factors affecting I, which is the energy difference between the vacuum level and the highest occupied molecular orbita. Possible microscopic mechanisms of the observed variation of I on these levels are also discussed in terms of the energy change in these levels.

Nondestructive inductive measurement of local critical current densities in Bi-2223 thickfilms

The local critical current densityJc of Bi-2223 thick films (thickness mm) was nondestructively measured using an ac inductive technique previously developed for measuringJc of large bulk superconductors (Mawatari et al 2003 Appl. Phys. Lett. 83 3972).In this method an ac magnetic field is generated by an ac drive current(I0cosωt) in a small flat coil placed just above the superconducting specimen. Whenthe magnetic fluxes penetrate the superconductor, a third-harmonic voltage(V3cos3ωt) is generated inthe coil, and V3 canthen be calculated as V3 = (G3ω/Jc)I02, where G3 is a coil coefficient calculated from the size and configuration of the coil. Thus,Jc can be measured in the surface region (typically down to mm beneath the surface) of the bulk superconductor by measuringV3 as a functionof I0. In themeasurement of Jc of Bi-2223 thick films, in regions with smallI0,V3 followed the expected behaviour, , and thus the surface Jc can be measured from the slope of theV3–I0 curves.With larger I0,V3 gradually deviated from this behaviour. With further increase inI0,V3 suddenly changed its curvature, reaching a plateau and then increasing again, due tomagnetic-field penetration below the bottom of the film. The threshold currentIth at the change in curvature is nearly proportional toJcd, and thusthe total Jc can be estimated as the average critical current density for the entire thickness. The distribution ofJc in a large superconducting thick film can be measured by scanning the measuring coil overthe entire sample surface.

Phosphoenolpyruvate carboxylase in mistletoe leaves: Regulation of gene expression, protein content, and covalent modification.

Seasonal changes in the activity of phosphoenolpyruvate carboxylase (PEPCase, EC 4.1.1.31), a key enzyme in the interaction of carbohydrate and nitrogen metabolism, were studied in leaves of the C3 semiparasitic mistletoe, Viscum album, growing on different host trees. Maximum extractable PEPCase activities were higher in leaves of mistletoes growing on Betula pendula and Alnus glutinosa hosts compared with those on the conifers, Abies alba and Larix decidua. Independent of host, maximum extractable PEPCase activities were high in spring and autumn while low in summer. Samples with higher PEPCase activities showed higher amounts of PEPCase protein and higher PEPCase mRNA levels. A curvilinear correlation between leaf total nitrogen content and the maximum extractable PEPCase activity as well as PEPCase mRNA level suggested that nitrogen might affect the activity of PEPCase of mistletoe by up-regulating gene expression. In addition to extractable activity, seasonal changes of the PEPCase activation state, the ratio of activities resulting from limited:non-limited assays, were found, which was correlated to the variation of malate content in leaves of mistletoe. ATP-dependent activation of PEPCase was characterized by an increase in I0.5(L-malate), indicating that PEPCase of leaves of mistletoes is probably regulated via phosphorylation.

Functional imaging by I0- and T2*-parameter mapping using multi-image EPI.

A new functional imaging method has been developed and used to measure T2*- and initial intensity (I0)-parameter maps of multiple slices during activation of the cortex with high temporal resolution. Multiple echo-planar images (EPIs) are read out after a single excitation of the spin system, leading to several images with increasing effective echo times. Changes induced by primary visual stimulation in T2* and I0 were measured in eight subjects. Although stimulation-induced increases in I0 only occurred at short repetition times, T2* increased from 57.3 to 60.9 ms on average. The method combines the high stability of a single shot EPI experiment with the high information content of a multiecho acquisition. In addition, stimulation-induced changes in inflow can be easily separated from true blood oxygenation level dependent (BOLD) signal changes.

Ion implantation into Nb/Nb oxide/PbAuIn Josephson tunnel junctions

Boron ions have been implanted into complete planar and edge Nb/Nb oxide/PbAuIn Josephson tunnel junctions to directly trim the Josephson current I0. Implantation caused reproducible increases in I0 and in the junction subgap conductance and decreases in the junction energy gap voltage Vg. The variations in junction properties were monotonic with 11B implant dose. Trimming of I0 was optimized when the 11B ions were implanted with the depth distribution peaked near the tunnel barrier.

Limiting currents in the compression of magnetic flux between flat and coaxial conductors

Experiments are described on magnetic flux compression by flat and coaxial conductors. As the initial current I0 is increased the final current I1 obtained as a result of flux compression at first increases proportionally to I0 and then reaches a maximum and remains constant for further increases in I0. Analysis of the experiments shows that in coaxial structures when a small explosive charge accelerates the conductors the limiting current is determined by the maximum work which a conductor can perform in compressing the magnetic field. In experiments with flat busbars and large explosive charges the limiting currents appear to be determined by the flux losses in short-circuited voids formed in the linking of irregular surfaces of the busbars. This assumption is shown to be in qualitative agreement with experiment.