Surface plasmon enhanced spontaneous emission rate of InGaN/GaN quantum wells probed by time-resolved photoluminescence spectroscopy

We observed a 32-fold increase in the spontaneous emission rate of InGaN/GaN quantum well (QW) at 440 nm by employing surface plasmons (SPs) probed by time-resolved photoluminescence spectroscopy. We explore this remarkable enhancement of the emission rates and intensities resulting from the efficient energy transfer from electron-hole pair recombination in the QW to electron vibrations of SPs at the metal-coated surface of the semiconductor heterostructure. This QW-SP coupling is expected to lead to a new class of super bright and high-speed light-emitting diodes (LEDs) that offer realistic alternatives to conventional fluorescent tubes

Spatio-Temporal Progression of Two-Stage Autoignition for Diesel Sprays in a Low-Reactivity Ambient: n-Heptane Pilot-Ignited Premixed Natural Gas

[EN] The spatial and temporal locations of autoignition depend on fuel chemistry and the temperature, pressure, and mixing trajectories in the fuel jets. Dual-fuel systems can provide insight into fuel-chemistry aspects through variation of the proportions of fuels with different reactivities, and engine operating condition variations can provide information on physical effects. In this context, the spatial and temporal progression of two-stage autoignition of a diesel-fuel surrogate, n-heptane, in a lean-premixed charge of synthetic natural gas (NG) and air is imaged in an optically accessible heavy-duty diesel engine. The lean-premixed charge of NG is prepared by fumigation upstream of the engine intake manifold. Optical diagnostics include: infrared (IR) imaging for quantifying both the in-cylinder NG concentration and the pilot-jet penetration rate and spreading angle, high-speed cool-flame chemiluminescence imaging as an indicator of low-temperature heat release (LTHR), and high-speed OH* chemiluminescence imaging as an indicator high-temperature heat release (HTHR). To aid interpretation of the experimental observations, zero-dimensional chemical kinetics simulations provide further understanding of the underlying interplay between the physical and chemical processes of mixing (pilot fuel-jet entrainment) and autoignition (two-stage ignition chemistry). Increasing the premixed NG concentration prolongs the ignition delay of the pilot fuel and increases the combustion duration. Due to the relatively short pilot-fuel injections utilized, the transient increase in entrainment near the end of injection (entrainment wave) plays an important role in mixing. To achieve desired combustion characteristics, i.e., ignition and combustion timing (e.g., for combustion phasing) and location (e.g., for reducing wall heat-transfer or tailoring charge stratification), injection parameters can be suitably selected to yield the necessary mixing trajectories that potentially help offset changes in fuel ignition chemistry, which could be a valuable tool for combustion design.This research was sponsored by the U.S. Department of Energy (DOE) Office of Energy Efficiency and Renewable Energy (EERE). Optical engine experiments were conducted at the Combustion Research Facility of Sandia National Laboratories in Livermore, CA. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration (NNSA) under contract DE-NA0003525. We gratefully acknowledge the contributions of Keith Penney and Dave Cicone for their assistance in developing research tools and maintaining the optical engine.Rajasegar, R.; Niki, Y.; García-Oliver, JM.; Li, Z.; Musculus, M. (2021). Spatio-Temporal Progression of Two-Stage Autoignition for Diesel Sprays in a Low-Reactivity Ambient: n-Heptane Pilot-Ignited Premixed Natural Gas. SAE International. 1-16. https://doi.org/10.4271/2021-01-052511

Verification of diesel spray ignition phenomenon in dual-fuel diesel-piloted premixed natural gas engine

[EN] Dual-fuel (DF) engines, in which premixed natural gas and air in an open-type combustion chamber is ignited by diesel-fuel pilot sprays, have been more popular for marine use than pre-chamber spark ignition (PCSI) engines because of their superior durability. However, control of ignition and combustion in DF engines is more difficult than in PCSI engines. In this context, this study focuses on the ignition stability of n-heptane pilot-fuel jets injected into a compressed premixed charge of natural gas and air at low-load conditions. To aid understanding of the experimental data, chemical-kinetics simulations were carried out in a simplified engine-environment that provided insight into the chemical effects of methane (CH4) on pilot-fuel ignition. The simulations reveal that CH4 has an effect on both stages of n-heptane autoignition: the small, first-stage, cool-flame-type, low-temperature ignition (LTI) and the larger, second-stage, high-temperature ignition (HTI). As the ratio of pilot-fuel to CH4 entrained into the spray decreases, the initial oxidization of CH4 consumes the OH radicals produced by pilot-fuel decomposition during LTI, thereby inhibiting its progression to HTI. Using imaging diagnostics, the spatial and temporal progression of LTI and HTI in DF combustion are measured in a heavy-duty optical engine, and the imaging data are analyzed to understand the cause of severe fluctuations in ignition timing and combustion completeness at low-load conditions. Images of cool-flame and hydroxyl radical (OH*) chemiluminescence serve as indicators of LTI and HTI, respectively. The cycle-to-cycle and spatial variation in ignition extracted from the imaging data are used as key metrics of comparison. The imaging data indicate that the local concentration of the pilot-fuel and the richness of the surrounding natural-gas air mixture are important for LTI and HTI, but in different ways. In particular, higher injection pressures and shorter injection durations increase the mixing rate, leading to lower concentrations of pilot-fuel more quickly, which can inhibit HTI even as LTI remains relatively robust. Decreasing the injection pressure from 80 MPa to 40 MPa and increasing the injection duration from 500 mu s to 760 mu s maintained constant pilot-fuel mass, while promoting robust transition from LTI to HTI by effectively slowing the mixing rate. This allows enough residence time for the OH radicals, produced by the two-stage ignition chemistry of the pilot-fuel, to accelerate the transition from LTI to HTI before being consumed by CH4 oxidation. Thus from a practical perspective, for a premixed natural gas fuel-air equivalence-ratio, it is possible to improve the "stability" of the combustion process by solely manipulating the pilot-fuel injection parameters while maintaining constant mass of injected pilot-fuel. This allows for tailoring mixing trajectories to offset changes in fuel ignition chemistry, so as to promote a robust transition from LTI to HTI by changing the balance between the local concentration of the pilot-fuel and richness of the premixed natural gas and air. This could prove to be a valuable tool for combustion design to improve fuel efficiency or reduce noise or perhaps even reduce heat-transfer losses by locating early combustion away from in-cylinder walls.This research was sponsored in part by the U.S. Department of Energy (DOE) Office of Energy Efficiency and Renewable Energy (EERE). Optical engine experiments were conducted at the Combustion Research Facility of Sandia National Laboratories in Livermore, CA. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration (NNSA) under contract DE-NA0003525.Niki, Y.; Rajasegar, R.; Li, Z.; Musculus, MP.; García-Oliver, JM.; Takasaki, K. (2022). Verification of diesel spray ignition phenomenon in dual-fuel diesel-piloted premixed natural gas engine. International Journal of Engine Research. 23(2):180-197. https://doi.org/10.1177/146808742098306018019723

Surface plasmon enhanced InGaN light emitter

We report a dramatic increase in the photoluminescence (PL) emitted from InGaN/GaN quantum wells (QW), obtained by covering these sample surface with thin metallic films. Remarkable enhancements of PL peak intensities were obtained from In_(0.3)Ga_(0.7)N QWs with 50 nm thick silver and aluminum coating with 10 nm GaN spacer. These PL enhancements can be attributed to strong interaction between QWs and surface plasmons (SPs). No such enhancements were obtained from samples coated with gold, as its well-known plasmon resonance occurs only at longer wavelengths. We also showed that QW-SP coupling increase the internal quantum efficiencies by measuring the temperature dependence of PL intensities. QW-SP coupling is a very promising method for developing the super bright light emitting diodes (LEDs). Moreover, we found that the metal nano-structure is very important facto to decide the light extraction. A possible mechanism of QW-SP coupling and emission enhancement has been developed, and high-speed and efficient light emission is predicted for optically as well as electrically pumped light emitters

ION-SENSITIVE FIELD-EFFECT TRANSISTORS WITH INORGANIC GATE OXIDE FOR PH SENSING

Ion-sensitive fieldeffect transistors (ISFET’s) have been fabricated by using silicon fiims on sapphire substrates (SOS). Using this structure Si02, Zr02, and TazO5 films are examined as hydrogenion- sensitive materials, and TazO5 fiim has been found to have the highest pH sensitivity (56 mV/pH) among them. The measured pH sensitivity of this SOS-ISFET’s is compared with the theoretical sensitivity based on the site-binding model of proton dimciation reaction on the metal oxide f i i and good agreement between them is obtained

Association between suicide-related ideations and affective temperaments in the Japanese general adult population

Background: Suicide rates are vastly higher in Japan than in many other countries, although the associations between affective temperaments and suicide-related ideations in the general adult population remain unclear. Therefore, we aimed to elucidate these associations in the present study. Methods: We analyzed data from 638 Japanese volunteers who completed both the Patient Health Questionnaire (PHQ-9) and the Temperament Evaluation of the Memphis, Pisa, Paris, and San Diego Auto-questionnaire (TEMPS-A). Participants were then divided into three groups based on PHQ-9 summary scores and responses to the suicide-related ideation item: non-depressive control group (NC; N = 469), depressive symptoms without suicide-related ideations group (non-SI; N = 135), and depressive symptoms with suicide-related ideations group (SI; N = 34). The depressive symptoms were defined for PHQ-9 summary scores ≥5, and the suicide-related ideations were defined for PHQ-9 #9 score ≥1. We then compared TEMPS-A scores among the groups using Kruskal-Wallis tests. Then the 95% confidence intervals of differences in TEMPS-A subscale scores between the NC and non-SI groups, or between NC and SI groups, were calculated. Results: Participants of the SI group exhibited significantly higher scores on the depressive, irritable, and anxious temperament subscales than those of the non-SI group. Similarly, women of the SI group exhibited significantly higher scores of the depressive and irritable temperament subscales than women of the non-SI group, while men of the SI group exhibited significantly higher depressive temperament scores than those of the non-SI group. Among all participants and only men, cyclothymic subscale scores were higher in those of the SI group than the non-SI group (not significant), although the 95% confidence intervals did not overlap. Limitations: The cross-sectional study design was the main limitation. Conclusions: Depressive, irritable, and anxious temperaments are significant risk factors for suicide-related ideations in the Japanese general adult population. Furthermore, irritable temperament in women and depressive temperament in men are associated with suicide-related ideations

Surface plasmon enhanced InGaN light emitter

We report a dramatic increase in the photoluminescence (PL) emitted from InGaN/GaN quantum wells (QW), obtained by covering these sample surface with thin metallic films. Remarkable enhancements of PL peak intensities were obtained from In_(0.3)Ga_(0.7)N QWs with 50 nm thick silver and aluminum coating with 10 nm GaN spacer. These PL enhancements can be attributed to strong interaction between QWs and surface plasmons (SPs). No such enhancements were obtained from samples coated with gold, as its well-known plasmon resonance occurs only at longer wavelengths. We also showed that QW-SP coupling increase the internal quantum efficiencies by measuring the temperature dependence of PL intensities. QW-SP coupling is a very promising method for developing the super bright light emitting diodes (LEDs). Moreover, we found that the metal nano-structure is very important facto to decide the light extraction. A possible mechanism of QW-SP coupling and emission enhancement has been developed, and high-speed and efficient light emission is predicted for optically as well as electrically pumped light emitters