Spectrally Matched Quantum Dot Photoluminescence in GaAs-Si Tandem Luminescent Solar Concentrators

Luminescent solar concentrators (LSCs) can capture both direct and diffuse irradiance via isotropic absorption of waveguide-embedded luminophores. Additionally, LSCs have the potential to reduce the overall cost of a photovoltaic (PV) module by concentrating incident irradiance onto an array of smaller cells. Historically, LSC efficiencies have suffered in part from incomplete light absorption and non-unity quantum yield (QY) of the luminophores. Inorganic quantum dot (QD) luminophores allow the spectral tuning of the absorption and photoluminescence bands, and have near-unity QYs. In a four-terminal tandem LSC module scheme, visible light is trapped within the LSC waveguide and is converted by GaAs cells, and near infrared light is optically coupled to a Si subcell. Here, we investigate the efficiency of a GaAs/Si tandem LSC as a function of luminophore absorption edge and emission wavelength for QD luminophores dispersed in an LSC waveguide with embedded, coplanar GaAs cells. We find that positioning the luminophore absorption edge at 660 nm yields a maximum module power efficiency of approximately 26%, compared with 21% for the non-optimized luminophore and 19% for the bare Si cases

Micro-optical Tandem Luminescent Solar Concentrators

Traditional concentrating photovoltaic (CPV) systems utilize multijunction cells to minimize thermalization losses, but cannot efficiently capture diffuse sunlight, which contributes to a high levelized cost of energy (LCOE) and limits their use to geographical regions with high direct sunlight insolation. Luminescent solar concentrators (LSCs) harness light generated by luminophores embedded in a light-trapping waveguide to concentrate light onto smaller cells. LSCs can absorb both direct and diffuse sunlight, and thus can operate as flat plate receivers at a fixed tilt and with a conventional module form factor. However, current LSCs experience significant power loss through parasitic luminophore absorption and incomplete light trapping by the optical waveguide. Here we introduce a tandem LSC device architecture that overcomes both of these limitations, consisting of a PLMA polymer layer with embedded CdSe/CdS quantum dot (QD) luminophores and InGaP micro-cells, which serve as a high bandgap absorber on top of a conventional Si photovoltaic. We experimentally synthesize CdSe/CdS QDs with exceptionally high quantum-yield (99%) and ultra-narrowband emission optimally matched to fabricated III-V InGaP micro-cells. Using a Monte Carlo ray-tracing model, we show the radiative limit power conversion efficiency for a module with these components to be 30.8% diffuse sunlight conditions. These results indicate that a tandem LSC-on-Si architecture could significantly improve upon the efficiency of a conventional Si photovoltaic module with simple and straightforward alterations of the module lamination steps of a Si photovoltaic manufacturing process, with promise for widespread module deployment across diverse geographical regions and energy markets

Do We Get What We Need from Clinical Acoustic Voice Measurements?

Instrumental acoustic measurements of the human voice have enormous potential to objectively describe pathology and, thereby, to assist clinical treatment decisions. Despite the increasing application and accessibility of technical knowledge and equipment, recent research has highlighted a lack of understanding of physiologic, speech/language-, and culture-related influencing factors. This article presents a critical review of the current state of the art in the clinical application of instrumental acoustic voice quality measurements and points out future directions for improving its applications and dissemination in less privileged populations. The main barriers to this research relate to (a) standardization and reporting of acoustic analysis techniques; (b) understanding of the relation between perceptual and instrumental acoustic results; (c) the necessity to account for natural speech-related covariables, such as differences in speaking voice sound pressure level (SPL) and fundamental frequency f0; (d) the need for a much larger database to understand normal variability within and between voice-disordered and vocally healthy individuals related to age, training, and physiologic factors; and (e) affordable equipment, including mobile communication devices, accessible in various settings. This calls for further research into technical developments and optimal assessment procedures for pathology-specific patient groups

Early visual ERPs show stable body-sensitive patterns over a 4-week test period

Event-related potential (ERP) studies feature among the most cited papers in the field of body representation, with recent research highlighting the potential of ERPs as neuropsychiatric biomarkers. Despite this, investigation into how reliable early visual ERPs and body-sensitive effects are over time has been overlooked. This study therefore aimed to assess the stability of early body-sensitive effects and visual P1, N1 and VPP responses. Participants were asked to identify pictures of their own bodies, other bodies and houses during an EEG test session that was completed at the same time, once a week, for four consecutive weeks. Results showed that amplitude and latency of early visual components and their associated body-sensitive effects were stable over the 4-week period. Furthermore, correlational analyses revealed that VPP component amplitude might be more reliable than VPP latency and specific electrode sites might be more robust indicators of body-sensitive cortical activity than others. These findings suggest that visual P1, N1 and VPP responses, alongside body-sensitive N1/VPP effects, are robust indications of neuronal activity. We conclude that these components are eligible to be considered as electrophysiological biomarkers relevant to body representation

Sovereign Debt and Tax Collection Dynamics in Argentina

This manuscript examines how the dynamic macroeconomic effects from shocks to taxes and inflation differ between the United States and Argentina. On the fiscal side, wages, private capital, and consumption tax cuts have long-run revenue growth effects (in both countries) that mitigate initial tax receipt losses. These growth effects, however, are larger in Argentina - a country where both the consumption tax rate and sensitivity to wage changes are higher. Specifically, Chapter 2 finds that growth from a U.S. capital tax cut pays for roughly 60% of the initial static loss, whereas the corresponding effect in Argentina is 80%. On the monetary side, multiple regimes are then considered with money in the utility function to determine optimal scenarios, holding tax revenues constant. Chapter 3 concludes that distortions from taxes on wages, private capital, and inflation outweigh the efficiency losses from a consumption tax, and as such, an economy whose government places more emphasis on consumption to generate tax receipts achieves higher utility. The tax frameworks introduced in Chapters 2 and 3 build from the neoclassical Ramsey growth models. Inflation\u27s role as a source of revenue via seigniorage in Chapter 3 is extended to the Argentine fixed income market in Chapter 4. Using proprietary pricing data and a structural vector autoregression framework, Chapter 4 finds that inflation as a predictor of the probability of default in Argentina is much larger than the government claims it to be; despite non-investment-grade government bonds, Argentina\u27s fixed income market actually became more attractive during the U.S. mortgage crisis; and global risk aversion has predictive power in explaining sovereign spreads

Knowledge Fusion in Soil Hydrology

The mathematical representation of soil water movement exhibits uncertainties in all model components. Data assimilation methods, like the ensemble Kalman filter (EnKF), combine models and measurements into an improved representation and can – at least in principle – account for all uncertainties. However, a proper description of the uncertainties is required, which is particularly difficult in soil hydrology, where model errors typically vary rapidly in space and time. Inflation methods can account for unrepresented model errors. To improve the EnKF performance, I designed an inflation method specifically for soil hydrology, that is capable of adjusting inflation factors to spatiotemporally varying model errors. For the application on a real-world case, I assessed the key uncertainties for the specific hydraulic situation of a 1-D soil profile with TDR (time domain reflectometry)-measured water contents. With the EnKF, I directly represented and reduced all key uncertainties (initial condition, soil hydraulic parameters, small-scale heterogeneity, and upper boundary condition), except for an intermittent violation of the local equilibrium assumption by the Richards equation. To bridge this time, I introduced a closed-eye period, which ensures constant parameters and improves the EnKF towards the goal of knowledge fusion – the consistent aggregation of all information pertinent to some observed reality

Letter From Ricky Brewster to Eleanor Snell

This letter from Ruth Ricky Bauser, Ursinus College Class of 1956, congratulates Eleanor Snell on the occasion of her retirement from Ursinus College and remarks on Eleanor\u27s patience and compassion.https://digitalcommons.ursinus.edu/snell_docs/1063/thumbnail.jp