We describe the development of solar water-splitting cells comprising earth-abundant elements that operate in near-neutral pH conditions, both with and without connecting wires. The cells consist of ...a triple junction, amorphous silicon photovoltaic interfaced to hydrogen-and oxygen-evolving catalysts made from an alloy of earth-abundant metals and a cobaltlborate catalyst, respectively. The devices described here carry out the solar-driven water-splitting reaction at efficiencies of 4.7% for a wired configuration and 2.5% for a wireless configuration when illuminated with 1 sun (100 milliwatts per square centimeter) of air mass 1.5 simulated sunlight. Fuel-forming catalysts interfaced with light-harvesting semiconductors afford a pathway to direct solar-to-fuels conversion that captures many of the basic functional elements of a leaf.
One of the important factors limiting solar-cell efficiency is that incident photons generate one electron-hole pair, irrespective of the photon energy. Any excess photon energy is lost as heat. The ...possible generation of multiple charge carriers per photon (carrier multiplication) is therefore of great interest for future solar cells. Carrier multiplication is known to occur in bulk semiconductors, but has been thought to be enhanced significantly in nanocrystalline materials such as quantum dots, owing to their discrete energy levels and enhanced Coulomb interactions. Contrary to this expectation, we demonstrate here that, for a given photon energy, carrier multiplication occurs more efficiently in bulk PbS and PbSe than in quantum dots of the same materials. Measured carrier-multiplication efficiencies in bulk materials are reproduced quantitatively using tight-binding calculations, which indicate that the reduced carrier-multiplication efficiency in quantum dots can be ascribed to the reduced density of states in these structures.
Integrating a silicon solar cell with a recently developed cobalt-based water-splitting catalyst (Co-Pi) yields a robust, monolithic, photo-assisted anode for the solar fuels process of water ...splitting to Oâ at neutral pH. Deposition of the Co-Pi catalyst on the Indium Tin Oxide (ITO)-passivated p-side of a np-Si junction enables the majority of the voltage generated by the solar cell to be utilized for driving the water-splitting reaction. Operation under neutral pH conditions fosters enhanced stability of the anode as compared to operation under alkaline conditions (pH 14) for which long-term stability is much more problematic. This demonstration of a simple, robust construct for photo-assisted water splitting is an important step towards the development of inexpensive direct solar-to-fuel energy conversion technologies.
Vitamin C is a crucial micronutrient for human immune cell function and has potent antioxidant properties. It is hypothesized that vitamin C serum levels decline during infection. However, the ...precise mechanisms remain unknown. To gain deeper insights into the true role of vitamin C during infections, we aimed to evaluate the body’s vitamin C storage during a SARS-CoV-2 infection. In this single-center study, we examined serum and intracellular vitamin C levels in peripheral blood mononuclear cells (PBMCs) of 70 hospitalized COVID-19 patients on the first and fifth days of hospitalization. Also, clinical COVID-19 severity was evaluated at these timepoints. Our findings revealed a high prevalence of hypovitaminosis C and vitamin C deficiency in hospitalized COVID-19 patients (36% and 15%). Moreover, patients with severe or critical disease exhibited a higher prevalence of low serum vitamin C levels than those with moderate illness. Serum vitamin C levels had a weak negative correlation with clinical COVID-19 severity classification on the day of hospitalization; however, there was no correlation with intracellular vitamin C. Intracellular vitamin C levels were decreased in this cohort as compared to a healthy cohort and showed further decline during hospitalization, while serum levels showed no relevant change. Based on this observation, it can be suggested that the reduction of intracellular vitamin C may be attributed to its antioxidative function, the need for replenishing serum levels, or enhanced turnover by immune cells. These data give an incentive to further investigate the role of intracellular vitamin C in a larger and more heterogeneous cohort as well as the underlying mechanisms.
•The dividing manifold induces an uneven flow distribution in a spacer-filled channel.•A simple parametric RTD model fails to describe the real flow pattern.•The repetitive unit cell CFD model does ...not represent the experimental RTD curves.•The segregated laminar flow model (SLFM) can emulate the RTD in the dividing manifold.•A combined SLFM with plug exchange dispersion (PED) model approximates the global RTD.
Manifolds are critical to the performance of different membrane-based technologies. These stack components distribute the inlet and outlet flow with the aim of providing a homogenous flow pattern inside the spacer-filled channels. This work analyzes the role of manifolds on the flow pattern within the channels of membrane stacks used primarily for electrodialysis and acid-base flow batteries. First, residence time distribution (RTD) curves are predicted for a spacer-filled channel by means of three strategies: (a) computational fluid dynamics (CFD) simulation using a periodic unit cell model, (b) parametric models: axial dispersion model (ADM) and the plug dispersion exchange (PED) model using Danckwerts-type boundary conditions, and (c) the ADM and PED model using the segregate flow laminar model (SFLM) as flow pattern at the left-hand side (z=0-) in the Danckwerts-type inlet boundary condition. In contrast to previous studies, it is shown that the dividing manifold generates experimental RTD curves with several peaks characteristic of uneven distribution and long-tailing phenomena with small fluctuations related to the woven spacer and the combining manifold, respectively. The periodic unit cell CFD model, the ADM and PED model with convectional Danckwerts-type boundary conditions do not predict the RTD experimental curves because they do not consider the effect of RTD curves for the manifolds. On the other hand, the SFLM described these RTD curves adequately, as obtained by CFD simulations; this model used the left-hand side of Danckwerts inlet boundary condition for the PDE model, which had a good agreement to the global RTD experimental curves and their peaks. This study demonstrates that the global RTD curve of electrolytes in rectangular, spacer-filled channels must consider the effect of dividing and combining manifolds as inlet/outlet distributors. The strategy developed here can be used to design and scale-up membrane stacks for industrial and energy conversion applications.
We report on the gradual evolution of the conductivity of spherical CdTe nanocrystals of increasing size from the regime of strong quantum confinement with truly discrete energy levels to the regime ...of weak confinement with closely spaced hole states. We use the high-frequency (terahertz) real and imaginary conductivities of optically injected carriers in the nanocrystals to report on the degree of quantum confinement. For the smaller CdTe nanocrystals (3 nm < radius < 5 nm), the complex terahertz conductivity is purely imaginary. For nanocrystals with radii exceeding 5 nm, we observe the onset of real conductivity, which is attributed to the increasingly smaller separation between the hole states. Remarkably, this onset occurs for a nanocrystal radius significantly smaller than the bulk exciton Bohr radius a(B) ∼ 7 nm and cannot be explained by purely electronic transitions between hole states, as evidenced by tight-binding calculations. The real-valued conductivity observed in the larger nanocrystals can be explained by the emergence of mixed carrier-phonon, that is, polaron, states due to hole transitions that become resonant with, and couple strongly to, optical phonon modes for larger QDs. These polaron states possess larger oscillator strengths and broader absorption, and thereby give rise to enhanced real conductivity within the nanocrystals despite the confinement.
•Irradiance based measure of solar yields in the Netherlands.•Estimates are on a regional, national, daily and annual basis.•Current annual yields for 2016 and 2017 were under and over ...estimated.•Sensitivity analysis for representativeness of photovoltaic system population.•Orientation, tilt and inverter to photovoltaic capacity ratio are important factors.
This paper presents a classical estimation problem for calculating the energy generated by photovoltaic solar energy systems, on a daily, annual, regional and national basis. Our methodology relies on two data sources: PVOutput, an online portal with solar energy production measurements, and modelled irradiance data available for large parts of Africa and Europe, from the Royal Netherlands Meteorological Institute. Combining these, we obtain probability functions of observing energy production, given the irradiation. These are applied to a PV systems database, using Monte Carlo sampling, allowing daily and annual solar energy production to be calculated. These are, in turn, used to calculate solar energy production per municipality. As a case study, we apply this methodology to one country in particular, namely the Netherlands. By examining the variation in our estimates as a result of taking different subsets of PVOutput systems with certain specifications such as azimuth, tilt and inverter loading ratio, we obtain specific annual energy yields in the range of 877-946kWh/kWp and 838-899kWh/kWp for 2016 and 2017 respectively. The current method used at Statistics Netherlands assumes this to be 875kWh/kWp, irrespective of irradiation, meaning the yields were underestimated in 2016 and overestimated in 2017. In the case of the Netherlands, this research demonstrates that an irradiation based measure of solar energy generation is necessary. More generally, this research shows that different types of open data sources may be combined to develop models that calculate the energy production of PV system populations.
Classically, mossy fiber and climbing fiber terminals are regarded as having very different spatial distributions in the cerebellar cortex. However, previous anatomical studies have not studied these ...two major cerebellar inputs with sufficient resolution to confirm this assumption. Here, we examine the detailed pattern of collateralization of both types of cerebellar afferent using small injections of the bidirectional tracer cholera toxin b subunit into the posterior cerebellum. The cortical and zonal location of these injections was characterized by mapping climbing fiber field potentials, the distribution of retrogradely labeled olivary neurons, and the intrinsic zebrin pattern of Purkinje cells. Labeled climbing fiber collaterals were distributed as longitudinal strips and were always accompanied by clusters of labeled mossy fiber rosettes in the subjacent granular layer. Two- and three-dimensional reconstructions and quantitative analysis showed that mossy fibers also collateralized to other stripe-like regions usually below Purkinje cells with the same zebrin-positive or zebrin-negative characteristics as that of the injection site and associated climbing fiber collaterals. The distribution of retrogradely labeled neurons in two major sources of mossy fibers, the lateral reticular and basilar pontine nuclei, revealed interlobular and some interzonal differences. These data indicate that nonadjacent cerebellar zones, sharing the same climbing fiber input and zebrin identity, also share a common mossy fiber input. Other cerebellar cortical regions that receive collaterals from the same mossy fibers usually also have the same zebrin signature. Together with the distribution of neurons in precerebellar centers, the findings suggest a revision of the modular hypothesis for information processing in the cerebellar cortex.
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