Systematic derivation of a surface polarization model for planar perovskite solar cells

Increasing evidence suggests that the presence of mobile ions in perovskite solar cells can cause a current-voltage curve hysteresis. Steady state and transient current-voltage characteristics of a planar metal halide CH$_3$NH$_3$PbI$_3$ perovskite solar cell are analysed with a drift-diffusion model that accounts for both charge transport and ion vacancy motion. The high ion vacancy density within the perovskite layer gives rise to narrow Debye layers (typical width $\sim$2nm), adjacent to the interfaces with the transport layers, over which large drops in the electric potential occur and in which significant charge is stored. Large disparities between (I) the width of the Debye layers and that of the perovskite layer ($\sim$600nm) and (II) the ion vacancy density and the charge carrier densities motivate an asymptotic approach to solving the model, while the stiffness of the equations renders standard solution methods unreliable. We derive a simplified surface polarisation model in which the slow ion dynamic are replaced by interfacial (nonlinear) capacitances at the perovskite interfaces. Favourable comparison is made between the results of the asymptotic approach and numerical solutions for a realistic cell over a wide range of operating conditions of practical interest.Comment: 32 pages, 7 figure

Clinically Actionable Hypercholesterolemia and Hypertriglyceridemia in Children with Nonalcoholic Fatty Liver Disease

OBJECTIVE: To determine the percentage of children with nonalcoholic fatty liver disease (NAFLD) in whom intervention for low-density lipoprotein cholesterol or triglycerides was indicated based on National Heart, Lung, and Blood Institute guidelines. STUDY DESIGN: This multicenter, longitudinal cohort study included children with NAFLD enrolled in the National Institute of Diabetes and Digestive and Kidney Diseases Nonalcoholic Steatohepatitis Clinical Research Network. Fasting lipid profiles were obtained at diagnosis. Standardized dietary recommendations were provided. After 1 year, lipid profiles were repeated and interpreted according to National Heart, Lung, and Blood Institute Expert Panel on Integrated Guidelines for Cardiovascular Health and Risk Reduction. Main outcomes were meeting criteria for clinically actionable dyslipidemia at baseline, and either achieving lipid goal at follow-up or meeting criteria for ongoing intervention. RESULTS: There were 585 participants, with a mean age of 12.8 years. The prevalence of children warranting intervention for low-density lipoprotein cholesterol at baseline was 14%. After 1 year of recommended dietary changes, 51% achieved goal low-density lipoprotein cholesterol, 27% qualified for enhanced dietary and lifestyle modifications, and 22% met criteria for pharmacologic intervention. Elevated triglycerides were more prevalent, with 51% meeting criteria for intervention. At 1 year, 25% achieved goal triglycerides with diet and lifestyle changes, 38% met criteria for advanced dietary modifications, and 37% qualified for antihyperlipidemic medications. CONCLUSIONS: More than one-half of children with NAFLD met intervention thresholds for dyslipidemia. Based on the burden of clinically relevant dyslipidemia, lipid screening in children with NAFLD is warranted. Clinicians caring for children with NAFLD should be familiar with lipid management

Data assimilation with correlated observation errors: experiments with a 1-D shallow water model

Remote sensing observations often have correlated errors, but the correlations are typically ignored in data assimilation for numerical weather prediction. The assumption of zero correlations is often used with data thinning methods, resulting in a loss of information. As operational centres move towards higher-resolution forecasting, there is a requirement to retain data providing detail on appropriate scales. Thus an alternative approach to dealing with observation error correlations is needed. In this article, we consider several approaches to approximating observation error correlation matrices: diagonal approximations, eigendecomposition approximations and Markov matrices. These approximations are applied in incremental variational assimilation experiments with a 1-D shallow water model using synthetic observations. Our experiments quantify analysis accuracy in comparison with a reference or ‘truth’ trajectory, as well as with analyses using the ‘true’ observation error covariance matrix. We show that it is often better to include an approximate correlation structure in the observation error covariance matrix than to incorrectly assume error independence. Furthermore, by choosing a suitable matrix approximation, it is feasible and computationally cheap to include error correlation structure in a variational data assimilation algorithm

IonMonger: a free and fast planar perovskite solar cell simulator with coupled ion vacancy and charge carrier dynamics

Details of an open-source planar perovskite solar cell simulator, that includes ion vacancy migration within the perovskite layer coupled to charge carrier transport throughout the perovskite and adjoining transport layers in one dimension, are presented. The model equations are discretised in space using a finite element scheme and temporal integration of the resulting system of differential-algebraic equations is carried out in MATLAB. The user is free to modify device parameters, as well as the incident illumination and applied voltage. Time-varying voltage and/or illumination protocols can be specified, e.g. to simulate current-voltage sweeps, or to track the open-circuit conditions as the illumination is varied. Typical simulations, e.g. current-voltage sweeps, only require computation times of seconds to minutes on a modern personal computer. An example set of hysteretic current-voltage curves is presented

Evaluation of the MOCAGE Chemistry Transport Model during the ICARTT/ITOP Experiment

We evaluate the Meteo-France global chemistry transport 3D model MOCAGE (MOdele de Chimie Atmospherique a Grande Echelle) using the important set of aircraft measurements collected during the ICARRT/ITOP experiment. This experiment took place between US and Europe during summer 2004 (July 15-August 15). Four aircraft were involved in this experiment providing a wealth of chemical data in a large area including the North East of US and western Europe. The model outputs are compared to the following species of which concentration is measured by the aircraft: OH, H2O2, CO, NO, NO2, PAN, HNO3, isoprene, ethane, HCHO and O3. Moreover, to complete this evaluation at larger scale, we used also satellite data such as SCIAMACHY NO2 and MOPITT CO. Interestingly, the comprehensive dataset allowed us to evaluate separately the model representation of emissions, transport and chemical processes. Using a daily emission source of biomass burning, we obtain a very good agreement for CO while the evaluation of NO2 points out incertainties resulting from inaccurate ratio of emission factors of NOx/CO. Moreover, the chemical behavior of O3 is satisfactory as discussed in the paper

The Role of Surface Recombination on the Performance of Perovskite Solar Cells:Effect of Morphology and Crystalline Phase of TiO₂ Contact

Herein, the preparation of 1D TiO2 nanocolumnar films grown by plasma-enhanced chemical vapor deposition is reported as the electron selective layer (ESL) for perovskite solar devices. The impact of the ESL architecture (1D and 3D morphologies) and the nanocrystalline phase (anatase and amorphous) is analyzed. For anatase structures, similar power conversion efficiencies are achieved using an ESL either the 1D nanocolumns or the classical 3D nanoparticle film. However, lower power conversion efficiencies and different optoelectronic properties are found for perovskite devices based on amorphous 1D films. The use of amorphous TiO2 as electron selective contact produces a bump in the reverse scan of the current–voltage curve as well as an additional electronic signal, detected by impedance spectroscopy measurements. The dependence of this additional signal on the optical excitation wavelength used in the IS experiments suggests that it stems from an interfacial process. Calculations using a drift-diffusion model which explicitly considers the selective contacts reproduces qualitatively the main features observed experimentally. These results demonstrate that for a solar cell in which the contact is working properly the open-circuit photovoltage is mainly determined by bulk recombination, whereas the introduction of a “bad contact” shifts the balance to surface recombination.</p

In Children with Nonalcoholic Fatty Liver Disease, Zone 1 Steatosis is Associated with Advanced Fibrosis

Background & Aims Focal zone 1 steatosis, although rare in adults with nonalcoholic fatty liver disease (NAFLD), does occur in children with NAFLD. We investigated whether focal zone 1 steatosis and focal zone 3 steatosis are distinct subphenotypes of pediatric NAFLD. We aimed to determine associations between the zonality of steatosis and demographic, clinical, and histologic features in children with NAFLD. Methods We performed a cross-sectional study of baseline data from 813 children (age <18 years; mean age, 12.8 ± 2.7 years). The subjects had biopsy-proven NAFLD and were enrolled in the Nonalcoholic Steatohepatitis Clinical Research Network. Liver histology was reviewed using the Nonalcoholic Steatohepatitis Clinical Research Network scoring system. Results Zone 1 steatosis was present in 18% of children with NAFLD (n = 146) and zone 3 steatosis was present in 32% (n = 244). Children with zone 1 steatosis were significantly younger (10 vs 14 years; P < .001) and a significantly higher proportion had any fibrosis (81% vs 51%; P < .001) or advanced fibrosis (13% vs 5%; P < .001) compared with children with zone 3 steatosis. In contrast, children with zone 3 steatosis were significantly more likely to have steatohepatitis (30% vs 6% in children with zone 1 steatosis; P < .001). Conclusions Children with zone 1 or zone 3 distribution of steatosis have an important subphenotype of pediatric NAFLD. Children with zone 1 steatosis are more likely to have advanced fibrosis and children with zone 3 steatosis are more likely to have steatohepatitis. To achieve a comprehensive understanding of pediatric NAFLD, studies of pathophysiology, natural history, and response to treatment should account for the zonality of steatosis

First Observations of G-Band Radar Doppler Spectra

The first Doppler spectra ever acquired by an atmospheric radar at 200 GHz (G-band) are presented. The observations were taken during a light precipitation event in May (rain rates <2 mm hr−1) at Chilbolton Observatory, UK, with coincident Ka-band and W-band Doppler radar measurements. The collected rain spectra agree with Mie theory predictions: at G-band they show significant reductions in the spectral power return—as compared to theoretical Rayleigh scattering—corresponding to high Doppler velocities (i.e., large raindrops) with the presence of multiple peaks and “Mie notches” in correspondence to the maxima and minima of the raindrop backscattering cross sections. The first two G-band Mie troughs correspond to smaller velocities/sizes than the first W-band Mie notch. These features offered by G-band radars pave the way toward applying, in rain, Mie notch vertical wind retrievals and multifrequency drop size distribution microphysical retrievals to smaller rain rates and smaller characteristic sizes than ever before

Targeted molecular characterization shows differences between primary and secondary myelofibrosis

INTRODUCTION: In BCR-ABL1-negative myeloproliferative neoplasms, myelofibrosis (MF) is either primary (PMF) or secondary (SMF) to polycythemia vera or essential thrombocythemia. MF is characterized by an increased risk of transformation to acute myeloid leukemia (AML) and a shortened life expectancy. METHODS: Because natural histories of PMF and SMF are different, we studied by targeted next generation sequencing the differences in the molecular landscape of 86 PMF and 59 SMF and compared their prognosis impact. RESULTS: PMF had more ASXL1 (47.7%) and SRSF2 (14%) gene mutations than SMF (respectively 27.1% and 3.4%, P = .04). Poorer survival was associated with RNA splicing mutations (especially SRSF2) and TP53 in PMF (P = .0003), and with ASXL1 and TP53 mutations in SMF (P &lt; .0001). These mutations of poor prognosis were associated with biological features of scoring systems (DIPSS and MYSEC-PM score). Mutations in TP53/SRSF2 in PMF or TP53/ASXL1 in SMF were more frequent as the risk of these scores increased. This allowed for a better stratification of MF patients, especially within the DIPSS intermediate-1 risk group (DIPSS) or the MYSEC-PM high risk group. AML transformation occurred faster in SMF than in PMF and patients who transformed to AML were more SRSF2-mutated and less CALR-mutated at MF sampling. CONCLUSIONS: PMF and SMF have different but not specific molecular profiles and different prognosis depending on the molecular profile. This may be due to differences in disease history. Combining mutations and existing scores should improve prognosis assessment