53 research outputs found
Enhanced Open-Circuit Voltage of Wide-Bandgap Perovskite Photovoltaics by Using Alloyed (FA1–xCsx)Pb(I1–xBrx)3 Quantum Dots
We report a detailed study on APbX3 (A=Formamidinium (FA+), Cs+; X=I-, Br-) perovskite quantum dots (PQDs) with combined A- and X-site alloying that exhibit, both, a wide bandgap and high open circuit voltage (Voc) for the application of a potential top cell in tandem junction photovoltaic (PV) devices. The nanocrystal alloying affords control over the optical bandgap and is readily achieved by solution-phase cation and anion exchange between previously synthesized FAPbI3 and CsPbBr3 PQDs. Increasing only the Br- content of the PQDs widens the bandgap but results in shorter carrier lifetimes and associated Voc losses in devices. These deleterious effects can be mitigated by replacing Cs+ with FA+, resulting in wide bandgap PQD absorbers with improved charge-carrier mobility and PVs with higher Voc. Although further device optimization is required, these results demonstrate the potential of FA1–xCsx)Pb(I1–xBrx)3 PQDs for wide bandgap perovskite PVs with high Voc
Adults’ number-line estimation strategies: Evidence from eye movements
Although the development of number-line estimation ability is well documented, little is known of the processes underlying successful estimators’ mappings of numerical information onto spatial representations during these tasks. We tracked adults’ eye movements during a number-line estimation task to investigate the processes underlying number-to-space translation, with three main results. First, eye movements were strongly related to the target number’s location, and early processing measures directly predicted later estimation performance. Second, fixations and estimates were influenced by the size of the first number presented, indicating that adults calibrate their estimates online. Third, adults’ number-line estimates demonstrated patterns of error consistent with the predictions of psychophysical models of proportion estimation, and eye movement data predicted the specific error patterns we observed. These results support proportion-based accounts of number-line estimation and suggest that adults’ translation of numerical information into spatial representations is a rapid, online process
Exoplanet Biosignatures: Understanding Oxygen as a Biosignature in the Context of Its Environment
Here we review how environmental context can be used to interpret whether O2
is a biosignature in extrasolar planetary observations. This paper builds on
the overview of current biosignature research discussed in Schwieterman et al.
(2017), and provides an in-depth, interdisciplinary example of biosignature
identification and observation that serves as a basis for the development of
the general framework for biosignature assessment described in Catling et al.,
(2017). O2 is a potentially strong biosignature that was originally thought to
be an unambiguous indicator for life at high-abundance. We describe the
coevolution of life with the early Earth's environment, and how the interplay
of sources and sinks in the planetary environment may have resulted in
suppression of O2 release into the atmosphere for several billion years, a
false negative for biologically generated O2. False positives may also be
possible, with recent research showing potential mechanisms in exoplanet
environments that may generate relatively high abundances of atmospheric O2
without a biosphere being present. These studies suggest that planetary
characteristics that may enhance false negatives should be considered when
selecting targets for biosignature searches. Similarly our ability to interpret
O2 observed in an exoplanetary atmosphere is also crucially dependent on
environmental context to rule out false positive mechanisms. We describe future
photometric, spectroscopic and time-dependent observations of O2 and the
planetary environment that could increase our confidence that any observed O2
is a biosignature, and help discriminate it from potential false positives. By
observing and understanding O2 in its planetary context we can increase our
confidence in the remote detection of life, and provide a model for
biosignature development for other proposed biosignatures.Comment: 55 pages. The paper is the second in a series of 5 review manuscripts
of the NExSS Exoplanet Biosignatures Workshop. Community commenting is
solicited at https://nexss.info/groups/ebww
Spatial Intuition in Elementary Arithmetic: A Neurocomputational Account
Elementary arithmetic (e.g., addition, subtraction) in humans has been shown to exhibit spatial properties. Its exact nature has remained elusive, however. To address this issue, we combine two earlier models for parietal cortex: A model we recently proposed on number-space interactions and a modeling framework of parietal cortex that implements radial basis functions for performing spatial transformations. Together, they provide us with a framework in which elementary arithmetic is based on evolutionarily more basic spatial transformations, thus providing the first implemented instance of Dehaene and Cohen's recycling hypothesis
Q/R site interactions with the M3 helix in GluK2 kainate receptor channels revealed by thermodynamic mutant cycles
RNA editing at the Q/R site near the apex of the pore loop of AMPA and kainate receptors controls a diverse array of channel properties, including ion selectivity and unitary conductance and susceptibility to inhibition by polyamines and cis-unsaturated fatty acids, as well as subunit assembly into tetramers and regulation by auxiliary subunits. How these different aspects of channel function are all determined by a single amino acid substitution remains poorly understood; however, several lines of evidence suggest that interaction between the pore helix (M2) and adjacent segments of the transmembrane inner (M3) and outer (M1) helices may be involved. In the present study, we have used double mutant cycle analysis to test for energetic coupling between the Q/R site residue and amino acid side chains along the M3 helix. Our results demonstrate interaction with several M3 locations and particularly strong coupling to substitution for L614 at the level of the central cavity. In this location, replacement with smaller side chains completely and selectively reverses the effect of fatty acids on gating of edited channels, converting strong inhibition of wild-type GluK2(R) to nearly 10-fold potentiation of GluK2(R) L614A
Life Beyond the Solar System: Remotely Detectable Biosignatures
For the first time in human history, we will soon be able to apply to the scientific method to the question "Are We Alone?" The rapid advance of exoplanet discovery, planetary systems science, and telescope technology will soon allow scientists to search for life beyond our Solar System through direct observation of extrasolar planets. This endeavor will occur alongside searches for habitable environments and signs of life within our Solar System. While these searches are thematically related and will inform each other, they will require separate observational techniques. The search for life on exoplanets holds potential through the great diversity of worlds to be explored beyond our Solar System. However, there are also unique challenges related to the relatively limited data this search will obtain on any individual world
Lunar Volatiles and Solar System Science
Understanding the origin and evolution of the lunar volatile system is not
only compelling lunar science, but also fundamental Solar System science. This
white paper (submitted to the US National Academies' Decadal Survey in
Planetary Science and Astrobiology 2023-2032) summarizes recent advances in our
understanding of lunar volatiles, identifies outstanding questions for the next
decade, and discusses key steps required to address these questions
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Hybrid organic-inorganic perovskites : humidity stability and CdTe tandem photovoltaics
Solution-processed hybrid organic-inorganic perovskites (HOIPs) have garnered significant interest for tandem photovoltaics (PVs)-solar cell architectures that employ two absorber layers to overcome the PV thermodynamic efficiency limit. Perovskites have been coupled in tandem with silicon, CIGS, and other perovskites to boost PV efficiency. However, they have not been employed in tandem with popular PV material CdTe. Additionally, HOIPs suffer from rapid humidity-induced degradation, which limits their commercial application in general. Here, compositional engineering of the B-site is used to tune humidity stability of model HOIP semiconductors, and HOIP materials for tandem CdTe-HOIP PV are developed. Substituting Pb²⁺ 5% with Bi³⁺ in model HOIP CH₃NH₃PbI₃ (MAPI) is seen to stabilize MAPI at 90% humidity, but destabilize MAPI at 60% humidity, making bismuth the first HOIP additive observed to have a stabilizing and destabilizing effect at different humidity conditions. From mechanistic insight and kinetic modeling, this stabilizing and destabilizing effect is shown to be due to Bi³⁺ impacting the kinetics of different steps of the degradation reaction mechanism distinctly. The related humidity-induced degradation/deliquescence of transition metal halide thin films is then made use of in thin films of NiI₂. Water vapor uptake is seen to rapidly modulate light transmittance uniformly across the visible spectra, making NiI₂ films candidates for color-neutral smart windows. HOIP-CdTe tandem cells are then studied. Traditional iodide-based HOIPs have band gaps that are too similar to CdTe for efficient tandem PV; therefore, CdTe is coupled with wide band gap CH₃NH₃PbBr₃ (MAPBr). MAPBr films exhibit a significant amount of haze due to optical loss in the MAPBr layer, which correlates with poor tandem PV performance. The Semiconductor Capacitance Simulator (SCAPS) software package is then utilized to determine the degree of haze that can be tolerated in a MAPBr-CdTe tandem before MAPBr begins to worsen CdTe PV efficiency. Inclusion of Ag⁺ is seen to produce MAPBr films with uniform crystallographic orientation due to surface segregation of Ag and respective lowering of the surface energy of (100) MAPBr facets. Finally, initial steps towards Tl-based low band gap HOIP nanostructures for CdTe-HOIP tandem PV with ideally matched band gaps are undertakenChemical Engineerin
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