2,383 research outputs found
Impact of Active Layer Morphology, Density of States, Charge Carrier Concentration, and Local Charge Density Fluctuations on Bimolecular Recombination of Bulk Heterojunction Solar Cells: A Theoretical Perspective
We study the merits of a reaction-diffusion model to unravel the effects of active layer morphology and donor-acceptor interfacial roughness, density of states, charge carrier concentration, and local charge density fluctuations on the bimolecular recombination kinetics in bulk heterojunction organic semiconductors. We consider the cases of a single and composite electronic density of states (DoS) that consists of a superposition of a Gaussian and an exponential DoS. Using kinetic Monte Carlo (KMC) simulations, we apply the reaction-diffusion model in order to investigate the factors impacting bimolecular recombination (BMR) kinetics and rates at short and long time scales. We find that morphology, donor-acceptor interfacial roughness, and charge carrier concentration only affect BMR time, whereas DoS characteristics as well as local charge density fluctuations can significantly impact BMR kinetics and rates
Mapping out the time-evolution of exoplanet processes
There are many competing theories and models describing the formation,
migration and evolution of exoplanet systems. As both the precision with which
we can characterize exoplanets and their host stars, and the number of systems
for which we can make such a characterization increase, we begin to see
pathways forward for validating these theories. In this white paper we identify
predicted, observable correlations that are accessible in the near future,
particularly trends in exoplanet populations, radii, orbits and atmospheres
with host star age. By compiling a statistically significant sample of
well-characterized exoplanets with precisely measured ages, we should be able
to begin identifying the dominant processes governing the time-evolution of
exoplanet systems.Comment: Astro2020 white pape
Faking Is as Faking Does: A Rejoinder to Marcus (2021)
Applicant faking poses serious threats to achieving personality-based fit, negatively affecting both the worker and the organization. In articulating this âfaking-is-badâ (FIB) position, Tett and Simonet (2021) identify Marcusâ (2009) self-presentation theory (SPT) as representative of the contrarian âfaking-is-goodâ camp by its advancement of self-presentation as beneficial in hiring contexts. In this rejoinder, we address 20 of Marcusâ (2021) claims in highlighting his reliance on an outdated empiricist rendering of validity, loosely justified rejection of the negative and moralistic âfakingâ label, disregard for the many challenges posed by blatant forms of faking, inattention to faking research supporting the FIB position, indefensibly ambiguous constructs, and deep misunderstanding of personâworkplace fit based on personality assessment. In demonstrating these and other limitations of Marcusâ critique, we firmly uphold the FIB position and clarify SPT as headed in the wrong direction
Triangulations Admit Dominating Sets of Size
We show that every planar triangulation on vertices has a dominating
set of size . This approaches the bound conjectured by
Matheson and Tarjan [MT'96], and improves significantly on the previous best
bound of by \v{S}pacapan [\v{S}'20].
From our proof it follows that every 3-connected -vertex
near-triangulation (except for 3 sporadic examples) has a dominating set of
size . On the other hand, for 3-connected near-triangulations, we show a
lower bound of , demonstrating that the conjecture by
Matheson and Tarjan [MT'96] cannot be strengthened to 3-connected
near-triangulations.
Our proof uses a penalty function that, aside from the number of vertices,
penalises vertices of degree 2 and specific constellations of neighbours of
degree 3 along the boundary of the outer face. To facilitate induction, we not
only consider near-triangulations, but a wider class of graphs (skeletal
triangulations), allowing us to delete vertices more freely. Our main technical
contribution is a set of attachments, that are small graphs we inductively
attach to our graph, in order both to remember whether existing vertices are
already dominated, and that serve as a tool in a divide and conquer approach.
Along with a well-chosen potential function, we thus both remove and add
vertices during the induction proof.
We complement our proof with a constructive algorithm that returns a
dominating set of size . Our algorithm has a quadratic running time
A Search for a Sub-Earth Sized Companion to GJ 436 and a Novel Method to Calibrate Warm Spitzer IRAC Observations
We discovered evidence for a possible additional 0.75 R_Earth transiting
planet in the NASA EPOXI observations of the known M dwarf exoplanetary system
GJ 436. Based on an ephemeris determined from the EPOXI data, we predicted a
transit event in an extant Spitzer Space Telescope 8 micron data set of this
star. Our subsequent analysis of those Spitzer data confirmed the signal of the
predicted depth and at the predicted time, but we found that the transit depth
was dependent on the aperture used to perform the photometry. Based on these
suggestive findings, we gathered new Warm Spitzer Observations of GJ 436 at 4.5
microns spanning a time of transit predicted from the EPOXI and Spitzer 8
micron candidate events. The 4.5 micron data permit us to rule out a transit at
high confidence, and we conclude that the earlier candidate transit signals
resulted from correlated noise in the EPOXI and Spitzer 8 micron observations.
In the course of this investigation, we developed a novel method for correcting
the intrapixel sensitivity variations of the 3.6 and 4.5 micron channels of the
Infrared Array Camera (IRAC) instrument. We demonstrate the sensitivity of Warm
Spitzer observations of M dwarfs to confirm sub-Earth sized planets. Our
analysis will inform similar work that will be undertaken to use Warm Spitzer
observations to confirm rocky planets discovered by the Kepler mission.Comment: 22 pages, 8 figures, accepted for publication in PAS
eleanor: An open-source tool for extracting light curves from the TESS Full-Frame Images
During its two year prime mission the Transiting Exoplanet Survey Satellite
(TESS) will perform a time-series photometric survey covering over 80% of the
sky. This survey comprises observations of 26 24 x 96 degree sectors that are
each monitored continuously for approximately 27 days. The main goal of TESS is
to find transiting planets around 200,000 pre-selected stars for which fixed
aperture photometry is recorded every two minutes. However, TESS is also
recording and delivering Full-Frame Images (FFIs) of each detector at a 30
minute cadence. We have created an open-source tool, eleanor, to produce light
curves for objects in the TESS FFIs. Here, we describe the methods used in
eleanor to produce light curves that are optimized for planet searches. The
tool performs background subtraction, aperture and PSF photometry,
decorrelation of instrument systematics, and cotrending using principal
component analysis. We recover known transiting exoplanets in the FFIs to
validate the pipeline and perform a limited search for new planet candidates in
Sector 1. Our tests indicate that eleanor produces light curves with
significantly less scatter than other tools that have been used in the
literature. Cadence-stacked images, and raw and detrended eleanor light curves
for each analyzed star will be hosted on MAST, with planet candidates on
ExoFOP-TESS as Community TESS Objects of Interest (CTOIs). This work confirms
the promise that the TESS FFIs will enable the detection of thousands of new
exoplanets and a broad range of time domain astrophysics.Comment: 21 pages, 13 figures, 2 tables, Accepted to PAS
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