50 research outputs found
Reducing the impact of source brightness fluctuations on spectra obtained by Fourier-transform spectrometry
We present a method to reduce the impact of source brightness fluctuations (SBFs) on spectra recorded by Fourier-transform spectrometry (FTS). Interferograms are recorded without AC coupling of the detector signal (DC mode). The SBF are determined by low-pass filtering of the DC interferograms, which are then reweighted by the low-pass, smoothed signal. Atmospheric solar absorption interferograms recorded in DC mode have been processed with and without this technique, and we demonstrate its efficacy in producing more consistent retrievals of atmospheric composition. We show that the reweighting algorithm improves retrievals from interferograms subject to both gray and nongray intensity fluctuations, making the algorithm applicable to atmospheric data contaminated by significant amounts of aerosol or cloud cover
Momentum flow in black-hole binaries: II. Numerical simulations of equal-mass, head-on mergers with antiparallel spins
Research on extracting science from binary-black-hole (BBH) simulations has
often adopted a "scattering matrix" perspective: given the binary's initial
parameters, what are the final hole's parameters and the emitted gravitational
waveform? In contrast, we are using BBH simulations to explore the nonlinear
dynamics of curved spacetime. Focusing on the head-on plunge, merger, and
ringdown of a BBH with transverse, antiparallel spins, we explore numerically
the momentum flow between the holes and the surrounding spacetime. We use the
Landau-Lifshitz field-theory-in-flat-spacetime formulation of general
relativity to define and compute the density of field energy and field momentum
outside horizons and the energy and momentum contained within horizons, and we
define the effective velocity of each apparent and event horizon as the ratio
of its enclosed momentum to its enclosed mass-energy. We find surprisingly good
agreement between the horizons' effective and coordinate velocities. To
investigate the gauge dependence of our results, we compare pseudospectral and
moving-puncture evolutions of physically similar initial data; although
spectral and puncture simulations use different gauge conditions, we find
remarkably good agreement for our results in these two cases. We also compare
our simulations with the post-Newtonian trajectories and near-field
energy-momentum. [Abstract abbreviated; full abstract also mentions additional
results.]Comment: Submitted to Phys. Rev.
If I Hear You Correctly: Building and Evaluating Interview Chatbots with Active Listening Skills
Interview chatbots engage users in a text-based conversation to draw out
their views and opinions. It is, however, challenging to build effective
interview chatbots that can handle user free-text responses to open-ended
questions and deliver engaging user experience. As the first step, we are
investigating the feasibility and effectiveness of using publicly available,
practical AI technologies to build effective interview chatbots. To demonstrate
feasibility, we built a prototype scoped to enable interview chatbots with a
subset of active listening skills - the abilities to comprehend a user's input
and respond properly. To evaluate the effectiveness of our prototype, we
compared the performance of interview chatbots with or without active listening
skills on four common interview topics in a live evaluation with 206 users. Our
work presents practical design implications for building effective interview
chatbots, hybrid chatbot platforms, and empathetic chatbots beyond interview
tasks.Comment: Working draft. To appear in the ACM CHI Conference on Human Factors
in Computing Systems (CHI 2020
Co-limitation towards lower latitudes shapes global forest diversity gradients
The latitudinal diversity gradient (LDG) is one of the most recognized global patterns of species richness exhibited across a wide range of taxa. Numerous hypotheses have been proposed in the past two centuries to explain LDG, but rigorous tests of the drivers of LDGs have been limited by a lack of high-quality global species richness data. Here we produce a high-resolution (0.025° × 0.025°) map of local tree species richness using a global forest inventory database with individual tree information and local biophysical characteristics from ~1.3 million sample plots. We then quantify drivers of local tree species richness patterns across latitudes. Generally, annual mean temperature was a dominant predictor of tree species richness, which is most consistent with the metabolic theory of biodiversity (MTB). However, MTB underestimated LDG in the tropics, where high species richness was also moderated by topographic, soil and anthropogenic factors operating at local scales. Given that local landscape variables operate synergistically with bioclimatic factors in shaping the global LDG pattern, we suggest that MTB be extended to account for co-limitation by subordinate drivers
Design and analysis a researcher s handbook/ Keppel
xiii, 669 hal.: ill.; 24 cm
Design and analysis a researcher s handbook/ Keppel
xiii, 669 hal.: ill.; 24 cm
Introduction to Design and Analysis : A Student's Handbook
X, 490 tr.; 23 cm