316 research outputs found
Distinct phase-amplitude couplings distinguish cognitive processes in human attention
Abstract
Spatial attention is the cognitive function that coordinates the selection of visual stimuli with appropriate behavioral responses. Recent studies have reported that phase-amplitude coupling (PAC) of low and high frequencies covaries with spatial attention, but differ on the direction of covariation and the frequency ranges involved. We hypothesized that distinct phase-amplitude frequency pairs have differentiable contributions during tasks that manipulate spatial attention. We investigated this hypothesis with electrocorticography (ECoG) recordings from participants who engaged in a cued spatial attention task. To understand the contribution of PAC to spatial attention we classified cortical sites by their relationship to spatial variables or behavioral performance. Local neural activity in spatial sites was sensitive to spatial variables in the task, while local neural activity in behavioral sites correlated with reaction time. We found two PAC frequency clusters that covaried with different aspects of the task. During a period of cued attention, delta-phase/high-gamma (DH) PAC was sensitive to cue direction in spatial sites. In contrast, theta-alpha-phase/beta-low-gamma-amplitude (TABL) PAC robustly correlated with future reaction times in behavioral sites. Finally, we investigated the origins of TABL PAC and found it corresponded to behaviorally relevant, sharp waveforms, which were also coupled to a low frequency rhythm. We conclude that TABL and DH PAC correspond to distinct mechanisms during spatial attention tasks and that sharp waveforms are elements of a coupled dynamical process
Greenhouse: A Zero-Positive Machine Learning System for Time-Series Anomaly Detection
This short paper describes our ongoing research on Greenhouse - a zero-positive machine learning system for time-series anomaly detection
Precision and Recall for Range-Based Anomaly Detection
Classical anomaly detection is principally concerned with point- based anomalies, anomalies that occur at a single data point. In this paper, we present a new mathematical model to express range- based anomalies, anomalies that occur over a range (or period) of time
Prospects for the cavity-assisted laser cooling of molecules
Cooling of molecules via free-space dissipative scattering of photons is
thought not to be practicable due to the inherently large number of Raman loss
channels available to molecules and the prohibitive expense of building
multiple repumping laser systems. The use of an optical cavity to enhance
coherent Rayleigh scattering into a decaying cavity mode has been suggested as
a potential method to mitigate Raman loss, thereby enabling the laser cooling
of molecules to ultracold temperatures. We discuss the possibility of
cavity-assisted laser cooling particles without closed transitions, identify
conditions necessary to achieve efficient cooling, and suggest solutions given
experimental constraints. Specifically, it is shown that cooperativities much
greater than unity are required for cooling without loss, and that this could
be achieved via the superradiant scattering associated with intracavity
self-localization of the molecules. Particular emphasis is given to the polar
hydroxyl radical (OH), cold samples of which are readily obtained from Stark
deceleration.Comment: 18 pages, 10 figure
Experimentally measured thermal masses of adsorption heat exchangers
The thermal masses of components influence the performance of many adsorption heat pump systems. However, typically when experimental adsorption systems are reported, data on thermal mass are missing or incomplete. This work provides original measurements of the thermal masses for experimental sorption heat exchanger hardware. Much of this hardware was previously reported in the literature, but without detailed thermal mass data. The data reported in this work are the first values reported in the literature to thoroughly account for all thermal masses, including heat transfer fluid. The impact of thermal mass on system performance is also discussed, with detailed calculation left for future work. The degree to which heat transfer fluid contributes to overall effective thermal mass is also discussed, with detailed calculation left for future work. This work provides a framework for future reporting of experimental thermal masses. The utilization of this framework will enrich the data available for model validation and provide a more thorough accounting of adsorption heat pumps
Evidence for He I 10830 \AA~ absorption during the transit of a warm Neptune around the M-dwarf GJ 3470 with the Habitable-zone Planet Finder
Understanding the dynamics and kinematics of out-flowing atmospheres of hot
and warm exoplanets is crucial to understanding the origins and evolutionary
history of the exoplanets near the evaporation desert. Recently, ground based
measurements of the meta-stable Helium atom's resonant absorption at 10830
\AA~has become a powerful probe of the base environment which is driving the
outflow of exoplanet atmospheres. We report evidence for the He I 10830 \AA~in
absorption (equivalent width \AA) in the exosphere of
a warm Neptune orbiting the M-dwarf GJ 3470, during three transits using the
Habitable Zone Planet Finder (HPF) near infrared spectrograph. This marks the
first reported evidence for He I 10830 \AA\, atmospheric absorption for a
planet orbiting an M-dwarf. Our detected absorption is broad and its
blueshifted wing extends to -36 km/sec, the largest reported in the literature
to date. We modelled the state of Helium atoms in the exosphere of GJ3470b
based on assumptions on the UV and X-ray flux of GJ 3470, and found our
measurement of flux-weighted column density of meta-stable state Helium
, derived from our transit
observations, to be consistent with model, within its uncertainties. The
methodology developed here will be useful to study and constrain the
atmospheric outflow models of other exoplanets like GJ 3470b which are near the
edge of the evaporation desert.Comment: Accepted in Ap
Integrating Multiple Lines of Evidence into Historical Biogeography Hypothesis Testing: A Bison bison Case Study
One of the grand goals of historical biogeography is to understand how and why species’ population sizes and distributions change over time. Multiple types of data drawn from disparate fields, combined into a single modelling framework, are necessary to document changes in a species’s demography and distribution, and to determine the drivers responsible for change. Yet truly integrated approaches are challenging and rarely performed. Here, we discuss a modelling framework that integrates spatio-temporal fossil data, ancient DNA, palaeoclimatological reconstructions, bioclimatic envelope modelling and coalescence models in order to statistically test alternative hypotheses of demographic and potential distributional changes for the iconic American bison (Bison bison). Using different assumptions about the evolution of the bioclimatic niche, we generate hypothetical distributional and demographic histories of the species. We then test these demographic models by comparing the genetic signature predicted by serial coalescence against sequence data derived from subfossils and modern populations. Our results supported demographic models that include both climate and human-associated drivers of population declines. This synthetic approach, integrating palaeoclimatology, bioclimatic envelopes, serial coalescence, spatio-temporal fossil data and heterochronous DNA sequences, improves understanding of species’ historical biogeography by allowing consideration of both abiotic and biotic interactions at the population level
Persistent starspot signals on M dwarfs: multi-wavelength Doppler observations with the Habitable-zone Planet Finder and Keck/HIRES
Young, rapidly-rotating M dwarfs exhibit prominent starspots, which create
quasiperiodic signals in their photometric and Doppler spectroscopic
measurements. The periodic Doppler signals can mimic radial velocity (RV)
changes expected from orbiting exoplanets. Exoplanets can be distinguished from
activity-induced false positives by the chromaticity and long-term incoherence
of starspot signals, but these qualities are poorly constrained for
fully-convective M stars. Coherent photometric starspot signals on M dwarfs may
persist for hundreds of rotations, and the wavelength dependence of starspot RV
signals may not be consistent between stars due to differences in their
magnetic fields and active regions. We obtained precise multi-wavelength RVs of
four rapidly-rotating M dwarfs (AD Leo, G 227-22, GJ 1245B, GJ 3959) using the
near-infrared (NIR) Habitable-zone Planet Finder, and the optical Keck/HIRES
spectrometer. Our RVs are complemented by photometry from Kepler, TESS, and the
Las Cumbres Observatory (LCO) network of telescopes. We found that all four
stars exhibit large spot-induced Doppler signals at their rotation periods, and
investigated the longevity and optical-to-NIR chromaticity for these signals.
The phase curves remain coherent much longer than is typical for Sunlike stars.
Their chromaticity varies, and one star (GJ 3959) exhibits optical and NIR RV
modulation consistent in both phase and amplitude. In general, though, we find
that the NIR amplitudes are lower than their optical counterparts. We conclude
that starspot modulation for rapidly-rotating M stars frequently remains
coherent for hundreds of stellar rotations, and gives rise to Doppler signals
that, due to this coherence, may be mistaken for exoplanets.Comment: Accepted for publication in the Astrophysical Journa
LCDM halo substructure properties revealed with high resolution and large volume cosmological simulations
We investigate the structural properties, distribution and abundance of LCDM
dark matter subhaloes using the Phi-4096 and Uchuu suite of N-body cosmological
simulations. Thanks to the combination of their large volume, high mass
resolution and superb statistics, we are able to quantify -- for the first time
consistently over more than seven decades in ratio of subhalo-to-host-halo mass
-- dependencies of subhalo properties with mass, maximum circular velocity,
Vmax, host halo mass and distance to host halo centre. We also dissect the
evolution of these dependencies over cosmic time. We provide accurate fits for
the subhalo mass and velocity functions, both exhibiting decreasing power-law
slopes in the expected range of values and with no significant dependence on
redshift. We also find subhalo abundance to depend weakly on host halo mass. We
explore the distribution of subhaloes within their hosts and its evolution over
cosmic time for subhaloes located as deep as ~0.1 per cent of the host virial
radius. Subhalo structural properties are codified via a concentration
parameter, cV, that does not depend on any specific, pre-defined density
profile and relies only on Vmax. We derive the cV-Vmax relation in the range
7-1500 km/s and find an important dependence on distance of the subhalo to the
host halo centre, as already described in Molin\'e et al. (2017).
Interestingly, we also find subhaloes of the same mass to be significantly more
concentrated into more massive hosts. Finally, we investigate the redshift
evolution of cV, and provide accurate fits that take into account all mentioned
dependencies. Our results offer an unprecedented detailed characterization of
the subhalo population, consistent over a wide range of subhalo and host halo
masses, as well as cosmic times. Our work enables precision work in any future
research involving dark matter halo substructure.Comment: 17 pages, 15 figures, 5 tables. Submitted to the journal. Comments
welcome
Detection of a Companion Lens Galaxy using the Mid-infrared Flux Ratios of the Gravitationally Lensed Quasar H1413+117
We present the first resolved mid-IR (11 micron) observations of the
four-image quasar lens H1413+117 using the Michelle camera on Gemini North. All
previous observations (optical, near-IR, and radio) of this lens show a "flux
anomaly," where the image flux ratios cannot be explained by a simple, central
lens galaxy. We attempt to reproduce the mid-IR flux ratios, which are
insensitive to extinction and microlensing, by modeling the main lens as a
singular isothermal ellipsoid. This model fails to reproduce the flux ratios.
However, we can explain the flux ratios simply by adding to the model a nearby
galaxy detected in the H-band by HST/NICMOS-NIC2. This perturbing galaxy lies
4.0" from the main lens and it has a critical radius of 0.63" +/- 0.02" which
is similar to that of the main lens, as expected from their similar H-band
fluxes. More remarkably, this galaxy is not required to obtain a good fit to
the system astrometry, so this represents the first clear detection of an
object through its effect on the image fluxes of a gravitational lens. This is
a parallel to the detections of visible satellites from astrometric anomalies,
and provides a proof of the concept of searching for substructure in galaxies
using anomalous flux ratios.Comment: 11 pages, 4 figures, 4 tables, Submitted to ApJ. v4: Figure 1
correcte
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