20,304 research outputs found
An introduction to time-resolved decoding analysis for M/EEG
The human brain is constantly processing and integrating information in order
to make decisions and interact with the world, for tasks from recognizing a
familiar face to playing a game of tennis. These complex cognitive processes
require communication between large populations of neurons. The non-invasive
neuroimaging methods of electroencephalography (EEG) and magnetoencephalography
(MEG) provide population measures of neural activity with millisecond precision
that allow us to study the temporal dynamics of cognitive processes. However,
multi-sensor M/EEG data is inherently high dimensional, making it difficult to
parse important signal from noise. Multivariate pattern analysis (MVPA) or
"decoding" methods offer vast potential for understanding high-dimensional
M/EEG neural data. MVPA can be used to distinguish between different conditions
and map the time courses of various neural processes, from basic sensory
processing to high-level cognitive processes. In this chapter, we discuss the
practical aspects of performing decoding analyses on M/EEG data as well as the
limitations of the method, and then we discuss some applications for
understanding representational dynamics in the human brain
Statistical features of the thermal neutron capture cross sections
We discuss the existence of huge thermal neutron capture cross sections in
several nuclei. The values of the cross sections are several orders of
magnitude bigger than expected at these very low energies. We lend support to
the idea that this phenomenon is random in nature and is similar to what we
have learned from the study of parity violation in the actinide region. The
idea of statistical doorways is advanced as a unified concept in the
delineation of large numbers in the nuclear world. The average number of maxima
per unit mass, in the capture cross section is calculated and related
to the underlying cross section correlation function and found to be , where is a characteristic mass
correlation width which designates the degree of remnant coherence in the
system. We trace this coherence to nucleosynthesis which produced the nuclei
whose neutron capture cross sections are considered here.Comment: 7 pages, 6 figures. To appear in Acta Physica Polonica B as a
Contribution to the proceedings of:Jagiellonian Symposium of Fundamental and
Applied Subatomic Physics, June 7- 12, 2015 Krakow, Polan
Noise Predictions for STM in Systems with Local Electron Nematic Order
We propose that thermal noise in local stripe orientation should be readily
detectable via STM on systems in which local stripe orientations are strongly
affected by quenched disorder. Stripes, a unidirectional, nanoscale modulation
of electronic charge, are strongly affected by quenched disorder in
two-dimensional and quasi-two-dimensional systems. While stripe orientations
tend to lock to major lattice directions, dopant disorder locally breaks
rotational symmetry. In a host crystal with otherwise rotational
symmetry, stripe orientations in the presence of quenched disorder map to the
random field Ising model. While the low temperature state of such a system is
generally a stripe glass in two dimensional or strongly layered systems, as the
temperature is raised, stripe orientational fluctuations become more prevalent.
We propose that these thermally excited fluctuations should be readily
detectable in scanning tunneling spectroscopy as {\em telegraph noise} in the
high voltage part of the local curves. We predict the spatial, temporal,
and thermal evolution of such noise, including the circumstances under which
such noise is most likely to be observed. In addition, we propose an in-situ
test, amenable to any local scanning probe, for assessing whether such noise is
due to correlated fluctuations rather than independent switchers.Comment: 8 pages, 8 figure
Hysteresis and Noise from Electronic Nematicity in High Temperature Superconductors
An electron nematic is a translationally invariant state which spontaneously
breaks the discrete rotational symmetry of a host crystal. In a clean square
lattice, the electron nematic has two preferred orientations, while dopant
disorder favors one or the other orientations locally. In this way, the
electron nematic in a host crystal maps to the random field Ising model (RFIM).
Since the electron nematic has anisotropic conductivity, we associate each
Ising configuration with a resistor network, and use what is known about the
RFIM to predict new ways to test for electron nematicity using noise and
hysteresis. In particular, we have uncovered a remarkably robust linear
relation between the orientational order and the resistance anisotropy which
holds over a wide range of circumstances.Comment: References added; minor wording change
Primer selection impacts specific population abundances but not community dynamics in a monthly time-series 16S rRNA gene amplicon analysis of coastal marine bacterioplankton.
Primers targeting the 16S small subunit ribosomal RNA marker gene, used to characterize bacterial and archaeal communities, have recently been re-evaluated for marine planktonic habitats. To investigate whether primer selection affects the ecological interpretation of bacterioplankton populations and community dynamics, amplicon sequencing with four primer sets targeting several hypervariable regions of the 16S rRNA gene was conducted on both mock communities constructed from cloned 16S rRNA genes and a time-series of DNA samples from the temperate coastal Santa Barbara Channel. Ecological interpretations of community structure (delineation of depth and seasonality, correlations with environmental factors) were similar across primer sets, while population dynamics varied. We observed substantial differences in relative abundances of taxa known to be poorly resolved by some primer sets, such as Thaumarchaeota and SAR11, and unexpected taxa including Roseobacter clades. Though the magnitude of relative abundances of common OTUs differed between primer sets, the relative abundances of the OTUs were nonetheless strongly correlated. We do not endorse one primer set but rather enumerate strengths and weaknesses to facilitate selection appropriate to a system or experimental goal. While 16S rRNA gene primer bias suggests caution in assessing quantitative population dynamics, community dynamics appear robust across studies using different primers
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