1,053 research outputs found
Serial Correlations in Single-Subject fMRI with Sub-Second TR
When performing statistical analysis of single-subject fMRI data, serial
correlations need to be taken into account to allow for valid inference.
Otherwise, the variability in the parameter estimates might be under-estimated
resulting in increased false-positive rates. Serial correlations in fMRI data
are commonly characterized in terms of a first-order autoregressive (AR)
process and then removed via pre-whitening. The required noise model for the
pre-whitening depends on a number of parameters, particularly the repetition
time (TR). Here we investigate how the sub-second temporal resolution provided
by simultaneous multislice (SMS) imaging changes the noise structure in fMRI
time series. We fit a higher-order AR model and then estimate the optimal AR
model order for a sequence with a TR of less than 600 ms providing whole brain
coverage. We show that physiological noise modelling successfully reduces the
required AR model order, but remaining serial correlations necessitate an
advanced noise model. We conclude that commonly used noise models, such as the
AR(1) model, are inadequate for modelling serial correlations in fMRI using
sub-second TRs. Rather, physiological noise modelling in combination with
advanced pre-whitening schemes enable valid inference in single-subject
analysis using fast fMRI sequences
Multiple CSLs for the body centered cubic lattice
Ordinary Coincidence Site Lattices (CSLs) are defined as the intersection of
a lattice with a rotated copy of itself. They are useful for
classifying grain boundaries and have been studied extensively since the mid
sixties. Recently the interests turned to so-called multiple CSLs, i.e.
intersections of rotated copies of a given lattice , in particular
in connection with lattice quantizers. Here we consider multiple CSLs for the
3-dimensional body centered cubic lattice. We discuss the spectrum of
coincidence indices and their multiplicity, in particular we show that the
latter is a multiplicative function and give an explicit expression of it for
some special cases.Comment: 4 pages, SSPCM (31 August - 7 September 2005, Myczkowce, Poland
Coincidences in 4 dimensions
The coincidence site lattices (CSLs) of prominent 4-dimensional lattices are
considered. CSLs in 3 dimensions have been used for decades to describe grain
boundaries in crystals. Quasicrystals suggest to also look at CSLs in
dimensions . Here, we discuss the CSLs of the root lattice and the
hypercubic lattices, which are of particular interest both from the
mathematical and the crystallographic viewpoint. Quaternion algebras are used
to derive their coincidence rotations and the CSLs. We make use of the fact
that the CSLs can be linked to certain ideals and compute their indices, their
multiplicities and encapsulate all this in generating functions in terms of
Dirichlet series. In addition, we sketch how these results can be generalised
for 4--dimensional --modules by discussing the icosian ring.Comment: 6 pages, conference "Quasicrystals - The Silver Jubilee
Interpretation of Some of the Basic Features of Field-Ion Image Projections from a Hemispherical to a Planar Surface using Moire Patterns
USE OF HISTORICAL AERIAL IMAGES FOR 3D MODELLING OF GLACIERS IN THE PROVINCE OF TRENTO
Abstract. Historical aerial images represent a source of information of great value for glacier monitoring, as they cover the area of interest at a well-defined epoch and allow for visual interpretation and metric analysis. Typically, the aerial images are used to produce orthophotos and manually digitize the perimeters of the glaciers for analysis of the surface extent of the glaciers, while the extraction of height information is more challenging due to data quality and characteristics. This article discusses the potential of historical aerial images for glacier modelling. More specifically, it analyses the impact of their coverage, radiometric- and geometric accuracy, state of preservation and completeness on the photogrammetric workflow. The data set used consists of scans of 300 (analog) aerial images acquired between August and October 1954 by the U.S. Air Force with a Fairchild KF7660 camera over the entire Province of Trento. For the modelling of the glaciers, different techniques such as manual stereoscopic measurement and dense image matching were tested on sample glaciers and the results were analysed in detail. Due to local radiometric saturation in a large part of the glacial surfaces and other disturbances affecting the historical images (e.g. scratches, scanning errors, dark shadows), dense image matching did not produce any valuable results, and stereo plotting could be used only on images (or image parts) with acceptable quality. The derived Digital Terrain Models (DTMs) were compared with a reference DTM obtained with dense image matching from digital aerial images acquired in September 2015 with an UltraCam Eagle sensor, and, for some glaciers, to a DTM obtained with dense image matching from scanned aerial images acquired in September 1983 with a RC30 analog camera. The differences between 1954 and 2015 DTMs showed values up to 70–80 m in height and a behaviour that is confirmed by the models employed by the glaciology experts in Trento
Coincidence isometries of a shifted square lattice
We consider the coincidence problem for the square lattice that is translated
by an arbitrary vector. General results are obtained about the set of
coincidence isometries and the coincidence site lattices of a shifted square
lattice by identifying the square lattice with the ring of Gaussian integers.
To illustrate them, we calculate the set of coincidence isometries, as well as
generating functions for the number of coincidence site lattices and
coincidence isometries, for specific examples.Comment: 10 pages, 1 figure; paper presented at Aperiodic 2009 (Liverpool
Exploring the path through which career adaptability increases job satisfaction and lowers work stress : the role of affect
The construct of career adaptability, or the ability to successfully manage one's career development and challenges, predicts several important outcomes; however, little is known about the
mechanisms contributing to its positive effects. The present study investigated the impact of career adaptability on job satisfaction and work stress, as mediated by individuals' affective states. Using a representative sample of 1671 individuals employed in Switzerland we hypothesized that, over time, career adaptability amplifies job satisfaction and attenuates work stress, through higher positive affect and lower negative affect, respectively. The data resulted from the first three waves of a longitudinal project on professional paths conducted in Switzerland. For each wave, participants completed a survey. Results of the 3-wave cross-lagged longitudinal model show that employees with higher career adaptability at Time 1 indeed experienced at Time 3 higher job satisfaction and lower work stress than those with lower career adaptability. The effect of career adaptability on job satisfaction and work stress was accounted for by negative affect: Individuals higher on career adaptability experienced less negative affect, which led to lower levels of stress and higher levels of job satisfaction, beyond previous levels of job satisfaction and work stress. Overall results support the conception of career adaptability as a self-regulatory resource that may promote a virtuous cycle in which individuals' evaluations of their resources to cope with the environment (i.e., career adaptability) shape their affective states, which in turn influence the evaluations of their job
Grain boundary energies and cohesive strength as a function of geometry
Cohesive laws are stress-strain curves used in finite element calculations to
describe the debonding of interfaces such as grain boundaries. It would be
convenient to describe grain boundary cohesive laws as a function of the
parameters needed to describe the grain boundary geometry; two parameters in 2D
and 5 parameters in 3D. However, we find that the cohesive law is not a smooth
function of these parameters. In fact, it is discontinuous at geometries for
which the two grains have repeat distances that are rational with respect to
one another. Using atomistic simulations, we extract grain boundary energies
and cohesive laws of grain boundary fracture in 2D with a Lennard-Jones
potential for all possible geometries which can be simulated within periodic
boundary conditions with a maximum box size. We introduce a model where grain
boundaries are represented as high symmetry boundaries decorated by extra
dislocations. Using it, we develop a functional form for the symmetric grain
boundary energies, which have cusps at all high symmetry angles. We also find
the asymptotic form of the fracture toughness near the discontinuities at high
symmetry grain boundaries using our dislocation decoration model.Comment: 12 pages, 19 figures, changed titl
Expansion and Divergence of Argonaute Genes in the Oomycete Genus Phytophthora
Modulation of gene expression through RNA interference is well conserved in eukaryotes and is involved in many cellular processes. In the oomycete Phytophthora, research on the small RNA machinery and function has started to reveal potential roles in the pathogen, but much is still unknown. We examined Argonaute (AGO) homologs within oomycete genome sequences, especially among Phytophthora species, to gain a clearer understanding of the evolution of this well-conserved protein family. We identified AGO homologs across many representative oomycete and stramenopile species, and annotated representative homologs in P. sojae. Furthermore, we demonstrate variable transcript levels of all identified AGO homologs in comparison to previously identified Dicer-like (DCL) and RNA-dependent RNA polymerase (RDR) homologs. Our phylogenetic analysis further refines the relationship of the AGO homologs in oomycetes and identifies a conserved tandem duplication of AGO homologs in a subset of Phytophthora species
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