1,250 research outputs found
Cyclotron Resonance Study of the Two-Dimensional Electron Layers and Double-Layers in Tilted Magnetic Fields
The far-infrared absorption in two-dimensional electron layers subject to
magnetic field of general orientation was studied theoretically. The Kubo
formula is employed to derive diagonal components of the magneto-conductivity
tensor of two-dimensional electron single-layers and double-layers. The
parabolic quantum well is used to model a simple single-layer system. Both
single-layer and double-layer systems can be realized in a pair of
tunnel-coupled, strictly two-dimensional quantum wells. Obtained results are
compared to experimental data.Comment: 4 pages, 6 figures, elsart/PHYEAUTH macros; presented on the EP2DS-15
Conference in Nara, Japan. To be published in Physica
The category of compact Hausdorff spaces is not algebraic if there are too many measurable cardinals
Broadcasting through a noisy one-dimensional network
We study the expected time complexity of two graph partitioning problems: the graph coloring and the cut into equal parts. If , we can test whether two vertices of a -colorable graph can be -colored by the same color in time per pair of vertices with -time preprocessing in such a way that for almost all -colorable graphs the answer is correct for all pairs of vertices. As a consequence, we obtain a sublinear (with respect to the number of edges) expected time algorithm for -coloring of -colorable graphs (assuming the uniform input distribution). Similarly, if , a constant, and is a graph having cut of the vertex set into two equal parts with at most cross-edges, we can test whether two vertices belong to the same class of some -cut in time per vertex with -time preprocessing in such a way that for almost all graphs having a -cut the answer is correct for all pairs of vertices. The methods presented in the paper can also be used to other graph partitioning problems, e.g. the largest clique or independent subset
Arithmetic complexity via effective names for random sequences
We investigate enumerability properties for classes of sets which permit
recursive, lexicographically increasing approximations, or left-r.e. sets. In
addition to pinpointing the complexity of left-r.e. Martin-L\"{o}f, computably,
Schnorr, and Kurtz random sets, weakly 1-generics and their complementary
classes, we find that there exist characterizations of the third and fourth
levels of the arithmetic hierarchy purely in terms of these notions.
More generally, there exists an equivalence between arithmetic complexity and
existence of numberings for classes of left-r.e. sets with shift-persistent
elements. While some classes (such as Martin-L\"{o}f randoms and Kurtz
non-randoms) have left-r.e. numberings, there is no canonical, or acceptable,
left-r.e. numbering for any class of left-r.e. randoms.
Finally, we note some fundamental differences between left-r.e. numberings
for sets and reals
Sensitivity to species selection indicates the effect of nuisance variables on marine microfossil transfer functions
The species composition of many groups of marine plankton appears well
predicted by sea surface temperature (SST). Consequently, fossil plankton
assemblages have been widely used to reconstruct past SST. Most applications
of this approach make use of the highest possible taxonomic resolution.
However, not all species are sensitive to temperature, and their distribution
may be governed by other parameters. There are thus reasons to question the
merit of including information about all species, both for transfer function
performance and for its effect on reconstructions.
Here we investigate the effect of species selection on planktonic
foraminifera transfer functions. We assess species importance for transfer
function models using a random forest technique and evaluate the performance
of models with an increasing number of species. Irrespective of using models
that use the entire training set (weighted averaging) or models that use
only a subset of the training set (modern analogue technique), we find that
the majority of foraminifera species does not carry useful information for
temperature reconstruction. Less than one-third of the species in the
training set is required to provide a temperature estimate with a prediction
error comparable to a transfer function that uses all species in the
training set. However, species selection matters for paleotemperature
estimates. We find that transfer function models with a different number of
species but with the same error may yield different reconstructions of sea
surface temperature when applied to the same fossil assemblages. This
ambiguity in the reconstructions implies that fossil assemblage change
reflects a combination of temperature and other environmental factors. The
contribution of the additional factors is site and time specific, indicating
ecological and geological complexity in the formation of the sedimentary
assemblages. The possibility of obtaining multiple different reconstructions
from a single sediment record presents a previously unrecognized source of
uncertainty for sea surface temperature estimates based on planktonic
foraminifera assemblages. This uncertainty can be evaluated by determining
the sensitivity of the reconstructions to species pruning.</p
Distributions and habitats of the two partly allopatric cryptic species of the vulnerable moss <i>Hamatocaulis vernicosus </i>(Bryophyta) in Europe
Multivariate calibration approach for quantitative determination of cell-line cross contamination by intact cell mass spectrometry and artificial neural networks
Cross-contamination of eukaryotic cell lines used in biomedical research represents a highly relevant problem. Analysis of repetitive DNA sequences, such as Short Tandem Repeats (STR), or Simple Sequence Repeats (SSR), is a widely accepted, simple, and commercially available technique to authenticate cell lines. However, it provides only qualitative information that depends on the extent of reference databases for interpretation. In this work, we developed and validated a rapid and routinely applicable method for evaluation of cell culture cross-contamination levels based on mass spectrometric fingerprints of intact mammalian cells coupled with artificial neural networks (ANNs). We used human embryonic stem cells (hESCs) contaminated by either mouse embryonic stem cells (mESCs) or mouse embryonic fibroblasts (MEFs) as a model. We determined the contamination level using a mass spectra database of known calibration mixtures that served as training input for an ANN. The ANN was then capable of correct quantification of the level of contamination of hESCs by mESCs or MEFs. We demonstrate that MS analysis, when linked to proper mathematical instruments, is a tangible tool for unraveling and quantifying heterogeneity in cell cultures. The analysis is applicable in routine scenarios for cell authentication and/or cell phenotyping in general
Electronic Structure of Three-Dimensional Superlattices Subject to Tilted Magnetic Fields
Full quantum-mechanical description of electrons moving in 3D structures with
unidirectional periodic modulation subject to tilted magnetic fields requires
an extensive numerical calculation. To understand magneto-oscillations in such
systems it is in many cases sufficient to use the quasi-classical approach, in
which the zero-magnetic-field Fermi surface is considered as a
magnetic-field-independent rigid body in k-space and periods of oscillations
are related to extremal cross-sections of the Fermi surface cut by planes
perpendicular to the magnetic-field direction. We point out cases where the
quasi-classical treatment fails and propose a simple tight-binding
fully-quantum-mechanical model of the superlattice electronic structure.Comment: 8 pages, 7 figures, RevTex, submitted to Phys. Rev.
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Priming Older Adults and People with Alzheimer’s Disease Analogical Problem Solving with True and False Memories
We investigated the extent to which activation of specific information in associative networks during a memory task could facilitate subsequent analogical problem solving in healthy older adults as well as those with early onset Alzheimer’s disease. We also examined whether these priming effects were stronger when the activation of the critical solution term during the memory task occurred when the item was actually presented (true memories) or when this item arose due to spreading activation to a related but nonpresented item (false memory). Older adult controls (OACs) and people with Alzheimer’s disease (AD) were asked to solve 9 verbal proportional analogies, 3 of which had been primed by Deese/Roediger-McDermott lists where the critical lure (and problem solution) was presented as a word in the list (true memory), 3 of which were primed by DRM lists whose critical lures were spontaneously activated during list presentation (false memory), and 3 of which were unprimed. As expected, OACs were better (both in terms of speed and accuracy) at solving problems than people with AD and both groups were better when false memories were primes than when true memories were primes or there were no primes. There were no reliable differences between unprimed and true prime problems. These findings demonstrate that (a) priming of problem solutions extends to verbal proportional analogies in OACs and people with AD, (b) false memories are more effective at priming problem solutions than true memories, and (c) there are clear positive consequences to the production of false memories
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