8,962 research outputs found
Aharonov-Bohm oscillations in the local density of states
The scattering of electrons with inhomogeneities produces modulations in the
local density of states of a metal. We show that electron interference
contributions to these modulations are affected by the magnetic field via the
Aharonov-Bohm effect. This can be exploited in a simple STM setup that serves
as an Aharonov-Bohm interferometer at the nanometer scale.Comment: 4 pages, 2 figures. v2 added reference
Quantum critical behavior of electrons at the edge of charge order
We consider quantum critical points (QCP) in which quantum fluctuations
associated with charge rather than magnetic order induce unconventional
metallic properties. Based on finite-T calculations on a two-dimensional
extended Hubbard model we show how the coherence scale T* characteristic of
Fermi liquid behavior of the homogeneous metal vanishes at the onset of charge
order. A strong effective mass enhancement reminiscent of heavy fermion
behavior indicates the possible destruction of quasiparticles at the QCP.
Experimental probes on quarter-filled layered organic materials are proposed
for unveiling the behavior of electrons across the quantum critical region.Comment: 4 pages, 4 figures, accepted for publication in Phys. Rev. Let
Bioclimatology, structure, and conservation perspectives of Quercus pyrenaica, Acer opalus subsp. Granatensis, and Corylus avellana deciduous forests on Mediterranean bioclimate in the South-Central part of the Iberian Peninsula
The plant variability in the southern Iberian Peninsula consists of around 3500 different taxa due to its high bioclimatic, geographic, and geological diversity. The deciduous forests in the southern Iberian Peninsula are located in regions with topographies and specific bioclimatic conditions that allow for the survival of taxa that are typical of cooler and wetter bioclimatic regions and therefore represent the relict evidence of colder and more humid paleoclimatic conditions. The floristic composition of 421 samples of deciduous forests in the south-central part of the Iberian Peninsula were analyzed. The ecological importance index (IVI) was calculated, where the most important tree species were Quercuspyrenaica, Aceropalus subsp. Granatensis, and Corylusavellana. These species are uncommon in the south-central part of the Iberian Peninsula, forming forests of little extension. An analysis of the vertical distribution of the species (stratum) shows that the majority of the species of stratum 3 (hemicriptophics, camephytes, geophites, and nanophanerophytes) are characteristic of deciduous forests, and their presence is positively correlated with high values of bioclimatic variables related to humidity and presence of water in the soil (nemoral environments), while they are negatively correlated with high values of bioclimatic variables related to high temperatures, evapotranspiration, and aridity. This work demonstrates that several characteristic deciduous forest taxa are more vulnerable to disappearance due to the loss of their nemoral conditions caused by gaps in the tree or shrub canopy. These gaps lead to an increase in evapotranspiration, excess insolation, and a consequent loss of water and humidity in the microclimatic conditions.info:eu-repo/semantics/publishedVersio
Multi-Objective Genetic Programming for Feature Extraction and Data Visualization
Feature extraction transforms high dimensional
data into a new subspace of lower dimensionalitywhile keeping
the classification accuracy. Traditional algorithms do not
consider the multi-objective nature of this task. Data transformations
should improve the classification performance
on the new subspace, as well as to facilitate data visualization,
which has attracted increasing attention in recent years.
Moreover, new challenges arising in data mining, such as
the need to deal with imbalanced data sets call for new algorithms
capable of handling this type of data. This paper
presents a Pareto-basedmulti-objective genetic programming
algorithm for feature extraction and data visualization. The
algorithm is designed to obtain data transformations that optimize
the classification and visualization performance both
on balanced and imbalanced data. Six classification and visualization
measures are identified as objectives to be optimized
by the multi-objective algorithm. The algorithm is
evaluated and compared to 11 well-known feature extraction
methods, and to the performance on the original high
dimensional data. Experimental results on 22 balanced and
20 imbalanced data sets show that it performs very well on
both types of data, which is its significant advantage over
existing feature extraction algorithms
Scalable CAIM Discretization on Multiple GPUs Using Concurrent Kernels
CAIM(Class-Attribute InterdependenceMaximization) is one of the stateof-
the-art algorithms for discretizing data for which classes are known. However, it
may take a long time when run on high-dimensional large-scale data, with large number
of attributes and/or instances. This paper presents a solution to this problem by
introducing a GPU-based implementation of the CAIM algorithm that significantly
speeds up the discretization process on big complex data sets. The GPU-based implementation
is scalable to multiple GPU devices and enables the use of concurrent
kernels execution capabilities ofmodernGPUs. The CAIMGPU-basedmodel is evaluated
and compared with the original CAIM using single and multi-threaded parallel
configurations on 40 data sets with different characteristics. The results show great
speedup, up to 139 times faster using 4 GPUs, which makes discretization of big
data efficient and manageable. For example, discretization time of one big data set is
reduced from 2 hours to less than 2 minute
Cold atoms near superconductors: Atomic spin coherence beyond the Johnson noise limit
We report on the measurement of atomic spin coherence near the surface of a
superconducting niobium wire. As compared to normal conducting metal surfaces,
the atomic spin coherence is maintained for time periods beyond the Johnson
noise limit. The result provides experimental evidence that magnetic near field
noise near the superconductor is strongly suppressed. Such long atomic spin
coherence times near superconductors open the way towards the development of
coherently coupled cold atom / solid state hybrid quantum systems with
potential applications in quantum information processing and precision force
sensing.Comment: Major revisions of the text for submission to New Journal of Physics
8 pages, 4 figure
Broad-lined type Ic supernova iPTF16asu: A challenge to all popular models
It is well-known that ordinary supernovae (SNe) are powered by 56Ni cascade
decay. Broad-lined type Ic SNe (SNe Ic-BL) are a subclass of SNe that are not
all exclusively powered by 56Ni decay. It was suggested that some SNe Ic-BL are
powered by magnetar spin-down. iPTF16asu is a peculiar broad-lined type Ic
supernova discovered by the intermediate Palomar Transient Factory. With a
rest-frame rise time of only 4 days, iPTF16asu challenges the existing popular
models, for example, the radioactive heating (56Ni-only) and the magnetar+56Ni
models. Here we show that this rapid rise could be attributed to interaction
between the SN ejecta and a pre-existing circumstellar medium ejected by the
progenitor during its final stages of evolution, while the late-time light
curve can be better explained by energy input from a rapidly spinning magnetar.
This model is a natural extension to the previous magnetar model. The mass-loss
rate of the progenitor and ejecta mass are consistent with a progenitor that
experienced a common envelope evolution in a binary. An alternative model for
the early rapid rise of the light curve is the cooling of a shock propagating
into an extended envelope of the progenitor. It is difficult at this stage to
tell which model (interaction+magnetar+56Ni or cooling+magnetar+56Ni) is better
for iPTF16asu. However, it is worth noting that the inferred envelope mass in
the cooling+magnetar+56Ni is very high.Comment: 11 pages, 4 figures, 3 table
Aligned Drawings of Planar Graphs
Let be a graph that is topologically embedded in the plane and let
be an arrangement of pseudolines intersecting the drawing of .
An aligned drawing of and is a planar polyline drawing
of with an arrangement of lines so that and are
homeomorphic to and . We show that if is
stretchable and every edge either entirely lies on a pseudoline or it has
at most one intersection with , then and have a
straight-line aligned drawing. In order to prove this result, we strengthen a
result of Da Lozzo et al., and prove that a planar graph and a single
pseudoline have an aligned drawing with a prescribed convex
drawing of the outer face. We also study the less restrictive version of the
alignment problem with respect to one line, where only a set of vertices is
given and we need to determine whether they can be collinear. We show that the
problem is NP-complete but fixed-parameter tractable.Comment: Preliminary work appeared in the Proceedings of the 25th
International Symposium on Graph Drawing and Network Visualization (GD 2017
Polyimide foams
A fully imidized, solvent-free polyimide foam having excellent mechanical, acoustic, thermal, and flame resistant properties is produced. A first solution is provided, which includes one or more aromatic dianhydrides or derivatives of aromatic dianhydrides, and may include one or more aromatic diamines, dissolved in one or more polar solvents, along with an effective amount of one or more blowing agents. This first solution may also advantageously include effective amounts respectively of one or mores catalysts, one or more surfactants, and one or more fire retardants. A second solution is also provided which includes one or more isocyanates. The first and second solutions are rapidly and thoroughly mixed to produce an admixture, which is allowed to foam--in an open container, or in a closed mold--under ambient conditions to completion produce a foamed product. This foamed product is then cured by high frequency electromagnetic radiation, thermal energy, or a combination thereof. Alternatively, the process is adapted for spraying or extrusion
Polyimide foams
A fully imidized, solvent-free polyimide foam having excellent mechanical, acoustic, thermal, and flame resistant properties is produced. A first solution is provided, which includes one or more aromatic dianhydrides or derivatives of aromatic dianhydrides, and may include one or more aromatic diamines, dissolved in one or more polar solvents, along with an effective amount of one or more blowing agents. This first solution may also advantageously include effective amounts respectively of one or mores catalysts, one or more surfactants, and one or more fire retardants. A second solution is also provided which includes one or more isocyanates. The first and second solutions are rapidly and thoroughly mixed to produce an admixture, which is allowed to foam?in an open container, or in a closed mold?under ambient conditions to completion produce a foamed product. This foamed product is then cured by high frequency electromagnetic radiation, thermal energy, or a combination thereof. Alternatively, the process is adapted for spraying or extrusion
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