4,433 research outputs found
InAs/InP single quantum wire formation and emission at 1.5 microns
Isolated InAs/InP self-assembled quantum wires have been grown using in situ
accumulated stress measurements to adjust the optimal InAs thickness. Atomic
force microscopy imaging shows highly asymmetric nanostructures with average
length exceeding more than ten times their width. High resolution optical
investigation of as-grown samples reveals strong photoluminescence from
individual quantum wires at 1.5 microns. Additional sharp features are related
to monolayer fluctuations of the two dimensional InAs layer present during the
early stages of the quantum wire self-assembling process.Comment: 4 pages and 3 figures submitted to Applied Physics Letter
The lifespan method as a tool to study criticality in absorbing-state phase transitions
In a recent work, a new numerical method (the lifespan method) has been
introduced to study the critical properties of epidemic processes on complex
networks [Phys. Rev. Lett. \textbf{111}, 068701 (2013)]. Here, we present a
detailed analysis of the viability of this method for the study of the critical
properties of generic absorbing-state phase transitions in lattices. Focusing
on the well understood case of the contact process, we develop a finite-size
scaling theory to measure the critical point and its associated critical
exponents. We show the validity of the method by studying numerically the
contact process on a one-dimensional lattice and comparing the findings of the
lifespan method with the standard quasi-stationary method. We find that the
lifespan method gives results that are perfectly compatible with those of
quasi-stationary simulations and with analytical results. Our observations
confirm that the lifespan method is a fully legitimate tool for the study of
the critical properties of absorbing phase transitions in regular lattices
Prediction of lethal and synthetically lethal knock-outs in regulatory networks
The complex interactions involved in regulation of a cell's function are
captured by its interaction graph. More often than not, detailed knowledge
about enhancing or suppressive regulatory influences and cooperative effects is
lacking and merely the presence or absence of directed interactions is known.
Here we investigate to which extent such reduced information allows to forecast
the effect of a knock-out or a combination of knock-outs. Specifically we ask
in how far the lethality of eliminating nodes may be predicted by their network
centrality, such as degree and betweenness, without knowing the function of the
system. The function is taken as the ability to reproduce a fixed point under a
discrete Boolean dynamics. We investigate two types of stochastically generated
networks: fully random networks and structures grown with a mechanism of node
duplication and subsequent divergence of interactions. On all networks we find
that the out-degree is a good predictor of the lethality of a single node
knock-out. For knock-outs of node pairs, the fraction of successors shared
between the two knocked-out nodes (out-overlap) is a good predictor of
synthetic lethality. Out-degree and out-overlap are locally defined and
computationally simple centrality measures that provide a predictive power
close to the optimal predictor.Comment: published version, 10 pages, 6 figures, 2 tables; supplement at
http://www.bioinf.uni-leipzig.de/publications/supplements/11-01
WC-Cu thermal barriers for fusion applications
ABSTRACT: WC-Cu cermets have been devised for thermal barriers between the plasma facing tungsten tiles and the copperbased heat sink in the first wall of nuclear fusion reactors. Composite materials with 50 and 75 v/v% WC have been prepared by hot pressing at 1333 and 1423 K with pressures of 37 and 47 MPa, respectively. Microstructural changes have been investigated by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy and X-ray diffraction. The materials consolidated have also been evaluated in terms of Archimedes' density, thermal diffusivity, Vickers hardness and elastic modulus. Implantation was carried out at room temperature with Ar+ at 100 keV ion beam with a fluence of 4 · 1020 at/m2. The materials consisted of homogeneous dispersions of WC particles in a Cu matrix and presented densifications of about 90%. Incipient swelling in copper-rich regions have been observed on the implanted surfaces, however no significant changes have been detected by X-ray diffraction. Higher WC content in the cermet materials increased hardness and the elastic modulus. The cermets' thermal diffusivity was significantly lower than that of pure copper or tungsten, as desirable for a thermal barrier.info:eu-repo/semantics/acceptedVersio
Cosmological measurement of neutrino mass in the presence of leptonic asymmetry
We show that even the smallest neutrino mass consistent with the
Super--Kamiokande data is relevant for cosmological models of structure
formation and cosmic microwave background (CMB) anisotropies, provided that a
relic neutrino asymmetry exists. We calculate the precision with which a 0.07
eV neutrino mass could be extracted from CMB anisotropy and large-scale
structure data by the future Planck satellite and Sloan Digital Sky Survey. We
find that such a mass can be detected, assuming a large relic neutrino
asymmetry still allowed by current experimental data. This measurement of the
absolute value of the neutrino mass would be crucial for our understanding of
neutrino models.Comment: 8 pages, 2 PS figures, version to be publishe
Повседневность первобытного человека
Seven samples of Siluro-Devonian sedimentary rocks from the Cantabrian and Central Iberian zones of the Iberian
Variscan belt have been investigated for provenance and contain four main age populations in variable relative proportion:
Ediacaran–Cryogenian (c. 0.55–0.8Ga), Tonian–Stenian (0.85–1.2Ga), Palaeoproterozoic (c. 1.8–2.2Ga) and Archaean (c.
2.5–3.3Ga). Five samples contain very minor Palaeozoic (Cambrian) zircons and six samples contain minor but significant
zircons of Middle and Early Mesoproterozoic (Ectasian–Calymmian, 1.6–1.8) age. These data highlight the transition from
an arc environment to a stable platform following the opening of the Rheic Ocean. Variations in detrital zircon populations
in Middle–Late Devonian times reflect the onset of Variscan convergence between Laurussia and Gondwana. The presence
of a high proportion of zircons of Tonian–Stenian age in Devonian sedimentary rocks may be interpreted as (1) the existence
of a large Tonian–Stenian arc terrane exposed in the NE African realm (in or around the Arabian–Nubian Shield), (2) the
participation, from the Ordovician time, of a more easterly alongshore provenance of Tonian–Stenian zircons, and (3) an
increase in the relative proportion of Tonian–Stenian zircons with respect to the Ediacaran–Cryogenian population owing to
the drift of the Avalonian–Cadomian ribbon continent, or the progressive burial of Ediacaran–Cryogenian rocks coeval with
the denudation of older source rocks from the craton interior
Noncollinear magnetic ordering in small Chromium Clusters
We investigate noncollinear effects in antiferromagnetically coupled clusters
using the general, rotationally invariant form of local spin-density theory.
The coupling to the electronic degrees of freedom is treated with relativistic
non-local pseudopotentials and the ionic structure is optimized by Monte-Carlo
techniques. We find that small chromium clusters (N \le 13) strongly favor
noncollinear configurations of their local magnetic moments due to frustration.
This effect is associated with a significantly lower total magnetization of the
noncollinear ground states, ameliorating the disagreement between Stern-Gerlach
measurements and previous collinear calculations for Cr_{12} and Cr_{13}. Our
results further suggest that the trend to noncollinear configurations might be
a feature common to most antiferromagnetic clusters.Comment: 9 pages, RevTeX plus .eps/.ps figure
Exponential and power law distribution of mass clusters in a (magnetic-like) deposition model of elongated grains in 2D piles
A generalized so called magnetically controlled ballistic rain-like
deposition (MBD) model of granular piles has been numerically investigated in
2D. The grains are taken to be elongated disks whence characterized by a
two-state scalar degree of freedom, called ''nip'', their interaction being
described through a Hamiltonian. Results are discussed in order to search for
the effect of nip flip (or grain rotation from vertical to horizontal and
conversely) probability in building a granular pile. The characteristics of
creation of + (or ) nip's clusters and clusters of holes (missing nips) are
analyzed. Two different cluster-mass regimes have been identified, through the
cluster-mass distribution function which can be exponential or have a power law
form depending on whether the nip flip (or grain rotation) probability is large
or small. Analytical forms of the exponent are empirically found in terms of
the Hamiltonian parameters.Comment: submitted to Int.J. Mod. Phys. C; 16 figures; 79 reference
Finding and evaluating community structure in networks
We propose and study a set of algorithms for discovering community structure
in networks -- natural divisions of network nodes into densely connected
subgroups. Our algorithms all share two definitive features: first, they
involve iterative removal of edges from the network to split it into
communities, the edges removed being identified using one of a number of
possible "betweenness" measures, and second, these measures are, crucially,
recalculated after each removal. We also propose a measure for the strength of
the community structure found by our algorithms, which gives us an objective
metric for choosing the number of communities into which a network should be
divided. We demonstrate that our algorithms are highly effective at discovering
community structure in both computer-generated and real-world network data, and
show how they can be used to shed light on the sometimes dauntingly complex
structure of networked systems.Comment: 16 pages, 13 figure
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