2,241 research outputs found
Direct observation of melting in a 2-D superconducting vortex lattice
Topological defects such as dislocations and disclinations are predicted to
determine the twodimensional (2-D) melting transition. In 2-D superconducting
vortex lattices, macroscopic measurements evidence melting close to the
transition to the normal state. However, the direct observation at the scale of
individual vortices of the melting sequence has never been performed. Here we
provide step by step imaging through scanning tunneling spectroscopy of a 2-D
system of vortices up to the melting transition in a focused-ion-beam
nanodeposited W-based superconducting thin film. We show directly the
transition into an isotropic liquid below the superconducting critical
temperature. Before that, we find a hexatic phase, characterized by the
appearance of free dislocations, and a smectic-like phase, possibly originated
through partial disclination unbinding. These results represent a significant
step in the understanding of melting of 2-D systems, with impact across several
research fields, such as liquid crystal molecules, or lipids in membranes.Comment: Submitted to Nature Physic
International Courts and the Crime of Genocide
En este trabajo realizo un análisis jurídico de los elementos constitutivos (tanto subjetivos como objetivos) del crimen de genocidio, tal y como han sido interpretados y aplicados por la jurisprudencia internacional. En concreto, se estudia la jurisprudencia de la Corte Internacional de Justicia, del Tribunal Internacional Penal para la antigua Yugoslavia y del Tribunal Internacional Penal para Ruanda sobre el crimen de genocidio
Magnetotransport properties of iron microwires fabricated by focused electron beam induced autocatalytic growth
We have prepared iron microwires in a combination of focused electron beam
induced deposition (FEBID) and autocatalytic growth from the iron
pentacarbonyl, Fe(CO)5, precursor gas under UHV conditions. The electrical
transport properties of the microwires were investigated and it was found that
the temperature dependence of the longitudinal resistivity (rhoxx) shows a
typical metallic behaviour with a room temperature value of about 88
micro{\Omega} cm. In order to investigate the magnetotransport properties we
have measured the isothermal Hall-resistivities in the range between 4.2 K and
260 K. From these measurements positive values for the ordinary and the
anomalous Hall coefficients were derived. The relation between anomalous Hall
resistivity (rhoAN) and longitudinal resistivity is quadratic, rhoAN rho^2 xx,
revealing an intrinsic origin of the anomalous Hall effect. Finally, at low
temperature in the transversal geometry a negative magnetoresistance of about
0.2 % was measured
Produtos de hidratação em argamassas geopoliméricas à base de argila da Tunísia para reparação de estruturas de concreto
A reparação de estruturas degradadas de concreto representa uma oportunidade para a indústria da construção
mas também um desafio para a comunidade científica. O desenvolvimento de novas argamassas de reparação
constitui por isso uma importante área de investigação. Os geopolímeros são ligantes inovadores alternativos
ao cimento Portland pelo que as argamassas à base destes materiais, geopolíméricas, apresentam algumas
potencialidades no campo da reparação das estruturas de concreto.
O presente artigo apresenta resultados de uma investigação sobre o desenvolvimento de argamassas
geopoliméricas à base de uma argila da Tunísia sujeita a tratamento térmico. É incluída uma análise da argila
e também dos produtos de hidratação da argamassa os quais apresentam fases geopoliméricas típicas
A magnetic shift register with out-of-plane magnetized layers
Using out-of-plane magnetized layers, a lateral shift register made from discrete elements is demonstrated. By carefully designing the in-plane shape of the elements which make up the shift register, both the position of nucleation of new domains and the coercivity of the element can be controlled. The dipole field from a neighbouring element placed tens of nanometers away creates a bias field on the nucleation site, which can be used to create a NOT gate. By chaining these NOT gates together, a shift register can be created where data bits consisting of neighbouring layers with aligned magnetization are propagated synchronously under a symmetric applied magnetic field. The operation of a 16 element shift register is shown, including field coupled data injection.This research is funded by the European Community under the Seventh Framework Program ERC Contract No. 247368: 3SPIN, and by EMRP JRP EXL04 SpinCal. The EMRP is jointly funded by the EMRP participating countries within EURAMET and the EU. AB acknowledges DTA funding from the EPSRC. A.F.-P. acknowledges support from the EPSRC Early Career Fellowship EP/M008517/1 and a Winton Fellowship
When the optimal is not the best: parameter estimation in complex biological models
Background: The vast computational resources that became available during the
past decade enabled the development and simulation of increasingly complex
mathematical models of cancer growth. These models typically involve many free
parameters whose determination is a substantial obstacle to model development.
Direct measurement of biochemical parameters in vivo is often difficult and
sometimes impracticable, while fitting them under data-poor conditions may
result in biologically implausible values.
Results: We discuss different methodological approaches to estimate
parameters in complex biological models. We make use of the high computational
power of the Blue Gene technology to perform an extensive study of the
parameter space in a model of avascular tumor growth. We explicitly show that
the landscape of the cost function used to optimize the model to the data has a
very rugged surface in parameter space. This cost function has many local
minima with unrealistic solutions, including the global minimum corresponding
to the best fit.
Conclusions: The case studied in this paper shows one example in which model
parameters that optimally fit the data are not necessarily the best ones from a
biological point of view. To avoid force-fitting a model to a dataset, we
propose that the best model parameters should be found by choosing, among
suboptimal parameters, those that match criteria other than the ones used to
fit the model. We also conclude that the model, data and optimization approach
form a new complex system, and point to the need of a theory that addresses
this problem more generally
Nucleobindin-1 regulates ECM degradation by promoting intra-Golgi trafficking of MMPs.
Matrix metalloproteinases (MMPs) degrade several ECM components and are crucial modulators of cell invasion and tissue organization. Although much has been reported about their function in remodeling ECM in health and disease, their trafficking across the Golgi apparatus remains poorly understood. Here we report that the cis-Golgi protein nucleobindin-1 (NUCB1) is critical for MMP2 and MT1-MMP trafficking along the Golgi apparatus. This process is Ca2+-dependent and is required for invasive MDA-MB-231 cell migration as well as for gelatin degradation in primary human macrophages. Our findings emphasize the importance of NUCB1 as an essential component of MMP transport and its overall impact on ECM remodeling. © 2020 Pacheco-Fernandez et al
Effects of Zn Substitution in the Magnetic and Morphological Properties of Fe-Oxide-Based Core-Shell Nanoparticles Produced in a Single Chemical Synthesis
Magnetic, compositional, and morphological properties of Zn-Fe-oxide core-shell bimagnetic nanoparticles were studied for three samples with 0.00, 0.06, and 0.10 Zn/Fe ratios, as obtained from particle-induced X-ray emission analysis. The bimagnetic nanoparticles were produced in a one-step synthesis by the thermal decomposition of the respective acetylacetonates. The nanoparticles present an average particle size between 25 and 30 nm as inferred from transmission electron microscopy (TEM). High-resolution TEM images clearly show core-shell morphology for the particles in all samples. The core is composed by an antiferromagnetic (AFM) phase with a Wüstite (Fe1-yO) structure, whereas the shell is composed by a ZnxFe3-xO4 ferrimagnetic (FiM) spinel phase. Despite the low solubility of Zn in the Wüstite, electron energy-loss spectroscopy analysis indicates that Zn is distributed almost homogeneously in the whole nanoparticle. This result gives information on the formation mechanisms of the particle, indicating that the Wüstite is formed first, and the superficial oxidation results in the FiM ferrite phase with similar Zn concentration than the core. Magnetization and in-field Mössbauer spectroscopy of the Zn-richest nanoparticles indicate that the AFM phase is strongly coupled to the FiM structure of the ferrite shell, resulting in a bias field (HEB) appearing below TNFeO, with HEB values that depend on the core-shell relative proportion. Magnetic characterization also indicates a strong magnetic frustration for the samples with higher Zn concentration, even at low temperatures
The one-dimensional contact process: duality and renormalisation
We study the one-dimensional contact process in its quantum version using a
recently proposed real space renormalisation technique for stochastic
many-particle systems. Exploiting the duality and other properties of the
model, we can apply the method for cells with up to 37 sites. After suitable
extrapolation, we obtain exponent estimates which are comparable in accuracy
with the best known in the literature.Comment: 15 page
On the possible sources of gravitational wave bursts detectable today
We discuss the possibility that galactic gravitational wave sources might
give burst signals at a rate of several events per year, detectable by
state-of-the-art detectors. We are stimulated by the results of the data
collected by the EXPLORER and NAUTILUS bar detectors in the 2001 run, which
suggest an excess of coincidences between the two detectors, when the resonant
bars are orthogonal to the galactic plane. Signals due to the coalescence of
galactic compact binaries fulfill the energy requirements but are problematic
for lack of known candidates with the necessary merging rate. We examine the
limits imposed by galactic dynamics on the mass loss of the Galaxy due to GW
emission, and we use them to put constraints also on the GW radiation from
exotic objects, like binaries made of primordial black holes. We discuss the
possibility that the events are due to GW bursts coming repeatedly from a
single or a few compact sources. We examine different possible realizations of
this idea, such as accreting neutron stars, strange quark stars, and the highly
magnetized neutron stars (``magnetars'') introduced to explain Soft Gamma
Repeaters. Various possibilities are excluded or appear very unlikely, while
others at present cannot be excluded.Comment: 24 pages, 20 figure
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