48 research outputs found
Stress engineering at the nanometer scale: Two-component adlayer stripes
Spontaneously formed equilibrium nanopatterns with long-range order are
widely observed in a variety of systems, but their pronounced temperature
dependence remains an impediment to maintain such patterns away from the
temperature of formation. Here, we report on a highly ordered stress-induced
stripe pattern in a two-component, Pd-O, adsorbate monolayer on W(110),
produced at high temperature and identically preserved at lower temperatures.
The pattern shows a tunable period (down to 16 nm) and orientation, as
predicted by a continuum model theory along with the surface stress and its
anisotropy found in our DFT calculations. The control over thermal fluctuations
in the stripe formation process is based on the breaking/restoring of
ergodicity in a high-density lattice gas with long-range interactions upon
turning off/on particle exchange with a heat bath.Comment: 6 pages, 4 figure
Temperature dependence of surface stress across an order-disorder transition: p(1x2)O/W(110)
Strain relaxations of a p(1x2) ordered oxygen layer on W(110) are measured as
a function of temperature across the disordering transition using low-energy
electron diffraction. The measured strains approach values of 0.027 in the
[1-10] and -0.053 in the [001] direction. On the basis of the measured strain
relaxations, we give quantitative information on temperature-dependent surface
stress using the results of ab initio calculations. From the surface formation
energy for different strains, determined by first-principles calculations, we
estimate that surface stress changes from -1.1 for the ordered phase to -0.2N/m
for the disordered one along [1-10], and from 5.1 to 3.4 N/m along [001].
Moreover, our observation that the strains scale inversely with domain size
confirms that the strain relaxation takes place at the domain boundaries.Comment: 8 pages, 5 figure
Friction stir welding (FSW) process of copper alloys
The present paper analyzes the structure of the weld joint of technically pure copper, which is realized using friction stir welding (FSW). The mechanism of thermo-mechanical processes of the FSW method has been identified and a correlation between the weld zone and its microstructure established. Parameters of the FSW welding technology influencing the zone of the seam material and the mechanical properties of the resulting joint were analyzed. The physical joining consists of intense mixing the base material along the joint line in the “doughy” phase. Substantial plastic deformations immediately beneath the frontal surface of tool provide fine-grained structure and a good quality joint. The optimum shape of the tool and the optimum welding regime (pressure force, rotation speed and the traverse speed of the tool) in the heat affected zone enable the achievement of the same mechanical properties as those of the basic material, which justifies its use in welding reliable structures
Surface stress of Ni adlayers on W(110): the critical role of the surface atomic structure
Puzzling trends in surface stress were reported experimentally for Ni/W(110)
as a function of Ni coverage. In order to explain this behavior, we have
performed a density-functional-theory study of the surface stress and atomic
structure of the pseudomorphic and of several different possible 1x7
configurations for this system. For the 1x7 phase, we predict a different, more
regular atomic structure than previously proposed based on surface x-ray
diffraction. At the same time, we reproduce the unexpected experimental change
of surface stress between the pseudomorphic and 1x7 configuration along the
crystallographic surface direction which does not undergo density changes. We
show that the observed behavior in the surface stress is dominated by the
effect of a change in Ni adsorption/coordination sites on the W(110) surface.Comment: 14 pages, 3 figures Published in J. Phys.: Condens. Matter 24 (2012)
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Strain relaxation in small adsorbate islands: O on W(110)
The stress-induced lattice changes in a p(1x2) ordered oxygen layer on W(110)
are measured by low-energy electron diffraction. We have observed that small
oxygen islands show a mismatch with the underlying lattice. Our results
indicate that along [1-10] the average mismatch scales inversely with the
island size as 1/L for all oxygen coverages up to 0.5 ML, while along [001] it
is significant only for the smallest oxygen islands and scales as a higher
power of the inverse island size. The behaviour along [1-10] is described by a
one-dimensional finite-size Frenkel-Kontorova model. Using this model, together
with calculated force constants, we make a quantitative estimate for the change
of surface-stress upon oxygen adsorption. The result is consistent with our
ab-initio calculations, which give a relative compressive stress of -4.72 N/m
along [1-10] and a minute relative tensile stress of 0.15 N/m along [001]. The
scaling along [001] is qualitatively explained as an effect induced by the
lattice relaxation in the [1-10] direction.Comment: 22 pages, 5 figure
Kappa Snyder deformations of Minkowski spacetime, realizations and Hopf algebra
We present Lie-algebraic deformations of Minkowski space with undeformed
Poincar\'{e} algebra. These deformations interpolate between Snyder and
-Minkowski space. We find realizations of noncommutative coordinates in
terms of commutative coordinates and derivatives. By introducing modules, it is
shown that although deformed and undeformed structures are not isomorphic at
the level of vector spaces, they are however isomorphic at the level of Hopf
algebraic action on corresponding modules. Invariants and tensors with respect
to Lorentz algebra are discussed. A general mapping from -deformed
Snyder to Snyder space is constructed. Deformed Leibniz rule, the Hopf
structure and star product are found. Special cases, particularly Snyder and
-Minkowski in Maggiore-type realizations are discussed. The same
generalized Hopf algebraic structures are as well considered in the case of an
arbitrary allowable kind of realisation and results are given perturbatively up
to second order in deformation parameters.Comment: 38 pages, LaTeX2e class fil
Microcalcifications Detection using PFCM and ANN
This work presents a method to detect Microcalcifications in Regions of Interest from digitized mammograms. The method is based mainly on the combination of Image Processing, Pattern Recognition and Artificial Intelligence. The Top-Hat transform is a technique based on mathematical morphology operations that, in this work is used to perform contrast enhancement of microcalcifications in the region of interest. In order to find more or less homogeneous regions in the image, we apply a novel image sub-segmentation technique based on Possibilistic Fuzzy c-Means clustering algorithm. From the original region of interest we extract two window-based features, Mean and Deviation Standard, which will be used in a classifier based on a Artificial Neural Network in order to identify microcalcifications. Our results show that the proposed method is a good alternative in the stage of microcalcifications detection, because this stage is an important part of the early Breast Cancer detectio
Ab initio simulation of photoemission spectroscopy in solids: Plane-wave pseudopotential approach, with applications to normal-emission spectra of Cu(001) and Cu(111)
We introduce a new method for simulating photoemission spectra from bulk
crystals in the ultra-violet energy range, within a three-step model. Our
method explicitly accounts for transmission and matrix-element effects, as
calculated from state-of-the-art plane-wave pseudopotential techniques within
density-functional theory. Transmission effects, in particular, are included by
extending to the present problem a technique previously employed with success
to deal with ballistic conductance in metal nanowires. The spectra calculated
for normal emission in Cu(001) and Cu(111) are in fair agreement with previous
theoretical results and with experiments, including a newly determined
spectrum. The residual discrepancies between our results and the latter are
mainly due to the well-known deficiencies of density-functional theory in
accounting for correlation effects in quasi-particle spectra. A significant
improvement is obtained by the LDA+U method. Further improvements are obtained
by including surface-optics corrections, as described by Snell's law and
Fresnel's equations.Comment: 25 pages, 7 figures, accepted in PR
Improvement for detection of microcalcifications through clustering algorithms and artificial neural networks
A new method for detecting microcalcifications in regions of interest (ROIs) extracted from digitized mammograms is proposed. The top-hat transform is a technique based on mathematical morphology operations and, in this paper, is used to perform contrast enhancement of the mi-crocalcifications. To improve microcalcification detection, a novel image sub-segmentation approach based on the possibilistic fuzzy c-means algorithm is used. From the original ROIs, window-based features, such as the mean and standard deviation, were extracted; these features were used as an input vector in a classifier. The classifier is based on an artificial neural network to identify patterns belonging to microcalcifications and healthy tissue. Our results show that the proposed method is a good alternative for automatically detecting microcalcifications, because this stage is an important part of early breast cancer detectio
PO-410 Cytotoxicity and genotoxicity of new gadolinium, iron oxide, cobalt ferrite and graphene oxide nanoparticles on some tumour cell lines in vitro
Nanoparticles (NPs) are increasingly used in cancer
therapy as delivery agents and in the diagnosis of malignant diseases
as contrast agents for magnetic resonance imaging (MRI).
The aim of this work was in vitro assessments of Gd-NPs, Fe-
NPs, CoFe-NPs and Graphene Oxide-NPs cytotoxicity and genotoxicity
on some tumour and normal human cell lines.Abstracts of the 25th Biennial Congress of the European Association for Cancer Research, Amsterdam, The Netherlands, 30 June – 3 July 201