1,796 research outputs found
Sharp-Interface Limit of a Fluctuating Phase-Field Model
We present a derivation of the sharp-interface limit of a generic fluctuating
phase-field model for solidification. As a main result, we obtain a
sharp-interface projection which presents noise terms in both the diffusion
equation and in the moving boundary conditions. The presented procedure does
not rely on the fluctuation-dissipation theorem, and can therefore be applied
to account for both internal and external fluctuations in either variational or
non-variational phase-field formulations. In particular, it can be used to
introduce thermodynamical fluctuations in non-variational formulations of the
phase-field model, which permit to reach better computational efficiency and
provide more flexibility for describing some features of specific physical
situations. This opens the possibility of performing quantitative phase-field
simulations in crystal growth while accounting for the proper fluctuations of
the system.Comment: 21 pages, 1 figure, submitted to Phys. Rev.
A probabilistic model for crystal growth applied to protein deposition at the microscale
A probabilistic discrete model for 2D protein crystal growth is presented.
This model takes into account the available space and can describe growing
processes of different nature due to the versatility of its parameters which
gives the model great flexibility. The accuracy of the simulation is tested
against a real protein (SbpA) crystallization experiment showing high agreement
between the proposed model and the actual images of the nucleation process.
Finally, it is also discussed how the regularity of the interface (i.e. the
curve that separates the crystal from the substrate) affects to the evolution
of the simulation.Comment: 13 pages, 12 figure
Spin precession and spin Hall effect in monolayer graphene/Pt nanostructures
Spin Hall effects have surged as promising phenomena for spin logics
operations without ferromagnets. However, the magnitude of the detected
electric signals at room temperature in metallic systems has been so far
underwhelming. Here, we demonstrate a two-order of magnitude enhancement of the
signal in monolayer graphene/Pt devices when compared to their fully metallic
counterparts. The enhancement stems in part from efficient spin injection and
the large resistivity of graphene but we also observe 100% spin absorption in
Pt and find an unusually large effective spin Hall angle of up to 0.15. The
large spin-to-charge conversion allows us to characterise spin precession in
graphene under the presence of a magnetic field. Furthermore, by developing an
analytical model based on the 1D diffusive spin-transport, we demonstrate that
the effective spin-relaxation time in graphene can be accurately determined
using the (inverse) spin Hall effect as a means of detection. This is a
necessary step to gather full understanding of the consequences of spin
absorption in spin Hall devices, which is known to suppress effective spin
lifetimes in both metallic and graphene systems.Comment: 14 pages, 6 figures. Accepted in 2D Materials.
https://doi.org/10.1088/2053-1583/aa882
The ALHAMBRA photometric system
This paper presents the characterization of the optical range of the ALHAMBRA
photometric system, a 20 contiguous, equal-width, medium-band CCD system with
wavelength coverage from 3500A to 9700A. The photometric description of the
system is done by presenting the full response curve as a product of the
filters, CCD and atmospheric transmission curves, and using some first and
second order moments of this response function. We also introduce the set of
standard stars that defines the system, formed by 31 classic spectrophotometric
standard stars which have been used in the calibration of other known
photometric systems, and 288 stars, flux calibrated homogeneously, from the
Next Generation Spectral Library (NGSL). Based on the NGSL, we determine the
transformation equations between Sloan Digital Sky Survey (SDSS) ugriz
photometry and the ALHAMBRA photometric system, in order to establish some
relations between both systems. Finally we develop and discuss a strategy to
calculate the photometric zero points of the different pointings in the
ALHAMBRA project.Comment: Astronomical Journal on the 14th of January 201
Low molecular weight ϵ-caprolactone-pcoumaric acid copolymers as potential biomaterials for skin regeneration applications
ϵ-caprolactone-p-coumaric acid copolymers at different mole ratios (ϵ-caprolactone:p-coumaric acid 1:0, 10:1, 8:1, 6:1, 4:1, and 2:1) were synthesized by melt-polycondensation and using 4-dodecylbenzene sulfonic acid as catalyst. Chemical analysis by NMR and GPC showed that copolyesters were formed with decreasing molecular weight as p-coumaric acid content was increased. Physical characteristics, such as thermal and mechanical properties, as well as water uptake and water permeability, depended on the mole fraction of pcoumaric acid. The p-coumarate repetitive units increased the antioxidant capacity of the copolymers, showing antibacterial activity against the common pathogen Escherichia coli. In addition, all the synthesized copolyesters, except the one with the highest concentration of the phenolic acid, were cytocompatible and hemocompatible, thus becoming potentially useful for skin regeneration applications
Vortices on demand in multicomponent Bose-Einstein condensates
We present a simple mechanism to produce vortices at any desired spatial
locations in harmonically trapped Bose-Einstein condensates (BEC) with
multicomponent spin states coupled to external transverse and axial magnetic
fields. The vortices appear at the spatial points where the spin-transverse
field interaction vanishes and, depending on the multipolar magnetic field
order, the vortices can acquire different predictable topological charges. We
explicitly demonstrate our findings, both numerically and analytically, by
analyzing a 2D BEC via the Gross-Pitaevskii equation for atomic systems with
either two or three internal states. We further show that, by an spontaneous
symmetry breaking mechanism, vortices can appear in any spin component, unless
symmetry is externally broken at the outset by an axial field. We suggest that
this scenario may be tested using an ultracold gas of Rb occupying all
three states in an optical trap.Comment: 11 pages, 9 figures, (Accepted in PRA
The Cluster Lensing and Supernova Survey with Hubble (CLASH): Strong Lensing Analysis of Abell 383 from 16-Band HST WFC3/ACS Imaging
We examine the inner mass distribution of the relaxed galaxy cluster Abell
383 in deep 16-band HST/ACS+WFC3 imaging taken as part of the CLASH multi-cycle
treasury program. Our program is designed to study the dark matter distribution
in 25 massive clusters, and balances depth with a wide wavelength coverage to
better identify lensed systems and generate precise photometric redshifts. This
information together with the predictive strength of our strong-lensing
analysis method identifies 13 new multiply-lensed images and candidates, so
that a total of 27 multiple-images of 9 systems are used to tightly constrain
the inner mass profile, (r<160 kpc).
We find consistency with the standard distance-redshift relation for the full
range spanned by the lensed images, 1.01<z<6.03, with the higher redshift
sources deflected through larger angles as expected. The inner mass profile
derived here is consistent with the results of our independent weak-lensing
analysis of wide-field Subaru images, with good agreement in the region of
overlap. The overall mass profile is well fitted by an NFW profile with
M_{vir}=(5.37^{+0.70}_{-0.63}\pm 0.26) x 10^{14}M_{\odot}/h and a relatively
high concentration, c_{vir}=8.77^{+0.44}_{-0.42}\pm 0.23, which lies above the
standard c-M relation similar to other well-studied clusters. The critical
radius of Abell 383 is modest by the standards of other lensing clusters,
r_{E}\simeq16\pm2\arcsec (for z_s=2.55), so the relatively large number of
lensed images uncovered here with precise photometric redshifts validates our
imaging strategy for the CLASH survey. In total we aim to provide similarly
high-quality lensing data for 25 clusters, 20 of which are X-ray selected
relaxed clusters, enabling a precise determination of the representative mass
profile free from lensing bias. (ABRIDGED)Comment: 15 pages, 14 figures, 2 tabels; V3 matches the submitted version
later published in Ap
The ALHAMBRA Project: A large area multi medium-band optical and NIR photometric survey
(ABRIDGED) We describe the first results of the ALHAMBRA survey which
provides cosmic tomography of the evolution of the contents of the Universe
over most of Cosmic history. Our approach employs 20 contiguous, equal-width,
medium-band filters covering from 3500 to 9700 A, plus the JHKs bands, to
observe an area of 4 sqdeg on the sky. The optical photometric system has been
designed to maximize the number of objects with accurate classification by SED
and redshift, and to be sensitive to relatively faint emission lines. The
observations are being carried out with the Calar Alto 3.5m telescope using the
cameras LAICA and O-2000. The first data confirm that we are reaching the
expected magnitude limits of AB<~25 mag in the optical filters from the blue to
8300 A, and from AB=24.7 to 23.4 for the redder ones. The limit in the NIR is
(Vega) K_s~20, H~21, J~22. We expect to obtain accurate redshift values, Delta
z/(1+z) <~ 0.03 for about 5x10^5 galaxies with I<~25 (60% complete), and
z_med=0.74. This accuracy, together with the homogeneity of the selection
function, will allow for the study of the redshift evolution of the large scale
structure, the galaxy population and its evolution with redshift, the
identification of clusters of galaxies, and many other studies, without the
need for any further follow-up. It will also provide targets for detailed
studies with 10m-class telescopes. Given its area, spectral coverage and its
depth, apart from those main goals, the ALHAMBRA-Survey will also produce
valuable data for galactic studies.Comment: Accepted to the Astronomical Journal. 43 pages, 18 figures. The
images have been reduced in resolution to adapt to standard file sizes.
Readers can find the full-resolution version of the paper at the ALHAMBRA web
site (http://www.iaa.es/alhambra) under the "Publications" lin
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