278 research outputs found
Solid-to-solid isostructural transition in the hard sphere/attractive Yukawa system
A thermodynamically consistent density functional-perturbation theory is used
to study the isostructural solid-to-solid transition which takes place in the
hard sphere/attractive Yukawa system when the Yukawa tail is sufficiently
short-ranged. A comparison with results for the square well potential allows us
to study the effect of the attractive potential form on the solid-solid
transition. Reasonable agreement with simulations is found for the main
transition properties as well as for the phase diagram evolution with the the
range of the attractive potential.Comment: 14 pages, latex, 5 figures available upon request:
([email protected]
Laser-treated electrospun fibers loaded with nano-hydroxyapatite for bone tissue engineering
Core-shell polycaprolactone/polycaprolactone (PCL/PCL) and polycaprolactone/polyvinyl acetate (PCL/PVAc) electrospun fibers loaded with synthesized nanohydroxyapatite (HAn) were lased treated to create microporosity. The prepared materials were characterized by XRD, FTIR, TEM and SEM. Uniform and randomly oriented beadless fibrous structures were obtained in all cases. Fibers diameters were in the 150â300 nm range. Needle-like HAn nanoparticles with mean diameters of 20 nm and length of approximately 150 nm were mostly encase inside the fibers. Laser treated materials present micropores with diameters in the range 70â120 ”m for PCL-HAn/PCL fibers and in the 50â90 ”m range for PCL-HAn/PVAC material. Only samples containing HAn presented bioactivity after incubation during 30 days in simulated body fluid. All scaffolds presented high viability, very low mortality, and human osteoblast proliferation. Biocompatibility was increased by laser treatment due to the surface and porosity modification
Surface tension fluctuations and a new spinodal point in glass-forming liquids
The dramatic slowdown of glass-forming liquids has been variously linked to
increasing dynamic and static correlation lengths. Yet, empirical evidence is
insufficient to decide among competing theories. The random first order theory
(RFOT) links the dynamic slowdown to the growth of amorphous static order,
whose range depends on a balance between configurational entropy and surface
tension. This last quantity is expected to vanish when the temperature
surpasses a spinodal point beyond which there are no metastable states. Here we
measure for the first time the surface tension in a model glass-former, and
find that it vanishes at the energy separating minima from saddles,
demonstrating the existence of a spinodal point for amorphous metastable order.
Moreover, the fluctuations of surface tension become smaller for lower
temperatures, in quantitative agreement with recent theoretical speculation
that spatial correlations in glassy systems relax nonexponentially because of
the narrowing of the surface tension distribution.Comment: 6 pages, 5 figure
Three-slit experiments and quantum nonlocality
An interesting link between two very different physical aspects of quantum
mechanics is revealed; these are the absence of third-order interference and
Tsirelson's bound for the nonlocal correlations. Considering multiple-slit
experiments - not only the traditional configuration with two slits, but also
configurations with three and more slits - Sorkin detected that third-order
(and higher-order) interference is not possible in quantum mechanics. The EPR
experiments show that quantum mechanics involves nonlocal correlations which
are demonstrated in a violation of the Bell or CHSH inequality, but are still
limited by a bound discovered by Tsirelson. It now turns out that Tsirelson's
bound holds in a broad class of probabilistic theories provided that they rule
out third-order interference. A major characteristic of this class is the
existence of a reasonable calculus of conditional probability or, phrased more
physically, of a reasonable model for the quantum measurement process.Comment: 9 pages, no figur
A Methane Isolated Planetary Mass Object in Orion
We report on the discovery of a free-floating methane dwarf toward the
direction of the young star cluster sigma Orionis. Based on the object's
far-red optical and near-infrared photometry and spectroscopy, we conclude that
it is a possible member of this association. We have named it as S Ori
J053810.1-023626 (S Ori 70 is the abridged name). If it is a true member of
sigma Orionis, the comparison of the photometric and spectroscopic properties
of S Ori 70 with state-of-the-art evolutionary models yields a mass of 3
(+5/-1) Jupiter mass for ages between 1 Myr and 8 Myr. The presence of such a
low-mass object in our small search area (55.4 sq. arcmin) would indicate a
rising substellar initial mass function in the sigma Orionis cluster even for
planetary masses.Comment: Accepted for publication in the ApJ. Twelve pages, figures and tables
include
Panchromatic observations and modeling of the HV Tau C edge-on disk
We present new high spatial resolution (<~ 0.1") 1-5 micron adaptive optics
images, interferometric 1.3 mm continuum and 12CO 2-1 maps, and 350 micron, 2.8
and 3.3 mm fluxes measurements of the HV Tau system. Our adaptive optics images
reveal an unusually slow orbital motion within the tight HV Tau AB pair that
suggests a highly eccentric orbit and/or a large deprojected physical
separation. Scattered light images of the HV Tau C edge-on protoplanetary disk
suggest that the anisotropy of the dust scattering phase function is almost
independent of wavelength from 0.8 to 5 micron, whereas the dust opacity
decreases significantly over the same range. The images further reveal a marked
lateral asymmetry in the disk that does not vary over a timescale of 2 years.
We further detect a radial velocity gradient in the disk in our 12CO map that
lies along the same position angle as the elongation of the continuum emission,
which is consistent with Keplerian rotation around an 0.5-1 Msun central star,
suggesting that it could be the most massive component in the triple system. We
use a powerful radiative transfer model to compute synthetic disk observations
and use a Bayesian inference method to extract constraints on the disk
properties. Each individual image, as well as the spectral energy distribution,
of HV Tau C can be well reproduced by our models with fully mixed dust provided
grain growth has already produced larger-than-interstellar dust grains.
However, no single model can satisfactorily simultaneously account for all
observations. We suggest that future attempts to model this source include more
complex dust properties and possibly vertical stratification. (Abridged)Comment: 26 pages, 11 figures, editorially accepted for publication in Ap
Combination of exosomes and near-infrared responsive gold nanoparticles: new selective and specific therapeutic vehicle
P602
Exosomes are extracellular vesicles (50 -150 nm of diameter) considered key elements for the intercellular communication. Although they are proposed to be ideal vehicles for the targeting of novel therapies, very little is known about the selectiveness and specificity of the transference processes involving exosomes released from different cells. PEGylated Hollow gold nanoparticles (PEG-HGNs) are near-infrared (NIR) responsive nanoparticles (NPs) which are able to generate localized heat by the use of NIR light leading to cell death when applying optical hyperthermia. In this study, we demonstrate the selectivity of in vitro exosomal transfer between certain cell types and how this phenomenon can be exploited to develop new specific vectors for advanced therapies. Firstly, PEG-HGNs were successfully incorporated in the exosome biogenesis pathway of placental stem cells (MSCs) and they were released as PEG-HGNs-loaded exosomes (PEGHGNs_ MSCs_EXOs). Exosomes were characterized by confocal microscopy, western blot, nanosight, zeta potential and electronic microscopy. Afterwards, time lapse microscopy and atomic emission spectroscopy demonstrated the selective transfer of the ..
The Substellar Mass Function in sigma Orionis
We combine results from imaging searches for substellar objects in the sigma
Orionis cluster and follow-up photometric and spectroscopic observations to
derive a census of the brown dwarf population in a region of 847 arcmin^2. We
identify 64 very low-mass cluster member candidates in this region. We have
available three color (IZJ) photometry for all of them, spectra for 9 objects,
and K photometry for 27% of our sample. These data provide a well defined
sequence in the I vs I-J, I-K color magnitude diagrams, and indicate that the
cluster is affected by little reddening despite its young age (~5 Myr). Using
state-of-the-art evolutionary models, we derive a mass function from the
low-mass stars (0.2 Msol) across the complete brown dwarf domain (0.075 Msol to
0.013 Msol), and into the realm of free-floating planetary-mass objects (<0.013
Msol). We find that the mass spectrum (dN/dm ~ m^{-alpha}) increases toward
lower masses with an exponent alpha = 0.8+/-0.4. Our results suggest that
planetary-mass isolated objects could be as common as brown dwarfs; both kinds
of objects together would be as numerous as stars in the cluster. If the
distribution of stellar and substellar masses in sigma Orionis is
representative of the Galactic disk, older and much lower luminosity
free-floating planetary-mass objects with masses down to about 0.005 Msol
should be abundant in the solar vicinity, with a density similar to M-type
stars.Comment: Accepted for publication in ApJ. 19 pages, 3 figures include
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