8,095 research outputs found
Decomposition driven interface evolution for layers of binary mixtures: I. Model derivation and stratified base states
A dynamical model is proposed to describe the coupled decomposition and
profile evolution of a free surface film of a binary mixture. An example is a
thin film of a polymer blend on a solid substrate undergoing simultaneous phase
separation and dewetting. The model is based on model-H describing the coupled
transport of the mass of one component (convective Cahn-Hilliard equation) and
momentum (Navier-Stokes-Korteweg equations) supplemented by appropriate
boundary conditions at the solid substrate and the free surface.
General transport equations are derived using phenomenological
non-equilibrium thermodynamics for a general non-isothermal setting taking into
account Soret and Dufour effects and interfacial viscosity for the internal
diffuse interface between the two components. Focusing on an isothermal setting
the resulting model is compared to literature results and its base states
corresponding to homogeneous or vertically stratified flat layers are analysed.Comment: Submitted to Physics of Fluid
White dwarf constraints on a varying
A secular variation of modifies the structure and evolutionary time
scales of white dwarfs. Using an state-of-the-art stellar evolutionary code, an
up-to-date pulsational code, and a detailed population synthesis code we
demonstrate that the effects of a running are obvious both in the
properties of individual white dwarfs, and in those of the white dwarf
populations in clusters. Specifically, we show that the white dwarf
evolutionary sequences depend on both the value of , and on the value
of when the white dwarf was born. We show as well that the pulsational
properties of variable white dwarfs can be used to constrain .
Finally, we also show that the ensemble properties of of white dwarfs in
clusters can also be used to set upper bounds to . Precisely, the
tightest bound --- yr --- is obtained
studying the population of the old, metal-rich, well populated, open cluster
NGC 6791. Less stringent upper limits can be obtained comparing the theoretical
results obtained taking into account the effects of a running with the
measured rates of change of the periods of two well studied pulsating white
dwarfs, G117--B15A and R548. Using these white dwarfs we obtain yr, and
yr, respectively, which although less restrictive than the previous
bound, can be improved measuring the rate of change of the period of massive
white dwarfs.Comment: 6 pages, 3 figures. To be published in the proceedings of the
conference "Varying fundamental constants and dynamical dark energy" (8 - 13
July 2013, Sexten Center for Astrophysics
Fragmentation of Nuclei at Intermediate and High Energies in Modified Cascade Model
The process of nuclear multifragmentation has been implemented, together with
evaporation and fission channels of the disintegration of excited remnants in
nucleus-nucleus collisions using percolation theory and the intranuclear
cascade model. Colliding nuclei are treated as face--centered--cubic lattices
with nucleons occupying the nodes of the lattice. The site--bond percolation
model is used. The code can be applied for calculation of the fragmentation of
nuclei in spallation and multifragmentation reactions.Comment: 19 pages, 10 figure
Improving the economic value of photographic screening for optical coherence tomography-detectable macular oedema : a prospective, multicentre, UK study
Peer reviewedPublisher PD
Quantifying the contamination by old main-sequence stars in young moving groups: the case of the Local Association
The associations and moving groups of young stars are excellent laboratories
for investigating stellar formation in the solar neighborhood. Previous results
have confirmed that a non-negligible fraction of old main-sequence stars is
present in the lists of possible members of young stellar kinematic groups. A
detailed study of the properties of these samples is needed to separate the
young stars from old main-sequence stars with similar space motion, and
identify the origin of these structures. We used stars possible members of the
young (~ 10 - 650 Myr) moving groups from the literature. To determine the age
of the stars, we used several suitable age indicators for young main sequence
stars, i.e., X-ray fluxes and other photometric data. We also used
spectroscopic data, in particular the equivalent width of the lithium line Li I
and Halpha, to constrain the range of ages of the stars. By combining
photometric and spectroscopic data, we were able to separate the young stars
(10 - 650 Myr) from the old (> 1 Gyr) field ones. We found, in particular, that
the Local Association is contaminated by old field stars at the level of ~30%.
This value must be considered as the contamination for our particular sample,
and not of the entire Local Association. For other young moving groups, it is
more difficult to estimate the fraction of old stars among possible members.
However, the level of X-ray emission can, at least, help to separate two age
populations: stars with <200 Myr and stars older than this. Our results are
consistent with a scenario in which the moving groups contain both groups of
young stars formed in a recent star-formation episode and old field stars with
similar space motion. Only by combining X-ray and optical spectroscopic data is
it possible to distinguish between these two age populations.Comment: 7 pages, 7 figures. Accepted for publication in A&
Iconicity emerges and is maintained in spoken language
Iconicity is the property whereby signs (vocal or manual) resemble their referents. Iconic signs are easy to relate to the world, facilitating learning and processing. In this study, we examined whether the benefits of iconicity would lead to its emergence and to maintenance in language. We focused on shape iconicity (the association between rounded objects and round-sounding words like âboubaâ and between spiky objects and spiky-sounding words like âkikiâ) and motion iconicity (the association between longer words and longer events). In Experiment 1, participants generated novel labels for round versus spiky shapes and long versus short movements (Experiment 1a: text, Experiment 1b: speech). Labels for each kind of stimulus differed in a way that was consistent with previous studies of iconicity. This suggests that iconicity emerges even on a completely unconstrainted task. In Experiment 2 (Experiment 2a: text, Experiment 2b: speech), we simulated language change in the laboratory (as iterated learning) and found that both forms of iconicity were introduced and maintained through generations of language users. Thus, we demonstrate the emergence of iconicity in spoken languages, and we argue that these results reflect a pressure for language systems to be referential, which favors iconic forms in the cultural evolution of language (at least up to a point where it is balanced by other pressures, e.g., discriminability). This can explain why we have iconicity across natural languages and may have implications for debates on language origins. (PsycInfo Database Record (c) 2021 APA, all rights reserved
Discovery of a luminous white dwarf in a young star cluster in the Large Magellanic Cloud
We have identified a candidate 1-2 x 10^5 year old luminous white dwarf in
NGC 1818, a young star cluster in the Large Magellanic Cloud. This discovery
strongly constrains the boundary mass M_c at which stars stop forming neutron
stars and start forming white dwarfs, to M_c > 7.6 Msun.Comment: 4 pages, 2 figures, greyscale image available by ftp from
[email protected]. ApJLetters, accepted 17 March 199
- âŠ