1,124 research outputs found
Inertial Coupling Method for particles in an incompressible fluctuating fluid
We develop an inertial coupling method for modeling the dynamics of
point-like 'blob' particles immersed in an incompressible fluid, generalizing
previous work for compressible fluids. The coupling consistently includes
excess (positive or negative) inertia of the particles relative to the
displaced fluid, and accounts for thermal fluctuations in the fluid momentum
equation. The coupling between the fluid and the blob is based on a no-slip
constraint equating the particle velocity with the local average of the fluid
velocity, and conserves momentum and energy. We demonstrate that the
formulation obeys a fluctuation-dissipation balance, owing to the
non-dissipative nature of the no-slip coupling. We develop a spatio-temporal
discretization that preserves, as best as possible, these properties of the
continuum formulation. In the spatial discretization, the local averaging and
spreading operations are accomplished using compact kernels commonly used in
immersed boundary methods. We find that the special properties of these kernels
make the discrete blob a particle with surprisingly physically-consistent
volume, mass, and hydrodynamic properties. We develop a second-order
semi-implicit temporal integrator that maintains discrete
fluctuation-dissipation balance, and is not limited in stability by viscosity.
Furthermore, the temporal scheme requires only constant-coefficient Poisson and
Helmholtz linear solvers, enabling a very efficient and simple FFT-based
implementation on GPUs. We numerically investigate the performance of the
method on several standard test problems...Comment: Contains a number of corrections and an additional Figure 7 (and
associated discussion) relative to published versio
Hydrodynamics of Suspensions of Passive and Active Rigid Particles: A Rigid Multiblob Approach
We develop a rigid multiblob method for numerically solving the mobility
problem for suspensions of passive and active rigid particles of complex shape
in Stokes flow in unconfined, partially confined, and fully confined
geometries. As in a number of existing methods, we discretize rigid bodies
using a collection of minimally-resolved spherical blobs constrained to move as
a rigid body, to arrive at a potentially large linear system of equations for
the unknown Lagrange multipliers and rigid-body motions. Here we develop a
block-diagonal preconditioner for this linear system and show that a standard
Krylov solver converges in a modest number of iterations that is essentially
independent of the number of particles. For unbounded suspensions and
suspensions sedimented against a single no-slip boundary, we rely on existing
analytical expressions for the Rotne-Prager tensor combined with a fast
multipole method or a direct summation on a Graphical Processing Unit to obtain
an simple yet efficient and scalable implementation. For fully confined
domains, such as periodic suspensions or suspensions confined in slit and
square channels, we extend a recently-developed rigid-body immersed boundary
method to suspensions of freely-moving passive or active rigid particles at
zero Reynolds number. We demonstrate that the iterative solver for the coupled
fluid and rigid body equations converges in a bounded number of iterations
regardless of the system size. We optimize a number of parameters in the
iterative solvers and apply our method to a variety of benchmark problems to
carefully assess the accuracy of the rigid multiblob approach as a function of
the resolution. We also model the dynamics of colloidal particles studied in
recent experiments, such as passive boomerangs in a slit channel, as well as a
pair of non-Brownian active nanorods sedimented against a wall.Comment: Under revision in CAMCOS, Nov 201
Mixed hydrogen-deuterium plasmas on JET ILW
A study of mixed hydrogen-deuterium H-mode plasmas has been carried out in JET-ILW to strengthen the physics basis for extrapolations to JET D-T operation and to support the development of strategies for isotope ratio control in future experiments.
Variations of input power, gas fuelling and isotopic mixture were performed in H-mode plasmas of the same magnetic field, plasma current and divertor configuration. The analysis of the energy confinement as a function of isotope mixture reveals that the biggest change is seen in plasmas with small fractions of H or D, in particular when including pure isotope plasmas. To interpret the results correctly, the dependence of the power threshold for access to type-I ELMing H-modes on the isotope mixture must be taken into account. For plasmas with effective mass between 1.2 and 1.8 the plasma thermal stored energy (Wth) scales as m 0.1 eff, which is weaker than that in the ITER physics basis, IPB98 scaling.
At fixed stored energy, deuterium-rich plasmas feature higher density pedestals, while the temperature at the pedestal top is lower, showing that at the same gas fuelling rate and power level, the pedestal pressure remains constant with an exchange of density and temperature as the isotope ratio is varied. Isotope control was successfully tested in JET-ILW by changing the isotope ratio throughout a discharge, switching from D to H gas puffing. Several energy confinement times (300 ms) are needed to fully change the isotope ratio during a discharge.EUROfusion Consortium Grant Agreement No. 633 053RCUK Energy Programme (Grant Number EP/I501 045)H2020 Marie-Sklodowska Curie programme (Grant No. 708 257)Spanish Ministry of Economy and Competitiveness (Grant No. FJCI-201 422 139
Connection of Isolated Stereoclusters by Combining C-13-RCSA, RDC, and J-Based Configurational Analyses and Structural Revision of a Tetraprenyltoluquinol Chromane Meroterpenoid from Sargassum muticum
The seaweed Sargassum muticum, collected on the southern coast of Galicia, yielded a tetraprenyltoluquinol chromane meroditerpene compound known as 1b, whose structure is revised. The relative configuration of 1b was determined by J-based configurational methodology combined with an iJ/DP4 statistical analysis and further confirmed by measuring two anisotropic properties: carbon residual chemical shift anisotropies (13C-RCSAs) and one-bond 1H-13C residual dipolar couplings (1DCH-RDCs). The absolute configuration of 1b was deduced by ECD/OR/TD-DFT methods and established as 3R,7S,11R
Magnetic Fields in Evolved Stars: Imaging the Polarized Emission of High-Frequency SiO Masers
We present Submillimeter Array observations of high frequency SiO masers
around the supergiant VX Sgr and the semi-regular variable star W Hya. The
J=5-4, v=1 28SiO and v=0 29SiO masers of VX Sgr are shown to be highly linearly
polarized with a polarization from ~5-60%. Assuming the continuum emission
peaks at the stellar position, the masers are found within ~60 mas of the star,
corresponding to ~100 AU at a distance of 1.57 kpc. The linear polarization
vectors are consistent with a large scale magnetic field, with position and
inclination angles similar to that of the dipole magnetic field inferred in the
H2O and OH maser regions at much larger distances from the star. We thus show
for the first time that the magnetic field structure in a circumstellar
envelope can remain stable from a few stellar radii out to ~1400 AU. This
provides further evidence supporting the existence of large scale and
dynamically important magnetic fields around evolved stars. Due to a lack of
parallactic angle coverage, the linear polarization of masers around W Hya
could not be determined. For both stars we observed the 28SiO and 29SiO
isotopologues and find that they have a markedly different distribution and
that they appear to avoid each other. Additionally, emission from the SO
5_5-4_4 line was imaged for both sources. Around W Hya we find a clear offset
between the red- and blue-shifted SO emission. This indicates that W Hya is
likely host to a slow bipolar outflow or a rotating disk-like structure.Comment: 8 pages, 7 figures, accepted for publication in ApJ. Online table
will be available with published versio
Chronic exposure to cannabinoids during adolescence causes long-lasting behavioral deficits in adult mice
Regular use of marijuana during adolescence enhances the risk of long-lasting neurobiological changes in adulthood. The present study was aimed at assessing the effect of long-term administration of the synthetic cannabinoid WIN55212.2 during adolescence in young adult mice. Adolescent mice aged 5 weeks were subjected daily to the pharmacological action of WIN55212.2 for 3 weeks and were then left undisturbed in their home cage for a 5-week period and finally evaluated by behavioral testing. Mice that received the drug during adolescence showed memory impairment in the Morris water maze, as well as a dose-dependent memory impairment in fear conditioning. In addition, the administration of 3 mg/kg WIN55212.2 in adolescence increased adult hippocampal AEA levels and promoted DNA hypermethylation at the intragenic region of the intracellular signaling modulator Rgs7, which was accompanied by a lower rate of mRNA transcription of this gene, suggesting a potential causal relation. Although the concrete mechanisms underlying the behavioral observations remain to be elucidated, we demonstrate that long-term administration of 3 mg/kg of WIN during adolescence leads to increased endocannabinoid levels and altered Rgs7 expression in adulthood and establish a potential link to epigenetic changes.Beca Ramón y Caja
Serotonin transporter clustering in blood lymphocytes predicts the outcome on anhedonia scores in naïve depressive patients treated with antidepressant medication
BACKGROUND:
We have shown that serotonin transporter (SERT) clustering in blood lymphocytes is altered in major depression and correlates with pharmacological therapeutic responses measured with the Hamilton scale. In the present report, we extend these results to the self-assessment anhedonia scale, as anhedonia is a cardinal symptom of major depression that is difficult to treat with first-line antidepressants.
METHODS:
We collected blood samples from 38 untreated depression patients at the time of enrolment and 8 weeks after pharmacological treatment. We used the self-assessment anhedonia scale to evaluate anhedonia symptoms before and after treatment. We also used quantitative immunocytochemistry to measure SERT clusters in blood lymphocytes.
RESULTS:
Evaluation of the distribution of SERT clusters size in the plasma membrane of lymphocytes identified two subpopulations of naive depression patients: Depression I (D-I) and Depression II (D-II). While naïve D-I and D-II patients initially showed similar anhedonia scores, D-II patients showed a good response in anhedonia symptoms after 8 weeks of psychopharmacological treatment, whereas D-I patients failed to show any improvement. Psychopharmacological treatment also induced an increase in the number of SERT clusters in lymphocytes in the D-II group, and this increase correlated with the improvement in anhedonia symptoms.
CONCLUSIONS:
SERT clustering in peripheral lymphocytes can be used to identify patient response to antidepressant therapy as ascertained by anhedonia scores
Staggered Schemes for Fluctuating Hydrodynamics
We develop numerical schemes for solving the isothermal compressible and
incompressible equations of fluctuating hydrodynamics on a grid with staggered
momenta. We develop a second-order accurate spatial discretization of the
diffusive, advective and stochastic fluxes that satisfies a discrete
fluctuation-dissipation balance, and construct temporal discretizations that
are at least second-order accurate in time deterministically and in a weak
sense. Specifically, the methods reproduce the correct equilibrium covariances
of the fluctuating fields to third (compressible) and second (incompressible)
order in the time step, as we verify numerically. We apply our techniques to
model recent experimental measurements of giant fluctuations in diffusively
mixing fluids in a micro-gravity environment [A. Vailati et. al., Nature
Communications 2:290, 2011]. Numerical results for the static spectrum of
non-equilibrium concentration fluctuations are in excellent agreement between
the compressible and incompressible simulations, and in good agreement with
experimental results for all measured wavenumbers.Comment: Submitted. See also arXiv:0906.242
Motile dislocations knead odd crystals into whorls
The competition between thermal fluctuations and potential forces governs the stability of matter in equilibrium, in particular the proliferation and annihilation of topological defects. However, driving matter out of equilibrium allows for a new class of forces that are neither attractive nor repulsive, but rather transverse. The possibility of activating transverse forces raises the question of how they affect basic principles of material self-organization and control. Here we show that transverse forces organize colloidal spinners into odd elastic crystals crisscrossed by motile dislocations. These motile topological defects organize into a polycrystal made of grains with tunable length scale and rotation rate. The self-kneading dynamics drive super-diffusive mass transport, which can be controlled over orders of magnitude by varying the spinning rate. Simulations of both a minimal model and fully resolved hydrodynamics establish the generic nature of this crystal whorl state. Using a continuum theory, we show that both odd and Hall stresses can destabilize odd elastic crystals, giving rise to a generic state of crystalline active matter. Adding rotations to a material’s constituents has far-reaching consequences for continuous control of structures and transport at all scales.The National Science Foundation (NSF) under award no. DMR-2011854.
NSF DMR-1905974, NSF EFRI NewLAW 1741685 and the Packard Foundation.
NSF grants DMR-1420073 (NYU-MRSEC) and DMR-2004469.
ARN grant WTF and IdexLyon Tore.
The National Science Foundation Graduate Research Fellowship under grant no. 1746045. D.B.
The Chicago-France FACCTS programme.
‘la Caixa’ Foundation (ID 100010434), fellowship LCF/BQ/PI20/11760014 and from the European Union’s Horizon 2020 research and innovation programme under Marie Skłodowska-Curie grant agreement no. 847648.
NSF DMR-1828629 and US NSF grant no. DMR-201185
Un proyecto escultórico: la tortuga
En enero de 2003, los escultores Pablo de Arriba del Amo y José de las Casas Gómez presentaron la idea de una posible creación escultórica a la Junta municipal de Villaverde Alto.
Este proyecto fue aprobado; por tanto, contó con la financiación necesaria para llevarlo a
cabo, posteriormente fue instalado en la localización final propuesta, que era en la plaza
Ágata de ese mismo distrito. En este artículo se van a desarrollar pormenorizadamente
todos los pasos que se siguieron en el proceso de creación de este monumento, el cual por
su envergadura era especialmente complejo. Desde la elección del tema, los materiales y los
procesos hasta el desarrollo y estudio de la cimentación, todo ello será explicado para dar
cuenta de un proyecto de máximo interés no sólo para los propios escultores, sino que, para
el público general, la aproximación a este procedimiento puede hacer valorar el universo de la
escultura mucho más. Hay que tener en consideración que ambos escultores se inventaron un
procedimiento escultórico mediante la aplicación de sus conocimientos en una configuración
novedosa, tanto por el procedimiento como por el método de aplicación de los materiales.
Durante las páginas que siguen se verán y comprenderán las dificultades que tuvieron que
afrontar no sólo a nivel técnico, sino a nivel conceptual para hilvanar todos los aspectos del
proyecto, viéndose, así mismo, los ámbitos en los que este proyecto concreto es singular.In January 2003, the sculptors Pablo de Arriba del Amo and José de las Casas Gómez,
presented the idea of a possible sculptural creation to the Municipal Board of Villaverde
Alto, this project was approved, therefore, it had the necessary financing to carry it out. It
was later installed in the proposed final location, which was in Plaza Ágata in that same
district. In this article, all the steps that were followed in the process of creating this monument, which was especially complex due to its size, will be developed in detail. From the
choice of theme, materials and processes to the development and study of the foundation,
all of this will be explained to account for a project of maximum interest not only for the
sculptors themselves, but also for the general public. The approach to this procedure can
make the universe of sculpture much more appreciated. It must be taken into account,
that both sculptors invented a sculptural procedure by applying their knowledge in a novel
configuration, both in terms of the procedure and the method of applying the materials.
During the following pages you will see and understand the difficulties they had to face
not only at a technical level but also at a conceptual level to put together all the aspects of
the project, seeing, likewise, the areas in which this specific project is unique
- …