166 research outputs found
A framework for large-scale relativistic simulations in the characteristic approach
We present a new computational framework (LEO), that enables us to carry out
the very first large-scale, high-resolution computations in the context of the
characteristic approach in numerical relativity. At the analytic level, our
approach is based on a new implementation of the ``eth'' formalism, using a
non-standard representation of the spin-raising and lowering angular operators
in terms of non-conformal coordinates on the sphere; we couple this formalism
to a partially first-order reduction (in the angular variables) of the Einstein
equations. The numerical implementation of our approach supplies the basic
building blocks for a highly parallel, easily extensible numerical code. We
demonstrate the adaptability and excellent scaling of our numerical code by
solving, within our numerical framework, for a scalar field minimally coupled
to gravity (the Einstein-Klein-Gordon problem) in 3-dimensions. The nonlinear
code is globally second-order convergent, and has been extensively tested using
as reference a calibrated code with the same boundary-initial data and radial
marching algorithm. In this context, we show how accurately we can follow
quasi-normal mode ringing. In the linear regime, we show energy conservation
for a number of initial data sets with varying angular structure. A striking
result that arises in this context is the saturation of the flow of energy
through the Schwarzschild radius. As a final calibration check we perform a
large simulation with resolution never achieved before.Comment: RevTeX4, 22 pages, 21 figures, to appear in Phys. Rev.
Quantum dynamics of a model for two Josephson-coupled Bose--Einstein condensates
In this work we investigate the quantum dynamics of a model for two
single-mode Bose--Einstein condensates which are coupled via Josephson
tunneling. Using direct numerical diagonalisation of the Hamiltonian, we
compute the time evolution of the expectation value for the relative particle
number across a wide range of couplings. Our analysis shows that the system
exhibits rich and complex behaviours varying between harmonic and non-harmonic
oscillations, particularly around the threshold coupling between the
delocalised and self-trapping phases. We show that these behaviours are
dependent on both the initial state of the system as well as regime of the
coupling. In addition, a study of the dynamics for the variance of the relative
particle number expectation and the entanglement for different initial states
is presented in detail.Comment: 15 pages, 8 eps figures, accepted in J. Phys.
PHYSICAL PROPERTIES OF THE JUVENILE AND MATURE WOOD OF Pinus elliottii Engelm var. elliottii AND Eucalyptus grandis Hill ex Maiden
O lenho juvenil apresenta grande diferen\ue7a em suas propriedades
anat\uf4micas e f\uedsicas em rela\ue7\ue3o ao lenho adulto.
Essa heterogeneidade da madeira causa uma s\ue9rie de transtornos
para a ind\ufastria de transforma\ue7\ue3o e processamento. O
presente trabalho teve como objetivo o estudo das propriedades
f\uedsicas dos lenhos juvenil e adulto de Pinus elliottii Engelm
var. elliottii, com 25 anos de idade, e de Eucalyptus grandis Hill ex
Maiden, com 30 anos de idade, provenientes da Esta\ue7\ue3o
Experimental de Itapetininga e da Floresta Estadual de Santa
B\ue1rbara, pertencentes ao Instituto Florestal do Estado de S\ue3o
Paulo. Para tanto, de ambas as esp\ue9cies, foram retirados, de
t\ue1buas radiais, corpos de prova com dimens\uf5es de 20x30x50 mm,
para a determina\ue7\ue3o das massas espec\uedficas, dos
inchamentos e dos coeficientes de retratibilidade dos lenhos juvenil e
adulto. Os resultados das esp\ue9cies mostraram que os lenhos adultos
comparados com os lenhos juvenis apresentaram: (1) um aumento nos
valores das massas espec\uedficas b\ue1sica, a 0% e a 12% de
umidade, dos inchamentos volum\ue9tricos e lineares tangencial e
radial a 12% de umidade e m\ue1ximos, e dos coeficientes de
retratibilidade tangencial e radial; (2) uma redu\ue7\ue3o nos
valores de inchamentos lineares longitudinais a 12% de umidade e
m\ue1ximos, e do coeficiente de retratibilidade longitudinal.The juvenile wood presents great difference in its anatomical and
physical properties in relation to the mature wood. That heterogeneity
of the wood causes a series of upset for the processing industry. The
present research had as objective the study of the physical properties
of the juvenile and mature wood of Pinus elliottii Engelm var.
elliottii, with 25 years of age and of Eucalyptus grandis Hill ex
Maiden, with 30 years of age, coming from the Experimental Station of
Itapetininga and State Forest of Santa Barbara, belonging to the Forest
Institute of the state of S\ue3o Paulo. From both species there were
taken from radial boards, specimens with dimensions of 20x30x50 mm, for
the determination of density, swelling and swelling coefficient of the
juvenile and mature wood. The results of the species showed that the
mature compared with the juvenile wood presented: (1) an increase in
the values of the basic density, at 0% and at 12% of moisture content
and of the volumetric, radial and tangential swelling at 12% moisture
content and maximum coefficient of radial and tangential swelling; (2)
a reduction in the values of longitudinal swelling at 12% and maximum
and of the longitudinal swelling coefficient
Influences of H on the Adsorption of a Single Ag Atom on Si(111)-7 × 7 Surface
The adsorption of a single Ag atom on both clear Si(111)-7 × 7 and 19 hydrogen terminated Si(111)-7 × 7 (hereafter referred as 19H-Si(111)-7 × 7) surfaces has been investigated using first-principles calculations. The results indicated that the pre-adsorbed H on Si surface altered the surface electronic properties of Si and influenced the adsorption properties of Ag atom on the H terminated Si surface (e.g., adsorption site and bonding properties). Difference charge density data indicated that covalent bond is formed between adsorbed Ag and H atoms on 19H-Si(111)-7 × 7 surface, which increases the adsorption energy of Ag atom on Si surface
Early Planet Formation in Embedded Disks (eDisk). I. Overview of the Program and First Results
We present an overview of the Large Program, ``Early Planet Formation in
Embedded Disks (eDisk)'', conducted with the Atacama Large
Millimeter/submillimeter Array (ALMA). The ubiquitous detections of
substructures, particularly rings and gaps, in protoplanetary disks around T
Tauri stars raise the possibility that at least some planet formation may have
already started during the embedded stages of star formation. In order to
address exactly how and when planet formation is initiated, the program focuses
on searching for substructures in disks around 12 Class 0 and 7 Class I
protostars in nearby (200 pc) star-forming regions through 1.3 mm continuum
observations at a resolution of au (0.04"). The initial results show
that the continuum emission, mostly arising from dust disks around the sample
protostars, has relatively few distinctive substructures, such as rings and
spirals, in marked contrast to Class II disks. The dramatic difference may
suggest that substructures quickly develop in disks when the systems evolve
from protostars to Class II sources or alternatively that high optical depth of
the continuum emission could obscure internal structures. Kinematic information
obtained through CO isotopologue lines and other lines reveals the presence of
Keplerian disks around protostars, providing us with crucial physical
parameters, in particular, the dynamical mass of the central protostars. We
describe the background of the eDisk program, the sample selection and their
ALMA observations, the data reduction, and also highlight representative
first-look results.Comment: This is a publication of a series of eDisk ALMA large program
first-look paper
Perceptions of climate change and willingness to save energy related to flood experience
One of the reasons that people may not take action to mitigate climate change is that they lack first-hand experience of its potential consequences. From this perspective, individuals who have direct experience of phenomena that may be linked to climate change would be more likely to be concerned by the issue and thus more inclined to undertake sustainable be- haviours. So far, the evidence available to test this hypothesis is limited, and in part contradictory1–4. Here we use national survey data collected from 1,822 individuals across the UK in 2010, to examine the links between direct flooding experience, perceptions of climate change and preparedness to reduce energy use. We show that those who report experience of flooding express more concern over climate change, see it as less uncertain and feel more confident that their actions will have an effect on climate change. Importantly, these perceptual differences also translate into a greater willingness to save energy to mitigate climate change. Highlighting links between local weather events and climate change is therefore likely to be a useful strategy for increasing concern and action
- …